Combined effects of carbon ion radiation and PARP inhibitor on non-small cell lung carcinoma cells: Insights into DNA repair pathways and cell death mechanisms.

The utilization of high linear energy transfer (LET) carbon ion (C-ion) in radiotherapy has witnessed a notable rise in managing highly metastatic, recurrent, and chemo/radio-resistant human cancers. Non-small cell lung cancer (NSCLC) presents a formidable challenge due to its chemo-resistance and aggressive nature, resulting in poor prognosis and survival rates. In a previous study, we demonstrated that the combination of C-ion with the poly (ADP-ribose) polymerase (PARP) inhibitor (PARPi) olaparib significantly mitigated metastasis in A549 cells. Here, we delve into the underlying rationale behind the combined action of olaparib with C-ion, focusing on DNA repair pathways and cell death mechanisms in asynchronous NSCLC A549 cells following single and combined treatments. Evaluation included analysis of colony-forming ability, DNA damage assessed by γH2AX foci, expression profiling of key proteins involved in Homologous Recombination (HR) and Non-Homologous End Joining (NHEJ) repair pathways, caspase-3 activation, apoptotic body formation, and autophagic cell death. Our findings reveal that both PARPi olaparib and rucaparib sensitize A549 cells to C-ion exposure, with olaparib exhibiting superior sensitization. Moreover, C-ion exposure alone significantly downregulates both HR and NHEJ repair pathways by reducing the expression of MRE11--RAD51 and Ku70-Ku80 protein complexes at 24 h post-treatment. Notably, the combination of olaparib pre-treatment with C-ion markedly inhibits both HR and NHEJ pathways, culminating in DNA damage-induced apoptotic and autophagic cell death. Thus we are the first to demonstrate that olaparib sensitizes NSCLC cells to carbon ion by interfering with HR and NHEJ pathway. These insights underscore the promising therapeutic potential of combining PARP inhibition with carbon ion exposure for effective NSCLC management.