Molecular imaging of EGFR and CD44v6 for prediction and response monitoring of HSP90 inhibition in an in vivo squamous cell carcinoma model

Comprehensive pan-cancer analysis identifies PLAG1 as a key regulator of tumor immune microenvironment and prognostic biomarker

Background

The literature on the role of pleomorphic adenoma gene 1 (PLAG1) in malignant tumors is limited. This study aimed to perform pan-cancer analysis of PLAG1.

Methods

The expression of PLAG1 was analyzed by Human Protein Atlas (HPA). The differential expression and prognosis of PLAG1 were analyzed based on TCGA pan-cancer data. The relationship between PLAG1 expression and tumor heterogeneity, stemness and immune infiltration was investigated. The enrichment analysis and biological function of PLAG1 in bladder cancer were analyzed.

Results

The expression of PLAG1 was increased in a variety of tumors and significantly correlated with the prognosis of patients. Their expression levels were associated with key immune checkpoint genes (CD274, HAVCR2), immune infiltration and immune stimulation factors (CD48, CD27). In bladder cancer, functional enrichment analysis indicated that PLAG1 was involved in epidermal related processes and immune pathways. PLAG1 gene expression reduction can significantly inhibit the proliferation of bladder cancer cells.

Conclusions

PLAG1 has the potential to be a prognostic marker and a potential therapeutic target for patients with malignant tumors.

Evaluation of a Novel Gd-FAPI Dimer Molecular Probe Targeting Fibroblast Activation Protein for Imaging of Solid Tumors

Cancer-associated fibroblasts (CAFs) are essential components of the tumor microenvironment. Fibroblast activation protein (FAP) is overexpressed in CAFs. FAP-targeted molecular imaging agents, including the FAP inhibitors (FAPIs), have shown promising results in tumor diagnosis. We aimed to design a Gd-labeled FAPI Dimer, Gd-DOTA-Suc-Lys-(FAPI04)2, to optimize the pharmacokinetics and evaluate its potential capacity for targeting FAP-positive solid tumors in vivo. The Gd-labeled FAPI Dimer was successfully synthesized with exceeding 98% purity. Preclinical pharmacokinetics were determined in assessed FAP-positive U87 cell-derived xenografts and FAP-negative C6-derived xenografts using small-animal T1-weighted 7.0T MR imaging. The longitudinal correlation coefficient (r1) of the agent was 3.813 mM-1·S-1. The administration of the Gd-FAPI04 Dimer probe showed a notable enhancement of tumor contrast on T1-weighted whole-body MRI. At 10 and 30 minutes post-injection, the U87 subcutaneous tumor demonstrated significantly greater contrast enhancement than the C6 subcutaneous tumor (P <0.05). In vivo, the safety of the Gd-FAPI-04 Dimer probe was evaluated, which showed no tissue damage in vital organs like the heart, liver, spleen, lung, and kidneys, as indicated by unchanged morphology compared to a normal saline control group. The novel Gd-FAPI04 Dimer molecular probe, Gd-DOTA-Suc-Lys-(FAPI-04)2 specifically targeting FAP may serve as a safe and promising tool for the diagnostic imaging of solid tumors.

ImmunoPET: Antibody-Based PET Imaging in Solid Tumors

Immuno-positron emission tomography (immunoPET) is a molecular imaging modality combining the high sensitivity of PET with the specific targeting ability of monoclonal antibodies. Various radioimmunotracers have been successfully developed to target a broad spectrum of molecules expressed by malignant cells or tumor microenvironments. Only a few are translated into clinical studies and barely into clinical practices. Some drawbacks include slow radioimmunotracer kinetics, high physiologic uptake in lymphoid organs, and heterogeneous activity in tumoral lesions. Measures are taken to overcome the disadvantages, and new tracers are being developed. In this review, we aim to mention the fundamental components of immunoPET imaging, explore the groundbreaking success achieved using this new technique, and review different radioimmunotracers employed in various solid tumors to elaborate on this relatively new imaging modality.

Radiotheranostic Targeting Cancer Stem Cells in Human Colorectal Cancer Xenografts

PURPOSE

The aim of this study was to perform radiotheranostics with radioiodinated monoclonal antibodies (mAbs) for targeting cancer stem cells (CSCs) in human colorectal cancer xenografts and evaluate the relative advantage of a cocktail containing both [¹³¹I]CD133 mAb and [¹³¹I]CD44 mAb.

