Molecular causes of the aberrant phosphatidylcholine metabolism in human epithelial ovarian cancer

The introduction of magnetic resonance spectroscopy (MRS) in cancer biology allowed the detection of abnormal profiles of aqueous choline-containing metabolites of the phosphatidylcholine (PtdCho) cycle in cancer cells and tissues at preclinical and clinical level. This evidence supported the inclusion of an aberrant phospholipid metabolism as a novel candidate hallmark for cancer. In the present study we measured the concentrations of PtdCho metabolites, and the activities of phosphocholine (PCho)-producing enzymes in human ovary carcinoma cell (EOC) lines compared with normal or immortalized ovary epithelial cells (EONT). Quantification of PtdCho metabolites contributing to the so called 1H-NMR “total choline” resonance (tCho, 3.20-3.24 ppm) showed that the levels of 2.6  0.3 and 5.4  0.6 nmol/106cells for [PCho] and [tCho] respectively, whereas average [PCho] was 3- to 8-fold higher in EOC cells (P<0.0001), becoming the predominant tCho component. Enzymatic assays and protein and mRNA expression analyses demonstrated that the most relevant changes in EOC cells compared with EONT were: 1) 12- to 25-fold of choline kinase (ChoK) activation, associated with a 3-fold higher protein content and an increased isoform alpha (ChoK) (but not beta isoform, ChoK) mRNA expression levels; 2) 5- to 17-fold activation of PtdCho–specific phospholipase C (PtdCho-PLC), consistent with higher protein expression. In view of the predominant role of the ChoK isoform in steering the overall ChoK activity, we specifically silenced the CHKA gene expression by transient RNA interference in two human EOC cell lines and evaluated the main effects induced on the reduction of cell proliferation, migration and concomitant changes of the tCho profile. On the other hand, pharmacological inhibition of PtdCho-PLC induced a 30-to-40% reduction of PCho content and blocked the in vitro cell proliferation in two EOC cell lines and their in vivo tumor growth in immunodeficient SCID mice. Our findings, confirmed a major role of ChoK and PtdCho-PLC enzymes in the deregulated choline metabolism of EOC cells and suggested these enzymes as promising targets for anticancer treatment. The overall body of the here presented data may help to elucidate novel aspects of EOC biology and provide a rational basis for further developing clinical non-invasive imaging methods suitable for ovary cancer diagnosis and follow-up.