Abstract
Histone deacetylase (HDAC) inhibitors have emerged as effective antineoplastic agents in the clinic. Studies from our lab and others have reported that magnetic resonance spectroscopy (MRS)-detectable phosphocholine (PC) is elevated following SAHA treatment, providing a potential noninvasive biomarker of response. Typically, elevated PC is associated with cancer while a decrease in PC accompanies response to antineoplastic treatment. The goal of this study was therefore to elucidate the underlying biochemical mechanism by which HDAC inhibition leads to elevated PC. We investigated the effect of SAHA on MCF-7 breast cancer cells using (13)C MRS to monitor [1,2-(13)C] choline uptake and phosphorylation to PC. We found that PC synthesis was significantly higher in treated cells, representing 154±19% of control. This was within standard deviation of the increase in total PC levels detected by (31)P MRS (129±7% of control). Furthermore, cellular choline kinase activity was elevated (177±31%), while cytidylyltransferase activity was unchanged. Expression of the intermediate-affinity choline transporter SLC44A1 and choline kinase α increased (144% and 161%, respectively) relative to control, as determined by mRNA microarray analysis with protein-level confirmation by Western blotting. Taken together, our findings indicate that the increase in PC levels following SAHA treatment results from its elevated synthesis. Additionally, the concentration of glycerophosphocholine (GPC) increased significantly with treatment to 210±45%. This is likely due to the upregulated expression of several phospholipase A2 (PLA2) isoforms, resulting in increased PLA2 activity (162±18%) in SAHA-treated cells. Importantly, the levels of total choline (tCho)-containing metabolites, comprised of choline, PC and GPC, are readily detectable clinically using (1)H MRS. Our findings thus provide an important step in validating clinically translatable non-invasive imaging methods for follow-up diagnostics of HDAC inhibitor treatment.