PDE5 inhibitors enhance the lethality of [pemetrexed + sorafenib]

Advancements in Phosphodiesterase 5 Inhibitors: Unveiling Present and Future Perspectives

Phosphodiesterase 5 (PDE5) inhibitors presented themselves as important players in the nitric oxide/cGMP pathway, thus exerting a profound impact on various physiological and pathological processes. Beyond their well-known efficacy in treating male erectile dysfunction (ED) and pulmonary arterial hypertension (PAH), a plethora of studies have unveiled their significance in the treatment of a myriad of other diseases, including cognitive functions, heart failure, multiple drug resistance in cancer therapy, immune diseases, systemic sclerosis and others. This comprehensive review aims to provide an updated assessment of the crucial role played by PDE5 inhibitors (PDE5-Is) as disease-modifying agents taking their limiting side effects into consideration. From a medicinal chemistry and drug discovery perspective, the published PDE5-Is over the last 10 years and their binding characteristics are systemically discussed, and advancement in properties is exposed. A persistent challenge encountered with these agents lies in their limited isozyme selectivity; considering this obstacle, this review also highlights the breakthrough development of the recently reported PDE5 allosteric inhibitors, which exhibit an unparalleled level of selectivity that was rarely achievable by competitive inhibitors. The implications and potential impact of these novel allosteric inhibitors are meticulously explored. Additionally, the concept of multi-targeted ligands is critically evaluated in relation to PDE5-Is by inspecting the broader spectrum of their molecular interactions and effects. The objective of this review is to provide insight into the design of potent, selective PDE5-Is and an overview of their biological function, limitations, challenges, therapeutic potentials, undergoing clinical trials, future prospects and emerging uses, thus guiding upcoming endeavors in both academia and industry within this domain.

How do phosphodiesterase-5 inhibitors affect cancer? A focus on glioblastoma multiforme

Since the discovery of phosphodiesterase-5 (PDE5) enzyme overexpression in the central nervous system (CNS) malignancies, investigations have explored the potential capacity of current PDE5 inhibitor drugs for repositioning in the treatment of brain tumors, notably glioblastoma multiforme (GBM). It has now been recognized that these drugs increase brain tumors permeability and enhance standard chemotherapeutics effectiveness. More importantly, studies have highlighted the promising antitumor functions of PDE5 inhibitors, e.g., triggering apoptosis, suppressing tumor cell growth and invasion, and reversing tumor microenvironment (TME) immunosuppression in the brain. However, contradictory reports have suggested a pro-oncogenic role for neuronal cyclic guanosine monophosphate (cGMP), indicating the beneficial function of PDE5 in the brain of GBM patients. Unfortunately, due to the inconsistent preclinical findings, only a few clinical trials are evaluating the therapeutic value of PDE5 inhibitors in GBM treatment. Accordingly, additional studies should be conducted to shed light on the precise effect of PDE5 inhibitors in GBM biology regarding the existing molecular heterogeneities among individuals. Here, we highlighted and discussed the previously investigated mechanisms underlying the impacts of PDE5 inhibitors in cancers, focusing on GBM to provide an overview of current knowledge necessary for future studies.

Sildenafil in Combination Therapy against Cancer: A Literature Review

The concepts of drug repurposing and Sildenafil or blue pill are tightly linked over the years. Indeed, in addition to its initial clinical application as an anti-hypertensive drug in the pulmonary system, Sildenafil is also known for its beneficial effects in erectile dysfunction. Moreover, evidence has been accumulated to support its value in anti-cancer therapy, either alone or in combination with other clinically efficient chemotherapy drugs. In this review, we focused on the old and recent in vitro and in vivo studies demonstrating the cellular and molecular rationale for the application of Sildenafil in combination therapy in various types of cancer. We emphasized on the different molecular targets as well as the different signaling pathways involved in cancer cells. The pro-apoptotic effect of Sildenafil through nitric oxide (NO)/ phosphodiesterase type 5 (PDE5)-dependent manner seems to be one of the most common mechanisms. However, the activation of autophagy, as well as the modulation of the anti-tumor immunity, constitutes the other pathways triggered by Sildenafil. Overall, the studies converged to reveal the complexity of the anti-cancer potential of Sildenafil. Thus, through our review, we aimed to present an updated and simplified picture of such repurposing of Sildenafil in the field of oncology.

