Abstract 2097: ABT co-dose accelerated target validation with a fit-for-purpose HPK1 inhibitor tool

Abstract Target validation can be challenging when mouse efficacy studies require achieving a high therapeutic exposure of a tool compound, ideally with a low peak-to-trough (P/T) ratio to avoid Cmax-induced toxicity. Herein, we describe the daily co-administration of the CYP inhibitor aminobenzotriazole (ABT) as a well-tolerated PK enhancer for medium-term efficacy studies in mice, enabling faster decision-making in the early space with imperfect tools. Genetic studies in mice have suggested that HPK1 inhibition would lead to enhanced effector T-cell function, decreased tumor growth and enhanced αPD-L1 efficacy. However, it remains unknown whether immune activation by pharmacological inhibition of HPK1 will recapitulate the genetic deletions. We developed a fit for purpose tool compound with picomolar HPK1 potency, excellent kinome selectivity (98% 100x, ATP-Km corrected), dose-dependent inhibition of pSLP76, sustained IL2 elevation in PBMCs, and IL6/TNFa elevation in dendritic cells. The mouse PK for this tool was inadequate, having a low exposure (AUC 16 uM-hr at 100 mg/kg po) and a high P/T ratio of 13 that could lead to an erosion of kinome selectivity in vivo; complicating efficacy interpretation and limiting overall tolerability. However, when co-dosed with ABT (50 mg/kg po 2 h prior to the HPK1 inhibitor), improved exposure of our tool was achieved (AUC 63 uM-hr at 100 mg/kg po), 90% inhibition of pSLP76 was maintained at C (trough), and the P/T ratio was reduced to 3 to avoid Cmax-induced toxicity. The inhibitor was well-tolerated co-dosed with ABT for three weeks in mice, enabling studies sooner to probe HPK1 pharmacological inhibition in cancer immunotherapy as a monotherapy as well as in combination with a mouse anti-PD-1 antibody. Citation Format: Joey L. Methot, Joanna L. Chen, Elsie Yu, Ryan D. Otte, Haiyan Xu, Zangwei Xu, Brian Lacey, Jason Laskey, Robbie Mcleod, Dustin Smith, Alexander Pasternak. ABT co-dose accelerated target validation with a fit-for-purpose HPK1 inhibitor tool abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2097.