The discovery of mutant specific inhibitors changed the landscape of RAS-mutant cancer therapy dramatically. However, despite initially achieving impressive tumour regressions, cancers treated with these inhibitors relapse and derive no extension to overall survival. Therefore, novel combination therapies are needed enhance these outcomes. Pre-clinical evidence shows that KRAS-G12C inhibitors reverse the immune suppressive mechanisms driven by oncogenic KRAS and support the use of combination strategies that reactivate the immune system. Diacylglycerol kinases (DGKs) play an important role in the signalling cascade during lymphocyte activation, in part by attenuating activation of RAS by diacylglycerol dependent RAS-GRPs due to depletion of diacylglycerol. Inhibiting DGKs enhances RAS/ERK and PKCΘ activation in lymphocytes and has been shown to have a treatment benefit in models of colon cancer. We hypothesised DGK inhibition would improve treatment of KRAS-mutant lung cancer when used in combination with KRAS-mutant specific inhibitors.
To investigate the impact of DGK inhibition in addition to KRAS mutant specific inhibition, we treated an orthotopic immune-hot model (KPARG12C), and an immune-cold model (3LL ΔNRAS) with the KRAS-G12C specific inhibitor adagrasib, with and without a DGKα/ζ inhibitor. In the immune hot model, addition of the DGKα/ζ inhibitor improved survival outcomes. However, this was not the case in the immune-cold model, in which there was no survival benefit. To delve further into the mechanism by which DGK inhibition improves survival in the immune-hot setting, we performed immunophenotyping by flow cytometry of the tumour and tumour-draining lymph node for the major immune subsets. As a single agent, DGK inhibition increased proliferation of all major T cell subsets and NK cells. T cell activation markers such as CD69 and PD-1 were also increased. To analyse spatial interactions between the immune cells and the cancer cells and spatial arrangement of immune populations, we are currently performing immunofluorescence staining.
Overall, our data suggests inhibiting DGK provides an additional benefit to KRAS-mutant specific inhibition in immune-hot lung cancer settings. Future work is focused on confirming the functional state of these lymphocytes and if they have enhanced cytotoxic activity against the tumour cells.