Abstract 1804: IND-ready clinical candidate for HPK1 developed with excellent efficacy and safety profile

Abstract

Abstract Background Hematopoietic progenitor kinase 1 (HPK1) is a member of the mitogen-activated protein kinase (MAP4K) family of protein serine/threonine kinases1,2 and is a negative regulator of T and B cell receptor signaling3. Inhibition of HPK1 is an attractive therapeutic strategy for immuno-oncology based treatment of solid tumors3. We present in vitro, in vivo, pharmacokinetic (PK) and early safety profiles of a novel and differentiated HPK1 inhibitor GRC 54276. Methods GRC 54276 is our clinical candidate, designed and developed using intuitive medicinal chemistry design and supported by computational approaches. SAR studies included a battery of biochemical assays, functional read-outs and primary human in vitro T-cell activation assays. In vivo efficacy was demonstrated in syngeneic mouse tumor models, both as a single agent and combination with immune check-point blockers (ICB), mouse anti-CTLA4 antibody or Atezolizumab (human anti-PD-L1 antibody). ADME-PK properties was evaluated cross-species. GLP and non-GLP safety tolerability studies were conducted in mice and monkeys. Results GRC 54276 demonstrated sub-nanomolar HPK1 potency, strong target engagement of pSLP76 inhibition, anti-tumor cytokines (IL-2 and IFN-γ) induction, reversal of immunosuppression by prostaglandin E2 (PGE2) or adenosine in both human and mouse systems. GRC 54276 demonstrated very strong tumor growth inhibition (TGI) efficacy as single agent and significantly enhanced TGI in combination with ICB antibodies anti-CTLA4 (CT26 model) or Atezolizumab (MC38-hPD-L1 model). The in vivo TGI efficacy mechanistically correlated with increased immune responses of cytokine induction, infiltration of cytotoxic T cells, tumor rejections accompanied by immune memory T cells induction. Pharmacokinetic profile of GRC 54276 included cross-species oral bioavailability (30 to 100%), predominant clearance by CYP3A4 with no significant inhibition of major CYP isoforms, negative activation potency in human PXR assay at several-fold over EDmax exposures. Safety profile demonstrated that GRC 54276 is non-genotoxic in the bone marrow micronucleus assay in mice and has no hERG liability. The no observed adverse effect levels in the 14-day and 17-day exploratory studies in mice and monkeys were 50 and 15 mg/kg/day, respectively. Conclusions GRC 54276, our clinical candidate is potent, selective, orally bioavailable HPK1 inhibitor demonstrating strong single-agent and combination efficacy, low DDI liability accompanied by acceptable early safety profile in mice and monkeys. GRC 54276 is undergoing IND enabling studies to advance to Phase 1 clinical trial. Acknowledgements We thank Vidya Kattige, Pooja Sawant, Shital More, Rahul B. Bhadane, Ajit Jagadale, Sanjay Gaikwad, Pramod Sagar for their contributions to the project