Radiographic Imaging in Autosomal Dominant Polycystic Kidney Disease: A Claims Analysis.

BACKGROUND: Progression of autosomal dominant polycystic kidney disease (ADPKD) is highly variable, with some patients progressing rapidly to end-stage renal disease (ESRD). Abdominal imaging is an important modality for verifying diagnosis in patients at risk for rapidly progressing ADPKD, targeting them for early treatment that could slow onset of ESRD. Published literature is limited on the real-world abdominal imaging utilization patterns in ADPKD. METHODS: A retrospective healthcare administrative claims analysis examining abdominal imaging scans occurring from January 1, 2014, through June 30, 2017, was conducted using the IBM MarketScan® commercial and Medicare supplemental databases. Patients in the United States who were at least 18 years old and had at least 1 inpatient claim or 2 outpatient claims (with different dates of service) with an ADPKD diagnosis code, as defined by the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM codes 753.12 [polycystic kidney, unspecified type] and 753.13 [polycystic kidney, autosomal dominant] and/or Tenth Revision (ICD-10-CM codes Q61.2 [polycystic kidney, adult type] and Q61.3 [polycystic kidney, unspecified]) were included. RESULTS: Of the 4637 patients with ADPKD (mean age, 51.2 years [SD = 15.52]), 59% had ≥1 abdominal imaging scan. Of these patients, 46% had ≥1 computed tomography (CT) scan, 25% had ≥1 ultrasound, 10% had ≥1 magnetic resonance imaging scan. Among the 1754 patients (38%) with chronic kidney disease (CKD) stage information, CT imaging was more frequent in later stages (31% stage 1 versus 68% stage 5). The proportion of patients undergoing at least 1 CT or MRI scan increased with disease severity (37% in stage 1, 42% in stage 2, 48% in stage 3, 56% in stage 4, and 71% in stage 5). CONCLUSION: Results of this analysis support the need for further investigation into abdominal imaging utilization in managing patients with ADPKD. Future research could clarify barriers and increase access to imaging, which has the potential to inform risk stratification, help patients delay dialysis or transplantation associated with ESRD, and help health systems avoid the costs associated with ESRD.

Disconnect in Assessments of Autosomal Dominant Polycystic Kidney Disease Burden Between Patients and Physicians: A Survey Study.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is a rare inherited kidney disorder with considerable symptom burden and negative effects even in early-stage disease. Patients' reporting of ADPKD symptom burden may differ from physicians' impressions. In this quantitative, cross-section survey study, we evaluated patient and physician assessments of symptom burden at early- and late-stage ADPKD. METHODS: In the United States, 300 patients with ADPKD and 155 physicians treating patients with ADPKD completed online surveys administered by Kantar. Disease stage was categorized as early (chronic kidney disease [CKD] stages 1-3) or late (stages 4-5). Patients completed the Work Productivity and Activity Impairment Questionnaire and reported current disease symptoms. Patients and physicians assessed impacts of ADPKD on daily life and burden of specific symptoms. Statistical analyses compared patient versus physician responses stratified by early- versus late-stage ADPKD. RESULTS: We found that impairment in work productivity was statistically greater in late- versus early-stage CKD. Compared with physicians' impressions, patients were more likely at early stages and less likely at later stages to report a moderate/strong impact of ADPKD on daily life. Among patients, 74% with early- and 88% with late-stage disease reported that ADPKD caused them to modify their daily lives. In early-stage disease, patients reported a statistically greater burden from feeling exhausted and less burden from dull kidney pain, cardiovascular problems, high blood pressure, and liver cysts than physicians assumed. At later stages, patients reported feeling exhausted and skeletal/joint pain as more burdensome, and frequent urination, high blood pressure, liver cysts, and hematuria as less burdensome, compared with physicians' impressions. CONCLUSION: The results of this survey study demonstrate a disconnect between patients' experiences and physicians' awareness of the burden of ADPKD and highlight the need for more patient/physician discussion of symptoms and disease management.

