Preliminary efficacy of [90Y]DOTA-biotin-avidin radiotherapy against non-muscle invasive bladder cancer

PURPOSE

Bladder cancer represents 3% of all new cancer diagnoses per year. We propose intravesical radionuclide therapy using the β-emitter ⁹⁰Y linked to DOTA-biotin-avidin ([⁹⁰Y]DBA) to deliver short-range radiation against non-muscle invasive bladder cancer (NMIBC).

MATERIAL AND METHODS

Image-guided biodistribution of intravesical DBA was investigated in an animal model by radiolabeling DBA with the ⁶⁸Ga and dynamic microPET imaging following intravesical infusion of [⁶⁸Ga]DBA for up to 4 h and post-necropsy γ-counting of organs. The antitumor activity of [⁹⁰Y]DBA was investigated using an orthotopic MB49 murine bladder cancer model. Mice were injected with luciferase-expressing MB49 cells and treated via intravesical administration with 9.2 MBq of [⁹⁰Y]DBA or unlabeled DBA 3 days after the tumor implantation. Bioluminescence imaging was conducted after tumor implantation to monitor the bladder tumor growth. In addition, we investigated the effects of [⁹⁰Y]DBA radiation on urothelial histology with immunohistochemistry analysis of bladder morphology.

RESULTS

Our results demonstrated that DBA is contained in the bladder for up to 4 h after intravesical infusion. A single dose of [⁹⁰Y]DBA radiation treatment significantly reduced growth of MB49 bladder carcinoma. Attaching ⁹⁰Y-DOTA-biotin to avidin prevents its re-absorption into the blood and distribution throughout the rest of the body. Furthermore, immunohistochemistry demonstrated that [⁹⁰Y]DBA radiation treatment did not cause short-term damage to urothelium at day 10, which appeared similar to the normal urothelium of healthy mice.

CONCLUSION

Our data demonstrates the potential of intravesical [⁹⁰Y]DBA as a treatment for non-muscle invasive bladder cancer.

Evaluating the Combined Anticancer Response of Checkpoint Inhibitor Immunotherapy and FAP-Targeted Molecular Radiotherapy in Murine Models of Melanoma and Lung Cancer

Simple Summary

Although newer cancer medicines that help the immune system recognize and attack cancer cells have improved responses to therapy, most patients ultimately have cancer recurrence. Additional therapies and therapy combinations are needed so that responses can last longer or indefinitely. Molecular targeted radiotherapy is another kind of therapy that targets radioactive particles directly to cancer in the hopes of killing cancer cells to stop tumor growth with limited side effects. Prior studies have shown that targeted radiotherapies activate the immune system and can work together with immunotherapy to improve response. Here, we tested a promising new therapy targeting fibroblast activation protein (FAP) with a therapeutic radionuclide ¹⁷⁷Lu alone and with immunotherapy in mouse models of melanoma and lung cancer. The FAP-targeted radiotherapy reduced tumor growth in both models and melanoma, resulting in tumor regression. We saw increased tumor cell death in dual-treated tumors. We also found that myeloid cells were affected by the combined therapy to a greater degree than the additive effect of either therapy. These results demonstrate that this is a promising new therapy regimen and requires further preclinical and clinical study to better understand the molecular mechanisms underpinning response.

Abstract

Immunotherapy has dramatically improved outcomes for some cancer patients; however, novel treatments are needed for more patients to achieve a long-lasting response. FAP-targeted molecular radiotherapy has shown efficacy in both preclinical and clinical models and has immunomodulatory effects. Here, we studied if combined immunotherapy and radiotherapy could increase antitumor efficacy in murine models of lung cancer and melanoma and interrogated the mechanisms by which these treatments attenuate tumor growth. Using LLC1 and B16F10 murine models of lung cancer and melanoma, respectively, we tested the efficacy of ¹⁷⁷Lu-FAPI-04 alone and in combination with immunotherapy. Alone, ¹⁷⁷Lu-FAPI-04 significantly reduced tumor growth in both models. In animals with melanoma, combined therapy resulted in tumor regression while lung tumor growth was attenuated, but tumors did not regress. Combined therapy significantly increased caspase-3 and decreased Ki67 compared with immunotherapy alone. Flow cytometry demonstrated that tumor-associated macrophages responded in a tumor-dependent manner which was distinct in animals treated with both therapies compared with either therapy alone. These data demonstrate that ¹⁷⁷Lu-FAPI-04 is an effective anticancer therapy for melanoma and lung cancer which mediates effects at least partially through induction of apoptosis and modulation of the immune response. Translational studies with immunotherapy and ¹⁷⁷Lu-FAPI-04 are needed to demonstrate the clinical efficacy of this combined regimen.

Immuno-PET monitoring of lymphocytes using the CD8-specific antibody REGN5054

Assessment of immune-cell subsets within the tumor immune microenvironment is a powerful approach to better understand cancer immunotherapy responses. However, the use of biopsies to assess the tumor immune microenvironment poses challenges, including the potential for sampling error, restricted sampling over time and inaccessibility of some tissues/organs, as well as the fact that single biopsy analyses do not reflect discordance across multiple intrapatient tumor lesions. Immuno-PET presents a promising translational imaging approach to address the limitations and assess changes in the tumor microenvironment. We have developed 89Zr-DFO-REGN5054, a fully human CD8A-specific antibody conjugate, to assess CD8+ tumor-infiltrating lymphocytes (TILs) pre- and post-therapy. We used multiple assays, including in vitro T-cell activation, proliferation, and cytokine production, and in vivo viral clearance and CD8 receptor occupancy, to demonstrate that REGN5054 has minimal impact on T-cell activity. Preclinical immuno-PET studies demonstrated that 89Zr-DFO-REGN5054 specifically detected CD8+ T cells in lymphoid tissues of CD8-genetically humanized immunocompetent mice (VelociT mice) and discerned therapy-induced changes in CD8+ TILs in two models of response to a CD20xCD3 T-cell activating bispecific antibody (REGN1979, odronextamab). Toxicology studies in cynomolgus monkeys showed no overt toxicity, and immuno-PET imaging in cynomolgus monkeys demonstrated dose-dependent clearance and specific targeting to lymphoid tissues. This work supports the clinical investigation of 89Zr-DFO-REGN5054 to monitor T-cell responses in patients undergoing cancer immunotherapy.

Abstract 1303: FAP-targeted molecular radiotherapy attenuates tumor growth and synergizes with immunotherapy for the treatment of malignant melanoma

Immunotherapy has drastically improved outcomes in many patients with melanoma, however the majority do not attain a durable response to treatment and therefore additional agents are desperately needed. Here, we tested the efficacy of 177Lu-FAPI-04, a novel FAP-targeted radiotherapy, alone and in combination with anti-PD-1 and anti-CTLA-4 immunotherapy in a mouse model of melanoma to attenuate tumor growth. Using B16F10 murine melanoma cells, we implanted tumors in C57BL/6 mice. Animals were divided into four groups: untreated control, molecular targeted 177Lu-FAPI-04 radiotherapy treatment, immunotherapy treatment, and combined radio- and immunotherapy treatment. We assessed tumor growth over time and animals were sacrificed at 21 days. After sacrifice, tumors were dissected out and preserved for immunohistochemistry and flow cytometry. Growth curves demonstrated that immunotherapy and radiotherapy each individually attenuated tumor growth, but together they resulted in tumor regression in the majority of animals. Immunohistochemistry demonstrated increased caspase-3 staining in tumors treated with combined 177Lu-FAPI-04 radiotherapy and immunotherapy compared to untreated tumors or tumors treated with either therapy alone indicating an increase in apoptotic cell death. Ki67 expression exhibited inverse staining with moderate expression in untreated samples, low expression in immunotherapy and radiotherapy treated samples, and no staining in tumors treated with combined therapy. Flow cytometric analysis demonstrated that tumors treated with either therapy exhibited an increase in M2 macrophages, however this population was obliterated in dual-treated tumors. Together, these data support that targeting FAP with targeted radiotherapy is an effective treatment which synergizes with immunotherapy to modulate cells of the myeloid lineage as an effective anticancer therapy for melanoma. Future translational studies are needed to further study the synergies between FAP-targeted radiotherapies and immunotherapy.

