Using unbiased high-throughput screening, Wichroski et al. identified a small molecule series of intracellular T cell checkpoint inhibitors that act complementary to PD-1 blockade. Use of lipid-based chemoproteomic probes in primary human T cells led to defining potent selective inhibitors of the hard-to-drug negative regulator of TCR signaling, diacylglycerol (DAG) lipid kinase (DGKα and ζ). The DGKα/ζ inhibitors translocated DGK to the plasma membrane, enhanced DAG-mediated TCR signaling stimulated by low-affinity antigen and low MHC-I on tumor cells, and combined with anti-PD-1, induced robust antitumor immunity and memory in syngeneic mouse tumor models.
Contributed by Paula Hochman
ABSTRACT: 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 αPD-1 blockade. Target identification was facilitated by chemical proteomic profiling with a lipid-based photoaffinity probe, which displayed enhanced binding to diacylglycerol kinase α (DGKα) in the presence of the active compound, a phenomenon that correlated with the translocation of DGKα to the plasma membrane. We further found that optimized leads within this chemical series were potent and selective inhibitors of both DGKα and DGKζ, lipid kinases that constitute an intracellular T cell checkpoint that blunts T cell signaling through diacylglycerol metabolism. We show that dual DGKα/ζ 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, DGKα/ζ inhibitors combined with αPD-1 therapy to elicit robust tumor regression in syngeneic mouse tumor models. Together, these findings support targeting DGKα/ζ as a next-generation T cell immune checkpoint strategy.