Ghana’s Mangrove Wetland Endophytic Fungi: Cytotoxicity, Anti-Plasmodial and Apoptotic Activity of Quinolactacin A1/A2, Citrinadin A and Butrecitrinadin

Abstract

Marine-derived endophytic fungi isolated from mangrove plants are an important and novel resource of natural bioactive compounds with their potential applications in medicine, agriculture and food industry. There are many instances that seem to suggest that, some of the novel metabolites previously isolated from certain species of marine plants and invertebrates are actually metabolites of marine-derived endophytic fungi. In this project, chemical screening of mangrove plantsConocarpus erectus, Laguncularia racemosa and Rhizophora racemosacollected along the banks of the River Butre showed that the compound 14S-bromo-1S-hydroxy-1,2,13,14-tetrahydrosphaerococenol A is not a biosynthetic product of the red alga Sphaerococcus coronopifolius but a product of possible endophytic fungi living inside the alga tissues. The compound 3-(phenethylamino)demethyl(oxy)aaptamine and its derivatives like aaptamine are not necessarily the biosynthetic products of the sea sponge Aaptos aaptos but originate from endophytic fungi within the tissues of the sponge. The mycospurine amino acid N-methylpalythine-serine originally deemed to be the metabolites of the stony coral Pocillopora eydouxicould actually be the biosynthetic products of marine-derived endophytic fungi. Mangrove plants sampled along the banks of River Butre were investigated for new or novel secondary metabolites. The HRESI/HPLC-DAD-MSn dereplication technique was employed in identifying and isolating new secondary metabolites from the mangrove plants. Out of twenty-four (24) marine-derived endophytic fungi isolated from various parts of three major mangrove plants growing in and along the banks of the River Butre in the Western Region of Ghana, six (6) different species were selected for chemical profiling, prioritization, identification and subsequent isolation

of compounds. Measurement and analysis of HRESI/HPLC-DAD-MSn data of the small scale culture of these six (6) species led to the prioritization of Penicillum sp. BRS2A-AR2. Penicillum sp. BRS2A-AR2 was prioritized due to its ability to make a wide range of interesting secondary metabolites with biosynthesis prowess and ingenuity. The HRESI/HPLC-DAD-MSn analysis of Penicillum sp. BRS2A-AR2 was prioritised for further investigation because it produced metabolites which did not give any relevant hit when their masses were entered in the marine natural product based commercial database MarinLit, AntiMarin and Antibase database for novelty. The structures of these metabolites were elucidated by 1D and 2D NMR data interpretation. Quinolactacin A1/A2 was isolated with m/z of 270.1362. Citrinadin A and a new compound Butrecitrinadin were also isolated with m/z of 625.3962 and 681.4226 respectively. Citrinadin A and Butrecitrinadin were virtually identical with similar mass fragmentation pattern, eluting at the same time, having same retention time and collected together. Biological activity studies on the compounds and other compounds from the research group showed the anti-proliferative ability of the two steroidal compounds to inhibit human prostate cancer cell line with IC50 of 5.58 and 5.28 μM. Butrepyrazinone, Citrinadin Aand Butrecitrinadin showed cytotoxicity against cell lines tested. Quinolactacins isolated also showed anti-plasmodial activity with IC50 of 24.80 μM and also, showed apoptotic activity via the loss of mitochondrion membrane potential of the plasmodium parasite.