DGKα/ζ inhibitors combine with PD-1 checkpoint therapy to promote T cell-mediated antitumor immunity

Programmed cell death protein 1 (PD-1) immune checkpoint blockade therapy has revolutionized cancer treatment. Although PD-1 blockade is effective in a subset of patients with cancer, many fail to respond because of either primary or acquired resistance. Thus, next-generation strategies are needed to expand the depth and breadth of clinical responses. Toward this end, we designed a human primary T cell phenotypic high-throughput screening strategy to identify small molecules with distinct and complementary mechanisms of action to PD-1 checkpoint blockade. Through these efforts, we selected and optimized a chemical series that showed robust potentiation of T cell activation and combinatorial activity with alpha PD-1 blockade. Target identification was facilitated by chemical proteomic profiling with a lipid-based photoaffinity probe, which displayed enhanced binding to diacylglycerol kinase alpha (DGK alpha) in the presence of the active compound, a phenomenon that correlated with the translocation of DGK alpha to the plasma membrane. We further found that optimized leads within this chemical series were potent and selective inhibitors of both DGK alpha and DGK zeta, lipid kinases that constitute an intracellular T cell checkpoint that blunts T cell signaling through diacylglycerol metabolism. We show that dual DGK alpha/zeta inhibition amplified suboptimal T cell receptor signaling mediated by low-affinity antigen presentation and low major histocompatibility complex class I expression on tumor cells, both hallmarks of resistance to PD-1 blockade. In addition, DGK alpha/zeta inhibitors combined with alpha PD-1 therapy to elicit robust tumor regression in syngeneic mouse tumor models. Together, these findings support targeting DGK alpha/zeta as a next-generation T cell immune checkpoint strategy.