Irinotecan hydrochloride (CPT-11) can display severe toxicities in individual cancer patients. CPT-11 is bio-activated through CES, detoxified through UGT1A1 and inhibits TOP1. CPT-11 toxicity and UGT1A1, CES2 and TOP1 mRNAs and UGT1A1 protein were determined in male and female C57BL/6, B6D2F1 and B6CBAF1, as potential models for tailoring CPT-11 delivery. CPT-11 was administered intravenously (40-90 mg/kg/day for 4 days at 7h after light onset). The relations between dose and lethal toxicity or body weight loss were steep and similar in C57BL/6 (lethality, p=0.001; weight loss, p=0.002) and B6D2F1 (p=0.01; p=0.03, respectively), but weak in B6CBAF1. Females displayed less toxicity than males (p<0.001). Mean mRNA expression of UGT1A1 was highest in B6CBAF1 (p=0.039) and in females (p<0.001). Both CES2 and TOP1 varied according to strain and gender (p<0.001). The three gene expression data explained the most severe toxicity of CPT-11 in male B6D2F1, but displayed inconsistent relations with toxicity in the other groups. Mean UGT1A1 protein expression was highest in males as compared to females, and so by approximately 8-fold in C57BL/6 as compared to B6D2F1 (p<0.0001). Genetic background and gender significantly altered the molecular prediction of irinotecan toxicity by UGT1A1, CES2 and TOP1 mRNA expressions.
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