Fruit Extract of Sechium chinantlense (Lira & F. Chiang) Induces Apoptosis in the Human Cervical Cancer HeLa Cell Line

Abstract

Sechium edule (Cucurbitaceae) is a commercial species of chayote and is just one of several species in the genus Sechium, whose extracts inhibit proliferation in tumor cell lines. The capacity of the wild species Sechium chinantlense (SCH) as an antitumor agent is unknown, as is the mechanism of action. In the present study, HeLa cervical cancer and HaCaT normal cell lines were treated with SCH and cell proliferation was inhibited in both cell lines in a dose-dependent manner similar to the effect of the antineoplastic agent cisplatin (Cis). Additionally, SCH arrested cell cycle progression but only in HeLa cells and induced apoptosis, as shown by phosphatidylserine translocation and caspase-3 activation, while Cis did so in both cell lines. Exploration of the mechanism of action of SCH in HeLa cells suggests that apoptosis was mediated by the intrinsic signaling pathway since there was no activation of caspase-8, but there was a release of cytochrome-c. These findings suggest that the SCH extract has the potential to selectively kill tumor cells by promoting apoptosis, without harming nontumor cells.

Keywords: apoptosis; cervical cancer; intrinsic signaling pathway.

Figure 1

Effect of different S. chinantlense extract concentrations on the proliferation of HeLa and HaCaT cell lines. The proliferation of HeLa and HaCaT cells was evaluated after 72 h in the presence of S. chinantlense extract or cisplatin. Average values of three independent experiments ± S.D. * p < 0.01 ANOVA—Tukey’s test with respect to the control of each cell line.

Figure 2

Effects of S. chinantlense extract or cisplatin at the IC₅₀ value on cell cycle distribution in HeLa and HaCaT cells. Histograms represent flow cytometric analysis of untreated control, S. chinantlense extract-treated, and cisplatin-treated HeLa and HaCaT cells. The X-axis represents the intensity of PI staining, which is directly proportional to the amount of DNA in cells, and the Y-axis represents cell number.

Figure 3

Effect of incubation with S. chinantlense extract or cisplatin at the IC₅₀ value for 48 h on the level of active p53 in HeLa and HaCaT cell lines.

Figure 4

Apoptosis analysis upon treatment of HeLa and HaCaT cells with S. chinantlense extract at the IC₅₀ value. The distribution of cells undergoing early and late apoptosis together with viable cells was determined at 72 h in comparison to control or cisplatin at the IC₅₀ value, using Annexin V-FITC and propidium iodide flow cytometric analysis.

Figure 5

Activation of caspase-8 in HeLa cancer cells after incubation with S. chinantlense extract or cisplatin at the IC₅₀ value for 24 h. The values are presented as the mean ± S.D., where ∗ indicates a significant difference relative to the control (p < 0.05).

Figure 6

Activation of caspase-3 in HeLa and HaCaT cell lines after incubation with S. chinantlense extract or cisplatin at the IC₅₀ value for 48 h.