title: Preclinical study of treatment response in HCT-116 cells and xenografts with (1) H-decoupled (31) P MRS.
abstract: 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.
authors: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA.
authors: Moses M
authors: MM
authors: Darpolor
authors: Peter T
authors: PT
authors: Kennealey
authors: H Carl
authors: HC
authors: Le
authors: Kristen L
authors: KL
authors: Zakian
authors: Ellen
authors: E
authors: Ackerstaff
authors: Asif
authors: A
authors: Rizwan
authors: Jin-Hong
authors: JH
authors: Chen
authors: Elliot B
authors: EB
authors: Sambol
authors: Gary K
authors: GK
authors: Schwartz
authors: Samuel
authors: S
authors: Singer
authors: Jason A
authors: JA
authors: Koutcher
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D002453:Cell Cycle / Q000187:drug effects; D002797:Choline Kinase / Q000302:isolation & purification / Q000378:metabolism; D019916:Choline-Phosphate Cytidylyltransferase / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000188:drug therapy*; D005260:Female; D005419:Flavonoids / Q000494:pharmacology / Q000627:therapeutic use; D045325:HCT116 Cells; D006801:Humans; D000077146:Irinotecan; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D051379:Mice; D010759:Phosphorus Isotopes; D010880:Piperidines / Q000494:pharmacology / Q000627:therapeutic use; D011522:Protons; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology; D016896:Treatment Outcome; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D005419:Flavonoids; D010759:Phosphorus Isotopes; D010880:Piperidines; D011522:Protons; C077990:alvocidib; D000077146:Irinotecan; D002797:Choline Kinase; D019916:Choline-Phosphate Cytidylyltransferase; D002166:Camptothecin