Preclinical efficacy of a PSMA-targeted actinium-225 conjugate (225Ac-macropa-pelgifatamab) - a targeted alpha therapy for prostate cancer

PURPOSE

Initially, prostate cancer responds to hormone therapy but eventually resistance develops. Beta emitter-based PSMA (prostate-specific membrane antigen)-targeted radionuclide therapy is approved for the treatment of metastatic castration-resistant prostate cancer. Here we introduce a targeted alpha therapy (TAT) consisting of the PSMA antibody pelgifatamab covalently linked to a macropa chelator and labeled with actinium-225 and compare its efficacy and tolerability with other TATs.

EXPERIMENTAL DESIGN

The in vitro characteristics and in vivo biodistribution, antitumor efficacy, and tolerability of 225Ac-macropa-pelgifatamab (225Ac-pelgi) and other TATs were investigated in cell line- and patient-derived prostate cancer xenograft models. The antitumor efficacy of 225Ac-pelgi was also investigated in combination with the androgen receptor inhibitor darolutamide.

RESULTS

Actinium-225-labeling of 225Ac-pelgi was efficient already at room temperature. Potent in vitro cytotoxicity was seen in PSMA-expressing (LNCaP, MDA-PCa-2b, and C4-2) but not in PSMA-negative (PC-3 and DU-145) cell lines. High tumor accumulation was seen for both 225Ac-pelgi and 225Ac-DOTA-pelgi in the MDA-PCa-2b xenograft model. In the C4-2 xenograft model, 225Ac-pelgi showed enhanced antitumor efficacy with a T/Cvolume (treatment/control) ratio of 0.10 compared with 225Ac-DOTA-pelgi, 225Ac-DOTA-J591, and 227Th-HOPO-pelgifatamab (227Th-pelgi) (all at 300 kBq/kg) with T/Cvolume ratios of 0.37, 0.39, and 0.33, respectively. 225Ac-pelgi was less myelosuppressive than 227Th-pelgi. 225Ac-pelgi showed dose-dependent treatment efficacy in the patient-derived KuCaP-1 model and strong combination potential with darolutamide in both cell line- (22Rv1) and patient-derived (ST1273) xenograft models.

CONCLUSIONS

These results provide a strong rationale to investigate 225Ac-pelgi in patients with prostate cancer. A clinical phase 1 study has been initiated (NCT06052306).

Suitability of machine learning models for prediction of clinically defined Stage III/IV periodontitis from questionnaires and demographic data in Danish cohorts

AIM

To evaluate if, and to what extent, machine learning models can capture clinically defined Stage III/IV periodontitis from self-report questionnaires and demographic data.

MATERIALS AND METHODS

Self-reported measures of periodontitis, demographic data and clinically established Stage III/IV periodontitis status were extracted from two Danish population-based cohorts (The Copenhagen Aging and Midlife Biobank [CAMB] and The Danish Health Examination Survey [DANHES]) and used to develop cross-validated machine learning models for the prediction of clinically established Stage III/IV periodontitis. Models were trained using 10-fold cross-validations repeated three times on the CAMB dataset (n = 1476), and the resulting models were validated in the DANHES dataset (n = 3585).

RESULTS

The prevalence of Stage III/IV periodontitis was 23.2% (n = 342) in the CAMB dataset and 9.3% (n = 335) in the DANHES dataset. For the prediction of clinically established Stage III/IV periodontitis in the CAMB cohort, models reached area under the receiver operating characteristics (AUROCs) of 0.67-0.69, sensitivities of 0.58-0.64 and specificities of 0.71-0.80. In the DANHES cohort, models derived from the CAMB cohort achieved AUROCs of 0.64-0.70, sensitivities of 0.44-0.63 and specificities of 0.75-0.84.

CONCLUSIONS

Applying cross-validated machine learning algorithms to demographic data and self-reported measures of periodontitis resulted in models with modest capabilities for the prediction of Stage III/IV periodontitis in two Danish cohorts.

A Targeted Thorium-227 Conjugate Demonstrates Efficacy in Preclinical Models of Acquired Drug Resistance and Combination Potential with Chemotherapeutics and Antiangiogenic Therapies

Targeted alpha therapies (TAT) are an innovative class of therapies for cancer treatment. The unique mode-of-action of TATs is the induction of deleterious DNA double-strand breaks. Difficult-to-treat cancers, such as gynecologic cancers upregulating the chemoresistance P-glycoprotein (p-gp) and overexpressing the membrane protein mesothelin (MSLN), are promising targets for TATs. Here, based on the previous encouraging findings with monotherapy, we investigated the efficacy of the mesothelin-targeted thorium-227 conjugate (MSLN-TTC) both as monotherapy and in combination with chemotherapies and antiangiogenic compounds in ovarian and cervical cancer models expressing p-gp. MSLN-TTC monotherapy showed equal cytotoxicity in vitro in p-gp-positive and -negative cancer cells, while chemotherapeutics dramatically lost activity on p-gp-positive cancer cells. In vivo, MSLN-TTC exhibited dose-dependent tumor growth inhibition with treatment/control ratios of 0.03-0.44 in various xenograft models irrespective of p-gp expression status. Furthermore, MSLN-TTC was more efficacious in p-gp-expressing tumors than chemotherapeutics. In the MSLN-expressing ST206B ovarian cancer patient-derived xenograft model, MSLN-TTC accumulated specifically in the tumor, which combined with pegylated liposomal doxorubicin (Doxil), docetaxel, bevacizumab, or regorafenib treatment induced additive-to-synergistic antitumor efficacy and substantially increased response rates compared with respective monotherapies. The combination treatments were well tolerated and only transient decreases in white and red blood cells were observed. In summary, we demonstrate that MSLN-TTC treatment shows efficacy in p-gp-expressing models of chemoresistance and has combination potential with chemo- and antiangiogenic therapies.

Abstract 5039: Development of a prostate cancer PDX model radioresistant to PSMA targeted radionuclide therapy

Prostate cancer is the second most common cancer diagnosis worldwide and the fifth leading cause of cancer related death among men. Lutetium Lu 177 vivivotide tetraxetetan was recently approved by the FDA for treatment of prostate-specific membrane antigen (PSMA)-positive metastatic castration-resistant prostate cancer. However, not all patients respond to treatment and combination therapies may improve outcomes. One approach is to combine targeted radionuclide therapy with inhibitors targeting DNA damage response pathways such as ATM/ATR inhibitors to enhance the radiosensitivity of the cancer cells. Currently, models used to study radioresistance in prostate cancer are based on cancer cell lines or cell-line derived xenograft models, but these models do not account for the heterogenous and complex biology of the disease.

To overcome this issue, we aimed at developing a radioresistant PSMA positive prostate cancer patient-derived xenograft (PDX) model based on the ST1273 model (XenoSTART). ST1273 originates from a sixty-five-year-old Hispanic male that did not receive treatment prior to sampling. The model is characterized by overexpression of androgen receptor and PSMA. Tumors were implanted in nude mice and radioresistance was induced by external beam radiation therapy (3 × 2Gy per cycle) until tumor growth was unresponsive to the treatment. Flow cytometry were applied to evaluate if altered proliferation rate or changes in the tumor microenvironment (TME) convers the resistance.

Out of five initially treated tumors, one tumor re-occurred after 19 days. Repeating the treatment led to an initial decrease in tumor volume but the growth delay was reduced to 12 days. A third treatment rendered the tumor resistant as tumor growth was unaffected. Current evidence confirms that radioresistance was maintained when passaging, and PSMA expression was unaffected. Next, we tested whether the tumor would also withstand targeted radionuclide therapy. Animals implanted with parental or radioresistant ST1273 tumors were treated with Lu177-PSMA-617 (5MBq, QW x2). The treatment reduced tumor size in both tumor types, but significantly less in the resistant model. Moreover, parental tumors had a significantly slower recurrence of 45 days compared to the resistant tumors that relapsed 24 days after the first dosing. Flow cytometry analysis of control and treated tumors (parental and radioresistant) showed that the radioresistance might be attributed to alterations in the cell cycle control.

Altogether, we developed a PDX prostate cancer model that is resistance to external beam radiation and PSMA targeted radionuclide therapy. This model will allow us to further characterize radioresistance and evaluate combinatorial therapy in a clinically relevant model.

Citation Format: Maria Thaysen, Esben Christensen, Rikke N. Nielsen, Michael Wick, Mette M. Wessel, Lotte K. Kristensen, Sebastian Gnosa, Carsten H. Nielsen. Development of a prostate cancer PDX model radioresistant to PSMA targeted radionuclide therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5039.

First-in-Humans PET Imaging of Tissue Factor in Patients with Primary and Metastatic Cancers Using 18F-labeled Active-Site Inhibited Factor VII (18F-ASIS): Potential as Companion Diagnostic

Tissue factor (TF) expression in cancers correlates with poor prognosis. Recently, the first TF-targeted therapy was approved by the U.S. Food and Drug Administration for cervical cancer. To unfold the potential of TF-targeted therapies, correct stratification and selection of patients eligible for treatments may become important for optimization of patient outcomes. TF-targeted PET imaging based on ¹⁸F-radiolabeled active-site inhibited versions of the TF natural ligand coagulation factor VII (¹⁸F-ASIS) has in preclinical models convincingly demonstrated its use for noninvasive quantitative measurements of TF expression in tumor tissue. ¹⁸F-ASIS PET imaging thus has the potential to act as a diagnostic companion for TF-targeted therapies in the clinical setting. Methods: In this first-in-humans trial, we included 10 cancer patients (4 pancreatic, 3 breast, 2 lung, and 1 cervical cancer) for ¹⁸F-ASIS PET imaging. The mean and SD of administered ¹⁸F-ASIS activity was 157 ± 35 MBq (range, 93-198 MBq). PET/CT was performed after 1, 2, and 4 h. The primary objectives were to establish the safety, biodistribution, pharmacokinetics, and dosimetry of ¹⁸F-ASIS. Secondary objectives included quantitative measurements of SUVs in tumor tissue with PET and evaluation of the correlation (Pearson correlation) between tumor SUV_max and ex vivo TF expression in tumor tissue. Results: Administration of ¹⁸F-ASIS was safe, and no adverse events were observed. No clinically significant changes in vital signs, electrocardiograms, or blood parameters were observed after injection of ¹⁸F-ASIS. Mean ¹⁸F-ASIS plasma half-life was 3.2 ± 0.6 h, and the radiotracer was predominantly excreted in the urine. For injection activity of 200 MBq of ¹⁸F-ASIS, effective whole-body dose was 4 mSv and no prohibitive organ-specific absorbed doses were found. Heterogeneous radiotracer uptake was observed across patients and within tumors. We found a trend of a positive correlation between tumor SUV_max and ex vivo TF expression (r = 0.84, P = 0.08, n = 5). Conclusion: ¹⁸F-ASIS can be safely administered to cancer patients for PET imaging of TF expression in tumors. The trial marks the first test of a TF-targeted PET radiotracer in humans (first-in-class). The findings represent important first steps toward clinical implementation of ¹⁸F-ASIS PET imaging of TF expression.

The Initial Cardiac Tissue Response to Cryopreserved Allogeneic Adipose Tissue-Derived Mesenchymal Stromal Cells in Rats with Chronic Ischemic Cardiomyopathy

Mesenchymal stromal cells have proven capable of improving cardiac pump function in patients with chronic heart failure, yet little is known about their mode of action. The aim of the study was to investigate the short-term effect of cryopreserved allogeneic rat adipose tissue-derived stromal cells (ASC) on cardiac composition, cellular subpopulations, and gene transcription in a rat model of chronic ischemic cardiomyopathy (ICM). Myocardial infarction (MI) was induced by permanent ligation of the left anterior descending coronary artery. After 6 weeks, the rats were treated with ASCs, saline, or no injection, using echo-guided trans-thoracic intramyocardial injections. The cardiac tissue was subsequently collected for analysis of cellular subpopulations and gene transcription 3 and 7 days after treatment. At day 3, an upregulation of genes associated with angiogenesis were present in the ASC group. On day 7, increases in CCR2+ and CD38+ macrophages (p = 0.047 and p = 0.021), as well as in the CD4/CD8 lymphocyte ratio (p = 0.021), were found in the ASC group compared to the saline group. This was supported by an upregulation of genes associated with monocytes/macrophages. In conclusion, ASC treatment initiated an immune response involving monocytes/macrophages and T-cells and induced a gene expression pattern associated with angiogenesis and monocyte/macrophage differentiation.

Uptake of [68Ga]-NODAGA-E[(cRGDyK)]2 is related to improvement in pump function in rats with chronic ischemic cardiomyopathy treated with cell therapy

Background

An increasing number of patients living with chronic ischemic cardiomyopathy (ICM) are potential candidates for cell therapy, including adipose tissue-derived mesenchymal stromal cells (ASC). However, proper assessment of clinical effects in relation to cellular effector mechanisms, such as angiogenesis, is currently lacking.

Purpose

To investigate the prognostic value of assessing angiogenesis non-invasively using novel PET imaging in terms of functional outcome after cell therapy in a homologous animal model of ICM.

Methods

Myocardial infarction was induced by permanent ligation of the left anterior descending coronary artery. Four weeks after infarction, the rats were scanned with [18F]-FDG and echocardiography, and based on left ventricular ejection fraction (LVEF) and infarct size randomized to allogeneic ASC treatment (n=14) or saline (n=9). Animals were treated using echo-guided trans-thoracic intramyocardial injections. Follow-up echocardiography was performed four weeks after treatment. Angiogenesis was assessed non-invasively using the [68Ga]-NODAGA-E[(cRGDyK)]2 (RGD) PET-tracer before treatment and two weeks after the treatment (Figure). The output was RGD-uptake by maximum standardized uptake value (SUVmax).

