Nuphar lutea thioalkaloids inhibit the nuclear factor κB pathway, potentiate apoptosis and are synergistic with cisplatin and etoposide

We screened thirty-four methanolic plant extracts for inhibition of the constitutive nuclear factor κB (NFκB) activity by a NFκB-luciferase reporter gene assay. strong inhibition of NFκB activity was found in extracts of leaf and rhizome from Nuphar lutea L. SM. (Nuphar). The inhibitory action was narrowed down to a mixture of thionupharidines and/or thionuphlutidines that were identified in chromatography fractions by one- and two-dimensional NMR analysis. Dimeric sesquiterpene thioalkaloids were identified as the major components of the mixture. The Nuphar alkaloids mixture (NUP) showed a dose dependent inhibition of NFκB activity in a luciferase reporter gene assay as well as reduction of nuclear NFκB subunits expression as tested by western blots and immunohistochemistry. Decreased DNA binding was demonstrated in electro mobility shift assays. NUP inhibited both inducible and constitutive NFκB activation and affected the canonical and alternative pathways. suppression of NFκB was not cell type specific. Induction of apoptosis by the alkaloid mixture was demonstrated by time-dependent and dose-dependent cleavage of procaspase-9 and PARP. Synergistic cytotoxicity of the active mixture with cisplatin and etoposide was demonstrated. Overall, our results show that NUP inhibits the NFκB pathway and acts as a sensitizer to conventional chemotherapy, enabling the search for its specific target and application against cancer and inflammation.