Phytochemistry and anti-cancer potential of compounds isolated from Kenyan medicinal plants, Moringa oleifera and Prunus africana.

Abstract

Cancer is one of the leading causes of death worldwide and of all the cancer related deaths occurring worldwide, 70% are in low and middle income countries. In Africa, the disease kills more people than HIV, TB and malaria combined. In Kenya, cancer continues to claim millions of lives. The poor prognosis of cancer in Kenya is due to a lack of facilities for diagnosis and treatment which is further worsened by poor access to these facilities resulting in the majority of Kenyans turning to herbal medicine for treatment. Natural products have been an invaluable source of therapeutic drugs with 60% of cancer chemotherapy in the market today being plant-derived drugs. However, challenges such as drug toxicity and resistance facing chemotherapy it has become imperative to find alternate drugs with improved specificity and efficiency. The current study focuses on two plants, Moringa oleifera and Prunus africana which are widely used in Kenya for cancer treatment and are reputed to cure various malignancies. There is need to obtain insight into the phytochemistry of these plants and their supposed activity as well as bioprospecting for potential novel anticancer drugs. In this work, the phytochemistry, in-vitro cytotoxicity and apoptosis induction activity of isolated phytocompounds on mammalian colorectal adenocarcinoma (Caco-2), hepatocellular carcinoma (HepG2) and the non-cancer human embryonic kidney cell (HEK293) cell lines are reported. Phytochemical studies using different chromatographic and spectroscopic techniques led to the isolation of six compounds, namely quercetin-3-O-glucoside, 4-(β-d-glucopyranosyl-1→4-α-l-rhamnopyranosyloxy)-benzyl isothiocyanate, lutein, β-sitosterol, β-amyrin and sitosterol-3-O-glucoside. These were successfully purified and their structures were confirmed using spectroscopic techniques. GC-MS profiling of P. africana extract revealed 9 compounds of interest. Four of the purified compounds were tested for potential anticancer activity using in-vitro cytotoxic and immunofluorescent techniques. The MTT cell proliferation assay was used to test for cytotoxic activity and dual staining using acridine orange and ethidium bromide were used to study apoptosis. A concentration dependent cytotoxicity was observed across all cell lines with low activity on the non-cancer HEK293 cell line. 4-(β-d-glucopyranosyl-1→4-α-l-rhamnopyranosyloxy)-benzyl isothiocyanate was the most cytotoxic compound tested across all cell lines based on IC50 values with β-amyrin being the least cytotoxic. All compounds tested exhibited higher cytotoxic activity on the colorectal adenocarcinoma (Caco-2) cell line than the hepatocellular (HepG2) cancer cell line. Further investigation on possible mechanisms of action using immunofluorescent studies confirmed apoptosis as one of the modes of cell death which was also selective to cancer cells. Higher apoptotic indices were observed on the cancer cell lines than the non-cancer cell line. The findings in this study will contribute to the existing knowledge on natural products and their anticancer activity and will provide a basis for development of potential novel cancer drugs.