Anti-VEGF antibody treatment accelerates polycystic kidney disease

Computational drug discovery approaches identify mebendazole as a candidate treatment for autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a rare genetic disorder characterised by numerous renal cysts, the progressive expansion of which can impact kidney function and lead eventually to renal failure. Tolvaptan is the only disease-modifying drug approved for the treatment of ADPKD, however its poor side effect and safety profile necessitates the need for the development of new therapeutics in this area. Using a combination of transcriptomic and machine learning computational drug discovery tools, we predicted that a number of existing drugs could have utility in the treatment of ADPKD, and subsequently validated several of these drug predictions in established models of disease. We determined that the anthelmintic mebendazole was a potent anti-cystic agent in human cellular and in vivo models of ADPKD, and is likely acting through the inhibition of microtubule polymerisation and protein kinase activity. These findings demonstrate the utility of combining computational approaches to identify and understand potential new treatments for traditionally underserved rare diseases.

Investigational agents for autosomal dominant polycystic kidney disease: preclinical and early phase study insights

INTRODUCTION

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common inherited kidney condition caused by a single-gene mutation. It leads patients to kidney failure in more than 50% of cases by the age of 60, and, given the dominant inheritance, this disease is present in the family history in more than 90% of cases.

AREAS COVERED

This review aims to analyze the set of preclinical and early-phase studies to provide a general view of the current progress on ADPKD therapeutic options. Articles from PubMed and the current status of the trials listed in clinicaltrials.gov were examined for the review.

EXPERT OPINION

Many potential therapeutic targets are currently under study for the treatment of ADPKD. A few drugs have reached the clinical phase, while many are currently still in the preclinical phase. Organoids could be a novel approach to the study of drugs in this phase. Other than pharmacological options, very important developing approaches are represented by gene therapy and the use of MiRNA inhibitors.

Evidence of retinal arteriolar narrowing in patients with autosomal-dominant polycystic kidney disease

Introduction

The aim of this study was to examine retinal vessels in autosomal dominant polycystic kidney disease (ADPKD) patients with normal kidney function and without diabetes mellitus.

Materials and Methods

We enrolled 39 adult individuals with ADPKD and 45 gender- and age-matched individuals as controls. A full ophthalmologic examination, including retinal vessel caliber and reactions to flicker stimulation analysis and grading of hypertensive retinopathy according to the Keith-Wagener classification, was performed.

Results

Multivariable analysis of ADPKD patients and controls, adjusted for age, gender, estimated glomerular filtration rate (e-GFR) and the presence of hypertension, revealed that ADPKD was an independent factor associated with lower arteriovenous ratio (AVR) values (by 0.069 on average, β = −0.50, p < 0.0001). The severity of hypertensive retinopathy according to the Keith-Wagener classification appeared to be more advanced in the ADPKD group than in the controls, despite the lack of vascular abnormalities, such as retinal hemorrhages, exudates, cotton wool spots or papilledema, as well as microaneurysms, which are very characteristic signs of ADPKD in other vascular beds.

Conclusions

Lower AVR values could be a specific pathophysiological ocular manifestation of systemic vasculopathy in the course of ADPKD.

Evidence of retinal arteriolar narrowing in patients with autosomal-dominant polycystic kidney disease

Introduction

The aim of this study was to examine retinal vessels in autosomal dominant polycystic kidney disease (ADPKD) patients with normal kidney function and without diabetes mellitus.

Materials and Methods

We enrolled 39 adult individuals with ADPKD and 45 gender- and age-matched individuals as controls. A full ophthalmologic examination, including retinal vessel caliber and reactions to flicker stimulation analysis and grading of hypertensive retinopathy according to the Keith-Wagener classification, was performed.

Results

Multivariable analysis of ADPKD patients and controls, adjusted for age, gender, estimated glomerular filtration rate (e-GFR) and the presence of hypertension, revealed that ADPKD was an independent factor associated with lower arteriovenous ratio (AVR) values (by 0.069 on average, β = −0.50, p < 0.0001). The severity of hypertensive retinopathy according to the Keith-Wagener classification appeared to be more advanced in the ADPKD group than in the controls, despite the lack of vascular abnormalities, such as retinal hemorrhages, exudates, cotton wool spots or papilledema, as well as microaneurysms, which are very characteristic signs of ADPKD in other vascular beds.

