A phase I, pharmacokinetic, and pharmacodynamic evaluation of the DNA methyltransferase inhibitor 5-fluoro-2′-deoxycytidine, administered with tetrahydrouridine

Purpose: Inhibitors of DNA (cytosine-5)-methyltransferases (DNMT) are active antineoplastic agents. We conducted the first-in-human phase I trial of 5-fluoro-2′-deoxycytidine (FdCyd), a DNMT inhibitor stable in aqueous solution, in patients with advanced solid tumors. Objectives were to establish the safety, maximum tolerated dose (MTD), pharmacokinetics, and pharmacodynamics of FdCyd + tetrahydrouridine (THU). Methods: FdCyd + THU were administered by 3 h IV infusion on days 1-5 every 3 weeks, or days 1-5 and 8-12 every 4 weeks. FdCyd was administered IV with a fixed 350 mg/m²/day dose of THU to inhibit deamination of FdCyd. Pharmacokinetics of FdCyd, downstream metabolites and THU were assessed by LC-MS/MS. RBC γ-globin expression was evaluated as a pharmacodynamics biomarker. Results: Patients were enrolled on the 3-week schedule at doses up to 80 mg/m²/day without dose-limiting toxicity (DLT) prior to transitioning to the 4-week schedule, which resulted in an MTD of 134 mg/m²/day; one of six patients had a first-cycle DLT (grade 3 colitis). FdCyd ≥40 mg/m²/day produced peak plasma concentrations >1 μM. Although there was inter-patient variability, γ-globin mRNA increased during the first two treatment cycles. One refractory breast cancer patient experienced a partial response (PR) of >90 % decrease in tumor size, lasting over a year. Conclusions: The MTD was established at 134 mg/m² FdCyd + 350 mg/m² THU days 1-5 and 8-12 every 4 weeks. Based on toxicities observed over multiple cycles, good plasma exposures, and the sustained PR observed at 67 mg/m²/day, the phase II dose for our ongoing multi-histology trial is 100 mg/m²/day FdCyd with 350 mg/m²/day THU.