Characterization of UGTs Active against SAHA and Association between SAHA Glucuronidation Activity Phenotype with UGT Genotype

Suberoylanilide hydroxamic acid (SAHA) is a histone deacetylase inhibitor used in the treatment of cutaneous T-cell lymphoma and in clinical trials for treatment of multiple other cancers. A major mode of SARA metabolism is by glucuronidation via the UDP-glucuronosyltransferase (UGT) family of enzymes. To characterize the UGTs active against SARA, homogenates from HEK293 cell lines overexpressing UGT wild-type or variant UGT were used. The hepatic UGTs 2B17 and 1A9 and the extrahepatic UGTs 1A8 and 1A10 exhibited the highest overall activity against SAHA as determined by V-max/K-M (16 +/- 6.5, 7.1 +/- 2.2, 33 +/- 6.3, and 24 +/- 2.4 nL.min(-1.)mu g UGT protein(-1), respectively), with UGT2B17 exhibiting the lowest K-M (300 mu mol/L) against SAHA of any UGT in vitro. Whereas the UGT1A8p.Ala173Gly variant exhibited a 3-fold (P < 0.005) decrease in glucuronidation activity against SAHA compared with wild-type UGT1A8, the UGT1A8p.Cys277Tyr variant exhibited no detectable glucuronidation activity; a similar lack of detectable glucuronidation activity was observed for the UGT1A10p.Gly139Lys variant. To analyze the effects of the UGT2B17 gene deletion variant (UGT2B17*2) on SAHA glucuronidation phenotype, human liver microsomes (HLM) were analyzed for glucuronidation activity against SAHA and compared with UGT2B17 genotype. HLM from subjects homozygous for UGT2B17*2 exhibited a 45% (P < 0.01) decrease in glucuronidation activity and a 75% (P < 0.002) increase in KM compared with HLMs from subjects homozygous for the wild-type UGT2B17*1 allele. Overall, these results suggest that several UGTs play an important role in the metabolism of SAHA and that UGT2B17-null individuals could potentially exhibit altered SAHA clearance rates with differences in overall response. [Cancer Res 2009;69(7):2981-9]