Abstract PR06: The glutaminase inhibitor CB-839 potentiates antimelanoma activity of standard-of-care targeted therapies and immunotherapies

Abstract

Abstract Nearly all metastatic melanoma patients who respond to targeted therapies will relapse with the disease within a year. Although more durable responses are seen with immune therapies, about half of the melanoma patients do not respond to them, and a significant number of responders eventually relapse. Most relapsed melanomas also exhibit post-treatment resistance to these treatments. Hence, there is a clear and present need to develop therapeutics that counteract resistance associated with relapse. We and others earlier showed that melanomas with elevated mitochondrial activity possess improved cellular rigor and are intrinsically resistant to the antitumor effects of BRAF and MEK inhibitors. In many other instances, melanomas that initially respond to these inhibitors acquire resistance by elevating mitochondrial activity. Mitochondrial activity is elevated in part by increased cellular uptake of glutamine, and its conversion to alpha-ketoglutarate in the TCA cycle, with glutaminase enzyme playing a rate-limiting role. In this study, we show that BRAFV600E-mutant melanomas with intrinsic or acquired resistance to MAPK pathway inhibitors have lower glucose uptake and increased glutamine uptake compared to those that are sensitive. Treatment of these resistant melanomas with single-agent glutaminase inhibitor, CB-839, moderately inhibited their growth. However, a more robust inhibition of their growth was achieved when CB-839 was combined with BRAF and MEK inhibitors. In addition, CB-839 increased the in vivo activity of tumor-infiltrating lymphocytes (TILs) in a mouse vaccine model and also enhanced the proapoptotic effect of human autologous patient-derived TILs on their cognate melanoma cells. Seahorse bioenergetics stress tests showed that CB-839 inhibited mitochondrial OxPhos in tumor cells to a greater extent than in activated TILs. Additional molecular studies are currently in progress. A recent clinical trial in melanoma patients showed that combination treatment with CB-839 and the immune checkpoint blocker, nivolumab, caused an objective response in three melanoma patients who had earlier progressed on treatment with immune checkpoint blockade. Our preclinical results complement this clinical finding and suggest that CB-839 combination could potentiate the efficacy of targeted and immune therapies in refractory melanomas. Citation Format: Sruthy Varghese, Snigdha Pramanik, Rishika Prasad, Hannah Hodges, Leila Williams, Weiyi Peng, Hussein Tawbi, Vashisht Yennu Nanda. The glutaminase inhibitor CB-839 potentiates antimelanoma activity of standard-of-care targeted therapies and immunotherapies [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr PR06.