Effects of impaired renal function on the pharmacokinetics and toxicity of i.v. ZD9331, a novel non-polyglutamated thymidylate synthase inhibitor, in adult patients with solid tumors

A phase I and pharmacokinetic study of the nonpolyglutamatable thymidylate synthase inhibitor ZD9331 plus docetaxel in patients with advanced solid malignancies

PURPOSE

To assess the feasibility of administering ZD9331, a thymidylate synthase (TS) inhibitor that does not undergo polyglutamation and has broad antitumor activity, in combination with docetaxel in patients with advanced solid malignancies. The study also sought to determine the principal toxicities of the regimen and recommend appropriate doses for phase II studies, characterize the pharmacokinetics of the agents, evaluate the possibility of major drug-drug interactions, and seek preliminary evidence of anti-cancer activity.

PATIENTS AND METHODS

Patients with advanced solid malignancies were treated with escalating doses of docetaxel as a 60-minute intravenous (IV) infusion followed 30 minutes later by ZD9331 as a 30-minute IV infusion every 3 weeks. At least three patients were treated at each dose level, and the maximum tolerated dose level was defined as the highest dose level that was not associated with an unacceptably high incidence of severe toxicity. The pharmacokinetics of both ZD9331 and docetaxel were also characterized.

RESULTS

Nineteen patients were treated with 71 cycles of ZD9331 and docetaxel (ZD9331/docetaxel) at dose levels that encompassed dosing iterations of ZD9331 ranging from 65 to 260 mg/m(2) and docetaxel doses in the range of 50 to 75 mg/m(2). Neutropenia was the principal toxicity of the ZD9331/docetaxel regimen. Since five of six patients treated at the ZD9331/docetaxel dose-level of 260/60 mg/m(2) had grade 4 neutropenia that was brief and uncomplicated in the first course, a rigorous exploration of higher dose levels was not undertaken. Nonhematologic toxicities, consisting of malaise, diarrhea, rash, nausea, and vomiting, were also observed, but these effects were rarely severe. No major antitumor responses were observed. The pharmacokinetics of both ZD9331 and docetaxel were similar to those reported in previous studies of each agent administered alone, suggesting the lack of major drug-drug interactions.

CONCLUSION

The combination regimen, consisting of ZD9331 and docetaxel, is feasible and well tolerated at single-agent doses that are clinically-relevant. This ZD9331/docetaxel regimen does not appear to be associated with either major pharmacokinetic or toxicologic drug-drug interactions. A ZD9331/docetaxel dose level of 260/60 mg/m(2) is recommended as an initial dose level in disease-directed studies of the regimen, with further dose escalation of docetaxel to 75 mg/m(2) if the initial treatment is well tolerated. Further studies with this regimen are warranted in tumor types that have demonstrated sensitivity to both agents.

Novel antifolate drugs

Antimetabolites are active chemotherapeutic agents for many solid tumor and hematologic malignancies. Folate antagonists, purine analogues, and pyrimidine analogues are the three main categories of antimetabolites. Methotrexate, the most studied folate antagonist, is effective in many malignancies. Methotrexate inhibits dihydrofolate reductase, which leads to accumulation of polyglutamated folates, causing further inhibition of thymidylate synthase and glycinamide ribonucleotide formyltransferase. Subsequently, the lack of reduced folate substrates impairs synthesis of purine nucleotides, thymidylate, and certain amino acids, which can lead to cell death. However, methotrexate resistance develops through several mechanisms, including decreased folate carrier-mediated membrane transport, dihydrofolate reductase gene amplification, specific transcription-translational modifications, and downregulation of intracellular methotrexate polyglutamation. Antifolate drug development has focused on agents designed to overcome different aspects of methotrexate resistance. This article reviews the enzymatic targets for antifolates, describes the known mechanisms of antifolate resistance, and summarizes the current development of novel antifolate agents. Discussed specifically are trimetrexate, edatrexate, raltitrexed, pemetrexed, ZD9331, lometrexol, LY309887, GW1843, OSI-7904(L), and nolatrexed, all of which have unique clinical pharmacology and are in various stages of development. The toxicity of antifolates has been sporadic and difficult to predict clinically. Supplementation with folic acid and vitamin B(12) has been shown to reduce the toxicity of pemetrexed without affecting efficacy and has increased the therapeutic index for this novel agent.