Polymer-prodrug conjugates as candidates for degradable, long-acting implants, releasing the water-soluble nucleoside reverse-transcriptase inhibitor emtricitabine

Circulating, soluble polymer-drug conjugates have been utilised for many years to aid the delivery of sensitive, poorly-soluble or cytotoxic drugs, prolong circulation times or minimise side effects. Long-acting therapeutics are increasing in their healthcare importance, with intramuscular and subcutaneous administration of liquid formulations being most common. Degradable implants also offer opportunities and the use of polymer-prodrug conjugates as implant materials has not been widely reported in this context. Here, the potential for polymer-prodrug conjugates of the water soluble nucleoside reverse transciption inhibitor emtricitabine (FTC) is studied. A novel diol monomer scaffold, allowing variation of prodrug substitution, has been used to form polyesters and polycarbonates by step-growth polymerisation. Materials have been screened for physical properties that enable implant formation, studied for drug release to provide mechanistic insights, and tunable prolonged release of FTC has been demonstrated over a period of at least two weeks under relevant physiological conditions.

Linear and branched polymer prodrugs of the water-soluble nucleoside reverse-transcriptase inhibitor emtricitabine as structural materials for long-acting implants

Long-acting drug delivery is a growing area of interest as it overcomes many challenges related to patient adherence to therapy and the pill burden associated with chronic illness. Injectable formulations are becoming more common and drug-releasing implants also provide several opportunities. Highly water soluble drug compounds are poor candidates for long-acting delivery. Here, the water-soluble nucleoside reverse transcriptase inhibitor emtricitabine (FTC) has been used as a novel A-B monomer in step-growth polymerisation with chloroformate functional Cn monomers, to produce new poly(carbamate/carbonate) structures with varying architecture. The polymer prodrugs were all solid at ambient temperature and have been shown to release FTC when subjected to mixed gender human plasma. Vacuum compression moulding has been used to form solid rod implants without polymer degradation; the rods show FTC release over long periods in the presence of microsomes, establishing the basis of a polymer prodrug strategy for FTC delivery.

PolyMorphine provides extended analgesic-like effects in mice with spared nerve injury

Morphine is a well-characterized and effective analgesic commonly used to provide pain relief to patients suffering from both acute and chronic pain conditions. Despite its widespread use and effectiveness, one of the major drawbacks of morphine is its relatively short half-life of approximately 4 h. This short half-life often necessitates multiple administrations of the drug each day, which may contribute to both dependence and tolerance to morphine. Here, we tested the analgesic properties of a new polymer form of morphine known as PolyMorphine. This polymer has monomeric units of morphine incorporated into a poly(anhydride-ester) backbone that has been shown to hydrolyze into free morphine in vitro. Using an animal model of chronic pain, the spared nerve injury surgery, we showed that PolyMorphine is able to block spared nerve injury-induced hypersensitivity in mice for up to 24-h post-administration. Free morphine was shown to only block spared nerve injury-induced hypersensitivity for up to 2-h post-injection. PolyMorphine was also shown to act through the mu opioid receptor due to the ability of naloxone (a mu opioid receptor antagonist) to block PolyMorphine-induced analgesia in spared nerve injury animals pretreated with PolyMorphine. Additionally, we observed that PolyMorphine causes similar locomotor and constipation side effects as free morphine. Finally, we investigated if PolyMorphine had any effects in a non-evoked pain assay, conditioned place preference. Pretreatment of spared nerve injury mice with PolyMorphine blocked the development of conditioned place preference for 2-methyl-6-(phenylethynyl)pyridine (MPEP), a short-lasting mGluR5 antagonist with analgesic-like properties. Free morphine does not block the development of preference for MPEP, suggesting that PolyMorphine has longer lasting analgesic effects compared to free morphine. Together, these data show that PolyMorphine has the potential to provide analgesia for significantly longer than free morphine while likely working through the same receptor.

Synthesis and Characterization of Salicylic Acid-Based Poly(Anhydride-Ester) Copolymers

A series of poly(anhydride-esters) based on poly(1,10-bis(o-car-boxyphenoxy)decanoate) (CPD) and poly(1,6-bis(p-carboxyphenoxy)hexane) (p-CPH) were synthesized by melt-condensation polymerization. Poly-(anhydride-esters) that contain CPD hydrolytically degraded into salicylic acid, however, these homopolymers have mechanical and thermal characteristics that limit their use in clinical applications. The synthesis and characterization of copolymers of CPD with p-CPH, a monomer known to generate mechanically stable homopolymers, was investigated. By changing the CPD to p-CPH monomer ratios, the salicylic acid loading and thermal/mechanical properties of the copolymers was a controlling factor; increasing the CPD concentration increased the salicylate loading but decreased the polymer stability; whereas increasing the p-CPH concentration increased the thermal and mechanical stability of the copolymers. Specifically, decreasing the CPD:p-CPH ratio resulted in lower salicylate loading and increased thermal decomposition temperatures. The glass transition temperatures (°C) varied from 27 to 38°C, a desirable range for elastomeric biomedical implants.