Citation Format: Kathleen M. Capaccione, Mikhail Doubrovin, Brian Braumuller, Dvora Leibowiz, Nikunj Bhatt, Andrei Molotkov, Michael Kissner, Fatemeh Momen-Heravi, Akiva Mintz. FAP-targeted molecular radiotherapy attenuates tumor growth and synergizes with immunotherapy for the treatment of malignant melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1303.

Real-Time Positron Emission Tomography Evaluation of Topotecan Brain Kinetics after Ultrasound-Mediated Blood-Brain Barrier Permeability

Glioblastoma (GBM) is the most common primary adult brain malignancy with an extremely poor prognosis and a median survival of fewer than two years. A key reason for this high mortality is that the blood-brain barrier (BBB) significantly restricts systemically delivered therapeutics to brain tumors. High-intensity focused ultrasound (HIFU) with microbubbles is a methodology being used in clinical trials to noninvasively permeabilize the BBB for systemic therapeutic delivery to GBM. Topotecan is a topoisomerase inhibitor used as a chemotherapeutic agent to treat ovarian and small cell lung cancer. Studies have suggested that topotecan can cross the BBB and can be used to treat brain metastases. However, pharmacokinetic data demonstrated that topotecan peak concentration in the brain extracellular fluid after systemic injection was ten times lower than in the blood, suggesting less than optimal BBB penetration by topotecan. We hypothesize that HIFU with microbubbles treatment can open the BBB and significantly increase topotecan concentration in the brain. We radiolabeled topotecan with 11C and acquired static and dynamic positron emission tomography (PET) scans to quantify [11C] topotecan uptake in the brains of normal mice and mice after HIFU treatment. We found that HIFU treatments significantly increased [11C] topotecan brain uptake. Moreover, kinetic analysis of the [11C] topotecan dynamic PET data demonstrated a substantial increase in [11C] topotecan volume of distribution in the brain. Furthermore, we found a decrease in [11C] topotecan brain clearance, confirming the potential of HIFU to aid in the delivery of topotecan through the BBB. This opens the potential clinical application of [11C] topotecan as a tool to predict topotecan loco-regional brain concentration in patients with GBMs undergoing experimental HIFU treatments.

3D optical/CT as a preclinical companion imaging platform for glioblastoma drug development

Multimodality 3D Optical Imaging (OI)/CT has the potential to play a major role in drug development for glioblastomas (GBM), as it is an accessible preclinical method. To demonstrate the potential of 3D OI/CT to visualize orthotopic GBM implantation, we labeled GBM cells with Cy7 and imaged their location using 3D OI/CT. To confirm the accuracy of the spatial localization and demonstrate the ability to image locoregionally delivered therapies, we labeled mouse albumin with Cy7 (Cy7ALB) and delivered it via locoregional infusion 1 mm or 3 mm into the brain and demonstrated correlation of signal between the 3D OI/CT and post necropsy brain slices. In addition, we demonstrated the potential of systemically delivered Cy7ALB contrast to detect blood-brain barrier (BBB) permeability caused by orthotopic GBMs using 3D OI/CT. We also tested the potential of 3D OI/CT to assess focal BBB permeability induced by high intensity focused ultrasound (HIFU), a methodology being used in clinical trials to noninvasively permeabilize the BBB for systemic therapeutic delivery to GBM. We demonstrated the ability of systemic Cy7ALB contrast together with 3D OI/CT to accurately assess real-time HIFU-induced BBB permeability, which correlated to post necropsy imaging of brains. Furthermore, we demonstrated that 3D OI/CT can also image the therapeutic distribution of a Cy7-labeled anti-PD-1 antibody, a prototype translational antibody therapy. We successfully imaged real-time antibody distribution after HIFU-induced BBB permeability, which correlated with post necropsy Cy7 signal and translational PET imaging after injection of [89Zr] anti-PD-1 antibody. Thus, we demonstrated the broad potential of using 3D OI/CT as an accessible preclinical tool to develop anti-GBM therapies.

Abstract 4062: Chemotherapy-induced therapeutic expression in stem cell vehicles

Stem cells are being studies as therapeutic vehicles due to their tumor homing properties that make them ideal to track down and attack infiltrating tumor cells that are not easily accessed. In order for stem cells to exert their therapeutic effect, they are engineered with therapeutic payloads that are typically secreted in the vicinity of the tumor. While many have shown that constitutive expression of a therapeutic by a tumor-homing stem cell can potentially treat a variety of cancers, we and others have focused on designing inducible systems that allow us to control the therapeutic expression and thus potentially limit systemic effects. In past work, we created an ultrasound-inducible stem cell that expressed reporter and/or therapeutic genes under the heat shock protein 70 (HSP70) promoter. In the current work, we hypothesize that we can potentially exploit the HSP70 promoter activation that has been reported after cellular stresses induced by standard-of care-chemotherapy, such as temozolomide, that is used to treat Glioblastoma (GBM), a fatal disease with a median survival of only 15 months after diagnosis. To test our hypothesis, we infected bone marrow derived mesenchymal stem cells (MSCs) with a plasmid that expresses GFP and firefly luciferase under the control of the HSP70 promoter and treated them with 100 or 400 ug/ml of temozolomide. We observed significant induction of GFP reporter 24 hours after treatment. We subsequently implanted our stem cells subcutaneously in mice and treated them with temozolomide. 24 hours after treatment, we observed gene activation using bioluminescent and fluorescent imaging. To further test this gene activation in a disease model, we stereotactically implanted our engineered stem cells along with patient derived (PDX) GBM cells intracranially. 5 days post implantation, mice were treated with a single therapeutic dose of temozolomide (200 mg/kg) and sacrificed 24 hours after treatment. After sectioning the brains and examining under fluorescent microscope, we observed significant GFP induction in the temozolomide treated mice compared to untreated controls. In order to demonstrate a biologic effect of induced therapeutics we performed a preliminary experiment where we intracranially implanted engineered stem cells that expressed HSP70 promotor inducible TNFα, a cytokine that we demonstrated can be delivered by stem cells to treat GBM and open the blood brain barrier (BBB) to further systemic therapies. We subsequently induced with 200 mg/kg of systemically administered temozolomide and observed BBB permeability via optical/CT imaging that demonstrated brain deposition of systemically administered cy7-albumin, in contrast to the untreated control. In conclusion, we successfully demonstrated the potential of engineering stem cells to express proteins/therapeutics after induction by temozolomide, a standard-of-care chemotherapy. We are therefore exploring using this strategy to express therapeutics that act in synergy with the inducing chemotherapy agent.

