Antineoplastic Activity of Selected Cytotoxic Plants from the Kalahari

Abstract

Plants are known to produce cytotoxic compounds, some of which are currently being used as chemotherapeutic agents for the treatment of cancer. With southern Africa’s rich biodiversity, it could be worthwhile to study indigenous herbal medicine to discover more effective and safe cancer treatments as complementary and alternative therapies. From Africa, several plant species have been used by traditional therapists for the treatment of cancer with well-known examples including Lessertia frutescens (L.) Goldblatt & J.C.Manning (syn. Sutherlandia frutescence (L.) W:T.Aiton), Fabaceae, Catharanthus roseus (L.) G.Don, Apocynaceae, and Tulbaghia violacea Harv., Amaryllidaceae. Recently, Artemisia afra Jacq., Asteraceae, has also been shown to exhibit strong in vitro antineoplastic activity. This review focuses on A. afra and some lesser studied southern African plants from the Kalahari region. This selection was made based on field observations, traditional use, and literature summarizing recent developments and their potential as anticancer agents. Ammocharis coranica Herb., Amaryllidaceae, A. afra, Dipcadi glaucum (Burch. ex Ker Gawl.) Baker, Asparagaceae, Elephantorrhiza elephantina (Burch.) Skeels, Fabaceae, Geigeria ornativa O.Hoffm., Asteraceae, Neltuma juliflora (Sw.) Raf. (syn. Prosopis juliflora (Sw.) DC.), Fabaceae, and Senna italica Mill., Fabaceae, can be found in the Kalahari region stretching across three countries. Databases were consulted (Science Direct, Web of Science, Scopus, PubMed, and Google Scholar) and textbooks to collate scientific literature on the selected species. Lycorine seems to be the most promising bioactive compound isolated from A. coranica with in vitro cytotoxicity of 0.21 µg/ml (IC50). Methanol extracts of N. juliflora appear to be highly active, while butanolic extracts are cytotoxic at a low concentration of 5.17 µg/ml against MCF-7. Isoalantolactone identified in A. afra also expressed good activity, being cytotoxic at a low concentration of 1.89 µg/ml. Tea infusions of A. afra were found to be cytotoxic at 6.0 µg/ml with a selectivity index of 10. Identification of active constituents, more in-depth ex vivo/in situ experiments, and eventually clinical trials should be conducted on the most promising plant extracts and/or compounds identified therein. Graphical Abstract