A Phase 1 Study of CAL-101, An Isoform-Selective Inhibitor of Phosphatidylinositol 3-Kinase P110δ, In Combination with Rituximab and/or Bendamustine In Patients with Relapsed or Refractory B-Cell Malignancies.
Authors: Flinn Ian W. , Schreeder Marshall T. , Wagner-Johnston Nina , Boccia Ralph V. , Leonard John P. , Coutre Steven E. , Holes Leanne M. , Peterman Sissy , Yu Albert S. 
Published: October 2019

Abstract
Abstract 2832

Introduction:
The class I phosphatidylinositol 3-kinases (PI3Ks) regulate a variety of cellular functions relevant to oncogenesis. Expression of the PI3K p110δ isoform (PI3Kδ) is restricted to cells of hematopoietic origin where it plays a key role in B cell proliferation and survival. CAL-101 is an isoform-selective inhibitor of PI3Kδ (EC50 of 8 nM in a cell-based assay with >200-fold selectivity relative to other PI3K isoforms). A Phase 1 study of single-agent CAL-101 demonstrated clinical activity in patients with indolent B-cell non-Hodgkin lymphoma (NHL), mantle cell lymphoma, and chronic lymphocytic leukemia (CLL); a favorable safety profile suggested that CAL-101 might successfully be combined with other agents active against lymphoid malignancies.

Methods and Patients:
This Phase 1 study was undertaken to evaluate the safety and activity of CAL-101 in combination with rituximab and/or bendamustine in patients with relapsed or refractory B-cell indolent NHL and CLL. All patients received CAL-101 100 mg orally twice per day (BID) in 28-day cycles for up to 12 cycles. Patients also received either rituximab 375 mg/m2 administered weekly for 8 weeks, starting on Day 1 of Cycle 1, or bendamustine 90 mg/m2 administered on Days 1 and 2 of each cycle for 6 cycles. Tumor response was evaluated according to standard criteria.

Results:
At data cutoff, 12 patients were enrolled in the study, including 6 with NHL and 6 with CLL. Patients included: males/females n=8 (67%)/4 (33%) with median age [range] of 65 [55-80] years, and relapsed/refractory disease n=8 (67%)/4 (33%). The median [range] number of prior therapies was 3 [1-11]. The number (%) of patients with specific prior therapies included: rituximab n=12 (100%), alkylating agent n= 10 (83%), purine analog n=9 (75%), and anthracycline/anthracenedione n=6 (50%). All patients received CAL-101 100 mg BID; 6 patients received rituximab and 6 received bendamustine. One patient with NHL had a dose reduction of bendamustine due to hiccups and 1 patient with NHL had a dose reduction of CAL-101 due to increased ALT/AST; all other patients received the full-dose regimen with acceptable tolerability. Preliminary clinical response assessments were available for 6 patients who had completed 2 cycles of combination treatment; the results are shown in the table.
Enrollment is ongoing and dose escalation of CAL-101 is planned. Updated data will be presented at the meeting.

Conclusions:
Early results from this Phase 1 study of CAL-101, an oral PI3Kδ isoform-selective inhibitor, in combination with rituximab or bendamustine show acceptable safety and promising clinical activity in patients with relapsed or refractory indolent B-cell NHL and CLL.

Disclosures:
Flinn: calistoga: Research Funding. Off Label Use: CAL-101 for NHL. Leonard:Calistoga: Consultancy, Research Funding. Holes:Calistoga: Employment. Peterman:Calistoga: Employment. Yu:Calistoga: Employment.