Clinical Safety and Activity in a Phase 1 Trial of IPI-145, a Potent Inhibitor of Phosphoinositide-3-Kinase-δ,γ, in Patients with Advanced Hematologic Malignancies

Phosphoinositide-3-kinases (PI3Ks) play pivotal roles in cell signaling and regulate a variety of cellular functions relevant to oncogenesis. Impaired development and function of B and T lymphocytes has been demonstrated in PI3K-δ and PI3K-γ isoform knockout mice, supporting the development of PI3K-δ,γ specific inhibitors for B- and T-cell lymphoid malignancies. IPI-145 is a potent PI3K-δ,γ inhibitor in clinical development for patients (pts) with hematologic malignancies. The activity of IPI-145 via PI3K-δ and PI3K-γ isoform inhibition has been characterized in biochemical and cellular assays and demonstrated in preclinical models of B- and T-cell mediated disease. Early results of the Phase 1 study in pts with advanced hematologic malignancies are reported here.

This Phase 1 dose-escalation study is designed to evaluate the safety, pharmacokinetics (PK) and activity of orally administered IPI-145 in pts with advanced hematologic malignancies, including T-cell lymphomas/leukemias. Sequential cohorts of pts are enrolled at progressively higher dose levels with expansion cohorts of pts with select hematologic malignancies. IPI-145 is administered orally 2 times per day (BID) continuously in 28-day cycles. Tumor response is evaluated based on disease-specific standard criteria.

As of 16 July 2012, the study had enrolled 20 pts; 5 pts with chronic lymphocytic leukemia (CLL)/small lymphocytic leukemia (SLL), 4 with indolent non-Hodgkin's lymphoma (iNHL), 3 with aggressive B-cell NHL [including diffuse large B-cell lymphoma (DLBCL) n=2 and Richter's transformation n=1], 3 with multiple myeloma (MM), 2 with Hodgkin's lymphoma (HL), 2 with T-cell lymphoma [anaplastic large-cell lymphoma (ALCL) n=2] and 1 with mantle cell lymphoma (MCL). Of these pts, 11 are male and 9 female, with a median [range] age of 63 years [30–81], with 36% <6 month from most recent prior systemic therapy. The median [range] number of prior therapies was 3 [1–8]. IPI-145 doses administered include 8 mg BID (n=1), 15 mg BID (n=6), 25 mg BID (n=7), 35 mg BID (n=3), and 50 mg BID (n=3). The median [range] number of treatment cycles was 2 [1–8], with 12 (60%) pts continuing on treatment. Adverse events (AEs) have occurred in 13 (65%) pts, including 7 (35%) pts with AEs Grade ≥3. Treatment-related AEs occurred in 11 pts (55%) with Grade ≥3 occurring in 5 pts (25%). Grade 4 neutropenia was the one dose limiting toxicity observed to date (15 mg dose cohort). New Grade ≥3 hematological laboratory abnormalities included neutropenia [n= 6 (30%)] and thrombocytopenia [n= 1 (5%)]. Grade 3 ALT/AST elevations occurred in 1 (5%) MM pt with onset 6 weeks after IPI-145 initiation.

Preliminary PK show dose-proportional increases in plasma C_max and AUC over the dose range studied. Further, the PK and initial pharmacodynamic (PD) data from the first 3 cohorts (8–25 mg BID) predict continuous suppression of the PI3K-δ pathway with increasing inhibition of the PI3K-γ pathway with a 25 mg BID dose or greater.

In the evaluable pts (n=11), responses were observed at the 8, 15, and 25 mg BID dose levels including 2/3 CLL/SLL pts (0 CR/2 PR/1 SD), 1/2 iNHL pts (1 CR/0 PR/1 SD), and 1/1 in MCL (1 PR). No responses have been observed to date in evaluable pts with MM (0/3) or aggressive NHL (0/2). All pts with at least SD after 2 cycles (n=6) remain on treatment including the first pt dosed.

Based on the PK/PD and the preliminary activity observed in pts with CLL, iNHL and MCL, an expansion cohort is enrolling pts in these select hematologic diseases dosed at 25 mg BID to further evaluate the safety and preliminary activity of IPI-145. Dose escalation continues with a focus on pts with T-cell malignancies and DLBCL where increasing suppression of the PI3K-γ isoform may improve the efficacy profile. Additional expansion cohorts in T-cell lymphoma, DLBCL, myeloproliferative neoplasms and the acute leukemias will better define disease specific activity.

IPI-145, an oral, potent PI3K-δ,γ inhibitor, appears to be well tolerated and has shown initial clinical activity in pts with iNHL, MCL, and CLL. A dose of 25 mg BID effectively inhibits PI3K-δ, providing a rationale for expansion in CLL/iNHL/MCL. Additional safety and efficacy data from the ongoing dose escalation evaluation in T-cell/aggressive NHL and the CLL/iNHL/MCL expansion cohort will be presented.

Flinn:Infinity Pharmaceuticals, Inc.: Research Funding. Horwitz:Seattle Genetics: Consultancy, Research Funding; Allos: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy; Genzyme: Consultancy; Kyowa Hakko Kirin Pharma: Consultancy; Johnson & Johnson: Consultancy; Infinity Pharmaceuticals, Inc. : Research Funding. Patel:Infinity Pharmaceuticals, Inc. : Research Funding. Younes:Novartis: Honoraria, Research Funding; Celgene: Honoraria; Seattle Genetics: Honoraria, Research Funding; Sanofi-Aventis: Honoraria, Research Funding; MIllenium: Honoraria; Incyte: Honoraria; Genentech: Research Funding; Infinity Pharmaceuticals, Inc. : Research Funding; Gilead: Research Funding. Porter:Infinity Pharmaceuticals, Inc. : Employment. Sweeney:Infinity Pharmaceuticals, Inc. : Employment. Allen:Infinity Pharmaceuticals, Inc. : Employment. Kelly:Infinity Pharmaceuticals, Inc. : Employment. Kahl:Infinity Pharmaceuticals, Inc. : Research Funding.