In vitro modulation of cyst formation by a novel tyrosine kinase inhibitor

The Efficacy and Safety of Tyrosine Kinase Inhibitors for Von Hippel-Lindau Disease: A Retrospective Study of 32 Patients

Background: Von Hippel-Lindau (VHL) disease is an autosomal-dominant hereditary cancer syndrome. Currently, studies on tyrosine kinase inhibitor (TKI) therapy for VHL disease are scarce. In this study, we retrospectively evaluated the efficacy and safety of four TKIs in patients with VHL disease. Methods: Patients diagnosed with VHL disease who were receiving TKIs were recruited. Patients were treated with sunitinib (n = 12), sorafenib (n = 11), axitinib (n = 6), or pazopanib (n = 3). The therapeutic response was evaluated according to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. Results: From July 2009 to September 2018, 32 patients with VHL disease were eligible and included in this study. The median duration of TKI therapy was 22 months (IQR 8.5-44.75), and the median follow-up period was 31.5 months (IQR 13.5-63.5). According to the RECIST, 9 (28%) of 32 patients showed a partial response, 15 (47%) achieved stable disease, and eight exhibited continued disease progression. A partial response was observed in 11 (31%) of 36 renal cell carcinomas, 4 (27%) of 15 pancreatic lesions, and 1 (20%) of five central nervous system (CNS) hemangioblastomas. The average tumor size decreased significantly for renal cell carcinomas (P = 0.0001), renal cysts (P = 0.027), and pancreatic lesions (P = 0.003) after TKI therapy. Common side effects included hand-foot skin reactions, diarrhea, alopecia, thrombocytopenia, and fatigue. Conclusions: Partial alleviation of VHL disease-related tumors can be achieved by TKI therapies in some patients, providing an alternative treatment strategy, and the side effects of TKIs are acceptable. Larger prospective studies are warranted to further evaluate the efficacy and safety of TKIs in patients with VHL disease.

Pharmacokinetic Evaluation of Nimotuzumab in Patients With Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease characterized by an overexpression and mislocalization of epidermal growth factor receptor (EGFR) to the apical membranes of cystic epithelial cells. Nimotuzumab is a humanized antibody that recognizes an extracellular domain III of human EGFR. The aim of this study was to assess the pharmacokinetic behavior of nimotuzumab in patients with ADPKD given as a single dose. A phase I, single-center, and noncontrolled open clinical study was conducted. Five patients were enrolled at each of the following fixed-dose levels: 50, 100, 200, and 400 mg. Intravenous continuous infusions of nimotuzumab were administered every 14 days during a year, except the first administration, when blood samples were drawn during 28 days for pharmacokinetic assessments. Subjects were closely monitored during the trial and at completion of the administration of nimotuzumab, including the anti-idiotypic response. For the first time, nimotuzumab was used for treating a nononcological disease. The administration of nimotuzumab showed dose-dependent kinetics. Nimotuzumab does not develop anti-idiotypic response against the murine portion present in the hypervariable region of the antibody present in the serum of the patients treated. No significant differences were found in the systemic clearance between the 100- and 400-mg dose, which indicates that the optimal biological dose is in this range of dose.

Use of kinase inhibitors to correct ΔF508-CFTR function

The most common mutation in cystic fibrosis (CF) is a deletion of Phe at position 508 (ΔF508-CFTR). ΔF508-CFTR is a trafficking mutant that is retained in the ER, unable to reach the plasma membrane. To identify compounds and drugs that rescue this trafficking defect, we screened a kinase inhibitor library enriched for small molecules already in the clinic or in clinical trials for the treatment of cancer and inflammation, using our recently developed high-content screen technology (Trzcinska-Daneluti et al. Mol. Cell. Proteomics 8:780, 2009). The top hits of the screen were further validated by (1) biochemical analysis to demonstrate the presence of mature (Band C) ΔF508-CFTR, (2) flow cytometry to reveal the presence of ΔF508-CFTR at the cell surface, (3) short-circuit current (Isc) analysis in Ussing chambers to show restoration of function of the rescued ΔF508-CFTR in epithelial MDCK cells stably expressing this mutant (including EC(50) determinations), and importantly (4) Isc analysis of Human Bronchial Epithelial (HBE) cells harvested from homozygote ΔF508-CFTR transplant patients. Interestingly, several inhibitors of receptor Tyr kinases (RTKs), such as SU5402 and SU6668 (which target FGFRs, VEGFR, and PDGFR) exhibited strong rescue of ΔF508-CFTR, as did several inhibitors of the Ras/Raf/MEK/ERK or p38 pathways (e.g. (5Z)-7-oxozeaenol). Prominent rescue was also observed by inhibitors of GSK-3β (e.g. GSK-3β Inhibitor II and Kenpaullone). These results identify several kinase inhibitors that can rescue ΔF508-CFTR to various degrees, and suggest that use of compounds or drugs already in the clinic or in clinical trials for other diseases can expedite delivery of treatment for CF patients.

