BLM and melanoma: To set high measures for the cytotoxicity tests, we expressed ChR2(D156A) in the human melanoma cell line BLM,13 as melanoma is renowned for its resistance apoptosis.14 To avoid cellular stress as a consequence of permanent ChR2(D156A) expression and potential activation by daylight, we generated a doxycycline-inducible transgenic TetOn-BLM cell line in the text referred to as the ChR2(D156A)-YFP BLM cell line.