Results

RGD-uptake in the infarct area significantly decreased in the saline group (p=0.04), while this decline was not significant in the ASC group (p=0.58). There was no effect on LVEF of the cell therapy in this study (p=0.70). When the rats were grouped by RGD-uptake post treatment, the high RGD-uptake group (n=8) improved LVEF compared to the rats with medium or low RGD-uptake (n=15, p=0.04) irrespective of the treatment. This could indicate that non-invasive detection of a high degree of myocardial angiogenesis measured using RGD is predictive of improvement in cardiac pump function in ICM.

Conclusions

Following injection of ASC or saline, a high RGD-uptake precluded improvement in pump function. This is the first evidence of how uptake of the novel RGD tracer relates to changes in pump function in ICM and the results could affect the design of future clinical trials using regenerative therapy for ICM patients.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Aase and Ejnar Danielsens FondDoctor Sofus Carl Emil Friis and wife Olga Doris Friis' Scholarship Study design, RGD-uptake, and results

Immunostimulatory effects of targeted thorium-227 conjugates as single agent and in combination with anti-PD-L1 therapy

Background

Targeted thorium-227 conjugates (TTCs) are an emerging class of targeted alpha therapies (TATs). Their unique mode of action (MoA) is the induction of difficult-to-repair clustered DNA double-strand breaks. However, thus far, their effects on the immune system are largely unknown. Here, we investigated the immunostimulatory effects of the mesothelin-targeted thorium-227 conjugate (MSLN-TTC) in vitro and in vivo in monotherapy and in combination with an inhibitor of the immune checkpoint programmed death receptor ligand 1 (PD-L1) in immunocompetent mice.

Methods

The murine cell line MC38 was transfected with the human gene encoding for MSLN (hMSLN) to enable binding of the non-cross-reactive MSLN-TTC. The immunostimulatory effects of MSLN-TTC were studied in vitro on human cancer cell lines and MC38-hMSLN cells. The efficacy and MoA of MSLN-TTC were studied in vivo as monotherapy or in combination with anti-PD-L1 in MC38-hMSLN tumor-bearing immunocompetent C57BL/6 mice. Experiments were supported by RNA sequencing, flow cytometry, immunohistochemistry, mesoscale, and TaqMan PCR analyses to study the underlying immunostimulatory effects. In vivo depletion of CD8+ T cells and studies with Rag2/Il2Rg double knockout C57BL/6 mice were conducted to investigate the importance of immune cells to the efficacy of MSLN-TTC.

Results

MSLN-TTC treatment induced upregulation of DNA sensing pathway transcripts (IL-6, CCL20, CXCL10, and stimulator of interferon genes (STING)-related genes) in vitro as determined by RNASeq analysis. The results, including phospho-STING activation, were confirmed on the protein level. Danger-associated molecular pattern molecules were upregulated in parallel, leading to dendritic cell (DC) activation in vitro. MSLN-TTC showed strong antitumor activity (T:C 0.38, p<0.05) as a single agent in human MSLN-expressing MC38 tumor-bearing immunocompetent mice. Combining MSLN-TTC with anti-PD-L1 further enhanced the efficacy (T:C 0.08, p<0.001) as evidenced by the increased number of tumor-free surviving animals. MSLN-TTC monotherapy caused migration of CD103+ cDC1 DCs and infiltration of CD8+ T cells into tumors, which was enhanced on combination with anti-PD-L1. Intriguingly, CD8+ T-cell depletion decreased antitumor efficacy.

Conclusions

These in vitro and in vivo data on MSLN-TTC demonstrate that the MoA of TTCs involves activation of the immune system. The findings are of relevance for other targeted radiotherapies and may guide clinical combination strategies.

Darolutamide Potentiates the Antitumor Efficacy of a PSMA-targeted Thorium-227 Conjugate by a Dual Mode of Action in Prostate Cancer Models

PURPOSE

Androgen receptor (AR) inhibitors are well established in the treatment of castration-resistant prostate cancer and have recently shown efficacy also in castration-sensitive prostate cancer. Although most patients respond well to initial therapy, resistance eventually develops, and thus, more effective therapeutic approaches are needed. Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer and presents an attractive target for radionuclide therapy. Here, we evaluated the efficacy and explored the mode of action of the PSMA-targeted thorium-227 conjugate (PSMA-TTC) BAY 2315497, an antibody-based targeted alpha-therapy, in combination with the AR inhibitor darolutamide.

EXPERIMENTAL DESIGN

The in vitro and in vivo antitumor efficacy and mode of action of the combination treatment were investigated in preclinical cell line-derived and patient-derived prostate cancer xenograft models with different levels of PSMA expression.

RESULTS

Darolutamide induced the expression of PSMA in androgen-sensitive VCaP and LNCaP cells in vitro, and the efficacy of darolutamide in combination with PSMA-TTC was synergistic in these cells. In vivo, the combination treatment showed synergistic antitumor efficacy in the low PSMA-expressing VCaP and in the high PSMA-expressing ST1273 prostate cancer models, and enhanced efficacy in the enzalutamide-resistant KUCaP-1 model. The treatments were well tolerated. Mode-of-action studies revealed that darolutamide induced PSMA expression, resulting in higher tumor uptake of PSMA-TTC, and consequently, higher antitumor efficacy, and impaired PSMA-TTC-mediated induction of DNA damage repair genes, potentially contributing to increased DNA damage.

CONCLUSIONS

These results provide a strong rationale to investigate PSMA-TTC in combination with AR inhibitors in patients with prostate cancer.

COVID-19 as a mediator of interferon deficiency and hyperinflammation: Rationale for the use of JAK1/2 inhibitors in combination with interferon

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) elicits an interferon (IFN) deficiency state, which aggravates the type I interferon deficiency and slow IFN responses, which associate with e.g. aging and obesity. Additionally, SARS-CoV-2 may also elicit a cytokine storm, which accounts for disease progression and ultimately the urgent need of ventilator support. Based upon several reports, it has been argued that early treatment with IFN-alpha2 or IFN-beta, preferentially in the early disease stage, may prohibit disease progression. Similarly, preliminary studies have shown that JAK1/2 inhibitor treatment with ruxolitinib or baricitinib may decrease mortality by dampening the deadly cytokine storm, which - in addition to the virus itself - also contributes to multi-organ thrombosis and multi-organ failure. Herein, we describe the rationale for treatment with IFNs (alpha2 or beta) and ruxolitinib emphasizing the urgent need to explore these agents in the treatment of SARS-CoV-2 - both as monotherapies and in combination. In this context, we take advantage of several safety and efficacy studies in patients with the chronic myeloproliferative blood cancers (essential thrombocythemia, polycythemia vera and myelofibrosis) (MPNs), in whom IFN-alpha2 and ruxolitinib have been used successfully for the last 10 (ruxolitinib) to 30 years (IFN) as monotherapies and most recently in combination as well. In the context of these agents being highly immunomodulating (IFN boosting immune cells and JAK1/2 inhibitors being highly immunosuppressive and anti-inflammatory), we also discuss if statins and hydroxyurea, both agents possessing anti-inflammatory, antithrombotic and antiviral potentials, might be inexpensive agents to be repurposed in the treatment of SARS-CoV-2.

Microvesicles in active lupus nephritis show Toll-like receptor 9-dependent co-expression of galectin-3 binding protein and double-stranded DNA

Circulating microvesicles (MVs) from patients with systemic lupus erythematosus (SLE) express the type 1 interferon (IFN)-inducible protein galectin-3 binding protein (G3BP), which may enhance their deposition in the glomerular basement membrane. The release of G3BP-expressing MVs from normal peripheral blood mononuclear cells (PBMCs) is induced by Toll-like receptor 9 (TLR-9) ligands, and these vesicles contain autoantibody-accessible double-stranded DNA (dsDNA). This study compares the release of MVs expressing G3BP and dsDNA from PBMCs derived from SLE patients with or without active lupus nephritis (LN) and from healthy donors, and taps further into the potential dependency on IFN-α for their generation and impacts of TLR-7/TLR-9 co-stimulation. PBMCs from 10 healthy donors and 12 SLE patients, six of whom had active LN at study inclusion, were stimulated in-vitro with recombinant human IFN-α and the TLR-9 agonists oligodeoxynucleotide (ODN)2216 or ODN2395 alone or in combination with the TLR-7 agonist gardiquimod. MVs in the supernatants were subsequently isolated by differential centrifugation and their expression of G3BP and dsDNA was quantified by flow cytometry. Stimulation with ODN2395 significantly increased the release of MVs co-expressing G3BP and dsDNA from PBMCs isolated from healthy donors and SLE patients. The expression of G3BP on individual MVs and the proportion of G3BP and dsDNA double-positive MVs released were increased in active LN patients. Neither co-stimulation with gardiquimod nor with the IFN-α inhibitor IN-1 had any effect on the MV release induced by ODN2395. In conclusion, the TLR-9-mediated inducibility of MVs co-expressing G3BP and dsDNA is increased in SLE patients with active LN.

Quantitative PET imaging of PD-L1 expression in xenograft and syngeneic tumour models using a site-specifically labelled PD-L1 antibody

Purpose

Despite remarkable clinical responses and prolonged survival across several cancers, not all patients benefit from PD-1/PD-L1 immune checkpoint blockade. Accordingly, assessment of tumour PD-L1 expression by immunohistochemistry (IHC) is increasingly applied to guide patient selection, therapeutic monitoring, and improve overall response rates. However, tissue-based methods are invasive and prone to sampling error. We therefore developed a PET radiotracer to specifically detect PD-L1 expression in a non-invasive manner, which could be of diagnostic and predictive value.

Methods

Anti-PD-L1 (clone 6E11, Genentech) was site-specifically conjugated with DIBO-DFO and radiolabelled with ⁸⁹Zr (⁸⁹Zr-DFO-6E11). ⁸⁹Zr-DFO-6E11 was optimized in vivo by longitudinal PET imaging and dose escalation with excess unlabelled 6E11 in HCC827 tumour-bearing mice. Specificity of ⁸⁹Zr-DFO-6E11 was evaluated in NSCLC xenografts and syngeneic tumour models with different levels of PD-L1 expression. In vivo imaging data was supported by ex vivo biodistribution, flow cytometry, and IHC. To evaluate the predictive value of ⁸⁹Zr-DFO-6E11 PET imaging, CT26 tumour-bearing mice were subjected to external radiation therapy (XRT) in combination with PD-L1 blockade.

Results

⁸⁹Zr-DFO-6E11 was successfully labelled with a high radiochemical purity. The HCC827 tumours and lymphoid tissue were identified by ⁸⁹Zr-DFO-6E11 PET imaging, and co-injection with 6E11 increased the relative tumour uptake and decreased the splenic uptake. ⁸⁹Zr-DFO-6E11 detected the differences in PD-L1 expression among tumour models as evaluated by ex vivo methods. ⁸⁹Zr-DFO-6E11 quantified the increase in PD-L1 expression in tumours and spleens of irradiated mice. XRT and anti-PD-L1 therapy effectively inhibited tumour growth in CT26 tumour-bearing mice (p < 0.01), and the maximum ⁸⁹Zr-DFO-6E11 tumour-to-muscle ratio correlated with response to therapy (p = 0.0252).

Conclusion

PET imaging with ⁸⁹Zr-DFO-6E11 is an attractive approach for specific, non-invasive, whole-body visualization of PD-L1 expression. PD-L1 expression can be modulated by radiotherapy regimens and ⁸⁹Zr-DFO-6E11 PET is able to monitor these changes and predict the response to therapy in an immunocompetent tumour model.

Electronic supplementary material

The online version of this article (10.1007/s00259-019-04646-4) contains supplementary material, which is available to authorized users.

Abstract PR06: PET imaging of biomarkers in immuno-oncology for response prediction and treatment monitoring

Background: Cancer immuno-therapy has been established as a powerful way of treating several types of cancer. Expression of biomarkers on tumor and associated immune cells in the tumor microenvironment (TME) seems to reflect clinical outcome. The objective of the current work was to develop a toolbox for non-invasive PET imaging of PD-L1 expression and imaging of CD4+ and CD8a+ tumor-infiltrating lymphocytes for response prediction and treatment monitoring of immune stimulating therapies. Methods: PET radiotracers were generated from intact antibodies (anti-PD-L1, clone 6E11) or antibody fragments (R-anti-M-CD8a+ or R-anti-M-CD4+) and labeled with 89Zr or 64Cu. Syngeneic mouse models were selected based on their respective TME as analyzed by flow cytometry and immunohistochemistry (IHC). PET/CT imaging with 64Cu-NOTA-CD8a-F(ab)’2 in tumor-bearing CT26 mice after treatment with external radiation therapy (XRT) and anti-CTLA-4 was performed for treatment monitoring. Prediction of response to therapy with XRT and anti-PD-L1 was evaluated with 89Zr-DFO-6E11 in 4T1 and CT26 syngeneic mouse models. In vivo imaging data was compared with IHC and flow cytometry. Finally, murine CD3+ T-cells were directly labeled with 89Zr and evaluated in vivo in immunocompetent- and incompetent mice. The labeling efficiency and viability of the cells were evaluated ex vivo, and in vivo cell tracking was performed by longitudinal PET/CT imaging after injection of labeled T-cells in naive immune-competent mice. Results: Optimized protocols for labeling of anti-PD-L1 and fragments directed at CD8a+ and CD4+ with 89Zr or 64Cu were developed with high radiochemical yield and RCP of &gt;99%. PET/CT imaging with all tracers was performed to compare tumor, spleen and lymph node uptake. Blocking of endogenous CD8a+ and PD-L1 was successfully reflected by PET imaging with 89Zr-DFO-CD8a-F(ab)’2 and 89Zr-DFO-6E11, respectively. Fractionated XRT induced infiltration of CD8a+ cells in spleen and CT26 tumors which was detected by in vivo 89Zr-DFO-CD8a-F(ab)’2 PET imaging and ex vivo by IHC analysis. Increased tumor uptake of 64Cu-NOTA-CD8a-F(ab)’2 was seen in CT26 tumor bearing mice treated with fractionated XRT and anti-CTLA-4, and tumor growth was effectively inhibited in treatment groups with high uptake. Imaging with 89Zr-labeled anti-PD-L1 in the CT26 tumor model was able to predict subsequent response to PD-L1 therapy. Finally, longitudinal PET/CT imaging was able to track CD3+ T-cells directly labeled with 89Zr for up to 7 days following intra venous administration in immunocompetent mice. Conclusion: The developed radiotracers enable whole-body visualization of CD8a+ and CD4+ T-cells and PD-L1 expression in various syngeneic mouse models. These radiotracers can be used as tools to predict and monitor immune stimulating therapies in preclinical drug development. Furthermore, PET imaging of direct labeled T-cells is an attractive tool for investigating the distribution of cell-based therapies.

