Purpose: This clinical trial investigated the safety, tolerability, pharmacokinetic (PK), and pharmacodynamic (PD) profile of CHR-3996, a selective class I histone deacetylase inhibitor.

Patients and methods: CHR-3996 was administered orally once a day. This phase I trial used a 3+3 dose-escalation design. PK profiles were analyzed by liquid chromatography-tandem mass spectroscopic methods and PD studies were conducted using ELISA studying histone H3 acetylation in peripheral blood mononuclear cells.

Results: Thirty-nine patients were treated at dose levels of 5 mg (n = 3), 10 mg (n = 4), 20 mg (n = 3), 40 mg (n = 10), 80 mg (n = 10), 120 mg (n = 4), and 160 mg (n = 5) administered orally once daily. The dose-limiting toxicities seen were thrombocytopenia (160 mg), fatigue (80 and 120 mg), plasma creatinine elevation (80 and 120 mg), and atrial fibrillation (40 mg). The area under the curve was proportional to the administered dose and a maximal plasma concentration of 259 ng/mL at a dose of 40 mg exceeded the concentrations required for antitumor efficacy in preclinical models. Target inhibition measured by quantification of histone acetylation was shown at doses of 10 mg/d and was maximal at 40 mg. A partial response was seen in one patient with metastatic acinar pancreatic carcinoma.

Conclusions: Taking the toxicity and PK/PD profile into consideration, the recommended phase II dose (RP2D) is 40 mg/d. At this dose, CHR-3996 has a favorable toxicologic, PK, and PD profile. CHR-3996 has shown preliminary clinical activity and should be evaluated in further clinical trials.