Abstract 6038: Copper-67 based targeted radiotherapy primes immunologically cold PDAC for immunotherapy
Authors: Rao Yi , Viray Tara , Gehlsen Kurt , Harris Matt , McInnes Lachlan , Majekodunmi Olufolake , Lewis Jason 
Published: March 2024

Background and Purpose: Immune checkpoint therapy (ICT) has revolutionized cancer treatment however efficacy remains dismal for some cancers, including pancreatic cancers. Strategies to enhance immune responses include combining ICT with other existing cancer therapies. Targeted radiotherapy (TRT) uses a radiolabeled cancer-targeting vector, allowing for systematic delivery of specific radiation to all tumor sites while minimizing radiation exposure to healthy tissues. We propose Targeted Copper Theranostics (TCTs) as a TRT, utilizing copper-67 to irradiate and prime immunologically “cold” pancreatic adenocarcinoma (PDAC) and evaluate the efficacy of copper-67-based TRT-ICT combination therapy.

Methods: We evaluated two tumor-targeting vectors conjugated to a sarcophagine macrobicyclic chelator (SAR), an antibody—5B1, targeting the PDAC-specific biomarker carbohydrate antigen-19-9 (CA19-9), and a peptide RGD, targeting the αvβ3 integrin receptor, which is highly expressed in some PDAC tumors. We administrated ~1.1 MBq of [64Cu]Cu-SAR-bisRGD (~0.1 μg) or [64Cu]Cu-SAR-5B1 (~10 μg) to FC1245 Ft2Ab PDAC (a murine PDAC cell line expressing CA19-9) tumor-bearing C57BL/6 mice and performed biodistribution studies at 1 and 4 h for [64Cu]Cu-SAR-bisRGD-injected mice and at 24 and 48 h for [64Cu]Cu-5B1-injected mice. [67Cu]Cu-SAR-bisRGD- and [67Cu]Cu-SAR-5B1-based dose escalation studies and the combination of a copper-67-based TRT and ICT were performed to evaluate therapeutic efficacy of copper-67-based TRT and potential synergistic effects of combination therapy.

Results: Tumor uptake of [64Cu]Cu-SAR-bisRGD is ~5 %ID/g at 4h-post injection, and tumor uptake of [64Cu]Cu-SAR-5B1 is ~55 %ID/g 24h-post injection. In dose escalation studies, administration of ~11, 22, and 37 MBq of [67Cu]Cu-SAR-bisRGD (~1 μg) or administration of ~4, 11, 18 MBq of [67Cu]Cu-5B1(~150 μg) improved overall survival to 25 or 32 days respectively, compared to the control cohort (14 days). Based on weekly whole-blood analyses, no significant radiotoxicity was observed in mice receiving various doses of TRTs. The combination of 11 MBq of either [67Cu]Cu-SAR-bisRGD or [67Cu]Cu-SAR-5B1 in combination with either antiPD-L1/PD1 or antiCTLA4, improved overall survival by ~7 days compared to ICT-treated control groups.

Conclusion: Biodistribution studies demonstrated relatively high tumor specific uptake for [64Cu]Cu-SAR-bisRGD and [64Cu]Cu-SAR-5B1. Dose escalation study results suggest copper-67-based TRT could effectively inhibit tumor growth with minimal radiotoxicity. The combination of TRT with ICTs improved overall survival compared to single-ICT-treated control groups. Collectively, our results strongly support the hypothesis that TRT with [67Cu]Cu-SAR-bisRGD or [67Cu]Cu-SAR-5B1 could prime immunologically “cold” pancreatic adenocarcinoma (PDAC) to be responsive to ICTs.

Citation Format: Yi Rao, Tara Viray, Kurt Gehlsen, Matt Harris, Lachlan McInnes, Olufolake Majekodunmi, Jason Lewis. Copper-67 based targeted radiotherapy primes immunologically cold PDAC for immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6038.