PT - JOURNAL ARTICLE AU - Onkar S Bains AU - Morgan J Karkling AU - Joanna M Lubieniecka AU - Thomas A Grigliatti AU - Ronald E Reid AU - Kenneth W Riggs TI - Naturally occurring variants of human CBR3 alter anthracycline <em>In vitro</em> metabolism AID - 10.1124/jpet.109.160614 DP - 2009 Jan 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - jpet.109.160614 4099 - http://jpet.aspetjournals.org/content/early/2009/12/09/jpet.109.160614.short 4100 - http://jpet.aspetjournals.org/content/early/2009/12/09/jpet.109.160614.full AB - Doxorubicin (DOX) and daunorubicin (DAUN) are anthracycline anti-cancer agents; however, considerable interpatient variability exists in their pharmacokinetics. This interpatient variability is partly attributed to altered metabolism by non-synonymous single nucleotide polymorphisms (ns-SNPs) in genes encoding the carbonyl reductases. This study examines the effect of seven naturally occurring ns-SNPs in the CBR3 gene on in vitro metabolism of anthracyclines to doxorubicinol and daunorubicinol. Kinetic assays measure metabolite levels by HPLC separation with fluorescence detection using purified, histidine-tagged, human CBR3 wild-type and variant enzymes. The V224M, C4Y and V93I variants resulted in significantly reduced Vmax for both anthracyclines compared to the wild-type enzyme, whereas the M235L variant had significantly reduced Vmax for DOX only. Significant increases in Km were found for the V244M variant with DAUN as well as the C4Y and V93I variants with DOX. The kcat/Km values for the V244M, C4Y, and V93I variants were significantly lower than the wild-type for DAUN and DOX. Furthermore, DOX was observed to be a better substrate than DAUN for the wild-type enzyme and its variants. HapMap analysis indicated a haplotype carrying the C4Y and V244M mutations may occur in some individuals in the eleven ethnic populations studied in the HapMap project. Our preparation of the double mutant indicated a significant reduction in activity compared to the wild-type enzyme and single mutant preparations. These findings suggest that commonly occurring ns-SNPs in human CBR3 significantly alter the in vitro metabolism of DOX and DAUN.The American Society for Pharmacology and Experimental Therapeutics