Deficiency of Bloom syndrome helicase activity is radiomimetic.

Bloom syndrome is caused by homozygous mutations in BLM, which encodes a RecQ DNA helicase. Patient-derived cells deficient in BLM helicase activity exhibit genetic instability-apparent cytogenetically as sister chromatid exchanges-and activated DNA damage signaling. In this report, we show that BLM-knockout colorectal cancer cells exhibited endogenous, ATM-dependent double-strand DNA break responses similar to those recently observed in Bloom syndrome patient-derived cells. Xenograft tumors established from BLM-deficient cancer cells were not radiosensitive, but exhibited growth impairment that was comparable to that of wild type tumors treated with a single, high dose of ionizing radiation. These results suggest that pharmacological inhibitors of BLM would have a radiomimetic effect and that transient inhibition of BLM activity might be a viable strategy for anticancer therapy.