Orthogonally targeted tumor radiosensitization using cell penetrating peptide-ATM inhibitor conjugates to stimulate anti-tumor immune responses.

Tumor resistance to radiotherapy continues to be a significant problem in improving cancer patient outcomes. To overcome radioresistance, drugs that sensitize cancer cells to ionizing radiation have been tested. In theory, radiosensitizers should increase irradiated tumor kill and improve patient outcomes. In practice, the clinical utility of such drugs is curtailed by radiosensitization of peri-tumoral normal tissues causing toxicities. To address these issues, we developed an activatable cell penetrating peptide-drug conjugate to deliver a small molecule radiosensitizer with spatial precision to tumors. The activatable cell penetrating peptide (ACPP) scaffold cloaks a cell penetrating peptide-drug conjugate until it is unmasked within tumors through matrix metalloproteinase cleavage. Using antibody-drug conjugate linker chemistry, we attached the potent ataxia-telangiectasia mutated (ATM) kinase inhibitor AZD0156 to ACPP and created ACPP-AZD0156. In immune-competent murine cancer models, tumor-targeted ACPP-AZD0156 in combination with ionizing radiation stimulated tumor immune infiltration by CD8+ T cells and increased tumor control when compared to non-targeted ATM inhibitor. Mechanistically, ACPP-AZD0156 radiosensitized tumor control was dependent on the adaptive arm of the immune system. Finally, the combination of radiotherapy and ACPP-AZD0156 potentiated immune checkpoint inhibitors that resulted in durable tumor control. The therapeutic synergies of ACPP targeted ATM inhibitor to radiosensitize and stimulate anti-tumor immune responses provides a rationale for developing tumor-targeted radiosensitizer drug conjugates that restrict radiosensitization to cancer cells that then engages anti-tumor immune responses to improve cancer patient outcomes.