Citation Format: Carsten H. Nielsen, Lotte K. Kristensen, Camilla Christensen, Andreas Kjaer. PET imaging of biomarkers in immuno-oncology for response prediction and treatment monitoring [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr PR06. doi:10.1158/1535-7163.TARG-19-PR06

Abstract A011: Preclinical models of breast cancer brain metastasis for drug efficacy studies

Background: Overall, 10-30% of patients with metastatic breast cancer (BC) will develop brain metastases. Depending on the subtype of the primary breast cancer the incidence of brain metastases varies ranging from 14% (hormone receptor positive BC) to 46% (triple-negative BC) and approximately about 34% for patients with HER2-positive BC. The major impact of the blood-brain-barrier (BBB), BBB efflux pumps and the local microenvironment in the brain represent a challenge for treatment of BC brain metastasis and treatment options remain limited. The aim of this study was to develop a model system of breast cancer brain metastases for evaluation of drugs directed at BC brain metastases. Methods: Models of BC brain metastasis were established by intracranial stereotactic injection of enzymatically digested PDX tumors (ST340, ST941, ST1339, ST1616B, ST1360B, and ST3338) or by intracardiac or intracarotid injection of cell suspensions in nude mice. Contrast-enhanced T1- and T2-weighted magnetic resonance imaging (MRI) or bioluminescence imaging was used to determine tumor take and growth. Drug sensitivity to single agent trastuzumab emtansine (T-DM1) administered intravenously were performed at confirmed tumor take in a subset of the models. Mice were treated with either saline or T-DM1, 10 mg/kg/week x4 or 2 mg/kg/week x4. PET imaging with 18F-FES was applied in estrogen receptor (ER) positive models as a PD biomarker of anti-estrogen receptor endocrine therapy. Results: T-DM1 treatment in the intracranial ST1339 or ST3338 HER2 positive (3+) PDX models inhibited tumor growth and prolonged survival compared to non-treated animals. However, T-DM1 treatment only caused a modest growth delay in the ST3338 model established intracranially compared to a complete response in the model established subcutaneously. Delivery of T-DM1 across the BBB to the intracranial tumors was visualized by 64Cu-trastuzumab PET/CT and high tumor uptake was associated with a response to T-DM1 therapy in the ST1339 model. Models of BC brain metastasis were successfully established by the intracardiac or intracarotid methods for the triple negative BC cell line MDA-MB-231, the HER2 positive cell line BT474, and an ER positive cell line (ST941C). In vivo imaging with 18F-FES PET/CT was able to visualize intracranial ER positive BC tumors, and animals treated with fulvestrant exhibited reduced 18F-FES tumor uptake. Conclusion: We have established model systems of BC brain metastasis and drug efficacy evaluation. Treatment response to T-DM1 was observed in intracranial HER2 positive models and delivery of T-DM1 to the tumors was visualized by 64Cu-trastuzumab PET/CT imaging. Together, the established breast cancer brain metastases models in combination with advanced non-invasive imaging can be used as a relevant translational platform for evaluation of new drugs.

Citation Format: Carsten H. Nielsen, Michael J. Wick, Lotte K. Kristensen, Henriette S. Joergensen, Maria Z. Alfsen, Mark U. Juul, Alyssa Moriarty, Kyriakos P. Papadopoulos, Andreas Kjaer. Preclinical models of breast cancer brain metastasis for drug efficacy studies [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A011. doi:10.1158/1535-7163.TARG-19-A011

Proteomics-Based Comparative Mapping of the Secretomes of Human Brown and White Adipocytes Reveals EPDR1 as a Novel Batokine

Adipokines secreted from white adipose tissue play a role in metabolic crosstalk and homeostasis, whereas the brown adipose secretome is less explored. We performed high-sensitivity mass-spectrometry-based proteomics on the cell media of human adipocytes derived from the supraclavicular brown adipose and from the subcutaneous white adipose depots of adult humans. We identified 471 potentially secreted proteins covering interesting categories such as hormones, growth factors, extracellular matrix proteins, and proteins of the complement system, which were differentially regulated between brown and white adipocytes. A total of 101 proteins were exclusively quantified in brown adipocytes, and among these was ependymin-related protein 1 (EPDR1). EPDR1 was detected in human plasma, and functional studies suggested a role for EPDR1 in thermogenic determination during adipogenesis. In conclusion, we report substantial differences between the secretomes of brown and white human adipocytes and identify novel candidate batokines that can be important regulators of human metabolism.

CD4+ and CD8a+ PET imaging predicts response to novel PD-1 checkpoint inhibitor: studies of Sym021 in syngeneic mouse cancer models

Predicting the outcome of immunotherapy is essential for efficient treatment. The recent clinical success of immunotherapy is increasingly changing the paradigm of cancer treatment. Accordingly, the development of immune-based agents is accelerating and the number of agents in the global immuno-oncology pipeline has grown 60-70% over the past year. However, despite remarkable clinical efficacy in some patients, only few achieve a lasting clinical response. Treatment failure can be attributed to poorly immunogenic tumors that do not attract tumor infiltrating lymphocytes (TILs). Therefore, we developed positron emission tomography (PET) radiotracers for non-invasive detection of CD4⁺ and CD8a⁺ TILs in syngeneic mouse tumor models for preclinical studies.

Methods: Seven syngeneic mouse tumor models (B16F10, P815, CT26, MC38, Renca, 4T1, Sa1N) were quantified for CD4⁺ and CD8a⁺ TILs using flow cytometry and immunohistochemistry (IHC), as well as for tumor growth response to Sym021, a humanized PD-1 antibody cross-reactive with mouse PD-1. Radiotracers were generated from F(ab)'2 fragments of rat-anti-mouse CD4 and CD8a antibodies conjugated to the p-SCN-Bn-Desferrioxamine (SCN-Bn-DFO) chelator and radiolabeled with Zirconium-89 (⁸⁹Zr-DFO-CD4/⁸⁹Zr-DFO-CD8a). Tracers were optimized for in vivo PET/CT imaging in CT26 tumor-bearing mice and specificity was evaluated by depletion studies and isotype control imaging. ⁸⁹Zr-DFO-CD4 and ⁸⁹Zr-DFO-CD8a PET/CT imaging was conducted in the panel of syngeneic mouse models prior to immunotherapy with Sym021.

Results: Syngeneic tumor models were characterized as “hot” or “cold” according to number of TILs determined by flow cytometry and IHC. ⁸⁹Zr-DFO-CD4 and ⁸⁹Zr-DFO-CD8a were successfully generated with a radiochemical purity >99% and immunoreactivity >85%. The optimal imaging time-point was 24 hours post-injection of ~1 MBq tracer with 30 µg non-labeled co-dose. Reduced tumor and spleen uptake of ⁸⁹Zr-DFO-CD8a was observed in CD8a⁺ depleted mice and the uptake was comparable with that of isotype control (⁸⁹Zr-DFO-IgG2b) confirming specificity. PET imaging in syngeneic tumor models revealed a varying maximum tumor-to-heart ratio of ⁸⁹Zr-DFO-CD4 and ⁸⁹Zr-DFO-CD8a across tumor types and in-between subjects that correlated with individual response to Sym021 at day 10 relative to start of therapy (p=0.0002 and p=0.0354, respectively). The maximum ⁸⁹Zr-DFO-CD4 tumor-to-heart ratio could be used to stratify mice according to Sym021 therapy response and overall survival was improved in mice with a ⁸⁹Zr-DFO-CD4 ratio >9 (p=0.0018).

Conclusion: We developed ⁸⁹Zr-DFO-CD4 and ⁸⁹Zr-DFO-CD8a PET radiotracers for specific detection and whole-body assessment of CD4⁺ and CD8a⁺ status. These radiotracers can be used to phenotype preclinical syngeneic mouse tumor models and to predict response to an immune checkpoint inhibitor. We foresee development of such non-invasive in vivo biomarkers for prediction and evaluation of clinical efficacy of immunotherapeutic agents, such as Sym021.

Abstract 1133: ImmunoPET and T cell labeling for in vivo monitoring of immunotherapy: Development of CD8 Fab2’ and Fab tracers for immunoPET and direct labeling of T cells for in vivo tracking

Objectives: Cancer immunotherapy is becoming an increasingly important treatment strategy across a broad spectrum of tumor types. Non-invasive imaging methods for in vivo tracking of T-cells can be used for longitudinal monitoring of tumor infiltrating T-cells to assess the effect of immune checkpoint therapy or cell-based immunotherapies. The objective of the current work was to develop and optimize Fab-based tracers directed at CD8 for PET imaging of T cells. The imaging performance of radiolabeled Fab fragments was compared to Fab2’ fragments in terms of kinetics and image contrast. Furthermore, Zirconium-89 (89Zr) labeled T cells were tracked in a murine transplantation model.

Methods: Anti-mouse CD8α antibody was cleaved into Fab2’ by enzymatic cleavage followed by reduction of disulfide bridge into Fab fragments. Fab2’ was conjugated to NCS-DFO for 89Zr labeling, while both Fab2’ and Fab were conjugated to SCN-NOTA for Cupper-64 (Cu-64) labeling.

Radiochemical yield, radiochemical purity (RCP) and plasma/buffer stability was assessed by high-performance liquid chromatography. Furthermore, the immunoreactivity and binding affinity was evaluated for the radiolabeled tracers.

In vivo comparison of radiolabeled Fab2’ and Fab fragments was performed by longitudinal PET/CT imaging at various time-points after injection in CT26 (murine colon carcinoma) tumor bearing mice. CD3+ T-cells were directly labeled with 89Zr for tracking experiments. The labeling efficiency and viability of the cells was evaluated ex vivo, and in vivo cell tracking was performed by longitudinal PET/CT imaging after injection of labeled T-cells in naive immune-competent mice.

Results: The cleavage of anti-CD8 into Fab2’ and subsequent purification by HPLC was optimized to achieve a product with high yield and purity. The optimal Fab2’ reduction conditions were determined followed by conjugation to SCN-NOTA An optimized protocol for 89Zr/64Cu-CD8-Fab2’ and 64Cu-CD8-Fab was developed with high radiochemical yield and RCP of &gt;99%. PET/CT imaging with all tracers was performed to compare tumor, spleen and lymph node uptake. The highest uptake was found 24h post injection, but a clear delineation of lymphoid organs and tumors was evident already after 6h for the single Fab allowing same day imaging. T-cells labeled with 89Zr and cell tracking PET/CT imaging showed homing primarily to the spleen.

Conclusions: Different tracers directed at T-cells were successfully developed and evaluated in in vivo PET imaging of T cells. The reduced circulation time of Fab vs. Fab2’ and the use of 64Cu instead of 89Zr allows repeated imaging every 3 days due to the shorter physical half-life (12.7 h) of 64Cu. The study furthermore demonstrates the use of direct radiolabeling of T-cells as an attractive tool for investigating the distribution of cell-based therapies.

Citation Format: Camilla Christensen, Lotte K. Kristensen, Carsten H. Nielsen, Andreas Kjær. ImmunoPET and T cell labeling for in vivo monitoring of immunotherapy: Development of CD8 Fab2’ and Fab tracers for immunoPET and direct labeling of T cells for in vivo tracking [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1133.

Abstract 89: Development and characterization of a panel of orthotopic glioblastoma multiforme (GBM) patient-derived xenograft (PDX) mouse models for drug efficacy evaluation

Background

Glioblastoma multiforme (GBM) is an aggressive cancer type with poor prognosis and survival. The lack of effective treatment may be due to the complex molecular composition and the heterogeneity of the tumors. Subcutaneous patient derived xenograft (PDX) mouse models are widely used in drug development. However, the models fail at modeling the complex microenvironment in the brain and the impact of the blood brain barrier on drug bioavailability. Here we report the development and characterization a panel of orthotopic PDX mouse models.

Methods

Low passage subcutaneous tumors from ten different PDX GBM models (ST108, ST112, ST146, ST545, ST610, ST1388, ST2473, ST3537, ST3713, and ST3720) were implanted orthotopically. Tumor development and growth was monitored by T2-weighted magnetic resonance imaging (MRI). Mice were treated with either temozolomide or vehicle when tumor take was confirmed on an individual basis by MRI. Tumor treatment response was evaluated by MRI, and the final end-point was survival by humane endpoints. Whole brains and tumors were formalin fixed or snap frozen for histological evaluation of markers of invasiveness and cancer stem cells (Nestin, CD44, SOX2, and CXCR4).

In addition, the radiosensitivity of the models was characterized by fractionated external radiation therapy (XRT) delivered as 2 Gy QD x5 or sham in the subcutaneous setting. Expression of EGFR, EGFRvIII, MGMT and mGluR3 were evaluated by qPCR.

Results

The models displayed a wide range in expression levels of EGFR, EGFRvIII, MGMT and mGluR3. Mice treated with XRT showed a variable treatment outcome on both tumor volume and survival. The impact of XRT on prolongation of median survival ranged from 45% to 141%. In the orthotopic setting a variable range of sensitivities was observed in the models ranging from sensitive (ST610 and ST2473) to highly resistant (ST112).

