The pharmacokinetics of fosfestrol and diethylstilbestrol in chronic hemodialysis patients with prostate cancer

Human UDP-Glucuronosyltransferases 1A1, 1A3, 1A9, 2B4 and 2B7 are Inhibited by Diethylstilbestrol

Inhibition of UDP-glucuronosyltransferases (UGTs) can result in many undesired side effects. Diethylstilbestrol (DES), a synthetic oestrogen famous for its multiple toxicities, was once widely administered to women in high dosages and now still gains application in clinics. This study investigated in vitro inhibitory effects of DES on catalytic activities of human UGTs, aiming at disclosing new potential toxic mechanisms on the basis of interactions between DES and metabolizing enzymes. DES (10 μM) could decrease activities of UGT1A1, 1A3, 1A9, 2B4 and 2B7 in catalysing 4-methylumbelliferone (4-Mu) glucuronidation. Further kinetic analyses showed that inhibition of these UGTs followed competitive (UGT1A1 and 1A9), mixed (UGT1A3 and 2B4) and non-competitive (UGT2B7) mechanisms, with K_i values ranging from 0.91 to 4.1 μM. The inhibition potentials of UGT1A9 and 2B7 in human liver microsomes (HLM) were further tested by employing propofol and zidovudine as probe substrates, respectively. The inhibition of human liver microsomal UGT1A9 followed mixed mechanism, with the K_i value of 3.5 μM and α of 4.1. On the other hand, DES displayed non-competitive inhibition against UGT2B7 in HLM, with the K_i value of 9.8 μM. The risks of in vivo inhibition of human UGTs were also predicted by calculation of plasma C/K_i values. Results suggest that DES can trigger in vivo inhibition of UGT1A1, 1A3, 1A9, 2B4 and 2B7 after the intravenous administration in high doses.

Assay of the synthetic estrogen fosfestrol in pharmaceutical formulations using capillary electrophoresis

This study reports--for the first time--a capillary electrophoretic method for the determination of fosfestrol, a synthetic estrogen used in the treatment of metastatic prostate cancer. The effects of the carrier ion concentration, injected volume and applied voltage were studied and optimized. A 10 mM sodium tetraborate solution was selected as the carrier electrolyte solution, while the sample was injected hydrodynamically by applying a 20 mmHg vacuum for 1 s. The driving voltage was 30 kV and the absorbance of the analyte (peak height) was monitored at 240 nm. Under the above-mentioned conditions, the migration time of fosfestrol was 6.6 min. Linearity was achieved in the analyte range 3-150 mgL(-1) with the detection limit being 1 mgL(-1). The proposed method is adequately precise (s(r)=2.8% at 100 mgL(-1) fosfestrol, n=10) without the use of an internal standard and was applied to the determination of fosfestrol in a pharmaceutical formulation. The results obtained by the proposed method were in good agreement with those derived from the USP reference method.