Cilium, centrosome and cell cycle regulation in polycystic kidney disease

Polycystic kidney disease is the defining condition of a group of common life-threatening genetic disorders characterized by the bilateral formation and progressive expansion of renal cysts that lead to end stage kidney disease. Although a large body of information has been acquired in the past years about the cellular functions that characterize the cystic cells, the mechanisms triggering the cystogenic conversion are just starting to emerge. Recent findings link defects in ciliary functions, planar cell polarity pathway, and centrosome integrity in early cystic development. Many of the signals dysregulated during cystogenesis may converge on the centrosome for its central function as a structural support for cilia formation and a coordinator of protein trafficking, polarity, and cell division. Here, we will discuss the contribution of proliferation, cilium and planar cell polarity to the cystic signal and will analyze in particular the possible role that the basal bodies/centrosome may play in the cystogenetic mechanisms. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Novel targets for the treatment of autosomal dominant polycystic kidney disease

IMPORTANCE OF THE FIELD

Autosomal dominant (AD) polycystic kidney disease (PKD) is the most common life-threatening hereditary disorder. There is currently no therapy that slows or prevents cyst formation and kidney enlargement in humans. An increasing number of animal studies have advanced our understanding of molecular and cellular targets of PKD.

AREAS COVERED IN THE REVIEW

The purpose of this review is to summarize the molecular and cellular targets involved in cystogenesis and to update on the promising therapies that are being developed and tested based on knowledge of these molecular and cellular targets.

WHAT THE READER WILL GAIN

Insight into the pathogenesis of PKD and how a better understanding of the pathogenesis of PKD has led to the development of potential therapies to inhibit cyst formation and/or growth and improve kidney function.

TAKE HOME MESSAGE

The results of animal studies in PKD have led to the development of clinical trials testing potential new therapies to reduce cyst formation and/or growth. A vasopressin V2 receptor antagonist, mTOR inhibitors, blockade of the renin-angiotensin system and statins that reduce cyst formation and improve renal function in animal models of PKD are being tested in interventional studies in humans.

Acceleration of polycystic kidney disease progression in cpk mice carrying a deletion in the homeodomain protein Cux1

Polycystic kidney diseases (PKD) are inherited as autosomal dominant (ADPKD) or autosomal recessive (ARPKD) traits and are characterized by progressive enlargement of renal cysts. Aberrant cell proliferation is a key feature in the progression of PKD. Cux1 is a homeobox gene that is related to Drosophila cut and is the murine homolog of human CDP (CCAAT Displacement Protein). Cux1 represses the cyclin kinase inhibitors p21 and p27, and transgenic mice ectopically expressing Cux1 develop renal hyperplasia. However, Cux1 transgenic mice do not develop PKD. Here, we show that a 246 amino acid deletion in Cux1 accelerates PKD progression in cpk mice. Cystic kidneys isolated from 10-day-old cpk/Cux1 double mutant mice were significantly larger than kidneys from 10-day-old cpk mice. Moreover, renal function was significantly reduced in the Cux1 mutant cpk mice, compared with cpk mice. The mutant Cux1 protein was ectopically expressed in cyst-lining cells, where expression corresponded to increased cell proliferation and apoptosis, and a decrease in expression of the cyclin kinase inhibitors p27 and p21. While the mutant Cux1 protein altered PKD progression, kidneys from mice carrying the mutant Cux1 protein alone were phenotypically normal, suggesting the Cux1 mutation modifies PKD progression in cpk mice. During cell cycle progression, Cux1 is proteolytically processed by a nuclear isoform of the cysteine protease cathepsin-L. Analysis of the deleted sequences reveals that a cathepsin-L processing site in Cux1 is deleted. Moreover, nuclear cathepsin-L is significantly reduced in both human ADPKD cells and in Pkd1 null kidneys, corresponding to increased levels of Cux1 protein in the cystic cells and kidneys. These results suggest a mechanism in which reduced Cux1 processing by cathepsin-L results in the accumulation of Cux1, downregulation of p21/p27, and increased cell proliferation in PKD.

Polycystic kidney disease: genes, proteins, animal models, disease mechanisms and therapeutic opportunities

An increased understanding of the genetic, molecular and cellular mechanisms responsible for the development of polycystic kidney disease has laid out the foundation for the development of rational therapies. Many animal models where these therapies can be tested are currently available. This review summarizes the rationale for these treatments, the results of preclinical trials and the prospects for clinical trials, some already in early phases of implementation.

Mechanisms of Disease: autosomal dominant and recessive polycystic kidney diseases

Autosomal dominant polycystic kidney disease and autosomal recessive polycystic kidney disease are the best known of a large family of inherited diseases characterized by the development of renal cysts of tubular epithelial cell origin. Autosomal dominant and recessive polycystic kidney diseases have overlapping but distinct pathogeneses. Identification of the causative mutated genes and elucidation of the function of their encoded proteins is shedding new light on the mechanisms that underlie tubular epithelial cell differentiation. This review summarizes recent literature on the role of primary cilia, intracellular calcium homeostasis, and signaling involving Wnt, cyclic AMP and Ras/MAPK, in the pathogenesis of polycystic kidney disease. Improved understanding of pathogenesis and the availability of animal models orthologous to the human diseases provide an excellent opportunity for the development of pathophysiology-based therapies. Some of these have proven effective in preclinical studies, and clinical trials have begun.

