On November 11, 2016 Calithera Biosciences, Inc. (Nasdaq:CALA), a clinical stage biotechnology company focused on discovering and developing novel small molecule drugs directed against tumor metabolism and tumor immunology targets for the treatment of cancer, reported that data for its drug candidates CB-839, the company’s novel glutaminase inhibitor, and CB-1158, the company’s novel arginase inhibitor, will be presented at the Society for Immunotherapy of Cancer (SITC) (Free SITC Whitepaper) 2016 Annual Meeting, which is being held from November 9-13, 2016 in National Harbor, Maryland (Press release, Calithera Biosciences, NOV 11, 2016, View Source;p=RssLanding&cat=news&id=2221726 [SID1234516491]).

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"Both CB-839 and CB-1158 have the distinction of targeting metabolic and immune checkpoints which we believe, through rational combinations, have the potential to be transformational in the treatment of cancer. CB-839 and CB-1158 are each in clinical trials with cohorts planned in combination with approved immunotherapy agents," said Susan Molineaux, Ph.D., President and Chief Executive Officer of Calithera. "We are pleased that CB-1158 shows significant pharmacodynamic effects in patients at the first dose level tested."

Preclinical CB-839 data will be presented in a poster titled, "Targeting tumor glutamine metabolism with CB-839 enhances the efficacy of immune checkpoint inhibitors," by Andy MacKinnon, Ph.D., Calithera Biosciences (Poster #230). Included in the presentation are data that provide further insights into the mechanism by which inhibition of glutaminase by CB-839 enhances T-cell activation and increases the anti-tumor activity of anti-PD-L1 and anti-PD-1 antibodies. Glutamine deprivation during T-cell activation was shown to block Myc expression and Myc-driven metabolic re-programming, and to promote expression of T-cell suppressive markers such as BTLA, CTLA-4, PD-1, and CD73. In two syngeneic animal models, CT26 (colon cancer) and B16 (melanoma) the combination of CB-839 and anti-PD-L1 or anti-PD-1 showed significantly enhanced anti-tumor activity over checkpoint inhibition alone resulting in increased tumor regressions in the CT26 model. Depletion of CD8+ T-cells from these tumor-bearing animals reversed the anti-tumor effects of the combination, confirming an immune-mediated mechanism of action.

CB-1158 data will be presented in a poster titled, "Arginase inhibitor CB-1158 alleviates immunosuppression and enhances anti-tumor responses as a single agent and in combination with other immunotherapies," by Amani Makkouk, Ph.D., Calithera Biosciences (Poster #231). Arginase is expressed in myeloid derived suppressor cells (MDSCs) and exerts an immunosuppressive effect on T-cells and NK cells by depleting arginine and blocking activation. Tumor cell infiltrates in patients with solid tumor cancers contain significant numbers of arginase-expressing MDSCs; as a result, these patients have increased levels of plasma arginase and decreased levels of plasma arginine compared to healthy individuals. CB-1158, a highly selective, orally bioavailable, small molecule inhibitor of human arginase with nanomolar potency, has single agent immune-mediated efficacy in multiple syngeneic animal models. Inhibition of tumor growth was accompanied by an increase in the local concentration of arginine, and the induction of multiple pro-inflammatory changes in the tumor microenvironment. Treatment with CB-1158 also enhanced the anti-tumor activity of adoptive T-cell therapy, checkpoint blockade and chemotherapy in these animal models. CB-1158 is currently being tested in a Phase 1 clinical trial in patients with solid tumors. Three patients in the first cohort were treated with 50 mg of CB-1158 twice daily. This dose was well-tolerated and was pharmacologically active, resulting in sustained elevation of arginine in the plasma of all three patients. The trial is continuing to enroll patients to complete the dose escalation phase of the study, to be followed by combination studies with a PD-1 antibody.

In addition, two posters describing trial design will be presented during the "Clinical Trials in Progress" session:

CX-1158-101: A first-in-human phase I study of a small molecule inhibitor of arginase (CB-1158) as monotherapy and in combination with an anti-PD-1 checkpoint inhibitor in patients with solid tumors

Presenter: Siqing Fu, M.D., Ph.D., University of Texas, MD Anderson Cancer Center, Poster #155

CX-839-004: A phase I/II study of the safety, pharmacokinetics, and pharmacodynamics of the glutaminase inhibitor CB-839 combined with nivolumab in patients with renal cell carcinoma, melanoma, and non-small cell lung cancer

Presenter: Elaine Lam, M.D., University of Colorado, Denver, Poster #166