Lovastatin causes sensitization of HeLa cells to ionizing radiation‐induced apoptosis by the abrogation of G2 blockage

Abstract

PURPOSE: To investigate the effect of inhibition of Ras/Rho-regulated signalling by 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) on radiation-induced cell killing and apoptosis. MATERIALS AND METHODS: Different human cell lines were pretreated or not with lovastatin before exposure to gamma-rays. Afterwards, radiation-induced cell killing, formation and repair of double-strand breaks, activation of radiation-inducible signal mechanisms (i.e. p53, p21, extracellular-signal-related kinase (ERK), NF-kappaB), changes in cell cycle progression and apoptosis were analysed. RESULTS: As shown by a colony formation assay, lovastatin sensitized HeLa cells to gamma-radiation-induced cell killing. The lovastatin effect was cell-type specific. Neither the level of gamma-ray-induced double-strand breaks nor its repair were affected by lovastatin. Sensitization was independent of p53/p21Waf1- and NF-kappaB-related mechanisms. Radiation-stimulated activation of ERKs was attenuated by lovastatin. Cell cycle analyses revealed that the level of gamma-ray-induced G2 blockage was not affected by lovastatin. However, as analysed up to 72 h after irradiation, lovastatin pretreated cells showed an accelerated abrogation of G2 blockage as compared with the control. G2 abrogation is paralleled by an increase in the frequency of apoptotic and necrotic cells. CONCLUSIONS: The data show that lovastatin can render human cells more sensitive to the cytotoxic effect of gamma-rays. This is related to abrogation of G2 blockage and a concomitant increase in apoptotic/necrotic cell death.