Equivalent effect of DNA damage-induced apoptotic cell death or long-term cell cycle arrest on colon carcinoma cell proliferation and tumour growth

Knowledge of the type of biological reaction to chemotherapy is a prerequisite for its rational enhancement. We previously showed that irinotecan-induced DNA damage triggers in the HCT116p53wt colon carcinoma cell line a long-term cell cycle arrest and in HCT116p53−/− cells apoptosis (Magrini et al., 2002). To compare the contribution of long-term cell cycle arrest and that of apoptosis to inhibition of cell proliferation after irinotecan-induced DNA damage, we used this isogenic system as well as the cell lines LS174T (p53wt) and HT-29 (p53mut). Both p53wt cell lines responded to damage by undergoing a long-term tetraploid G1 arrest, whereas the p53mut cell lines underwent apoptosis. Cell cycle arrest as well as apoptosis caused a similar delay in cell proliferation. Irinotecan treatment also induced in mouse tumours derived from the p53wt cell lines a tetraploid G1 arrest and in those derived from the p53-deficient cell lines a transient G2/M arrest and apoptosis. The delay of tumour growth was in the same range in both groups, that is, arrest- and apoptosis-mediated tumour growth inhibition was comparable. In conclusion, cell cycle arrest as well as apoptosis may be equipotent mechanisms mediating the chemotherapeutic effects of irinotecan.