A phase I clinical and pharmacokinetic study of CS-682 administered orally in advanced malignant solid tumors

CS-682 (1-(2-C-cyano-2-deoxy-β-D-arabino-pentofuranosyl)-N ⁴-palmitoylcytosine) is a novel orally administered 2′-deoxycytidine-type antimetabolite, which has a wide spectrum of antitumor activity in human tumor xenograft models. We conducted a phase I study to define the toxicity, pharmacokinetics and antitumor activity of CS-682 in patients with advanced solid tumors. Forty patients were enrolled to receive escalating doses of CS-682. CS-682 was given orally, once daily three times a week (Monday, Wednesday and Friday), for four weeks consecutively, followed by a two-week rest period. Twenty-two men and 18 women, median age 63.5 (range 31 to 82) were treated. The most common tumor type was colorectal cancer with 15 patients. Others tumors occurring in 3 or more patients included prostate, breast and lung carcinomas. Sixty percent of the patients had received greater than 2 prior chemotherapy programs. Patients have been treated at each of the following dose levels (mg/m²/day): 1.5, 12, 20, 25, 30, 50, 67, 90, 120, 160 and 220. Non hematologic toxicities grade 3 [NCI Common Toxicity Criteria (version 2.0)] related to treatment included nausea in 2, vomiting in 1, anorexia and asthenia in 2, and dehydration in 1. Severe hematologic toxicities (grade 3-4) were seen more frequently with 10 patients experiencing grade 3-4 neutropenia, 2 with grade 4 thrombocytopenia and 2 with grade 3 anemia. Neutropenia requiring hospitalization occurred in 3 patients. Dose-limiting neutropenia was observed at 220 mg/m²/day. The maximum tolerated dose was determined to be 160 mg/m²/day. No tumor responses were observed in this study. Six patients experienced stable disease, including one who has stable disease after having received 34 courses of CS-682. After oral administration, CS-682 is rapidly absorbed and metabolized to CNDAC, which is further metabolized by cytidine deaminase to the inactive product CNDAU. Peak plasma concentrations of CNDAC were achieved 2.2 ± 0.9 h after drug administration and the terminal elimination half-life was 1.7 ± 1.5 h. Measurable concentrations of CNDAU were first seen 0.60 ± 0.31 h, peak plasma concentrations were achieved 3.1 ± 0.9 h after the CS-682 dose, and the terminal elimination half-life was 2.3 ± 1.7 h. The recommended phase 2 starting dose for the 3 days/week regimen of CS-682 is 160 mg/m ²/day for 4 weeks repeated after a 2-week rest period.