Citation Format: Andrei Molotkov, Mikhail Doubrovin, Alessandra Ali, Akiva Mintz. Chemotherapy-induced therapeutic expression in stem cell vehicles [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4062.

Radiosynthesis and evaluation of [18F]FMTP, a COX-2 PET ligand

BACKGROUND

The upregulation of cyclooxygenase-2 (COX-2) is involved in neuroinflammation associated with many neurological diseases as well as cancers of the brain. Outside the brain, inflammation and COX-2 induction contribute to the pathogenesis of pain, arthritis, acute allograft rejection, and in response to infections, tumors, autoimmune disorders, and injuries. Herein, we report the radiochemical synthesis and evaluation of [¹⁸F]6-fluoro-2-(4-(methylsulfonyl)phenyl)-N-(thiophen-2-ylmethyl)pyrimidin-4-amine ([¹⁸F]FMTP), a high-affinity COX-2 inhibitor, by cell uptake and PET imaging studies.

METHODS

The radiochemical synthesis of [¹⁸F]FMTP was optimized using chlorine to fluorine displacement method, by reacting [¹⁸F]fluoride/K222/K₂CO₃ with the precursor molecule. Cellular uptake studies of [¹⁸F]FMTP was performed in COX-2 positive BxPC3 and COX-2 negative PANC-1 cell lines with unlabeled FMTP as well as celecoxib to define specific binding agents. Dynamic microPET image acquisitionwas performed in anesthetized nude mice (n = 3), lipopolysaccharide (LPS) induced neuroinflammation mice (n = 4), and phosphate-buffered saline (PBS) administered control mice (n = 4) using a Trifoil microPET/CT for a scan period of 60 min.

RESULTS

A twofold higher binding of [¹⁸F]FMTP was found in COX-2 positive BxPC3 cells compared with COX-2 negative PANC-1 cells. The radioligand did not show specific binding to COX-2 negative PANC-1 cells. MicroPET imaging in wild-type mice indicated blood-brain barrier (BBB) penetration and fast washout of [¹⁸F]FMTP in the brain, likely due to the low constitutive COX-2 expression in the normal brain. In contrast, a ~ twofold higher uptake of the radioligand was found in LPS-induced mice brain than PBS treated control mice.

CONCLUSIONS

Specific binding to COX-2 in BxPC3 cell lines, BBB permeability, and increased brain uptake in neuroinflammation mice qualifies [¹⁸F]FMTP as a potential PET tracer for studying inflammation.

Impact of MYCN status on response of high-risk neuroblastoma to neoadjuvant chemotherapy

BACKGROUND/PURPOSE

MYCN-amplification in neuroblastoma is associated with an aggressive clinical phenotype. We evaluated the association of MYCN amplification with tumor response to neoadjuvant chemotherapy.

METHODS

Primary tumor response, assessed by percentage volume change on CT scan and degree of tumor resection, assessed by the operating surgeon, were retrospectively compared in 84 high-risk neuroblastoma patients. There were thirty-four (40%) with MYCN-amplified tumors and fifty (60%) with non-amplified tumors treated at our institution from 1999 to 2016. Metastatic disease response was assessed on MIBG scan by change in Curie score.

RESULTS

MYCN-amplification was associated with a greater mean percentage reduction in primary tumor volume after neoadjuvant chemotherapy (72.27% versus 46.83% [non-amplified tumors], p = 0.001). The percentage of patients with a Curie score > 2 at diagnosis who then had a score ≤ 2 after neoadjuvant chemotherapy was not significantly different (8 [61.5%] and 8 [34.8%], respectively, p = 0.37). Twenty-eight (85.7%) patients with MYCN-amplification had ≥90% surgical resection compared to 45 (91.84%) patients with non-amplified tumors (p = 0.303).

CONCLUSIONS

MYCN-amplification in high-risk neuroblastoma was associated with a better response of the primary tumor to neoadjuvant chemotherapy, but not metastatic sites, than in patients with non-amplified tumors. This did not significantly impact the ability to resect ≥90% of the primary tumor/locoregional disease.

TYPE OF STUDY

Treatment Study LEVEL OF EVIDENCE: Level III.

Multimodality molecular imaging of the alveolar-capillary barrier in lung disease using albumin based optical and PET tracers

Inflammatory changes caused by viruses, bacteria, exposure to toxins, commonly used drugs and even surgical intervention have the potential of causing abnormal epithelial permeability, which is manifest as infiltrative processes on computed tomography (CT), including the widespread infiltrates seen in COVID-19 pneumonia and acute respiratory distress syndrome (ARDS). We utilized a previously published mouse model of ARDS, intranasal delivery of LPS, to induce the alveolar-capillary barrier permeability seen in lung disease. We intravenously injected mice with Cy7 or 68-Gallium (⁶⁸Ga) labeled mouse albumin and imaged using optical imaging (OI)/CT and PET. We observed significantly increased lung levels of Cy7-albumin on 3D OI/CT, which matched the abnormal appearance on microCT. This uptake correlated with fluorescence seen on sectioned lungs. To examine the translational potential of these findings, we radiolabeled albumin with ⁶⁸Ga. We found that in mice with LPS-induced lung injury, ⁶⁸Ga-albumin PET correlated with our optical imaging findings and demonstrated abnormal activity in the lung fields, indicative of abnormal epithelial permeability. These findings indicate ⁶⁸Ga-albumin can be utilized as a sensitive translational radiotracer for quantifying the abnormal epithelial permeability that is seen in various lung pathologies, including COVID-19 induced pneumonia and ARDS. The ability to use Cy7-albumin 3D OI/CT imaging as a preclinical translational surrogate for ⁶⁸Ga-albumin offers an accessible high throughput means to rapidly screen potential therapeutics against lung diseases that clinically manifest with endothelial permeability.

eIF4A supports an oncogenic translation program in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy with limited treatment options. Although metabolic reprogramming is a hallmark of many cancers, including PDA, previous attempts to target metabolic changes therapeutically have been stymied by drug toxicity and tumour cell plasticity. Here, we show that PDA cells engage an eIF4F-dependent translation program that supports redox and central carbon metabolism. Inhibition of the eIF4F subunit, eIF4A, using the synthetic rocaglate CR-1-31-B (CR-31) reduced the viability of PDA organoids relative to their normal counterparts. In vivo, CR-31 suppresses tumour growth and extends survival of genetically-engineered murine models of PDA. Surprisingly, inhibition of eIF4A also induces glutamine reductive carboxylation. As a consequence, combined targeting of eIF4A and glutaminase activity more effectively inhibits PDA cell growth both in vitro and in vivo. Overall, our work demonstrates the importance of eIF4A in translational control of pancreatic tumour metabolism and as a therapeutic target against PDA.

