Bioresorbable polystatin fourth-generation stents.

OBJECTIVE: Stents have evolved through three generations, the latest of which are totally bioresorbable to include drugs targeting restenosis, the surface polymer eluting those drugs, and scaffolds on which those drugs are coated. These scaffolds, however, thus far, have been pharmacologically inactive and remain a potential site for delivering a second drug. Therefore, we sought to evaluate the possibility of modifying a bioresorbable polymer so that it can double as a scaffold for both a stent and a drug targeting impaired re-endothelialization and stent thrombosis. METHODS AND RESULTS: We successfully modified a standard bioresorbable terpolymer in a way found to be consistent with the covalent incorporation of lovastatin, as seen on NMR, into a backbone comprised of lactide, glycolide, ε-caprolactone, and lovastatin (60 : 15 : 10 : 15 parts by weight), respectively. This was accomplished through a reaction of the four components of the polymer at 100°C for 18 h in the presence of an alcohol initiator and a scandium catalyst. The resulting terpolymer was fabricated into a scaffold using a novel RSF system developed by 3D Biotek. CONCLUSION: It preliminarily appears feasible to fabricate a fourth-generation bioresorbable stent that has the potential to deliver two drugs to the site of the procedure-related vessel lumen injury.

Human papillomavirus episome stability is reduced by aphidicolin and controlled by DNA damage response pathways.

A highly reproducible quantitative PCR (Q-PCR) assay was used to study the stability of human papillomavirus (HPV) in undifferentiated keratinocytes that maintain viral episomes. The term "stability" refers to the ability of episomes to persist with little copy number variation in cells. In investigating the mechanism of action of PA25, a previously published compound that destabilizes HPV episomes, aphidicolin was also found to markedly decrease episome levels, but via a different pathway from that of PA25. Since aphidicolin is known to activate DNA damage response (DDR) pathways, effects of inhibitors and small interfering RNAs (siRNAs) acting within DDR pathways were investigated. Inhibitors of Chk1 and siRNA directed against ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia Rad3-related (ATR) pathways significantly reduced viral episomes, suggesting that these pathways play a role in maintaining HPV episome stability. Inhibitors of Chk2 and DNA-PK had no effect on episome levels. Pharmacological inhibition of ATM proteins had no effect on episome levels, but ATM knockdown by siRNA significantly reduced episome levels, suggesting that ATM proteins are playing an important role in HPV episome stability that does not require kinase activity. These results outline two pathways that trigger episome loss from cells and suggest the existence of a little-understood mechanism that mediates viral DNA elimination. Together, our results also indicate that HPV episomes have a stability profile that is remarkably similar to that of fragile sites; these similarities are outlined and discussed. This close correspondence may influence the preference of HPV for integration into fragile sites.

HPV episome levels are potently decreased by pyrrole-imidazole polyamides.

Human papillomavirus (HPV) causes cervical cancer and other hyperproliferative diseases. There currently are no approved antiviral drugs for HPV that directly decrease viral DNA load and that have low toxicity. We report the potent anti-HPV activity of two N-methylpyrrole-imidazole polyamides of the hairpin type, polyamide 1 (PA1) and polyamide 25 (PA25). Both polyamides have potent anti-HPV activity against three different genotypes when tested on cells maintaining HPV episomes. The compounds were tested against HPV16 (in W12 cells), HPV18 (in Ker4-18 cells), and HPV31 (in HPV31 maintaining cells). From a library of polyamides designed to recognize AT-rich DNA sequences such as those in or near E1 or E2 binding sites of the HPV16 origin of replication (ori), four polyamides were identified that possessed apparent IC(50)s≤150nM with no evidence of cytotoxicity. We report two highly-active compounds here. Treatment of epithelia engineered in organotypic cultures with these compounds also causes a dose-dependent loss of HPV episomal DNA that correlates with accumulation of compounds in the nucleus. Bromodeoxyuridine (BrdU) incorporation demonstrates that DNA synthesis in organotypic cultures is suppressed upon compound treatment, correlating with a loss of HPV16 and HPV18 episomes. PA1 and PA25 are currently in preclinical development as antiviral compounds for treatment of HPV-related disease, including cervical dysplasia. PA1, PA25, and related polyamides offer promise as antiviral agents and as tools to regulate HPV episomal levels in cells for the study of HPV biology. We also report that anti-HPV16 activity for Distamycin A, a natural product related to our polyamides, is accompanied by significant cellular toxicity.

Biocompatibility: meeting a key functional requirement of next-generation medical devices.

The array of polymeric, biologic, metallic, and ceramic biomaterials will be reviewed with respect to their biocompatibility, which has traditionally been viewed as a requirement to develop a safe medical device. With the emergence of combination products, a paradigm shift is occurring that now requires biocompatibility to be designed into the device. In fact, next-generation medical devices will require enhanced biocompatibility by using, for example, pharmacological agents, bioactive coatings, nano-textures, or hybrid systems containing cells that control biologic interactions to have desirable biologic outcomes. The concept of biocompatibility is moving from a "do no harm" mission (i.e., nontoxic, nonantigenic, nonmutagenic, etc.) to one of doing "good," that is, encouraging positive healing responses. These new devices will promote the formation of normal healthy tissue as well as the integration of the device into adjacent tissue. In some contexts, biocompatibility can become a disruptive technology that can change therapeutic paradigms (e.g., drug-coated stents). New database tools to access biocompatibility data of the materials of construction in existing medical devices will facilitate the use of existing and new biomaterials for new medical device designs.

How to commercialize nanotechnology.

If we want nano-enabled tools that can increase our understanding of the physical and biological world, and also improve our quality of life, it will be necessary to overcome a complex set of commercialization challenges. Michael Helmus explains.

Styrenic block copolymers for biomaterial and drug delivery applications.

The use of styrenic block copolymers has undergone a renaissance as a biomaterial and drug delivery matrix. The early promise posed by the physical and biological properties of these block copolymers for implantable medical devices was not met. However, there has been an increased understanding of the role of microphase separation on the mediation of the biological response. Poly (styrene-b-isobutylene-b-styrene) (SIBS) block copolymer has critical enabling properties related to processing, vascular compatibility and bio-stability that has resulted in its use as the matrix for paclitaxel delivery from Boston Scientific's TAXUS coronary stent. These enabling properties will allow the continuing development of medical devices based on SIBS that meet demanding physical and biological requirements.

Physical characterization of controlled release of paclitaxel from the TAXUS Express2 drug-eluting stent.

The polymer carrier technology in the TAXUS drug-eluting stent consists of a thermoplastic elastomer poly(styrene-b-isobutylene-b-styrene) (SIBS) with microphase-separated morphology resulting in optimal properties for a drug-delivery stent coating. Comprehensive physical characterization of the stent coatings and cast film formulations showed that paclitaxel (PTx) exists primarily as discrete nanoparticles embedded in the SIBS matrix. Thermal and chemical analysis did not show any evidence of solubility of PTx in SIBS or of any molecular miscibility between PTx and SIBS. Atomic force microscope data images revealed for the first time three-dimensional stent coating surfaces at high spatial resolutions in air and in situ under phosphate-buffered saline as drug was released. PTx release involves the initial dissolution of drug particles from the PTx/SIBS coating surface. Morphological examination of the stent coatings in vitro supported an early burst release in most formulations because of surface PTx followed by a sustained slower release of PTx from the bulk coating. The in vitro PTx release kinetics were dependent on the formulation and correlated to the drug-to-polymer ratio. Atomic force microscopy analysis confirmed this correlation and further supported the concept of a matrix-based drug-release coating.