Implications of early diagnosis of autosomal dominant polycystic kidney disease: A post hoc analysis of the TEMPO 3:4 trial.

It is unknown whether early diagnosis of autosomal dominant polycystic kidney disease (ADPKD) can enable earlier management and improve outcomes. We conducted a post hoc analysis of data from the TEMPO 3:4 trial. Subjects were stratified by ADPKD diagnosis at age ≤18 (childhood diagnosis [CD]) or>18 (adulthood diagnosis [AD]). Groups were compared for baseline characteristics and total kidney volume (TKV) growth and estimated glomerular filtration rate (eGFR) decline over 3 years. 294 CD and 1148 AD subjects were analyzed. At inclusion, CD subjects were younger (mean age 34.2 versus 39.8 years; p < 0.0001) and had better eGFR (mean ± SD 87.4 ± 23.9 versus 80.1 ± 20.7 mL/min/1.73 m2; p < 0.0001), while CD had more severe Mayo risk classification (p < 0.0001) and more PKD1 mutations (p = 0.003). No statistical differences were found in TKV or eGFR change. At study end, placebo-treated CD subjects had better eGFR than projected by a prediction equation (mean difference ±SD for observed versus predicted eGFR: 2.18 ± 10.7 mL/min/1.73 m2; p = 0.0475). However, these results are not confirmed when excluding stage 1 CKD. Whether CD subjects, despite their risk profile, have a slower disease course than predicted remains inconclusive. Future studies are needed to confirm that early diagnosis and management can alter the disease course of ADPKD.

Soluble Urokinase Plasminogen Activator Receptor and Decline in Kidney Function in Autosomal Dominant Polycystic Kidney Disease.

BACKGROUND: Levels of soluble urokinase plasminogen activator receptor (suPAR), an inflammation marker, are strongly predictive of incident kidney disease. Patients with autosomal dominant polycystic kidney disease (ADPKD) experience progressive decline in renal function, but rates of decline and outcomes vary greatly. Whether suPAR levels are predictive of declining kidney function in patients with ADPKD is unknown. METHODS: We assessed suPAR levels in 649 patients with ADPKD who underwent scheduled follow-up for at least 3 years, with repeated measurements of height-adjusted total kidney volume and creatinine-derived eGFR. We used linear mixed models for repeated measures and Cox proportional hazards to characterize associations between baseline suPAR levels and follow-up eGFR or incident ESRD. RESULTS: The median suPAR level was 2.47 ng/ml and median height-adjusted total kidney volume was 778, whereas mean eGFR was 84 ml/min per 1.73 m2. suPAR levels were associated with height-adjusted total kidney volume (ß=0.02; 95% confidence interval, 0.01 to 0.03), independent of age, sex, race, hypertension, and eGFR. Patients in the lowest suPAR tertile (<2.18 ng/ml) had a 6.8% decline in eGFR at 3 years and 22% developed CKD stage 3, whereas those in the highest tertile (suPAR>2.83 ng/ml) had a 19.4% decline in eGFR at 3 years and 68% developed CKD stage 3. suPAR levels >2.82 ng/ml had a 3.38-fold increase in the risk of incident ESRD. CONCLUSIONS: suPAR levels were associated with progressive decline in renal function and incident ESRD in patients with ADPKD, and may aid early identification of patients at high risk of disease progression.

Discovery of a First-in-Class Receptor Interacting Protein 1 (RIP1) Kinase Specific Clinical Candidate (GSK2982772) for the Treatment of Inflammatory Diseases.

RIP1 regulates necroptosis and inflammation and may play an important role in contributing to a variety of human pathologies, including immune-mediated inflammatory diseases. Small-molecule inhibitors of RIP1 kinase that are suitable for advancement into the clinic have yet to be described. Herein, we report our lead optimization of a benzoxazepinone hit from a DNA-encoded library and the discovery and profile of clinical candidate GSK2982772 (compound 5), currently in phase 2a clinical studies for psoriasis, rheumatoid arthritis, and ulcerative colitis. Compound 5 potently binds to RIP1 with exquisite kinase specificity and has excellent activity in blocking many TNF-dependent cellular responses. Highlighting its potential as a novel anti-inflammatory agent, the inhibitor was also able to reduce spontaneous production of cytokines from human ulcerative colitis explants. The highly favorable physicochemical and ADMET properties of 5, combined with high potency, led to a predicted low oral dose in humans.

