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.

(1) Background: Globally, about 600 million people are afflicted with diabetes, and one of its most prevalent complications is neuropathy, a debilitating condition. At present, the exploration of novel therapies for alleviating diabetic neuropathy-associated pain is genuinely captivating, considering that current therapeutic options are characterized by poor efficacy and significant risk of side effects. In the current research, we evaluated the antihyperalgesic effect of sildenafil (phosphodiesterase-5 inhibitor) – metformin (antihyperglycemic agent) combination and its impact on biochemical markers in alloxan-induced diabetic neuropathy in rats; (2) Methods: The study comprised a cohort of 70 diabetic rats and 10 non-diabetic rats which were submitted to hot, cold, and tactile stimulus tests. Morover, we investigated the influence of this combination on TNF-α, IL-6 nitrites and thiols levels in brain and liver tissues; (3) Results: The results demonstrated that all sildenafil-metformin combinations decreased the pain sensitivity in von Frey test, Hot-plate test and Cold-plate test. Furthermore, alterations in nitrites and thiols concentrations and pro-inflammatory cytokines (specifically TNF-α and IL-6) were noted following a 15-day regimen of various sildenafil-metformin combinations. (4) Conclusions: The combination of sildenafil and metformin has a synergistic effect in alleviating pain in alloxan-induced diabetic neuropathy rats. Additionally, the combination effectively decreased inflammation, inhibited the rise in NOS activity, and provided protection against glutathione depletion.

Background and objectives: Contrast-induced nephropathy (CIN), is an acute renal damage due to contrast agents. This study is conducted to determine the potential diagnostic value of hypoxia-inducible factor 2-alpha (HIF2-α) and to evaluate the renal protective effects of N-acetyl cysteine (NAC) and sildenafil in a rat CIN model. Material/Methods: This randomized, controlled, interventional animal study was conducted on Wistar rats. Totally, rats (n = 36) were randomly assigned to four groups: control (n = 9), CIN group (n = 9), CIN+NAC group (n = 9), and sildenafil (n = 9). The rat model was used to form iohexol-originated CIN. During the modelling, prophylactic treatment was performed at 24th and 48th hours. After 48 hours of the modelling; blood, urine, tissue samples were obtained for biochemical analyses. HIF-2-α levels were measured in renal tissue, serum and urine samples. Renal sections were performed in order for histopathologic and immunohistochemical evaluations. Results: In the CIN model, HIF-2α levels and other biochemical parameters were significantly increased (p < 0.01). Both sildenafil and NAC, efficiently decreased the renal damage due to contrast agents (p < 0.05). Similarly, after treatment with sildenafil and NAC, HIF-2α levels were significantly decreased (p < 0.05). Conclusions: The current study constructs an experimental base for the use of HIF-2α for clinical prevention and treatment of CIN. Several mechanisms may be postulated for the changes in HIF-2α levels. Besides, the increased HIF-2α levels with CIN and decreased HIF-2α levels after treatment may be used for the treatment and follow-up of patients with CIN.