Testosterone deficiency in men with end stage renal disease and kidney transplantation: a narrative review

Testosterone deficiency is a prevalent condition that frequently affects individuals with end-stage renal disease (ESRD) and those who have undergone renal transplantation. While the etiology of this condition is complex, its implications in this population are far-reaching, impacting various domains such as endocrine profile, sexual and erectile function, bone mineral density (BMD), anemia, and graft survival following renal transplantation. Herein, we review the most recent literature exploring the pathophysiology of testosterone deficiency in ESRD and renal transplant patients, examining its diverse effects on this demographic, and assessing the advantages of testosterone replacement therapy (TRT). Existing evidence suggests that TRT is a safe intervention in ESRD and renal transplant patients, demonstrating improvements across multiple domains. Despite valuable insights from numerous studies, a critical need persists for larger, high-quality prospective studies to comprehensively grasp the nuances of TRT, especially in this vulnerable population. Proactive screening and treatment of testosterone deficiency may prove beneficial, emphasizing the urgency for further research in this area.

Surgical management of extravaginal testicular torsion in a 16-year-old male: a case report

Extravaginal torsion (EVT) is a rare type of testicular torsion that usually occurs in neonates. The primary type of testicular torsion that occurs in adolescents is intravaginal torsion (IVT). In this case report, we describe the first case of EVT reported in a 16-year-old male with a contralateral bell clapper deformity and subsequent surgical management using a tunica vaginalis flap (TVF) and bilateral orchiopexy. In discussion of this case, we examine possible anatomical causes of EVT and suggestions for appropriate surgical management.

Non-cutaneous presentation of mycosis fungoides involving the penile corpora: Case report and review of current literature

Mycosis fungoides involvement of genitalia is rare. We present a 63-year-old man with history of cutaneous T cell lymphoma with large cell transformation status post multiple electron beam radiation cycles who presented with a new, enlarging penile mass. He underwent ultrasound, MRI, and excisional biopsy. Pathological results indicated hematogenous spread of T cell lymphoma with large cell transformation. Peri-operative radiation was performed, and the patient had significant reduction in penile mass size but some subsequent erectile dysfunction. In discussion of this case, we examine management of penile mycosis fungoides.

The use of low-intensity extracorporeal shockwave therapy in management of erectile dysfunction following prostate cancer treatment: a review of the current literature

Background and Objective

Erectile dysfunction (ED) is a prevalent and impactful complication post definitive management of prostate cancer. The mechanism of ED is thought to be secondary to vascular and neural injury as well as corporal smooth muscle damage with resultant fibrosis. The use of penile rehabilitation in ED following treatment for prostate cancer has been studied. Low-intensity extracorporeal shockwave therapy (Li-ESWT) is a novel treatment for ED thought to stimulate neovascularization and nerve regeneration, and as such, has gained interest in treatment of ED related to radical prostatectomy or radiation therapy. Herein, we performed a narrative review on the use of Li-ESWT in management of ED following treatment for prostate cancer.

Methods

A literature review was performed using PubMed and Google Scholar. Studies evaluating Li-ESWT following prostate cancer treatment were included.

Key Content and Findings

We identified three randomized controlled trials and two observational studies that assessed use of Li-ESWT for ED after prostate surgery. Use of Li-ESWT across most studies showed improvements in the International Index of Erectile Function-erectile function (IIEF-EF) domain scores, but this improvement was not statistically significant. Additionally, use of Li-ESWT in an early versus delayed fashion does not appear to affect changes in long-term sexual function scores. No data on use of Li-ESWT after radiotherapy were identified.

Conclusions

There is a paucity of data regarding use of Li-ESWT for penile rehabilitation in treatment of ED post-prostate cancer therapy. Current protocols for Li-ESWT are not standardized and have a limited number of participants with short duration of follow-up. Additional evaluation is needed to determine optimal Li-ESWT protocols. Ideally, studies should have longer follow-up to truly evaluate the clinical significance of Li-ESWT in the treatment of post-prostatectomy ED. Furthermore, the role of Li-ESWT after radiotherapy remains elusive.

Deciphering the Molecular Mechanism of HCV Protease Inhibitor Fluorination as a General Approach to Avoid Drug Resistance

Third generation Hepatitis C virus (HCV) NS3/4A protease inhibitors (PIs), glecaprevir and voxilaprevir, are highly effective across genotypes and against many resistant variants. Unlike earlier PIs, these compounds have fluorine substitutions on the P2-P4 macrocycle and P1 moieties. Fluorination has long been used in medicinal chemistry as a strategy to improve physicochemical properties and potency. However, the molecular basis by which fluorination improves potency and resistance profile of HCV NS3/4A PIs is not well understood. To systematically analyze the contribution of fluorine substitutions to inhibitor potency and resistance profile, we used a multi-disciplinary approach involving inhibitor design and synthesis, enzyme inhibition assays, co-crystallography, and structural analysis. A panel of inhibitors in matched pairs were designed with and without P4 cap fluorination, tested against WT protease and the D168A resistant variant, and a total of 22 high-resolution co-crystal structures were determined. While fluorination did not significantly improve potency against the WT protease, PIs with fluorinated P4 caps retained much better potency against the D168A protease variant. Detailed analysis of the co-crystal structures revealed that PIs with fluorinated P4 caps can sample alternate binding conformations that enable adapting to structural changes induced by the D168A substitution. Our results elucidate molecular mechanisms of fluorine-specific inhibitor interactions that can be leveraged in avoiding drug resistance.

Discovery of Quinoxaline-Based P1-P3 Macrocyclic NS3/4A Protease Inhibitors with Potent Activity against Drug-Resistant Hepatitis C Virus Variants

The three pan-genotypic HCV NS3/4A protease inhibitors (PIs) currently in clinical use-grazoprevir, glecaprevir, and voxilaprevir-are quinoxaline-based P2-P4 macrocycles and thus exhibit similar resistance profiles. Using our quinoxaline-based P1-P3 macrocyclic lead compounds as an alternative chemical scaffold, we explored structure-activity relationships (SARs) at the P2 and P4 positions to develop pan-genotypic PIs that avoid drug resistance. A structure-guided strategy was used to design and synthesize two series of compounds with different P2 quinoxalines in combination with diverse P4 groups of varying sizes and shapes, with and without fluorine substitutions. Our SAR data and cocrystal structures revealed the interplay between the P2 and P4 groups, which influenced inhibitor binding and the overall resistance profile. Optimizing inhibitor interactions in the S4 pocket led to PIs with excellent antiviral activity against clinically relevant PI-resistant HCV variants and genotype 3, providing potential pan-genotypic inhibitors with improved resistance profiles.

Drug Design Strategies to Avoid Resistance in Direct-Acting Antivirals and Beyond

Drug resistance is prevalent across many diseases, rendering therapies ineffective with severe financial and health consequences. Rather than accepting resistance after the fact, proactive strategies need to be incorporated into the drug design and development process to minimize the impact of drug resistance. These strategies can be derived from our experience with viral disease targets where multiple generations of drugs had to be developed to combat resistance and avoid antiviral failure. Significant efforts including experimental and computational structural biology, medicinal chemistry, and machine learning have focused on understanding the mechanisms and structural basis of resistance against direct-acting antiviral (DAA) drugs. Integrated methods show promise for being predictive of resistance and potency. In this review, we give an overview of this research for human immunodeficiency virus type 1, hepatitis C virus, and influenza virus and the lessons learned from resistance mechanisms of DAAs. These lessons translate into rational strategies to avoid resistance in drug design, which can be generalized and applied beyond viral targets. While resistance may not be completely avoidable, rational drug design can and should incorporate strategies at the outset of drug development to decrease the prevalence of drug resistance.

Evolution of robotic-assisted kidney transplant: successes and barriers to overcome

PURPOSE OF REVIEW

The aim of this study was to provide an updated review of robotic-assisted kidney transplant (RAKT) with an emphasis on advantages over the open kidney transplant (OKT), utility in special populations and resources available to overcome the learning curve of robotic surgery.

RECENT FINDINGS

The majority of the reported studies showed that RAKT and OKT have similar functional outcomes including similar ischemia times and time to postoperative normalization of creatinine. However, RAKT results in fewer wound complications, decreased estimated blood loss and pain. Given these benefits, RAKT is a promising approach for obese patient across BMI subtypes and several studies showed decreased wound complications in this population compared with the open approach. Moreover, new 3D-print techniques are promising resources for robotic simulation, which may decrease the learning curve of robotic surgery.

SUMMARY

Overall, RAKT is a feasible approach especially in obese patients. However, more data with long-term follow-up are needed to fully elucidate the advantages over OKT before universal implementation of this approach is possible.

Avoiding Drug Resistance by Substrate Envelope-Guided Design: Toward Potent and Robust HCV NS3/4A Protease Inhibitors

Hepatitis C virus (HCV) infects millions of people worldwide, causing chronic liver disease that can lead to cirrhosis, hepatocellular carcinoma, and liver transplant. In the last several years, the advent of direct-acting antivirals, including NS3/4A protease inhibitors (PIs), has remarkably improved treatment outcomes of HCV-infected patients. However, selection of resistance-associated substitutions and polymorphisms among genotypes can lead to drug resistance and in some cases treatment failure. A proactive strategy to combat resistance is to constrain PIs within evolutionarily conserved regions in the protease active site. Designing PIs using the substrate envelope is a rational strategy to decrease the susceptibility to resistance by using the constraints of substrate recognition. We successfully designed two series of HCV NS3/4A PIs to leverage unexploited areas in the substrate envelope to improve potency, specifically against resistance-associated substitutions at D168. Our design strategy achieved better resistance profiles over both the FDA-approved NS3/4A PI grazoprevir and the parent compound against the clinically relevant D168A substitution. Crystallographic structural analysis and inhibition assays confirmed that optimally filling the substrate envelope is critical to improve inhibitor potency while avoiding resistance. Specifically, inhibitors that enhanced hydrophobic packing in the S4 pocket and avoided an energetically frustrated pocket performed the best. Thus, the HCV substrate envelope proved to be a powerful tool to design robust PIs, offering a strategy that can be translated to other targets for rational design of inhibitors with improved potency and resistance profiles.IMPORTANCE Despite significant progress, hepatitis C virus (HCV) continues to be a major health problem with millions of people infected worldwide and thousands dying annually due to resulting complications. Recent antiviral combinations can achieve >95% cure, but late diagnosis, low access to treatment, and treatment failure due to drug resistance continue to be roadblocks against eradication of the virus. We report the rational design of two series of HCV NS3/4A protease inhibitors with improved resistance profiles by exploiting evolutionarily constrained regions of the active site using the substrate envelope model. Optimally filling the S4 pocket is critical to avoid resistance and improve potency. Our results provide drug design strategies to avoid resistance that are applicable to other quickly evolving viral drug targets.

Resistance outside the substrate envelope: hepatitis C NS3/4A protease inhibitors

Direct acting antivirals have dramatically increased the efficacy and tolerability of hepatitis C treatment, but drug resistance has emerged with some of these inhibitors, including nonstructural protein 3/4 A protease inhibitors (PIs). Although many co-crystal structures of PIs with the NS3/4A protease have been reported, a systematic review of these crystal structures in the context of the rapidly emerging drug resistance especially for early PIs has not been performed. To provide a framework for designing better inhibitors with higher barriers to resistance, we performed a quantitative structural analysis using co-crystal structures and models of HCV NS3/4A protease in complex with natural substrates and inhibitors. By comparing substrate structural motifs and active site interactions with inhibitor recognition, we observed that the selection of drug resistance mutations correlates with how inhibitors deviate from viral substrates in molecular recognition. Based on this observation, we conclude that guiding the design process with native substrate recognition features is likely to lead to more robust small molecule inhibitors with decreased susceptibility to resistance.

Molecular Mechanism of Resistance in a Clinically Significant Double-Mutant Variant of HCV NS3/4A Protease

Despite significant progress in hepatitis C virus (HCV) protease inhibitor (PI) drug design, resistance remains a problem causing treatment failure. Double-substitution variants, notably Y56H/D168A, have emerged in patients who fail therapy with a PI-containing regimen. The resistance conferred by Asp168 substitutions has been well characterized and avoided in newer inhibitors. However, an additional mutation at Tyr56 confers resistance to even the most robust inhibitors. Here, we elucidate the molecular mechanisms of resistance for the Y56H/D168A variant against grazoprevir (and four analogs), paritaprevir, and danoprevir through inhibition assays, co-crystal structures, and molecular dynamics simulations. The PIs' susceptibility to Y56H/D168A varies, with those stacking on the catalytic His57 losing the most potency. For such inhibitors, the Y56H substitution disrupts favorable stacking interactions with the neighboring catalytic His57. This indirect mechanism of resistance threatens to cause multi-PI failure as all HCV PIs in clinical development rely on interactions with the catalytic triad.

Quinoxaline-Based Linear HCV NS3/4A Protease Inhibitors Exhibit Potent Activity against Drug Resistant Variants

A series of linear HCV NS3/4A protease inhibitors was designed by eliminating the P2-P4 macrocyclic linker in grazoprevir, which, in addition to conferring conformational flexibility, allowed structure-activity relationship (SAR) exploration of diverse quinoxalines at the P2 position. Biochemical and replicon data indicated preference for small hydrophobic groups at the 3-position of P2 quinoxaline for maintaining potency against resistant variants R155K, A156T, and D168A/V. The linear inhibitors, though generally less potent than the corresponding macrocyclic analogues, were relatively easier to synthesize and less susceptible to drug resistance. Three inhibitor cocrystal structures bound to wild-type NS3/4A protease revealed a conformation with subtle changes in the binding of P2 quinoxaline, depending on the 3-position substituent, likely impacting both inhibitor potency and resistance profile. The SAR and structural analysis highlight inhibitor features that strengthen interactions of the P2 moiety with the catalytic triad residues, providing valuable insights to improve potency against resistant variants.

Purification of metal-dependent lysine deacetylases with consistently high activity

Metal-dependent lysine deacetylases (KDACs) are involved in regulation of numerous biological and disease processes through control of post-translational acetylation. Characterization of KDAC activity and substrate identification is complicated by inconsistent activity of prepared enzyme and a range of multi-step purifications. We describe a simplified protocol based on two-step affinity chromatography. The purification method is appropriate for use regardless of expression host, and we demonstrate purification of several representative members of the KDAC family as well as a selection of mutated variants. The purified proteins are highly active and consistent across preparations.

Hepatitis C Virus NS3/4A Protease Inhibitors Incorporating Flexible P2 Quinoxalines Target Drug Resistant Viral Variants

A substrate envelope-guided design strategy is reported for improving the resistance profile of HCV NS3/4A protease inhibitors. Analogues of 5172-mcP1P3 were designed by incorporating diverse quinoxalines at the P2 position that predominantly interact with the invariant catalytic triad of the protease. Exploration of structure-activity relationships showed that inhibitors with small hydrophobic substituents at the 3-position of P2 quinoxaline maintain better potency against drug resistant variants, likely due to reduced interactions with residues in the S2 subsite. In contrast, inhibitors with larger groups at this position were highly susceptible to mutations at Arg155, Ala156, and Asp168. Excitingly, several inhibitors exhibited exceptional potency profiles with EC₅₀ values ≤5 nM against major drug resistant HCV variants. These findings support that inhibitors designed to interact with evolutionarily constrained regions of the protease, while avoiding interactions with residues not essential for substrate recognition, are less likely to be susceptible to drug resistance.