Targeting cyclic nucleotide phosphodiesterase 5 (PDE5) in brain: Toward the development of a PET radioligand labeled with fluorine-18

With the aim to develop a specific radioligand for imaging the cyclic nucleotide phosphodiesterase 5 (PDE5) in brain by positron emission tomography (PET), seven new fluorinated inhibitors (3-9) were synthesized on the basis of a quinoline core. The inhibitory activity for PDE5 together with a panel of other PDEs was determined in vitro and two derivatives were selected for IC₅₀ value determination. The most promising compound 7 (IC₅₀ = 5.92 nM for PDE5A), containing a 3-fluoroazetidine moiety, was further radiolabeled by aliphatic nucleophilic substitution of two different leaving groups (nosylate and tosylate) using [¹⁸F]fluoride. The use of the nosylate precursor and tetra-n-butyl ammonium [¹⁸F]fluoride ([¹⁸F]TBAF) in 3-methyl-3-pentanol combined with the addition of a small amount of water proved to be the best radiolabeling conditions achieving a RCY of 4.9 ± 1.5% in an automated procedure. Preliminary biological investigations in vitro and in vivo were performed to characterize this new PDE5 radioligand. Metabolism studies of [¹⁸F]7 in mice revealed a fast metabolic degradation with the formation of radiometabolites which have been detected in the brain.

The progression of HMGB1-induced autophagy in cancer biology

Autophagy is an important process of cellular degradation and has been proven to contribute to tumorigenesis. High-mobility group box 1 (HMGB1) is an abundant nonhistone protein that has been widely reported to play a central role in the induction of autophagy. In nucleus, HMGB1 upregulates the expression of HSP27 to induce autophagy. In cytoplasm, the Beclin-1/PI3K-III complex can be activated by HMGB1 to promote autophagy. Extracellular HMGB1 binds to the receptor for advanced glycation end products to induce autophagy. Recent studies have shown that HMGB1-induced autophagy exerts multiple functions in various cancers like proliferation. Moreover, inhibition of HMGB1-induced autophagy can reverse chemoresistance, which is regulated by noncoding RNAs such as microRNAs and lncRNAs. Here, we provide a brief introduction to HMGB1 and HMGB1-induced autophagy in cancer. We also discuss the challenges associated with performing further investigations on this issue. HMGB1-induced autophagy exerts significant functions in cancer and has potential utility for new strategy to reverse drug resistance.

[pemetrexed + sildenafil], via autophagy-dependent HDAC downregulation, enhances the immunotherapy response of NSCLC cells

Pemetrexed is an approved therapeutic in NSCLC and ovarian cancer. Our studies focused on the ability of [pemetrexed + sildenafil] exposure to alter the immunogenicity of lung and ovarian cancer cells. Treatment of lung and ovarian cancer cells with [pemetrexed + sildenafil] in vitro rapidly reduced the expression of PD-L1, PD-L2 and ornithine decarboxylase (ODC), and increased the expression of class I MHCA. In a cell-specific fashion, some cells also released the immunogenic nuclear protein HMGB1 into the extracellular environment. [Pemetrexed + sildenafil] reduced the expression of multiple histone deacetylases that was blocked by knock down of autophagy regulatory proteins. [Pemetrexed + sildenafil] lethality was enhanced by the histone deacetylase inhibitors AR42 and sodium valproate; AR42 and valproate as single agents also rapidly reduced the expression of PD-L1, PD-L2 and ODC, and increased expression of MHCA and CerS6. Nitric oxide and CerS6 signaling was required for drug-induced death receptor activation and tumor cell killing. In vivo, [pemetrexed + sildenafil] lethality against lung cancer cells was enhanced by sodium valproate. Using syngeneic mouse lung cancer cells [pemetrexed + sildenafil] enhanced the anti-tumor effects of antibodies directed to inhibit PD-1 or CTLA4. [Pemetrexed + sildenafil] interacted with the anti-PD-1 antibody to strongly enhance tumor infiltration by M1 macrophages; activated NK cells and activated T cells. Our data demonstrate that treatment of tumor cells with [pemetrexed + sildenafil] results in tumor cell killing and via autophagy-dependent downregulation of HDACs, it opsonizes the remaining tumor cells to anti-tumor immunotherapy antibodies.

Repurposing drugs in oncology (ReDO)-selective PDE5 inhibitors as anti-cancer agents

Selective phosphodiesterase 5 inhibitors, including sildenafil, tadalafil and vardenafil, are widely-used in the treatment of erectile dysfunction and pulmonary arterial hypertension. They are also well-known as examples of successful drug repurposing in that they were initially developed for angina and only later developed for erectile dysfunction. However, these drugs may also be effective cancer treatments. A range of evidentiary sources are assessed in this paper and the case made that there is pre-clinical and clinical evidence that these drugs may offer clinical benefit in a range of cancers. In particular, evidence is presented that these drugs have potent immunomodulatory activity that warrants clinical study in combination with check-point inhibition.