PROCEDURES

Tumor-bearing mice were randomly divided into eight groups: [¹³¹I]CD133mAb, [¹³¹I]CD44 mAb, [¹³¹I]IgG isotype control, radioiodinated mAb cocktail, CD133 mAb, CD44 mAb, unradioiodinated mAb cocktail, and saline groups. In vivo single photon emission computed tomography (SPECT) imaging was used to monitor dynamically changes in the CSC population after treatment. The radioactivity uptake of tumors was quantified ex vivo. The expression of CD133 and CD44 after treatment was also assessed by immunohistochemistry and western blot. Tumor growth curves and survival curves were generated to assess treatment efficacy. Cell apoptosis and proliferation in xenografts 30 days after treatment were measured by TdT-mediated dUTP-biotin nick end labeling (aka, TUNEL) and Ki67 staining. The expression levels of biomarkers in xenografts 30 days after treatment were measured by flow cytometry.

RESULTS

The radioimmunoimaging (RII) with in vivo SPECT showed that the CSC-targeting radioimmunotherapy (RIT) groups ([¹³¹I]CD133 mAb, [¹³¹I]CD44 mAb, and radioiodinated mAb cocktail groups) had intense accumulations of radiolabeled agents in the tumor areas. The ex vivo biodistribution confirmed these findings. In the CSC-targeting RIT groups, immunohistochemistry and western blot indicated significant reduction of specific target expression in the xenografts. The tumor growth curves and survival curves showed that the CSC-targeting RIT significantly inhibited tumor growth and prolonged mean survival, respectively. Significantly increased apoptosis and decreased proliferation in xenografts further confirmed the therapeutic efficacy of CSC-targeting RIT. Flow cytometry showed that the decreases in CSCs correlated with the presence of the corresponding antibodies.

CONCLUSIONS

Our results suggest that the CSC-targeting RIT can effectively reduce CSCs which consequently inhibits tumor development. The radioiodinated mAb cocktail may generate enhanced CSC-targeting specificity.

89Zr anti-CD44 immuno-PET monitors CD44 expression on splenic myeloid cells and HT29 colon cancer cells

CD44 is a cell-surface glycoprotein involved in cell–cell interaction, adhesion, and migration. CD44 is found on colon cancer cells and on immune cells. Previous studies of ⁸⁹Zr PET imaging of CD44 have relied on an anti-human antibody (Ab), which can influence biodistribution in murine models. In this study, we used an Ab that cross-reacts with both human and mouse origin CD44 of all isoforms to unveil the type of leukocyte responsible for high splenic anti-CD44 uptake and investigate how its regulation can influence tumor immuno-PET. The Ab was site-specifically labeled with ⁸⁹Zr-deferoxamine on cysteine residues. ⁸⁹Zr-anti-CD44 demonstrated high-specific binding to HT29 human colon cancer cells and monocytic cells that showed CD44 expression. When ⁸⁹Zr-anti-CD44 was administered to Balb/C nude mice, there was remarkably high splenic uptake but low SNU-C5 tumor uptake (1.2 ± 0.7%ID/g). Among cells isolated from Balb/C mouse spleen, there was greater CD44 expression on CD11b positive myeloid cells than lymphocytes. In cultured monocytic and macrophage cells, LPS stimulation upregulated CD44 expression and increased ⁸⁹Zr-anti-CD44 binding. Similarly, normal Balb/C mice that underwent lipopolysaccharide (LPS) stimulation showed a significant upregulation of CD44 expression on splenic myeloid cells. Furthermore, LPS treatment stimulated a 2.44-fold increase of ⁸⁹Zr-anti-CD44 accumulation in the spleen, which was attributable to splenic myeloid cells. Finally, in Balb/C nude mice bearing HT29 tumors, we injected ⁸⁹Zr-anti-CD44 with greater Ab doses to reduce binding to splenic cells. The results showed lower spleen uptake and improved tumor uptake (2.9 ± 1.3%ID/g) with a total of 300 μg of Ab dose, and further reduction of spleen uptake and greater tumor uptake (5.7 ± 0.0%ID/g) with 700 μg Ab dose. Thus, using an ⁸⁹Zr labeled Ab that cross-reacts with both human and mouse CD44, we demonstrate that CD44 immuno-PET has the capacity to monitor CD44 regulation on splenic myeloid cells and may also be useful for imaging colon tumors.

A Pretargeted Imaging Strategy for EGFR-Positive Colorectal Carcinoma via Modulation of Tz-Radioligand Pharmacokinetics

PURPOSE

Previously, we successfully developed a pretargeted imaging strategy (atezolizumab-TCO/[^99mTc]HYNIC-PEG₁₁-Tz) for evaluating programmed cell death ligand-1 (PD-L1) expression in xenograft mice. However, the surplus unclicked [^99mTc]HYNIC-PEG₁₁-Tz is cleared somewhat sluggishly through the intestines, which is not ideal for colorectal cancer (CRC) imaging. To shift the excretion of the Tz-radioligand to the renal system, we developed a novel Tz-radioligand by adding a polypeptide linker between HYNIC and PEG₁₁.

