Decreased lactate concentration and glycolytic enzyme expression reflect inhibition of mTOR signal transduction pathway in B-cell lymphoma.
The application of kinase inhibitors in cancer treatment is growing rapidly. However, methods for monitoring the effectiveness of the inhibitors are still poorly developed and currently rely mainly on the tracking of changes in the tumor volume, a rather late and relatively insensitive marker of the therapeutic response. In contrast, MRS can detect changes in cell metabolism and has the potential to provide early and patient-specific markers of drug activity. Using human B-cell lymphoma models and MRS, we have demonstrated that the inhibition of the mTOR signaling pathway can be detected in malignant cells in vitro and noninvasively in vivo by the measurement of lactate levels. An mTOR inhibitor, rapamycin, suppressed lactic acid production in lymphoma cell line cultures and also diminished steady-state lactate levels in xenotransplants. The inhibition was time dependent and was first detectable 8 h after drug administration in cell cultures. In xenotransplants, 2 days of rapamycin treatment produced significant changes in lactic acid concentration in the tumor measured in vivo, which were followed by tumor growth arrest and tumor volume regression. The rapamycin-induced changes in lactate production were strongly correlated with the inhibition of expression of hexokinase II, the key enzyme in the glycolytic pathway. These studies suggest that MRS or (18) F-fluorodeoxyglucose positron emission tomography (FDG PET) detection of changes in glucose metabolism may represent effective noninvasive methods for the monitoring of mTOR targeting therapy in lymphomas and other malignancies. Furthermore, the measurement of glucose metabolic inhibition by MRS or FDG PET imaging may also prove to be effective in monitoring the efficacy of other kinase inhibitors given that the rapamycin-sensitive mTOR lies downstream of many oncogenic signaling pathways.
Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA.
Seung-Cheol
SC
Lee
Michal
M
Marzec
Xiaobin
X
Liu
Suzanne
S
Wehrli
Kanchan
K
Kantekure
Puthiyaveettil N
PN
Ragunath
David S
DS
Nelson
Edward J
EJ
Delikatny
Jerry D
JD
Glickson
Mariusz A
MA
Wasik
D000818:Animals; D015536:Down-Regulation / Q000187:drug effects; D006019:Glycolysis / Q000187:drug effects*; D019344:Lactic Acid / Q000378:metabolism*; D016393:Lymphoma, B-Cell / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D051379:Mice; D016513:Mice, SCID; D015398:Signal Transduction / Q000187:drug effects*; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D019344:Lactic Acid; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus