Carbazole alkaloids from Murraya koenigii trigger apoptosis and autophagic flux inhibition in human oral squamous cell carcinoma cells
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Carbazole alkaloids, a major constituent of Murraya koenigii (L.) Sprengel (Rutaceae), exhibit biological effects such as anticancer activity via the induction of apoptosis, and they represent candidate chemotherapeutic agents. Oral squamous cell carcinoma (OSCC) is the most prevalent cancer of the oral cavity and a growing and serious health problem worldwide. In this study, we investigated the anticancer properties and mechanisms of action of two carbazole alkaloids derived from M. koenigii leaves, mahanine and isomahanine, in the OSCC cell line CLS-354. At 15 μM, mahanine and isomahanine were cytotoxic to CLS-354 cells, triggering apoptosis via caspase-dependent and -independent mechanisms. Autophagosomes, visualised using monodansylcadaverine (MDC) labelling, were numerous in carbazole alkaloid-treated cells. Mahanine and isomahanine markedly induced the expression of the autophagosome marker microtubule-associated protein 1 light chain 3, type II (LC3B-II). Genetic and chemical inhibition of autophagy via silencing of the Autophagy protein 5 gene and exposure to bafilomycin A1 (BafA1), respectively, did not arrest carbazole alkaloid-induced apoptosis, indicating that it occurs independently of autophagic activation. Surprisingly, both carbazole alkaloids caused increased accumulation of p62/sequestosome1 (p62/SQSTM1), with coordinated expression of LC3B-II and cleaved caspase-3, suggesting inhibition of autophagic flux. Our results suggest that inhibition of autophagic flux is associated with carbazole alkaloid-induced apoptosis. Our findings provide evidence of a novel cytotoxic action of natural carbazole alkaloids and support their use as candidate chemotherapeutic agents for the treatment of OSCC.
KeywordsMurraya koenigii Carbazole alkaloid Autophagy Apoptosis Oral squamous cell carcinoma
This work was supported by the programme strategic scholarships fellowships frontier research networks for the Ph.D. sandwich programme doctoral degree from the Office of the Higher Education Commission (OHEC), Thailand (06/2556); Walailak University (WU56113); Walailak University Fund for graduate studentship (27/2556 and WU55603); The Thailand Research Fund (DBG5980003); Centre of Excellence for Innovation in Chemistry, OHEC. We would like to thank Enago (https://www.enago.com/) for editing and reviewing this manuscript for English language.
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Conflict of interest
The authors declare no conflicts of interest.
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