A Dose Escalation Study of RP6530, a Novel Dual PI3K δ/γ Inhibitor, in Patients with Relapsed/Refractory T-Cell Lymphoma

Introduction: The δ isoform of PI3K is highly expressed in cells of hematopoietic origin. The γ isoform is associated with T-lymphocytes and neutrophils and plays a distinct role in T-cell function. Since δ/γ isoforms are synergistic in the growth and survival of certain T-cell malignancies, dual targeting of PI3K δ/γ is an attractive intervention strategy in patients with T-cell lymphoma. RP6530 is a novel, highly specific dual PI3K δ/γ inhibitor with nanomolar inhibitory potency for both isotypes. It has shown acceptable safety profile and efficacy in patients (pts) with advanced hematologic malignancies in a Phase 1 study (ASH 2015). Herein, we present the preliminary results from an ongoing Phase 1/1b, dose escalation study of RP6530 in 11 pts with mature T-cell neoplasms (NCT02567656).

Methods: The study consists of dose escalation cohorts to determine the MTD of RP6530 using a standard 3+3 design, followed by two expansion cohorts enrolling 20 pts with peripheral T-cell lymphoma (PTCL) and 20 pts with cutaneous T-cell lymphoma (CTCL). Pts with a diagnosis of PTCL or CTCL who have received at least one prior systemic therapy, ECOG performance status ≤ 2 and measurable/evaluable disease are eligible. This study evaluated the safety, maximum tolerated dose (MTD), pharmacokinetics, pharmacodynamics, and clinical activity of RP6530 administered twice daily (BID) in 28-day cycles. Responses were evaluated for PTCL and CTCL based on IWG criteria (Cheson 2014) and the modified Severity Weighted Assessment Tool (mSWAT) respectively. Dose limiting toxicity (DLT) was defined by a toxicity of grade 3/4 that is considered related to treatment during the first cycle of treatment.

Results: To date eleven pts (6 PTCL and 5 CTCL) (5 males and six females) have been enrolled at three dose levels: 200 mg BID, 400 mg BID and 800 mg BID. ECOG performance status score was 0/1/2 in 10/1/0 pts, respectively, with a mean age of 68 yrs (range 52-76). Pts had a median of 3 (range: 3-6) prior treatment regimens, and 5 pts had refractory disease and 6 relapsed on prior treatments.

RP6530 was well tolerated without any DLT or related serious adverse event reported to date. A total of 52 non-serious adverse events were reported: 41 Grade 1/2 and 11 Grade 3/4. The most common adverse events included mild vomiting (18%), diarrhoea (18%), fatigue (18%), and rash (18%). No Grade 3/4 adverse events were deemed related to RP6530 except for ALT/AST elevation in one pt. No pt discontinued treatment due to a safety issue. Dose-proportional increases in plasma concentrations were observed in PKs. Dose escalation is currently ongoing at 800 mg BID.

Five pts were evaluated for responses at Cycle 3, Day1. Two pts (1 PTCL and 1 CTCL) experienced PR (40%) that are ongoing >5 months, and three pts experienced stable disease lasting for >3 months (60%). Three pts experienced rapid disease progression during first cycle, and discontinued treatment prematurely.

Conclusion: This ongoing study of RP6530 demonstrated an acceptable safety profile at doses evaluated, with a promising clinical activity. The results support further evaluation of RP6530 in pts with mature T-cell neoplasms.