Development Of A Novel Radiation-Induced Targeted Immunotherapy Strategy Through Oligonucleotide Aptamer Conjugation

Monoclonal antibodies (mAbs) produce dramatic anti-tumor responses in multiple solid tumors. Unfortunately, systemic administration can result in end organ retention and dose-limiting toxicities. Radiotherapy (RT) is a standard-of-care treatment modality that induces direct tumor cell kill through DNA damage. While studies assessing the synergy of RT-induced tumor cell kill with mAbs are ongoing, an additional unexploited effect of RT is the induction of stress response products in the tumor microenvironment, such as vascular endothelial growth factor (VEGF). Oligonucleotide aptamers are short pieces of nucleic acid that exhibit little to no immunogenicity compared to mAbs, making them ideal delivery vehicles for therapeutic mAbs. The purpose of this study was to assess the feasibility of a novel strategy for targeted tumor delivery of existing immunotherapeutic mAbs through conjugation to ligands that bind to radiation induced products. An antibody recognizing the costimulatory molecule 41BB was covalently modified with a 21-mer ssDNA oligonucleotide linker sequence that serves as an anchor site for the VEGF aptamer synthesized with a 3’ extension. Annealing of complementary strands formed a 41BB mAb-VEGF aptamer conjugate. First, VEGF aptamer conjugation to modified 41BB mAb was verified by polyacrylamide gel electrophoresis analysis which revealed the expected size shift of the 41BB mAb-VEGF aptamer conjugate versus the unannealed controls. Conjugation was then verified using flow cytometry. Recombinant mouse 41BB-Fc was immobilized on Protein A Dynabeads and 41BB mAb conjugated with 5’ biotinylated VEGF aptamer. 41BB mAb-VEGF aptamer conjugate retention on Dynabeads was confirmed by using streptavidin-PE 5’ biotin of aptamer attached to mAb in conjugate binding epitope target. Functionality of 41BB mAb-VEGF aptamer conjugate was confirmed in vitro using a CD8+ T cell costimulation assay. CD8+ T cells were isolated from 8 week old female C57BL6/J splenocytes, and exposed to sub-optimal levels of CD3 mAb. 41BB mAb-VEGF aptamer conjugate, unconjugated 41BB mAb and isotype control were added to activated cells. Elevated levels of interferon gamma were observed and equivalent in conjugated and unconjugated 41BB mAbs. These results indicate that conjugation of 41BB mAb-VEGF aptamer is feasible and that conjugation does not affect 41BB mAb functionality. Use of this novel targeting approach to improve the therapeutic index of immunotherapeutic mAbs requires validation in murine tumor models. Citation Format: Ana Paula Benaduce, Randall Brenneman, Diana Cardero, Brett Schrand, Eli Gilboa, Adrian Ishkanian. Development of a novel radiation-induced targeted immunotherapy strategy through oligonucleotide aptamer conjugation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4992.