Histologic evaluation showed typical characteristics of GBM tumors such as pseudopalisading cells. Furthermore, cell populations positive for cancer stem cell and invasiveness markers were detected by immunofluorescence imaging.

Conclusion

A panel of GBM PDX models was characterized for several molecular markers and the panel reflected the heterogeneity of human GBM tumors. The models displayed varying sensitivity towards XRT and TMZ.

The established panel of orthotopic GBM PDX models can be used as a platform for testing of new drugs in a setting that more closely mimics the GBM tumor microenvironment and impact of the blood brain barrier.

Citation Format: Carsten H. Nielsen, Maria Z. Alfsen, Michael J. Wick, Melissa Rundle, Johann M. Gudbergsson, Mette M. Jensen, Lotte K. Kristensen, Mark U. Juul, Kyriakos P. Papadopoulos, Andreas Kjaer. Development and characterization of a panel of orthotopic glioblastoma multiforme (GBM) patient-derived xenograft (PDX) mouse models for drug efficacy evaluation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 89.

Abstract 1130: PET imaging of tumor-immune status for response prediction and treatment monitoring in syngeneic mouse models

Introduction: Cancer immuno-therapy has been established as a powerful way of treating several types of cancer and the degree of immune cell infiltration in tumors seems to reflect the clinical outcome. Accordingly, non-invasive PET imaging of key immune cell subsets could become a valuable tool for tailoring cancer immuno-therapy. Therefore, we developed antibody-based PET tracers specific for CD8a+ and PD-L1 enabling visualization of tumor infiltrating T-cells and tumor PD-L1 status in syngeneic mouse models. Furthermore, we evaluated the ability of theses tracers to predict and monitor combinations of immune-stimulating therapies.

Experimental procedures: Radiotracers were generated from intact antibodies (anti-PD-L1, clone 6E11, humanized cross-reactive to mouse) or antibody fragments (R-anti-M-CD8a+) and were radiolabeled with 89Zr or 64Cu. Tracer specificity was evaluated by immuno-reactive fraction assays and blocking studies and compared to radiolabeled isotype controls. Syngeneic mouse models were selected based on their respective tumor microenvironment (TME) as analyzed by flow cytometry and immunohistochemistry (IHC). Treatment efficacy of external radiation therapy (XRT) and anti-CTLA-4 was evaluated by baseline and post-therapy scans with 64Cu-NOTA-CD8a-F(ab)’2 in CT26 tumor-bearing mice. Prediction of response to therapy with XRT and anti-PD-L1 was evaluated with 89Zr-DFO-6E11 in various syngeneic mouse models. In vivo imaging data was compared with IHC and flow cytometry.

Results: Tracers were highly specific for their targets with an immuno-reactivity &gt;85%. Blocking of endogenous CD8a+ and PD-L1 was successfully reflected by PET imaging with 89Zr-DFO-CD8a-F(ab)’2 and 89Zr-DFO-6E11, respectively. Fractionated XRT induced infiltration of CD8a+ cells in spleen and CT26 tumors which was detected by in vivo 89Zr-DFO-CD8a-F(ab)’2 PET imaging and ex vivo by IHC analysis. Studies with 89Zr-DFO-CD8a-F(ab)’2 PET imaging of combination therapies with fractionated XRT and immune checkpoint inhibitors are ongoing. 89Zr-DFO-6E11 successfully detected various degrees of PD-L1 expression in xenograft mouse models as well as the upregulated PD-L1 expression in syngeneic mouse models following fractionated XRT. Studies with 89Zr-DFO-6E11 PET imaging of combination therapies with fractionated XRT and immune checkpoint inhibitors are ongoing.

Conclusions: The developed radiotracers enable whole-body visualization of CD8a+ T cells and PD-L1 expression in various syngeneic mouse models. These radiotracers can be used as tools to predict efficacy of immuno-therapy in preclinical drug development. In addition, they may be valuable in vivo biomarkers of response to immune-therapy in patients.

Citation Format: Lotte K. Kristensen, Camilla Christensen, Carsten H. Nielsen, Andreas Kjaer. PET imaging of tumor-immune status for response prediction and treatment monitoring in syngeneic mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1130.

Abstract 3922: Biodistribution of Ra-224 and its daughter Pb-212 after intraperitoneal infusion of Ra-224 labeled microparticles in rats

Introduction: Radium-224 (Ra-224) labeled calcium carbonate (CaCO3) microparticles were developed with the intent to treat micrometastases located in the abdominal cavity. The slowly degradable microparticles act as carriers for the α-emitter Ra-224 and ensure high intraperitoneal (IP) retention of the radioactivity without cellular targeting. This novel α-therapy has a short action range in tissue and is designed to confine the radiation exposure to the IP cavity, treating both linings of the peritoneal surfaces and liquid volumes. The distribution of the Ra-224 labeled microparticles was examined by planar gamma imaging, SPECT and CT. The ex vivo biodistribution of Ra-224 and its progeny Pb-212 was also determined.

Experimental procedures: Fifteen female Wistar rats were infused IP with Ra-224-labeled microparticles (200-400 kBq, 100 mg CaCO3). The injections were performed by use of a perforated catheter (pigtail catheter), followed by a Plasmalyte flush to mimic the planned clinical administration. The Ra-224 labeled microparticles were imaged using both planar gamma imaging, SPECT and CT to evaluate the distribution over time in the abdominal region. Ex vivo biodistribution was performed 2, 24, 96, 168 and 336 hours after particle infusion and organs were harvested for activity measurements. The activity was determined at 2 hours and 48 hours after harvesting for all samples. This allowed differentiation between the biodistribution of Ra-224 and the biodistribution of its progeny Pb-212. Furthermore, 4 rats were injected IP with free Ra-224 and 2 rats were injected intravenously with free Ra-224 to achieve a baseline for the biodistribution. These control animals were euthanized at 24 and 168 hours, and 168 hours, respectively.

Results: Based on both CT and SPECT images, the particles distributed to the entire peritoneum, albeit with local areas of high microparticle concentration. Over the course of the experiment there was, as expected, a modest but evident systemic leakage of Ra-224 from the particles in the peritoneal cavity. The amount was estimated by the bone uptake of radioisotopes Pb-212 and Ra-224, using IP administered free Ra-224 as reference. The retention of Ra-224 in the peritoneal cavity was found to be &gt; 87% at 24 hours and &gt; 77% at 168 hours. Redistribution of the progeny Pb-212 was observed as modest uptake in the kidneys.

Conclusions: High peritoneal retention of both Ra-224 and its progeny Pb-212 after IP injection of Ra-224 labeled CaCO3 microparticles, was found in rats with high translational value to the clinical setting. SPECT imaging supported distribution of the Ra-224 labeled microparticles to the entire peritoneal lumen in the animals. SPECT and CT revealed some clusters of labeled microparticles. Due to the short range of the therapeutic relevant α-particles, the clusters are not expected to have an impact on therapeutic or safety aspects.

Citation Format: Jesper Fonslet, Carsten H. Nielsen, Lotte K. Kristensen, Ida S. Jorstad, Kim Lindland, Roy H. Larsen, Øyvind S. Bruland, Andreas Kjaer, Tina B. Bønsdorff. Biodistribution of Ra-224 and its daughter Pb-212 after intraperitoneal infusion of Ra-224 labeled microparticles in rats [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3922.

Site-specifically labeled 89Zr-DFO-trastuzumab improves immuno-reactivity and tumor uptake for immuno-PET in a subcutaneous HER2-positive xenograft mouse model

Antibody-based PET tracers are exceptionally well-suited for determination of the in vivo biodistribution and quantification of therapeutic antibodies. The continued expansion in antibody-based therapeutics has accordingly driven the development towards more robust conjugation strategies in order to reliably predict the performance of such agents. We therefore aimed to evaluate the effect of site-specific labeling by enzymatic remodeling on the stability, immuno-reactivity and tumor-targeting properties of the monoclonal antibody (mAb) trastuzumab and compare it to conventional, random labeling in a HER2-positive xenograft mouse model.

Methods: Trastuzumab was conjugated with the p-SCN-Bn-Desferrioxamine (SCN-Bn-DFO) chelator randomly on lysine residues or site-specifically on enzymatically modified glycans using either β-galactosidase or endoglycosidase S2 prior to ⁸⁹Zr radiolabeling. ⁸⁹Zr-DFO-trastuzumab was injected into SK-OV-3 tumor-bearing NMRI nude mice. The antibody dose was titrated with either 100 µg or 500 µg of unlabeled trastuzumab. Mice underwent small animal PET/CT imaging 24, 70 and 120 hours post-injection for longitudinal assessment. Parallel experiments were conducted with an isotype control matched antibody. In vivo imaging was supported by conventional ex vivo biodistribution and HER2 immuno-histochemistry. Furthermore, site-specifically labeled ⁸⁹Zr-DFO-trastuzumab was evaluated in a panel of subcutaneous patient-derived xenograft (PDX) models. Additionally, the affinity, in vitro stability and immuno-reactivity were assessed for all tracers.

Results: Site-specific labeling significantly increased PET tumor uptake (One-way ANOVA, p<0.0001) at all time-points when compared to random labeling. Mean tumor uptakes were 6.7 ± 1.7, 13.9 ± 3.3 and 15.3 ± 3.8 % injected dose per gram tissue (%ID/g) at 70 hours post-injection, for random, β-galactosidase or endoglycosidase S2 labeled probes, respectively. Co-injection with unlabeled trastuzumab increased the circulation time of tracers but did not alter tumor uptake notably. Site-specific probes presented with a superior in vitro stability and immuno-reactivity compared to the randomly labeled probe. Ex vivo biodistribution confirmed the data obtained by in vivo PET imaging, and site-specific ⁸⁹Zr-DFO-trastuzumab successfully detected HER2-positive tumors in PDX mouse models.

Conclusion: ⁸⁹Zr-DFO-trastuzumab is well-matched for specific immuno-PET imaging of HER2-positive tumors and site-specific labeling of trastuzumab by the SiteClick^TM technology minimizes the impact of the DFO chelator on immuno-reactivity, stability and biodistribution. These findings support further development of site-specifically radiolabeled mAbs for immuno-PET.

Lewis and AB0 blood group-phenotypes in periodontitis, cardiovascular disease, obesity and stroke

The AB0 blood group has been linked to ischaemic heart disease, stroke, and periodontal disease, while the Lewis blood group has been linked to ischaemic heart disease and obesity, all of which have been associated with periodontitis. AB0 or Lewis blood group phenotype may therefore constitute common hereditary components predisposing to these disorders. In this study, we investigated if blood group phenotype associated with periodontitis in a subpopulation consisting of 702 participants from a Danish cross-sectional cohort and, secondarily, attempted to confirm their association with hypertension, ischaemic heart disease, stroke, and obesity. No significant association between blood group phenotype and periodontitis was detected, nor were previously reported associations between blood group phenotype and hypertension, ischaemic heart disease, stroke, and obesity confirmed. This may, at least partly, be attributed to differences in study type, outcome definitions, cohort sizes, and population attributable factors. However, our results suggested a strong association between self-reported stroke and the Lewis (a−b−) phenotype (P = 0.0002, OR: 22.28; CI 95: 4.72–131.63).

Oxime Coupling of Active Site Inhibited Factor Seven with a Nonvolatile, Water-Soluble Fluorine-18 Labeled Aldehyde

A nonvolatile fluorine-18 aldehyde prosthetic group was developed from [¹⁸F]SFB, and used for site-specific labeling of active site inhibited factor VII (FVIIai). FVIIai has a high affinity for tissue factor (TF), a transmembrane protein involved in angiogenesis, proliferation, cell migration, and survival of cancer cells. A hydroxylamine N-glycan modified FVIIai (FVIIai-ONH₂) was used for oxime coupling with the aldehyde [¹⁸F]2 under mild and optimized conditions in an isolated RCY of 4.7 ± 0.9%, and a synthesis time of 267 ± 5 min (from EOB). Retained binding and specificity of the resulting [¹⁸F]FVIIai to TF was shown in vitro. TF-expression imaging capability was evaluated by in vivo PET/CT imaging in a pancreatic human xenograft cancer mouse model. The conjugate showed exceptional stability in plasma (>95% at 4 h) and a binding fraction of 90%. In vivo PET/CT imaging showed a mean tumor uptake of 3.8 ± 0.2% ID/g at 4 h post-injection, a comparable uptake in liver and kidneys, and low uptake in normal tissues. In conclusion, FVIIai was labeled with fluorine-18 at the N-glycan chain without affecting TF binding. In vitro specificity and a good in vivo imaging contrast at 4 h postinjection was demonstrated.

A blood biomarker for monitoring response to anti-EGFR therapy

BACKGROUND AND OBJECTIVE

To monitor therapies targeted to epidermal growth factor receptors (EGFR) in non-small cell lung cancer (NSCLC), we investigated Peroxiredoxin 6 (PRDX6) as a biomarker of response to anti-EGFR agents.

METHODS

We studied cells that are sensitive (H3255, HCC827) or resistant (H1975, H460) to gefitinib. PRDX6 was examined with either gefitinib or vehicle treatment using enzyme-linked immunosorbent assays. We created xenograft models from one sensitive (HCC827) and one resistant cell line (H1975) and monitored serum PRDX6 levels during treatment.

RESULTS

PRDX6 levels in cell media from sensitive cell lines increased significantly after gefitinib treatment vs. vehicle, whereas there was no significant difference for resistant lines. PRDX6 accumulation over time correlated positively with gefitinib sensitivity. Serum PRDX6 levels in gefitinib-sensitive xenograft models increased markedly during the first 24 hours of treatment and then decreased dramatically during the following 48 hours. Differences in serum PRDX6 levels between vehicle and gefitinib-treated animals could not be explained by differences in tumor burden.

