Altered metabolism of daunorubicin and doxorubicin by genetic variants of human aldo-keto and carbonyl reductases

• Main Author: Bains, Onkar Singh
• Language: English
• Published: University of British Columbia 2010
• Online Access: http://hdl.handle.net/2429/29557

The anthracyclines, doxorubicin (DOX) and daunorubicin (DAUN) are commonly used to treat a variety of cancers. Their use is associated with life-threatening adverse events, especially chronic cardiotoxicity, in some patients. There may be a genetic basis for this variation, arising from altered metabolism by non-synonymous single nucleotide polymorphisms (ns-SNPs) in genes encoding for the aldo-keto reductase (AKR) and carbonyl reductase (CBR) enzymes, which are responsible for the biotransformation of these two drugs. The first two studies (Chapters 2 and 3) of this thesis examined the effect of ns-SNPs in 8 AKR and 3 CBR genes on the in vitro metabolism of both anthracyclines to their major metabolites, doxorubicinol (DOXol) and daunorubicinol (DAUNol) using purified, human wild-type and genetic variant enzymes. Michaelis-Menten kinetic curves were plotted and the metabolic capacities of the wild-type and variant enzymes were compared using catalytic efficiency (kcat/Km). In the presence of DAUN, 7 AKR and 5 CBR variants exhibited significantly reduced metabolic activity while 3 AKR and 5 CBR variants demonstrated significantly reduced activity with DOX as substrate. These findings suggest that genetic variants of human AKRs and CBRs are capable of decreasing the in vitro metabolism of DOX and DAUN. There is considerable controversy in the literature on how DAUN and DOX contribute to the variable adverse events seen in patients treated with these drugs. Some studies suggest that the toxic species are the major metabolites, DAUNol and DOXol, while others suggest the parent drug is more toxic. To study this, I examined whether a strong and consistent association exists between metabolic activity and drug toxicity among nine cell lines from different tissues (Chapter 4). My findings indicated that there is a strong, and inversely proportional, association between cytotoxicity and DAUN or DOX metabolism. Furthermore, the cell lines that were resistant to the toxic effects of these drugs had significantly greater expression of the AKRs and CBRs. Overall, these data provide a foundation of biochemical evidence to design in vivo studies that will elucidate the role of altered metabolism by genetic variants of human AKRs and CBRs in the development of anthracycline-induced cardiotoxicity.