Therapeutics in renal disease: the road ahead for antiproliferative targets

Discovery into the molecular basis of renal disease is occurring at an unprecedented rate. With the advent of the NIH Roadmap, there is a greater expectation of translating this knowledge into new treatments. Here, we review the therapeutic strategy to preserve renal function in proliferative renal diseases by directly inhibiting the mitogenic pathways within renal parenchymal cells that promote G0 to G1/S cell-cycle phase progression. Reductionist methodologies have identified several antiproliferative molecular targets, and promising preclinical testing of leading small-molecule drugs to modulate these targets has now led to landmark clinical trials. Yet, this advancement into targeted therapy highlights important differences between the therapeutic goals of molecular nephrology versus molecular oncology and, by extension, the poorly understood role of alternative target activity in drug efficacy. Systems research to clarify these issues should accelerate the development of this promising therapeutic strategy.

A mechanistic approach to inherited polycystic kidney disease

There are approximately six and a half million people, of the estimated world population of six billion, with inherited polycystic kidney disease. Polycystic kidney diseases have a broad spectrum of associated findings that distinguish and define them as specific disease states. The dysregulation of renal tubular epithelial cell biology, including cell polarity, cell signaling, proliferation and apoptosis, basement membrane and matrix abnormalities, and fluid transport, has been postulated to contribute to cystogenesis. Evidence is currently accumulating that supports an association of the primary cilium and basal body, as well as the focal adhesion assembly, with polycystic kidney diseases. Renal cystogenesis may be the result of a disruption of a critical feedback loop that regulates tissue morphology based on the epithelial cell environment.

Epidermal growth factor receptor tyrosine kinase inhibition is not protective in PCK rats

BACKGROUND

Advances in the understanding of cystogenesis, identification of the PKHD1 gene and availability of a rat model (the PCK rat) caused by a Pkhd1 mutation facilitate testing of therapies for autosomal-recessive polycystic kidney disease (ARPKD). Considerable support exists for the importance of the epidermal growth factor (EGF)/transforming growth factor-alpha (TGF-alpha)/EGF receptor (EGFR) axis and of the adenylyl cyclase-adenosine 3',5'-cyclic monophosphate (cAMP) pathway in the pathogenesis of cyst formation and progressive enlargement.

METHODS

To determine whether EGFR tyrosine kinase inhibition is protective in the PCK rat, male and female animals were treated with EKI-785 or EKB-569 or with vehicle alone between 3 and 10 weeks of age. Biochemical and histomorphometric analysis, immunohistochemistry, immunoblotting, enzyme immunoassay, and quantitative reverse transcription-polymerase chain reaction (RT-PCR) were used to ascertain the effects of treatment.

RESULTS

Contrary to other murine models of ARPKD, overexpression and apical mislocalization of EGFR were not detected in the PCK rats. Consistent with these expression results, EKI-785 or EKB-569 administration had no effect or worsened PKD, and had no effect on the development of fibrocystic liver disease. Increased renal cAMP and vasopressin V2 receptor expression were observed in the EKI-785-treated animals.

CONCLUSION

EGFR tyrosine kinase inhibition did not protect PCK rats from the development of PKD. This may be due to effects on collecting duct cAMP that counteract possible beneficial effects on the extracellular-regulated protein kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway, particularly in the absence of EGFR overexpression or mislocalization. The relevance of these observations to the treatment of human cystic kidney diseases deserves further study.

Receptor tyrosine kinases mediate epithelial Na(+) channel inhibition by epidermal growth factor

Epidermal growth factor (EGF) decreases Na(+) reabsorption across distal nephron epithelia. Activity of the epithelial Na(+) channel (ENaC) is limiting for Na(+) transport in this portion of the nephron. Abnormal ENaC activity and EGF signaling are both associated with polycystic kidney disease localized to the distal nephron. We tested here whether EGF and other ligands for receptor tyrosine kinases (RTK) decrease ENaC activity. EGF markedly and quickly decreased ENaC activity. The RTK inhibitor erbstatin blocked EGF actions on ENaC and when added alone increased channel activity, uncovering basal suppression by endogenous RTK. The protein tyrosine phosphatase inhibitor vanadate, similar to EGF, decreased ENaC activity. Growth factors and vanadate decreased ENaC activity by decreasing open probability. ENaC was not phosphorylated in response to EGF, indicating that intermediary proteins transduce the inhibitory signal from the EGF receptor (EGFR) to ENaC. We find that neither MAPK 1/2 nor c-Src is signaling intermediaries between EGFR and ENaC. Inhibition of ENaC paralleled decreases in plasma membrane phosphatidylinositol 4,5-bisphosphate levels [PtdIns(4,5)P(2)] and was abolished by clamping PtdIns(4,5)P(2). We conclude that EGF and other ligands for RTK decrease ENaC open probability by decreasing membrane PtdIns(4,5)P(2) levels.

