Comparison of AMG 416 and cinacalcet in rodent models of uremia.

BACKGROUND: AMG 416 is a novel peptide agonist of the calcium-sensing receptor (CaSR). This report describes the activity of AMG 416 in two different rodent models of uremia, compared in each case to cinacalcet, an approved therapeutic for secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease on dialysis. METHODS: AMG 416 was administered as a single intravenous (IV) bolus in a severe, acute model of renal insufficiency (the "1K1C" model) and plasma parathyroid hormone (PTH) and serum calcium levels were monitored for 24 hours. In a chronic, less severe model of renal dysfunction, the 5/6 nephrectomy (5/6 Nx) model, AMG 416 was administered as a once-daily IV bolus for 28 days. Both studies included a control (vehicle) group and a comparison cinacalcet group (po dosing at 30 mg/kg and 10 mg/kg for the 1K1C and 5/6 Nx studies, respectively). RESULTS: Administration of AMG 416 by IV bolus injection into rats with acute renal dysfunction (1K1C model) resulted in a sustained reduction in plasma PTH from the initial elevated values. Following a single IV bolus (0.5 mg/kg), AMG 416 caused a substantial drop in PTH levels which remained approximately 50% below their initial level at 24 hrs. In the same model, oral treatment with cinacalcet (30 mg/kg) resulted in an acute drop in PTH which almost returned to the starting level by 24 hours after dosing. In the 5/6 Nx chronic uremia model, daily IV dosing of AMG 416 over 4 weeks (1 mg/kg) resulted in a sustained reduction in PTH, with approximately 50% of the initial level observed 48 hours post treatment throughout the study. Cinacalcet treatment (10 mg/kg) in the same model resulted in acutely lowered plasma PTH levels which returned to placebo levels by 24 hours post-dose. Consistent with the reductions in plasma PTH, reductions in serum calcium were observed in both AMG 416- and cinacalcet-treated animals. CONCLUSIONS: As a long-acting CaSR agonist suitable for administration by the IV route, AMG 416 is a potential new therapy for the treatment of CKD patients with SHPT receiving hemodialysis.

Pharmacology of AMG 416 (Velcalcetide), a novel peptide agonist of the calcium-sensing receptor, for the treatment of secondary hyperparathyroidism in hemodialysis patients.

A novel peptide, AMG 416 (formerly KAI-4169, and with a United States Adopted Name: velcalcetide), has been identified that acts as an agonist of the calcium-sensing receptor (CaSR). This article summarizes the in vitro and in vivo characterization of AMG 416 activity and the potential clinical utility of this novel compound. AMG 416 activates the human CaSR in vitro, acting by a mechanism distinct from that of cinacalcet, the only approved calcimimetic, since it can activate the CaSR both in the presence or the absence of physiologic levels of extracellular calcium. Administration of AMG 416 in vivo into either normal or renally compromised rats results in dose-dependent reductions in parathyroid hormone (PTH) levels and corresponding decreases in serum calcium, regardless of the baseline level of PTH. Treatment of 5/6 nephrectomized rats with AMG 416 resulted in dramatic improvements in their metabolic profile, including lower PTH and serum creatinine levels, reduced amounts of vascular calcification, attenuated parathyroid hyperplasia, and greater expression of the parathyroid gland regulators CaSR, vitamin D receptor, and FGF23 receptor compared with vehicle-treated animals. No drug accumulation was observed under this dosing regimen, and the terminal half-life of AMG 416 was estimated to be 2-4.5 hours. As a long-acting CaSR agonist, AMG 416 is an innovative new therapy for the treatment of hemodialysis patients with secondary hyperparathyroidism.

Therapeutic applications of cell-penetrating peptides.