DNA-Encoded Library Screening Identifies Benzo[b][1,4]oxazepin-4-ones as Highly Potent and Monoselective Receptor Interacting Protein 1 Kinase Inhibitors.

The recent discovery of the role of receptor interacting protein 1 (RIP1) kinase in tumor necrosis factor (TNF)-mediated inflammation has led to its emergence as a highly promising target for the treatment of multiple inflammatory diseases. We screened RIP1 against GSK's DNA-encoded small-molecule libraries and identified a novel highly potent benzoxazepinone inhibitor series. We demonstrate that this template possesses complete monokinase selectivity for RIP1 plus unique species selectivity for primate versus nonprimate RIP1. We elucidate the conformation of RIP1 bound to this benzoxazepinone inhibitor driving its high kinase selectivity and design specific mutations in murine RIP1 to restore potency to levels similar to primate RIP1. This series differentiates itself from known RIP1 inhibitors in combining high potency and kinase selectivity with good pharmacokinetic profiles in rodents. The favorable developability profile of this benzoxazepinone template, as exemplified by compound 14 (GSK'481), makes it an excellent starting point for further optimization into a RIP1 clinical candidate.

Discovery of Small Molecule RIP1 Kinase Inhibitors for the Treatment of Pathologies Associated with Necroptosis.

Potent inhibitors of RIP1 kinase from three distinct series, 1-aminoisoquinolines, pyrrolo[2,3-b]pyridines, and furo[2,3-d]pyrimidines, all of the type II class recognizing a DLG-out inactive conformation, were identified from screening of our in-house kinase focused sets. An exemplar from the furo[2,3-d]pyrimidine series showed a dose proportional response in protection from hypothermia in a mouse model of TNFα induced lethal shock.

Role of the amino terminus of G protein-coupled receptor kinase 2 in receptor phosphorylation.

G protein-coupled receptor kinases (GRKs) specifically phosphorylate activated G protein-coupled receptors. While the X-ray crystal structures of several GRKs have been determined, the mechanism of interaction of GRK with GPCRs is currently unknown. To further characterize the role of the GRK2 amino terminus in receptor interaction and phosphorylation, we generated a series of point mutations within the first 10 amino acids of GRK2 and tested their ability to phosphorylate receptor and nonreceptor substrates. Although all mutants exhibited some impairment in receptor phosphorylation, three of the mutants, D3K, L4A, and D10A, were the most severely affected. Using the beta2-adrenergic receptor and rhodopsin as receptor substrates and tubulin as a nonreceptor substrate, we demonstrated that the kinase activity toward the receptors was severely decreased in the mutants, while they fully retained their ability to phosphorylate tubulin. Moreover, the amino-terminal mutants were able to bind to the receptor but, in contrast to wild-type GRK2, were not activated by receptor binding. A synthetic peptide containing residues 1-14 of GRK2 served as a noncompetitive inhibitor of receptor phosphorylation by GRK2, while a comparable peptide from GRK5 had no effect on GRK2 activity. Secondary structure prediction and circular dichroism suggest that the GRK2 amino-terminal peptide forms an amphipathic alpha-helix. Taken together, we propose a mechanism whereby the extreme amino terminus of GRK2 forms an intramolecular interaction that selectively enhances the catalytic activity of the kinase toward receptor substrates.

Arrestin-2 and G protein-coupled receptor kinase 5 interact with NFkappaB1 p105 and negatively regulate lipopolysaccharide-stimulated ERK1/2 activation in macrophages.

