Characterization of UGTs active against SAHA and association between SAHA glucuronidation activity phenotype with UGT genotype

Suberoylanilide hydroxamic acid (SAHA) is a histone deace-tylase inhibitor used in the treatment of cutaneous T-cell lymphoma and in clinical trials for treatment of multiple other cancers. A major mode of SAHA metabolism is by glucuronidation via the UDP-glucuronosyltransferase (UGT) family of enzymes. To characterize the UGTs active against SAHA, homogenates from HEK293 cell lines overexpressing UGT wild-type or variant UGT were used. The hepatic UGTs 2B17 and 1A9 and the extrahepatic UGTs IAS and IAlO exhibited the highest overall activity against SAHA as determined by Fmax/KM (16 ± 6.5, 7.1 ± 2.2, 33 ± 6.3, and 24 ± 2.4 nLmin-,-|i,g UGT protein-1, respectively), with UGT2B17 exhibiting the lowest KM (300 jxmoI/L) against SAHA of any UGT in vitro. Whereas the UGTlA8p.Alal73Gly variant exhibited a 3-fold (P < 0.005) decrease in glucuronidation activity against SAHA compared with wild-type UGT1A8, the UGTlA8p.Cys277Tyr variant exhibited no detectable glucur-onidation activity; a similar lack of detectable glucuronidation activity was observed for the UGTlA10p.Glyl39Lys 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 75% (P < 0.002) increase in KM compared with HLMs from subjects homozygous for the wild-type VGT2B17H 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.