Exposure-dependent incorporation of trifluridine into DNA of tumors and white blood cells in tumor-bearing mouse.

PURPOSE: Trifluridine (TFT) is an antitumor component of a novel nucleoside antitumor agent, TAS-102, which consists of TFT and tipiracil hydrochloride (thymidine phosphorylase inhibitor). Incorporation of TFT into DNA is a probable mechanism of antitumor activity and hematological toxicity. The objective of this study was to examine the TFT incorporation into tumor- and white blood cell-DNA, and to elucidate the mechanism of TFT-related effect and toxicity. TFT effect on the colony formation of mouse bone marrow cells was also investigated. METHODS: Pharmacokinetics of TFT was determined in nude mice after single oral administration of TAS-102, while the antitumor activity and body weight change were evaluated in the tumor-bearing nude mice after multiple oral administrations for 2 weeks. TFT concentrations in the blood- and tumor-DNA were determined by LC/MS/MS. The colony formation was evaluated by CFU-GM assay. RESULTS: TFT systemic exposure in plasma increased dose-dependently. The tumor growth rate and body weight gain decreased dose-dependently, but TFT concentrations in the DNA of tumor tissues and white blood cells increased dose-dependently. TFT inhibited colony formation of bone marrow cells in a concentration-dependent manner. CONCLUSIONS: A significant relationship between systemic exposure of TFT and pharmacological effects including the antitumor activity and body weight change was well explained by the TFT incorporation into DNA. TFT inhibited proliferations of mouse bone marrow cells and human colorectal carcinoma cells implanted to nude mice dose-dependently. The highest tolerable TFT exposure provides the highest antitumor activity, and the hematological toxicity may serve as a potential surrogate indicator of TAS-102 efficacy.

Involvement of concentrative nucleoside transporter 1 in intestinal absorption of trifluorothymidine, a novel antitumor nucleoside, in rats.

ααα-Trifluorothymidine (TFT), an anticancer nucleoside analog, is a potent thymidylate synthase inhibitor. TFT exerts its antitumor activity primarily by inducing DNA fragmentation after incorporation of the triphosphate form of TFT into the DNA. Although an oral combination of TFT and a thymidine phosphorylase inhibitor has been clinically developed, there is little information regarding TFT absorption. Therefore, we investigated TFT absorption in the rat small intestine. After oral administration of TFT in rats, more than 75% of the TFT was absorbed. To identify the uptake transport system, uptake studies were conducted by using everted sacs prepared from rat small intestines. TFT uptake was saturable, significantly reduced under Na(+)-free conditions, and strongly inhibited by the addition of an endogenous pyrimidine nucleoside. From these results, we suggested the involvement of concentrative nucleoside transporters (CNTs) in TFT absorption into rat small intestine. In rat small intestines, the mRNAs coding for rat CNT1 (rCNT1) and rCNT2, but not for rCNT3, were predominantly expressed. To investigate the roles of rCNT1 and rCNT2 in TFT uptake, we conducted uptake assays by using Xenopus laevis oocytes injected with rCNT1 complementary RNA (cRNA) and rCNT2 cRNA. TFT uptake by X. laevis oocytes injected with rCNT1 cRNA, and not rCNT2 cRNA, was significantly greater than that by water-injected oocytes. In addition, in situ single-pass perfusion experiments performed using rat jejunum regions showed that thymidine, a substrate for CNT1, strongly inhibited TFT uptake. In conclusion, TFT is absorbed via rCNT1 in the intestinal lumen in rats.

Phase I clinical study of three times a day oral administration of TAS-102 in patients with solid tumors.

TAS-102 is a novel formulation of the fluorinated pyrimidine analogue trifluorothymidine (FTD) with an inhibitor of thymidine phosphorylase. The purpose of this study was to determine the MTD and DLT for TAS-102 administered three times a day on days 1-5 and 8-12 every 4 weeks. Fifteen patients were enrolled with two patients experiencing dose-limiting fatigue and granulocytopenia at the first dose level (80 mg/m2/day). Granulocytopenia was the primary toxicity: 7 patients experienced grade 3 or 4 granulocytopenia with the first course. No responses were noted, but nine patients demonstrated prolonged stable disease in this heavily pretreated 5-FU refractory population.