PROCEDURES

Pretargeted molecular probes [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz and cetuximab-TCO were synthesized. [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz was evaluated for in vitro stability and in vivo blood pharmacokinetics. In vitro ligation reactivity of [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz towards cetuximab-TCO was also tested. Biodistribution assay and imaging of [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz were performed to observe its excretion pathway. Pretargeted biodistribution was measured at three different accumulation intervals to determine the optimal pretargeted interval time. Pretargeted (cetuximab-TCO 48 h/[^99mTc]HYNIC-PEG₁₁-Tz 6 h) and (cetuximab-TCO 48 h/[^99mTc]HYNIC-Polypeptide-PEG₁₁-Tz 6 h) imagings were compared to examine the effect of the excretion pathway on tumor imaging.

RESULTS

[^99mTc]HYNIC-polypeptide-PEG₁₁-Tz showed favorable in vitro stability and rapid blood clearance in mice. SEC-HPLC revealed almost complete reaction between cetuximab-TCO and [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz in vitro, with the 8:1 Tz-to-mAb reaction providing a conversion yield of 87.83 ± 3.27 %. Biodistribution and imaging analyses showed that the Tz-radioligand was cleared through the kidneys. After 24, 48, and 72 h of accumulation in HCT116 tumor, the tumor-to-blood ratio of cetuximab-TCO was 0.83 ± 0.13, 1.40 ± 0.31, and 1.15 ± 0.21, respectively. Both pretargeted (cetuximab-TCO 48 h/[^99mTc]HYNIC-PEG₁₁-Tz 6 h) and (cetuximab-TCO 48 h/[^99mTc]HYNIC-polypeptide-PEG₁₁-Tz 6 h) clearly delineated HCT116 tumor. Pretargeted imaging strategy using cetuximab-TCO/[^99mTc]HYNIC-polypeptide-PEG₁₁-Tz could be used for diagnosing CRC, as the surplus unclicked [^99mTc]HYNIC-polypeptide-PEG₁₁-Tz was cleared through the urinary system, leading to low abdominal uptake background.

CONCLUSION

Our novel pretargeted imaging strategy (cetuximab-TCO/[^99mTc]HYNIC-polypeptide-PEG₁₁-Tz) was useful for imaging CRC, broadening the application scope of pretargeted imaging strategy. The pretargeted imaging strategy clearly delineated HCT116 tumor, showing that its use could be extended to selection of internalizing antibodies.

Tumor-Targeted Delivery of the p53-Activating Peptide VIP116 with PEG-Stabilized Lipodisks

Stapled peptides targeting the interaction between p53 and its negative regulators MDM2 and MDM4 have exhibited great potential as anti-cancer drugs, albeit with room for improvement in formulation and tumor specificity. Lipid bilayer disks (lipodisks) have emerged as promising drug nanocarriers and can by attachment of targeting moieties be directed selectively towards tumor cells. Tumor-targeted delivery of stapled peptides by use of lipodisks may therefore increase the uptake in the tumors and limit toxicity in healthy tissue. Here, we utilized epidermal growth factor receptor (EGFR)-targeted lipodisks to deliver p53-activating stapled peptide VIP116 to EGFR-expressing tumor cells. We demonstrate that VIP116 can be stably formulated in lipodisks (maximum peptide/lipid molar ratio 0.11). In vitro cell studies verify specific binding of EGF-decorated lipodisks to tumor cells and confirm that targeted delivery of VIP116 significantly decreases tumor cell viability.

Enhancing the therapeutic effects of in vitro targeted radionuclide therapy of 3D multicellular tumor spheroids using the novel stapled MDM2/X-p53 antagonist PM2

BACKGROUND

Precision therapeutics continuously make advances in cancer therapy, and a field of growing interest is the combination of targeted radionuclide therapy (TRNT) with potential radiosensitizing agents. This study evaluated whether the effects of in vitro TRNT, using the 177Lu-labeled anti-CD44v6 antibody AbN44v6, were potentiated by the novel stapled MDM2/X-p53 antagonist PM2.