Conclusions

Lower AVR values could be a specific pathophysiological ocular manifestation of systemic vasculopathy in the course of ADPKD.

The tyrosine-kinase inhibitor Nintedanib ameliorates autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and is characterized by progressive growth of fluid-filled cysts. Growth factors binding to receptor tyrosine kinases (RTKs) stimulate cell proliferation and cyst growth in PKD. Nintedanib, a triple RTK inhibitor, targets the vascular endothelial growth-factor receptor (VEGFR), platelet-derived growth-factor receptor (PDGFR), and fibroblast growth-factor receptor (FGFR), and is an approved drug for the treatment of non-small-cell lung carcinoma and idiopathic lung fibrosis. To determine if RTK inhibition using nintedanib can slow ADPKD progression, we tested its effect on human ADPKD renal cyst epithelial cells and myofibroblasts in vitro, and on Pkd1f/fPkhd1Cre and Pkd1RC/RC, orthologous mouse models of ADPKD. Nintedanib significantly inhibited cell proliferation and in vitro cyst growth of human ADPKD renal cyst epithelial cells, and cell viability and migration of human ADPKD renal myofibroblasts. Consistently, nintedanib treatment significantly reduced kidney-to-body-weight ratio, renal cystic index, cystic epithelial cell proliferation, and blood-urea nitrogen levels in both the Pkd1f/fPkhd1Cre and Pkd1RC/RC mice. There was a corresponding reduction in ERK, AKT, STAT3, and mTOR activity and expression of proproliferative factors, including Yes-associated protein (YAP), c-Myc, and Cyclin D1. Nintedanib treatment significantly reduced fibrosis in Pkd1RC/RC mice, but did not affect renal fibrosis in Pkd1f/fPkhd1Cre mice. Overall, these results suggest that nintedanib may be repurposed to effectively slow cyst growth in ADPKD.

Therapeutic advances in ADPKD: the future awaits

Autosomal dominant polycystic kidney disease (ADPKD) is a heterogeneous genetic disorder included in ciliopathies, representing the fourth cause of end stage renal disease (ESRD), with an estimated prevalence between 1:1000 and 1:2500. It is mainly caused by mutations in the PKD1 and PKD2 genes encoding for polycystin 1 (PC1) and polycystin 2 (PC2), which regulate differentiation, proliferation, survival, apoptosis, and autophagy. The advances in the knowledge of multiple molecular pathways involved in the pathophysiology of ADPKD led to the development of several treatments which are currently under investigation. Recently, the widespread approval of tolvaptan and, in Italy, of long-acting release octreotide (octreotide-LAR), represents but the beginning of the new therapeutic management of ADPKD patients. Encouraging results are expected from ongoing randomized controlled trials (RCTs), which are investigating not only drugs acting on the calcium/cyclic adenosin monoposphate (cAMP) pathway, the most studied target so far, but also molecules targeting specific pathophysiological pathways (e.g. epidermal growth factor (EGF) receptor, AMP-activated protein kinase (AMPK) and KEAP1-Nrf2) and sphingolipids. Moreover, studies on animal models and cultured cells have also provided further promising therapeutic strategies based on the role of intracellular calcium, cell cycle regulation, MAPK pathway, epigenetic DNA, interstitial inflammation, and cell therapy. Thus, in a near future, tailored therapy could be the key to changing the natural history of ADPKD thanks to the vigorous efforts that are being made to implement clinical and preclinical studies in this field. Our review aimed to summarize the spectrum of drugs that are available in the clinical practice and the most promising molecules undergoing clinical, animal, and cultured cell studies.

