Baicalein-rich Fraction of Oroxylum indicum Leaves induces Apoptosis by Repressing E6 and E7 Expression in HPV-associated Cervical Cancer Cell Lines

Abstract

Oroxylum indicum (O. indicum) has been implicated as a promising anti-cancer agent for cancer treatment including cervical cancer. It has been shown that this plant was able to inhibit the proliferation of cancer cells by acting as anti-human papillomavirus (HPV) and an apoptosis inducer. The therapeutic anti-cancer properties of O. indicum is strongly postulated due to its major chemical constituents such as chrysin, oroxylin A and baicalein. In this pre- sent study, the baicalein-rich fraction was extracted to elucidate its anti-cancer activity against cervical cancer cells, SiHa (HPV 16 positive) and HeLa (HPV 18 positive) cells. Utilizing preparative thin layer chromatography (PTLC) (n-hexane: ethyl acetate; 50:50), this fraction was prepared from the methanolic crude extract of O. indicum and subjected to high-performance liquid chromatography (HPLC) for baicalein quantitation. Biological activities of this fraction were tested using methylene blue assay and western blot to observe the expression of HPV oncoproteins; E6 and E7, and the tumour suppressor proteins; p53 and pRb. From the IC50 values obtained for both SiHa and HeLa cell lines, the baicalein-rich fraction was the most potent com- pound compared to cisplatin and the methanol crude extract of O. indicum. After 24 hours treatment period, western blot analysis showed that MCE- and BRF-treated SiHa and HeLa cells exhibited anti-HPV effects by down-regulating the expression of E6 and E7 which explain the induction of apoptosis through the up-regulation of p53 and pRb. The overall data suggested that baicalein-rich fraction from O. indicum has anti-proliferative activity and strongly induced apoptosis in treated cervical cancer cell lines via E6 and E7 repression. Therefore, baicalein isolated from O. indicum can be further exploited as a potential anti-cancer candidate for cervical cancer treatment.