MATERIALS AND METHODS

Two wt p53 cell lines, HCT116 (colorectal carcinoma) and UM-SCC-74B (head and neck squamous cell carcinoma), expressing different levels of the target antigen, CD44v6, were used. Antigen-specific binding of 177Lu-AbN44v6 was initially verified in a 2D cell assay, after which the potential effects of unlabeled AbN44v6 on downstream phosphorylation of Erk1/2 were evaluated by western blotting. Further, the therapeutic effects of unlabeled AbN44v6, 177Lu-AbN44v6, PM2, or a combination (labeled/unlabeled AbN44v6 +/- PM2) were assessed in 3D multicellular tumor spheroid assays.

RESULTS

Radiolabeled antibody bound specifically to CD44v6 on both cell lines. Unlabeled AbN44v6 binding did not induce downstream phosphorylation of Erk1/2 at any of the concentrations tested, and repeated treatments with the unlabeled antibody did not result in any spheroid growth inhibition. 177Lu-AbN44v6 impaired spheroid growth in a dose-dependent and antigen-dependent manner. A single modality treatment with 20 μM of PM2 significantly impaired spheroid growth in both spheroid models. Furthermore, the combination of TRNT and PM2-based therapy proved significantly more potent than either monotherapy. In HCT116 spheroids, this resulted in a two- and threefold spheroid growth rate decrease for the combination of PM2 and 100 kBq 177Lu-AbN44v6 compared to monotherapies 14-day post treatment. In UM-SCC-74B spheroids, the combination therapy resulted in a reduction in spheroid size compared to the initial spheroid size 10-day post treatment.

CONCLUSION

TRNT using 177Lu-AbN44v6 proved efficient in stalling spheroid growth in a dose-dependent and antigen-dependent manner, and PM2 treatment demonstrated a growth inhibitory effect as a monotherapy. Moreover, by combining TRNT with PM2-based therapy, therapeutic effects of TRNT were potentiated in a 3D multicellular tumor spheroid model. This proof-of-concept study exemplifies the strength and possibility of combining TRNT targeting CD44v6 with PM2-based therapy.

The HSP90 inhibitor Onalespib exerts synergistic anti-cancer effects when combined with radiotherapy: an in vitro and in vivo approach

Oncogenic client-proteins of the chaperone Heat shock protein 90 (HSP90) insure unlimited tumor growth and are involved in resistance to chemo- and radiotherapy. The HSP90 inhibitor Onalespib initiates the degradation of oncoproteins, and might also act as a radiosensitizer. The aim of this study was therefore to evaluate the efficacy of Onalespib in combination with external beam radiotherapy in an in vitro and in vivo approach. Onalespib downregulated client proteins, lead to increased apoptosis and caused DNA-double-strands. Monotherapy and combination with radiotherapy reduced colony formation, proliferation and migration assessed in radiosensitive HCT116 and radioresistant A431 cells. In vivo, a minimal treatment regimen for 3 consecutive days of Onalespib (3 × 10 mg/kg) doubled survival, whereas Onalespib with radiotherapy (3 × 2 Gy) caused a substantial delay in tumor growth and prolonged the survival by a factor of 3 compared to the HCT116 xenografted control group. Our results demonstrate that Onalespib exerts synergistic anti-cancer effects when combined with radiotherapy, most prominent in the radiosensitive cell models. We speculate that the depletion and downregulation of client proteins involved in signalling, migration and DNA repair mechanisms is the cause. Thus, individually, or in combination with radiotherapy Onalespib inhibits tumor growth and has the potential to improve radiotherapy outcomes, prolonging the overall survival of cancer patients.

The radiosensitizer Onalespib increases complete remission in 177Lu-DOTATATE-treated mice bearing neuroendocrine tumor xenografts

PURPOSE

177Lu-DOTATATE targeting the somatostatin receptor (SSTR) is utilized for treatment of neuroendocrine tumors (NETs). Onalespib, a heat shock protein 90 (HSP90) inhibitor, has demonstrated radiosensitizing properties and may thus enhance the effect of 177Lu-DOTATATE. Consequently, the aim of this study was to assess the potential of Onalespib in combination with 177Lu-DOTATATE in vivo and to examine the toxicity profiles of the treatments.

METHODS

177Lu-DOTATATE selectivity and distribution in NET xenografts were studied using biodistribution and autoradiography. Therapeutic effects of Onalespib in combination with 177Lu-DOTATATE were studied in NET xenografts. Histological analyses were used to assess molecular effects from treatment and to establish toxicity profiles.

RESULTS

Biodistribution and autoradiography confirmed the SSTR-selective tumor uptake of 177Lu-DOTATATE, which was unaffected by Onalespib treatment. Immunohistochemistry verified molecular responses to Onalespib therapy in the tumors. While Onalespib and 177Lu-DOTATATE monotherapies resulted in a 10% and 33% delay in tumor doubling time compared with control, the combination treatment resulted in a 73% delayed tumor doubling time. Moreover, combination treatment increased complete remissions threefold from 177Lu-DOTATATE monotherapy, resulting in 29% complete remissions. In addition, histological analyses demonstrated radiation-induced glomerular injury in the 177Lu-DOTATATE monotherapy group. The damage was decreased tenfold in the combination group, potentially due to Onalespib-induced HSP70 upregulation in the kidneys.

