Recombinant Human Elastase Alters the Compliance of Atherosclerotic Tibial Arteries After Ex Vivo Angioplasty.

PURPOSE: This study was designed to determine whether vonapanitase (formerly PRT-201), a recombinant human elastase, treatment can fragment the protein elastin in elastic fibers and cause dilation of atherosclerotic human peripheral arteries subjected to ex vivo balloon angioplasty. MATERIALS AND METHODS: Seven patients undergoing lower limb amputation for peripheral artery disease or who died and donated their bodies to science donated 11 tibial arteries (5 anterior, 6 posterior) for this study. All arteries were atherosclerotic by visual inspection. The arteries underwent ex vivo balloon angioplasty and thereafter were cut into rings and studied on wire myographs where the rings were stretched and tension was recorded. After treatment with vonapanitase 2 mg/mL or vehicle control, myography was repeated and the rings were then subject to elastin content measurement using a desmosine radioimmunoassay and elastic fiber visualization by histology. The wire myography data were used to derive compliance, stress-strain, and incremental elastic modulus curves. RESULTS: Vonapanitase treatment reduced elastin (desmosine) content by 60% and decreased elastic fiber histologic staining. Vonapanitase-treated rings experienced less tension at any level of stretch and as a result had shifts in the compliance and stress-strain curves relative to vehicle-treated rings. Vonapanitase treatment did not alter the incremental elastic modulus curve. CONCLUSIONS: Vonapanitase treatment of atherosclerotic human peripheral arteries after ex vivo balloon angioplasty fragmented elastin in elastic fibers, decreased tension in the rings at any level of stretch, and altered the compliance and stress-strain curves in a manner predicting arterial dilation in vivo. Based on this result, local treatment of balloon angioplasty sites may increase blood vessel diameter and thereby improve the success of balloon angioplasty in peripheral artery disease.

Effects of recombinant human type I pancreatic elastase on human atherosclerotic arteries.

RATIONALE: At physiologic pressures, elastic fibers constrain artery diameter. Local treatment of atherosclerotic arteries with PRT-201, a recombinant type I elastase, could result in fragmentation and removal of elastin fibers and increased vessel diameter. OBJECTIVE: To investigate the use of PRT-201 as a treatment for human atherosclerotic arteries. METHODS AND RESULTS: Arteries were harvested from donor legs amputated due to severe peripheral artery disease or from recently deceased persons who donated their bodies to science. Three- to four-centimeter artery segments were studied on a perfusion myograph to obtain baseline diameter data. After treatment with PRT-201 3.6 mg/mL or saline for 30 minutes myography was repeated. PRT-201 treatment resulted in an increase in vessel diameter across a range of transmural pressures. Average anterior tibial artery diameter increased by 0.78 ± 0.21 mm (27% ± 12%), whereas average posterior tibial artery diameter increased by 0.58 ± 0.30 mm (21% ± 11%), both P < 0.001. Elastin content as measured by desmosine radioimmunoassay was reduced by approximately 50%, P < 0.001. CONCLUSIONS: The results suggest that PRT-201 treatment of atherosclerotic peripheral arteries in patients could increase artery diameter, and thus luminal area, possibly alleviating some of the symptoms of peripheral artery disease.

The ability of serum from alpha 1-antitrypsin-deficient patients to inhibit PRT-201, a recombinant human type I pancreatic elastase.

