Platinum drugs are among the most effective anticancer agents, but their mode of action is still not fully understood. We therefore carried out a systematic investigation on the cellular activities of cisplatin, carboplatin and oxaliplatin in A498 kidney cancer cells. Cytotoxicity was higher for cisplatin and oxaliplatin compared to carboplatin, with induction of apoptosis as the preferred mode of cell death. Gene expression profiling displayed modulation of genes related to DNA damage response/repair, cell cycle regulation and apoptosis which was more pronounced upon oxaliplatin treatment. Furthermore, repression of specific DNA repair genes was restricted to oxaliplatin. Transcriptional level observations were further analyzed on the functional level. Uptake studies revealed low intracellular platinum accumulation and DNA platination upon carboplatin treatment. Removal of overall DNA platination was comparable for the three drugs. However, no processing of oxaliplatin-induced interstrand crosslinks was observed. Cisplatin and carboplatin influenced cell cycle distribution comparably, while oxaliplatin had no effect. Altogether, we found a similar mode of action for cisplatin and carboplatin, while the activity of oxaliplatin appeared to differ. This might be clinically relevant as due to the difference in mode of action oxaliplatin could be active in tumors which show resistance towards cisplatin and carboplatin.

No abstract

PARP1 and p53 are key players in maintaining genomic stability, but their interplay is still not fully understood. We investigated the impact of PARP1 knockout on the DNA damage response after ionizing radiation (IR) by comparing a U2OS-based PARP1-knockout cell line, established by using the genome-editing system CRISPR/Cas9, with its wild-type counterpart. We intended to gain more insight into the impact of PARP1 on the transcriptional level under basal conditions, after low dose (1 Gy) and high dose (10 Gy) DNA damage induced by IR, aiming to reveal the potential connections between the involved pathways. In the absence of additionally induced DNA damage, lacking PARP1 led to an increased up-regulation of CDKN1A (p21), which caused a G1 arrest and slightly diminished cell proliferation. While a small but comparable transcriptional DNA damage response was observed upon 1 Gy IR in both cell lines, a pronounced transcriptional induction of p53 target genes was evident after treatment with 10 Gy IR exclusively in PARP1-proficient cells, suggesting that PARP1 facilitates the p53 signaling response after IR. Additionally, PARP1 appeared to be required for the ATM-dependent activation of PLK3, which in turn activates p53, leading to its transcriptional damage response. Our results support the involvement of PARP1 activation among the first steps in IR-induced DNA damage response.