High-affinity interaction of tyrosine kinase inhibitors with the ABCG2 multidrug transporter

Tyrosine kinase inhibitors (TKIs) are promising new agents for specific inhibition of malignant cell growth and metastasis formation. Because most of the TKIs have to reach an intracellular target, specific membrane transporters may significantly modulate their effectiveness. In addition, the hydrophobic TKIs may interact with so-called multidrug transporters and thus alter the cellular distribution of unrelated pharmacological agents. In the present work, we show that certain TKIs, already in the clinical phase of drug development, directly interact with the ABCG2 multidrug transporter protein with a high affinity. We found that in several in vitro assay systems, STI-571 (Gleevec; imatinib mesylate), ZD1839 (Iressa; gefitinib), and N-[4-[(3-bromophenyl)amino]-6-quinazolinyl]-2-butynamide (EKI-785) interacted with ABCG2 at submicromolar concentrations, whereas other multidrug transporters, human multidrug resistance protein (P-glycoprotein, ABCB1) and human multidrug resistance protein 1 (ABCC1), showed much lower reactivity toward these agents. Low concentrations of the TKIs examined selectively modulated ABCG2-ATPase activity, inhibited ABCG2-dependent active drug extrusion, and significantly affected drug resistance patterns in cells expressing ABCG2. Our results indicate that multidrug resistance protein modulation by TKIs may be an important factor in the clinical treatment of cancer patients. These data also raise the possibility that an extrusion of TKIs by multidrug transporters, e.g., ABCG2, may be involved in tumor cell TKI resistance.

Murine models of polycystic kidney disease: molecular and therapeutic insights

Numerous murine (mouse and rat) models of polycystic kidney disease (PKD) have been described in which the mutant phenotype results from a spontaneous mutation or engineering via chemical mutagenesis, transgenic technologies, or gene-specific targeting in mouse orthologs of human PKD genes. These murine phenotypes closely resemble human PKD, with common abnormalities observed in tubular epithelia, the interstitial compartment, and the extracellular matrix of cystic kidneys. In both human and murine PKD, genetic background appears to modulate the renal cystic phenotype. In murine models, these putative modifying effects have been dissected into discrete factors called quantitative trait loci and genetically mapped. Several lines of experimental evidence support the hypothesis that PKD genes and their modifiers may define pathways involved in cystogenesis and PKD progression. Among the various pathway abnormalities described in murine PKD, recent provocative data indicate that structural and/or functional defects in the primary apical cilia of tubular epithelia may play a key role in PKD pathogenesis. This review describes the most widely studied murine models; highlights the data regarding specific gene defects and genetic modifiers; summarizes the data from these models that have advanced our understanding of PKD pathogenesis; and examines the effect of various therapeutic interventions in murine PKD.

EGF receptor tyrosine kinase inhibition attenuates the development of PKD in Han:SPRD rats

BACKGROUND

Increasing evidence supports an important role for the epidermal growth factor (EGF)/transforming growth factor-alpha (TGF-alpha)/EGF receptor (EGFR) axis in promoting tubular epithelial cell proliferation and cyst formation in polycystic kidney disease (PKD).

METHODS

To determine whether the inhibition of EGFR tyrosine kinase activity can attenuate the development of PKD in the Han:SPRD rat, a frequently used animal model of autosomal-dominant slowly progressive PKD (ADPKD), wild-type and cy/+ rats were treated with EKI-785 or EKB-569 or with vehicle alone. Western analysis, immunoprecipitation, and immunohistochemistry were used to ascertain the expression, activation, and localization of EGFR.

RESULTS

Overexpression, activation and apical mislocalization of EGFR were observed in the cy/+ rats. The intraperitoneal administration of EKI-785 reversed the activation of the EGFR to the level observed in wild-type animals. The intraperitoneal administration of EKI-785 (90 mg/kg body weight every third day) or of EKB-569 (20 mg/kg body weight every third day) to cy/+ rats resulted in lower kidney weights, serum concentrations of blood urea nitrogen (BUN), cyst volumes, and fibrosis scores. The administration of EKB-569 by gavage was less effective probably because of lower bioavailability.

CONCLUSION

These results support a significant role for the EGF/TGF-alpha/EGFR axis in the development of PKD in the Han:SPRD rat and the therapeutic potential of EGFR tyrosine kinase inhibition in ADPKD.

Combination treatment of PKD utilizing dual inhibition of EGF-receptor activity and ligand bioavailability

BACKGROUND

We have previously demonstrated an essential role for increased epidermal growth factor receptor (EGFR) activity in mediating renal cyst formation and biliary ductal ectasia (BDE) in murine models of autosomal-recessive polycystic kidney disease (ARPKD) such as the BPK mouse. The current study was designed to determine (1). if treatment with a second-generation inhibitor of EGFR tyrosine kinase activity, EKB-569, was effective in treatment of ARPKD; (2). if tyrosine kinase inhibitor therapy used in combination with pharmacologic reduction of the availability of transforming growth factor-alpha (TGF-alpha), using WTACE2, could provide improved therapeutic efficacy and/or decrease potential toxicity; and (3). if effectiveness of treatment could be monitored noninvasively in murine ARPKD models by use of serial ultrasonography.

METHODS

BPK litters were treated with EKB-569 by intraperitoneal injection from postnatal day 7 to postnatal day 21. EKB-569's effectiveness alone or in combination with WTACE2 was measured by reduction in kidney weight/body weight ratios, morphometric renal cystic index, and evaluation of renal function. Renal ultrasound was performed on normal and cystic animals, under different therapeutic regimens, utilizing a 15 mHz linear array transducer, and ultrasound data were compared with histology and renal functional data.

