ИСТИНА

7-Methylguanine (7-MG) is a natural compound which inhibits DNA repair protein poly(ADP-ribose)polymerase 1 (PARP-1) in vitro and thus may be considered as a potential anticancer drug candidate for a combination chemotherapy. We previously demonstrated the ability of 7-MG to suppress the activity of recombinant human PARP-1 using the radiolabeled substrate NAD+ and activated DNA, and here we present in more detail analysis of its inhibitory and anti-proliferative effects. (1) The inhibitory properties of 7-MG against purified PARP-1 were confirmed by a novel fluorescent method for the real-time measurement of the enzyme activity. 7-MG was shown to be a competitive inhibitor of NAD+ binding to the catalytic fragment of PARP-1. (2) The effect on PARP-1 binding to nucleosomes was studied using spFRET microscopy. 7-MG exhibited a minimal effect on the nucleosome structure, but induced PARP-1 trapping in non-productive complexes. (3) 7-MG cytotoxicity was evaluated on human cancer cell lines HCT116 (colorectal carcinoma) and U2OS (osteosarcoma) by measuring Sub-G1 (apoptotic) population of cells with flow cytometry. At the PARP-1 inhibitory concentrations, 7-MG itself was not cytotoxic, but it was able to accelerate apoptotic cell death in combination with cisplatin (a DNA-damaging drug). (4) QSAR-modeling of the ADMET profile of 7-MG was done with ACD/Percepta. The safety of 7-MG was predicted and confirmed by preliminary in vivo tests on mice. Despite the fact that 7-MG is a weaker inhibitor than olaparib and some other PARP inhibitors, this natural compound may possess better pharmacokinetics and an adverse-effect profile compared to synthetic inhibitors and become a promising new constituent of anticancer therapy.