Toll-like receptors (TLRs) are a recently described receptor class involved in the regulation of innate and adaptive immunity. Here, we demonstrate that arrestin-2 and GRK5 (G protein-coupled receptor kinase 5), proteins that regulate G protein-coupled receptor signaling, play a negative role in TLR4 signaling in Raw264.7 macrophages. We find that lipopolysaccharide (LPS)-induced ERK1/2 phosphorylation is significantly enhanced in arrestin-2 and GRK5 knockdown cells. To elucidate the mechanisms involved, we tested the effect of arrestin-2 and GRK5 knockdown on LPS-stimulated signaling components that are upstream of ERK phosphorylation. Upon LPS stimulation, IkappaB kinase promotes phosphorylation and degradation of NFkappaB1 p105 (p105), which releases TPL2 (a MAP3K), which phosphorylates MEK1/2, which in turn phosphorylates ERK1/2. We demonstrate that knockdown of arrestin-2 leads to enhanced LPS-induced phosphorylation and degradation of p105, enhanced TPL2 release, and enhanced MEK1/2 phosphorylation. GRK5 knockdown also results in enhanced IkappaB kinase-mediated p105 phosphorylation and degradation, whereas GRK2 and GRK6 knockdown have no effect on this pathway. In vitro analysis demonstrates that arrestin-2 directly binds to the COOH-terminal domain of p105, whereas GRK5 binds to and phosphorylates p105. Taken together, these results suggest that p105 phosphorylation by GRK5 and binding of arrestin-2 negatively regulates LPS-stimulated ERK activation. These results reveal that arrestin-2 and GRK5 are important negative regulatory components in TLR4 signaling.

Structure/function analysis of alpha2A-adrenergic receptor interaction with G protein-coupled receptor kinase 2.

G protein-coupled receptors (GPCRs) mediate the ability of a diverse array of extracellular stimuli to control intracellular signaling. Many GPCRs are phosphorylated by G protein-coupled receptor kinases (GRKs), a process that mediates agonist-specific desensitization in many cells. Although GRK binding to activated GPCRs results in kinase activation and receptor phosphorylation, relatively little is known about the mechanism of GRK/GPCR interaction or how this interaction results in kinase activation. Here, we used the alpha2A-adrenergic receptor (alpha(2A)AR) as a model to study GRK/receptor interaction because GRK2 phosphorylation of four adjacent serines within the large third intracellular loop of this receptor is known to mediate desensitization. Various domains of the alpha(2A)AR were expressed as glutathione S-transferase fusion proteins and tested for the ability to bind purified GRK2. The second and third intracellular loops of the alpha(2A)AR directly interacted with GRK2, whereas the first intracellular loop and C-terminal domain did not. Truncation mutagenesis identified three discrete regions within the third loop that contributed to GRK2 binding, the membrane proximal N- and C-terminal regions as well as a central region adjacent to the phosphorylation sites. Site-directed mutagenesis revealed a critical role for specific basic residues within these regions in mediating GRK2 interaction with the alpha(2A)AR. Mutation of these residues within the holo-alpha(2A)AR diminished GRK2-promoted phosphorylation of the receptor as well as the ability of the kinase to be activated by receptor binding. These studies provide new insight into the mechanism of interaction and activation of GRK2 by GPCRs and suggest that GRK2 binding is critical not only for receptor phosphorylation but also for full activity of the kinase.

Phosphorylation-independent desensitization of G protein-coupled receptors?

G protein-coupled receptors (GPCRs) are involved in a multitude of signaling processes and respond to a wide range of ligands. The activity of GPCRs is subject to three principal modes of regulation: desensitization, trafficking, and down-regulation. Desensitization is defined as a loss in the responsiveness of a signaling system. The generally established paradigm for GPCR desensitization involves receptor phosphorylation by GPCR kinases (GRKs), initiated by agonist-induced conformational changes in the receptor or by kinases activated by specific signaling pathways. GRKs have several interaction domains and may be able to contribute to receptor desensitization through mechanisms that do not involve the kinase activity of GRK. Pao and Benovic discuss some of these interactions and their relevance for the regulation of GPCR signaling.