Type I interferon regulation by USP18 is a key vulnerability in cancer.

Precise regulation of Type I interferon signaling is crucial for combating infection and cancer while avoiding autoimmunity. Type I interferon signaling is negatively regulated by USP18. USP18 cleaves ISG15, an interferon-induced ubiquitin-like modification, via its canonical catalytic function, and inhibits Type I interferon receptor activity through its scaffold role. USP18 loss-of-function dramatically impacts immune regulation, pathogen susceptibility, and tumor growth. However, prior studies have reached conflicting conclusions regarding the relative importance of catalytic versus scaffold function. Here, we develop biochemical and cellular methods to systematically define the physiological role of USP18. By comparing a patient-derived mutation impairing scaffold function (I60N) to a mutation disrupting catalytic activity (C64S), we demonstrate that scaffold function is critical for cancer cell vulnerability to Type I interferon. Surprisingly, we discovered that human USP18 exhibits minimal catalytic activity, in stark contrast to mouse USP18. These findings resolve human USP18's mechanism-of-action and enable USP18-targeted therapeutics.

Optimization and Mechanistic Investigations of Novel Allosteric Activators of PKG1α.

Activation of PKG1α is a compelling strategy for the treatment of cardiovascular diseases. As the main effector of cyclic guanosine monophosphate (cGMP), activation of PKG1α induces smooth muscle relaxation in blood vessels, lowers pulmonary blood pressure, prevents platelet aggregation, and protects against cardiac stress. The development of activators has been mostly limited to cGMP mimetics and synthetic peptides. Described herein is the optimization of a piperidine series of small molecules to yield activators that demonstrate in vitro phosphorylation of vasodilator-stimulated phosphoprotein as well as antiproliferative effects in human pulmonary arterial smooth muscle cells. Hydrogen/deuterium exchange mass spectrometry experiments with the small molecule activators revealed a mechanism of action consistent with cGMP-induced activation, and an X-ray co-crystal structure with a construct encompassing the regulatory domains illustrated a binding mode in an allosteric pocket proximal to the low-affinity cyclic nucleotide-binding domain.

Circulating bone morphogenetic protein 1-3 isoform increases renal fibrosis.

Bone morphogenetic proteins (BMPs) participate in organ regeneration through autocrine and paracrine actions, but the existence and effects of these proteins in the systemic circulation is unknown. Using liquid chromatography-mass spectrometry, we identified BMP6, GDF15, and the BMP1-3 isoform of the Bmp1 gene in plasma samples from healthy volunteers and patients with CKD. We isolated the endogenous BMP1-3 protein and demonstrated that it circulates as an active enzyme, evidenced by its ability to cleave dentin matrix protein-1 in vitro. In rats with CKD, administration of recombinant BMP1-3 increased renal fibrosis and reduced survival. In contrast, administration of a BMP1-3-neutralizing antibody reduced renal fibrosis, preserved renal function, and increased survival. In addition, treating with the neutralizing antibody was associated with low plasma levels of TGFß1 and connective tissue growth factor. In HEK293 cells and remnant kidneys, BMP1-3 increased the transcription of collagen type I, TGFß1, ß-catenin, and BMP7 via a BMP- and Wnt-independent mechanism that involved signaling through an integrin ß1 subunit. The profibrotic effect of BMP1-3 may, in part, be a result of the accompanied decrease in decorin (DCN) expression. Taken together, inhibition of circulating BMP1-3 reduces renal fibrosis, suggesting that this pathway may be a therapeutic target for CKD.

Pharmacodynamic model of parathyroid hormone modulation by a negative allosteric modulator of the calcium-sensing receptor.

In this study, a pharmacodynamic model is developed, based on calcium-parathyroid hormone (PTH) homeostasis, which describes the concentration-effect relationship of a negative allosteric modulator of the calcium-sensing receptor (CaR) in rats. Plasma concentrations of drug and PTH were determined from plasma samples obtained via serial jugular vein sampling following single subcutaneous doses of 1, 5, 45, and 150 mg/kg to male Sprague-Dawley rats (n = 5/dose). Drug pharmacokinetics was described by a one-compartment model with first-order absorption and linear elimination. Concentration-time profiles of PTH were characterized using a model in which the compound allosterically modulates Ca(+2) binding to the CaR that, in turn, modulates PTH through a precursor-pool indirect response model. Additionally, negative feedback was incorporated to account for tolerance observed at higher dose levels. Model fitting and parameter estimation were conducted using the maximum likelihood algorithm. The proposed model well characterized the data and provided compound specific estimates of the K(i) and cooperativity constant (α) of 1.47 ng/mL and 0.406, respectively. In addition, the estimated model parameters for PTH turnover were comparable to that previously reported. The final generalized model is capable of characterizing both PTH-Ca(+2) homeostasis and the pharmacokinetics and pharmacodynamics associated with the negative allosteric CaR modulator. As such, the model provides a simple platform for analysis of drugs targeting the PTH-Ca(+2) system.

Metabolism-guided design of short-acting calcium-sensing receptor antagonists.

