Dichlorobenzoprim and methylbenzoprim were the lead compounds to emerge from investigations on a series of lipophilic 2,4-diamino-5-aryl-6-ethylpyrimidines synthesized and evaluated for their inhibition of dihydrofolate reductase (DHFR). Here the results of further mechanism-of-action studies are summarized. As expected, growth inhibitory activity of these compounds in the National Cancer Institute 60-cell-line screen correlated positively with DHFR enzyme inhibitory activity. Interestingly, two other aspects of their activity have been revealed. First, as evidenced by reversal experiments using hypoxanthine and thymidine, the two compounds, dichlorobenzoprim and methylbenzoprim, have been shown to exert an additional non-folate mechanism. Secondly, by exploitation of the COMPARE algorithm, a positive correlation has been established between the activity of certain members of this series and the existence of a mutation in the Ki-ras gene of non-small-cell lung and colon cancer cell lines. These observations have suggested that modification of the lead structures may offer opportunities to generate novel molecules without DHFR-inhibitory activity, but which may interact with new molecular targets for anti-cancer drug design.

Animals↗

PubMedDate not supplied

Phase I clinical trial of mitozolomide.

Mitozolomide (NSC-353451; CCRG 81010; M and B 39565) is a novel potential anticancer agent that was selected for phase I study on the basis of broad spectrum activity in mouse tumors. Initially, mitozolomide was given iv as a short infusion to 37 patients in doses ranging from 8 to 153 mg/m2. Nausea and vomiting was dose-related but was not severe. The dose-limiting toxic effect was thrombocytopenia at doses greater than 115 mg/m2, and recovery from the thrombocytopenia was delayed up to 8 weeks. Partial responses were seen in two patients with adenocarcinoma of the ovary. The pharmacokinetics of mitozolomide showed that the half-life of the intact drug in the plasma was between 1 and 1.3 hours. The area under the curve was proportional to the dose administered. Mitozolomide is well-absorbed; therefore, future studies are recommended using a single-dose schedule orally or iv. In the phase I study reported here, a dose of 115 mg/m2 appeared to be safe, but additional studies have shown that when given orally to an older population, most patients experienced thrombocytopenia less than 50,000 cells/mm3. The recommended dose using current data is 90 mg/m2 iv or orally.

Administration, Oral↗