Chemical Composition and Biological Activity of Diterpenoids from Plectranthus mutabilis

Despite the great development in human medicine, cancer is still a serious threat to public health and consequently, research on new anticancer agents should be continued. Natural products from medicinal plants (e.g., Plectranthus species) continue to be a substantial resource to treat different diseases, particularly in developing countries. Plectranthus species are rich in diterpenoids, which are reported to be responsible for various pharmacological activities such as cytotoxic activity. P. mutabilis Codd. is a perennial succulent herb containing Nepetoidins A and Nepetoidins B in its essential oils and have limited information available in the literature.

In this study, we performed an ultrasound-assisted acetone extraction of air-dried P. mutabilis whole plant followed by a bio-guided fractionation using the Artemia salina general toxicity assay that resulted in the identification of four compounds: Coleon U quinone (1), 8α,9α-Epoxycoleon U quinone (2), Coleon U (3, maor) and 7-hydro,14-deoxycoleon U (4). The cytotoxicity of the isolated compounds and P. mutabilis extract was evaluated using a model system of sensitive (NCI-H460) and MDR (NCI-H460/R) cells, along with normal human embryonal bronchial epithelial cells (MRC-5). Studies of modulation of P-gp activity are ongoing to unveil the interaction of these compounds and extract with P-gp.