Evaluation of 11C-Methionine PET and Anatomic MRI Associations in Diffuse Intrinsic Pontine Glioma

The role of metabolic imaging in the diagnosis, treatment, and response assessment of diffuse intrinsic pontine glioma (DIPG) is poorly defined. We investigated the uptake of ¹¹C-methionine in pediatric patients with newly diagnosed DIPG and evaluated the associations of ¹¹C-methionine PET metrics with conventional MRI indices and survival outcomes. Methods: Twenty-two patients with newly diagnosed DIPG were prospectively enrolled on an institutional review board-approved investigational study of ¹¹C-methionine PET. All patients underwent baseline ¹¹C-methionine PET/CT, and initial treatment-response scans after chemotherapy or radiation therapy were obtained for 17 patients. Typical and atypical DIPGs were assessed clinically and radiographically and defined by multidisciplinary consensus. Three-dimensional regions of interest, reviewed by consensus between a nuclear medicine physician and a radiation oncologist, were delineated after coregistration of PET and MR images. Associations of ¹¹C-methionine uptake intensity and uniformity with survival, along with associations between ¹¹C-methionine uptake and conventional MRI tumor indices over time, were evaluated. ¹¹C-methionine PET voxel values within regions of interest were assessed as threshold values across proportions of the study population, and ¹¹C-methionine uptake at baseline was assessed relative to MRI-defined tumor progression. Results: ¹¹C-methionine uptake above that of uninvolved brain tissue was observed in 18 of 22 baseline scans (82%) and 15 of 17 initial response scans (88%). ¹¹C-methionine avidity within MRI-defined tumor was limited in extent, with 11 of 18 positive baseline ¹¹C-methionine PET scans (61%) showing less than 25% ¹¹C-methionine-avid tumor. The increase in total tumor volume with ¹¹C-methionine PET was relatively limited (17.2%; interquartile range, 6.53%-38.90%), as was the extent of ¹¹C-methionine uptake beyond the MRI-defined tumor (2.2%; interquartile range, 0.55%-10.88%). Although baseline ¹¹C-methionine PET intensity and uniformity metrics did not correlate with survival outcomes, initial ¹¹C-methionine avidity overlapped with recurrent tumor in 100% of cases. A clinical diagnosis of atypical DIPG was associated with borderline significantly prolonged progression-free survival (P  =  0.07), yet ¹¹C-methionine PET indices at diagnosis did not differ significantly between atypical and typical DIPGs. Conclusion: Most newly diagnosed DIPGs are successfully visualized by ¹¹C-methionine PET. Baseline ¹¹C-methionine uptake delineates regions at increased risk for recurrence, yet intensity and uniformity metrics did not correlate with treatment outcomes in children with DIPG in this study.

Characterization of a c-Rel Inhibitor That Mediates Anticancer Properties in Hematologic Malignancies by Blocking NF-κB-Controlled Oxidative Stress Responses

NF-κB plays a variety of roles in oncogenesis and immunity that may be beneficial for therapeutic targeting, but strategies to selectively inhibit NF-κB to exert antitumor activity have been elusive. Here, we describe IT-901, a bioactive naphthalenethiobarbiturate derivative that potently inhibits the NF-κB subunit c-Rel. IT-901 suppressed graft-versus-host disease while preserving graft-versus-lymphoma activity during allogeneic transplantation. Further preclinical assessment of IT-901 for the treatment of human B-cell lymphoma revealed antitumor properties in vitro and in vivo without restriction to NF-κB-dependent lymphoma. This nondiscriminatory, antilymphoma effect was attributed to modulation of the redox homeostasis in lymphoma cells resulting in oxidative stress. Moreover, NF-κB inhibition by IT-901 resulted in reduced stimulation of the oxidative stress response gene heme oxygenase-1, and we demonstrated that NF-κB inhibition exacerbated oxidative stress induction to inhibit growth of lymphoma cells. Notably, IT-901 did not elicit increased levels of reactive oxygen species in normal leukocytes, illustrating its cancer selective properties. Taken together, our results provide mechanistic insight and preclinical proof of concept for IT-901 as a novel therapeutic agent to treat human lymphoid tumors and ameliorate graft-versus-host disease.

Monitoring the induction of heat shock factor 1/heat shock protein 70 expression following 17-allylamino-demethoxygeldanamycin treatment by positron emission tomography and optical reporter gene imaging

The cell response to proteotoxic cell stresses is mediated primarily through activation of heat shock factor 1 (HSF1). This transcription factor plays a major role in the regulation of the heat shock proteins (HSPs), including HSP70. We demonstrate that an [124I]iodide-pQHNIG70 positron emission tomography (PET) reporter system that includes an inducible HSP70 promoter can be used to image and monitor the activation of the HSF1/HSP70 transcription factor in response to drug treatment (17-allylamino-demethoxygeldanamycin [17-AAG]). We developed a dual imaging reporter (pQHNIG70) for noninvasive imaging of the heat shock response in cell culture and living animals previously and now study HSF1/HSP70 reporter activation in both cell culture and tumor-bearing animals following exposure to 17-AAG. 17-AAG (10-1,000 nM) induced reporter expression; a 23-fold increase was observed by 60 hours. Good correspondence between reporter expression and HSP70 protein levels were observed. MicroPET imaging based on [124I]iodide accumulation in pQHNIG70-transduced RG2 xenografts showed a significant 6.2-fold reporter response to 17-AAG, with a corresponding increase in tumor HSP70 and in tumor human sodium iodide symporter and green fluorescent protein reporter proteins. The HSF1 reporter system can be used to screen anticancer drugs for induction of cytotoxic stress and HSF1 activation both in vitro and in vivo.

Abstract 5515: WT1 specific T cells can efficiently eliminate tumorigenic ovarian carcinoma cells and prevent or inhibit the tumor growth in NOD/SCID model of ovarian carcinoma

The Wilms tumor protein, WT-1 is expressed in over 60% of serous adenocarcinomas of the ovary. Its expression has been hypothesized to be critical for the growth or survival of tumorigenic stem cells. In this study, we have assessed the capacity of in vitro generated T-cells specific for a series of immunogenic WT1 peptide epitopes presented by different HLA class I alleles to prevent the outgrowth of two human ovarian adenocarcinoma cell lines expressing either low (SKOV3-A2) or high (OVCAR3) levels of WT1 by FACS in NOD/SCID mice. For this study, epitope-specific HLA restricted WT1-CTLs were generated from PBMC of 4 normal donors by in vitro sensitization with autologous EBV BLCL loaded with a pool of 141 15-mers overlapping by 11aa and spanning the entire sequence of the WT1 protein. WT1-CTL restricted by HLA alleles expressed on the OVCAR3 and SKOV-3 lines were pre-incubated in vitro for 8 hours at different E:T ratios (0:1, 5:1, 10:1, 50:1, 100:1) with 0.05×10⁁6 ovarian carcinoma cells transduced to express a luciferase reporter gene. The cell mixtures were injected i.p. into NOD/SCID mice. Tumor growth was monitored weekly by intensity of their bioluminescent signal. In all animals injected with the tumor cells alone the bioluminescent signal could be detected in the abdomen by day 10-15 and increased steadily through 60 days of observation (by which time, all mice died). The tumor engraftment was either markedly inhibited (SKOV3-A2WT1low) or completely abrogated (in OVCAR-3WT1high) by pre-incubation at 100:1 E:T ratio and was correlated with higher survival of the animals (80%) over a period of 120 days. In the animals injected with tumor cells pre-incubated with the WT1-CTLs at a 50:1 and 10:1 E:T ratios, tumor growth was suppressed as reflected by weaker bioluminescent signal in the abdomen which increased much later in the course of the study. Pre-incubation of the tumor cells with WT1-CTL at a 5:1 E:T ratio did not significantly affect tumor engraftment and growth or survival of the mice. WT1-CTL specific for the 398-406LKTHTTRTHT epitope presented by the A0201 allele induced significantly greater suppression of tumor growth than T-cells specific for the (−125)-(−117)RQRPHPGAL peptide that can be presented by either HLA-A0301 or B0702.

