T Cell Reinvigoration upon ACK1/TNK2 inhibition Overcomes Immune Resistance

Solid tumors are highly refractory to immune checkpoint blockade (ICB) therapies due to the functional impairment of the effector T cells and its trafficking back to the tumor. The T cell activation is negatively regulated by C-terminal Src kinase (CSK), however, the exact mechanism of CSK's T cell-restraining activity remains unknown. Here, we show that the primeval oncogenic tyrosine kinase, ACK1 dampens T-cell response by augmenting CSK activity through a novel Tyr18-phosphorylation. Ack1/Tnk2-knockout mice exhibited a loss of CSK Tyr18-phosphorylation and activation of CD8+ and CD4+ T cells, compromising ICB-resistant tumor growth. Further, ICB-treated Castration-resistant prostate cancer (CRPC) patients revitalized ACK1/pY18-CSK signaling, revealing it to be the critical molecular mechanism for ICB insensitivity. Consistently, ICB-resistant tumor growth was suppressed upon treatment with a new class of ACK1 small-molecule inhibitor, (R)-9b. Interestingly, (R)-9b caused increase in leukocyte attractant, CXCL10 in cancer cells, thus navigating newly activated T cells to the tumors, creating a `self-sabotaging loop'. Overall, harnessing unique dichotomous mode of ACK1 that controls immune response of the T cells, and cytokine levels in tumor microenvironment, provides an unprecedented opportunity to sensitize immune-resistance. Overall design: C4-2B cancer cells were treated overnight with 1µM (R)-9b (overnight) and RNA was prepared from these cells.