Giant Cavernous Hemangioma of the Liver in a Patient with Autosomal Dominant Polycystic Kidney Disease

Patient: Male, 41-year-old

Final Diagnosis: Autosomal dominant polycystic kidney disease

Symptoms: Pain

Medication: —

Clinical Procedure: Computed tomography • ultrasonography

Specialty: Gastroenterology and Hepatology • Medicine, General and Internal • Nephrology

Hypoxia and Endothelial Dysfunction in Autosomal-Dominant Polycystic Kidney Disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most prevalent inherited kidney disease, characterized by growth of bilateral renal cysts, hypertension, and multiple extrarenal complications that eventually can lead to renal failure. It is caused by mutations in PKD1 or PKD2 genes encoding the proteins polycystin-1 and polycystin-2, respectively. Over the past few years, studies investigating the role of primary cilia and polycystins, present not only on the surface of renal tubular cells but also on vascular endothelial cells, have advanced our understanding of the pathogenesis of ADPKD and have shown that mechanisms other than cyst formation also contribute to renal functional decline in this disease. Among them, increased oxidative stress, endothelial dysfunction, and hypoxia may play central roles because they occur early in the disease process and precede the onset of hypertension and renal functional decline. Endothelial dysfunction is linked to higher asymmetric dimethylarginine levels and reduced nitric oxide bioavailability, which would cause regional vasoconstriction and impaired renal blood flow. The resulting hypoxia would increase the levels of hypoxia-inducible-transcription factor 1α and other angiogenetic factors, which, in turn, may drive cyst growth. In this review, we summarize the existing evidence for roles of endothelial dysfunction, oxidative stress, and hypoxia in the pathogenesis of ADPKD.

Molecular pathways involved in injury-repair and ADPKD progression

The major hallmark of Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the formation of many fluid-filled cysts in the kidneys, which ultimately impairs the normal renal structure and function, leading to end-stage renal disease (ESRD). A large body of evidence suggests that injury-repair mechanisms are part of ADPKD progression. Once cysts have been formed, proliferation and fluid secretion contribute to the cyst size increase, which eventually causes stress on the surrounding tissue resulting in local injury and fibrosis. In addition, renal injury can cause or accelerate cyst formation. In this review, we will describe the various mechanisms activated during renal injury and tissue repair and show how they largely overlap with the molecular mechanisms activated during PKD progression. In particular, we will discuss molecular mechanisms such as proliferation, inflammation, cell differentiation, cytokines and growth factors secretion, which are activated following the renal injury to allow the remodelling of the tissue and a proper organ repair. We will also underline how, in a context of PKD-related gene mutations, aberrant or chronic activation of these developmental pathways and repair/remodelling mechanisms results in exacerbation of the disease.

Endothelial-epithelial communication in polycystic kidney disease: Role of vascular endothelial growth factor signalling

Whereas targeting the cyst epithelium and its molecular machinery has been the prevailing clinical strategy for polycystic kidney disease, the endothelium, including blood vasculature and lymphatics, is emerging as an important player in this disorder. In this Review, we provide an overview of the structural and functional alterations to blood vasculature and lymphatic vessels in the polycystic kidney. We also discuss evidence for vascular endothelial growth factor signalling, otherwise critical for endothelial cell development and maintenance, as being a fundamental molecular pathway in polycystic kidney disease and a potential therapeutic target for modulating cyst expansion.

Targeting angiogenesis and lymphangiogenesis in kidney disease

The kidney is permeated by a highly complex vascular system with glomerular and peritubular capillary networks that are essential for maintaining the normal functions of glomerular and tubular epithelial cells. The integrity of the renal vascular network depends on a balance of proangiogenic and antiangiogenic factors, and disruption of this balance has been identified in various kidney diseases. Decreased levels of the predominant proangiogenic factor, vascular endothelial growth factor A (VEGFA), can result in glomerular microangiopathy and contribute to the onset of preeclampsia, whereas upregulation of VEGFA has roles in diabetic kidney disease (DKD) and polycystic kidney disease (PKD). Other factors that regulate angiogenesis, such as angiopoietin 1 and vasohibin 1, have been shown to be protective in animal models of DKD and renal fibrosis. The renal lymphatic system is important for fluid homeostasis in the kidney, as well as the transport of immune cells and antigens. Experimental studies suggest that the lymphangiogenic factor VEGFC might have protective effects in PKD, DKD and renal fibrosis. Understanding the physiological and pathological roles of factors that regulate angiogenesis and lymphangiogenesis in the kidney has led to the development of novel therapeutic strategies for kidney diseases.