T cells specific for different WT1 epitopes administered i.v. at a dose of 2.5×10⁁6 cells/animal inhibited the growth of the pre-established OVCAR3 tumor xenografts inoculated i.p. as compared to the growth of the same tumors in control animals. Mice treated with WT-1 specific T-cells also had a significantly extended survival. Our results provide evidence that tumorigenic ovarian carcinoma cells expressing WT1+ are susceptible to eradication in vivo by high doses of WT1-CTL. However, the effectiveness of these T cells may differ depending on the level of WT1 expressed by the tumor cells and peptide epitope of WT1 targeted.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5515. doi:10.1158/1538-7445.AM2011-5515

(124)I-iodopyridopyrimidinone for PET of Abl kinase-expressing tumors in vivo

Because of the recent development of an iodopyridopyrimidinone Abl protein kinase inhibitor (PKI), (124)I-SKI-212230 ((124)I-SKI230), we investigated the feasibility of a PET-based molecular imaging method for the direct visualization of Abl kinase expression and PKI treatment.

METHODS

In vitro pharmacokinetic properties, including specific and nonspecific binding of (124)I-SKI230 to its Abl kinase target and interaction with other PKIs, were assessed in cell-free medium and chronic myelogenous leukemia (CML) cells overexpressing BCR-Abl (K562), in comparison with BT-474 cells that are low in Abl expression. In a xenograft tumor model, we assessed the in vivo pharmacokinetics of (124)I-SKI230 using PET and postmortem tissue sampling. We also tested a paradigm of (124)I-SKI230 PET after treatment of the animal with a dose of Abl-specific PKI for the monitoring of the tumor response.

RESULTS

In vitro studies confirmed that SKI230 binds to Abl kinase with nanomolar affinity, that selective uptake occurs in cell lines known to express Abl kinase, that RNAi knock-down supports specificity of cellular uptake due to Abl kinase, and that imatinib, an archetype Abl PKI, completely displaces SKI230. With SKI230, we obtained successful in vivo PET of Abl-expressing human tumors in a nude rat. We were also able to demonstrate evidence of substrate inhibition of in vivo radiotracer uptake in the xenograft tumor after treatment of the animal as a model of PKI treatment monitoring.

CONCLUSION

These results support the hypothesis that molecular imaging using PET will be useful for the study of in vivo pharmacodynamics of Abl PKI molecular therapy in humans.

HSP70-inducible hNIS-IRES-eGFP reporter imaging: response to heat shock

A retroviral vector pQHSP70/hNIS-IRES-eGFP (pQHNIG70) was constructed containing the hNIS-IRES-eGFP dual-reporter genes under the control of an inducible human heat shock protein (HSP)70 promoter and RG2-pQHSP70/hNIS-IRES-eGFP (RG2-pQHNIG70) transduced cells were generated. Heat-induced expression of both reporter genes in RG2-pQHNIG70 cells was validated by enhanced green fluorescent protein (eGFP) fluorescence-activated cell sorter, in vitro radiotracer assays, and immunoblot and immunocytochemistry. A 2.2- to 6.1-fold ((131)I(-)), a 6.1- to 14.4-fold ((99m)TcO(4)(-)), and a 5.1- to 39-fold (fluorescence) increase above baseline was observed in response to graded hyperthermia (39-43 degrees C). Increases in eGFP fluorescence and radiotracer uptake were first noted at 6 hours, reached a maximum at 24 hours, and fell toward baseline at 72 hours. A stable ratio of radiotracer uptake to eGFP fluorescence and to heat shock protein (HSP)70 protein was demonstrated over a wide range of expression levels, induced by different levels of heating. We also demonstrate that the local application of heat on RG2-pQHNIG70 xenografts can effectively induce hNIS and eGFP gene expression in vivo and that this expression can be efficiently visualized by fluorescence, scintigraphic, and micro-positron emission tomography imaging. Endogenous HSP70 protein and reporter expression was confirmed by postmortem tissue evaluations (immunoblot and immunohistochemistry). The pQHNIG70 reporter system can be used to study stress and drug responses in transduced cells and tissues.

Molecular imaging of EGFR kinase activity in tumors with 124I-labeled small molecular tracer and positron emission tomography

Positron emission tomography (PET) with epidermal growth factor receptor (EGFR) kinase-specific radiolabeled tracers could provide the means for noninvasive and repetitive imaging of heterogeneity of EGFR expression and signaling activity in tumors in individual patients before and during therapy with EGFR signaling inhibitors. We developed the synthesis and (124)I-radiolabeling of the (E)-But-2-enedioic acid [4-(3-[(124)I]iodoanilino)-quinazolin-6-yl]-amide-(3-morpholin-4-yl-propyl)-amide (morpholino-[(124)I]-IPQA), which selectively, irreversibly, and covalently binds the adenosine-triphosphate-binding site to the activated (phosphorylated) EGFR kinase, but not to the inactive EGFR kinase. The latter was demonstrated using in silico modeling with crystal structures of the wild type and different gain-of-function mutants of EGFR kinases. Also, this was demonstrated by selective radiolabeling of the EGFR kinase domain with morpholino-[(131)I]-IPQA in A431 human epidermoid carcinoma cells and Western blot autoradiography. In vitro radiotracer accumulation and washout studies demonstrated a rapid accumulation and progressive retention postwashout of morpholino-[(131)I]-IPQA in A431 epidermoid carcinoma and in U87 human glioma cells genetically modified to express the EGFRvIII mutant receptor, but not in the wild-type U87MG glioma cells under serum-starved conditions. Using morpholino-[(124)I]-IPQA, we obtained noninvasive PET images of EGFR activity in A431 subcutaneous tumor xenografts, but not in subcutaneous tumor xenografts grown from K562 human chronic myeloid leukemia cells in immunocompromised rats and mice. Based on these observations, we suggest that PET imaging with morpholino-[(124)I]-IPQA should allow for identification of tumors with high EGFR kinase signaling activity, including brain tumors expressing EGFRvIII mutants and nonsmall-cell lung cancer expressing gain-of-function EGFR kinase mutants. Because of significant hepatobiliary clearance and intestinal reuptake of the morpholino-[(124)I]-IPQA, additional [(124)I]-IPQA derivatives with improved water solubility may be required to optimize the pharmacokinetics of this class of molecular imaging agents.

Molecular imaging reveals skeletal engraftment sites of transplanted bone marrow cells

Molecular imaging holds great promise for the in vivo study of cell therapy. Our hypothesis was that multimodality molecular imaging can identify the initial skeletal engraftment sites post-bone marrow cell transplantation. Utilizing a standard mouse model of bone marrow (BM) transplantation, we introduced a combined bioluminescence (BLI) and positron emission tomography (PET) imaging reporter gene into mouse bone marrow cells. Bioluminescence imaging was used for monitoring serially the early in vivo BM cell engraftment/expansion every 24 h. Significant cell engraftment/expansion was noted by greatly increased bioluminescence about 1 week posttransplant. Then PET was applied to acquire three-dimensional images of the whole-body in vivo biodistribution of the transplanted cells. To localize cells in the skeleton, PET was followed by computed tomography (CT). Co-registration of PET and CT mapped the sites of BM engraftment. Multiple, discrete BM cell engraftment sites were observed. Taken together, this multimodality approach may be useful for further in vivo characterization of various therapeutic cell types.

