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A Phase I and Pharmacokinetic Study of 1843U89, a Noncompetitive Inhibitor of Thymidylate Synthase, in Patients with Advanced Solid Malignancies¹

Institute for Drug Development, Cancer Therapy and Research Center, and the University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229 [A. G., L. S., H. B., D. D. V. H., E. K. R.]; Brooke Army Medical Center, San Antonio, Texas 78234 [G. S., T. R. J.]; and GlaxoSmithKline, Inc., Research Triangle Park, North Carolina 27709 [T. L., J.S., J.A.H.]

This study was performed to assess the feasibility of administering 1843U89, a potent, noncompetitive inhibitor of thymidylate synthase that does not require polyglutamation for activity, as a 2-min i.v. infusion daily for 5 days every 3 weeks, to determine whether folic acid supplementation ameliorates the toxic effects of 1843U89 and permits further dose escalation, and to recommend doses of 1843U89 administered without and with folic acid for further clinical evaluations. The study also sought to characterize the pharmacokinetic behavior of 1843U89 and to seek preliminary evidence of anticancer activity. Patients with advanced solid malignancies were treated with escalating doses of 1843U89 as a 2-min i.v. infusion daily for 5 days every 3 weeks. Initially, patients were treated in the absence of high-dose folic acid until dose-limiting toxicity was consistently noted. Next, patients were treated with escalating doses of 1843U89 preceded by 1000 mg of folic acid administered p.o. 30 min before each of the 5 daily doses of 1843U89. Patients (32) received 101 total courses of 1843U89 at doses ranging from 1 to 6 mg/m²/day with and without folic acid. At the 2 mg/m²/day dose level without folic acid, 2 of 7 new patients experienced dose-limiting toxicity, principally neutropenia, mucositis, and malaise in 3 of 11 courses. 1843U89 doses were further increased with folic acid to 6 mg/m²/day, but repetitive treatment was not feasible at this dose level because of an unacceptable high incidence of severe neutropenia and mucositis. Other toxicities included thrombocytopenia, rash, and fever. In contrast, repetitive treatment at the 5 mg/m²/day dose level was feasible. The pharmacokinetics of 1843U89 were neither dose dependent nor affected by folic acid. On day 1, clearance, terminal half-life, and steady-state volume of distribution values averaged 47.1 ± 21.7 ml/min/m², 7.72 ± 4.09 h, and 16.7 ± 8.8 liter/m²/h, respectively. The results of the study indicate that the administration of 1843U89 as a 2-min infusion daily for 5 days every 3 weeks without and with folic acid is feasible at 1843U89 doses as high as 2 and 5 mg/m²/day, respectively. Because folic acid pretreatment results in no diminution of the antitumor activity of 1843U89 in preclinical studies and ameliorates the toxic effects of 1843U89 in both preclinical models and cancer patients, the therapeutic index of 1843U89 may be enhanced by folic acid pretreatment and, therefore, the development of 1843U89 with folic acid is warranted. However, the question of whether to administer 1843U89 at a dose of 2 mg/m²/day with folic acid, which is associated with negligible toxicity, or at its highest feasible dose with folic acid, 5 mg/m²/day, should be addressed in appropriately designed trials.

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