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

Abstract

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.