Frankincense and myrrh have been widely used in cancer treatment. However, its antitumor ability, especially in cancer progression has not been reported. In this study, we demonstrate that FM inhibited the invasion and metastasis in HCC cells. Moreover, we observed that FM-suppressed cancer progression was mediated by EMT. Finally, we clearly confirmed that FM inhibits the Wnt/β-catenin signaling pathway of EMT in HCC. Our findings show a novel antitumor/mechanism of this ancient herbal extract, which may provide a potential strategy for the clinical treatment of cancer.
The water extract of frankincense and myrrh have shown preliminary ability to inhibit cancer in vitro or in vivo studies. Peng Ren reported that frankincense could suppress tumor progress via regulating the AMPK/mTOR pathway[13]. Mengxue Sun also found that myrrh inhibits the proliferation and migration of cancer cells through the regulation of cyclooxygenase-2 expression[14]. Moreover, the Xihuang pill, mainly composed of frankincense and myrrh, has been applied for cancer therapy for more than 300 years[15]. In order to clarify the role of FM in tumor invasion and metastasis, the concentration of FM used in our study was non-toxic as 0.5mg/ml. Furthermore, by wound-healing and transwell assay, we found that FM markedly reduced the migration and invasion abilities of HCC cells. However, how FM suppresses the invasion and metastasis of HCC via the Wnt/β-catenin signaling of EMT is unclear.
Epithelial-mesenchymal transition (EMT) was primarily mediated by a set of core EMT transcription factors (EMT-TFs), including the Snail family, the E-box bound Zinc Finger Proteins (Zeb) family, and the Twist family[16]. In tumor cells, EMT was activated, EMT-TFS and downstream regulated genes influence a large number of stages in cancer progression, including caner development and metastasis[17]. As a member of the Snail family, snail1 overexpression is usually negatively correlated with E-cadherin expression, and positively correlated with tumor cell migration, invasion and enhancement of metastasis, which also predicts a worse prognosis[18].
Similar to snali1, slug is also a major inducer of EMT and an important mediator of Twist-induced EMT and tumor metastasis[19]. As a member of the Twist family, Twist1 is a key factor inducing Vimentin expression, which is also associated with poor prognosis and high metastasis rate[20]. The Zeb family consists of Zeb1 and Zeb2, which have similar functions and lead to the increased proliferation and malignancy via inhibiting E-cadherin[21]. In our study, we provided evidence that FM decreased the expression of mesenchymal markers (N-cadherin and Vimentin) and EMT-activating transcription factors (Snail, Slug, Twist1 and ZEB1) while increasing the expression of the epithelial marker E-cadherin.
The Wnt/β-catenin signaling is reported to promote the migration and invasion of cancer cells by mediating EMT mechanism[22]. Moreover, the Dishevelled protein(DVL) is critical for protecting the degradation of β-catenin in Wnt signaling, where the interaction of DVL and β-catenin promotes the transcription of Wnt signaling[23, 24]. Consistent with our assumptions, our study showed that FM could suppress the DVL2 nuclear translocation as well as its protein level, suggesting that instability of DVL2 play an important role in regulating the Wnt/β-catenin signaling pathway. Nevertheless, the detailed mechanisms deserve further intensive investigation.