Initial testing (stage 1) of temozolomide by the pediatric preclinical testing program

Area of Science:

• Pharmacology
• Oncology
• Cancer Therapeutics

Background:

• Temozolomide, a DNA methylating agent, is primarily used for glioblastoma.
• Preclinical data suggest its potential in treating childhood cancers.

Purpose of the Study:

• To evaluate the efficacy and toxicity of temozolomide in preclinical models of childhood cancer.
• To investigate the relationship between MGMT expression and temozolomide response.

Main Methods:

• In vitro testing of temozolomide against PPTP cell lines across a range of concentrations.
• In vivo testing of temozolomide in PPTP solid tumor and ALL models at various dose levels.
• Assessment of tumor regressions, complete response (CR), and maintained CR (MCR).

Main Results:

• Temozolomide exhibited cytotoxicity in vitro, with lower IC50 values correlating with reduced MGMT expression.
• In vivo, temozolomide demonstrated significant toxicity at high doses but induced tumor regressions in a majority of solid tumor and leukemia models.
• Tumor regressions at lower doses were observed primarily in models with low MGMT expression.

Conclusions:

• Temozolomide shows considerable antitumor activity in preclinical models of solid tumors and leukemia.
• Toxicity was observed at higher doses, and efficacy at clinically relevant exposures was diminished.
• MGMT expression is a critical factor in determining temozolomide responsiveness in pediatric cancer models.