Two different drug-coated balloons (DCBs) possessing different coating formulations were compared for rate of coating dissolution
Through continued innovation, percutaneous treatment of coronary and peripheral stenosis has evolved rapidly since balloon angioplasty was first introduced three decades ago. Significant advances were made with the introduction of bare metal stents and subsequently drug-eluting stents, which expanded the possibility of successful revascularization in complicated lesions. Despite these advantages, efforts are still ongoing to improve patient outcomes further. In recent years, drug-coated balloons (DCBs) have emerged as a promising technology capable of providing a durable antirestenotic response but leaving no permanent implants behind. In the coronary territory, DCBs have proven to be efficacious in complex subsets such as in-stent restenosis, small vessels, and diffuse lesions where stent results are suboptimal. In contrast, in the peripheral vascular field, DCBs are becoming first-line of therapy. Several DCBs developed for coronary and peripheral applications have been extensively evaluated in preclinical and clinical studies with encouraging results [
Paclitaxel, the active pharmaceutical ingredient (API) coated on the IN.PACT Admiral DCB and Lutonix 0.35 DCB, is a lipophilic, poorly water soluble compound [
Six IN.PACT Admiral DCBs (Medtronic PLC, Minneapolis, MN, USA; 6x80 mm) and six Lutonix DCBs (Bard, New Hope, MN, USA; 5x100 mm) were submerged into tubes containing 65 mL of porcine plasma at room temperature and deployed with gentile agitation for 20 seconds to dislodge the adherent coating. The balloons were then removed from the tubes and the tubes were placed horizontally in a 37°C shaking air bath at 50rpm. For the IN.PACT Admiral samples, aliquots of 0.5-mL were taken at 1, 2, 4, 6, and 24 hours. In addition to the sampling timepoints used for IN.PACT Admiral, the Lutonix DCB also required two earlier time points, at 0.167 hr (10 min) and 0.5 hr, in order to accommodate a faster elution profile without loss of early rate data. All aliquots were filtered with a 5-
Tissue histological responses were analyzed following treatment with IN.PACT Admiral DCB and Lutonix DCB in the porcine iliofemoral arteries on day 0 and 30 days, 60 days, and 90 days posttreatment, and tissue drug content was determined posttreatment on day 0 and 90 days. Twenty-four (24) domestic farm swine were treated and completed follow-up until termination. Vascular access was achieved via a carotid approach. A 6F or 8F guide catheter was placed into an 8F sheath and advanced under fluoroscopic guidance into the ostium of the right or left iliofemoral artery, over a 0.035 inch guide wire. The targeted vessels were evaluated via angiography prior to treatment. Test material treatments were placed using a targeted angioplasty overstretch of 1.25:1 to 1.30:1 at the device midpoint based on pretreatment online Quantitative Vascular Angiography (QVA) measurements of the target region of the peripheral artery, and the compliance chart for each test material for DCB platforms as noted on the product labeling. This amount of device overexpansion was expected to stretch the vessels without initiating extensive vessel wall injury. A single balloon was used to treat the target peripheral artery with a single, 60-second inflation and then removed. Animals planned for time 0 analysis were immediately terminated postprocedure; all remaining animals were survived for 30 days, 60 days, and 90 days posttreatment. Gross necropsy and tissue collection consisted of removal of the treated vessel specimens for bioanalytical drug analysis and histological examination.
Porcine arterial samples were received frozen on dry ice from the In-Life test site and were stored in a -80°C freezer until homogenization
The homogenized tissue suspension was thawed in ice water, and after vigorous mixing an aliquot of 150
For quantitation, the peak area ratio of the analyte and the internal standard were used to establish a weighted linear regression curve. For each batch, at least two standard curves with at least 8 concentrations other than zero were prepared over the range of the assay. In addition, replicates of quality control samples were prepared over the range of the assay. Each unknown sample was injected once during the analysis of a batch of samples. The dilution factor of 0.032 was applied to convert the concentration ng/mL to ng/mg for the arterial tissue samples.
Statistical comparisons of drug concentrations in tissue were determined on the day of treatment (day 0) and at 90 days posttreatment. Mean values and standard deviations were calculated using GraphPad Prism 7.0 and comparisons were conducted using a Mann-Whitney test.
While paclitaxel may inhibit cell proliferation though multiple mechanisms, the apoptotic cellular responses to high concentrations of paclitaxel are well established as relevant to smooth muscle cells (SMCs) responses in vivo and linked to arterial wall remodeling in treated segments [
Histopathology was conducted independently at CVPath Inc., Gaithersburg, MD, USA. All vessel segments were dehydrated in a graded series of alcohols and xylenes. All segments were further segmented at ~3 to 4mm intervals and embedded in paraffin. The most proximal segment was offset to maintain longitudinal orientation. Histologic sections were then cut on a rotary microtome at 4 to 6 microns, mounted on charged slides, and stained with hematoxylin and eosin (H&E) and Movat Pentachrome connective tissue stain.