Anti-vascular endothelial growth factor antibody monotherapy causes destructive advanced periodontitis in rice rats (Oryzomys palustris)

OBJECTIVE

Angiogenesis inhibitors (AgI) are commonly used in combination chemotherapy protocols to treat cancer, and have been linked to osteonecrosis of the jaw (ONJ). However, it is unknown if AgI therapy alone is sufficient to induce ONJ. We have previously established an ONJ model in rice rats with localized periodontitis that receive zoledronic acid (ZOL). The purpose of this study was to use this model to determine the role of anti-vascular endothelial growth factor A (anti-VEGF) antibody treatment of rice rats with localized maxillary periodontitis. We hypothesized that rice rats with localized maxillary periodontitis given anti-VEGF monotherapy will develop oral lesions that resemble ONJ, defined by exposed, necrotic alveolar bone.

METHODS

At age 4 weeks, 45 male rice rats were randomized into three groups (n = 15): 1) VEH (saline), 2) ZOL (80 μg/kg body weight, intravenously once monthly), and 3) anti-VEGF (5 mg B20-4.1.1/kg body weight, subcutaneously twice weekly). After 24 weeks, rats were euthanized, jaws were excised and a high-resolution photograph of each quadrant was taken to assign a severity grade based on gross appearance. Jaws were then fixed, scanned by MicroCT, decalcified and sectioned for histopathologic and immunohistochemical analyses.

RESULTS

40-80% of the rats in the three groups developed gross oral lesions. 50% of ZOL rats developed ONJ. In contrast, 80% of the anti-VEGF rats developed destructive advanced periodontitis that was characterized by extreme alveolar bone loss and fibrosis. Anti-VEGF rats never developed exposed, necrotic bone. Furthermore, only anti-VEGF rats developed mild to severe mandibular periodontitis. Compared to VEH rats, more T-cells were found in periodontal lesions of anti-VEGF rats and more cells of the monocyte lineage were found in ONJ lesions of ZOL rats.

CONCLUSIONS

Anti-VEGF monotherapy administered to a validated rodent model of ONJ caused a destructive advanced form of periodontitis that differed significantly from ONJ.

Autosomal dominant polycystic kidney disease: Disrupted pathways and potential therapeutic interventions

Autosomal dominant polycystic kidney disease (ADPKD) is a monogenic inherited renal cystic disease that occurs in different races worldwide. It is characterized by the development of a multitude of renal cysts, which leads to massive enlargement of the kidney and often to renal failure in adulthood. ADPKD is caused by a mutation in PKD1 or PKD2 genes encoding the proteins polycystin-1 and polycystin-2, respectively. Recent studies showed that cyst formation and growth result from deregulation of multiple cellular pathways like proliferation, apoptosis, metabolic processes, cell polarity, and immune defense. In ADPKD, intracellular cyclic adenosine monophosphate (cAMP) promotes cyst enlargement by stimulating cell proliferation and transepithelial fluid secretion. Several interventions affecting many of these defective signaling pathways have been effective in animal models and some are currently being tested in clinical trials. Moreover, the stem cell therapy can improve nephropathies and according to studies were done in this field, can be considered as a hopeful therapeutic approach in future for PKD. This study provides an in-depth review of the relevant molecular pathways associated with the pathogenesis of ADPKD and their implications in development of potential therapeutic strategies.

A small molecule fibrokinase inhibitor in a model of fibropolycystic hepatorenal disease

AIM

To evaluate the novel platelet-derived growth factor receptor and vascular endothelial growth factor receptor dual kinase inhibitor ANG3070 in a polycystic kidney disease-congenital hepatic fibrosis model.