[131I]FIAU labeling of genetically transduced, tumor-reactive lymphocytes: cell-level dosimetry and dose-dependent toxicity

PURPOSE

Donor T cells have been shown to be reactive against and effective in adoptive immunotherapy of Epstein-Barr virus (EBV) lymphomas which develop in some leukemia patients post marrow transplantation. These T cells may be genetically modified by incorporation of a replication-incompetent viral vector (NIT) encoding both an inactive mutant nerve growth factor receptor (LNGFR), as an immunoselectable surface marker, and a herpes simplex virus thymidine kinase (HSV-TK), rendering the cells sensitive to ganciclovir. The current studies are based on the selective HSV-TK-catalyzed trapping (phosphorylation) of the thymidine analog [(131)I]-2'-fluoro-2'-deoxy-1-beta-D-arabinofuransyl-5-iodo-uracil (FIAU) as a means of stably labeling such T cells for in vivo trafficking (including tumor targeting) studies. Because of the radiosensitivity of lymphocytes and the potentially high absorbed dose to the nucleus from intracellular (131)I (even at tracer levels), the nucleus absorbed dose (D ( n )) and dose-dependent immune functionality were evaluated for NIT(+) T cells labeled ex vivo in [(131)I]FIAU-containing medium.

METHODS

Based on in vitro kinetic studies of [(131)I]FIAU uptake by NIT(+) T cells, D ( n ) was calculated using an adaptation of the MIRD formalism and the recently published MIRD cellular S factors. Immune cytotoxicity of [(131)I]FIAU-labeled cells was assayed against (51)Cr-labeled target cells [B-lymphoblastoid cells (BLCLs)] in a standard 4-h release assay.

RESULTS AND CONCLUSION

At median nuclear absorbed doses up to 830 cGy, a (51)Cr-release assay against BLCLs showed no loss of immune cytotoxicity, thus demonstrating the functional integrity of genetically transduced, tumor-reactive T cells labeled at this dose level for in vivo cell trafficking and tumor targeting studies.

High-Resolution Imaging of Bone Precursor Cells Within the Intact Bone Marrow Cavity of Living Mice

Bone precursor cells (BPCs) play a critical role in bone maintenance and regeneration. Currently, no tool exists to study BPCs or other bone marrow cell types directly within their complex microenvironment. Here, we describe in vivo magnetic resonance imaging (MRI) of anatomical structures inside the medullary cavity of the mouse femur. We demonstrate that BPCs passively labeled with iron oxide-containing particles can be monitored by MRI within the intact bone marrow at an in-plane resolution of 43x25 microm. Anatomical detail provided by MRI is complemented by functional optical imaging of reporter gene expression. Single-cell dual iron oxide-reporter gene labeling has potential for combined cell tracking and cell biology studies. In summary, we describe a versatile platform suitable for studying the biology of many bone marrow cell types in living bone.

hNIS-IRES-eGFP Dual Reporter Gene Imaging

The human and rodent sodium iodide symporters ( NIS) have recently been cloned and are being investigated as potential therapeutic and reporter genes. We have extended this effort by constructing an internal ribosomal entry site (IRES)-linked human NIS (hNIS)-enhanced green fluorescent protein ( eGFP) hybrid reporter gene for both nuclear and optical imaging. A self-inactivating retroviral vector, termed pQCNIG, containing hNIS-IRES-eGFP dual reporter gene, driven by a constitutive CMV promoter, was constructed and used to generate RG2-pQCNIG cells and RG2-pQCNIG tumors. 131I-iodide and 99mTcO4-pertechnetate accumulation studies plus fluorescence microscopy and intensity assays were performed in vitro, and gamma camera imaging studies in RG2-pQCNIG and RG2 tumor-bearing athymic rats were performed. RG2-pQCNIG cells expressed high levels of hNIS protein and showed high intensity of eGFP fluorescence compared with RG2 wild-type cells. RG2-pQCNIG cells accumulated Na131I and 99mTcO4– to a 50:1 and a 170:1 tissue/medium ratio at 10 min, compared with 0.8:1.2 tissue/medium ratio in wild-type RG2 cells. A significant correlation between radiotracer accumulation and eGFP fluorescence intensity was demonstrated. RG2-pQCNIG and RG2 tumors were readily differentiated by in vivo gamma camera imaging; radiotracer uptake increased in RG2-pQCNIG but declined in RG2 tumors over the 50-min imaging period. Stomach and thyroid were the major organs of radionuclide accumulation. The IRES-linked hNIS-eGFP dual reporter gene is functional and stable in transduced RG2-pQCNIG cells. Optical and nuclear imaging of tumors produced from these cell lines provides the opportunity to monitor tumor growth and response to therapy. These studies indicate the potential for a wider application of hNIS reporter imaging and translation into patient studies using radioisotopes that are currently available for human use for both SPECT and PET imaging.

Distinct organ-specific metastatic potential of individual breast cancer cells and primary tumors

We used bioluminescence imaging to reveal patterns of metastasis formation by human breast cancer cells in immunodeficient mice. Individual cells from a population established in culture from the pleural effusion of a breast cancer patient showed distinct patterns of organ-specific metastasis. Single-cell progenies derived from this population exhibited markedly different abilities to metastasize to the bone, lung, or adrenal medulla, which suggests that metastases to different organs have different requirements. Transcriptomic profiling revealed that these different single-cell progenies similarly express a previously described "poor-prognosis" gene expression signature. Unsupervised classification using the transcriptomic data set supported the hypothesis that organ-specific metastasis by breast cancer cells is controlled by metastasis-specific genes that are separate from a general poor-prognosis gene expression signature. Furthermore, by using a gene expression signature associated with the ability of these cells to metastasize to bone, we were able to distinguish primary breast carcinomas that preferentially metastasized to bone from those that preferentially metastasized elsewhere. These results suggest that the bone-specific metastatic phenotypes and gene expression signature identified in a mouse model may be clinically relevant.

Imaging of dihydrofolate reductase fusion gene expression in xenografts of human liver metastases of colorectal cancer in living rats

Radionuclide imaging has been demonstrated to be feasible to monitor transgene expression in vivo. We hypothesized that a potential application of this technique is to non-invasively detect in deep tissue, such as cancer cells metastatic to the liver, a specific molecular response following systemic drug treatment. Utilizing human colon adenocarcinoma cells derived from a patient's liver lesion we first developed a nude rat xenograft model for colorectal cancer metastatic to the liver. Expression of a dihydrofolate reductase-herpes simplex virus 1 thymidine kinase fusion (DHFR-HSV1 TK) transgene in the hepatic tumors was monitored in individual animals using the tracer [(124)I]2'-fluoro-2'-deoxy-5-iodouracil-beta- d-arabinofuranoside (FIAU) and a small animal micro positron emission tomograph (microPET), while groups of rats were imaged using the tracer [(131)I]FIAU and a clinical gamma camera. Growth of the human metastatic colorectal cancer cells in the rat liver was detected using magnetic resonance imaging and confirmed by surgical inspection. Single as well as multiple lesions of different sizes and sites were observed in the liver of the animals. Next, using a subset of rats bearing hepatic tumors, which were retrovirally bulk transduced to express the DHFR-HSV1 TK transgene, we imaged the fusion protein expression in the hepatic tumor of living rats using the tracer [(124)I]FIAU and a microPET. The observed deep tissue signals were highly specific for the tumors expressing the DHFR-HSV1 TK fusion protein compared with parental untransduced tumors and other tissues as determined by gamma counting of tissue samples. A subsequent study used the tracer [(131)I]FIAU and a gamma camera to monitor two groups of transduced hepatic tumor-bearing rats. Prior to imaging, one group was treated with trimetrexate to exploit DHFR-mediated upregulation of the fusion gene product. Imaging in the living animal as well as subsequent gamma counting of tissue samples showed increased signal and tracer accumulation, respectively, as compared to the group not treated with the antifolate. It is concluded that the two examined nucleotide imaging methods are feasible techniques for monitoring of DHFR-HSV TK fusion protein expression in hepatic colorectal tumor tissue in living animals.

