Phase I Study of a Novel Bcl-2 Inhibitor, at-101 in Combination with Lenalidomide and Dexamethasone in Patients with Relapsed and/or Refractory Multiple Myeloma (RRMM)

Background: The development of novel treatment strategies has extended the median survival of MM to nearly a decade but the disease remains incurable and relapse is inevitable. The Bcl-2 pathway is highly relevant to MM cell survival and can be mitigated therapeutically. AT-101 is a novel, orally available pan Bcl-2 inhibitor (Bcl-2, Bcl-xl, Mcl-1, and Bcl-w). Preclinical in vitro and in vivo studies showed that AT-101 enhanced cytotoxicity of lenalidomide-dexamethasone (Rd). We conducted a phase I study in RRMM patients to establish the effective dose of AT-101 with Ld as well as record safety and preliminary efficacy of this combination (NCT02697344). Methods: Key eligibility criteria included: RRMM with measurable disease (serum monoclonal protein ≥1.0 g/dL or urine monoclonal protein >200mg/24 hour or serum immunoglobulin free light chain >10mg/dL AND abnormal serum free light chain ratio). Patients must have received 1-3 prior treatment regimens and have an absolute neutrophil count ≥1.0 x 109, platelets 75 x 109, creatinine clearance ≥50 mL/min, and ECOG performance status ≤2. AT-101 dosing was designed to reach a maximum daily target of 20mg (Cohort 1; 10 mg PO QD, Cohort 2; 20 mg PO QD) utilizing a standard 3 +3 dose escalation design in combination with standard doses of Rd. Treatment was given as outpatient for a maximum of 12, 28-day cycles. For pharmacodynamic studies, AT-101 alone was given in cycle 1, with R (25 mg on days 1-21) and d (40 mg weekly) added cycle 2 onwards. Results: Enrolled patients (n=10) included 60% males with median age 68.5 years (range 55-75) and median time since MM diagnosis 4.5 years (range 0.6-8.3). MM ISS stage was II/III in 7 patients and 8/10 had high-risk cytogenetics with 4 each having del17p and 1q+. Only 1 patient had t(11;14).Patients had received median 2 prior lines of therapy (range 1-3), with 7 having had prior autologous stem cell transplant (ASCT) and the initial induction regimen being bortezomib (V), R and dexamethasone (d) (VRd) in 8, Rd in 1 and cyclophosphamide (C) with Vd (VCd) in 1 patient. At the time of study entry, 3 patients were R refractory while 2 were refractory to both, V and daratumumab (Dara). Median duration of treatment was 7.5 cycles (range 2-12) and 3 patients completed all planned 12 cycles of treatment. Among the evaluable patients, dose limiting toxicities (DLTs) at 20 mg daily dose of AT-101 with 25 mg of R and 40 mg weekly included one patient with grade 4 febrile neutropenia