Phosphatidylcholine-specific phospholipase C inhibition reduces HER2-overexpression, cell proliferation andin vivotumor growth in a highly tumorigenic ovarian cancer model

Abstract

Antagonizing the oncogenic effects of human epidermal growth factor receptor 2 (HER2) with current anti-HER2 agents has not yet yielded major progress in the treatment of advanced HER2-positive epithelial ovarian cancer (EOC). Using preclinical models to explore alternative molecular mechanisms affecting HER2 overexpression and oncogenicity may lead to new strategies for EOC patient treatment. We previously reported that phosphatidylcholine-specific phospholipase C (PC-PLC) exerts a pivotal role in regulating HER2 overexpression in breast cancer cells. The present study, conducted on two human HER2-overexpressing EOC cell lines - SKOV3 and its in vivo-passaged SKOV3.ip cell variant characterized by enhanced in vivo tumorigenicity - and on SKOV3.ip xenografts implanted in SCID mice, showed: a) about 2-fold higher PC-PLC and HER2 protein expression levels in SKOV3.ip compared to SKOV3 cells; b) physical association of PC-PLC with HER2 in non-raft domains; c) HER2 internalization and ca. 50% reduction of HER2 mRNA and protein expression levels in SKOV3.ip cells exposed to the PC-PLC inhibitor tricyclodecan-9-yl-potassium xanthate (D609); d) differential effects of D609 and trastuzumab on HER2 protein expression and cell proliferation; e) decreased in vivo tumor growth in SKOV3.ip xenografts during in vivo treatment with D609; f) potential use of in vivo magnetic resonance spectroscopy (MRS) and imaging (MRI) parameters as biomarkers of EOC response to PC-PLC inhibition. Overall, these findings support the view that PC-PLC inhibition may represent an effective means to target the tumorigenic effects of HER2 overexpression in EOC and that in vivo MR approaches can efficiently monitor its effects.

Integration of MRI and MRS approaches to monitor molecular imaging and metabolomic effects of trabectedin on a preclinical ovarian cancer model

“…In a previous work on the same experimental model we reported that cisplatin induced cytostatic effects associated with a metabolic shift of cancer cells towards accumulation of MRS‐detected neutral lipids, whereas the tCho profile failed to be perturbed in either cultured cells or xenografts . On the other hand, the inhibition of PC‐plc by tricyclodecan‐9‐yl‐potassium xanthate induced a reduction of cell proliferation and in vivo tumor growth in SKOV3.ip xenografts . The tumor growth arrest was associated with an about 50% reduction of HER2 mRNA and protein expression levels, as well as with a drop in the intracellular PCho content in SKOV3.ip cells.…”

“…In vivo MRI technologies, including diffusion‐weighted MRI (DWI) and localized MRS, have been successfully applied by our group, shortly after the in vivo administration of either conventional or innovative drugs, for the identification of their induced functional changes and metabolic alterations in preclinical models, and even in the presence of tumor growth inhibition rather than tumor shrinkage . Clinical DWI applications also showed encouraging results in the imaging of a variety of gynecological cancer lesions …”

“…On the other hand, our previous investigations based on the use of high resolution MRS (HR‐MRS) allowed us to identify some peculiar metabolic changes that take place in tumors, such as an altered profile of phosphatidylcholine (PC) metabolites in EOC cells and tissues . Furthermore, the observed increase in the activity of enzymes involved in PC metabolism, such as choline kinase and PC‐specific phospholipase C (PC‐plc), suggested their potential exploitation as new targets for therapy …”

“…Compared with the parental cell line, SKOV3.ip cells are characterized by a more aggressive phenotype, including faster in vivo tumor growth and increased overexpression of human epidermal growth factor receptor‐2 (HER2+++). These features, along with the already known EGFR++, HER3+/−, HER4+/−, p53‐null and PTEN+/− profile typical of the SKOV3 cells, are associated with a low responsiveness of SKOV3.ip cells to cisplatin …”

Discovery of novel PC‐PLC activity inhibitors

“…Inhibition PC‐PLC activity was associated with progressive decreases of mesenchymal traits in breast cancer cells (Abalsamo et al, ). PC‐PLC inhibition could also reduce proliferation of epithelial ovarian cancer cells and in vivo tumor growth in a highly tumorigenic ovarian cancer model (Paris et al, ). In addition, inhibition PC‐PLC interferes with proliferation, invasion, and glycolysis in U87MG glioma cells (Mercurio et al, ).…”