A Phase 1 Study of the BET-Bromodomain Inhibitor OTX015 in Patients with Non-Leukemic Hematologic Malignancies

Rationale: BET-bromodomain (BRD) proteins are DNA readers that bind acetylated histone (H) tails preferentially at hyperacetylated superenhancer promoter regions and trigger gene transcription. The expression of several oncogenes, including c-MYC, is epigenetically regulated by BRD. OTX015 is a BRD 2, 3 and 4 inhibitor that prevents BRD binding to acetylated H4 and downregulates gene expression of BRD-dependent genes. OTX015 has been shown to inhibit the growth of diffuse large B-cell lymphoma (DLBCL) cells in vitroand in animal models.

Patients & Methods: Patients with non-leukemic hematologic malignancies refractory or resistant to standard therapies were enrolled in an ongoing phase 1 clinical study. Lymphoma patients had to have failed at least two lines of systemic therapy and have evaluable disease. OTX015 was given orally daily (QD) without a planned rest period, with 3-week cycles (cy). Successive cohorts of 3-6 patients were treated at increasing dose levels (DL) from 10 to 120 mg QD to determine the maximum tolerated dose (MTD) or the biologically optimal dose. A BID schedule was tested at DL 4 (40 mg x 2). Pharmacokinetics was assessed on day 1 and residual concentrations were measured on days 2, 8 and 15. Lymphoma assessment was performed according to Cheson’s criteria every 6-8 weeks.

Results: From January 2013 to June 2014, 37 non-leukemic patients (18 DLBCL, 9 other lymphomas, 10 myeloma) were treated over 5 dose levels, 33 of whom were evaluable for dose limiting toxicity (DLT). Median age was 67 years (range 27-83), 22 patients were male, 27 patients had ECOG 0-1. Patients had a median of 4 prior therapy lines (range 2-8), including 10 patients with autologous stem cell transplantation. The median number of OTX015 cycles administered was 2 (range 1-10+). No DLTs were observed through DL4 (80 mg QD). Asymptomatic and rapidly reversible grade 4 thrombocytopenia was the DLT at DL4 BID (40 mg x2) and 120 mg QD continuous. Sixteen patients experienced grade 3-4 thrombocytopenia and 3 patients had asymptomatic grade 3-4 neutropenia. Grade 3 non-hematologic toxicities were diarrhea, vomiting, hyperglycemia, and hypernatremia (1 patient each). Other toxicities were non-cumulative grade 1-2 gastrointestinal events (8 patients with diarrhea, 3 dysgueusia, 2 vomiting, 1 nausea, 1 anorexia, 1 abdominal pain), hyperglycemia (7 patients), skin rash (3 patients), asymptomatic coagulation factor VII decrease (2 patients), and direct bilirubin increase (1 patient). Dose proportional plasma concentrations were observed and trough concentrations > 500 nM occurred regularly from 80 mg/day. Additional patients are currently being treated at 80 mg QD or with various discontinuous schedules at 120 mg (5 days on/2 days off, 2 weeks on/1 week off, 1 week on/2 weeks off) to determine the recommended regimen. Clinically relevant activity was reported in 6 patients treated from 40 to 120 mg, including one CR (120 mg, 17+ weeks [wks]) and 1 PR (80 mg, 28 wks), both in DLBCL patients failing 3-4 prior therapy lines, and both with clinical benefit. Four other patients (two with DLBCL, one follicular, and one lymphoplasmacytic lymphoma) had minor tumor shrinkage with clinical benefit (40 mg, 36+ wks; 80 mg, 14 wks; 120 mg 15 wks; 120 mg, 17 wks).

Conclusions: OTX015 single agent exhibits clinically significant activity against resistant DLBCL with two responses and two minor tumor shrinkages among nine evaluable patients treated at doses ≥ 80 mg. Centralized pathology review including immunohistochemistry profiling is being performed retrospectively, and will be prospective in a DLBCL expansion cohort. Updated data including recommended regimen and correlations between clinical activity and biomarkers will be presented.