GZ17‐6.02 initiates DNA damage causing autophagosome‐dependent HDAC degradation resulting in enhanced anti‐PD1 checkpoint inhibitory antibody efficacy

Abstract Our studies examined the molecular mechanisms by which the novel cancer therapeutic GZ17‐6.02 (NCT03775525) killed GI tumor cells. TZ17‐6.02 activated ATM which was responsible for increased phosphorylation of nuclear γH2AX and AMPKα T172. ATM‐AMPK signaling was responsible for the subsequent inactivation of mTORC1 and mTORC2, dephosphorylation of ULK1 S757, and increased phosphorylation of ULK1 S317 and of ATG13 S318, which collectively caused enhanced autophagosome formation. GZ17‐6.02 interacted with 5‐fluorouracil in an additive to greater than additive fashion to kill all of the tested GI tumor cell types. This was associated with greater ATM activation and a greater mammalian target of rapamycin inactivation and autophagosome induction. As a result, autophagy‐dependent degradation of multiple histone deacetylase (HDAC) proteins and chaperone proteins occurred. Loss of HDAC expression was causal in reduced expression of programed death ligand 1 (PD‐L1), ornithine decarboxylase, and indole amine 2,3‐dioxygenase (IDO1) and in the elevated expression of major histocompatibility complex Class IA (MHCA). Treatment with GZ17‐6.02 also resulted in enhanced efficacy of a subsequently administered anti‐PD1 checkpoint inhibitory antibody. Thus, the primary mode of GZ17‐6.02 action is to induce a DNA damage response concomitant with ATM activation, that triggers a series of interconnected molecular events that result in tumor cell death and enhanced immunogenicity.