Phosphatidylcholine metabolic transformation and progression signature as a pharmacodynamic biomarker

Studies of Secondary Melanoma on C57BL/6J Mouse Liver Using 1H NMR Metabolomics

NMR metabolomics, consisting of solid state high resolution magic angle spinning (HR-MAS) ¹H-NMR, liquid state high resolution ¹H-NMR, and principal components analysis (PCA) has been used to study secondary metastatic B16-F10 melanoma in C57BL/6J mouse liver. The melanoma group can be differentiated from its control group by PCA analysis of the estimates of absolute concentrations from liquid state ¹H-NMR spectra on liver tissue extracts or by the estimates of absolute peak intensities of metabolites from ¹H HR-MAS-NMR data on intact liver tissues. In particular, we found that the estimates of absolute concentrations of glutamate, creatine, fumarate and cholesterol are elevated in the melanoma group as compared to controls, while the estimates of absolute concentrations of succinate, glycine, glucose, and the family of linear lipids including long chain fatty acids, total choline and acyl glycerol are decreased. The ratio of glycerophosphocholine (GPC) to phosphocholine (PCho) is increased by about 1.5 fold in the melanoma group, while the estimate of absolute concentration of total choline is actually lower in melanoma mice. These results suggest the following picture in secondary melanoma metastasis: Linear lipid levels are decreased by beta oxidation in the melanoma group, which contributes to an increase in the synthesis of cholesterol, and also provides an energy source input for TCA cycle. These findings suggest a link between lipid oxidation, the TCA cycle and the hypoxia-inducible factors (HIF) signal pathway in tumor metastases. Thus, this study indicates that the metabolic profile derived from NMR analysis can provide a valuable bio-signature of malignancy and cell hypoxia in metastatic melanoma.

Histone deacetylase inhibition increases levels of choline kinase α and phosphocholine facilitating noninvasive imaging in human cancers

Histone deacetylase (HDAC) inhibitors are currently approved for cutaneous T-cell lymphoma and are in mid-late stage trials for other cancers. The HDAC inhibitors LAQ824 and SAHA increase phosphocholine (PC) levels in human colon cancer cells and tumor xenografts as observed by magnetic resonance spectroscopy (MRS). In this study, we show that belinostat, an HDAC inhibitor with an alternative chemical scaffold, also caused a rise in cellular PC content that was detectable by (1)H and (31)P MRS in prostate and colon carcinoma cells. In addition, (1)H MRS showed an increase in branched chain amino acid and alanine concentrations. (13)C-choline labeling indicated that the rise in PC resulted from increased de novo synthesis and correlated with an induction of choline kinase α expression. Furthermore, metabolic labeling experiments with (13)C-glucose showed that differential glucose routing favored alanine formation at the expense of lactate production. Additional analysis revealed increases in the choline/water and phosphomonoester (including PC)/total phosphate ratios in vivo. Together, our findings provide mechanistic insights into the impact of HDAC inhibition on cancer cell metabolism and highlight PC as a candidate noninvasive imaging biomarker for monitoring the action of HDAC inhibitors.