Metabolic Imaging of Targeted Therapies in Cancer
PROJECT SUMMARY/ABSTRACT
Given the paradigm shift in cancer therapy including the ever-growing increase in the use of targeted
therapies, foremost small-molecule kinase inhibitors in cancer therapy, there is an urgent need to develop
reliable imaging techniques to detect and monitor the efficacy of such inhibitors in cancer patients. Because
direct evaluation of cell signaling is practically not feasible and changes in tumor volume occur late after
treatment initiation given the predominantly cytostatic effect of the inhibitors, we are proposing an alternative
approach to monitor changes in tumor metabolism induced by kinase inhibition. This will be achieved in three
stages: 1) analysis of gene expression/proteomic/phosphoproteomic to identify metabolic pathways perturbed
by inhibition of the signaling pathway performed both in vitro and in vivo in the mouse xenotransplant models
using patient derived cultured and primary cells (PDX), 2) metabolomic and metabolic fluxomic analysis of
effect of kinase inhibition on metabolic pathways, also done in in vitro and in vivo settings, 3) analysis of
biomarkers of inhibitor response validated by the above “-omics” studies by imaging techniques, preferably
non-invasive, such as 1H MRS or chemical exchange saturation-transfer (CEST) with standard FDG PET
imaging serving as control. In these proof-of-principle studies, we will focus on mTOR, the serine/threonine
kinase hyperactive in the majority of cancer types, and employ direct and indirect inhibitors of mTOR,
rapamycin/rapalog and Torin2, respectively, as index kinase/kinase inhibitor system. We will use diffuse large
B-cell lymphoma (DLBCL) as experimental cancer model. In preliminary studies, we have demonstrated that
rapamycin decreased concentrations of lactic acid in patient-derived lymphoma cell lines, both cultured in vitro
and xenotransplanted into mice, as detected by unique 1H MRS imaging-based detection pulse sequences
developed by us and our collaborators. The rapamycin-induced decrease in glycolytic metabolism correlated
with and, importantly, markedly preceded inhibition of tumor cell growth, strongly supporting the notion that
image-based evaluation of the key metabolic response is predictive of biological tumor cell response to the
inhibition. The response also correlated with and, hence, was at least in part attributable to decreased
expression of hexokinase II, other glycolytic enzymes and enzymes from other key metabolic pathways
including phosphoribosyl-amidotransferase and other enzymes involved in glutaminolysis. Utilizing 13C MRS
and 13C LC-MS, we have confirmed mTOR control of glycolysis and also noted decreases in fatty acid and
sterol metabolism as well as inhibition of the pentose phosphate shunt and the TCA cycle. We anticipate that
the proposed studies will extend our knowledge of the impact of mTOR inhibition on malignant cell metabolism
and, ultimately, set the stage for future clinical evaluation of MRS or other imaging method(s) for monitoring
response to inhibitors of mTOR and other cell-signaling kinases in DLBCL and other types of cancer.