A single proximal section and single distal section from each artery closest to the mid-treated segment were selected for analysis. To assess arterial response to drug treatment, ordinal histopathological data was collected to characterize smooth muscle cell loss (Table
Semi-quantitative analysis of pathologic changes in peripheral arteries.
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| none | Smooth muscle loss <25% of medial thickness | 25-50% of medial thickness | 51-75% of medial thickness | >75% of medial thickness |
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| none | <25% of circumference | 25-50% of circumference | 51-75% of circumference | >75% of circumference |
Based on analysis of the residual drug remaining on the balloon, the total paclitaxel available for solubilization was determined to be 687 ± 250
The normalized dissolution data for IN.PACT Admiral test arm (Figure
Dissolution of solid phase paclitaxel in plasma shown as nonconstrained normalized mean percentage of total solid phase drug solubilized ± SD (a) or remaining solid phase drug in suspension (b) calculated by subtraction from total normalized input drug.
The mid-sections (approximately a third) of the treated arterial tissues were selected as representative of the entire treated segment concentrations and submitted for analysis of paclitaxel content. Figure
Tissue pharmacokinetics of net paclitaxel content in treated arterial segments up to 90 days posttreatment. Values are shown as log-transformed means and SD at each time point studied.
Medial SMC loss was employed as an indicator of paclitaxel-associated induction of apoptosis, one of established mechanisms of drug action in controlling neointimal proliferation. Two different trends of SMC loss following treatment (Figures
Histological scores of smooth muscle cell (SMC) loss indexed by depth (a) and circumference (b). Symbols indicate mean scores at each time point for IN.PACT Admiral (blue circles) and Lutonix (red triangles). Significant differences at 90 days by Mann-Whitney,
Movat pentachrome stain of arterial sections 90 days posttreatment with Lutonix DCB (polysorbate/sorbitol/paclitaxel formulation; (a)) or IN.PACT DCB (urea/paclitaxel formulation; (b)). Areas of green staining indicate zones of SMC loss and proteoglycan deposition associated with local drug activity. Bar indicates 700
DCBs have been shown to be safe and efficacious in preventing restenosis following drug delivery in peripheral artery disease [
Urea is a highly hydrophilic molecule which dissolves readily in aqueous solutions as well as alcohols, although it and its aliphatic derivatives are poorly hydrotropic molecules in combination with paclitaxel, having minimal impact on drug solubility [
The
In previous studies, differential rates of drug release have been attributed to the crystallinity of the solid phase formulations, leading to a differential compartmentalization of released drug [
Total drug content in the treated vascular tissue is similar immediately following the deployment of both DCB types. However, differential clearance of drug in tissue leads to a significant difference in total drug content at 90 days posttreatment. This difference is further accentuated by a difference in drug content (dose density) in the DCB formulations, 3.5
Histological observation of SMC loss is consistent with differential rates of bioavailable drug release. The SMC loss seen following the Lutonix DCB treatment rises rapidly at a month following treatment then declines through 90 days as the net drug content in tissue declines. The SMC loss observed with the IN.PACT Admiral DCB increases at 30 days and is maintained through 90 days at levels significantly greater than that observed for the Lutonix DCB, in alignment with significantly greater levels of drug in tissue. Since suppression of SMC proliferation through loss of proliferating populations of cells by apoptosis and inhibition of other cellular mechanisms contributes to control of vascular intima and ultimately the maintenance of vascular patency, the durability of therapeutic action could be impacted by sustained pools of bioavailable drug at the treatment site long after the therapeutic procedure. The potential for durability of clinical responses to DCB treatment highlights the importance for careful design of the coating formulation to optimize formulation for the desired duration of pharmacological response [
Differential rates of bioavailable drug release from DCBs employing different excipients can impact the duration of drug in tissue and the resulting pharmacological activity at the site of drug delivery. An excipient with a low hydrotropic potential, such as urea, will produce a slower more even dissolution of drug than an excipient with high hydrotropic potential, such as polysorbate/sorbitol. Consequently, formulation selection must be carefully considered to provide a drug release profile most suitable for the desired pharmacological effect.
All the data regarding “in vitro paclitaxel dissolution, in vivo drug PK, arterial tissue response, and histological analysis” used to support the findings of this study are available from the corresponding author upon request.
Daniel Schulz-Jander, Stefan Tunev, and Robert J. Melder are full-time employees of Medtronic PLC, the manufacturer of the