Bloom (BLM) helicase is a DNA unwinding enzyme important for DNA repair in the homologous recombination pathway. Mutations of the BLM gene result in reduced BLM helicase activity that is associated with the rare genetic disorder, Bloom’s Syndrome, and a predisposition to developing cancer. ML-216 is the first identified small molecule inhibitor of BLM helicase (IC50 = 1.8 μM) that is 28-fold selective against the related helicases RECQ1, RECQ5, and E. coli UvrD (IC50s ≥ 50 μM). At 25-50 μM, ML-216 has been shown to dose-dependently inhibit the proliferation of BLM-expressing PSNF5 fibroblast cells but not BLM-deficient PSNG13 fibroblast cells.
Bloom (BLM) helicase is a DNA unwinding enzyme important for DNA repair in the homologous recombination pathway. Mutations of the BLM gene result in reduced BLM helicase activity that is associated with the rare genetic disorder, Bloom’s Syndrome, and a predisposition to developing cancer. ML-216 is the first identified small molecule inhibitor of BLM helicase (IC50 = 1.8 μM) that is 28-fold selective against the related helicases RECQ1, RECQ5, and E. coli UvrD (IC50s ≥ 50 μM). At 25-50 μM, ML-216 has been shown to dose-dependently inhibit the proliferation of BLM-expressing PSNF5 fibroblast cells but not BLM-deficient PSNG13 fibroblast cells.[Cayman Chemical]
ML216 has been used in cell proliferation assays.
ChEBI: 1-[4-fluoro-3-(trifluoromethyl)phenyl]-3-(5-pyridin-4-yl-1,3,4-thiadiazol-2-yl)urea is a member of ureas.
ML216 is a membrane permeable selective inhibitor of Bloom (BLM) helicase, a member of the RecQ DNA helicase family. Bloom′s syndrome, caused by a mutation in BLM, is associated with susceptibility to cancer, growth retardation, immunodeficiency, sunlight sensitivity, and fertility defects. ML216 is selective for BLM over other members of the RecQ family, especially in vivo, and appears to act at the BLM-nucleic acid substrate binding site, inhibiting DNA binding and blocking BLM′s helicase activity. ML216 could be useful in studies of tumor cells depending on the ALT (alternative lengthening of telomeres) mechanism for telomere maintenance rather than on telomerase, which are proposed to be susceptible to BLM inhibition.
Although ML216 inhibits unwinding by the sequence-related BLM and WRN helicases similarly in vitro, the apparent dependence on BLM for ML216 to exert its biological effects in human cells suggests BLM specificity for the drug’s mechanism of action in vivo. A co-crystal structure of BLM in complex with inhibitor would be informative. Cellular cues in vivo may induce a specific conformation of WRN that makes it resistant to ML216[2].
[1] GIANG HUONG NGUYEN. A small molecule inhibitor of the BLM helicase modulates chromosome stability in human cells.[J]. Chemistry & biology, 2013, 20 1: 55-62. DOI:
10.1016/j.chembiol.2012.10.016
