The Biflavonoid Amentoflavone Induces Apoptosis via Suppressing E7 Expression, Cell Cycle Arrest at Sub-G₁Phase, and Mitochondria-Emanated Intrinsic Pathways in Human Cervical Cancer Cells

Abstract

Amentoflavone, a biflavonoid from Selaginella tamariscina, is known to possess several bioactivities such as antitumor, anti-inflammatory, and antifungal effects. However, the mechanism of the anticancer effects of amentoflavone on human cervical cancer cells has not been studied in detail. In this study, we demonstrated that amentoflavone induces apoptosis in SiHa and CaSki cervical cancer cells by suppressing human papillomavirus protein E7 expression. The cyclins and tumor suppressors were modulated by amentoflavone in SiHa and CaSki human cervical cancer cells: cyclin and hyperphosphorylated retinoblastoma (p-pRb) were down-regulated, whereas cyclin-dependent kinase inhibitors and p53 were enhanced. Amentoflavone up-regulated peroxisome proliferator-activated receptor γ (PPARγ) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression levels while inhibiting E7-mediated cyclooxygenase-2 (COX-2)/interleukin-32 (IL-32) expressions were downregulated, and Akt phosphorlylation was decreased in an amentoflavone-induced apoptotic process, suggesting that amentoflavone may be a PPARγ activator. Additionally, the expression of the anti-apoptotic factor Bcl-2 was decreased, whereas that of the well-known apoptotic factor Bax was increased, thereby releasing cytochrome c into cytosol in amentoflavone-treated cervical cancer cells. Furthermore, amentoflavone treatment led to the activation of caspase-3 and -9 and proteolytic cleavage of poly(ADP-ribose) polymerase. The expression level of the extrinsic death receptor Fas (CD95) was not altered by amentoflavone treatment. When these findings are taken together, the biflavonoid amentoflavone activates PPARγ/PTEN expressions and induces apoptosis via suppressing E7 expression, cell cycle arrest at sub-G₁ phase, and mitochondria-emanated intrinsic pathways in SiHa and CaSki human cervical cancer cells. These findings suggest that amentoflavone has potential for development as a therapeutic agent for human cervical cancer.

Amentoflavone Protects against Hydroxyl Radical-induced DNA Damage via Antioxidant Mechanism

“…Thus, ultraviolet radiation was proved to cause several human cancers [22][23], especially skin cancer [24] and breast cancer [22][23][24][25]. In the study, however, amentoflavone was observed to be a treating agent for the carcinogenesis [26][27]. Therefore, it can be induced that the anti-cancer effect of amentoflavone could be partly attributed to its protective effect against DNA oxidative damage and antioxidant mechanism.…”

Unciflavones A–F, six novel flavonoids from Selaginella uncinata (Desv.) Spring

“…It displayed an [M-H] − ion peak at m/z 404.9 and its molecular formula of C 22 (Tables 1 and 2) of 4 also showed 1,2,5-trisubstituted benzene ring and the apigenin skeleton structure, implying compound 4 and compounds 1-3 were classified into same class of compounds. Compounds 1-3 had an α, β-unsaturated ketone group located at C-5″ in their structures, however, the corresponding NMR signals were not observed in compound 4, which was suggested by the reduction of unsaturation.…”

“…Previous phytochemical studies of S. uncinata led to the discovery of flavonoids [15][16][17], biflavonoids [18], chromone glycosides [19], and steroidal saponins [20]. Those compounds have a range of biological activities such as antitumor [21,22], antibacterial [19], antioxidation [23] and anti-anoxic [18,20]. As part of our continuing research program on these plants, chemical investigation of 75% EtOH extracts of S. uncinata was undertaken.…”

Amentoflavone enhances sorafenib-induced apoptosis through extrinsic and intrinsic pathways in sorafenib-resistant hepatocellular carcinoma SK-Hep1 cells in vitro

“…Based on selected published studies, it was hypothesized that restoration of sorafenib-induced apoptosis by sensitizers is critical in overcoming acquired sorafenib resistance in HCC cells. Amentoflavone has been demonstrated to inhibit tumor growth through induction of apoptosis in breast and cervical cancer cells (14,15). However, whether amentoflavone is able to act as a sorafenib sensitizer, which restores sorafenib-induced apoptosis in sorafenib-resistant HCC cells, has not been elucidated.…”

“…Amentoflavone, as a NF-κB signal inhibitor, induces anti-angiogenic and anti-metastatic effects via suppression of NF-κB activation in breast cancer and melanoma cells in vitro and in vivo (11,12). Amentoflavone has also been suggested to induce apoptosis and inhibit Akt phosphorylation in cervical and breast cancer cells (14,15). However, whether amentoflavone, as a sorafenib sensitizer, triggers sorafenib-induced apoptosis in sorafenib-resistant HCC cells remains ambiguous.…”