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

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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 (IR) have been tested. In theory, radiosensitizers should increase irradiated tumor kill and improve patient outcomes. However, in practice, the clinical utility of such drugs is curtailed by radiosensitization of peri-tumoral normal tissues causing toxicities. To target radiosensitizer delivery to tumors, we developed an activatable cell penetrating peptide (ACPP) drug conjugate for spatially tumor-restricted delivery of the potent ataxia-telangiectasia mutated kinase inhibitor (ATMi) AZD0156. The ACPP scaffold cloaks a cell penetrating peptide-drug conjugate until it is unmasked within tumors through tumor-associated matrix metalloproteinase thus promoting preferential tumor uptake. Using clinically validated antibody-drug conjugate linker chemistry, we conjugated AZD0156 to ACPP (ACPP-AZD0156) and evaluated its immune stimulating and therapeutic activity with IR in immune-competent murine cancer models. Transcriptomic profiling revealed combining ACPP-AZD0156 with IR enhanced radiation-induced immune activation programs, including type I interferon signaling and leukocyte activation network. Importantly, ACPP-AZD0156 combined with IR stimulated intratumoral CD8+ T cell infiltration and improved tumor control compared to non-targeted ATM inhibitor. Mechanistically, the therapeutic effect of ACPP-AZD0156 + IR was abrogated by CD8+ T-cell depletion, establishing a role for adaptive immunity engagement by ACPP-AZD0156 radiosensitization. Finally, the combination of IR and ACPP-AZD0156 with PD-1 blockade resulted in durable tumor control and long-term survival. Taken together, these data provide a basis for tumor-targeted ATMi delivery as a precision oncology based immunogenic radiosensitization strategy.