Phase 1 Dose Escalation and Expansion Study to Determine Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the BET Inhibitor FT-1101 As a Single Agent in Patients with Relapsed or Refractory Hematologic Malignancies

Background: BET inhibitors have demonstrated therapeutic potential in hematologic malignancies; however low therapeutic margins have limited clinical development. FT-1101 (also known as CC-95775) is a BET bromodomain inhibitor of all 4 BET family members BRD4, BRD2, BRD3, and BRDT (Kd ≤20 nM) and shows additional activity towards several non-BET bromodomain proteins (including CECR2 and BRD9). In vitro, FT-1101 displayed potent anti-proliferative activity across a broad panel of human leukemia cell lines. In xenograft and syngeneic models, FT-1101 achieved superior tumor growth inhibition (including regressions) relative to JQ1, another BET inhibitor (Millan 2015).

Methods: A Phase 1 study evaluated the safety, PK/PD, and clinical activity of FT-1101 in patients (pts) with relapsed/refractory (R/R) AML/MDS, or non-Hodgkin lymphoma (NHL) (NCT02543879). Oral FT-1101 (10 mg - 600 mg) was dosed once a week (QW), every other week (QOW), or monthly (QM) during dose escalation. Safety was assessed via treatment-emergent AEs (TEAEs) for all pts; efficacy (response) was assessed in evaluable pts by investigators. Pharmacodynamic biomarkers (CCR1 and HEXIM1 mRNA expression) were assessed in whole blood.

Results: Between 17-Nov-2015 and 05-Mar-2019, a total of 84 AML/MDS pts and 10 NHL pts received FT-1101 in dose escalation with a median of 2 (range 1-13) treatment cycles and median exposure of 43 (1-401) days for AML/MDS and 51.5 (1-183) days for NHL pts. Most AML/MDS pts (n=80) received FT-1101 monotherapy; a small cohort (n=4) received FT-1101 200 mg QOW in combination with azacitidine. FT-1101 appeared to demonstrate dose-proportional PK (10-600 mg/dose) with a median T_max of 4 (1-24) hrs and a mean T_1/2 of 52 (18-123) hrs. Pharmacodynamic responses correlated with FT-1101 concentrations; preliminary analysis indicated that PD biomarker modulation (↓ CCR1 and ↑ HEXIM1) was seen with FT-1101 doses as low as 80 mg, with more robust modulation observed at FT-1101 doses >180 mg. The most common (>20%) TEAEs (all grades) were diarrhea (32%), fatigue (30%), dyspnea (29%), nausea (27%), anemia (24%), and platelet count decreased (21%) among AML/MDS pts and diarrhea (60%), nausea or pleural effusion (40% each), and cough, decreased appetite or dyspnea (30% each) among NHL pts. The most common (>10%) severe (≥ grade 3) TEAEs were anemia (21%), decreased platelets (19%), pneumonia (16%), sepsis (13%), febrile neutropenia (12%), and disease progression (11%) among AML/MDS pts and pleural effusion or disease progression (20% each) among NHL pts. AEs led to treatment discontinuation in 22 AML/MDS pts (26%) and 2 NHL pts (20%). Twenty AML/MDS pts (24%) and 2 NHL pts (20%) died due to AEs, all assessed as unrelated to study treatment. Disease progression was the most common fatal TEAE in AML/MDS and NHL pts (10% and 20%, respectively). The maximum tolerated dose (MTD) on the QOW schedule was 400 mg FT-1101; MTDs were not determined for other schedules.

Among evaluable AML/MDS pts who received >180 mg FT-1101 monotherapy (n=30), one pt (3%) on the 400 mg QOW schedule achieved complete remission with incomplete hematologic recovery (CRi) and 19 pts (63%) achieved stable disease, including 2 pts receiving >7 cycles of treatment. Among evaluable NHL patients who received >180 mg FT-1101 monotherapy (n=3), one pt (33%) achieved stable disease.

Conclusions: FT-1101, as monotherapy, shows acceptable safety, PK, and modest clinical activity in R/R AML/MDS and NHL pts. Intermittent (QOW) dosing within a tolerable range elicits PD activity (CCR1 suppression and HEXIM1 upregulation) consistent with preclinical observations indicating antitumor activity, and provides a rationale for testing FT-1101 in combination with standard therapies in AML/MDS and NHL.