RESULTS

Treatment of BPK mice with EKB-569 alone resulted in a marked reduction of kidney weight/body weight ratios, dramatically reduced collecting tubule cystic index, as well as BDE, and improved renal function. The combined treatment with EKB-569 and WTACE2 permitted a 67% reduction in EKB-569 dosage necessary to achieve results equivalent to those produced with EKB-569 alone. Untreated cystic animals died of renal failure, on average, at postnatal day 24 with a collecting tubule cystic index of 4.8, significant BDE, and maximal urine osmolarity of 361 mOsm. Cystic animals treated with EKB-569 and WTACE2 to postnatal day 21 were alive and well with normal renal function, a reduced collecting tubule cystic index of 1.7 (P < 0.02), improvement in BDE, and a threefold increase in maximum urinary concentrating ability (P < 0.01). Renal ultrasound could reliably detect cystic kidneys as early as postnatal day 7 and the natural history as well as effects of therapeutic intervention were clearly delineated by ultrasound evaluation.

CONCLUSION

This study demonstrates that in murine ARPKD (1). EKB-569 is as effective as first-generation EGFR tyrosine kinase inhibitors in reducing cyst formation and preserving renal function; (2). combination therapy with EKB-569 and WTACE2 provides maximum efficacy in improving renal and biliary abnormalities, at lower doses, thereby minimizing potential toxicity; and (3). renal ultrasound provides a simple, reliable, noninvasive method of following natural history and effect of treatment regimens.

Delayed cystogenesis and increased ciliogenesis associated with the re-expression of polaris in Tg737 mutant mice

BACKGROUND

Renal cysts and shortened cilia on renal tubular epithelia have been observed in Tg737orpk (orpk) mutant mice, suggesting a potential connection between cystogenesis and ciliogenesis. To further test this hypothesis we have characterized the progression of cystic disease and cilia expression in orpk, orpk;Tg737Rsq (orpk rescue), and Tg737 Delta 2-3 beta Gal;Tg737Rsq (KO rescue) mice. Methods. Orpk, orpk rescue, and KO rescue animals were generated and analyzed from postnatal day (P) 0 to P21 (orpk mutants) or from P0 to P210 (orpk rescue and KO rescue animals). Proximal tubules (PT) and collecting tubules (CT) were identified by immunohistochemistry using segment-specific lectins and a segment-specific cystic index was calculated. Scanning electron microscopy was utilized to observe and measure cilia expression in cysts from orpk, orpk rescue, and KO rescue animals.

RESULTS

KO rescue and orpk rescue animals develop adult-onset autosomal-recessive polycystic kidney disease (ARPKD). Ultrastructural analysis of cilia expression revealed that cysts from orpk expressed short cilia, whereas cysts from KO rescue animals expressed normal length cilia and cysts from orpk rescue animals expressed cilia that are two to five times longer than wild type.

CONCLUSION

While this data is consistent with a role for polaris in ciliogenesis, it does not support a direct connection between ciliogenesis and cystic disease. Similarities in cyst formation and striking differences in cilia expression associated with these ARPKD mouse models indicates that cyst formation and cilia expression are independent phenotypic features regulated by polaris.

Multiorgan mRNA misexpression in murine autosomal recessive polycystic kidney disease

BACKGROUND

BALB/c mice homozygous for the cpk mutation develop a form of polycystic kidney disease (PKD) with multiorgan pathology similar to human autosomal recessive PKD. Messenger RNA expression in multiple affected organs was analyzed to determine if common gene cascades were misexpressed in the cystic kidney and extrarenal sites of disease. In cystic kidneys, misexpressed mRNAs were found in one of four general groups: proliferation/cell growth, apoptosis, differentiation or extracellular matrix.

METHODS

RNA was isolated from kidney, liver and pancreas of cystic and normal BALB/c-cpk mice. Using Northern blot hybridization and ribonuclease protection assays (RPA), the expression of several genes thought to be associated with PKD, namely c-myc, epidermal growth factor receptor (EGF-R) and PKD-1, were evaluated. RPAs were used to assess mRNA expression of cyclins and members of the bax/bcl-2 family. In addition, kidney, liver and pancreas were immunostained for c-Myc and PCNA.

RESULTS

Cystic kidney, liver and pancreas all exhibited similar patterns of mRNA misexpression of c-myc, EGF-R and PKD-1. In addition, a number of cell proliferation and apoptosis-related mRNAs also were elevated in cystic kidney and pancreas. Renal epithelial cells expressing proliferation-associated proteins [c-Myc and proliferating cell nuclear antigen (PCNA)] were nearly absent in normal kidney; however, cells of cystic and non-cystic renal tubules plus liver and pancreatic cyst exhibited an increased number of nuclei labeled with antibodies to these proteins.

CONCLUSIONS

These data suggest that similar pathologic mechanisms (including the expression of c-myc, EGF-R, PKD-1, cyclin, and bax/bcl-2 family mRNAs) may be responsible for the development of cystic changes in kidney, liver and pancreas in murine autosomal recessive PKD. Treatments targeting these similarly misexpressed mRNAs may be efficacious in ameliorating the cystic pathology in the kidney as well as the other affected organs in ARPKD.

