ATR and cancer: With the inhibition of DNA damage response (DDR) kinase ATR through VE-821, a regulator of the recombination carried out by RPA, chromosome destabilization, and cell death occurred in ALT-positive cancer cells; it should be noted, however, that ATRX knockdown did not induce cells to be hypersensitive to the serine/threonine protein kinase ATR treatment (59).