A new label-free screen for steroid 5α-reductase inhibitors using LC-MS

Steroid 5 alpha-reductase (S5 alpha R) plays an important role in metabolizing testosterone into active androgen dihydrotestosterone (DHT) which is involved in many androgen dependent disorders, such as androgenic alopecia, benign prostatic hyperplasia and acne. The method for screening for S5 alpha R inhibition is key in finding new antagonists. In this study, the label-free S5 alpha R inhibitory assay using LC-MS was developed. S5 alpha R type 1 enzyme was obtained from LNCaP prostate cancer cells. The enzymatic assay was optimised for enzyme-substrate (testosterone) concentration, NADPH-cofactor concentration, solvent tolerance, enzyme activity stability and incubation time. The developed assay was validated by measuring the signal to background ratio (SIB), the signal to noise ratio (S/N), the signal window (SW) and the zeta factor Z' in accordance with published bioassay guidelines. The enzymatic reaction was performed in 96-well plates and DHT formation was determined by LC-MS. SIB, S/N, SW and Z' factor were well above acceptable criteria and the reproducibility was good using Z' factor other 3 days and further validated by dutasteride and finasteride inhibition. The method was successfully applied to quantify S5 alpha R inhibitory activity of some Thai herbal extracts. Two plant extracts, Impatiens balsamina L and Curcuma longa L. showed IC50 at 5.4 +/- 0.2 and 9.0 +/- 1.2 mu g mL(-1) and are therefore promising sources of new S5 alpha R inhibitors. The assay has high selectability and reproducibility and suited to medium throughput screening required by phytochemistry. (C) 2016 Elsevier Inc. All rights reserved.