CONCLUSION

Treatment with Onalespib potentiated 177Lu-DOTATATE therapy of NET xenografts with a favorable toxicity profile. Utilizing Onalespib's radiosensitizing properties with 177Lu-DOTATATE may lead to better therapeutic results in the future and may reduce unwanted side effects in dose-limiting organs.

The HSP90 inhibitor onalespib potentiates 177Lu‑DOTATATE therapy in neuroendocrine tumor cells

¹⁷⁷Lu-DOTATATE was recently approved for the treatment of somatostatin receptor (SSTR)-positive neuroen-docrine tumors (NETs). However, despite impressive response rates, complete responses are rare. Heat shock protein 90 (HSP90) inhibitors have been suggested as suitable therapeutic agents for NETs, as well as a potential radiosensitizers. Consequently, the aim of this study was to investigate whether the HSP90-inhibitor onalespib could reduce NET cell growth and act as a radiosensitizer when used in combination with ¹⁷⁷Lu-DOTATATE. The NET cell lines BON, NCI-H727 and NCI-H460, were first characterized with regards to ¹⁷⁷Lu-DOTATATE uptake and sensitivity to onalespib treatment in monolayer cell assays. The growth inhibitory effects of the monotherapies and combination treatments were then examined in three-dimensional multicellular tumor spheroids. Lastly, the molecular effects of the treatments were assessed. ¹⁷⁷Lu-DOTATATE uptake was observed in the BON and NCI-H727 cells, while the NCI-H460 cells exhibited no detectable uptake. Accordingly, ¹⁷⁷Lu-DOTATATE reduced the growth of BON and NCI-H727 spheroids, while no effect was observed in the NCI-H460 spheroids. Onalespib reduced cell viability and spheroid growth in all three cell lines. Furthermore, the combination of onalespib and ¹⁷⁷Lu-DOTATATE exerted synergistic therapeutic effects on the BON and NCI-H727 spheroids. Western blot analysis of BON spheroids revealed the downregulation of epidermal growth factor receptor (EGFR) and the upregulation of γ H2A histone family member X (γH2AX) following combined treatment with onalespib and ¹⁷⁷Lu-DOTATATE. Moreover, flow cytometric analyses revealed a two-fold increase in caspase 3/7 activity in the combination group. In conclusion, the findings of this study demonstrate that onalespib exerts antitumorigenic effects on NET cells and may thus be a feasible treatment option for NETs. Furthermore, onalespib was able to synergistically potentiate ¹⁷⁷Lu-DOTATATE treatment in a SSTR-specific manner. The radiosensitizing mechanisms of onalespib involved the downregulation of EGFR expression and the induction of apoptosis. Consequently, the combination of onalespib and ¹⁷⁷Lu-DOTATATE may prove to be a promising strategy with which to improve therapeutic responses in patients with NETs. Further studies investigating this strategy in vivo regarding the therapeutic effects and potential toxicities are warranted to expand these promising findings.

Real-time molecular optical micro-imaging of EGFR mutations using a fluorescent erlotinib based tracer

BACKGROUND

EGFR mutations are routinely explored in lung adenocarcinoma by sequencing tumoral DNA. The aim of this study was to evaluate a fluorescent-labelled erlotinib based theranostic agent for the molecular imaging of mutated EGFR tumours in vitro and ex vivo using a mice xenograft model and fibred confocal fluorescence microscopy (FCFM).

METHODS

The fluorescent tracer was synthesized in our laboratory by addition of fluorescein to an erlotinib molecule. Three human adenocarcinoma cell lines with mutated EGFR (HCC827, H1975 and H1650) and one with wild-type EGFR (A549) were xenografted on 35 Nude mice. MTT viability assay was performed after exposure to our tracer. In vitro imaging was performed at 1 μM tracer solution, and ex vivo imaging was performed on fresh tumours excised from mice and exposed to a 1 μM tracer solution in PBS for 1 h. Real-time molecular imaging was performed using FCFM and median fluorescence intensity (MFI) was recorded for each experiment.

