PFM01 is a cell-permeable N-alkylated Mirin (Sigma Cat. No. 475954) derivative that selectively inhibits against MRE11 endo-, but not exo-, nuclease activity. PFM01 targets MRE11 at a site near the dimer interface, distinct from that occupied by Mirin and PFM39 to allow disruption of the ssDNA-binding groove and selective inhibition against MRE11 endo-, but not exo-, nuclease activity. While both endonuclease and exonuclease activities are required for MRE11-mediated homologous recombination (HR) repair, only FM01 (100 μM), but not the exonuclease inhibitors Mirin (500 μM) and PFM39 (100 μM), rescues G2-phase double-strand break (DSB) repair defect in HR protein BRCA2-deficient HSC62-hTERT fibroblasts following ionizing irradiation (IR) by blocking HR initiation and thereby allowing non-homologous end joining (NHEJ) to proceed.
