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The upregulation of the HER2 oncogene is associated with a variety of human cancers and is associated with poor prognosis. Baicalein is reported to have anti-tumor activity, but the molecular mechanism of this effect in HER2-positive cancer cells has not been studied. In this study, our data showed that baicalein can inhibit the proliferation and transformation potential of ovarian cancer cells overexpressing HER2. Baicalein treatment caused a dose-dependent inhibition of HER2 gene expression at the transcriptional level. Baicalein acted on ovarian cancer cells overexpressing HER2 to downregulate the PI3K/Akt signaling pathway downstream of HER2 and inhibit the expression or activity of downstream targets, such as VEGF and cyclin D1 and MMP2. Oral administration of baicalein supplemented with a pharmaceutical excipient significantly inhibited the growth of HER2-overexpressing ovarian SKOV-3 cancer xenografts in mice. These results suggest that downregulation of HER2 gene expression by baicalein at the transcriptional level contributes to inhibit the in vitro and in vivo proliferation and HER2-mediated malignant transformation of HER2-overexpressing ovarian cancer cells., (© 2023 Wiley Periodicals LLC.)

The availability of adequate cancer stem cells or cancer stem-like cell (CSC) is important in cancer study. From ovarian cancer cell lines, SKOV3 and OVCAR3, we induced peritoneal ascites tumors in immunodeficient mice. Among the cells (SKOV3.PX1 and OVCAR3.PX1) from those tumors, we sorted both CD44 and CD133 positive cells (SKOV3.PX1_133+44+, OVCAR3.PX1_133+44+), which manifest the characteristics of self-renewal, multi-lineage differentiation, chemoresistance and tumorigenicity, those of cancer stem-like cells (CSLC). Intraperitoneal transplantation of these CD44 and CD133 positive cells resulted in poorer survival in the engrafted animals. Clinically, increased CD133 expression was found in moderately and poorly differentiated (grade II and III) ovarian serous cystadenocarcinomas. The ascites tumor cells from human ovarian cancers demonstrated more CD133 and CD44 expressions than those from primary ovarian or metastatic tumors and confer tumorigenicity in immunodeficient mice. Compared to their parental cells, the SKOV3.PX1_133+44+ and OVCAR3.PX1_133+44+ cells uniquely expressed 5 CD markers (CD97, CD104, CD107a, CD121a, and CD125). Among these markers, CD97, CD104, CD107a, and CD121a are significantly more expressed in the CD133+ and CD44+ double positive cells of human ovarian ascites tumor cells (Ascites_133+44+) than those from primary ovarian or metastatic tumors. The cancer stem-like cells were enriched from 3% to more than 70% after this manipulation. This intraperitoneal enrichment of cancer stem-like cells, from ovarian cancer cell lines or primary ovarian tumor, potentially provides an adequate amount of ovarian cancer stem-like cells for the ovarian cancer study and possibly benefits cancer therapy.

Overexpression of the HER2 oncogene contributes to tumor cell invasion, metastasis and angiogenesis and correlates with poor prognosis. Magnolol has been reported to exhibit anti-tumor activities. However, the molecular mechanism of action of magnolol has not been investigated in HER2-positive cancer cells. Therefore, we examined the anti-cancer effects of magnolol on HER2-overexpressing ovarian cancer cells. Magnolol treatment caused a dose-dependent inhibition of HER2 gene expression at the transcriptional level, potentially in part through suppression of NF-κB activation. Treatment of HER2-overexpressing ovarian cancer cells with magnolol down-regulated the HER2 downstream PI3K/Akt signaling pathway, and suppressed the expression of downstream target genes, vascular endothelial growth factor (VEGF), matrix metalloproteinase 2 (MMP2) and cyclin D1. Consistently, magnolol-mediated inhibition of MMP2 activity could be prevented by co-treatment with epidermal growth factor. Migration assays revealed that magnolol treatment markedly reduced the motility of HER2-overexpressing ovarian cancer cells. Furthermore, magnolol-induced apoptosis in HER2-overexpressing ovarian cancer cells was characterized by the up-regulation of cleaved poly(ADP-ribose) polymerase (PARP) and activated caspase 3. These findings suggest that magnolol may act against HER2 and its downstream PI3K/Akt/mTOR-signaling network, thus resulting in suppression of HER2-mediated transformation and metastatic potential in HER2-overexpressing ovarian cancers. These results provide a novel mechanism to explain the anti-cancer effect of magnolol., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Interferon-gamma (IFN-gamma) is known to downregulate HER2 oncoprotein (p185(HER2) or briefly p185) in prostate cancer cells. We demonstrate that the IFN-gamma-induced retinoid-inducible gene 1 (RIG1) acts as a transrepressor of p185. Furthermore, we exhibit that RIG1 downregulates the activated (phosphorylated) form of p185 and phosphoinositide-3 kinase (PI3K)/serine/threonine-specific protein kinase (Akt) and the mammalian target of rapamycin (mTOR), downstream substrates of HER2. We also elucidate that heregulin (HRG) specifically restores the activation of p185 and Akt after their activities are reduced by RIG1. Additionally, expression of vascular endothelial growth factor (VEGF) increases through the HER2- and Akt/mTOR-signaling pathways, indicating that VEGF is downregulated by RIG1 within the cell. These findings suggest that RIG1 plays a role in IFN-gamma-mediated therapy by downregulating p185 and its downstream PI3K/Akt/mTOR/VEGF-signaling pathway. These results may provide a new therapeutic mechanism for the clinical use of IFN-gamma and RIG1.