METHODS

At 6 wk of age, PCK rats were randomized to vehicle or ANG3070 for 4 wk. At 10 wk, 24 h urine and left kidneys were collected and rats were continued on treatment for 4 wk. At 14 wk, 24 h urine was collected, rats were sacrificed, and liver and right kidneys were collected for histological evaluation. For Western blot studies, PCK rats were treated with vehicle or ANG3070 for 7 d and sacrificed approximately 30 min after the last treatments.

RESULTS

Compared to the wild-type cohort, the PCK kidney (Vehicle cohort) exhibited a marked increase in kidney and liver mass, hepato-renal cystic volume, hepato-renal fibrosis and hepato-renal injury biomarkers. Intervention with ANG3070 in PCK rats decreased kidney weight, reduced renal cystic volume and reduced total kidney hydroxyproline, indicating significantly reduced rental interstitial fibrosis compared to the PCK-Vehicle cohort. ANG3070 treatment also mitigated several markers of kidney injury, including urinary neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, cystatin C and interleukin-18 levels. In addition, this treatment attenuated key indices of renal dysfunction, including proteinuria, albuminuria and serum blood urea nitrogen and creatinine, and significantly improved renal function compared to the PCK-Vehicle cohort. ANG3070 treatment also significantly decreased liver enlargement, hepatic lesions, and liver fibrosis, and mitigated liver dysfunction compared to the PCK-Vehicle cohort.

CONCLUSION

These results suggest that ANG3070 has the potential to slow disease, and may serve as a bridge toward hepato-renal transplantation in patients with fibropolycystic disease.

The association of serum angiogenic growth factors with renal structure and function in patients with adult autosomal dominant polycystic kidney disease

PURPOSE

Autosomal dominant polycystic kidney disease (ADPKD) is a common congenital chronic kidney disease (CKD). We report here the relationship of serum angiopoietin-1 (Ang-1), Ang-2, and vascular endothelial growth factor (VEGF) with total kidney volume (TKV), total cyst volume (TCV), and renal failure in adult ADPKD patients at various stages of CKD.

METHODS

This cross-sectional study was conducted with 50 patients diagnosed with ADPKD and a control group of 45 age-matched healthy volunteers. In patient group, TKV and TCV were determined with upper abdominal magnetic resonance imaging, whereas in controls, TKV was determined with ultrasonography according to ellipsoid formula. Renal function was assessed with serum creatinine, estimated glomerular filtration rate (eGFR), and spot urinary protein/creatinine ratio (UPCR). Ang-1, Ang-2, and VEGF were measured using enzyme-linked immunosorbent assay.

RESULTS

Patients with ADPKD had significantly higher TKV (p < 0.001) and UPCR (p < 0.001), and lower eGFR (p ≤ 0.001) compared to the controls. Log₁₀Ang-2 was found to be higher in ADPKD patients at all CKD stages. Multiple linear regression analysis showed that there was no association between log₁₀Ang-1, log₁₀Ang-2, or log₁₀VEGF and creatinine, eGFR, UPCR, log₁₀TKV (p > 0.05).

CONCLUSION

There was no association of serum angiogenic growth factors with TKV or renal failure in ADPKD patients. Increased serum Ang-2 observed in stages 1-2 CKD suggests that angiogenesis plays a role in the progression of early stage ADPKD, but not at later stages of the disease. This may be explained by possible cessation of angiogenesis in advanced stages of CKD due to the increased number of sclerotic glomeruli.

SDF-1 Blockade Enhances Anti-VEGF Therapy of Glioblastoma and Can Be Monitored by MRI

