Antitumour imidazotetrazines--XVIII. Modification of the level of 5-methylcytosine in DNA by 3-substituted imidazotetrazinones

Population pharmacokinetics of temozolomide in cancer patients

PURPOSE

To evaluate covariate effects on the pharmacokinetics of temozolomide in cancer patients, and to explore the dose-pharmacokinetics-toxicity relationship of temozolomide.

METHODS

Non-linear mixed-effects modeling approach was used to analyze the data from 445 patients enrolled in eleven Phase I and Phase II clinical trials. All patients in the phase I trials had advanced cancer. Patients in the phase II trials had anaplastic astrocytoma (AA), glioblastoma multiforme (GBM) or malignant melanoma (MM). A sparse sampling scheme was prospectively developed using Phase I data and was successfully implemented in Phase II trials. Population factors included age, gender, height (HT), weight (WT), body surface area (BSA), serum creatinine (Sr.Cr.), estimated creatinine clearance, serum chemistry data as indices of hepatic function and disease, smoking status, and selected concomitant medications. Descriptive statistics were used to summarize the toxicity and temozolomide dose and exposure relationship.

RESULTS

The pharmacokinetics of temozolomide follows a one-compartment model with first order absorption and elimination. Temozolomide clearance (CL) increased with BSA for both genders. The population mean clearance for GBM or AA patients was 11.2 L/hr for male with BSA equal to 2.0 m2, and 8.8 L/hr for female with BSA equal to 1.7 m2. The mean clearance for MM patients was slightly higher. The inter-subject variability in clearance was 15%, and the residual variability was 26%. Other factors investigated in this analysis had little effect on clearance. The overall incidence of neutropenia and thrombocytopenia were 5-8%. Temozolomide dose and AUC did not predict nadir neutrophil and platelet counts due to large variability in counts.

CONCLUSIONS

The current dose regimen is administered according to BSA which is the most important factor influencing temozolomide clearance. No further dose adjustment is required.

Antitumour imidazotetrazines--XXIV. Growth suppression by DNA from cells treated with imidazotetrazinones

Transfection of a murine colon adenocarcinoma cell line (MAC13) with DNA extracted from GM892 or Raji cells previously treated with either the methyl- (temozolomide) or ethyl-(CCRG82019) imidazotetrazinones caused a dose-related suppression of cell growth. The effect was proportional to the concentration of DNA transfected and the time of incubation of the donor cell lines with the drugs. It was not shown with X-irradiated DNA suggesting that the effect did not arise from non-specific damage to the DNA. Transfection of MAC13 cells with DNA extracted from GM892 cells was more effective in inhibiting growth than DNA from Raji cells, and temozolomide treated cellular DNA was a more potent growth inhibitor than that from CCRG 82019 treated cells. For both agents the growth inhibitory effect was most marked with DNA extracted 6 hr after drug addition and thereafter the effect decreased up to 24 hr after drug addition. This suggests that the growth inhibitory effect is due to a repairable lesion, and that the terminal mechanism of action of these agents involves targets after DNA.