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

Abstract

We screened thirty-four methanolic plant extracts for inhibition of the constitutive nuclear

factor κB (NF-κB) activity by a NF-κB-luciferase reporter gene assay. Strong inhibition

of NF-κB 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 NF-κB activity in a luciferase reporter gene assay as well as

reduction of nuclear NF-κB 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 NF-κB activation and affected

the canonical and alternative pathways. Suppression of NF-κB 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 NF-κB pathway and acts as a sensitizer to conventional

chemotherapy, enabling the search for its specific target and application against cancer

and inflammation.