ATR and Miyoshi myopathy: To investigate the functional significance of STAT3 inactivation on the survival of MM cells exposed to ATR inhibitors, U266 cells were transfected with a vector expressing constitutively active STAT3 (FLAG-labeled CA-STAT3) [21], and subsequently exposed (48 h) to ATR inhibitors (BAY, AZD, VE), after which viability was determined by the Cell-Titer Glo bioluminescence assay.