The cellular DNA repair systems sufficiently provide the resistance of
tumors to ionizing radiation, and thus contribute to reducing the effectiveness of their
radiotherapy. Therefore, suppression of the activity of critical
DNA repair enzymes in
tumor cells is considered one of the promising directions to overcome this resistance. As can be seen from the literature analysis, the use of many inhibitors of
DNA repair enzymes have not yet yielded the results, which can be extrapolated to preclinical models or clinical trials. However, experimental studies show that the inhibitors of the
enzyme family of
poly(ADP-ribose) polymerases (PARP) are able to inhibit the growth of various human
tumor cells. Pre-clinical and clinical trials of the
PARP inhibitors also show promising results in terms of the possibility of their wide practical application. The effect of the
PARP inhibitors consists in the blockage of the most important DNA repair systems. This leads to the accumulation of
DNA single-strand breaks, the collapse of replication forks and to generation of lethal double-strand breaks (
DSB). The
PARP inhibitors can be used to suppress
breast cancer and
ovarian cancer with mutations in BRCA-1/2 genes ("BRCAness"
cancer) without combination with
radiotherapy or
chemotherapy. In the
tumor cells deficient in BRCA-1/2 genes
DSB repair by homologous recombination pathway does not function. Therefore, the process of
DNA DSB repair is switched to the non-homologous end-joining pathway, which operates with formation of the chromosomal rearrangements leading to cell death. Thus, the analysis results show that DNA repair inhibitors have the potential to improve the efficiency of
cancer radiotherapy. Further research in this direction is very promising.