Labelled PAC-1 is a caspase 3 activator. Caspase activation is a key strategy in cancer therapy. Caspase 3 is a key executioner caspase and direct effector of apoptosis. Hallmark of many cancers is the circumvention of signal in the activation of executioner caspases and loss of apoptotic response. EC50 for caspase 3 activation = 0.33 μM and caspase 7= 4.5 μM. The IC50 for apoptosis induction = 0.92 μM. Elevated caspase 3 level in cancerous cell lines and tissues allows PAC-1 to selectively induce apoptosis in tissues.