Aminomethylmorpholino Nucleosides as Novel Inhibitors of PARP1 and PARP2: Experimental and Molecular Modeling Analyses of Their Selectivity and Mechanism of Action

Poly(ADP-ribose) polymerases 1 and 2 (PARP1 and PARP2) play a key role in DNA repair. As major sensors of DNA damage, they are activated to produce poly(ADP-ribose). PARP1/PARP2 inhibitors have emerged as effective drugs for the treatment of cancers with BRCA deficiencies. Here, we explored aminomethylmorpholino and aminomethylmorpholino glycine nucleosides as inhibitors of PARP1 and PARP2, using different enzymatic assays. The compounds bearing thymine or 5-Br(I)-uracil bases displayed the highest inhibition potency, with all of them being more selective toward PARP1. Interaction of the inhibitors with the NAD⁺ binding cavity of PARP1 (PARP2) suggested by the mixed-type inhibition was demonstrated by molecular docking and the RoseTTAFold All-Atom AI-model. The best PARP1 inhibitors characterized by the inhibition constants in the range of 12-15 µM potentiate the cytotoxicity of hydrogen peroxide by displaying strong synergism. The inhibitors revealed no impact on PARP1/PARP2 affinity for DNA, while they reduced the dissociation rate of the enzyme-DNA complex upon the autopoly(ADP-ribosyl)ation reaction, thus providing evidence that their mechanism of action for PARP trapping is due primarily to catalytic inhibition. The most active compounds were shown to retain selectivity toward PARP1, despite the reduced inhibition potency in the presence of histone PARylation factor 1 (HPF1) capable of regulating PARP1/PARP2 catalytic activity and ADP-ribosylation reaction specificity. The inhibitors obtained seem to be promising for further research as potential drugs.