Development of a new reporter gene system--dsRed/xanthine phosphoribosyltransferase-xanthine for molecular imaging of processes behind the intact blood-brain barrier

We report the development of a novel dual-modality fusion reporter gene system consisting of Escherichia coli xanthine phosphoribosyltransferase (XPRT) for nuclear imaging with radiolabeled xanthine and Discosoma red fluorescent protein for optical fluorescent imaging applications. The dsRed/XPRT fusion gene was successfully created and stably transduced into RG2 glioma cells, and both reporters were shown to be functional. The level of dsRed fluorescence directly correlated with XPRT enzymatic activity as measured by ribophosphorylation of [14C]-xanthine was in vitro (Ki = 0.124 +/- 0.008 vs. 0.00031 +/- 0.00005 mL/min/g in parental cell line), and [*]-xanthine octanol/water partition coefficient was 0.20 at pH = 7.4 (logP = -0.69), meeting requirements for the blood-brain barrier (BBB) penetrating tracer. In the in vivo experiment, the concentration of [14C]-xanthine in the normal brain varied from 0.20 to 0.16 + 0.05% dose/g under 0.87 + 0.24% dose/g plasma radiotracer concentration. The accumulation in vivo in the transfected flank tumor was to 2.4 +/- 0.3% dose/g, compared to 0.78 +/- 0.02% dose/g and 0.64 +/- 0.05% dose/g in the control flank tumors and intact muscle, respectively. [14C]-Xanthine appeared to be capable of specific accumulation in the transfected infiltrative brain tumor (RG2-dsRed/XPRT), which corresponded to the 585 nm fluorescent signal obtained from the adjacent cryosections. The images of endogenous gene expression with the "sensory system" have to be normalized for the transfection efficiency based on the "beacon system" image data. Such an approach requires two different "reporter genes" and two different "reporter substrates." Therefore, the novel dsRed/XPRT fusion gene can be used as a multimodality reporter system in the biological applications requiring two independent reporter genes, including the cells located behind the BBB.

Serial in vivo imaging of the targeted migration of human HSV-TK-transduced antigen-specific lymphocytes

New technologies are needed to characterize the migration, survival, and function of antigen-specific T cells in vivo. Here, we demonstrate that Epstein-Barr virus (EBV)--specific T cells transduced with vectors encoding herpes simplex virus-1 thymidine kinase (HSV-TK) selectively accumulate radiolabeled 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodouracil (FIAU). After adoptive transfer, HSV-TK+ T cells labeled in vitro or in vivo with [131I]FIAU or [124I]FIAU can be noninvasively tracked in SCID mice bearing human tumor xenografts by serial images obtained by scintigraphy or positron emission tomography (PET), respectively. These T cells selectively accumulate in EBV+ tumors expressing the T cells' restricting HLA allele but not in EBV- or HLA-mismatched tumors. The concentrations of transduced T cells detected in tumors and tissues are closely correlated with the concentrations of label retained at each site. Radiolabeled transduced T cells retain their capacity to eliminate targeted tumors selectively. This technique for imaging the migration of ex vivo-transduced antigen-specific T cells in vivo is informative, nontoxic, and potentially applicable to humans.

Development of a new reporter gene system--dsRed/xanthine phosphoribosyltransferase-xanthine for molecular imaging of processes behind the intact blood-brain barrier

We report the development of a novel dual-modality fusion reporter gene system consisting of Escherichia coli xanthine phosphoribosyltransferase (XPRT) for nuclear imaging with radiolabeled xanthine and Discosoma red fluorescent protein for optical fluorescent imaging applications. The dsRed/XPRT fusion gene was successfully created and stably transduced into RG2 glioma cells, and both reporters were shown to be functional. The level of dsRed fluorescence directly correlated with XPRT enzymatic activity as measured by ribophosphorylation of [14C]-xanthine was in vitro (Ki = 0.124 +/- 0.008 vs. 0.00031 +/- 0.00005 mL/min/g in parental cell line), and [*]-xanthine octanol/water partition coefficient was 0.20 at pH = 7.4 (logP = -0.69), meeting requirements for the blood-brain barrier (BBB) penetrating tracer. In the in vivo experiment, the concentration of [14C]-xanthine in the normal brain varied from 0.20 to 0.16 + 0.05% dose/g under 0.87 + 0.24% dose/g plasma radiotracer concentration. The accumulation in vivo in the transfected flank tumor was to 2.4 +/- 0.3% dose/g, compared to 0.78 +/- 0.02% dose/g and 0.64 +/- 0.05% dose/g in the control flank tumors and intact muscle, respectively. [14C]-Xanthine appeared to be capable of specific accumulation in the transfected infiltrative brain tumor (RG2-dsRed/XPRT), which corresponded to the 585 nm fluorescent signal obtained from the adjacent cryosections. The images of endogenous gene expression with the "sensory system" have to be normalized for the transfection efficiency based on the "beacon system" image data. Such an approach requires two different "reporter genes" and two different "reporter substrates." Therefore, the novel dsRed/XPRT fusion gene can be used as a multimodality reporter system in the biological applications requiring two independent reporter genes, including the cells located behind the BBB.

Comparison of radiolabeled nucleoside probes (FIAU, FHBG, and FHPG) for PET imaging of HSV1-tk gene expression

The efficacy of 3 radiolabeled probes of current interest for imaging herpes simplex virus type 1 thymidine kinase (HSV1-tk) expression in vivo with PET, including (124)I- or (131)I-labeled 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodouracil (FIAU), (18)F-labeled 9-[4-fluoro-3-(hydroxymethyl)butyl]guanine (FHBG), and (18)F-labeled 9-[3-fluoro-1-hydroxy-2-propoxymethyl]guanine (FHPG), was compared.

METHODS

Two established rat glioma cell lines, stably transduced RG2TK+ and wild-type RG2, were used for paired comparisons of probe accumulation in vitro and for paired comparisons of subcutaneous xenografts produced from these cell lines in athymic rnu/rnu rats.