Controlled release kinetics of p-aminosalicylic acid from biodegradable crosslinked polyesters for enhanced anti-mycobacterial activity

Unlike conventional polymeric drug delivery systems, where drugs are entrapped in polymers, this study focuses on the incorporation of the drug into the polymer backbone to achieve higher loading and sustained release. Crosslinked, biodegradable, xylitol based polyesters have been synthesized in this study. The bioactive drug moiety, p-aminosalicylic acid (PAS), was incorporated in xylitol based polyesters to impart its anti-mycobacterial activity. To understand the influence of the monomer chemistry on the incorporation of PAS and its subsequent release from the polymer, different diacids have been used. Controlled release profiles of the drug from these polyesters were studied under normal physiological conditions. The degradation of the polyesters varied from 48% to 76% and the release of PAS ranged from 54% to 65% of its initial loading in 7days. A new model was developed to explain the release kinetics of PAS from the polymer that accounted for the polymer degradation and drug concentration. The thermal, mechanical, drug release and cytocompatibility properties of the polymers indicate their suitability in biomedical applications. The released products from these polymers were observed to be pharmacologically active against Mycobacteria. The high drug loading and sustained release also ensured enhanced efficacy. These polymers form biocompatible, biodegradable polyesters where the sustained release of PAS may be tailored for potential treatment of mycobacterial infections.

STATEMENT OF SIGNIFICANCE

In the present work, we report on novel polyesters with p-aminosalicylic acid (PAS) incorporated in the polymer backbone. The current work aims to achieve controlled release of PAS and ensures the delivered PAS is stable and pharmacologically active. The novelty of this work primarily involves the synthetic chemistry of polymerization and detailed analysis and efficacy of active PAS delivery. A new kinetic model has been developed to explain the PAS release profiles. These polymers are biodegradable, cytocompatible and anti-mycobacterial in nature.

PolyMorphine: an innovative biodegradable polymer drug for extended pain relief

Morphine, a potent narcotic analgesic used for the treatment of acute and chronic pain, was chemically incorporated into a poly(anhydride-ester) backbone. The polymer termed "PolyMorphine", was designed to degrade hydrolytically releasing morphine in a controlled manner to ultimately provide analgesia for an extended time period. PolyMorphine was synthesized via melt-condensation polymerization and its structure was characterized using proton and carbon nuclear magnetic resonance spectroscopies, and infrared spectroscopy. The weight-average molecular weight and the thermal properties were determined. The hydrolytic degradation pathway of the polymer was determined by in vitro studies, showing that free morphine is released. In vitro cytocompatibility studies demonstrated that PolyMorphine is non-cytotoxic towards fibroblasts. In vivo studies using mice showed that PolyMorphine provides analgesia for 3 days, 20 times the analgesic window of free morphine. The animals retained full responsiveness to morphine after being subjected to an acute morphine challenge.

Salicylic acid-derived poly(anhydride-ester) electrospun fibers designed for regenerating the peripheral nervous system

Continuous biomaterial advances and the regenerating potential of the adult human peripheral nervous system offer great promise for restoring full function to innervated tissue following traumatic injury via synthetic nerve guidance conduits (NGCs). To most effectively facilitate nerve regeneration, a tissue engineering scaffold within a conduit must be similar to the linear microenvironment of the healthy nerve. To mimic the native nerve structure, aligned poly(lactic-co-glycolic acid)/bioactive polyanhydride fibrous substrates were fabricated through optimized electrospinning parameters with diameters of 600 ± 200 nm. Scanning electron microscopy images show fibers with a high degree of alignment. Schwann cells and dissociated rat dorsal root ganglia demonstrated elongated and healthy proliferation in a direction parallel to orientated electrospun fibers with significantly longer Schwann cell process length and neurite outgrowth when compared to randomly orientated fibers. Results suggest that an aligned polyanhydride fiber mat holds tremendous promise as a supplement scaffold for the interior of a degradable polymer NGC. Bioactive salicylic acid-based polyanhydride fibers are not limited to nerve regeneration and offer exciting promise for a wide variety of biomedical applications.