Since the discovery over 15 years ago of a protein transcription factor that possessed the ability to cross the plasma membrane, cell-penetrating peptides (CPPs) have been evaluated for the ability to transport diverse cargoes into cells, tissues, and organs. Certain CPPs have been used for the intracellular delivery of information-rich molecules to modulate protein-protein interactions and thereby inhibit key cellular mechanisms of disease. The ability to introduce drugs into cells allows the conventional biodistribution of drugs to be altered in order to favorably impact toxicity, patient compliance, and other treatment factors. In this monograph, we present the current status and future prospects for the application of CPPs to the development of human therapeutics. We discuss some of the advantages and disadvantages of using CPPs in the in vivo setting, and review the current status of a number of preclinical and human clinical studies of CPP-mediated delivery of therapeutics. These include CPP-conjugated moieties directed against a growing variety of targets and disease areas, including cancer, cardiology, pain, and stroke. Our discussion focuses on those therapeutics that have been tested in humans, including a CPP conjugate for the treatment of acute myocardial infarction. The promising results obtained in a number of these studies indicate that CPPs may have an important role in the development of novel therapeutics.

Intracranial drug-delivery scaffolds: biocompatibility evaluation of sucrose acetate isobutyrate gels.

INTRODUCTION: Sucrose acetate isobutyrate (SAIB) is a water insoluble, biodegradable gel used for controlled-release oral and subcutaneous drug delivery. We investigated SAIB compatibility in the rat central nervous system (CNS) by implanting solutions of SAIB in adult and in neonatal brains. METHODS: 10-15 microL solutions of SAIB gels in 0-30% ethanol were injected into the cerebral cortex of adult Fischer 344 rats. Control animals were implanted with a 10 mg biodegradable poly anhydride copolymer of poly [bis (p-carboxyphenoxy) propane] anhydride and sebacic acid (PCPP:SA). Adult rats were evaluated for signs of pain and distress, including changes in posture, facial signs, and grooming behavior. 1-2 microL solutions of SAIB gels in 15% ethanol were injected into brains of 12-24 h-old rats. Neonatal rats were evaluated for survival. Adult and neonatal brains were examined by histopathology 3-48 days after implant. RESULTS: Gel implants produced elliptical compression of cortical tissue, cell loss, and inflammation. Cell loss appeared to be confined to the implantation wound and associated neuronal fields. In adult rats, neurophil compression, inflammation, and cell loss appeared similar with the 10-mg PCPP:SA implants and the 10-mg SAIB implants. There was no clinical evidence of pain or distress from SAIB implants. 1-2 microL implants of SAIB-15% ethanol had no effect on survival of neonatal animals. CONCLUSION: Brain implants of SAIB induce a mild to moderate inflammatory response and associated neuronal cell damage. The implants appeared to be biocompatible in adult and neonatal animals. These results suggest that further studies of SAIB as an injectable drug-delivery scaffold for CNS therapeutic agents are warranted.

Salicylate induces tinnitus through activation of cochlear NMDA receptors.

Salicylate, the active component of aspirin, is known to induce tinnitus. However, the site and the mechanism of generation of tinnitus induced by salicylate remains unclear. Here, we developed a behavioral procedure to measure tinnitus in rats. The behavioral model was based on an active avoidance paradigm in which rats had to display a motor task (i.e., to jump on a climbing pole when hearing a sound). Giving salicylate led to a decrease in the percentage of correct responses (score) and a drastic increase in the number of false positive responses (i.e., animals execute the motor task during a silent period). Presentation of the sound at a constant perceptive level prevents decrease of the score, leading to the proposal that score is related to hearing performance. In contrast, the increase of false positive responses remained unchanged. In fact, animals behaved as if they hear a sound, indicating that they are experiencing tinnitus. Mefenamate in place of salicylate also increased the number of false positive responses, suggesting that salicylate-induced tinnitus is related to an inhibition of cyclooxygenase. One physiological basis of salicylate ototoxicity is likely to originate from altered arachidonic acid metabolism. Because arachidonic acid potentiates NMDA receptor currents, we tested the involvement of cochlear NMDA receptors in the occurrence of tinnitus. Application of NMDA antagonists into the perilymphatic fluids of the cochlea blocked the increase in pole-jumping behavior induced by salicylate, suggesting that salicylate induces tinnitus through activation of cochlear NMDA receptors.