RESULTS

The in vitro paired probe uptake (0-3 h) comparisons in RG2TK+ cells showed that FIAU accumulation was 15-fold greater than that of FHBG and 41-fold greater than that of FHPG. The net accumulation rate values (+/-SD) calculated for RG2TK+ cells were 0.317 +/- 0.066, 0.022 +/- 0.001, and 0.0077 +/- 0.0003 mL/min/g cells for FIAU, FHBG, and FHPG, respectively. These results and similar uptake studies in RG2 wild-type cells suggest a possible cell membrane transport limitation for FHBG and FHPG. The paired 2-h in vivo uptake studies produced similar differences in RG2TK+ xenografts for FIAU and FHBG (1.22 +/- 0.21 vs. 0.074 +/- 0.49 %dose/g) and for FIAU and FHPG (1.27 +/- 0.14 vs. 0.023 +/- 0.008 %dose/g). These differences were clearly visible on the images. FIAU accumulation at 24 h was 1.53 +/- 0.40 %dose/g. Plasma clearance was FHBG > FHPG >> FIAU. The FIAU images showed significant stomach and some intestinal background radioactivities, whereas hepatobiliary and intestinal background activities were very high for the guanosine analogs (FHBG > FHPG). Dynamic imaging showed early ( approximately 10 min) selective localization of FIAU in RG2TK+ xenografts, whereas FHBG and FHPG are being cleared from the HSV1-tk transduced and wild-type xenografts over the initial 2-h imaging period.

CONCLUSION

The in vitro and in vivo results (including the PET images) show that FIAU is a substantially more efficient probe than FHBG or FHPG for imaging HSV1-tk expression, with greater sensitivity and contrast as well as lower levels of abdominal background radioactivity at 2 and 24 h.

Cells exposed to antifolates show increased cellular levels of proteins fused to dihydrofolate reductase: a method to modulate gene expression

Human cells exposed to antifolates show a rapid increase in the levels of the enzyme dihydrofolate reductase (DHFR). We hypothesized that this adaptive response mechanism can be used to elevate cellular levels of proteins fused to DHFR. In this study, mouse cells transfected to express a green fluorescent protein-DHFR fusion protein and subsequently exposed to the antifolate trimetrexate (TMTX) showed a specific and time-dependent increase in cellular levels of the fusion protein. Next, human HCT-8 and HCT-116 colon cancer cells retrovirally transduced to express a DHFR-herpes simplex virus 1 thymidine kinase (HSV1 TK) fusion protein and treated with the DHFR inhibitor TMTX exhibited increased levels of the DHFR-HSV1 TK fusion protein and an increase in ganciclovir sensitivity by 250-fold. The level of fusion protein in antifolate-treated human tumor cells was increased in response to a 24-h exposure of methotrexate, trimetrexate, as well as dihydrofolate. This effect depended on the antifolate concentration and was independent of the fusion-protein mRNA levels, consistent with this increase occurring at a translational level. In a xenograft model, nude rats bearing DHFR-HSV1 TK-transduced HCT-8 tumors and treated with TMTX showed, after 24 h, a 2- to 4-fold increase of fusion-protein levels in tumor tissue from treated animals compared with controls, as determined by Western blotting. The fusion-protein increase was imaged with positron-emission tomography, where a substantially enhanced signal of the transduced tumor was detected in animals after antifolate administration. Drug-mediated elevation of cellular DHFR-fused proteins is a very useful method to modulate gene expression in vivo for imaging as well as therapeutic purposes.

Tumor-specific transcriptional targeting of suicide gene therapy

Transcriptional targeting of gene expression has been plagued by the weakness of tissue-specific promoters. Thus, to increase promoter strength while maintaining tissue specificity, we constructed a recombinant adenovirus containing a binary promoter system with a tumor-specific promoter (CEA; carcinoembryonic antigen) driving a transcription transactivator, which then activates a minimal promoter to express a suicide gene (HSV-tk; herpes simplex virus thymidine kinase). This ADV/binary-tk induced equal or greater cell killing in a CEA-specific manner in vitro compared with the CEA-independent killing of a vector with a constitutive viral promoter driving HSV-tk (ADV/RSV-tk). To monitor adenovirus-mediated HSV-tk gene expression in vivo, we employed noninvasive nuclear imaging using a radioiodinated nucleoside analog ([((1)31)I]-FIAU) serving as a substrate for HSV-tk. [((1)31)I]-FIAU-derived radioactivity accumulated after intratumoral injection of ADV/binary-tk only in the area of CEA-positive tumors with significantly less spread to the adjacent liver tissue than after administration of the universally expressed ADV/RSV-tk. Both viruses exhibited similar antitumor efficacy upon injection of liver metastases. Importantly, in vivo dose escalation studies demonstrated significantly reduced toxicity after intravenous administration of ADV/binary-tk versus ADV/RSV-tk. In summary, the increased therapeutic index of this novel, amplified CEA-driven suicide gene therapy vector is a proof of principle for the powerful enhancement of a weak tissue-specific promoter for effective tumor restricted gene expression.

Imaging transcriptional regulation of p53-dependent genes with positron emission tomography in vivo

A noninvasive method for molecular imaging of the activity of different signal transduction pathways and the expression of different genes in vivo would be of considerable value. It would aid in understanding the role specific genes and signal transduction pathways have in various diseases, and could elucidate temporal dynamics and regulation at different stages of disease and during various therapeutic interventions. We developed and assessed a method for monitoring the transcriptional activation of endogenous genes by positron-emission tomography (PET) imaging. The HSV1-tk/GFP (TKGFP) dual reporter gene was used to monitor transcriptional activation of p53-dependent genes. A retrovirus bearing the Cis-p53/TKGFP reporter system was constructed in which the TKGFP reporter gene was placed under control of an artificial cis-acting p53-specific enhancer. U87 glioma and SaOS-2 osteosarcoma cells were transduced with this retrovirus and used to establish xenografts in rats. We demonstrated that DNA damage-induced up-regulation of p53 transcriptional activity correlated with the expression of p53-dependent downstream genes, such as p21, in U87 (wild-type p53), but not in SaOS-2 osteosarcoma (p53 -/-) cells. We showed that PET, with [(124)I]FIAU (2'-fluoro-2'-deoxy-1-beta-d-arabinofuranosyl-5-[(124)I]iodouracil) and the Cis-p53TKGFP reporter system, is sufficiently sensitive to image the transcriptional regulation of genes in the p53 signal transduction pathway. These imaging results were confirmed by independent measurements of p53 activity and the expression levels of downstream genes (e.g., p21) by using conventional molecular-biological assays. PET imaging of p53 transcriptional activity in tumor xenografts by using the Cis-p53TKGFP reporter system may be useful in assessing novel therapeutic approaches.

Positron emission tomography imaging for herpes virus infection: Implications for oncolytic viral treatments of cancer

Molecular therapy using viruses would benefit greatly from a non-invasive modality for assessing dissemination of viruses. Here we investigated whether positron emission tomography (PET) scanning using [(124)I]-5-iodo-2'-fluoro-1-beta-d-arabinofuranosyl-uracil (FIAU) could image cells infected with herpes simplex viruses (HSV). Using replication-competent HSV-1 oncolytic viruses with thymidine kinase (TK) under control of different promoters, we demonstrate that viral infection, proliferation and promoter characteristics all interact to influence FIAU accumulation and imaging. In vivo, as few as 1 x 107 viral particles injected into a 0.5-cm human colorectal tumor can be detected by [(124)I]FIAU PET imaging. PET signal intensity is significantly greater at 48 hours compared with that at 8 hours after viral injection, demonstrating that PET scanning can detect changes in TK activity resulting from local viral proliferation. We also show the ability of FIAU-PET scanning to detect differences in viral infectivity at 0.5 log increments. Non-invasive imaging might be useful in assessing biologically relevant distribution of virus in therapies using replication-competent HSV.