Despite the approval of antiangiogenic therapy for glioblastoma multiforme (GBM) patients, survival benefits are still limited. One of the resistance mechanisms for antiangiogenic therapy is the induction of hypoxia and subsequent recruitment of macrophages by stromal-derived factor (SDF)-1α (CXCL-12). In this study, we tested whether olaptesed pegol (OLA-PEG, NOX-A12), a novel SDF-1α inhibitor, could reverse the recruitment of macrophages and potentiate the antitumor effect of anti–vascular endothelial growth factor (VEGF) therapy. We also tested whether magnetic resonance imaging (MRI) with ferumoxytol as a contrast agent could provide early information on macrophage blockade. Orthotopic human G12 glioblastomas in nude mice and rat C6 glioblastomas were employed as the animal models. These were treated with bevacizumab or B-20, both anti-VEGF antibodies. Rats were MR imaged with ferumoxytol for macrophage detection. Tumor hypoxia and SDF-1α expression were elevated by VEGF blockade. Adding OLA-PEG to bevacizumab or B-20 significantly prolonged the survival of rodents bearing intracranial GBM compared with anti-VEGF therapy alone. Intratumoral CD68+ tumor associated macrophages (TAMs) were increased by VEGF blockade, but the combination of OLA-PEG + VEGF blockade markedly lowered TAM levels compared with VEGF blockade alone. MRI with ferumoxytol as a contrast agent noninvasively demonstrated macrophage reduction in OLA-PEG + anti-VEGF–treated rats compared with VEGF blockade alone. In conclusion, inhibition of SDF-1 with OLA-PEG inhibited the recruitment of TAMs by VEGF blockage and potentiated its antitumor efficacy in GBM. Noninvasive MRI with ferumoxytol as a contrast agent provides early information on the effect of OLA-PEG in reducing TAMs.

The hallmarks of cancer: relevance to the pathogenesis of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a progressive inherited disorder in which renal tissue is gradually replaced with fluid-filled cysts, giving rise to chronic kidney disease (CKD) and progressive loss of renal function. ADPKD is also associated with liver ductal cysts, hypertension, chronic pain and extra-renal problems such as cerebral aneurysms. Intriguingly, improved understanding of the signalling and pathological derangements characteristic of ADPKD has revealed marked similarities to those of solid tumours, even though the gross presentation of tumours and the greater morbidity and mortality associated with tumour invasion and metastasis would initially suggest entirely different disease processes. The commonalities between ADPKD and cancer are provocative, particularly in the context of recent preclinical and clinical studies of ADPKD that have shown promise with drugs that were originally developed for cancer. The potential therapeutic benefit of such repurposing has led us to review in detail the pathological features of ADPKD through the lens of the defined, classic hallmarks of cancer. In addition, we have evaluated features typical of ADPKD, and determined whether evidence supports the presence of such features in cancer cells. This analysis, which places pathological processes in the context of defined signalling pathways and approved signalling inhibitors, highlights potential avenues for further research and therapeutic exploitation in both diseases.

Vascular Endothelial Growth Factor C for Polycystic Kidney Diseases

Polycystic kidney diseases (PKD) are genetic disorders characterized by progressive epithelial cyst growth leading to destruction of normally functioning renal tissue. Current therapies have focused on the cyst epithelium, and little is known about how the blood and lymphatic microvasculature modulates cystogenesis. Hypomorphic Pkd1(nl/nl) mice were examined, showing that cystogenesis was associated with a disorganized pericystic network of vessels expressing platelet/endothelial cell adhesion molecule 1 and vascular endothelial growth factor receptor 3 (VEGFR3). The major ligand for VEGFR3 is VEGFC, and there were lower levels of Vegfc mRNA within the kidneys during the early stages of cystogenesis in 7-day-old Pkd1(nl/nl) mice. Seven-day-old mice were treated with exogenous VEGFC for 2 weeks on the premise that this would remodel both the VEGFR3(+) pericystic vascular network and larger renal lymphatics that may also affect the severity of PKD. Treatment with VEGFC enhanced VEGFR3 phosphorylation in the kidney, normalized the pattern of the pericystic network of vessels, and widened the large lymphatics in Pkd1(nl/nl) mice. These effects were associated with significant reductions in cystic disease, BUN and serum creatinine levels. Furthermore, VEGFC administration reduced M2 macrophage pericystic infiltrate, which has been implicated in the progression of PKD. VEGFC administration also improved cystic disease in Cys1(cpk/cpk) mice, a model of autosomal recessive PKD, leading to a modest but significant increase in lifespan. Overall, this study highlights VEGFC as a potential new treatment for some aspects of PKD, with the possibility for synergy with current epithelially targeted approaches.

