The multifaceted induction of apoptosis in skin cancer cells using extracts of South African plants

Dissertation (MSc (Medicinal Plant Science))--University of Pretoria, 2022.

Eleven plants were selected based on their phytochemical constituents, ethnobotanical usage and biological activity resulting in thirty-three plant extracts prepared using ethanol, dichloromethane and water. The plant extracts were evaluated for in vitro antiproliferative activity against human epidermoid carcinoma (A431) and human malignant melanoma (UCT-MEL-1). The Hypoestes forskaolii ethanolic extract (HF-EtOH) displayed significant in vitro antiproliferative activity that was statistically similar to the American cancer institute guidelines, that set the limit for in vitro antiproliferative activity of a plant extract after 72 h at < 30 µg/mL, with 50% minimum inhibitory concentration values (IC50) of 37.78 ± 2.31 and 39.02 ± 1.73 µg/mL against A431 and UCT-MEL-1 cells, respectively. The Hypoestes aristata ethanolic extract (HA-EtOH) displayed noteworthy in vitro antiproliferative activity with an IC50 of 70.66 ± 3.46 and 96.27 ± 1.10 µg/mL against A431 and UCT-MEL-1 cells, respectively. Gold nanoparticles (HF-AuNPs) were synthesized using HF-EtOH, to determine whether bioactivity could be increased and decrease systemic toxicity. The in vitro antiproliferative activity of HF- EtOH, HA-EtOH and HF-AuNPs was further evaluated on human malignant melanoma cells (A375, MeWo and RPMI-7951) and on non-tumorigenic cell lines (Vero and HaCat) where HF- EtOH displayed noteworthy in vitro antiproliferative activity against the MeWo cell line with an IC50 of 34.18 ± 1.73 µg/mL and an IC50 of 68.52 ± 3.46 µg/mL against the Vero cell line resulting in an SI value of 2.00 which was higher than actinomycin D (positive control) which displayed an SI value of 1.00. The HF-AuNPs displayed in vitro antiproliferative activity with an IC50 of 32.20 µg/mL against the RPMI-7951 cell line through the bisBenzamide H 33,342 trihydrochloride (Hoechst 33342)/propidium iodide (PI) method and no IC50 could be detected on the A431, UCT-MEL-1, A375, RPMI-7951, MeWo, Vero and HaCat cell lines using the PrestoBlue method. The genotoxic effect of HF-EtOH, HA-EtOH and HF-AuNPs was evaluated on Vero cells through the in vitro micronucleus assay and HA-EtOH was genotoxic at the lowest concentration (4.70 µg/mL) whereas HF-EtOH (0.75 µg/mL) and HF-AuNPs (25 µg/mL) were not genotoxic compared to griesofulvin (positive control) at 3.53 µg/mL. Furthermore, HF-EtOH at 3.10 and 6.25 µg/mL, elicited G0/G1 and late mitotic cell cycle arrest, induced apoptosis, inhibited protein kinase B (Akt) and upregulated phosphatase tensin homolog (PTEN) activity at 1.50 and 3.00 µg/mL by 18.94 ± 4.56 and 12.37 ± 0.93 % highlighting the restoration of equilibrium. The HF- AuNPs at 37.50 µg/mL elicited early mitotic cell cycle arrest, induced necrosis and upregulated PTEN activity by 7.05% at 25 µg/mL, highlighting that the HF-AuNPs did not display enhanced activity compared to HF-EtOH. This study highlights the first report of the in vitro antiproliferative activity of HF-EtOH and HA-EtOH on skin cancer cell lines as well as the synthesis of gold nanoparticles using HF- EtOH. Furthermore, this study provides the first report of the mechanistic potential of HF-EtOH through the inhibition of Akt activity, G0/G1 and late mitotic cell cycle arrest, apoptotic cell death and upregulation of PTEN activity.

National research foundation.

Plant Science

MSc (Medicinal Plant Science)

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