CONCLUSIONS

Our results show that changes in serum PRDX6 during the course of gefitinib treatment of xenograft models provide insight into tumor response and such an approach offers several advantages over imaging-based strategies for monitoring response to anti-EGFR agents.

Peptidylarginine deiminase-4 gene polymorphisms are associated with systemic lupus erythematosus and lupus nephritis

OBJECTIVE

Peptidylarginine deiminase-4 (PAD4) is highly expressed by neutrophils and essential for citrullination occurring during the formation of neutrophil extracellular traps, which have been implicated in the pathogenesis of systemic lupus erythematosus (SLE) and lupus nephritis (LN). Single-nucleotide polymorphisms (SNPs) in PADI4 influence PAD4 expression and functionality. Here, we investigate whether SNPs in PADI4 influence the risk of SLE or LN.

METHOD

Altogether, 234 SLE patients and 484 controls were genotyped for nine PADI4 SNPs known to alter PAD4 functionality and/or expression, or to be associated with other autoimmune diseases, using an in-house multiplex Luminex assay. All analyses were adjusted for age and gender.

RESULTS

Heterozygosity for rs1748033, and heterozygosity and homozygosity for rs1635564, were associated with increased occurrence of SLE [odds ratio (OR) 1.55, 95% confidence interval (CI) 1.08-2.23; OR 1.52, 95% CI 1.06-2.19; and OR 2.06, 95% CI 1.08-3.93, respectively]. Homozygosity for rs1635564 was also associated with increased occurrence of LN (OR 3.35, 95% CI 1.2-10.97). Notably, gene dose effects of the rs1635564 variant allele were observed for SLE (p = 0.005) and LN (p = 0.01). Carriage of minor alleles of five other SNPs (rs11203366, rs11203367, rs874881, rs2240340, and rs11203368) was associated with increased occurrence of LN and hypertension.

CONCLUSION

The rs1635564 polymorphism of PADI4 is a candidate risk factor for SLE, particularly with renal involvement. Additional PADI4 polymorphisms also conferred increased risk of LN. Overall, these findings support the notion of PAD4 contributing to the pathogenesis of SLE and LN.

Cardiolipin Synthesis in Brown and Beige Fat Mitochondria Is Essential for Systemic Energy Homeostasis

Activation of energy expenditure in thermogenic fat is a promising strategy to improve metabolic health, yet the dynamic processes that evoke this response are poorly understood. Here we show that synthesis of the mitochondrial phospholipid cardiolipin is indispensable for stimulating and sustaining thermogenic fat function. Cardiolipin biosynthesis is robustly induced in brown and beige adipose upon cold exposure. Mimicking this response through overexpression of cardiolipin synthase (Crls1) enhances energy consumption in mouse and human adipocytes. Crls1 deficiency in thermogenic adipocytes diminishes inducible mitochondrial uncoupling and elicits a nuclear transcriptional response through endoplasmic reticulum stress-mediated retrograde communication. Cardiolipin depletion in brown and beige fat abolishes adipose thermogenesis and glucose uptake, which renders animals insulin resistant. We further identify a rare human CRLS1 variant associated with insulin resistance and show that adipose CRLS1 levels positively correlate with insulin sensitivity. Thus, adipose cardiolipin has a powerful impact on organismal energy homeostasis through thermogenic fat bioenergetics.

Abstract 3030: Immuno PET imaging of PD-L1 expression in syngeneic and human xenograft tumor mouse models using a site-specific 89Zr labeled PD-L1 antibody

Objectives: One of the major checkpoints probed for therapy is programmed cell death protein 1 (PD-1) and its ligand PD-L1. Despite remarkable clinical efficacy, not all patients benefit from immune checkpoint therapy with PD-1/PD-L1 antibodies, and a cohort of non-responding patients exists. Tumor PD-L1 expression measured by immunohistochemistry has been applied as a biomarker for selecting patients to increase the response rate of PD-1/PD-L1 blockage, but the methods are invasive and prone to sampling error. The objective of the current work was therefore to develop an image-based biomarker for non-invasive Positron-Emission Tomography (PET) imaging of PD-L1 expression

Methods: Anti-PD-L1 (clone 6E11, Genentech) was site-specifically conjugated to dibenzocyclooctyne-Deferoxamine (DIBO-DFO) using GlyclNATOR® (EndoS2) and SiteClickTM technology. Site-specific conjugated 6E11 was subsequently radiolabeled with 89Zr.

The immunoreactivity and KD value were determined by cell binding assays. In vitro stability was assessed by high-performance liquid chromatography (HPLC) and the degree of labeling (DOL) was determined by LC/MS. A dose escalating study was performed with or without co-injection with unlabeled 6E11 to determine the optimal mass dose for PET imaging. Longitudinal PET/CT imaging was performed at various time-points after tracer injection in HCC827 tumor (lung adenocarcinoma) bearing animals and ex vivo biodistribution was performed after the last imaging time-point. Additionally, PET/CT imaging studies were carried out in different human xenograft and syngeneic tumor models with varying degree of PD-L1 expression. The syngeneic tumors received either fractionated external radiation therapy (XRT) or mouse Interferon gamma (IFNγ) treatment 3 days prior to 89Zr-DFO-6E11 PET/CT imaging in order to evaluate treatment induced up regulation of PD-L1 expression.

Results: 89Zr-DFO-6E11 was successfully labeled with a radiochemical purity &gt;99% and the KD value was determined to 0.23 nM. The HCC827 tumors were identified by 89Zr-DFO-6E11 PET imaging (3.7 ± 0.2 %ID/g, mean ± SD), and co-injection of unlabeled 6E11 increased the relative tumor uptake. Ex vivo biodistribution confirmed the in vivo results (5.4 ± 1.7 %ID/g) at 144 hours post injection. Non-invasive PET /CT imaging with 89Zr-DFO-6E11 was able to detect a treatment induced up regulation of PD-L1 expression following treatment with XRT or IFNγ.

Conclusions: Site-specific labeling of antibodies with 89Zr is feasible for immuno-PET imaging and tumor PD-L1 imaging by 89Zr-DFO-6E11. PET/CT is an attractive approach for non-invasive whole body visualization of PD-L1 expression and could potentially aid in therapy guidance. Site-specific labeled antibodies create the opportunity to utilize imaging biomarker-driven approaches to achieve best clinical outcomes in immunotherapy.

Citation Format: Camilla Christensen, Lotte K Kristensen, Hanna Toftevall, Maria Nordgren, Brian J. Agnew, Carsten H. Nielsen, Andreas Kjaer. Immuno PET imaging of PD-L1 expression in syngeneic and human xenograft tumor mouse models using a site-specific 89Zr labeled PD-L1 antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3030.

Abstract 2161: Characterization of a panel of orthotopic glioblastoma multiforme (GBM) patient-derived xenograft (PDX) mouse models and efficacy evaluation of temozolomide and external radiation therapy

Background Glioblastoma multiforme (GBM) is an aggressive cancer type with poor prognosis. The lack of effective treatment may be due to the complex molecular composition and the heterogeneity of the tumors. Standard of care treatment is surgery, external radiation therapy (XRT) and chemotherapy with temozolomide (TMZ); however, the response rate varies widely. Subcutaneous patient-derived xenograft (PDX) models are increasingly used during drug development. Implantation of GBM PDX tumors orthotopically in the brain displays an advantage as the tumors develop in a microenvironment that resembles that of the original patient tumor. In addition, the impact of the blood brain barrier (BBB) in terms of reduced drug bioavailability is also represented in the orthotopic GBM models. The aim of this study was to develop and characterize a panel of orthotopic GBM PDX models. The models were then used to study the efficacy of TMZ and XRT.

Methods A panel of 14 PDX GBM models was characterized for EGFR, EGFRvIII, MGMT and mGluR3 expression. Selected PDX GBM models were furthermore characterized for GBM stem cell markers by flow cytometry. Low passage subcutaneous tumors from seven PDX GBM models (ST108, ST112, ST146, ST545, ST610, ST1388 and ST2473) were used for assessment of XRT sensitivity. Mice were randomized to receive XRT (2 Gy/day for 5 days) or sham. Furthermore, subcutaneous tumors were enzymatically digested and used for intracranial stereotactic injection in nude mice. Tumor take and growth rate was determined by T2-weighted magnetic resonance imaging (MRI) and 18F-fluoro-ethyl-L-tyrosine (18F-FET) PET imaging. At confirmed tumor take, mice were treated with TMZ (20 mg/mg 5 days on/2 days off x3 or 100mg/kg/day for 5 days) or whole brain XRT (2 Gy/day for 5 days). Control groups received vehicle or sham XRT. Final endpoint was survival by humane endpoints and tumors were fixed in formalin for histologic evaluation.

Results A wide variation in expression levels of EGFR, EGFRvIII, MGMT and mGluR3 was observed in the PDX GBM panel. Three models had EGFRvIII mutation and all models had variable expression levels of EGFR. XRT showed a variable efficacy outcome on both tumor volume and survival in the PDX GBM models in the subcutaneous and orthotopic setting. TMZ showed efficacy in ST610 and ST2473 whereas ST146 and ST112 were resistant towards TMZ. Histologic evaluation showed typical characteristics of GBM tumors.

Conclusion A panel of GBM PDX models was characterized for several molecular markers and the panel reflected the heterogeneity of human GBM tumors. The orthotopic GBM PDX models showed a wide range of sensitivity towards both TMZ and XRT. The established panel of orthotopic GBM PDX models can be used as a platform for testing of new drugs in a setting that more closely mimic the GBM tumor microenvironment and impact of the BBB.

Citation Format: Mette Munk Jensen, Michael J. Wick, Lotte K. Kristensen, Maria Z. Alfsen, Laura A. Paludan, Mark Juul, Melissa Rundle, Kyriakos P. Papadopoulos, Andreas Kjær, Carsten H. Nielsen. Characterization of a panel of orthotopic glioblastoma multiforme (GBM) patient-derived xenograft (PDX) mouse models and efficacy evaluation of temozolomide and external radiation therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2161.

Abstract 1723: CD4+ and CD8a+ PET imaging in syngeneic mouse models for prediction of immuno-therapeutic response

Introduction: The clinical success of immune-checkpoint inhibitors in oncology has stimulated development of immune-based agents and revolutionized treatment for many types of cancer. With only a subpopulation of patients benefiting from immuno-therapeutic agents, the development of a predictive in vivo biomarker of response is critical to enhance the therapeutic efficacy of such agents. The level of immune infiltration in tumors seems to reflect the outcome of immuno-therapy, and treatment failure is usually attributed to the so-called “cold” tumors that do not attract T-cell infiltration. Thus, we sought to develop specific PET radiotracers for non-invasive in vivo detection, tracking and quantification of CD4+ and CD8a+ tumor-infiltrating lymphocytes (TILs).

Experimental procedures: A panel of syngeneic mouse tumor models was analyzed for the level of TILs using flow cytometry and immunohistochemistry (IHC), and for response to Sym021, a humanized anti-PD1 antibody cross-reactive with mouse PD1. Radiotracers were generated from F(ab)'2 fragments of rat-anti-mouse CD4 and CD8a antibodies conjugated to the p-SCN-Bn-Deferoxamine (p-SCN-Bn-DFO) chelator and radiolabeled with 89Zr. Immuno-reactivity of 89Zr-DFO-CD4-F(ab)'2 and 89Zr-DFO-CD8a-F(ab)'2 was assessed with murine T-cells. Tracers were assessed in vivo in a panel of syngeneic mouse models following optimization of dose and imaging time-points.

Results: Based on flow cytometry and IHC analysis, the syngeneic tumor models were characterized as “hot” or “cold” by the level of TILs. The “hot” tumor phenotype clearly correlated with response to Sym021 treatment. 89Zr-labeled CD4- and CD8a-targeting radiotracers were successfully generated with a radiochemical purity &gt;99% and an immuno-reactivity &gt;85%. The optimal imaging parameters were 24 hours post-injection of 1 MBq of tracer. Co-injection with 30 μg unlabeled CD4/CD8a-F(ab)'2 significantly decreased spleen and lymph node uptake, whereas tumor uptake was increased. PET imaging in syngeneic mouse models revealed differential uptake of 89Zr-DFO-CD4-F(ab)'2 and 89Zr-DFO-CD8a-F(ab)'2, with an increased uptake primarily seen in “hot” tumors. In addition, an increase in CD8a+ TILs after fractionated external radiation therapy (XRT) was successfully detected by 89Zr-DFO-CD8a-F(ab)'2 PET imaging.

Conclusions: We have developed 89Zr-DFO-CD4-F(ab)'2 and 89Zr-DFO-CD8a-F(ab)'2 PET imaging radiotracers for whole-body detection and assessment of CD4+ and CD8a+ status. These radiotracers can be used as tools to predict efficacy of immuno-therapeutic treatment in preclinical drug development. In addition, they may be used to develop non-invasive in vivo biomarkers for identifying patients responding to immuno-therapeutic agents, such as Sym021.

Citation Format: Lotte K. Kristensen, Camilla Fröhlich, Camilla Christensen, Maria C. Melander, Thomas T. Poulsen, Gunther R. Galler, Johan Lantto, Ivan D. Horak, Michael Kragh, Carsten H. Nielsen, Andreas Kjaer. CD4+ and CD8a+ PET imaging in syngeneic mouse models for prediction of immuno-therapeutic response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1723.

Abstract 2174: Intracranial PDX models of breast cancer brain metastases and PET imaging for drug efficacy studies

Background: Overexpression of the human epidermal growth factor receptor 2 (HER2) is an independent risk factor for development of brain metastases. Between 37-55% of patients with HER2-positive metastatic breast cancer develop brain metastases and the incidence is increasing. A reason for the increase of brain metastases is the improved control of systemic disease by novel therapeutics such as ado-trastuzumab emtansine (T-DM1). However, the major impact of the blood-brain-barrier (BBB), BBB efflux pumps and the local microenvironment in the brain represent a challenge for treatment of brain metastases. The aim of this study was to develop a model system of HER2 positive breast cancer brain metastases for evaluation of drugs directed at brain metastases.

