It has been found by the present inventors that agents that boost the expression of the opioid receptor kappa 1 (OPRK1) can enhance the cytotoxicity of chemotherapeutic agents in multiple cancer cell lines. Furthermore, the effect is dose dependent, where the greater the induced expression of OPRK1, the greater the cytotoxicity of the chemotherapeutic agent. The increase in overall cytotoxicity is independent of the cytotoxicity of the agent that increases the expression of OPRK1, which itself has no or minimal cytotoxic effect.
