Phase I and pharmacokinetic study of CCI-779, a novel cytostatic cell-cycle inhibitor, in combination with 5-fluorouracil and leucovorin in patients with advanced solid tumors

Background: CCI-779 is a novel ester of the immunosuppressive agent sirolimus that exerts cytostatic effects by the inhibition of the translation of cell-cycle regulatory proteins. We investigated the maximum tolerated dose (MTD) and pharmacokinetics (PK) of CCI-779 in combination with leucovorin (LV) and 5-fluorouracil (5-FU) in patients with advanced solid tumors. Patients and methods: Patients were treated with LV at 200 mg/m(2) as a 1-h i.v. infusion directly followed by continuous 24-h i.v. infusion of 5-FU, in the first patient at 2000 mg/m(2) and in subsequent patients at 2600 mg/m(2). CCI-779 was administered directly prior to LV as a 30-min i.v. infusion at a starting dose of 15 mg/m(2) beginning at day 8 and escalated in subsequent cohorts of patients. One cycle consisted of six weekly administrations followed by 1 week of rest. Blood samples were drawn to assess PK of CCI-779 as well as its effect on steady-state 5-FU exposures. Results: Twenty-eight patients entered the study, the majority having tumor types for which 5-FU is used as a treatment. CCI-779 doses of 15, 25, 45 and 75 mg/m(2) were investigated. Skin toxicity (rash) was prominent at all dose levels examined. Stomatitis was the dose-limiting toxicity (DLT) for 75 mg/m(2) doses of CCI-779. Subsequently the cohort at 45 mg/m(2) was expanded to a total of 15 patients, and at this dose level two treatment-related deaths occurred due to mucositis with bowel perforation. Based on the toxicities observed, it was decided to discontinue the study. Partial responses were observed in three patients with gastrointestinal tumors. No pharmacokinetic interaction between CCI-779 and 5-FU was observed. Conclusions: The safety profiles of CCI-779 and 5-FU/LV suggest an overlap of drug-related toxicities, and the administration of these drugs at these doses and schedule resulted in unacceptable toxicity and therefore cannot be recommended. If CCI-779 is to be used in combination with 5-FU/LV, other doses or schedules of administration will need to be explored.