Updated Preliminary Results of a Phase 1b Dose Escalation and Dose Expansion Study of Tirabrutinib in Combination with Idelalisib in Patients with B-Cell Lymphoma

Introduction: Tirabrutinib (TIRA; GS/ONO-4059) is a selective Bruton's tyrosine kinase (BTK) inhibitor. Idelalisib (IDELA), a first-in-class phosphatidylinositol-3-kinase delta (PI3Kδ) inhibitor, is approved for the treatment of CLL and follicular lymphoma (FL). Both have single agent activity in lymphoma and updated results from the combination of TIRA+IDELA from this ongoing phase 1b study (NCT02457598) are reported here.

Methods: Patients with previously treated non-germinal-center B-cell type (non-GCB) diffuse large B-cell lymphoma (DLBCL) or two prior lines of therapy for FL, small lymphocytic lymphoma (SLL), mantle cell lymphoma (MCL), marginal zone lymphoma (MZL), or Waldenstrom's macroglobulinemia (WM) and no prior exposure to targeted inhibitors were eligible for enrollment. Patients were enrolled using a 3+3 dose escalation design with a fixed dose of IDELA at either 50 mg BID or 100mg QD and TIRA ranging from 20mg to 160mg QD. Cohorts were subsequently enrolled at multiple dose levels to evaluate disease-specific safety and efficacy.

Results: As of March 5, 2018, 40 patients were enrolled on the combination. The median age was 65 (32-89) years and the disease subtypes were non-GCB DLBCL (n=17), FL (10), MZL (5), WM (5), SLL (2), and MCL (1). No maximum tolerated dose and no dose-response relationship was observed with daily dosing of both agents at the dose levels evaluated.

For patients with non-GCB DLBCL (n=17), the median number of prior therapies is 3 (range 1-4). The median duration of treatment is 8 weeks (range 0.9, 44.1) with 2 patients still on treatment. 4/15 (27%) evaluable patients achieved a response; best overall response is shown in table 1.

For the patients with indolent NHL (n=23), the median number of prior therapies is 3 (range 2-6). The median duration of treatment is 28 weeks (range 2.1, 120.0), with 5 patients still on treatment. 10/20 (50%) of the evaluable patients achieved a response with best overall response by indication shown in table 1.

The most common treatment-emergent adverse events (AEs) are listed in table 2. Of the 40 patients who received treatment on study, AEs led to treatment interruption or discontinuation of both study drugs in 22 and 3 patients, respectively. There have been 7 deaths on study, 6 due to disease progression and 1 from an unknown cause.

Conclusion: Once-daily dosing of GS-4059 up to 160 mg in combination with idelalisib 50 mg BID or 100 mg QD was generally safe and well tolerated. Early results show activity across all indications studied.

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