HDAC inhibitors enhance neratinib activity and when combined enhance the actions of an anti-PD-1 immunomodulatory antibody in vivo

Patients whose NSCLC tumors become afatinib resistant presently have few effective therapeutic options to extend their survival. Afatinib resistant NSCLC cells were sensitive to clinically relevant concentrations of the irreversible pan-HER inhibitor neratinib, but not by the first generation ERBB1/2/4 inhibitor lapatinib. In multiple afatinib resistant NSCLC clones, HDAC inhibitors reduced the expression of ERBB1/3/4, but activated c-SRC, which resulted in higher total levels of ERBB1/3 phosphorylation. Neratinib also rapidly reduced the expression of ERBB1/2/3/4, c-MET and of mutant K-/N-RAS; K-RAS co-localized with phosphorylated ATG13 and with cathepsin B in vesicles. Combined exposure of cells to [neratinib + HDAC inhibitors] caused inactivation of mTORC1 and mTORC2, enhanced autophagosome and subsequently autolysosome formation, and caused an additive to greater than additive induction of cell death. Knock down of Beclin1 or ATG5 prevented HDAC inhibitors or neratinib from reducing ERBB1/3/4 and K-/N-RAS expression and reduced [neratinib + HDAC inhibitor] lethality. Neratinib and HDAC inhibitors reduced the expression of multiple HDAC proteins via autophagy that was causal in the reduced expression of PD-L1, PD-L2 and ornithine decarboxylase, and increased expression of Class I MHCA. In vivo, neratinib and HDAC inhibitors interacted to suppress the growth of 4T1 mammary tumors, an effect that was enhanced by an anti-PD-1 antibody. Our data support the premises that neratinib lethality can be enhanced by HDAC inhibitors, that neratinib may be a useful therapeutic tool in afatinib resistant NSCLC, and that [neratinib + HDAC inhibitor] exposure facilitates anti-tumor immune responses.

Synergistic activity of sorafenib and betulinic acid against clonogenic activity of non-small cell lung cancer cells

The highly selective multi‐targeted agent sorafenib is an inhibitor of a number of intracellular signaling kinases with anti‐proliferative, anti‐angiogenic and pro‐apoptotic effects in various types of tumors, including human non‐small cell lung cancer (NSCLC). Betulin displays a broad spectrum of biological and pharmacological properties, including anticancer and chemopreventive activity. Combination of drugs with different targets is a logical approach to overcome multilevel cross‐stimulation among key signaling pathways in NSCLC progression. NSCLC cell lines, A549, H358 and A427, with different KRAS mutations, and normal human peripheral blood lymphocyte cells, were treated with sorafenib and betulinic acid alone and in combination. We examined the effect of different combined treatments on viability (MTS test), proliferation and apoptotic susceptibility based on flow cytometry, alterations in signaling pathways by western blotting and colony‐forming ability. The combination of sorafenib with betulinic acid had a strong effect on the induction of apoptosis of different NSCLC cell lines. In addition, this combination was not toxic for human peripheral blood lymphocytes. Combination treatment changed the expression of proteins involved in the mitochondrial apoptosis pathway and induced apoptotic death by caspase activation. Importantly, combination treatment with low drug concentrations tremendously reduced the colony‐forming ability of A549, H358 and A427 cells, as compared to both compounds alone. In this study, we showed that combination therapy with low concentrations of sorafenib and betulinic acid had the capacity to induce high levels of cell death and abolish clonogenic activity in some NSCLC cell lines regardless of KRAS mutations.

NEDD4 over-expression regulates the afatinib resistant phenotype of NSCLC cells

We focused on defining the role of the E3 ligase NEDD4 in NSCLC cell afatinib resistance. Afatinib resistant H1975 clones over-expressed NEDD4 and c-MET compared to control clones and expressed less ERBB1, ERBB3, ERBB4 and PTEN than control clones. Knock down of NEDD4 enhanced the expression of PTEN, ERBB1/3/4 and c-MET. This was also associated with a ∼3-fold enhancement in both mTOR expression and mTOR phosphorylation and a ∼4-fold elevation in phospho-ULK-1 S757 levels. In the absence of NEDD4 or the autophagy regulatory protein Beclin1, neither the drug combination of [pemetrexed + sildenafil] nor the HDAC inhibitor sodium valproate was as capable of: reducing the expression of ERBB1/3/4; reducing phosphorylation of ULK-1 S757; or at enhancing the phosphorylation of ULK-1 S317 and ATG13 S318. [Pemetrexed + sildenafil] exposure, via autophagic degradation, reduced the expression of multiple HDACs. Reduced expression of Class I HDACs lowered the expression of ERBB1/3/4 and PTEN. Treatment of afatinib resistant clones lacking NEDD4 with [pemetrexed + sildenafil] or sodium valproate resulted in a weaker induction of autophagosome and autolysosome formation and with reduced cell killing. Knock down of NEDD4 reduced [pemetrexed + sildenafil] lethality; knock down of PTEN enhanced drug-induced killing. Combined knock down of NEDD4 and PTEN reduced the elevated amount of killing caused by PTEN knock down alone back to basal levels. Collectively, our data argue that NEDD4 plays an essential role in maintaining the afatinib-resistant phenotype in our resistant H1975 clones.