Oral HDAC Inhibitor HBI8000 in Japanese Patients with Non-Hodgkin Lymphoma (NHL): Phase I Safety and Efficacy Results

Background: HBI-8000 is an orally bioavailable member of the benzamide class of histone deacetylase inhibitors (HDACi), that inhibits cancer-associated HDAC enzymes (Class I and IIb). HBI-8000 has anti-tumor activity through various mechanisms of action, including epigenetic reprogramming and immunomodulation. It was recently approved by the Chinese FDA under the name chidamide (Epidaza) for relapsed or refractory (R/R) peripheral T-cell lymphoma (PTCL) with a recommended dose of 30 mg twice weekly (BIW). HBI-8000 is also being manufactured in the USA for clinical development outside of China. The preliminary results of a phase I trial of HBI-8000 to confirm the safety and maximum tolerated dose (MTD) in Japanese patients (pts) with advanced NHL are presented (NCT02697552).

Methods: This is a multicenter, prospective phase I trial in Japan. Inclusion criteria: patients are eligible if they have histologically or cytologically proven NHL and no other standard therapy is available. The primary endpoint is the MTD based on the frequency of dose-limiting toxicities (DLTs) observed within 28 days of the first dose. Secondary endpoints include pharmacokinetic (PK) profile and anti-tumor activity. At the time of this abstract submission, the trial is still ongoing.

Results: Thirteen out of 14 pts were eligible for the 1^st cycle DLT assessment (6 pts in the 30 mg, 7 pts in the 40 mg cohort). Median age was 68 years, gender well balanced, and the majority of pts had ≥ 2 prior treatment regimens. Five pts had the diagnosis of adult T-cell leukemia-lymphoma (ATL), 2 pts presented with PTCL, 3 with diffuse large B-cell lymphoma (DLBLC), 2 with follicular lymphoma (FL), 1 with cutaneous T-cell lymphoma (CTCL), and 1 with marginal zone lymphoma. Overall, the treatment was well tolerated, and adverse drug reactions (ADRs) were predominantly hematologic, consistent with the previous experiences. There were 7 pts in the 40 mg dose cohort because one of the first 3 pts had to be replaced for incomplete dosing due to grade 3 hypertriglyceridemia which was not regarded as DLT by the Data Monitoring Safety Committee (DMC/SMC). In the 40 mg cohort, 2 pts were considered as DLTs by definition in the protocol: grade 4 neutropenia and grade 3 alanine transaminase (ALT) increase. Both pts were asymptomatic. The grade 4 neutropenia promptly resolved with the administration of G-CSF and the grade 3 ALT elevation resolved with dose interruption. The 30 mg dose cohort completed with no DLT after the 1^st cycle in 6 pts. The following hematologic grade 3/4 toxicities were noted in the 40 mg dose cohort (N=7): leukopenia (2 pts, 29%), neutropenia (3 pts, 43%), and thrombocytopenia (3 pts, 43%). Non-hematologic ADRs included fatigue, nausea, diarrhea, decreased appetite, erythema and pyrexia. The preliminary pharmacokinetic (PK) results from the 3 patients in the 30 mg cohort, and 7 patients in the 40 mg dose cohort show inter-patient variability as expected of an oral agent. Mean half-life (t ½ ) was between16.5 and 20 hours (h) with a T_max between 2.5 and 3.5h and consistent with previous findings. Mean C_max and AUC increased with dose (30 mg: 210 ng/mL; 3660 h*ng/mL and 40 mg: 590 ng/mL; 7200 h*ng/mL). The patient with neutropenia as DLT presented with the highest exposure. Cardiovascular assessments including serial ECGs and troponin assessments did not reveal clinically relevant findings. Best overall response was noted in 40 mg BIW cohort (N=7): 1 CR (10%), 5 PR (30%), 1 SD (20%). Four of the partial responders were ATL patients. In the 30 mg BIW dose cohort, 4/6 patients had stable disease after the 1^st cycle.

Summary: In this phase l trial evaluating the safety of twice weekly 30 mg and 40 mg doses, HBI-8000 was well tolerated with expected toxicities that could be managed with dose interruptions/reductions. Tumor response results in pts who completed at least one cycle of treatment indicate some clinical benefit especially in pts who started with the 40 mg dose level. The DMC/SMC has provided an opinion that the 2 observed DLTs with HBI-8000 in the phase I trial were clinically manageable and that 40 mg BIW would be recommended as the dosage for subsequent phase II studies. Registration enabling phase II trials to evaluate efficacy and safety in R/R ATL pts (Japan) and R/R PTCL pts (Japan and Korea) are being initiated.