Abstract 1709: Novel small molecule HPK1 inhibitor induces immunogenic anti-tumor effects (2021)

Abstract Background Hematopoietic progenitor kinase 1 (HPK1, MAP4K1), a member of the MAP4K family of protein serine/threonine kinases1,2 is a negative regulator of TCR and BCR3. Immunosuppressive mediators PGE2 and adenosine regulate activation of HPK13. In vivo anti-tumor activity by HPK1 gene deletion, kinase dead HPK1 and small molecule HPK1 inhibitors have been demonstrated in multiple immunogenic syngeneic tumor models3,4. Enhanced anti-tumor efficacy in these models was achieved by combining HPK1 inhibitors with immune check-point blockers (ICBs) like anti-PD-1, anti-PD-L1or anti-CTLA4 antibodies3,4. HPK1 inhibition is a target for immuno-oncology treatment in cancers responsive or non-responsive to current ICBs. Methods Creative medicinal chemistry design complemented by structured-based support was used to identify &amp; develop inhibitors of HPK1 with pico/nano-molar potency, optimal kinase selectivity, PK and efficacy profile. Our SAR efforts were guided by biochemical assays, functional read-outs and primary human in vitro T-cell activation assays. In vivo target engagement and pharmacodynamic data was generated using mouse models of the lung (LLC) and colon (MC38 and CT26) cancer. Results We describe novel and potent HPK1 inhibitors that can inhibit pSLP76 and enhance IL-2 production in Jurkat cells, IL-2 and IFN-γ production in human PBMCs, whole blood and primary T cells and TNF-α production by dendritic cells following stimulation. A reversal of PGE2 or adenosine mediated immunosuppression was also achieved by the inhibitors. These compounds on oral dosing showed strong tumor growth inhibition (TGI) in syngeneic models refractory to ICBs (subcutaneous LLC) as well as responsive to ICBs (subcutaneous MC38 and CT26; orthotopic LLC). TGI was accompanied by the immune response of increased cytokine (IL-2/IFNγ) levels and tumor infiltrating lymphocytes (TILs). Combination with ICBs induced enhanced TGI correlating with enhanced cytokine induction and TILs. We confirmed the immune-mediated mechanism of inhibitors by their lack of efficacy in immune-compromised mice. The lead compound demonstrated cardiac safety (hERG assay), lack of genotoxicity and very good safety margins in the mouse exploratory toxicology studies up to 28-days. Conclusion We have discovered a novel, orally active HPK1 inhibitor that demonstrates excellent stand-alone efficacy in multiple tumor models and also offers the potential to enhance current immunotherapy regimens in both responsive and refractory cancers. Further evaluation of our lead molecule towards the clinic is underway. Acknowledgements Sanjib D, Megha M, Jiju M, Sheetal K, Arti J, Swayam M, Srinivas K, Pradeep V, Vikram B, Abhay K, Jagmohan S, Ravi T, Mohammad Y, Rahul B, Ajit J, Sanjay G, Pramod S. References 1. Kiefer et al., EMBO Journal 1996; 2. Hu et al., Genes and Development 1996; 3. Sawasdikosol and Burakoff. eLife 2020;9:e55122; 4. AACR Annual Meeting June 22-24 2020 Citation Format: Sachin S. Chaudhari, Malini Bajpai, Sravan Mandadi, Vidya G. Kattige, Sandeep Thorat, Varada Potdar, Priyanka Pangre, Pooja Sawant, Chandrasekhar Misra, Subhadip Das, Atul Akarte, Anuj Singh, Sandeep Mahankali, Pandurang Lambade, Avratanu Das, Raju Patole, Venkatesha Udupa, Pavankumar Sancheti, Pramod K. Pawar, Somesh Kakade, Vinod K. R, Nilanjana Biswas, Heta Shah, Dayanidhi Behera, Pankaj Jain, Nagaraj Gowda, Pravin S. Iyer. Novel small molecule HPK1 inhibitor induces immunogenic anti-tumor effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1709.