As mentioned above, Galla chinensis has been reported to exhibit a variety of biochemical and pharmacological properties.17,18 In addition, in the past few decades, pterostilbene has been shown to exhibit excellent anti-cancer effects with regard to lung, colon, breast, and cervical cancers.19 However, the bioavailability of Galla chinensis is higher than that of pterostilbene, which contains two methoxy groups.20 Importantly, this is the first paper to propose and preliminarily explore the antitumor activity of Galla chinensis against cervical cancer.
More specifically, using a wide range of sublethal concentrations to evaluate the effects of Galla chinensis (i.e., 3, 6, and 12 µg/mL) to avoid any issues related to cytotoxicity, an IC50 value of 25 µg/mL was determined. Our results showed that at these low concentrations, Galla chinensis can inhibit the growth of SiHa cervical cancer cells, which are known to be clonal, and our research elucidated the viability of cells treated with sublethal concentrations of Galla chinensis. Indeed, clone formation experiments demonstrated that Galla chinensis has a long-term effect on SiHa cervical cancer cells after 24 h of treatment, wherein the surviving cells were allowed to grow in a normal growth medium for 15 d afterwards. At all three concentrations examined, the cloning ability of the viable cells was significantly reduced, and the observed effect was slightly superior to that observed for pterostilbene. These results indicate that Galla chinensis has the ability to inhibit the proliferation and growth of cervical cancer cells.
Since cell migration is a key step in metastasis,21 limiting such migration will help to better understand cancer metastasis to ultimately enable physiologically relevant drug and cell line screening.22 Our research found that at sublethal doses, both pterostilbene and Galla chinensis exhibited anti-migration effects. These findings are supported by those of previous studies, which have shown that Galla chinensis exhibits a significant ability to prevent the proliferation of human breast cancer cells through an effective h LDH-A inhibitor.23 These mechanisms may account for the inhibition of SiHa cell migration, but further studies are required to confirm this.
It has previously been demonstrated that pterostilbene promotes the arrest of the cancer cell cycle, and it has been confirmed that following treatment, cervical cancer cells remain in their S phase.24 We, therefore, decided to study the cycle arrest effect imparted by Galla chinensis, wherein cytometry analysis showed that this treatment caused SiHa cells to stagnate in the S phase, thereby preventing cell mitosis.
E6 is a known viral oncoprotein that induces cervical cancer by inactivating the tumor suppressor protein p53.25 The p53 gene is irreversibly mutated in most cancers; however, it has been reported that cervical cancer and cell lines retain the wild-type p53 gene, and its function is obscured by the viral E6 protein.26 In the current study, we observed that Galla chinensis reduced the expression of E6 in SiHa cervical cancer cells. This is of importance since the downregulation of E6 may lead to restoration of the tumor suppressor function of the p53 protein. This may result in the activation of downstream signaling molecules, leading to cell cycle arrest or cell apoptosis, which will lay the foundations for further exploration of the anti-cancer activity of Chinese Galla chinensis in cervical cancer.
In recent years, an increasing number of scientists have begun to study various naturally occurring antioxidants, which seems to be a feasible method to verify the development of traditional drugs. Although modern drug design prefers to use a single chemical entity with a specific molecular target, this can result in increased drug resistance or related side effects. In addition to the necessity to find affordable cervical cancer treatments for use in developing countries, there is an urgent need to develop affordable alternative therapies. In this context, Galla chinensis and polyphenol botanicals may therefore exhibit higher bioavailabilities and lower toxicities than individual molecular drug compounds; hence, whole plant extracts may prove to be more effective. Of course, this also requires additional experimental evidence, such as further in vivo experiments on animal models of ectopic tumor implants to better verify the anti-cancer activity potential of Chinese Galla chinensis against cervical cancer.