Screening for inhibitors of topoisomerase I from Lycoris radiata by combining ultrafiltration with liquid chromatography/mass spectrometry

Abstract

Rationale: Although crude Amaryllidaceae alkaloids (AAs) extracted from Lycoris radiata are reported to exhibit significant anti-cancer activity, both the specific responsible alkaloid(s) and their targets remain elusive. Screening anti-cancer AAs targeted on topoisomerase I from crude AAs could be very helpful in tackling these two challenging questions. Methods: An ultrafiltration method combined with liquid chromatography/electrospray ionization mass spectrometry (UF-LC/MS) was developed to screen for the inhibitors of topoisomerase I, which has been reported to mediate DNA unwinding during carcinoma proliferation. Enrichment factors (EFs) of different AAs were used to evaluate the binding affinity between AAs and topoisomerase I, and the AAs with higher EFs were further tested to validate the method. Results: Eleven AAs from Lycoris radiata (ten of which were identified) were screened using UF-LC/MS, and a glaring discrepancy in EFs was revealed for the first time. One of the AAs, hippeastrine, with the highest EF at 49.3%, was further tested against topoisomerase I, and the IC50 value of hippeastrine was determined to be 23.0 μmol/L, which is comparable with the well-known anti-cancer drug camptothecin at 19.3 μmol/L. Conclusions: A simple, rapid and effective screening method using UF-LC/MS was developed and successfully applied to screen candidate inhibitors of topoisomerase I from crude AAs in Lycoris radiata, which may pave the way to further understand the potential anti-cancer constituents and mechanisms of Lycoris radiata. Copyright © 2016 John Wiley & Sons, Ltd.