RESULTS

MTT viability assay confirmed that addition of fluorescein to erlotinib did not suppress the cytotoxic of erlotinib on tumoral cells. In vitro FCFM imaging showed that our tracer was able to distinguish cell lines with mutated EGFR from those lines with wild-type EGFR (p < 0.001). Ex vivo FCFM imaging of xenografts with mutated EGFR had a significantly higher MFI than wild-type (p < 0.001). At a cut-off value of 354 Arbitrary Units, MFI of our tracer had a sensitivity of 100% and a specificity of 96.3% for identifying mutated EGFR tumours.

CONCLUSION

Real time molecular imaging using fluorescent erlotinib is able to identify ex vivo tumours with EGFR mutations.

Evaluation of [11C]NMS-E973 as a PET tracer for in vivo visualisation of HSP90

Heat shock protein 90 is an ATP-dependent molecular chaperone important for folding, maturation and clearance of aberrantly expressed proteins and is abundantly expressed (1-2% of all proteins) in the cytosol of all normal cells. In some tumour cells, however, strong expression of HSP90 is also observed on the cell membrane and in the extracellular matrix and the affinity of tumoural HSP90 for ATP domain inhibitors was reported to increase over 100-fold compared to that of HSP90 in normal cells. Here, we explore [¹¹C]NMS-E973 as a PET tracer for in vivo visualisation of HSP90 and as a potential tool for in vivo quantification of occupancy of HSP90 inhibitors.

Methods: HSP90 expression was biochemically characterized in a panel of established cell lines including the melanoma line B16.F10. B16.F10 melanoma xenograft tumour tissue was compared to non-malignant mouse tissue. NMS-E973 was tested in vitro for HSP90 inhibitory activity in several tumour cell lines. HSP90-specific binding of [¹¹C]NMS-E973 was evaluated in B16.F10 melanoma cells and B16.F10 melanoma, prostate cancer LNCaP and PC3, SKOV-3 xenograft tumour slices and in vivo in a B16.F10 melanoma mouse model.

Results: Strong intracellular upregulation and abundant membrane localisation of HSP90 was observed in the different tumour cell lines, in the B16.F10 tumour cell line and in B16.F10 xenograft tumours compared to non-malignant tissue. NMS-E973 showed HSP90-specific inhibition and reduced proliferation of cells. [¹¹C]NMS-E973 showed strong binding to B16.F10 melanoma cells, which was inhibited by 200 µM of PU-H71, a non-structurally related HSP90 inhibitor. HSP90-specific binding was observed by in vitro autoradiography of murine B16.F10 melanoma, LNCaP and PC3 prostate cancer and SKOV-3 ovary carcinoma tissue slices. Further, B16.F10 melanoma-inoculated mice were subjected to a µPET study, where the tracer showed fast and persistent tumour uptake. Pretreatment of B16.F10 melanoma mice with PU-H71 or Ganetespib (50 mg/kg) completely blocked tumour accumulation of [¹¹C]NMS-E973 and confirmed in vivo HSP90 binding specificity. HSP90-specific binding of [¹¹C]NMS-E973 was observed in blood, lungs and spleen of tumour-bearing animals but not in control animals.

Conclusion: [¹¹C]NMS-E973 is a PET tracer for in vivo visualisation of tumour HSP90 expression and can potentially be used for quantification of HSP90 occupancy. Further translational evaluation of [¹¹C]NMS-E973 is warranted.

The Promise of Novel Biomarkers for Head and Neck Cancer from an Imaging Perspective

It is an agreed fact that overall survival among head and neck cancer patients has increased over the last decade. Several factors however, are still held responsible for treatment failure requiring more in-depth evaluation. Among these, hypoxia and proliferation-specific parameters are the main culprits, along with the more recently researched cancer stem cells. This paper aims to present the latest developments in the field of biomarkers for hypoxia, stemness and tumour proliferation, from an imaging perspective that includes both Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) as well as functional magnetic resonance imaging (MRI). Quantitative imaging of biomarkers is a prerequisite for accurate treatment response assessment, bringing us closer to the highly needed personalised therapy.

