Investigation of the Pharmacogenetic Influences of Carbonyl Reductase on Doxorubicin and Doxorubicinol in Breast Cancer Patients.

2594 Background: The anthracycline doxorubicin (DOX) is widely used to treat breast cancer. Doxorubicin is associated with pharmacokinetic and pharmacodynamic variability and despite its use for several years there is limited understanding behind it. Hepatic carbonyl reductases (CBR1 and CBR3) catalyze the reduction of DOX into its main circulating C-13 metabolite doxorubicinol (DOXOL). Polymorphisms in CBR1 and CBR3 influence synthesis of DOXOL, and could potentially play a role in the pharmacokinetic (PK) variability seen with doxorubicin treatment. In this study, we examined the influence of genetic polymorphisms in CBR1 and CBR3 on DOX and DOXOL PK. Methods: DOX was administered IV to 79 breast cancer patients at 60 mg/m2. Population PK modeling was performed on the parent concentration-time profiles with the following patient factors: [BSA (1.4-2.6 m2), weight (40-140 kg), age (25-75), race (78% white), CBR1 rs9024 (78% wild-type), CBR3 V244M (47% wild-type), CBR3 C4Y (20.5% wild-type); followed by model validation. Noncompartmental analysis (NCA) was performed for both DOX and DOXOL and the metabolic ratio was calculated as AUCDOXOL0-24:AUCDOX0-24. Results: A two-compartment model was used to describe DOX PK. Mean predicted (%SEM) clearance (CL), plasma volume (Vp), tissue volume and distribution clearance were 28.1 L/hr (7.72), 22.5 L (3.80), 257 L (13.8) and 13.6L (21.8), respectively. Interpatient variability on CL and Vp were 22.1% and 12.6%, respectively. BSA was found to be a significant predictor of the interpatient variability on CL. No other patient factors were found to be significant on parent drug PK. The metabolic ratio, assessing the conversion of DOX to DOXOL, was stratified by different polymorphisms of CBR1 and CBR3. There were no significant differences in metabolic ratio due to CBR1 and CBR3 genotypes. Conclusions: A PK model was developed that was able to characterize DOX pharmacokinetics. CBR1 and CBR3 polymorphisms were tested as covariates but were not found to be significant contributors to the variable pharmacokinetic profiles of DOX and DOXOL.