Cell cycle checkpoint evasion and protracted cell cycle arrest in X-irradiated small-cell lung carcinoma cells.
OBJECTIVE
To determine the longevity and dose-dependence of acute X-irradiation-induced cell cycle perturbations in a panel of seven small-cell lung carcinoma (SCLC) cell lines (COR-L32B, COR-L51B, COR-L88B, COR-L96C, COR-L103, COR-L266B, COR-L279), assessed for TP53 tumour suppressor gene status and showing characteristically long population doubling periods.


METHODS
Cell lines were screened for abnormalities in TP53. Cell cycle arrest and nuclear fragmentation were determined by flow cytometry under culture conditions that minimized the propensity of SCLC cells to form multicellular aggregates. A faster growing SCLC cell line (NCI-H69) and two breast tumour cell lines were used as controls.


RESULTS
NCI-H69 and five of the COR-SCLC cell lines showed clear evidence of TP53 abnormalities and the cycle arrest responses of the breast tumour cell lines established the effects of TP53 mutation on G1/S checkpoint loss. All SCLC lines, at 24 h after low dose irradiation, showed abrogation of the G1/S checkpoint together with a range of expression of a protracted G2/M delay. G2/M delay progressed in all panel cell lines up to 48 h post-irradiation while NCI-H69 showed significant recovery for the dose range 75-600cGy. Only NCI-H69 and one panel line showed dose-dependent progression to complete nuclear DNA fragmentation.


CONCLUSIONS
The culture method permits the measurement of cell cycle effects that reflect the TP53 status of SCLC cells. G1/S checkpoint failure, long-term radiation-induced G2 arrest, highly muted apoptotic responses and delayed recovery appear to be typical responses of the recently derived COR-SCLC lines. The results imply that low levels of unrepaired DNA damage, induced at clinically relevant doses, can persist for days in SCLC cells with long cell cycle traverse times, and can remain capable of checkpoint activation with implications for S phase-targeted therapies.
Smith
P J
PJ
Department of Pathology, University of Wales College of Medicine, Health Park, Cardiff, UK. smithpj2@cf.ac.uk
Wiltshire
M
M
Chin
S F
SF
Rabbitts
P
P
Souès
S
S
D017209:Apoptosis; D018288:Carcinoma, Small Cell / Q000473:pathology / Q000532:radiotherapy*; D002453:Cell Cycle / Q000528:radiation effects; D004249:DNA Damage; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000032:analysis
D016159:Tumor Suppressor Protein p53