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NATIONAL HARBOR, MD. – Combination treatment with the first-in-class glutaminase inhibitor CB-839 and nivolumab is well-tolerated and shows clinical activity in patients with advanced melanoma, renal cell carcinoma, or non-small cell lung cancer, including anti-PD-1/PD-L1 refractory patients, according to initial results from a phase 1/2 study.
Responses in melanoma patients who were progressing on nivolumab at study entry and who were refractory to multiple prior immunotherapy regimens are particularly notable, as they highlight the potential for CB-839, when added to nivolumab (Opdivo), to help overcome resistance to anti-PD-L1 therapy, Funda Meric‐Bernstam, MD, reported at the annual meeting of the Society for Immunotherapy of Cancer.
CB‐839 is highly selective and targets tumor glutamine metabolism, said Dr. Meric-Bernstam of the University of Texas MD Anderson Cancer Center, Houston.
Competition between tumor cells and immune cells for nutrients such as glutamine in the tumor microenvironment can create a metabolic checkpoint that induces local immune suppression. CB‐839 inhibits tumor glutamine consumption, thereby increasing glutamine availability to support T‐cell activity, she explained, noting that in preclinical models, CB‐839 increased intra‐tumoral glutamine and enhanced antitumor activity of PD‐1/PD‐L1 inhibitors.
In the phase 1 dose escalation study, she and her colleagues evaluated the safety and efficacy of CB-839 in combination with the PD‐1 inhibitor nivolumab in patients with melanoma, non-small cell lung cancer (NSCLC), or renal cell carcinoma (RCC). Phase 2 expansion cohorts include a melanoma rescue cohort of patients progressing on anti-PD-L1 therapy at study entry (22 patients), an NSCLC and RCC rescue cohort of patients who were progressing on anti-PD-L1 therapy at study entry or who had stable disease for 6 months or longer without a response (11 NSCLC and 11 RCC), an RCC cohort of patients with prior immunotherapy exposure and no response (10 patients), and an RCC cohort of patents who had no prior immunotherapy exposure (28 patients).
During dose escalation, patients received oral CB‐839 at 600 mg or 800 mg twice daily in combination with standard‐dose nivolumab. In the ongoing phase 2 expansion study, which continues to enroll, patients are receiving 800 mg of CB-839 twice daily with standard‐dose nivolumab, Dr. Meric-Bernstam said.
Patients in each of the cohorts were high risk and/or had intermediate or poor prognostic status at study entry. For example, 50% of patients in the melanoma rescue cohort had liver metastases, 77% had other visceral metastases, and 18% had brain metastases, and the majority of patients in the lung cancer/RCC cohort had visceral metastases. Most had progressive disease as their best response on their last line of immunotherapy.
Of 16 response-evaluable melanoma patients, 1 experienced a complete response, 2 had partial responses, and 4 had stable disease.
“So overall in this patient population that was progressing on a PD-1/PD-L1 inhibitor at enrollment, 19% had an objective response. The disease control rate in this group was 44%,” she said.
In evaluable patients in the lung cancer rescue cohort (6 patients), RCC rescue cohort (8 patients), and RCC prior exposure cohort (7 patients), disease control rates ranged from 57% to 75%, and in the immunotherapy-naive RCC cohort (19 patients), the partial response rate was 21%, and 53% had stable disease, so the overall disease control rate was 74%. Half of the patients in that group remain on study, she noted.
A closer look at the melanoma rescue cohort showed dramatic and rapid responses in two patients who each achieved a partial response in about 8 weeks with response durations of 3.7 months and 5.4 months, respectively. Additionally, pre-treatment biopsies in this cohort showed an elevated T-cell inflamed signature associated with clinical benefit from the addition of CB-839, and in one patient who had both a pretreatment and on-treatment biopsy that was evaluable, the latter showed an increase in T-cell inflamed signature and T-cell effector genes.
In all cohorts, the combination therapy was generally well tolerated. A maximum tolerated dose was not reached. Dose-limiting toxicity – a grade 3 alanine aminotransferase (ALT) increase – occurred in one patient on the 800-mg dose. The most common grade 3 or greater adverse events were fatigue, nausea, photophobia, rash, and elevated ALT, she said, noting that two patients discontinued for treatment-related adverse events (one for a grade 3 rash and one for grade 2 pneumonitis).
“Overall there appeared to be no apparent increase in immune-related adverse events, either in rate or severity, compared with [nivolumab] monotherapy,” she said.
The combination of CB-839 and nivolumab was well tolerated, and in some patients – as seen in the melanoma cohort – adding CB-839 to checkpoint blockade can overcome checkpoint blockade resistance, Dr. Meric-Bernstam concluded, noting that the disease control rates seen in the majority of lung cancer and RCC patients who were progressing on checkpoint blockade is encouraging, as is the objective response rate seen thus far in the RCC therapy-naive patients, and the stable and deep responses seen in the melanoma rescue cohort.
“Based on our encouraging signal in the melanoma rescue cohort, this [cohort] has been expanded,” she said.
Calithera Biosciences sponsored the study. Bristol-Myers Squibb provided nivolumab for the study. Dr. Meric-Bernstam has received grant or research support from Calithera Biosciences and many other companies. She also reported being a paid consultant for several companies and serving on an advisory committee or review panel, or as a board member for multiple companies.