The Natural Extracts of Schisandra chinensis and Pueraria lobata Induce Down-Regulation of Human Papillomavirus E6 Oncogene and Antiproliferative Effect on HeLa Cell Line
Introduction
Infection by high-risk HPV16 and 18 genotypes of human papillomaviruses (HPVs) is implicated in the etiology of cervical cancer. However, current treatment strategies of chemotherapy and radiotherapy fail to elicit therapeutic responses and cause severe systemic toxicity. Therefore, the development of a safer and more effective treatment modality is needed. Natural products are excellent candidates for the treatment of cervical cancer. Schisandra chinensis extracts, traditionally used in Asian medicine, contain bioactive compounds such as schisandrol A, schisandrol B, gomisin G, schisandrin A, schisandrin B, and schisandrin C, which are known for their antioxidant, antitumor, anti-inflammatory, and antiviral properties against dengue, hepatitis, and HIV viruses. On the other hand, Pueraria lobata (kudzu root) has a long history of traditional use in the treatment of cardiovascular disease, type 2 diabetes mellitus, hypertension and stroke. Its bioactive compounds, such as genistein and puerarin, have been shown to have antitumor effects on breast, esophageal, and colon cancer, as well as lymphoma. In addition, Pueraria lobata exhibits antiviral activity against respiratory syncytial virus and influenza A virus, making it a promising candidate for evaluating its effects on HPV-transformed cells. Therefore, extracts derived from both Pueraria lobata and Schisandra chinensis are excellent candidates for evaluating their effects on HPV-transformed cells. Therefore, this study evaluated the effect on viral oncogenes and antiproliferative potential of Schisandra chinensis and Pueraria lobata natural extracts on HPV18+ cells.
Methods
Ethanolic extracts of Schisandra chinensis and Pueraria lobata were obtained from Gelinna (https://www.greena-bio.com/) and used to treat HeLa cells at 0.1, 1.0, and 10 μg/mL for 24 or 48 hours in various experiments such as cell viability, expression of E6/E7 oncogenes, cell cycle, expression of cell cycle genes, and immunohistochemistry of p53, E2F-1, BCL-2, and Ki-67. Data were analyzed by Mann-Whitney U test and Kruskal-Wallis test using GraphPad Prism 6 software. The test extracts were chemically characterized by total content, antioxidant capacity, and LC-MS analysis.
Results
Natural extracts of Schisandra chinensis and Pueraria lobata showed no cytotoxic activity in HeLa cancer cell line (IC50 values > 100 µg/mL) or in healthy fibroblasts. These natural extracts induced G0/G1 and S phase arrest by increasing the gene expression of p53 (p<0.05), E2F-1 (p<0.05), Bcl2 (p<0.05), and E7 (p<0.05) and inducing a concomitant decrease in E6 oncogene expression (p<0.05). At the same time, natural extracts tended to increase p53 protein levels. In phytochemical characterization, the analyzed extracts contain significant amounts of phenolic compounds, including lignans (>89%) and isoflavonoids (>93%), with identified schisandrins A and B in Schisandra plants, and C-glycosylated isoflavonoids such as puerarin in Pueraria species. Both extracts exhibit different antioxidant capacities, with ABTS-+ being more effectively scavenged than DPPH-, possibly due to their polar nature.
Conclusion
The results show that the natural extracts of Schisandra chinensis and Pueraria lobata inhibit the expression of the HPV E6 oncogene and in turn can induce a significant increase in the expression of p53 and other factors such as BCL2 and E2F-1, resulting in cell cycle arrest of HeLa cells. Therefore, these extracts are good candidates for further investigation of their antiviral and antiproliferative potential in HPV-transformed cells.