Renal aspects of the term and preterm infant: a selective update

This review discusses new aspects of normal and abnormal renal development that expand insight into the adaptation of the neonatal kidneys to the stress of extrauterine life. Highlighted are some pitfalls in measuring glomerular filtration rate in the neonate mainly caused by postnatal fluctuations in serum creatinine levels. Serum creatinine levels are correlated with the authors' recent finding of tubular reabsorption of creatinine in the immature neonatal kidney. Renal maldevelopment in premature and small-for-date babies has been shown related to serious medical problems in adult life, including hypertension. This finding presents the pediatrician with a new role in the time-honored vocation of preventing disease. Mutations in several genes may be responsible for most cases of congenital or hereditary renal aberrations. Two renal disorders, congenital nephrotic syndrome and neonatal acute renal failure, and one form of treatment modality of newborn infants, renal replacement therapy, are discussed in detail. These conditions are rare in general pediatric practice, but they illustrate some of the new developments in the renal care of the newborn. A word of caution is offered about the use of nonsteroidal anti-inflammatory drugs during pregnancy and the newborn period. All nonsteroidal anti-inflammatory drugs administered indirectly to the unborn fetus and directly to the young newborn impair renal structure (fetus) and function (both fetus and newborn). The new data have been obtained with genetic and molecular biology techniques and with established methods of developmental renal physiology. A better understanding of the pathogenesis of neonatal renal disorders will result in new diagnostic procedures and improved preventive and therapeutic possibilities relevant to the neonate with a renal disorder.

cAMP-dependent protein kinase and proliferation differ in normal and polycystic kidney epithelia

Developmental control of cell proliferation is crucial, and abnormal principal cell proliferation may contribute to cystogenesis in polycystic kidney disease. This study investigates roles of cAMP and its primary effector, cAMP-dependent protein kinase (protein kinase A; PKA), in control of cell proliferation in filter-grown noncystic (NC) and cystic (CY)-derived principal cell cultures. These cultures had similar cAMP pathway characteristics upstream of PKA subunit distribution but differed in predicted PKA subtype distribution. Functionally, cultures were proliferative before polarization, with constitutively higher proliferation in CY cultures. NC cultures achieved levels similar to those of CY cultures on pharmacological manipulation of cAMP production or PKA activation or inhibition of PKA subtype I activity. Inhibition of overall PKA activity, or of PKA subtype II anchoring, diminished cAMP/PKA-mediated proliferation in NC cultures but had no effect on CY cultures. Polarized CY monolayers remained proliferative, but NC monolayers lost responsiveness. No large proliferation changes resulted from treatments of polarized cultures; however, polarized NC and CY cultures differed in poststimulation handling of PKA catalytic and type IIalpha regulatory subunits. Our results support PKA subtype regulation of prepolarization proliferation in NC principal cells and altered regulation of PKA in CY cells and suggest that differences at or downstream of PKA can contribute to altered proliferation in a developmental renal disease.

Microcyst formation and HIV-1 gene expression occur in multiple nephron segments in HIV-associated nephropathy

Tubular microcyst formation is a prominent histopathologic feature of HIV-associated nephropathy (HIVAN), but its pathogenesis is unknown. HIV-1 has recently been shown to infect renal tubular epithelial cells in patients with HIVAN. In addition, HIV-1 gene expression in renal epithelial cells has been shown to cause a renal disease that is identical to HIVAN in HIV-1 transgenic mice. In these studies, immunohistochemistry for tubular segment-specific markers and mRNA in situ hybridization for HIV-1 was used to determine which tubular segments develop microcysts and which segments express HIV-1 in the kidneys of transgenic mice and patients with HIVAN. It was found that microcysts involve multiple nephron segments in both patients with HIVAN and HIV-1 transgenic mice. Furthermore, HIV-1 infection in HIVAN and HIV-1 transgene expression also occurs in multiple segments of the nephron. These data support a direct role for HIV-1 infection of renal epithelial cells in the pathogenesis of microcyst formation in patients with HIVAN.

A novel inhibitor of tumor necrosis factor-alpha converting enzyme ameliorates polycystic kidney disease

BACKGROUND

Transforming growth factor-alpha (TGF-alpha) expression is abnormal in polycystic kidney disease. We previously demonstrated that blockade of the epidermal growth factor receptor (EGFR), the receptor for TGF-alpha, significantly slowed disease progression in the bpk murine model of autosomal-recessive kidney disease (ARPKD). In the present study, kidney TGF-alpha expression in this model is characterized, and the therapeutic potential of inhibiting TGF-alpha in ARPKD is examined using a novel inhibitor of tumor necrosis factor-alpha converting enzyme (TACE), the metalloproteinase that cleaves membrane-bound TGF-alpha to release the secreted ligand.

METHODS

Immunohistochemistry (IH) and Western analysis were performed on kidneys from cystic bpk mice and noncystic littermates at postnatal days 7, 14, and 21. Bpk mice and normal controls were treated with WTACE2, a competitive inhibitor of TACE, from day 7 until day 21, and the effects on kidney histology and renal function were assessed.

