Fascaplysin exhibits cytotoxicity against chemoresistant SCLC cell lines via several contributing pathways comprising, among others, generation of ROS and cellular mechanisms affecting topoisomerase I-activity and activation of PARP, possibly linked to its interaction with DNA in absence of a functional CDK4-RB1 axis in SCLC cell lines. The gene discussed is CDK4; the disease is small cell lung carcinoma.