Phase 1 study of TAS-102 administered once daily on a 5-day-per-week schedule in patients with solid tumors.

This study was designed to determine the safety and optimal dosing of TAS-102, a novel oral combination of alphaalphaalpha-trifluorothymidine (FTD) and an inhibitor of thymidine phoshorylase, in patients with solid tumors. Patients who met the eligibility criteria were treated with one of two different TAS-102 regimens: once per day on either days 1-5 and 8-12 every 4 weeks (schedule A) or days 1-5 every 3 weeks (schedule B). The primary objectives were the determination of the maximum tolerated dose, dose-limiting toxicities (DLTs), and recommended phase II dose. Pharmacokinetic analysis was conducted during courses 1 and 2. Sixty-three patients received a total of 172 courses of therapy with the median number of courses delivered on both schedules being 2. DLTs were observed in three patients on schedule A, 70 mg/m(2)/day (1) and 110 mg/m(2)/day (2); and in five patients on schedule B, 120 mg/m(2)/day (1), 170 mg/m(2)/day (2), 180 mg/m(2)/day (2). Granulocytopenia was the DLT in seven of the eight cases. The most frequent toxicities were nausea, fatigue, granulocytopenia, anemia, diarrhea, and abdominal pain. Twelve patients, 6 on schedule A and 6 on schedule B, were treated at the recommended phase II dose, with good tolerance. No objective responses were seen in this heavily pretreated, 5-FU-refractory population. The pharmacokinetic parameters of FTD are a T (max) of 0.53 to 3.15 h, t (1/2) of 1.46 to 4.20 h, volume of distribution of 0.0526 to 0.483 l/kg, and clearance of 0.0194 to 0.197 1/h/kg. The recommended phase II doses for TAS-102 are 100 mg/m(2)/day on schedule A and 160 mg/m(2)/day on schedule B. Future development of TAS-102 should focus upon multiple daily dosing schedules.

Phase I study to determine the safety and pharmacokinetics of oral administration of TAS-102 in patients with solid tumors.

BACKGROUND: The purpose of the current study was to determine the maximum tolerated dose, dose-limiting toxicities, pharmacokinetic profile, and recommended Phase II dose of oral administration of TAS-102, a novel nucleoside formed by the combination of alpha,alpha,alpha-trifluorothymidine (FTD) and a thymidine phosphorylase inhibitor (TPI: 5-chloro-6-(2-iminopyrrolidin-1-yl)methyl-2,4(1H,3H)-pyrimidinedione). METHODS: Eligible patients had advanced solid tumors, adequate organ function, and had not received anticancer therapy in the preceding 4 weeks. TAS-102 was administered orally once daily for 14 days, followed by a 1-week rest, repeated every 3 weeks. The initial dose of TAS-102 administered was 100 mg/m2/day. The first 2 patients treated at that dose experienced substantial toxicity and, therefore, lower dose levels of TAS-102 were subsequently explored. RESULTS: Fourteen patients were enrolled; all patients were evaluable for toxicity assessment and 12 were evaluable for response. The initial dose explored was 100 mg/m2/day, based on a preclinical monkey model. However, the first 2 patients experienced bone marrow suppression of Grade 3 or 4 in course 1. The protocol was amended to study the next cohort of patients at 50 mg/m2/day. At this dose level no Grade 3 or 4 toxicities were observed in course 1. In the subsequent dose level (60 mg/m2/day), 3 of 6 patients experienced Grade 3 or 4 granulocytopenia as dose-limiting toxicity. Three additional patients for a total of 6 were enrolled at 50 mg/m2/day without occurrence of dose-limiting toxicity. Thus, 50 mg/m2/day was declared the maximum tolerated dose for this schedule. CONCLUSIONS: The authors' study showed that 50 mg/m2/day was a tolerable dose of the novel antimetabolite FTD in combination with an inhibitor of its inactivating enzyme TP, and this is the recommended Phase II dose. Evaluation of this daily dose in malignancies for which fluoropyrimidines have failed is needed.