RESULTS

Increased TGF-alpha expression by IH was demonstrated in the proximal tubules (PT) at postnatal day 7 and collecting tubules (CT) by day 21. A parallel increase in kidney TGF-alpha expression was demonstrated by Western analysis. Treatment of cystic bpk mice with WTACE2 resulted in a 43% reduction in kidney weight to body weight ratio (11.2 vs. 19.7%), improved cystic index (3.2 vs. 4.8), reduced cystic CT to PT ratio (1.2 vs. 8), and a greater than 30% reduction in BUN and serum creatinine.

CONCLUSIONS

These findings support the pathophysiological role of the TGF-alpha/EGFR axis in murine ARPKD and demonstrate that inhibition of TGF-alpha secretion has therapeutic potential in PKD.

Treatment prospects for autosomal-dominant polycystic kidney disease

An increased understanding of the molecular genetic and cellular pathophysiologic mechanisms responsible for the development of autosomal-dominant polycystic kidney disease (ADPKD), made possible by the advances in molecular biology and genetics of the last three decades, has laid the foundation for the development of effective therapies. As the concept that a polycystic kidney is a neoplasm in disguise is becoming increasingly accepted, the development of therapies for ADPKD may benefit greatly from the expanding body of information on cancer chemoprevention and chemosuppression. This review summarizes the observations that already have been made and discusses therapies for PKD that deserve investigation.

A possible role for metalloproteinases in renal cyst development

The expansion of cysts in polycystic kidneys bears several similarities to the invasion of the extracellular matrix by benign tumors. We therefore hypothesized that cyst-lining epithelial cells produce extracellular matrix-degrading metalloproteinases and that the inhibition of these enzymes may represent a potential target for therapeutic intervention. Using in situ hybridization, we first analyzed the expression of membrane-type metalloproteinase 1 (MMP-14), an essential matrix metalloproteinase, of its inhibitor TIMP-2, and of the cytokine transforming growth factor (TGF)-beta2 in the (cy/+) rat model of autosomal-dominant polycystic kidney disease. Upregulated MMP-14 mRNA was predominantly located in cyst-lining epithelia and distal tubules, whereas TIMP-2 mRNA was confined almost exclusively to fibroblasts. TGF-beta2, a cytokine known to regulate the expression of matrix metalloproteinases and their inhibitors, was also expressed by cyst wall epithelia. We then treated (cy/+) rats with the metalloproteinase inhibitor batimastat for a period of 8 wk. The treatment with the metalloproteinase inhibitor batimastat resulted in a significant reduction of cyst number and kidney weight. Our study suggests that metalloproteinase inhibitors represent a new therapeutic tool against polycystic kidney disease, which should be applicable independently of the background of the disease.

An endocytosis defect as a possible cause of proteinuria in polycystic kidney disease

Because proteinuria has been demonstrated in patients with autosomal-dominant polycystic kidney disease (ADPKD), we have investigated whether proteinuria also occurs in the (cy/+) rat, a widely used model for ADPKD. Increased urinary excretion of proteins, in particular of albumin, can be found in 16-wk-old (cy/+) rats, with a gel electrophoresis pattern compatible with a tubular origin of proteinuria. Using FITC-labeled dextran as an in vivo tracer for renal tubular endosomal function, we could show that portions of cyst-lining epithelia from proximal tubules have lost the ability to endocytose, which is necessary for the reabsorption of low-molecular-weight proteins. By immunohistochemistry, the expression of other proteins implicated in endocytosis, such as the chloride channel ClC-5 and the albumin receptor megalin, correlated well with the presence and absence of FITC-dextran in cysts. As an example of growth factor systems possibly being affected by this endocytosis defect, we could detect increased urinary levels of insulin-like growth factor-I protein in (cy/+) animals. These data indicate that proteinuria and albuminuria in the aforementioned rat model for ADPKD are due to a loss of the endocytic machinery in epithelia of proximal tubular cysts. This may also affect the concentration of different growth factors and hormones in cyst fluids and thus modulate cyst development.

Development of autosomal recessive polycystic kidney disease in BALB/c-cpk/cpk mice

Autosomal recessive polycystic kidney disease (ARPKD) is a rare but devastating inherited disease in humans. Various strains of mice that are homozygous for the cpk gene display renal pathology similar to that seen in human ARPKD. The PKD progresses to renal insufficiency, azotemia, and ultimately a uremic death by approximately 3 wk of age. This study characterizes PKD in mice that are homozygous for the cpk gene on a BALB/c inbred mouse background. The BALB/c-cpk/cpk murine model displays renal as well as extrarenal pathology similar to that found in human ARPKD. The renal pathology includes the well-characterized early proximal tubule and, later, massive collecting duct cysts. The extrarenal defects in this murine model include common bile duct dilation, intrahepatic biliary duct cysts with periductal hyperplasia, and pancreatic dysplasia with cysts. Renal mRNA expression of c-myc, a proto-oncogene, and clusterin (SGP-2), a marker associated with immature collecting ducts, decreases during normal development but is upregulated in murine ARPKD. Expression of epidermal growth factor (EGF) mRNA is significantly diminished, whereas EGF receptor mRNA is upregulated in the BALB/c-cpk/cpk kidney compared with phenotypically normal littermates. To determine whether the altered EGF expression contributes to the development of PKD, neonatal mice were treated with exogenous EGF (1 microg/g body wt injected subcutaneously on postnatal days 3 through 9). EGF treatment reduced the relative kidney weight and common bile duct dilation and downregulated renal expression of clusterin and EGF receptor. However, exogenous EGF did not affect the degree of renal failure, the pancreatic pathology, or the misregulated renal expression of c-myc. In summary, the present study characterizes the renal and extrarenal pathology in the BALB/c-cpk/cpk murine model of ARPKD. Renal mRNA expression of EGF is diminished in this mouse model. EGF treatment did not prevent renal failure but ameliorated pathologic changes in the kidney and the biliary ducts of the BALB/c-cpk/cpk mouse.

