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.

Keywords: Viscum verrucosum; Antiproliferative; Cancer; Cytotoxicity; Medicinal plants; Phytochemistry; Zimbabwe.

Fig. 1

The effect of crude methanolic plant extracts on normal murine peritoneal cells. Crude methanolic plant extracts were tested on normal murine peritoneal cells for their cytotoxic activity at a concentration of 250 µg/mL and chlorambucil was used as a positive control at a concentration of 10 μg/mL. The negative control contained cells and RPMI media only. The cells were incubated with test solutions and cell viability was determined after 72 h. The values are for mean ± SD for n = 3. All treatments were compared to cells only to determine the significant difference. The level of significance was denoted as follows: ****P < 0.0001. Methanolic plant extracts (A. pungu, C. edulis, F. indica, S. cocculoides, S. spinosa and V. verrucosum) significantly reduced cell viability and they were considered cytotoxic

Fig. 2

Concentration-dependant effect of plant methanolic extracts on normal murine peritoneal cells. The cells were incubated with test solutions at a varying concentration from 32 to 250 μg/mL and cell viability was determined after 72 h. Chlorambucil was used as a positive control at a concentration from 1.25 to 10 μg/mL. The negative control contained cells and RPMI media only. The cell viability decreased with an increase in the concentration of the test extract

Fig. 3

The haemolytic effect of crude methanolic plant extracts on sheep erythrocytes. The erythrocyte suspension was incubated with an equal volume of test samples dissolved in PBS at a concentration range of 32 to 250 μg/mL at 37℃. Methanolic plant extracts had greater haemolytic activity at higher concentrations. F. indica and V. verrucosum methanolic extracts caused haemolysis at the highest concentration of 250 μg/mL, with V. verrucosum also exhibiting haemolytic activity at 125 μg/mL

Fig. 4

The effect of reduced—glutathione (GSH) on the cytotoxic activity of A.pungu and V. verrucosum. The effect of combining GSH and crude methanolic plant extracts of A. pungu and V. verrucosum was evaluated on normal murine peritoneal cells. GSH and crude methanolic plant extracts were used at concentration of 25 and 250 µg/mL respectively. The cells were incubated with the test solution and cell viability was determined after 72 h. To determine significance (cells + extracts) was compared with (cells + extracts + GSH). ****P < 0.0001 and *** P 0.0001. The addition of GSH to A. pungu and V. verrucosum increased the percentage of viable normal murine peritoneal cells

Fig. 5

The effects of crude methanolic plant extracts on Jurkat T cell lines. Crude methanolic plant extracts were tested for their antiproliferative effect on Jurkat T cell line at a concentration of 250 µg/mL. Chlorambucil was used as a positive control at a concentration of 10 μg/mL. The negative control contained cells and RPMI media only. The cells were incubated with test solutions and cell viability was determined after 72 h. The values are for the mean ± SD for n = 3. All treatments were compared to cells only to determine the level of significance. The level of significance is denoted as follows: **** P < 0.0001. A. pungu, C. edulis, F. indica, L. ocymifolia, L.martinicensis, P. kalachariensis, S. spinosa and V. verrucosum, significantly inhibited the proliferation of Jurkat T cell line and V. verrucosum had the greatest potency

Fig. 6

Concentration-dependent effect of crude methanolic plant extracts on Jurkat T cell lines. The concentration dependent effect of crude methanolic plant extracts of A. pungu, C. edulis, L. ocymifolia, L. martinicensis and V. verrucosum were evaluated on Jurkat T cell lines. The cells were incubated with crude methanolic plant extracts at varying concentrations ranging from 0 to 250 μg/mL and cell viability was determined after 72 h. Chlorambucil was used as a positive control at a concentration of 1.25 to 10 μg/mL. The negative control contained cells and RPMI media only. The cell viability decreased with an increase in the concentration of the extract

Fig. 7

The effects of crude methanolic plant extracts on HL60 cell lines. Crude methanolic plant extracts were tested for their antiproliferative effect on HL60 cell line at a concentration of 250 µg/mL. Camptothecin was used as a positive control at a concentration of 10 μg/mL. The negative control contained cells and RPMI media only. The cells were incubated with test solutions and cell viability was determined after 72 h. The values are for the mean ± SD for n = 3. All treatments were compared to cells only to determine the level of significance. The level of significance is denoted as follows: **** P < 0.0001. Plant extracts A. pungu, C. edulis, F. indica, L. ocymifolia, L. martinicensis, P. kalachariensis, S. cocculoides, S. spinosa and V. verrucosum significantly inhibited the proliferation of HL60 cells and V. verrucosum was the most active

Fig. 8

Concentration-dependent effect of crude methanolic plant extracts on HL60 cell lines. The concentration-dependent effect of crude methanolic plant extracts of A. pungu, C. edulis, L. ocymifolia, L. martinicensis and V. verrucosum were evaluated on HL60 cell lines. The cells were incubated with extracts at varying concentrations ranging from 0 to 250 μg/mL. Chlorambucil was used as a positive control at a concentration range of 1.25 to 10 µg/mL. The negative control contained cells and RPMI media only and cell viability was determined after 72 h. The cell viability decreased with an increase in the concentration of the extract

Fig. 9

Frequency of phytochemical constituents of the crude methanolic plant extracts. Among the 13 methanolic plant extracts screened, 10 contained alkaloids, 9 contained flavonoids, and 9 had saponins. Alkaloids, flavonoids and saponins were the most common phytochemical classes present in the plant extracts