Dynamics of cell cycle phase perturbations by trabectedin (ET-743) in nucleotide excision repair (NER)-deficient and NER-proficient cells, unravelled by a novel mathematical simulation approach.
OBJECTIVE
Trabectedin (ET-743, Yondelis) is a natural marine product, with antitumour activity, currently in phase II/III clinical trials. Previous studies have shown that cells hypersensitive to ultraviolet (UV)-rays because of nucleotide excision repair (NER) deficiency, were resistant to trabectedin. The purpose of this study was to investigate whether this resistance was associated with different drug-induced cell cycle perturbations.


METHODS
An isogenic NER-proficient cellular system (CHO-AA8) and a NER-deficient one (CHO-UV-96), lacking functional ERCC-1, were studied. Flow cytometric assays showed progressive accumulation of cells in G2 + M phase in NER-proficient but not in NER-deficient cells. Applying a computer simulation method, we realized that the dynamics of the cell cycle perturbations in all phases were complex.


RESULTS
Cells exposed to trabectedin during G1 and G2 + M first experienced a G1 block, while those exposed in S phase were delayed in S and G2 + M phases but eventually divided. In the presence of functional NER, exit from the G1 block was faster; then, cells progressed slowly through S phase and were subsequently blocked in G2 + M phase. This G2 + M processing of trabectedin-induced damage in NER-proficient cells was unable to restore cell cycling, suggesting a difficulty in repairing the damage.


CONCLUSIONS
This might be due either to important damage left unrepaired by previous G1 repair, or that NER activity itself caused DNA damage, or both. We speculate that in UV-96 cells repair mechanisms other than NER are activated both in G1 and G2 + M phases.
Tavecchio
M
M
Department of Oncology, Flow Cytometry Unit, Istituto di Richerche Farmacologiche Marco Negri, Milan, Italy.
Natoli
C
C
Ubezio
P
P
Erba
E
E
D'Incalci
M
M
D000818:Animals; D001973:Bromodeoxyuridine / Q000378:metabolism; D016466:CHO Cells; D002452:Cell Count; D002453:Cell Cycle / Q000187:drug effects*; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D003114:Colony-Forming Units Assay; D003198:Computer Simulation; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000096:biosynthesis; D004260:DNA Repair; D004149:Dioxoles / Q000494:pharmacology*; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects; D016195:G2 Phase / Q000187:drug effects; D008954:Models, Biological; D016196:S Phase / Q000187:drug effects; D044005:Tetrahydroisoquinolines / Q000494:pharmacology*; D000077606:Trabectedin
D004149:Dioxoles; D044005:Tetrahydroisoquinolines; D004247:DNA; D001973:Bromodeoxyuridine; D000077606:Trabectedin