Chemical profiling, bio-guided purification, and cytotoxic effect of two African spices: Hypodaphnis zenkeri Engl. Stapf (Lauraceae) and Staudtia kamerunensis warb (Myristicaceae) on human prostate cancer cell lines

Abstract

Ethnopharmacological relevanceProstate cancer remains a significant burden in low- and middle-income countries and the second leading cause of death around the world. Spices used in daily cuisine contain interesting phytochemical components capable of helping prevent and cure cancer. AimThis study aims to give sufficient phytochemical information on two understudied species, Staudtia kamerunensis Warb. (Myristicaceae) and Hypodaphnis zenkeri Engl. Stapf. (Lauraceae), and to study their cytotoxicity against prostate cancer cells in its early form and when they have developed metastasis. Materials and methodsTo reach this goal, normal procedures for phytochemical analysis were followed; these include collection, drying, crushing and extraction of plant materials using organic solvents. GC-MS (Gas chromatography- Mass Spectrometry) was used to evaluate the volatile phytochemicals contained in the extracts, and opened-column chromatography was used to isolate the pure compounds used in this study. A bio-guided exploration of Hypodaphnis zenkeri (Lauraceae) (leaves, seeds, stems) guided us in selecting the extract for further analysis. An established MTT assay was used to measure cell proliferation. Three prostate cancer cell lines were considered in this study, DU145 and PC3, human androgens-independent prostate carcinoma cells and LNCaP, which are cells derived from metastasis of a human prostate and respond to androgens, oestrogens and progestins. The eight compounds isolated were characterized using HREIMS, 1D and 2D NMR. ResultsAmong the three extracts from Hypodaphnis zenkeri, considered for biological testing, the leaf extract displayed better activities with a CC50 of 180 μg/mL against DU 145 cells, 184 μg/mL against PC3 cells and 194 μg/mL against LNCaP cells. These results were justified when GC-MS analysis of the different extracts was performed. Fifty compounds were identified from the leaves, representing 96.06% of the volatile components, with most displaying anticancer activities or activities against vectors favourising cancer growth (inflammation, etc.). An attempt to isolate the active principle responsible for the cancer activity led to the isolation of five pure compounds, namely Eicosane [1], Nonacos-1-ene [2], Palmitic acid [3], Glucoside Stigmasterol [4] and Butane-1,2,3,4-tetraol [5]. Eicosane was identified as being responsible in part for the observed activity, even though it exhibited weak cytotoxicity with the lowest CC50 equal to 30 μg/mL against DU 145 cells. Staudtia kamerunensis sap was investigated in our previous studies with the isolation of Oleanan-12-ene-2α,3β –diol [6] and 2α, 3β -dihydroxylup-20-ene [7] among the major components, with significant antibacterial properties. Oleanan-12-ene-2α,3β –diol [7] in this study displayed a CC50 of 20 μg/mL against DU145 cells, 22 μg/mL against PC3 cells, 18 μg/mL against LNCaP cells, and 32 μg/mL in HMEC affording a selectivity index >2. Contrary to what was observed in our previous study, the activity of Oleanan-12-ene-2α,3β –diol was lost in the presence of 2α, 3β -dihydroxylup-20-ene. Conclusionthe cytotoxic effect of extract from Staudtia and Hypodaphnis genera and pure isolates are here reported for the first time, as long as the pure isolates. These studies exhibit the cytotoxic potential of two traditional African spices and, more specifically, Oleanan-12-ene-2α,3β –diol and eicosane, isolated from these plant species.