TG-1701, a selective bruton tyrosine kinase (BTK) inhibitor, as monotherapy and in combination with ublituximab and umbralisib (U2) in patients with chronic lymphocytic leukemia

ABSTRACT

Introduction: TG-1701 is a selective, covalent BTK inhibitor administered once daily (QD). Both the 'U2' combination (anti-CD20 mAb ublituximab+the PI3Kd-CK1e inhibitor umbralisib) and BTK inhibitors are highly efficacious in treatment- naïve (TN) and relapsed/refractory (R/R) CLL, each having previously demonstrated superiority over standard chemoimmunotherapy. Here, we report results for patients treated with TG-1701 alone or in combination with U2 from an ongoing Phase 1 study, with a focus on patients with CLL. Methods: Patients with R/R CLL and B-cell non-Hodgkin lymphoma were enrolled in an ongoing Phase 1 study initially evaluating dose escalation (DE) of oral TG-1701 QD continuously administered in 28-day cycles (100, 200, 300, and 400 mg). After characterizing the safety profile of TG-1701 monotherapy, we implemented a parallel DE arm of TG-1701+U2. Select dose levels of TG-1701 monotherapy were also expanded. All patients were treated until disease progression, unacceptable toxicity, or investigator/patient decision to withdraw. Safety was evaluated in all treated patients, and efficacy was evaluated in all treated patients with CLL who had at least 1 post-baseline assessment. Results: As of 30 April 2021, 125 patients were treated with TG-1701, 49 of whom had CLL. Enrollment was 25 patients in the monotherapy DE arm (6 with CLL), 61 in the 200-mg disease-specific cohorts (20 CLL [5 TN], 21 mantle cell lymphoma [MCL, 4 TN], 20 Waldenström's macroglobulinemia [WM, 8 TN]), 20 in the 300-mg CLL cohort (4 TN), and 19 in the 1701+U2 DE arm (3 with CLL). Patients with MCL or WM in the 200-mg disease-specific cohorts were excluded from this analysis. The median # of prior therapies among CLL patients was 1 (range, 0-5) and all patients were BTKi-naïve. TG-1701 was well-tolerated and the maximum tolerated dose for monotherapy was not reached up to 400mg (near 100% saturation of the BTK at all dose levels studied). In the DE arms, the most common all-causality treatment-emergent adverse events (TEAE) were constipation (32%), increased ALT (28%), bruising (28%), and upper respiratory tract infection (28% of patients) with TG-1701 monotherapy;diarrhea (53%) and bruising (42%) with TG-1701+U2. Grade 3/4 AEs were limited. In the CLL-specific cohorts, the most common TEAE was increased ALT/AST (all grades, 17.5%;grade 3, 2.5%;grade ≥4, none), followed by diarrhea (all grades, 12.5%;grade ≥3, none), and COVID-19 (all grades, 12.5%;grade 3-4, none;grade 5, 7.5%). There were no cases of atrial fibrillation, major bleeding, or ventricular tachyarrhythmia in the CLL cohorts at a median follow-up of 10.5 months. TEAEs leading to TG-1701 dose reduction occurred in 7.5% of patients. TEAEs leading to treatment discontinuation occurred in 7.5% of patients (all COVID-19). At the data cut-off, 48 patients with CLL were evaluable for response, including nine in DE. ORR was 95.6% for TG-1701 monotherapy (all PR/PR-L) and 100% for TG-1701+U2 (all PR). The median duration of response has not been reached in either cohort. The best change from baseline in tumor burden in patients with CLL is presented in Figure 1, and treatment exposure and response duration data are presented in Figure 2 below. In patients with anemia and thrombocytopenia at baseline, sustained improvement in hematologic variables was observed in the 200- and 300-mg cohorts. Lymphocytosis was observed in 70% of the monotherapy patients, with a resolution to normal or <50% of baseline in 57.1%. Consistent response rates were observed across all subgroups, including age and high-risk genomic features, such as del17p/TP53, unmutated immunoglobulin heavy-chain variable-region (IGHV), and complex karyotype (defined as three or more cytogenetic abnormalities). Time to event data will be reported at the time of presentation. Conclusions: TG-1701 exhibits an encouraging safety and efficacy profile in patients with CLL, with promising activity and a manageable tolerability profile as monotherapy and in combination with U2 (Figure 1). Future registration trials ar being planned in CLL with TG-1701. Recruitment to this study (NCT03671590) continues.