Data from The Phosphoinositide 3-Kinase Inhibitor PI-103 Downregulates Choline Kinase α Leading to Phosphocholine and Total Choline Decrease Detected by Magnetic Resonance Spectroscopy

The phosphoinositide 3-kinase (PI3K) pathway is a major target for cancer drug development. PI-103 is an isoform-selective class I PI3K and mammalian target of rapamycin inhibitor. The aims of this work were as follows: first, to use magnetic resonance spectroscopy (MRS) to identify and develop a robust pharmacodynamic (PD) biomarker for target inhibition and potentially tumor response following PI3K inhibition; second, to evaluate mechanisms underlying the MRS-detected changes. Treatment of human PTEN null PC3 prostate and PIK3CA mutant HCT116 colon carcinoma cells with PI-103 resulted in a concentration- and time-dependent decrease in phosphocholine (PC) and total choline (tCho) levels (P < 0.05) detected by phosphorus (³¹P)- and proton (¹H)-MRS. In contrast, the cytotoxic microtubule inhibitor docetaxel increased glycerophosphocholine and tCho levels in PC3 cells. PI-103–induced MRS changes were associated with alterations in the protein expression levels of regulatory enzymes involved in lipid metabolism, including choline kinase α (ChoK_α), fatty acid synthase (FAS), and phosphorylated ATP-citrate lyase (pACL). However, a strong correlation (r² = 0.9, P = 0.009) was found only between PC concentrations and ChoK_α expression but not with FAS or pACL. This study identified inhibition of ChoK_α as a major cause of the observed change in PC levels following PI-103 treatment. We also showed the capacity of ¹H-MRS, a clinically well-established technique with higher sensitivity and wider applicability compared with ³¹P-MRS, to assess response to PI-103. Our results show that monitoring the effects of PI3K inhibitors by MRS may provide a noninvasive PD biomarker for PI3K inhibition and potentially of tumor response during early-stage clinical trials with PI3K inhibitors. Cancer Res; 70(13); 5507–17. ©2010 AACR.