The Potential Role of Sildenafil in CancerManagement Through EPR Augmentation

Abstract

Enhanced permeation retention (EPR) was a significant milestone discovery by Maeda et al. paving the road for the emerging nanomedicine as a powerful tool in the fight against cancer. Sildenafil is a potent inhibitor of phosphodiesterase 5 (PDE-5) used for treatment of erectile dysfunction (ED) through the relaxation of smooth muscles and the modulation of vascular endothelial permeability. Overexpression of PDE-5 was reported in lung, colon, metastatic breast cancers and bladder squamous carcinoma. Accordingly, there has been a growing interest in using sildenafil as monotherapy or chemoadjuvant in EPR augmentation and management of different types of cancer. Sildenafil had been reported to increase the sensitivity of tumor cells of different origins to the cytotoxic effect of chemotherapeutic agents with augmented apoptosis mediated through inducing the expression of Bad and Bax proapoptotic proteins. It was also reported that the use of sildenafil prior to the administration of Doxorubicin (DOX) increased its EPR-related concentration in breast cancer tissues by 2 folds. Further, a substantial reason of anticancer chemotherapeutic failure is due to multidrug resistance (MDR), exacerbated by the overexpression of ATP-binding cassette (ABC) transporters such as ABCB1 and ABCCs. Sildenafil has demonstrated inhibitory effects on the efflux activity of ABCC4, ABCC5, ABCB1, and ABCG2, ultimately reversing MDR caused by these transporters. In this review, we critically examine the overall potential of sildenafil in enhancing EPR-based anticancer drug delivery pointing up the outcome of the most important related preclinical and clinical studies.