Magnetic resonance spectroscopic pharmacodynamic markers of the heat shock protein 90 inhibitor 17-allylamino,17-demethoxygeldanamycin (17AAG) in human colon cancer models

Background. 17-Allylamino,17-demethoxygeldanamycin (17AAG) is a novel anticancer drug that inhibits heat shock protein 90 (Hsp90), resulting in proteasomal degradation of several oncogenic proteins. We used phosphorus magnetic resonance spectroscopy (P-31-MRS) to determine whether 17AAG treatment leads to alterations in phospholipids that could serve as pharmacodynamic markers for tumor response to 17AAG. Methods: HCT116, HT29, and SW620 colon cancer cells were treated with 17AAG, and extracts were examined by P-31-MRS. HT29 cells were also treated with the active metabolite of 17AAG, 17-amino,17-demethoxygeldanamycin (17AG), or the inactive 17AAG analog NSC683666. MF-1 nude mice carrying HT29 xenografts were examined using in vivo P-31-MRS before and after 17AAG treatment; xenograft. 3 tumor extracts were examined by P-31-MRS and proton MRS (H-1-MRS). Hsp90 client protein expression was determined by using western blots. Two-tailed t tests were used to compare metabolite concentrations and ratios, and a Mann-Whitney U test was used to compare proportions. All statistical tests were two-sided. Results: 17AAG treatment led to statistically significantly increased phosphocholine levels in all three cell lines (P =.02). 17AG treatment also increased phosphocholine levels in HT29 cells, whereas NSC683666 had no effect. The phosphomonoester/phosphodiester ratio was statistically significantly increased in the HT29 xenografts after 17AAG treatment relative to the pretreatment ratio (P =.02), whereas no statistically significant change was observed after vehicle treatment (P =.62). Statistically significant increases in phosphocholine, phosphoethanolamine, and valine levels were also observed in tumor extracts treated with 17AAG. Conclusions: Inhibition of Hsp90 by 17AAG resulted in altered phospholipid metabolism in cultured tumor cells and in tumor xenografts. The increases observed in phosphocholine and phosphomonoester levels suggest that these metabolites may have the potential to act as noninvasive pharmacodynamic markers for analyzing tumor response to treatment with 17AAG or other Hsp90 inhibitors.