As part of a strategy to deliver short-acting calcium-sensing receptor (CaSR) antagonists, the metabolically labile thiomethyl functionality was incorporated into the zwitterionic amino alcohol derivative 3 with the hope of increasing human clearance through oxidative metabolism, while delivering a pharmacologically inactive sulfoxide metabolite. The effort led to the identification of thioanisoles 22 and 23 as potent and orally active CaSR antagonists with a rapid onset of action and short pharmacokinetic half-lives, which led to a rapid and transient stimulation of parathyroid hormone in a dose-dependent fashion following oral administration to rats. On the basis of the balance between target pharmacology, safety, and human disposition profiles, 22 and 23 were advanced as clinical candidates for the treatment of osteoporosis.

Short-acting 5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one derivatives as orally-active calcium-sensing receptor antagonists.

Synthesis and structure-activity relationship (SAR) studies on 5-trifluoromethylpyrido[4,3-d]pyrimidin-4(3H)-ones, a novel class of calcium receptor antagonists is described with particular emphasis on optimization of the pharmacokinetic/pharmacodynamic parameters required for a short duration of action compound. Orally-active compounds were identified which displayed the desired animal pharmacology (rapid and transient stimulation of parathyroid hormone) essential for bone anabolic effects.

The discovery of novel calcium sensing receptor negative allosteric modulators.

The design and profile of a series of zwitterionic calcium sensing receptor negative allosteric modulators is described. Evaluation of key analogues using a rat model demonstrate a robust response, significantly improved potency over ronacaleret and have the potential as an oral, anabolic treatment for osteoporosis.

Mechanism-based pharmacokinetic/pharmacodynamic model of parathyroid hormone-calcium homeostasis in rats and humans.

The purpose of this study was to develop a mechanism-based pharmacokinetic/pharmacodynamic model that describes the regulation of the parathyroid hormone (PTH)-Ca(2+) system in rats and humans. Temporal concentration data for endogenous PTH and Ca(2+) were extracted from literature for rats (normal adult males) and humans. In addition, exogenous PTH was administered subcutaneously to male Sprague-Dawley rats with jugular vein catheters, and plasma concentrations were measured over time. A mathematical model was developed and fitted simultaneously to endogenous PTH, Ca(2+), and exogenous PTH concentrations in rats. Ca(2+) concentrations were described using a turnover model, with its depletion being induced by a chelating agent, and PTH concentrations were characterized using a precursor-dependent indirect response model. The same structural model was used for fitting data obtained in humans. PTH stimulation was driven by occupancy of the Ca(2+) sensing receptor, and lowering of physiological Ca(2+) concentrations increased PTH secretion, with PTH profiles being adequately described by the model. PTH stimulatory capacity was baseline-dependent in rats [S(max_rats) = 34.8 x PTH(0)] and humans [S(max_humans) = 392/PTH(0)]. Modeling results suggest that normal rats are twice as sensitive to Ca(2+)-induced PTH stimulation compared with humans. In conclusion, the developed model adequately characterizes the PTH-Ca(2+) regulation across species and may be useful in the development of therapeutic drugs targeting this system.

A novel, non-prostanoid EP2 receptor-selective prostaglandin E2 agonist stimulates local bone formation and enhances fracture healing.

UNLABELLED: CP-533,536, a newly discovered, non-prostanoid EP2 receptor-selective PGE2 agonist, stimulates local bone formation and enhances fracture healing in rat models. INTRODUCTION: There is a significant medical need for agents that can stimulate local bone formation and enhance fracture healing. We tested the effects of CP-533,536, a newly discovered, non-prostanoid EP2 receptor-selective prostaglandin E2 (PGE2) agonist, in stimulating local bone formation and enhancing fracture healing in rat models. MATERIALS AND METHODS: In the first model, a single injection of CP-533,536 at doses of 0.3, 1, or 3 mg/kg to the proximal tibial metaphysis of 6-week-old male rats was given on day 1, and the local bone anabolic effect was determined on day 7. We then tested the effects of this compound in inducing bone formation on rat periosteum of the femur. A single dose of 0.3 mg of CP-533,536 incorporated in a poly-(D,L-lactide-co-glycolide) (PLGH) matrix was injected onto the periosteum of the femur in 3-week-old male rats, and local bone formation was determined on day 14. Finally, the ability of CP-533,536 in PLGH matrix in enhancing fracture healing was tested using the rat femoral fracture model. CP-533,536 in PLGH matrix at doses of 0.05, 0.5, or 5 mg was delivered to the local fracture site on the same day of fracture, and its efficacy was evaluated on day 21. RESULTS AND CONCLUSIONS: A single injection of CP-533,536 at doses of 0.3, 1, or 3 mg/kg to the proximal tibial metaphysis dose-dependently stimulated local lamellar bone formation on trabecular, endocortical, and periosteal surfaces, and thus increased bone mineral content and bone strength at the injected site. Similarly, a single injection of 0.3 mg of CP-533,536 incorporated in PLGH matrix onto the periosteum of the femur induced significantly local bone formation. In the rat femoral fracture model, CP-533,536 in PLGH matrix at doses of 0.05, 0.5, and 5 mg dose-dependently increased callus size, density, and strength compared with PLGH matrix alone. These results show that CP-533,536 stimulates new bone formation on trabecular, endocortical, and periosteal surfaces and enhances fracture healing. These data reveal that EP2 receptor-selective agonists provide therapeutic potential for local bone augmentation, bone repair, and bone healing in humans.