MN58b is a novel anticancer
drug that inhibits
choline kinase, resulting in inhibition of
phosphocholine synthesis. The aim of this work was to develop a noninvasive and robust pharmacodynamic
biomarker for target inhibition and, potentially,
tumor response following
MN58b treatment. Human HT29 (colon) and MDA-MB-231 (
breast) carcinoma cells were examined by
proton (1H) and
phosphorus (31P) magnetic resonance spectroscopy (MRS) before and
after treatment with
MN58b both in culture and in xenografts. An in vitro time course study of
MN58b treatment was also carried out in MDA-MB-231 cells. In addition, enzymatic assays of
choline kinase activity in cells were done. A decrease in
phosphocholine and total
choline levels (P < 0.05) was observed in vitro in both cell lines after
MN58b treatment, whereas the inactive analogue ACG20b had no effect. In MDA-MB-231 cells,
phosphocholine fell significantly as early as 4 hours following
MN58b treatment, whereas a drop in cell number was observed at 48 hours. Significant correlation was also found between
phosphocholine levels (measured by MRS) and
choline kinase activities (r2 = 0.95, P = 0.0008) following
MN58b treatment. Phosphomonoesters also decreased significantly (P < 0.05) in both HT29 and MDA-MB-231 xenografts with no significant changes in controls. 31P-MRS and 1H-MRS of
tumor extracts showed a significant decrease in
phosphocholine (P < or = 0.05). Inhibition of
choline kinase by
MN58b resulted in altered
phospholipid metabolism both in cultured tumor cells and in vivo.
Phosphocholine levels were found to correlate with
choline kinase activities. The decrease in
phosphocholine, total
choline, and phosphomonoesters may have potential as noninvasive pharmacodynamic
biomarkers for determining
tumor response following treatment with
choline kinase inhibitors.