Background: PI3Kδ inhibitors have demonstrated efficacy in the treatment of B-cell malignancies, but off-target toxicity and/or the inability to achieve near-complete inhibition of the PI3Kδ pathway may affect the depth and duration of response. INCB050465 is a novel, potent, and selective PI3Kδ inhibitor (Shin et al. AACR 2015. Abstract 2671), with a differentiated profile for potency (whole blood IC50 = 10 nM), dose (<50 mg total daily dose), and preclinical safety (lack of hepatoxicity up to exposures that exceed IC90 coverage by >10-fold). An open-label phase 1 study was initiated to evaluate INCB050465 alone or in combination with other agents in patients with previously treated B-cell malignancies; preliminary results of the dose escalation of INCB050465 monotherapy are reported.

Methods: Adult patients with B-cell malignancies who were refractory to or for whom available treatments had failed were eligible. Dose escalation was conducted with a 3 + 3 design after an initial single patient cohort. Patients were observed for 21 days before enrollment of the next cohort.

Results: As of the data cutoff, 15 patients were enrolled and treated with INCB050465 at doses ranging from 5 to 30 mg once daily. The median age was 64 years and 47% were men. Patients received a median of 2 prior treatment regimens and the median time since initial diagnosis was 4.9 years. Disease subtypes included DLBCL (n = 6), CLL (n = 3), FL (n = 2), MZL (n = 2), MCL (n = 1), and HL (n = 1). Median exposure to INCB050465 was 15.4 weeks (range, 6.9 to 36.4+ weeks) and no patients required dose reduction. INCB050465 was well tolerated with no DLTs observed. Five patients discontinued treatment, 4 due to disease progression and 1 due to an adverse event (grade 2 exfoliative dermatitis). Ten grade 3 or greater treatment-emergent adverse events were seen in 6 patients: anemia (n = 2), bacteremia, Escherichia infection, hypotension, neutropenia, pneumonia, sepsis, syncope, and WBC count decreased (n = 1 each). To date, only grade 1 transaminase elevations have been observed. Responses were observed in DLBCL (3/6 patients), CLL (1/3), FL (2/2), MZL (2/2), and MCL (1/1). Clinical benefit was observed early in the course of treatment, and the longest duration of response was 27+ weeks. Terminal half-life and suppression of PI3Kδ signaling at trough support once daily dosing.

Conclusions: INCB050465 monotherapy was generally well tolerated at all doses tested. Robust and durable signaling pathway inhibition was achieved at all doses and INCB050465 showed promising efficacy in FL, DLBCL, and other lymphomas, with a potentially favorable toxicity profile vs other PI3Kδ inhibitors. Enrollment in dose-escalation, combination therapy, and disease-specific cohorts is ongoing.

Citation Format: Andres Forero-Torres, Michael S. Wertheim, Tycel J. Phillips, Martin E. Gutierrez, William J. Edenfield, Swamy Yeleswaram, Maureen Bleam, Li Zhou, Jennifer H. Pulini, Théa Faivre, Harry Miao, Matt Spear, Rod Ramchandren. Preliminary safety, efficacy, and pharmacodynamics of a highly selective PI3Kδ inhibitor, INCB050465, in patients with previously treated B-cell malignancies. [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 CT056.