Methods: Subcutaneous tumors from a panel of HER2-positive PDX breast cancer models designated ST340, ST1339, ST1616B, ST1360B and ST3338 were enzymatically digested and used for intracranial stereotactic injection or intra carotid injection in nude mice. Contrast-enhanced T1- and T2-weighted Magnetic Resonance Imaging (MRI) were used to determine tumor take and growth.

Drug sensitivity studies to single agent T-DM1 administered intravenously were performed at confirmed tumor take in a subset of the models. Mice were treated with either saline or T-DM1, 10 mg/kg/week x4 or 2 mg/kg/week x4. Delivery of T-DM1 to the tumor site was evaluated by PET/CT imaging with 64Cu-trastuzumab.

Results: Intracranial tumor growth was detected by MR imaging in all models. T-DM1 treatment of animals with intracranial ST1339 or ST3338 tumors inhibited tumor growth and prolonged survival compared to non-treated animals. A variable response within the treatment groups was observed. Delivery of T-DM1 across the BBB to the intracranial tumors was visualized by 64Cu-trastuzumab PET/CT and high tumor uptake was associated with a response to T-DM1 therapy in the ST1339 model.

Conclusion: We have established a model system for evaluating drug sensitivity in HER2 positive breast cancer brain metastases. Treatment response to T-DM1 was observed in the models. 64Cu-trastuzumab PET imaging confirmed delivery of trastuzumab to the tumors, and high uptake was associated with an increased response to T-DM1 therapy.

Together, the established PDX models of breast cancer and brain metastases can be used as a relevant translational platform in combination with advanced non-invasive imaging for evaluation of new drugs.

Citation Format: Carsten H. Nielsen, Michael J. Wick, Mette M. Jensen, Lotte K. Kristensen, Alyssa Moriarty, Melissa Rundle, Kyriakos P. Papadopoulos, Andreas Kjaer. Intracranial PDX models of breast cancer brain metastases and PET imaging for drug efficacy studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2174.

Abstract A011: HER2-positive PDX model of breast cancer brain metastasis obtained from patient prior to T-DM1 therapy

Background: Ado-trastuzumab emtansine (T-DM1), a recently approved antibody-drug conjugate (ADC), is approved for treatment of high HER2-expressing (3+), trastuzumab-resistant breast and gastric cancers. While this agent is effective, HER2-positive breast cancer patients have a high risk of brain relapse, seen in up to 37% of patients of whom half die as a result of failure to control the intracranial disease. The aim of this study was to develop a model system that reflects the breast cancer brain metastases seen in patients undergoing T-DM1 therapy. We collected brain metastasis tissue from an HER2-positive breast cancer patient prior to receiving T-DM1 therapy. Methods: The high HER2-expressing (3+) breast cancer brain metastasis model designated ST3338 was established subcutaneously in athymic nude mice using biopsy material from a brain metastasis obtained from a 42-year-old breast cancer patient. The patient was on T-DM1 therapy following sample collection and had received prior treatment with trastuzumab, bevacizumab, and lapatinib. Immunohisotochemistry of both clinical and PDX tissues was applied to assess the estrogen (ER), progesterone (PR), and HER2 receptor levels. Drug sensitivity studies were performed in the ST3338 model established subcutaneously in athymic nude mice to single-agent T-DM1 administered intravenously as a single dose at 10 mg/kg. The ST3338 was also established orthotopically by stereotactic intracranial inoculation of enzymatically digested ST3338 tumor tissue. Tumor development was monitored by T2-weighted MR imaging and the study endpoint was survival by humane endpoints. Results: Immunohistochemistry of PDX tissues was scored as ER (0), PR (0), and HER2 (3+), which corresponded to the clinical brain metastasis sample: ER (0), PR (0), and HER2 (3+). A single dose of T-DM1 at 10 mg/kg showed tumor regression compared with Day 0 (T/C = 0%) in the subcutaneous setting. The ST3338 model was successfully established orthotopically determined by longitudinal T2-weighted MR imaging, and efficacy data of T-DM1 in the orthotopic/intracranial setting are pending. Conclusion: We have established a model system for evaluating drug sensitivity in HER2-positive breast cancer brain metastases. Treatment response to T-DM1 was observed in the subcutaneous setting. With the combination of subcutaneous and intracranial PDX models of breast cancer brain metastases, new drugs can be tested in preclinical models that more closely mimic the microenvironment and the challenges of drug delivery across the blood-brain barrier in breast cancer patients.

Citation Format: Carsten H. Nielsen, Michael J. Wick, Lizette Gamez, Camilla S. Knudsen, Mette M. Jense, Melissa Rundle, Kyriakos P. Papadopoulos, Andreas Kjaer. HER2-positive PDX model of breast cancer brain metastasis obtained from patient prior to T-DM1 therapy [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A011.

Site-Specific 64Cu Labeling of the Serine Protease, Active Site Inhibited Factor Seven Azide (FVIIai-N3), Using Copper Free Click Chemistry

A method for site-specific radiolabeling of the serine protease active site inhibited factor seven (FVIIai) with ⁶⁴Cu has been applied using a biorthogonal click reaction. FVIIai binds to tissue factor (TF), a trans-membrane protein involved in hemostasis, angiogenesis, proliferation, cell migration, and survival of cancer cells. First a single azide moiety was introduced in the active site of this 50 kDa protease. Then a NOTA moiety was introduced via a strain promoted azide-alkyne reaction and the corresponding conjugate was labeled with ⁶⁴Cu. Binding to TF and the stability was evaluated in vitro. TF targeting capability of the radiolabeled conjugate was tested in vivo by positron emission tomography (PET) imaging in pancreatic human xenograft cancer mouse models with various TF expressions. The conjugate showed good stability (>91% at 16 h), an immunoreactivity of 93.5%, and a mean tumor uptake of 2.1 ± 0.2%ID/g at 15 h post injection. In conclusion, FVIIai was radiolabeled with ⁶⁴Cu in single well-defined position of the protein. This method can be utilized to prepare conjugates from serine proteases with the label at a specific position.

Uremia does not affect neointima formation in mice

Atherosclerotic cardiovascular disease is a major complication of chronic kidney disease (CKD). CKD leads to uremia, which modulates the phenotype of aortic smooth muscle cells (SMCs). Phenotypic modulation of SMCs plays a key role in accelerating atherosclerosis. We investigated the hypothesis that uremia potentiates neointima formation in response to vascular injury in mice. Carotid wire injury was performed on C57BL/6 wt and apolipoprotein E knockout (Apoe^−/−) mice two weeks after induction of uremia by 5/6 nephrectomy. Wire injury led to neointima formation and downregulation of genes encoding classical SMC markers (i.e., myocardin, α-smooth muscle actin, SM22-alpha, and smooth muscle myosin heavy chain) in both wt and Apoe^−/− mice. Contrary to our expectations, uremia did not potentiate neointima formation, nor did it affect intimal lesion composition as judged from magnetic resonance imaging and histological analyses. Also, there was no effect of uremia on SMC marker gene expression in the injured carotid arteries, suggesting that there may be different effects of uremia on SMCs in different vascular beds. In conclusion, uremia does not accelerate neointima formation in response to wire injury of the carotid artery in mice.

Neodymium-140 DOTA-LM3: Evaluation of an In Vivo Generator for PET with a Non-Internalizing Vector

¹⁴⁰Nd (t_1/2 = 3.4 days), owing to its short-lived positron emitting daughter ¹⁴⁰Pr (t_1/2 = 3.4 min), has promise as an in vivo generator for positron emission tomography (PET). However, the electron capture decay of ¹⁴⁰Nd is chemically disruptive to macrocycle-based radiolabeling, meaning that an in vivo redistribution of the daughter ¹⁴⁰Pr is expected before positron emission. The purpose of this study was to determine how the delayed positron from the de-labeled ¹⁴⁰Pr affects preclinical imaging with ¹⁴⁰Nd. To explore the effect, ¹⁴⁰Nd was produced at CERN-ISOLDE, reacted with the somatostatin analogue, DOTA-LM3 (1,4,7,10- tetraazacyclododecane, 1,4,7- tri acetic acid, 10- acetamide N - p-Cl-Phecyclo(d-Cys-Tyr-d-4-amino-Phe(carbamoyl)-Lys-Thr-Cys)d-Tyr-NH2) and injected into H727 xenograft bearing mice. Comparative pre- and post-mortem PET imaging at 16 h postinjection was used to quantify the in vivo redistribution of ¹⁴⁰Pr following ¹⁴⁰Nd decay. The somatostatin receptor-positive pancreas exhibited the highest tissue accumulation of ¹⁴⁰Nd-DOTA-LM3 (13% ID/g at 16 h) coupled with the largest observed redistribution rate, where 56 ± 7% (n = 4, mean ± SD) of the in situ produced ¹⁴⁰Pr washed out of the pancreas before decay. Contrastingly, the liver, spleen, and lungs acted as strong sink organs for free ¹⁴⁰Pr³⁺. Based upon these results, we conclude that ¹⁴⁰Nd imaging with a non-internalizing vector convolutes the biodistribution of the tracer with the accumulation pattern of free ¹⁴⁰Pr. This redistribution phenomenon may show promise as a probe of the cellular interaction with the vector, such as in determining tissue dependent internalization behavior.

Abstract 2858: Immuno-PET with site-specific labeled 89Zr-DFO-trastuzumab improves immuno-reactivity and tumor uptake in a subcutaneous HER2 positive xenograft mouse model of ovarian adenocarcinoma

Introduction: The combination of PET with the specificity of monoclonal antibodies (mAbs), immuno-PET, is an attractive approach to improve tumor detection and mAb quantification. 89Zirconium (89Zr) is particularly well-matched for the long circulatory half-life of intact mAbs. Previously, the use of 89Zr has been limited by the lack of suitable methods for stable coupling to mAbs. In addition, the conventional labeling strategies with random introduction of a chelator potentially reduce antibody binding and affinity towards target. Here we demonstrate the application of an enzyme- and click chemistry-mediated methodology for site-specifically labeled 89Zr immuno-PET imaging probes and compare them to a random labeled probe.

Experimental procedures: Trastuzumab was conjugated to the p-SCN-Bn-Deferoxamine (p-SCN-Bn-DFO) chelator in three alternate ways: (1) randomly on lysine residues or site-specifically on enzymatically treated glycans using either (2) ß-galactosidase or (3) endoglycosidase S2. DFO-trastuzumab was radiolabeled with 89Zr (89Zr-DFO-trastuzumab) and injected into SK-OV-3 tumor-bearing NMRI nude mice. In addition, a dose-escalation study was performed with co-injection of either 100 µg or 500 µg of unlabeled trastuzumab. At 24, 70 and 110 hours post-injection, mice underwent small animal PET/CT imaging for longitudinal assessment. Mice were euthanized and organs resected for ex vivo biodistribution after the last imaging time-point. Additionally, the immuno-reactivity and tracer stability in buffer and plasma were assessed for all three tracers.

Results: All tracers were found to be stable for up to 5 days post-labeling. PET imaging at 24, 70 and 110 hours after injection of 89Zr-DFO-trastuzumab revealed a gradual increase in tumor uptake and image contrast over the time-course. At 70 hours post-injection mean tumor uptakes were 6.7 ± 1.7, 13.9 ± 3.3 and 15.3 ± 3.8 % injected dose per gram tissue (%ID/g), for random, ß-galactosidase or endoglycosidase S2 labeled probes, respectively. Site-specific labeling significantly increased tumor PET uptake (One-way ANOVA, p &lt; 0.0001) at all time-points compared to random labeling. This was further supported by an immuno-reactivity of 93% for site-specific labeled probes compared to 80% for the random labeled trastuzumab. Titration with unlabeled trastuzumab did not affect tumor uptake considerably and the ex vivo biodistribution confirmed the data obtained by in vivo PET imaging.

Conclusions: 89Zr-DFO-trastuzumab is well suited for specific immuno-PET imaging of HER2 positive ovarian cancer and site-specific labeling of trastuzumab presents with markedly higher immuno-reactivity and tumor specificity. These findings support the further development of site-specific radiolabeled monoclonal antibodies for immuno-PET.

Citation Format: Lotte K. Kristensen, Camilla Christensen, Camilla S. Knudsen, Mette M. Jensen, Brian J. Agnew, Andreas Kjaer, Carsten H. Nielsen. Immuno-PET with site-specific labeled 89Zr-DFO-trastuzumab improves immuno-reactivity and tumor uptake in a subcutaneous HER2 positive xenograft mouse model of ovarian adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2858. doi:10.1158/1538-7445.AM2017-2858

Abstract 2805: A panel of orthotopic glioblastoma multiforme (GBM) patient derived xenograft (PDX) mouse models for efficacy evaluation of drugs

Background:

Patients with glioblastoma multiforme (GBM) have a poor prognosis and few treatment options; hence new treatments are needed. Subcutaneous patient derived xenograft (PDX) models are increasingly used for efficacy studies in drug development. However, orthotopic implantation confers a translational advantage as the cancer develops in a microenvironment more closely mimicking that of the original patient tumor. Also the major impact of the blood brain barrier that must be taking into account when targeting brain tumors as GBM in terms of drug bioavailability is better represented in the orthotopic models.

The aim of this study was therefore to develop a panel of orthotopic GBM PDX models for pre-clinical efficacy studies of new drugs. The models were then used to study the efficacy of standard of care such as temozolomide (TMZ) and external radiation therapy (XRT).