A surgical technique for safely placing a drug delivery catheter into the pons of primates: preliminary results of carboplatin infusion.

OBJECTIVE: We sought to develop a neurosurgical procedure to access the pons with a drug delivery device for chronic therapy and collect preliminary data on the toxicity of direct infusions of carboplatin in primates. METHODS: We made midline incisions on five cynomolgus monkeys, identified the inion, made a burr hole 2.5 cm below the inion, and inserted a catheter through the cerebellum into the roof of the pons. Pumps that infused saline for 90 days or carboplatin solutions for 30 to 35 days at 10 microl/d were placed subcutaneously in the low cervical/high thoracic region. Monkeys were assessed by computed tomography and magnetic resonance imaging, laboratory studies, daily neurological observation, postmortem examinations, and histopathology. RESULTS: Monkeys infused with saline and 82 microg of carboplatin remained neurologically intact throughout the infusion periods. Serial imaging showed that the catheter tip was in the pons and revealed no evidence of hemorrhage, edema, or migration. Two monkeys infused with up to 850 microg of carboplatin showed hyperintense magnetic resonance imaging signals at Days 15 and 18 and neurological deficits at approximately Week 3. Platinum levels greater than 10 ng/mg tissue were detected over a distance of 1 cm in tissue slices. Histopathology demonstrated significant tissue necrosis around the tip of the catheter. CONCLUSION: The pons of monkeys is safely accessed with a catheter for drug delivery by using a posterior midline approach. Clinical observations, radiographic imaging, and laboratory tests of animals infused with saline for 3 months or 0.26 mg/ml of carboplatin for 1 month were unremarkable. Neurotoxicity was seen with dose levels of 2.6 mg/ml of drug for 1 month. This procedure offers opportunities for examining the toxicity of brainstem antitumor therapy in primates.

Pharmacokinetic advantage of intrapericardially applied substances in the rat.

Intrapericardial application of therapeutic agents may open perspectives for target-directed therapy of the diseased heart. This study was performed to investigate whether intrapericardial drug application is beneficial from a pharmacokinetic point of view. Male Wistar rats were provided with intrapericardial and intravascular catheters for substance administration and sampling. Intrapericardial bolus injections of fluorescent macromolecules [fluorescein isothiocyanate (FITC)-rat IgG, molecular weight about 155 kDa; Texas Red rat serum albumin, mol. wt. 67 kDa; Texas Red fibroblast growth factor (FGF), mol. wt. 18 kDa; and FITC heparin, mean mol. wt. 18 kDa] resulted in substance concentrations in pericardial fluid that exceeded those in plasma, for several hours. Pericardial fluid volumes of catheter-instrumented rats, derived from (initial) central compartment volumes, ranged between 0.5 and 0.9 ml/kg. After chronic (7 days) intrapericardial infusions with osmotic minipumps, pericardial fluid/plasma concentration ratios (local advantages) were 7 to 10 for the fluorescent proteins and >30 for FITC-heparin. This can be explained by the low substance clearances in pericardial fluid compared with plasma. Local advantages of the small substances cortisol (mol. wt. = 362.5) and a carbonic acid derivative thereof (mol. wt. = 348) were 14 and 420. Intrapericardial infusion of (125)I-FGF-2 yielded 8 times higher cardiac tissue levels than systemic infusion, whereas (125)I-FGF-2 was found in the entire heart. Pharmacokinetic profiles of intrapericardially applied substances are such that desired local drug concentrations can be obtained at lower dosages, whereas systemic concentrations remain low (thus reducing the potential risk of peripheral side effects). Therefore, intrapericardial application of therapeutic agents provides a promising strategy for site-specific treatment of heart or coronary diseases.