ABCG2 and neoplasm: Consequently, PDE5 inhibitors were shown to synergize with anthracyclines (e.g., doxorubicin) and other chemotherapeutics by increasing tumor cell sensitization to drug-elicited apoptosis, decreasing drug efflux through ABC transporters (MDRs), and boosting anti-tumor immune response by virtue of their immunomodulatory activity.