Methods: Low passage subcutaneous tumors from six different PDX GBM models designated ST108, ST112, ST146, ST545, ST610 and ST2473 were digested and used for intracranial stereotactic injection in nude mice. Tumor take and growth was determined by T2-weighted magnetic resonance imaging (MRI). At confirmed tumor take mice were either treated with TMZ (100mg/kg/day for 5 days) or whole brain XRT (2 Gy/day for 5 days). Control groups receiving vehicle or sham XRT were included depending on treatment regiment. Final endpoint was survival by humane endpoints and tumors were fixed in formalin for histological evaluation.

Results: MRI confirmed tumor take in all models within 5 weeks of implantation. The take rate was &gt; 80% across all models. TMZ showed efficacy in the orthotopic ST610 GBM PDX model evaluated by MRI on day 14 (16.2±2.9 mm3 vs. 76.8±13.1 mm3, p=0.016), whereas the ST146 model displayed resistance to TMZ on day 14 (12.7±5.6 mm3 vs. 26.5±11.9 mm3, p=0.26). The median survival was 60 days vs. 14 days in the ST610 model (TMZ vs. vehicle, p=0.0005) and 27 days vs. 13 days in the ST146 model (TMZ vs. vehicle, p=0.007). XRT showed efficacy in the orthotopic ST2473 model. Tumor volume was significantly smaller in treated vs. sham animals 11 days after inclusion (6.9±1.4 mm3 vs. 28.9±3.3 mm3, p=0.001). Also, a survival benefit was observed in XRT treated animals compared to sham. Histology confirmed the presence of orthotopic tumors and typical GBM pathology characteristics such as pseudopalisading tumor cells surrounding necrosis and micro vascular proliferation were identified.

Conclusion: Six different orthotopic GBM PDX models were established from low passage subcutaneous PDX models. Models sensitive and resistant to TMZ were identified and histological GBM characteristics were identified. Together, the established panel of orthotopic PDX models can be used as a relevant translational platform for testing of new drugs in a setting that more closely mimics the GBM tumor microenvironment and the impact of the blood brain barrier in patients.

Citation Format: Mette M. Jensen, Camilla S. Knudsen, Lotte K. Kristensen, Mette K. Nedergaard, Michael J. Wick, Kyriakos P. Papadopoulos, Anthony W. Tolcher, Andreas Kjaer, Carsten H. Nielsen. A panel of orthotopic glioblastoma multiforme (GBM) patient derived xenograft (PDX) mouse models for efficacy evaluation of drugs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2805. doi:10.1158/1538-7445.AM2017-2805

Associations between levels of insulin-like growth factor 1 and sinusoidal obstruction syndrome after allogeneic haematopoietic stem cell transplantation

Allogeneic myeloablative haematopoietic stem cell transplantation (HSCT) is challenged by severe adverse events, as cytotoxic effects of the conditioning may result in systemic inflammation, leaky epithelial barriers and organ toxicities, contributing to treatment-related morbidity and mortality. We hypothesised that insulin-like growth factor-1 (IGF-1), a mediator of growth and proliferation of various tissues, may attenuate chemotherapy-induced tissue damage after HSCT. We prospectively measured plasma levels of IGF-1 and its binding protein 3 (IGFBP-3) in 41 patients undergoing myeloablative HSCT. IGF-1 and IGFBP-3 levels were inversely correlated with C-reactive protein and interleukin-6 levels post HSCT. In multivariate analyses, low levels of IGF-1 and IGFBP-3 before conditioning were associated with increased risk of developing sinusoidal obstruction syndrome (SOS; OR=5.00 per 1 SDS decrease in IGF-1 (95% CI: 1.45-16.67), P=0.011 and OR=5.00 (1.37-20.00), P=0.015, respectively). Furthermore, low pre-transplant levels of IGF-1 and IGFBP-3 were associated with increased fluid retention during the first 21 days post transplant (OR=7.69 (95% CI: 1.59-33.33), P=0.012, and OR=2.94 (1.03-8.33), P=0.045). These data suggest that high levels of IGF-1 and IGFBP-3 may have a protective effect against fluid retention and SOS, possibly by attenuating systemic inflammation, and may prove useful as predictive biomarkers of SOS.

In vitro complement activation, adherence to red blood cells and induction of mononuclear cell cytokine production by four strains of Aggregatibacter actinomycetemcomitans with different fimbriation and expression of leukotoxin

BACKGROUND AND OBJECTIVE

The periodontal pathogen Aggregatibacter actinomycetemcomitans has been proposed as pro-atherogenic, and complement-mediated adherence to red blood cells (RBCs) may facilitate its systemic spread. We investigated the ability of four strains of A. actinomycetemcomitans with differential expression of leukotoxin A (LtxA) and fimbriae to activate complement, adhere to RBCs and elicit cytokine responses by mononuclear cells (MNCs).

MATERIAL AND METHODS

Aggregatibacter actinomycetemcomitans serotype b strains HK 921, HK 1651, HK 2092 and HK 2108 were fluorescence-labeled, incubated with human whole blood cells in the presence of autologous serum, and assessed for RBC adherence by flow cytometry and for capacity to induce cytokine production by cytometric bead array analysis. The levels of IgG to A. actinomycetemcomitans serotype b were quantified by ELISA, as was consumption of complement.

RESULTS

The JP2 clone variants HK 1651 and, to a lesser extent, HK 2092, consumed complement efficiently, while HK 2108 (= strain Y4) consumed complement poorly. Nonetheless, the four tested strains adhered equally well to RBCs in the presence of autologous serum, without causing RBC lysis. The JP2 clone variant HK 2092, selectively lacking LtxA production, induced higher production of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-10 by MNCs than did the other three strains, while the four strains induced similar production of IL-12p70. RBCs facilitated the HK 2092-induced production of TNF-α and IL-1β, and IL-6 was enhanced by RBCs, and this facilitation could be counteracted by blockade of complement receptor 3 (CD11b/CD18).

CONCLUSION

Our data suggest that the JP2 clone of A. actinomycetemcomitans, most closely resembled by the variant HK 1651, activates complement well, while strain Y4, represented by HK 2108, activates complement poorly. However, all strains of A. actinomycetemcomitans adhere to RBCs and, when capable of producing LtxA, prevent production of inflammatory cytokines by MNCs. This "immunologically silent" immune adherence may facilitate systemic spread and atherogenesis.

In vivo imaging of therapy response to a novel pan-HER antibody mixture using FDG and FLT positron emission tomography

Purpose

Overexpression of the human epidermal growth factor receptor (HER) family and their ligands plays an important role in many cancers. Targeting multiple members of the HER family simultaneously may increase the therapeutic efficacy. Here, we report the ability to image the therapeutic response obtained by targeting HER family members individually or simultaneously using the novel monoclonal antibody (mAb) mixture Pan-HER.

Experimental design and results

Mice with subcutaneous BxPC-3 pancreatic adenocarcinomas were divided into five groups receiving vehicle or mAb mixtures directed against either EGFR (HER1), HER2, HER3 or all three receptors combined by Pan-HER. Small animal positron emission tomography/computed tomography (PET/CT) with 2′-deoxy-2′-[¹⁸F]fluoro-D-glucose (FDG) and 3′-deoxy-3′-[¹⁸F]fluorothymidine (FLT) was performed at baseline and at day 1 or 2 after initiation of therapy. Changes in tumor uptake of tracers were quantified and compared to reduction in tumor size. Imaging results were further validated by immunohistochemistry and qPCR. Mean FDG and FLT uptake in the Pan-HER treated group decreased by 19±4.3% and 24±3.1%, respectively. The early change in FDG and FLT uptake correlated with tumor growth at day 23 relative to day 0. Ex vivo molecular analyses of markers associated with the mechanisms of FDG and FLT uptake confirmed the in vivo imaging results.

Conclusions

Taken together, the study supports the use of FDG and FLT as imaging biomarkers of early response to Pan-HER therapy. FDG and FLT PET/CT imaging should be considered as imaging biomarkers in clinical evaluation of the Pan-HER mAb mixture.

Hypoxia-Inducible Factor-1α Expression in Macrophages Promotes Development of Atherosclerosis

OBJECTIVE

Atherosclerotic lesions contain hypoxic areas, but the pathophysiological importance of hypoxia is unknown. Hypoxia-inducible factor-1α (HIF-1α) is a key transcription factor in cellular responses to hypoxia. We investigated the hypothesis that HIF-1α has effects on macrophage biology that promotes atherogenesis in mice.

APPROACH AND RESULTS

Studies with molecular probes, immunostaining, and laser microdissection of aortas revealed abundant hypoxic, HIF-1α-expressing macrophages in murine atherosclerotic lesions. To investigate the significance of macrophage HIF-1α, Ldlr(-/-) mice were transplanted with bone marrow from mice with HIF-1α deficiency in the myeloid cells or control bone marrow. The HIF-1α deficiency in myeloid cells reduced atherosclerosis in aorta of the Ldlr(-/-) recipient mice by ≈72% (P=0.006).In vitro, HIF-1α-deficient macrophages displayed decreased differentiation to proinflammatory M1 macrophages and reduced expression of inflammatory genes. HIF-1α deficiency also affected glucose uptake, apoptosis, and migratory abilities of the macrophages.

CONCLUSIONS

HIF-1α expression in macrophages affects their intrinsic inflammatory profile and promotes development of atherosclerosis.

Abstract 4771: PET imaging of tissue factor using 64Cu-labeled active site-inhibited factor VII: A potential companion diagnostic for tissue factor targeted cancer therapies

Introduction: The transmembrane glycoprotein tissue factor (TF) is the primary initiator of coagulation. In addition to its physiological role, TF is associated with a variety of pathophysiological processes including tumor growth, tumor angiogenesis and metastasis. Increased TF expression has been reported in 53-89% of all pancreatic adenocarcinomas and clinically correlates with advanced stage and poor survival. Non-invasive imaging of tumor TF status holds great clinical potential as a companion diagnostic for anti-cancer therapy targeting TF. The goal of our study was to develop and evaluate a PET tracer for imaging of TF expression in pancreatic cancer by utilizing the natural ligand for TF, coagulation factor VII.

Experimental procedures: Active site-inhibited factor VII (FVIIai) was conjugated to 2-S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) followed by radiolabeling with 64Cu (64Cu-NOTA-FVIIai). Mice bearing subcutaneous pancreatic adenocarcinoma tumors (BxPC-3) were subjected to PET imaging 1, 4, 15 and 36 hours post-injection of 64Cu-NOTA-FVIIai for longitudinal assessment. The in vivo specificity of 64Cu-NOTA-FVIIai towards TF was evaluated in a competition blocking experiment and in a panel of subcutaneous pancreatic tumor models exhibiting low, medium and high TF expression. Additionally, the ability of 64Cu-NOTA-FVIIai to visualize TF expression in orthotopically implanted BxPC-3 tumors was evaluated by PET/MRI. Ex vivo biodistribution, immunohistochemistry and flow cytometry was performed to verify the in vivo imaging data.

Results: PET imaging at 1, 4, 15 and 36 hours after injection of 64Cu-NOTA-FVIIai revealed a tumor uptake of 2.3 ± 0.2, 3.7 ± 0.3, 3.4 ± 0.3 and 2.4 ± 0.3% injected dose per gram (%ID/g), respectively. A graduate increase in image contrast (tumor to background ratio) was observed over the imaging time course with no further increase beyond 15 hours. Competition with excess unlabeled FVIIai significantly reduced tumor uptake of 64Cu-NOTA-FVIIai (p&lt; 0.001) in subcutaneous BxPC-3 tumors, while the uptake was unaffected in other organs. The ex vivo biodistribution confirmed the data obtained by in vivo PET imaging. In pancreatic cancer models with different levels of TF expression, the tumor uptake was found to be significantly different from each other (p &lt; 0.001). This was in agreement with the TF level evaluated by immunohistochemistry and flow cytometry. Furthermore orthotopic BxPC-3 tumors were visualized and distinguishable by PET/MRI using 64Cu-NOTA-FVIIai as the PET tracer.

Conclusions: 64Cu-NOTA-FVIIai is well suited for specific PET imaging of TF in pancreatic cancer and its uptake is related to the tumor TF expression level. The data supports further development of 64Cu-NOTA-FVIIai as a companion diagnostic and theranostic agent.

Citation Format: Lotte K. Kristensen, Carsten H. Nielsen, Troels E. Jeppesen, Mette M. Jensen, Jacob Madsen, Bo Wiinberg, Lars C. Petersen, Andreas Kjaer. PET imaging of tissue factor using 64Cu-labeled active site-inhibited factor VII: A potential companion diagnostic for tissue factor targeted cancer therapies. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4771.

PET Imaging of Tissue Factor in Pancreatic Cancer Using 64Cu-Labeled Active Site-Inhibited Factor VII

Tissue factor (TF) is the main initiator of the extrinsic coagulation cascade. However, TF also plays an important role in cancer. TF expression has been reported in 53%-89% of all pancreatic adenocarcinomas, and the expression level of TF has in clinical studies correlated with advanced stage, increased microvessel density, metastasis, and poor overall survival. Imaging of TF expression is of clinical relevance as a prognostic biomarker and as a companion diagnostic for TF-directed therapies currently under clinical development. Factor VII (FVII) is the natural ligand to TF. The purpose of this study was to investigate the possibility of using active site-inhibited FVII (FVIIai) labeled with (64)Cu for PET imaging of TF expression.

METHODS

FVIIai was conjugated to 2-S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) and labeled with (64)Cu ((64)Cu-NOTA-FVIIai). Longitudinal in vivo PET imaging was performed at 1, 4, 15, and 36 h after injection of (64)Cu-NOTA-FVIIai in mice with pancreatic adenocarcinomas (BxPC-3). The specificity of TF imaging with (64)Cu-NOTA-FVIIai was investigated in subcutaneous pancreatic tumor models with different levels of TF expression and in a competition experiment. In addition, imaging of orthotopic pancreatic tumors was performed using (64)Cu-NOTA-FVIIai and PET/MRI. In vivo imaging data were supported by ex vivo biodistribution, flow cytometry, and immunohistochemistry.

