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Preclinical study of treatment response in HCT‐116 cells and xenografts with 1 H‐decoupled 31 P MRS
Author(s) -
Darpolor Moses M.,
Kennealey Peter T.,
Le H. Carl,
Zakian Kristen L.,
Ackerstaff Ellen,
Rizwan Asif,
Chen JinHong,
Sambol Elliot B.,
Schwartz Gary K.,
Singer Samuel,
Koutcher Jason A.
Publication year - 2011
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.1674
Subject(s) - phosphocholine , apoptosis , irinotecan , cell cycle , cancer research , chemistry , kinase , choline , medicine , pharmacology , cancer , biochemistry , colorectal cancer , phospholipid , membrane , phosphatidylcholine
The topoisomerase I inhibitor, irinotecan, and its active metabolite SN‐38 have been shown to induce G 2 /M cell cycle arrest without significant cell death in human colon carcinoma cells (HCT‐116). Subsequent treatment of these G 2 /M‐arrested cells with the cyclin‐dependent kinase inhibitor, flavopiridol, induced these cells to undergo apoptosis. The goal of this study was to develop a noninvasive metabolic biomarker for early tumor response and target inhibition of irinotecan followed by flavopiridol treatment in a longitudinal study. A total of eleven mice bearing HCT‐116 xenografts were separated into two cohorts where one cohort was administered saline and the other treated with a sequential course of irinotecan followed by flavopiridol. Each mouse xenograft was longitudinally monitored with proton ( 1 H)‐decoupled phosphorus ( 31 P) magnetic resonance spectroscopy (MRS) before and after treatment. A statistically significant decrease in phosphocholine ( p = 0.0004 ) and inorganic phosphate ( p = 0.0103 ) levels were observed in HCT‐116 xenografts following treatment, which were evidenced within twenty‐four hours of treatment completion. Also, a significant growth delay was found in treated xenografts. To discern the underlying mechanism for the treatment response of the xenografts, in vitro HCT‐116 cell cultures were investigated with enzymatic assays, cell cycle analysis, and apoptotic assays. Flavopiridol had a direct effect on choline kinase as measured by a 67% reduction in the phosphorylation of choline to phosphocholine. Cells treated with SN‐38 alone underwent 83 ± 5% G 2 /M cell cycle arrest compared to untreated cells. In cells, flavopiridol alone induced 5 ± 1% apoptosis while the sequential treatment (SN‐38 then flavopiridol) resulted in 39 ± 10% apoptosis. In vivo 1 H‐decoupled 31 P MRS indirectly measures choline kinase activity. The decrease in phosphocholine may be a potential indicator of early tumor response to the sequential treatment of irinotecan followed by flavopiridol in noninvasive and/or longitudinal studies. Copyright © 2011 John Wiley & Sons, Ltd.