PRT-201 is a recombinant human pancreatic elastase under development as a treatment for blood vessels to promote hemodialysis access patency. Proteases such as elastase are normally inactivated by antiproteases such as alpha 1-antitrypsin. It is unknown if serum from patients with alpha 1-antitrypsin deficiency will inhibit PRT-201 elastase activity. An assay for PRT-201 elastase activity in the presence of serum was developed and validated. PRT-201 elastase activity inhibition curves were developed using serum and also using purified alpha 1-antitrypsin and alpha 2-macroglobulin. Serum from 15 patients with documented alpha 1-antitrypsin deficiency, some of whom were receiving alpha 1-antitrypsin augmentation therapy, and four normal volunteers was analyzed. Serum from normal volunteers and patients with alpha 1-antitrypsin deficiency completely inactivated PRT-201 elastase activity in vitro. In the alpha 1-antitrypsin-deficient patients, the volume of serum necessary to inhibit elastase activity was related to the serum concentration of alpha 1-antitrypsin and augmentation therapy. Purified alpha 1-antitrypsin and alpha 2-macroglobulin were each alone capable of completely inhibiting PRT-201 elastase activity. It is unlikely that the use of PRT-201 will be associated with negative outcomes in patients with alpha 1-antitrypsin deficiency.

Studies of human pancreatic elastase treatment of rabbit and human vein rings to predict human therapeutic doses.

Vascular tissue contains abundant elastic fibers that contribute to vessel elasticity. Vonapanitase (formerly PRT-201) is a recombinant human chymotrypsin-like elastase family member 1 (CELA1) shown to cleave the elastin component of elastic fibers, resulting in increased vessel diameter. The purpose of these current studies was to determine vein diameter, wall thickness, elastin content, and vonapanitase potency in veins used in a model of arteriovenous fistula (AVF) and in patients undergoing AVF creation for hemodialysis access to guide dose selection for human trials. Rabbit linguofacial, maxillary, and external jugular veins, and human basilic and upper and lower arm cephalic veins were dissected postmortem and sectioned into 2 mm length rings. Rings were incubated in vonapanitase at 37°C at varying concentrations and times. Elastin content was estimated histologically and by quantifying desmosine, a protein cross-link unique to elastin. Rabbit veins were substantially thinner and contained less elastin than human veins. In human veins, elastin content was greatest in basilic and least in lower arm cephalic. Vonapanitase removed elastin in a time- and concentration-dependent manner in all vein types. A lower concentration of vonapanitase was required to remove elastin from rabbit relative to human veins. In summary, vonapanitase reduced the elastin content of rabbit and human veins but did so at a lower concentration in the rabbit veins. Rabbit models may overestimate the potency of vonapanitase in humans. These results indicate that human dose selection should be guided by human vein ring experiments.

Recombinant Human Elastase Treatment of Cephalic Veins.

BACKGROUND: Vessel injury at the time of Arteriovenous Fistula (AVF) creation may lead to neointimal hyperplasia that impairs AVF maturation. Vonapanitase, a recombinant human chymotrypsin-like elastase family member 1, is an investigational drug under development to improve AVF maturation and patency. The current studies were designed to document vonapanitase effects in human cephalic veins that are used in AVF creation. METHODS: Human cephalic veins were mounted on a perfusion myograph. Vonapanitase 1.2, 4, 13.2, and 40 µg/ml or saline was applied drop wise on the vein followed by saline rinse. Vein segments were cut into rings for elastin content determination by desmosine radioimmunoassay and histology. Fluorescently-labelled vonapanitase was applied to veins and adventitial imaging was performed using laser scanning confocal microscopy. In vivo time course experiments were performed by treating rabbit jugular veins and harvesting 1 h and 4 h after vonapanitase treatment. RESULTS / CONCLUSION: Vonapanitase reduced desmosine content in a dose-related manner. Histology also confirmed a dose-related reduction in elastic fiber staining. Fluorescently-labelled vonapanitase persistently localized to elastic fibers in the vein adventitia. In vivo experiments showed a reduction in desmosine content in jugular veins from 1 h to 4 h following treatment. These data suggest that vonapanitase targets elastin in elastic fibers in a dose related manner and that elastase remains in the vessel wall and has catalytic activity for at least 1 h.

In Vitro Study of a Medical Device to Enhance Arteriovenous Fistula Eligibility and Maturation.

