Antisense inhibition of cyclin D1 expression is equivalent to flavopiridol for radiosensitization of zebrafish embryos.
OBJECTIVE
Flavopiridol, a small molecule pan-cyclin inhibitor, has been shown to enhance the radiation response of tumor cells both in vitro and in vivo. The clinical utility of flavopiridol, however, is limited by toxicity, previously attributed to pleiotropic inhibitory effects on several targets affecting multiple signal transduction pathways. Here we used zebrafish embryos to investigate radiosensitizing effects of flavopiridol in normal tissues.


METHODS
Zebrafish embryos at the 1- to 4-cell stage were treated with 500 nM flavopiridol or injected with 0.5 pmol antisense hydroxylprolyl-phosphono nucleic acid oligomers to reduce cyclin D1 expression, then subjected to ionizing radiation (IR) or no radiation.


RESULTS
Flavopiridol-treated embryos demonstrated a twofold increase in mortality after exposure to 40 Gy by 96 hpf and developed distinct radiation-induced defects in midline development (designated as the "curly up" phenotype) at higher rates when compared with embryos receiving IR only. Cyclin D1-deficient embryos had virtually identical IR sensitivity profiles when compared with embryos treated with flavopiridol. This was particularly evident for the IR-induced curly up phenotype, which was greatly exacerbated by both flavopriridol and cyclin D1 downregulation.


CONCLUSIONS
Treatment of zebrafish embryos with flavopiridol enhanced radiation sensitivity of zebrafish embryos to a degree that was very similar to that associated with downregulation of cyclin D1 expression. These results are consistent with the hypothesis that inhibition of cyclin D1 is sufficient to account for the radiosensitizing action of flavopiridol in the zebrafish embryo vertebrate model.
McAleer
Mary Frances
MF
Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, PA 19107-5541, USA.
Duffy
Kevin T
KT
Davidson
William R
WR
Kari
Gabor
G
Dicker
Adam P
AP
Rodeck
Ulrich
U
Wickstrom
Eric
E
D000818:Animals; D019938:Cyclin D1 / Q000037:antagonists & inhibitors* / Q000235:genetics; D004307:Dose-Response Relationship, Radiation; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000528:radiation effects*; D005419:Flavonoids / Q000494:pharmacology*; D023421:Models, Animal; D009838:Oligodeoxyribonucleotides / Q000494:pharmacology*; D010641:Phenotype; D010880:Piperidines / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D016019:Survival Analysis; D015027:Zebrafish / Q000196:embryology*
D005419:Flavonoids; D009838:Oligodeoxyribonucleotides; D010880:Piperidines; D011838:Radiation-Sensitizing Agents; C505966:hydroxyprolyl-phospho peptide nucleic acid antisense oligonucleotide; D019938:Cyclin D1; C077990:alvocidib