CTSB and retinoblastoma: That chloroquine, a potent inhibitor of lysosome enzymes, could significantly block RB-induced cell death also remained consistent with evidence supporting the lysosome as a target of RB-mediated cell death,36, 37, 38 including evidence that siRNA knockdown of the lysosome enzyme cathepsin B protected melanoma cells from RB-induced cell death.39 Thus, our data provided an additional mechanistic connection between lysosome integrity and RB-induced cell death.