RESULTS

Longitudinal PET imaging with (64)Cu-NOTA-FVIIai showed a tumor uptake of 2.3 ± 0.2, 3.7 ± 0.3, 3.4 ± 0.3, and 2.4 ± 0.3 percentage injected dose per gram at 1, 4, 15, and 36 h after injection, respectively. An increase in tumor-to-normal-tissue contrast was observed over the imaging time course. Competition with unlabeled FVIIai significantly (P < 0.001) reduced the tumor uptake. The tumor uptake observed in models with different TF expression levels was significantly different from each other (P < 0.001) and was in agreement with the TF level evaluated by TF immunohistochemistry staining. Orthotopic tumors were clearly visible on the PET/MR images, and the uptake of (64)Cu-NOTA-FVIIai was colocalized with viable tumor tissue.

CONCLUSION

(64)Cu-NOTA-FVIIai is well suited for PET imaging of tumor TF expression, and imaging is capable of distinguishing the TF expression level of various pancreatic tumor models.

Abstract P5-01-04: uPAR PET imaging in breast cancer: First-in-humans studies using 64Cu-DOTA-AE105 and 68Ga-NOTA-AE105

Objective

The urokinase-type plasminogen activator receptor (uPAR) is a well-established prognostic biomarker in many cancer types including breast cancer (BC). Numerous studies using immunohistochemically evaluation of uPAR expression in tissue samples from BC patients have shown that not only is uPAR consistently overexpressed, but also carries strong prognostic value and is associates with overall survival. Accordingly, uPAR is an obvious target for identifying BC and for phenotyping aggressiveness in BC. Using whole body Positron Emission Tomography (PET) imaging rather than tissue specimens circumvents possible sampling error and allows for staging. Our objective was therefore to perform first-in-humans studies of uPAR-specific PET imaging in BC using either 64Cu-DOTA-AE105 or 68Ga-NOTA-AE105

Methods

Six patients with BC and scheduled for surgery were included. Prior to operation, patients were either PET/CT scanned 1, 3 and 24 h after injection of the uPAR PET ligand 64Cu-DOTA-AE105 (n=3; half life of 64Cu: 13 h) or PET/CT scanned 10 min, 1 h or 2 h after injection of 68Ga-NOTA-AE105 (n=3; half life of 68Ga: 1 h). PET Images were visually analyzed for visible tumor uptake of 64Cu-DOTA-AE105 or 68Ga-NOTA-AE105 and Standardized Uptake Values (SUV) were obtained by manually drawing volumes of interest (VOIs) around the primary tumor as well as identified metastases. Results are given as SUVmax. Tumor-to-background ratios relative to liver, kidney, blood and muscle were also calculated. Surgical tumor specimens were obtained from all patients during subsequent surgery. In addition to routine pathological examination, tissue was analyzed for ex vivo uPAR expression as target validation.

Results

Both primary tumors and metastases were visually detectable. For 64Cu-DOTA-AE105 SUVmax values were 2.9–4.0., and 2.9-4.0 after 1 and 3 h, respectively. Tumor-to-background ratios after 1 h were 0.91 (tumor-liver), 1.65 (tumor-kidney), 0.96 (tumor-blood) and 8.9 (tumor-muscle), respectively. Tumor-to-background ratios after 3 h were 0.50 (tumor-liver), 0.96 (tumor-kidney), 4.2 (tumor-blood) and 11.4 (tumor-muscle), respectively. Ex vivo analysis by immunohistochemistry confirmed uPAR expression in all primary cancer lesions. For 68Ga-NOTA-AE105, SUVmax was 5.0, 3.8 and 4.2 after 10 min, 1 h and 3 h, respectively (first patient analyzed). Tumor-to-background ratios after 10 min were 2.8 (tumor-liver), 0.4 (tumor-kidney), 1.6 (tumor-blood) and 8.4 (tumor-muscle), respectively. Tumor-to-background ratios after 1 h were 3.2 (tumor-liver), 0.6 (tumor-kidney), 1.7 (tumor-blood) and 7.1 (tumor-muscle), respectively.

Conclusion

This is the first study in humans using PET imaging of uPAR in BC. Both primary tumors and metastases were clearly visible with robust PET tracer uptake and a high and sufficient contrast between tumors and background. Our data supports continuation into phase II clinical studies using uPAR PET for staging and risk stratification, which potentially may be used for selection of treatment strategy in BC.

Citation Format: Kjaer A, Persson M, Skovgaard D, Brandt-Larsen M, Christensen C, Madsen J, Nielsen CH, Loft A, Berthelsen AK, Kroman N, Højgaard L. uPAR PET imaging in breast cancer: First-in-humans studies using 64Cu-DOTA-AE105 and 68Ga-NOTA-AE105. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-01-04.

Abstract P3-03-01: Intracranial PDX models of breast cancer metastasis

Background: Overexpression of the human epidermal growth factor receptor 2 (HER2) in breast cancer is an independent factor for development of brain metastases. Up to 37% of patients with HER2 positive disease relapse intracranially despite control of extra-cranial metastatic disease. Inability of anti-cancer agents to cross an intact blood-brain barrier (BBB) is a possible explanation for the increased incidence of brain metastases.

Subcutaneous (SQ) patient-derived xenograft (PDX) models are increasingly used for efficacy studies in drug development. However, orthotopic PDX models may confer a translational advantage as the patient tumor microenvironment is more closely mimicked. Especially when targeting brain tumors, the major impact of the BBB on drug bioavailability must be taken into consideration. The aim of this study was therefore to develop a panel of intracranial PDX models of breast cancer brain metastases for pre-clinical efficacy studies of new anticancer drugs.

Methods: SQ tumors from three different HER2 positive PDX breast cancer models designated ST340, ST1339 and ST1616B were enzymatically digested and used for intracranial stereotactic injection in nude mice. Contrast-enhanced T1- and T2-weighted Magnetic Resonance Imaging (MRI) were used to determine tumor take. Intracranial tumor growth was monitored using MRI and positron emission tomography (PET) in conjunction with the amino acid radio tracer 18F-FET.

Results: MRI confirmed tumor take in one model as early as 2 weeks after intracranial implantation. Increased 18F-FET uptake was detected in all models. MRI could be effectively used to monitor tumor growth and the corresponding 18F-FET PET images demonstrated increased 18F-FET uptake over time.

Conclusion: Three different HER2 positive intracranial PDX breast metastases models were established from low passage SQ PDX models. We suggest, that using these intracranial PDX models of brain metastases, new drugs for advanced breast cancer can be evaluated in preclinical models that more closely mimic the microenvironment and the BBB in patients. In addition, translational imaging techniques can be evaluated during preclinical testing and the potential of tracers like 18F-FET as imaging biomarkers of therapeutic response can be assessed. Together, the established SQ and orthotopic PDX models of breast cancer and brain metastases can be used as a relevant translational platform for testing of new drugs.

Citation Format: Nielsen CH, Nedergaard MK, Wick MJ, Papadopoulos K, Tolcher AW, Kjaer A. Intracranial PDX models of breast cancer metastasis. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-03-01.

Abstract A15: Efficacy of trastuzumab emtansine (T-DM1) in subcutaneous and intracranial patient derived xenograft models of breast cancer metastasis

Background: It is estimated that 10-30% of all breast cancer patients at some point develop brain metastases. Overexpression of the human epidermal growth factor receptor 2 (HER2) is a independent risk factor for development of brain metastases. Up to 37% of patients with HER2-positive metastatic breast cancer develop brain metastases and half of these patients die as a result of failure to control the intracranial disease. A reason for this is the challenge of efficient drug delivery across the blood brain barrier (BBB).

Subcutaneous patient derived xenograft (PDX) models are increasingly used for efficacy studies in drug development. However, when targeting brain tumors or metastases, the major impact of the BBB on drug bioavailability must be taken into consideration. The aim of this study was therefore to compare the efficacy of trastuzumab emtansine (T-DM1) in a HER2 positive breast cancer PDX model established subcutaneously and as an intracranial brain metastases model.

Methods: Mice were implanted subcutaneously with the HER2 positive breast cancer PDX model designated ST1339 and randomized into 3 treatment arms: Control, T-DM1 (5 mg/kg/week x4) and T-DM1 (10 mg/kg/week x4). Treatment response of subcutaneous tumors was monitored by caliper measurements. The intracranial PDX model was established by stereotactic intracranial injection of enzymatically digested ST1339 tumor tissue. At confirmed tumor take, mice were randomized into two arms: Control and T-DM1 (10 mg/kg/week x4). Treatment response was monitored by contrast-enhanced T1- and T2-weighted Magnetic Resonance Imaging (MRI) and positron emission tomography (PET) with the amino acid radiotracer O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET).

Results: T-DM1 at 10 mg/kg/week x4 effectively inhibited tumor growth in the subcutaneous model whereas treatment with 5 mg/kg/week x4 did not have any effect on tumor growth. T-DM1 treatment at 10 mg/kg/week x4 of mice with intracranial tumors inhibited tumor growth and prolonged survival compared to non-treated animals.

Conclusion: A treatment response to T-DM1 was observed in both the subcutaneous and intracranial ST1339 HER2 positive breast cancer PDX model. With the combination of subcutaneous and intracranial PDX models of breast cancer and breast cancer brain metastases new drugs can thus be tested in preclinical models that more closely mimic the microenvironment and the challenges of drug delivery across the BBB in patients.

Citation Format: Carsten H. Nielsen, Mette K. Nedergaard, Lotte K. Kristensen, Camilla S. Knudsen, Michael J. Wick, Kyri Papadopoulos, Anthony W. Tolcher, Andreas Kjaer. Efficacy of trastuzumab emtansine (T-DM1) in subcutaneous and intracranial patient derived xenograft models of breast cancer metastasis. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A15.

Quantitative PET Imaging of Tissue Factor Expression Using 18F-Labeled Active Site-Inhibited Factor VII

Tissue factor (TF) is upregulated in many solid tumors, and its expression is linked to tumor angiogenesis, invasion, metastasis, and prognosis. A noninvasive assessment of tumor TF expression status is therefore of obvious clinical relevance. Factor VII is the natural ligand to TF. Here we report the development of a new PET tracer for specific imaging of TF using an (18)F-labeled derivative of factor VII.

METHODS

Active site-inhibited factor VIIa (FVIIai) was obtained by inactivation with phenylalanine-phenylalanine-arginine-chloromethyl ketone. FVIIai was radiolabeled with N-succinimidyl 4-(18)F-fluorobenzoate and purified. The corresponding product, (18)F-FVIIai, was injected into nude mice with subcutaneous human pancreatic xenograft tumors (BxPC-3) and investigated using small-animal PET/CT imaging 1, 2, and 4 h after injection. Ex vivo biodistribution was performed after the last imaging session, and tumor tissue was preserved for molecular analysis. A blocking experiment was performed in a second set of mice. The expression pattern of TF in the tumors was visualized by immunohistochemistry and the amount of TF in tumor homogenates was measured by enzyme-linked immunosorbent assay and correlated with the uptake of (18)F-FVIIai in the tumors measured in vivo by PET imaging.

RESULTS

The PET images showed high uptake of (18)F-FVIIai in the tumor regions, with a mean uptake of 2.5 ± 0.3 percentage injected dose per gram (%ID/g) (mean ± SEM) 4 h after injection of 7.3-9.3 MBq of (18)F-FVIIai and with an average maximum uptake in the tumors of 7.1 ± 0.7 %ID/g at 4 h. In comparison, the muscle uptake was 0.2 ± 0.01 %ID/g at 4 h. At 4 h, the tumors had the highest uptake of any organ. Blocking with FVIIai significantly reduced the uptake of (18)F-FVIIai from 2.9 ± 0.1 to 1.4 ± 0.1 %ID/g (P < 0.001). The uptake of (18)F-FVIIai measured in vivo by PET imaging correlated (r = 0.72, P < 0.02) with TF protein level measured ex vivo.

CONCLUSION

(18)F-FVIIai is a promising PET tracer for specific and noninvasive imaging of tumor TF expression. The tracer merits further development and clinical translation, with potential to become a companion diagnostics for emerging TF-targeted therapies.

First-in-human uPAR PET: Imaging of Cancer Aggressiveness

A first-in-human clinical trial with Positron Emission Tomography (PET) imaging of the urokinase-type plasminogen activator receptor (uPAR) in patients with breast, prostate and bladder cancer, is described. uPAR is expressed in many types of human cancers and the expression is predictive of invasion, metastasis and indicates poor prognosis. uPAR PET imaging therefore holds promise to be a new and innovative method for improved cancer diagnosis, staging and individual risk stratification. The uPAR specific peptide AE105 was conjugated to the macrocyclic chelator DOTA and labeled with ⁶⁴Cu for targeted molecular imaging with PET. The safety, pharmacokinetic, biodistribution profile and radiation dosimetry after a single intravenous dose of ⁶⁴Cu-DOTA-AE105 were assessed by serial PET and computed tomography (CT) in 4 prostate, 3 breast and 3 bladder cancer patients. Safety assessment with laboratory blood screening tests was performed before and after PET ligand injection. In a subgroup of the patients, the in vivo stability of our targeted PET ligand was determined in collected blood and urine. No adverse or clinically detectable side effects in any of the 10 patients were found. The ligand exhibited good in vivo stability and fast clearance from plasma and tissue compartments by renal excretion. In addition, high uptake in both primary tumor lesions and lymph node metastases was seen and paralleled high uPAR expression in excised tumor tissue. Overall, this first-in-human study therefore provides promising evidence for safe use of ⁶⁴Cu-DOTA-AE105 for uPAR PET imaging in cancer patients.