Distinctive cyclic AMP-dependent protein kinase subunit localization is associated with cyst formation and loss of tubulogenic capacity in Madin-Darby canine kidney cell clones

Polycystic kidney disease is characterized by abnormal morphological development. Mechanisms that regulate cyst development may involve multiple signaling pathways. Cyst formation by Madin-Darby canine kidney (MDCK) cells in three-dimensional culture is assumed to be cyclic AMP-dependent and due to cyclic AMP-dependent protein kinase (cAPK) activation based on pharmacological responsiveness. To determine if different cyclic AMP (cAMP) pathways are associated with morphological development, the role of cAMP in regulating morphological change was examined in MDCK clones that form tumor-like or tubular structures under basal conditions. Pharmacological cAMP pathway activators induce cyst formation and diminish formation of other structures in three clones, whereas one clone is unaffected. Tyrosine kinase-mediated morphogens have little effect. Although all clones have intact cAMP signaling pathways, each has a unique subcellular distribution of cAPK regulatory subunits. This may reflect distinct mechanisms for cAPK anchoring, allowing cAPK subtype regulation of the unique phenotypic character of each clone through preferential access to substrates. These observations suggest a molecular basis for differential cAMP responsiveness in cells that develop distinct morphological phenotypes. This evidence establishes these MDCK clones as models for understanding the mechanism and functional significance of cAPK subunit localization and may have broader implications for cystogenesis in polycystic kidney disease.

Proximal tubular cysts in fetal human autosomal recessive polycystic kidney disease

Standard texts describe human autosomal recessive polycystic kidney disease (ARPKD) as a cystic kidney disease in which lesions are localized to collecting tubules. Murine models of ARPKD consistently demonstrate an early phase of proximal tubular (PT) cystic involvement, which disappears shortly after birth. This is followed by a phase of collecting tubular (CT) cyst formation and progressive enlargement leading to compromise of renal function and death. Because the description of cystic lesions in human ARPKD has been largely based on postnatal specimens, PT cyst formation was hypothesized to be a characteristic feature of fetal human, as well as murine, ARPKD. This study examines nephron segment-specific cyst localization histochemically by lectin binding in 11 human ARPKD specimens obtained at different fetal and postnatal ages. PT cysts were found in human fetal specimens from gestational age 14 wk to 26 wk. The percentage of cysts involving PT segments ranged from 2 to 41%. The cystic index of PT cysts ranged from 2 to 5. In all specimens in which PT cysts were found, both the percentage of CT cysts and their cystic index were equal to or greater than the percentage of PT cysts and the associated PT cystic index. PT cysts were absent in all kidney specimens older than 34 wk gestational age. It is concluded that human ARPKD, like murine ARPKD, has a transient phase of PT cyst formation during early fetal development.

Treatment of polycystic kidney disease with a novel tyrosine kinase inhibitor

Treatment of polycystic kidney disease with a novel tyrosine kinase inhibitor.

BACKGROUND

We have previously demonstrated an essential role for increased epidermal growth factor receptor (EGFR) activity in mediating renal cyst formation and biliary epithelial hyperplasia in murine models of autosomal recessive polycystic kidney disease (ARPKD). This study was designed to determine whether or not treatment with a newly developed inhibitor of EGFR tyrosine kinase activity (EKI-785) would reduce renal and biliary abnormalities in murine ARPKD.

METHODS

Balb/c-bpk/bpk (BPK) litters were treated with EKI-785, an EGFR-specific tyrosine kinase inhibitor. Animals were treated by intraperitoneal injection beginning at postnatal day 7 and were treated until postnatal day 24 or 48. EKI-785's effectiveness was measured by a reduction in the renal cystic index, an increased life span, and maintenance of normal renal function.

RESULTS

Treatment of BPK mice with EKI-785 resulted in a marked reduction of collecting tubule (CT) cystic lesions, improved renal function, decreased biliary epithelial abnormalities, and an increased life span. Untreated cystic animals died of renal failure at postnatal day 24 (P-24) with a CT cystic index of 4.8, a maximal urine osmolarity of 361 mOsm, and moderate to severe biliary abnormalities. Cystic animals treated with EKI-785 to postnatal day 48 (P-48) were alive and well with normal renal function, a reduced CT cystic index of 2.0 (P < 0.02), a threefold increased in maximum urinary concentrating ability (P < 0.01), and a significant decrease in biliary epithelial proliferation/fibrosis (P < 0.01).

CONCLUSION

This study demonstrates that EKI-785 has therapeutic effectiveness in improving histopathologic abnormalities and decreasing mortality in murine ARPKD.