The arteriovenous fistula eligibility (AFE) system (Flow Forward Medical, Olathe, KS) is a small, temporary, wearable rotary blood pump system designed to rapidly dilate peripheral veins in hemodialysis patients and improve outcomes after arteriovenous fistula (AVF) creation. A benchtop pulsatile mock circulatory loop was developed to model forearm circulation and to compare the hemodynamics of the AFE system with those of a conventional radiocephalic AVF. The AFE system maintained a mean wall shear stress (mWSS) within the 2.5-7.5 Pa target range for cephalic outflow veins of 2-6 mm diameter, which when applied clinically will provide better control of mWSS during the outflow vein maturation process when compared with a conventional AVF. These results support further study to determine whether or not vein preconditioning with the AFE system under controlled levels of mWSS will promote improved AVF outcomes.

Application of human type I pancreatic elastase (PRT-201) to the venous anastomosis of arteriovenous grafts in patients with chronic kidney disease.

PURPOSE: To explore the safety and efficacy of PRT-201 applied to the outflow vein of a newly created arteriovenous graft (AVG). METHODS: Randomized, double-blind, placebo-controlled, single-dose escalation study of PRT-201 (0.01 to 9 mg) applied to the graft-vein anastomosis and adjacent outflow vein immediately after AVG placement. The primary outcome measure was safety. The efficacy measures were intraoperative increases in outflow vein diameter and blood flow rate, primary unassisted patency, and secondary patency by dose groups (placebo, low, medium, high and All PRT-201). RESULTS: A total of 89 patients were treated (28 placebo and 61 PRT-201). There were no significant differences in the proportion of placebo and PRT-201 patients reporting adverse events. Intraoperative outflow vein diameter increased 5% (p=0.14) in the placebo group compared with 13% (p=0.01), 15% (p=0.07) and 12% (p<0.001), in the low, medium and high groups, respectively. The comparison between the high and placebo groups was marginally statistically significant (p=0.06). The intraoperative blood flow did not change in the placebo group, and increased in the low, medium and high groups by 19% (p=0.34), 36% (p=0.09) and 46% (p=0.02), respectively. The low group had the longest primary unassisted and secondary patency and the fewest procedures to restore or maintain patency; however, the differences between groups were not statistically significant. CONCLUSIONS: PRT-201 was well tolerated and increased AVG intraoperative outflow vein diameter and blood flow. Low dose tended to increase secondary patency and decrease the rate of procedures to restore or maintain patency. Larger studies with these doses will be necessary to confirm these results.

A multi-center, dose-escalation study of human type I pancreatic elastase (PRT-201) administered after arteriovenous fistula creation.

PURPOSE: To explore the safety and efficacy of PRT-201. METHODS: Randomized, double-blind, placebo-controlled, single-dose escalation study of PRT-201 (0.0033 to 9 mg) applied after arteriovenous fistula (AVF) creation. Participants were followed for one year. The primary outcome measure was safety. Efficacy measures were the proportion with intra-operative increases in AVF outflow vein diameter or blood flow ≥25% (primary), changes in outflow vein diameter and blood flow, AVF maturation and lumen stenosis by ultrasound criteria and AVF patency. RESULTS: The adverse events in the PRT-201 group (n=45) were similar to those in the placebo group (n=21). There were no differences in the proportion with ≥25% increase in vein diameter or blood flow, successful maturation or lumen stenosis. There was no statistically significant difference in primary patency between the dose groups (placebo n=21, Low Dose n=16, Medium Dose n=17 and High Dose n=12). In a subgroup analysis that excluded three participants with early surgical failures, the hazard ratio (HR) for primary patency loss of Low Dose compared with placebo was 0.38 (95% CI 0.10-1.41, P=0.15). In a Cox model, Low Dose (HR 0.27, 95% CI 0.04-0.79, P=0.09), white race (HR 0.17, 95% CI 0.03-0.79, P=0.02), and age <65 years (HR 0.25, CI 0.05-1.15, P=0.08) were associated (P<0.10) with a decreased risk of primary patency loss. CONCLUSIONS: PRT-201 was not different from placebo for safety or efficacy measures. There was a suggestion for improved AVF primary patency with Low Dose PRT-201 that is now being studied in a larger clinical trial.