The MDM2/MDMX-p53 Antagonist PM2 Radiosensitizes Wild-Type p53 Tumors

Radiotherapy amplifies p53 expression in cancer cells with wild-type (wt) p53. Blocking the negative regulators MDM2 and MDMX stabilizes p53 and may therefore potentiate radiotherapy outcomes. In this study, we investigate the efficacy of the novel anti-MDM2/X stapled peptide PM2 alone and in combination with external gamma radiation in vitro and in vivo PM2 therapy combined with radiotherapy elicited synergistic therapeutic effects compared with monotherapy in cells with wt p53 in both in vitro and in vivo assays, whereas these effects did not manifest in p53 ^-/- cells. Biodistribution and autoradiography of ¹²⁵I-PM2 revealed high and retained uptake homogenously distributed throughout the tumor. In mice carrying wt p53 tumors, PM2 combined with radiotherapy significantly prolonged the median survival by 50%, whereas effects of PM2 therapy on mutant and p53 ^-/- tumors were negligible. PM2-dependent stabilization of p53 was confirmed with ex vivo immunohistochemistry. These data demonstrate the potential of the stapled peptide PM2 as a radiotherapy potentiator in vivo and suggest that clinical application of PM2 with radiotherapy in wt p53 cancers might improve tumor control.Significance: These findings contribute advances to cancer radiotherapy by using novel p53-reactivating stapled peptides as radiosensitizers in wild-type p53 cancers. Cancer Res; 78(17); 5084-93. ©2018 AACR.

Radiolabeled F(ab')2-cetuximab for theranostic purposes in colorectal and skin tumor-bearing mice models

PURPOSE

This study aimed to investigate theranostic strategies in colorectal and skin cancer based on fragments of cetuximab, an anti-EGFR mAb, labeled with radionuclide with imaging and therapeutic properties, ¹¹¹In and ¹⁷⁷Lu, respectively.

METHODS

We designed F(ab')₂-fragments of cetuximab radiolabeled with ¹¹¹In and ¹⁷⁷Lu. ¹¹¹In-F(ab')₂-cetuximab tumor targeting and biodistribution were evaluated by SPECT in BalbC nude mice bearing primary colorectal tumors. The efficacy of ¹¹¹In-F(ab')₂-cetuximab to assess therapy efficacy was performed on BalbC nude mice bearing colorectal tumors receiving 17-DMAG, an HSP90 inhibitor. Therapeutic efficacy of the radioimmunotherapy based on ¹⁷⁷Lu-F(ab')₂-cetuximab was evaluated in SWISS nude mice bearing A431 tumors.

RESULTS

Radiolabeling procedure did not change F(ab')₂-cetuximab and cetuximab immunoreactivity nor affinity for HER1 in vitro. ¹¹¹In-DOTAGA-F(ab')₂-cetuximab exhibited a peak tumor uptake at 24 h post-injection and showed a high tumor specificity determined by a significant decrease in tumor uptake after the addition of an excess of unlabeled-DOTAGA-F(ab')₂-cetuximab. SPECT imaging of ¹¹¹In-DOTAGA-F(ab')₂-cetuximab allowed an accurate evaluation of tumor growth and successfully predicted the decrease in tumor growth induced by 17-DMAG. Finally, ¹⁷⁷Lu-DOTAGA-F(ab')₂-cetuximab radioimmunotherapy showed a significant reduction of tumor growth at 4 and 8 MBq doses.

CONCLUSIONS

¹¹¹In-DOTAGA-F(ab')₂-cetuximab is a reliable and stable tool for specific in vivo tumor targeting and is suitable for therapy efficacy assessment. ¹⁷⁷Lu-DOTAGA-F(ab')₂-cetuximab is an interesting theranostic tool allowing therapy and imaging.

Preclinical evaluation of a novel engineered recombinant human anti-CD44v6 antibody for potential use in radio-immunotherapy

CD44v6 is overexpressed in a variety of cancers, rendering it a promising target for radio-immunotherapy (RIT). In this study, we have characterized a novel engineered recombinant monoclonal anti-CD44v6 antibody, AbN44v6, and assessed its potential for use in RIT using either ¹⁷⁷Lu or ¹³¹I as therapeutic radionuclides. In vitro affinity and specificity assays characterized the binding of the antibody labeled with ¹⁷⁷Lu, ¹²⁵I or ¹³¹I. The therapeutic effects of ¹⁷⁷Lu-AbN44v6 and ¹³¹I-AbN44v6 were investigated using two in vitro 3D tumor models with different CD44v6 expression. Finally, the normal tissue biodistribution and dosimetry for ¹⁷⁷Lu-AbN44v6 and ¹²⁵I-AbN44v6/¹³¹I-AbN44v6 were assessed in vivo using a mouse model. All AbN44v6 radioconjugates demonstrated CD44v6-specific binding in vitro. In the in vitro 3D tumor models, dose-dependent therapeutic effects were observed with both ¹⁷⁷Lu-AbN44v6 and ¹³¹I-AbN44v6, with a greater significant therapeutic effect observed on the cells with a higher CD44v6 expression. Biodistribution experiments demonstrated a greater uptake of ¹⁷⁷Lu-AbN44v6 in the liver, spleen and bone, compared to ¹²⁵I-AbN44v6, whereas ¹²⁵I-AbN44v6 demonstrated a longer circulation time. In dosimetric calculations, the critical organs for ¹⁷⁷Lu-AbN44v6 were the liver and spleen, whereas the kidneys and red marrow were considered the critical organs for ¹³¹I-AbN44v6. The effective dose was in the order of 0.1 mSv/MBq for both labels. In conclusion, AbN44v6 bound specifically and with high affinity to CD44v6. Furthermore, in vitro RIT demonstrated growth inhibition in a CD44v6-specific activity-dependent manner for both radioconjugates, demonstrating that both ¹⁷⁷Lu-AbN44v6 and ¹³¹I-AbN44v6 may be promising RIT candidates. Furthermore, biodistribution and dosimetric analysis supported the applicability of both conjugates for RIT. The CD44v6-specific therapeutic effects observed with radiolabeled AbN44v6 in the 3D tumor models in vitro, combined with the beneficial dosimetry in vivo, render AbN44v6 a potential candidate for RIT.

