Plumbagin from Plumbago auriculata Lam. as a nanomolar antimutagen against N‑methyl‑N‑nitrosourea: bioassay‑guided isolation.

Mutagen-induced genotoxicity is instrumental in carcinogenesis, highlighting the need for effective chemopreventive agents. Naphthoquinones, such as plumbagin, exhibit diverse biological activities; however, their antimutagenic potency against direct‑acting alkylating agents at pharmacologically relevant concentrations remains poorly characterised. Here, we demonstrate for the first time that plumbagin exhibits potent antimutagenic activity against N‑methyl‑N‑nitrosourea (MNU) at nanomolar concentrations. In this study, the acetone extract of Plumbago auriculata Lam. roots was subjected to bioassay-guided fractionation, yielding two known naphthoquinone derivatives: plumbagin and cis-isoshinanolone. Antimutagenic activity was evaluated using the Ames test with Salmonella typhimurium TA1535 against MNU. The chloroform‑soluble fraction showed strong activity, and purified plumbagin inhibited MNU‑induced mutagenicity at nanomolar concentrations (IC50 = 12.9 ± 0.86 nmol/plate) without toxicity. Cis‑isoshinanolone exhibited only weak effects (IC50 > 2.0 µmol/plate). These findings identify P. auriculata as a source of nanomolar‑active antimutagenic naphthoquinones and highlight their chemopreventive potential, providing a foundation for future studies.