Angiogenesis and autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the growth of multiple cysts that in many cases result in end-stage renal disease. Current strategies to reduce cyst progression in ADPKD focus on modulating cell turnover, fluid secretion, and vasopressin signalling; but an alternative approach may be to target pathways providing "general support" for cyst growth, such as surrounding blood vessels. This could be achieved by altering the expression of growth factors involved in vascular network formation, such as the vascular endothelial growth factor (VEGF) and angiopoietin families. We highlight the evidence that blood vessels and vascular growth factors play a role in ADPKD progression. Recent experiments manipulating VEGF in ADPKD are described, and we discuss how alternative strategies to manipulate angiogenesis may be used in the future as a novel treatment for ADPKD.

Experimental therapies and ongoing clinical trials to slow down progression of ADPKD

The improvement of imaging techniques over the years has contributed to the understanding of the natural history of autosomal dominant polycystic kidney disease, and facilitated the observation of its structural progression. Advances in molecular biology and genetics have made possible a greater understanding of the genetics, molecular, and cellular pathophysiologic mechanisms responsible for its development and have laid the foundation for the development of potential new therapies. Therapies targeting genetic mechanisms in ADPKD have inherent limitations. As a result, most experimental therapies at the present time are aimed at delaying the growth of the cysts and associated interstitial inflammation and fibrosis by targeting tubular epithelial cell proliferation and fluid secretion by the cystic epithelium. Several interventions affecting many of the signaling pathways disrupted in ADPKD have been effective in animal models and some are currently being tested in clinical trials.

VEGF inhibition, hypertension, and renal toxicity

The use of anti-angiogenic agents as part of the therapeutic armamentarium for advanced stage solid tumors has become the standard of care in several instances, particularly for renal cell carcinoma, non-small cell lung carcinoma, colorectal carcinoma, and gastrointestinal stromal tumors. These agents primarily target vascular endothelial growth factor (VEGF) and/or its receptors, and include bevacizumab, a humanized monoclonal antibody against VEGF, as well as tyrosine kinase inhibitors that target several receptor tyrosine kinases (RTK), including VEGF receptors. These therapies, as a general class of anti-angiogenic medications, have been shown to have common adverse vascular effects attributable directly or indirectly to their anti-VEGF effects, including hypertension, renal vascular injury, often manifested by proteinuria and thrombotic microangiopathy, and congestive heart failure. Knowledge of these common side effects and their underlying mechanisms may allow for more accurate and prompt diagnoses, timely clinical interventions, and the development of rational and standard treatments. These measures may minimize patient morbidity and mortality, not only by the treatment of side effects, but also by minimizing the disruption of treatment of the underlying malignancy, as well as improving patient quality of life.

Understanding the mechanisms of proteinuria: therapeutic implications

A large body of evidence indicates that proteinuria is a strong predictor of morbidity, a cause of inflammation, oxidative stress and progression of chronic kidney disease, and development of cardiovascular disease. The processes that lead to proteinuria are complex and involve factors such as glomerular hemodynamic, tubular absorption, and diffusion gradients. Alterations in various different molecular pathways and interactions may lead to the identical clinical end points of proteinuria and chronic kidney disease. Glomerular diseases include a wide range of immune and nonimmune insults that may target and thus damage some components of the glomerular filtration barrier. In many of these conditions, the renal visceral epithelial cell (podocyte) responds to injury along defined pathways, which may explain the resultant clinical and histological changes. The recent discovery of the molecular components of the slit diaphragm, specialized structure of podocyte-podocyte interaction, has been a major breakthrough in understanding the crucial role of the epithelial layer of the glomerular barrier and the pathogenesis of proteinuria. This paper provides an overview and update on the structure and function of the glomerular filtration barrier and the pathogenesis of proteinuria, highlighting the role of the podocyte in this setting. In addition, current antiproteinuric therapeutic approaches are briefly commented.