A High-Affinity Repebody for Molecular Imaging of EGFR-Expressing Malignant Tumors

The accurate detection of disease-related biomarkers is crucial for the early diagnosis and management of disease in personalized medicine. Here, we present a molecular imaging of human epidermal growth factor receptor (EGFR)-expressing malignant tumors using an EGFR-specific repebody composed of leucine-rich repeat (LRR) modules. The repebody was labeled with either a fluorescent dye or radioisotope, and used for imaging of EGFR-expressing malignant tumors using an optical method and positron emission tomography. Our approach enabled visualization of the status of EGFR expression, allowing quantitative evaluation in whole tumors, which correlated well with the EGFR expression levels in mouse or patients-derived colon cancers. The present approach can be effectively used for the accurate detection of EGFR-expressing cancers, assisting in the development of a tool for detecting other disease biomarkers.

CD44v6-Targeted Imaging of Head and Neck Squamous Cell Carcinoma: Antibody-Based Approaches

Head and neck squamous cell carcinoma (HNSCC) is a common and severe cancer with low survival rate in advanced stages. Noninvasive imaging of prognostic and therapeutic biomarkers could provide valuable information for planning and monitoring of the different therapy options. Thus, there is a major interest in development of new tracers towards cancer-specific molecular targets to improve diagnostic imaging and treatment. CD44v6, an oncogenic variant of the cell surface molecule CD44, is a promising molecular target since it exhibits a unique expression pattern in HNSCC and is associated with drug- and radio-resistance. In this review we summarize results from preclinical and clinical investigations of radiolabeled anti-CD44v6 antibody-based tracers: full-length antibodies, Fab, F(ab′)₂ fragments, and scFvs with particular focus on the engineering of various antibody formats and choice of radiolabel for the use as molecular imaging agents in HNSCC. We conclude that the current evidence points to CD44v6 imaging being a promising approach for providing more specific and sensitive diagnostic tools, leading to customized treatment decisions and functional diagnosis. Improved imaging tools hold promise to enable more effective treatment for head and neck cancer patients.

MicroPET/CT Imaging of AXL Downregulation by HSP90 Inhibition in Triple-Negative Breast Cancer

AXL receptor tyrosine kinase is overexpressed in a number of solid tumor types including triple-negative breast cancer (TNBC). AXL is considered an important regulator of epithelial-to-mesenchymal transition (EMT) and a potential therapeutic target for TNBC. In this work, we used microPET/CT with ⁶⁴Cu-labeled anti-human AXL antibody (⁶⁴Cu-anti-hAXL) to noninvasively interrogate the degradation of AXL in vivo in response to 17-allylamino-17-demethoxygeldanamycin (17-AAG), a potent inhibitor of HSP90. 17-AAG treatment caused significant decline in AXL expression in orthotopic TNBC MDA-MB-231 tumors, inhibited EMT, and delayed tumor growth in vivo, resulting in significant reduction in tumor uptake of ⁶⁴Cu-anti-hAXL as clearly visualized by microPET/CT. Our data indicate that ⁶⁴Cu-anti-hAXL can be useful for monitoring anti-AXL therapies and for assessing inhibition of HSP90 molecular chaperone using AXL as a molecular surrogate.

Molecularly targeted therapies in cancer: a guide for the nuclear medicine physician

Molecular imaging continues to influence every aspect of cancer care including detection, diagnosis, staging and therapy response assessment. Recent advances in the understanding of cancer biology have prompted the introduction of new targeted therapy approaches. Precision medicine in oncology has led to rapid advances and novel approaches optimizing the use of imaging modalities in cancer care, research and development. This article focuses on the concept of targeted therapy in cancer and the challenges that exist for molecular imaging in cancer care.