Abstract 2329: Glutaminase inhibition with CB-839 enhances anti-tumor activity of PD-1 and PD-L1 antibodies by overcoming a metabolic checkpoint blocking T cell activation
Authors: Gross Matt , Chen Jason , Englert Judd , Janes Julie , Leone Robert , MacKinnon Andy , Parlati Francesco , Rodriquez Mirna , Shwonek Peter , Powell Jonathan 
Published: July 2016

Abstract
Recent studies have highlighted the importance of the tumor metabolic environment for controlling immune activation. T-cells activated through the TCR/CD28 receptor switch to a highly glycolytic metabolism and increase their requirement for glucose and glutamine. Consequently, limited availability of glucose or glutamine can block T-cell activation and proliferation. Likewise, immune checkpoints proteins, PD-1 and CTLA-4, suppress T cell metabolism by inhibiting glycolysis, glutamine uptake and glutaminolysis (Patsoukis et al Nat Comm. 2015). Chang et al (Cell. 2015) recently demonstrated that glucose consumption by tumors restricts glucose availability and blocks activation of T cells, and that treatment with CTLA-4, PD-1, or PD-L1 antibodies can re-activate T cell glycolysis.
CB-839 is a glutaminase inhibitor currently in Phase 1 trials in patients with solid and hematological malignancies. CB-839 blocks glutamine consumption in tumors and causes a significant elevation of tumor glutamine levels. Therefore, we hypothesized that CB-839 might enhance the activity of immune checkpoint inhibitors via metabolic modulation of the tumor microenvironment. We first confirmed that T- cell proliferation is dependent on glutamine but is only minimally inhibited by CB-839. In the absence of glutamine, splenic mouse T cells stimulated with anti-CD3/CD28 had reduced glucose consumption and did not proliferate. In contrast, CB-839 treatment did not mimic the effects of glutamine withdrawal on T-cells. CB-839 had no effect on glucose consumption by activated T-cells and only a minimal effect on proliferation. We also confirmed in the OVA vaccinia model that CB-839 had minimal effects on CD4 and CD8 T-cell proliferation in vivo, while the non-specific glutamine inhibitor DON caused a dramatic reduction in the number of CD4 and CD8 T-cells.
To determine if CB-839 could enhance the anti-tumor efficacy of immune checkpoint inhibitors, we treated mice bearing syngeneic CT26 colon carcinoma tumors with anti PD-1 or anti PD-L1 alone or in combination with CB-839. The addition of CB-839 to either anti PD-1 or anti PD-L1 treatment enhanced anti-tumor activity, augmenting tumor regression and promoting survival. Depletion of CD8+ T-cells from CT26 tumors reversed the anti-tumor effects of PD-L1 and CB-839, demonstrating that the combination targets CD8+ T-cells in the immune microenvironment.
These data are the first demonstration that modulation of glutamine metabolism in tumors can enhance the activity of checkpoint inhibitors and provide a rationale for combining CB-839 with immune checkpoint inhibitors in the clinic. Overall, these data highlight a new therapeutic approach to treating cancer by targeting tumor metabolism as a means of enhancing the efficacy of immunotherapy.
Citation Format: Matt Gross, Jason Chen, Judd Englert, Julie Janes, Robert Leone, Andy MacKinnon, Francesco Parlati, Mirna Rodriquez, Peter Shwonek, Jonathan Powell. Glutaminase inhibition with CB-839 enhances anti-tumor activity of PD-1 and PD-L1 antibodies by overcoming a metabolic checkpoint blocking T cell activation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2329.