Evaluation of the antiproliferative, cytotoxic and phytochemical properties of Zimbabwean medicinal plants used in cancer treatment.

Abstract

Background: Cancer cases have been on the rise globally and several treatment strategies have been developed but mortality rates remain high. Zimbabwe, like many other countries, has also experienced a surge in cancer cases. In Zimbabwe, medicinal plants have been widely used to treat cancer for centuries. However, there has been limited research on the effectiveness, safety, and chemical composition of these plants. The current study assessed antiproliferative, cytotoxic and phytochemical properties of selected Zimbabwean medicinal plants.

Method: Cytotoxic activity of Agelenthus pungu, Carissa edulis, Dombeya rotundifolia, Flacourtia indica, Lannea discolor, Leonotis ocymifolia, Leucas martinicensis, Plicosepalus kalachariensis, Pseudolachnostylis maproneifolia, Solanum incanum, Strychnos cocculoides, Strychnos spinosa and Viscum verrucosum extracts were evaluated on normal murine peritoneal cells and sheep erythrocytes while antiproliferative activity was assessed on Jurkat T and HL60 cell lines. Cell viability was determined using the trypan blue exclusion and sulforhodamine B assay. Additionally, the effect of reduced glutathione on cytotoxic extracts was examined. The phytochemicals of the methanolic extracts were qualitatively determined using standard methods.

Results: Agelenthus pungu, Carissa edulis, Flacourtia indica, Strychnos cocculoides, Strychnos spinosa and Viscum verrucosum were cytotoxic to normal murine peritoneal cells. Flacourtia indica and Viscum verruscosum caused haemolysis of sheep erythrocytes at a concentration of 250 µg/mL for both plant extracts and 125 µg/mL for Viscum verrucosum. Cell viability increased on addition of 25 µg/mL of reduced glutathione to the extracts considered the most cytotoxic extracts, Agelenthus pungu and Viscum verrucosum. Agelenthus pungu, Carissa edulis, Leonotis ocymifolia, Leucas martinicensis and Viscum verrucosum significantly inhibited Jurkat T and HL60 cell proliferation. Viscum verrucosum was the most potent with the lowest half-maximum inhibitory concentration (IC₅₀) values of 33 and 34 µg/mL on Jurkat T and HL60 cell lines respectively. The most dominant phytochemical classes were alkaloids, flavonoids and saponins.

Conclusion: This study demonstrates that Agelenthus pungu, Carissa edulis, Leonotis ocymifolia, Leucas martinicensis and Viscum verrucosum have antiproliferative activity against Jurkat T and HL60 cell lines. Viscum verrucosum was the most potent. These findings emphasise the importance of medicinal plants as well as their potential use as sources of novel compounds in anticancer drug discovery.