Genetic Variants In Human Carbonyl Reductase 3 (Cbr3) And Their Influence On Doxorubicin Pharmacokinetics In Asian Breast Cancer Patients

2505 Background: Human carbonyl reductase 3 (CBR3) is one of the main metabolizing enzymes to extensively reduce doxorubicin to its major active metabolite, doxorubicinol in normal and tumor tissues. Recently, the CBR3 958G>A (V244M) genetic variant has been described to alter function in vitro. We postulate that CBR3 genetic variants could contribute to the inter-individual variability of doxorubicin pharmacokinetics in breast cancer patients. Methods: We studied 101 female breast cancer patients (66 Chinese, 26 Malay, 7 Indian and 2 of other ethnic origins) who were treated with doxorubicin at 75mg/m2 every 3 weeks. Comprehensive sequencing of the 3 exons of CBR3, including the splice-site junctions was performed. Plasma concentrations of doxorubicin and doxorubicinol were analyzed during the first doxorubicin cycle. Results: Five CBR3 coding region variants (239G>A, 483C>T, 507C>T, 598G>A and 958G>A) were detected, of which 239G>A, 598G>A and 958G>A were non-synonymous. 598G>A was novel, and was found in 1 Malay patient who was heterozygous. The genotype distributions of 239G>A and 958G>A were 36%/30%/34%, and 40%/36%/24% respectively for GG/AG/AA. The 239GG variant was associated with significantly higher AUC of doxorubicinol and AUC ratio of doxorubicinol to doxorubicin than the AG and AA variants (AUC of doxorubicinol 2.18±1.37ug/ml*h (GG) vs 2.04±2.11ug/ml*h (AG), p=0.05, and 1.55±0.61ug/ml*h (AA), p=0.004; AUC ratio of doxorubicinol to doxorubicin 1.90±1.29 (GG) vs 1.72±1.34 (AG), p=0.025, and 1.45±0.67 (AA), p=0.006). Patients with the 958AA variant had significantly higher AUC of doxorubicinol than those with the 958GG variant (2.29±1.60ug/ml*h vs 1.56±0.60ug/ml*h, p=0.009). The 239GG variant was more common in our population than in Caucasians (36% vs 20%. p=0.027), while the 958AA variant was more common than reported in Caucasians (24% vs 8%, p=0.014) and Japanese (24% vs 7%, p=0.016). Conclusions: CBR3 genetic variants may influence the pharmacokinetics of doxorubicin and its major metabolite doxorubicinol. Inter-ethnic differences in frequencies of CBR3 genetic variants exist and may account for differences in pharmacokinetics and pharmacodynamics of doxorubicin between different populations. No significant financial relationships to disclose.