The cyclin-dependent kinase inhibitor flavopiridol potentiates γ-irradiation-induced apoptosis in colon and gastric cancer cells Journal Article

Authors: Jung, C.; Motwani, M.; Kortmansky, J.; Sirotnak, F. M.; She, Y.; Gonen, M.; Haimovitz-Friedman, A.; Schwartz, G. K.
Article Title: The cyclin-dependent kinase inhibitor flavopiridol potentiates γ-irradiation-induced apoptosis in colon and gastric cancer cells
Abstract: Purpose: Flavopiridol is a cyclin-dependent kinase inhibitor currently under development by the National Cancer Institute both as a single agent and in combination with chemotherapy. There have been numerous reports that flavopiridol potently enhances the induction of apoptosis by chemotherapy. However, the effect of flavopiridol on radiotherapy (RT)-induced apoptosis has been largely untested. RT has become the cornerstone of adjuvant treatment of colorectal and gastric cancer. In view of this, we elected to evaluate the effect of flavopiridol on potentiating RT-induced apoptosis in the human colon cancer cell line HCT-116 and the gastric cancer cell line MKN-74. Experimental Design: The efficacy of combination of γ-irradiation and flavopiridol was tested in vitro in MKN-74 and HCT-116 cells and correlated to changes in p21 expression. HCT-116 cells were also established as tumors in nude mice and treated with γ-irradiation and flavopiridol either as single agents or in sequential combinations such that flavopiridol was either given 7 h before, concomitantly, or 3 and 7 h after γ-irradiation. Results: Flavopiridol significantly enhanced the induction of apoptosis by γ-irradiation in both cell lines as measured by quantitative fluorescent microscopy, caspase-3 activation, poly(ADP-ribose) polymerase cleavage, and cytochrome c release. To achieve the best effect, it was important to expose the tumor cells to γ-irradiation before the flavopiridol. This sequence dependence was confirmed in vivo. When γ-irradiation was administered 7 h before flavopiridol, 42% of the tumor-bearing animals were rendered disease free, compared with no animals treated with either γ-irradiation or flavopiridol alone. Examination of the p21 status of HCT-116 and MKN-74 cells, after treatment with sequential γ-irradiation and flavopiridol, indicated a loss of p21 protein expression. Loss of p21 was mainly due to cleavage by caspases. HCT-116 cells that lack p21 (p21-/-) also exhibited sensitization to γ-irradiation and showed an even greater enhancement of γ-irradiation-induced apoptosis by flavopiridol when compared with the parental HCT-116 cells. Conclusions: These studies indicate that γ-irradiation followed by flavopiridol enhances apoptosis and yields significantly increased tumor regressions and cures that are not achievable with radiation alone. These results indicate that flavopiridol can potently enhance the effect of γ-radiation both in vitro and in vivo and may provide a new means to treat patients with locally advanced gastrointestinal cancers.
Keywords: controlled study; human tissue; protein expression; human cell; sequence analysis; advanced cancer; drug efficacy; drug potentiation; antineoplastic agents; cancer adjuvant therapy; cancer radiotherapy; quantitative assay; animals; mice; cell division; apoptosis; enzyme inhibition; colonic neoplasms; caspase 3; cancer cell culture; drug potency; enzyme activation; in vitro study; tumor cells, cultured; caspases; correlation analysis; statistical significance; mice, nude; enzyme inhibitors; colon cancer; transplantation, heterologous; stomach cancer; gamma irradiation; radiosensitivity; fluorescence microscopy; microscopy, fluorescence; flavonoids; flavopiridol; piperidines; cyclin-dependent kinase inhibitor p21; cyclin-dependent kinases; cyclins; cyclin dependent kinase inhibitor; protein p21; enzyme release; nicotinamide adenine dinucleotide adenosine diphosphate ribosyltransferase; stomach neoplasms; cytochrome c; cytochromes c; poly(adp-ribose) polymerases; dose time effect relation; gamma rays; human; male; priority journal; article
Journal Title: Clinical Cancer Research
Volume: 9
Issue: 16 Pt.1
ISSN: 1078-0432
Publisher: American Association for Cancer Research  
Date Published: 2003-12-01
Start Page: 6052
End Page: 6061
Language: English
PUBMED: 14676132
PROVIDER: scopus
Notes: Export Date: 12 September 2014 -- Source: Scopus