Metabolite changes in HT-29 xenograft tumors following HIF-1α inhibition with PX-478 as studied by MR spectroscopy in vivo and ex vivo

The hypoxia-inducible transcription factor (HIF- 1α) plays a central role in tumor development. PX-478 is an experimental anti-cancer drug known to inhibit HIF- 1α i experimental tumors. The purpose of this study was to identify MRS-visible metabolic biomarkers for PX-478 response prior to phase I/II clinical trials. Single-voxel in vivo localized ¹H spectra were obtained from HT-29 tumor xenografts prior and up to 24 h after treatment with a single dose of PX-478. Profiles of water-soluble and lipophilic metabolites were also examined ex vivo with both ¹H and ³¹P spectroscopy for peak identification and to interrogate the underlying biochemistry of the response. The total choline (tCho) resonance was significantly decreased in vivo 12 and 24 h following treatment with PX-478 and this was confirmed with high-resolution ¹H and ³¹P MRS. In non-aqueous extracts, significant reductions in cardiolipin, PtdEtn (phosphatidylethanolamine) and PtdI (phosphatidylinositol) were seen in response to PX-478. Although there were trends to a decrease in lactate (and lipid) resonances in vivo and ex vivo, these changes were not significant. This is in contrast to inhibition of in vitro glucose consumption and lactate production by PX-478 in HT-29 cells. The significant and robust change in tCho has identified this as a potential ¹H MRS-visible biomarker for drug response in vivo while high-resolution spectroscopy indicated that GPC, PC, myol, PE, GPE, CL, PtdEtn and PtdI are potential ex vivo response biomarkers.