A novel approach for incorporation of mono-functional bioactive phenols into polyanhydrides

Antiseptics based on phenol and phenolic derivatives were chemically incorporated into polyanhydrides as pendant groups via ester linkages. Polyanhydrides with antiseptic loadings of 46-58 wt.-% were obtained with molecular weights ranging from 9 400-23 000. In general, polymers with the bulkier antiseptics were more difficult to polymerize and yielded lower molecular weights. All polyanhydrides were amorphous with glass transition temperatures ranging from 27-58 °C. Polymers were deemed noncytotoxic after culturing L929 mouse fibroblast cells in media containing the polymers at two concentrations (0.10 and 0.01 mg · mL(-1) ) over three days. In summary, mono-functional bioactives can be chemically incorporated into noncytotoxic polyanhydrides.

Comparison of salicylate-based poly(anhydride-esters) formed via melt-condensation versus solution polymerization

Salicylate-based poly(anhydride-esters) were synthesized via two different methods, melt-condensation and solution polymerization, and the resulting polymers were compared. Acetylsalicylic acid was used as a model compound to mimic the active polymer chain-ends during melt-condensation, and formed a low-molecular-weight (<1500) polymer when subjected to melt-condensation polymerization conditions. The polymers and model compounds were analyzed by NMR ((1)H and (13)C) and IR spectroscopies to elucidate the structures. Spectroscopic analysis revealed the formation of a thermodynamically stable salicylate ester via salicylate-anhydride rearrangement during melt-condensation polymerization, which did not occur during solution polymerization. The salicylate-based poly(anhydride-esters) undergo a thermodynamic rearrangement during melt-condensation polymerization that is not observed for solution polymerization.

In vivo Degradation and histocompatibility of a novel class of fluorescent copolyanhydrides, poly{[di(p-carboxyphenyl) succinate]-co-(sebacic anhydride)}

In this work, the in vivo degradation and tissue compatibility of a novel class of inherently fluorescent copolyanhydrides, P(dCPS:SA), were investigated. It was found that the degradation of the copolyanhydrides increased with the increase of SA content in the copolymers. The in vivo degradation rate of the copolymers was slower than that studied in vitro. A surface erosion characteristic of the copolyanhydrides was revealed by SEM and fluorescent microscopy. Mild inflammatory reactions were observed on days 6 and 10 after implantation for all the studied copolymers. By the end of 30 d, there were almost no inflammation reactions taking place.

Characterization and in vitro degradation of poly(octadecanoic anhydride)

Poly(octadecanoic anhydride) (POA) has been prepared by melt polycondensation of octadecanoic diacid. POA was characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The results of in vitro degradation and SEM micrographs show that the erosion process of POA is neither bulk nor perfect surface erosion but rather has elements of both in phosphate buffer at 37 degrees C. The moving erosion front is characteristic of surface erosion whereas the remaining porous shell stems from bulk erosion. While a significant special degradation property of POA is that POA presents a very slow degradation rate in acidic condition (pH 5.98), only 1.64% weight loss for 20 days, and it completely degrades after 18 days in basic buffer (pH 7.4). Comparing with poly(sebacic anhydride) (PSA), POA has the higher crystallization degree, and the slower hydrolytic rate.

Trehalose click polymers inhibit nanoparticle aggregation and promote pDNA delivery in serum

Herein, three new glycopolymers have been synthesized via "click polymerization" to promote nucleic acid delivery in the presence of biological media containing serum. These structures were designed to contain a trehalose moiety to promote biocompatibility, water solubility, and stability against aggregation, amide-triazole groups to enhance DNA binding affinity, and an oligoamine unit to facilitate DNA encapsulation, phosphate neutralization, and interactions with cell surfaces. A 2,3,4,2',3',4'-hexa-O-acetyl-6,6'-diazido-6,6'-dideoxy-D-trehalose (4) monomer was polymerized via copper(I)-catalyzed azide-alkyne cycloaddition with a series of dialkyne-amide comonomers that contain either one, two, or three Boc-protected secondary amines (7a, 7b, or 7c, respectively). After deprotection, three water-soluble polycations (9a, 9b, or 9c) were obtained with similar degrees of polymerization (n = 56-61) to elucidate the role of amine number on nucleic acid binding, complex formation, stability, and cellular delivery. Gel electrophoresis and ethidium bromide experiments showed that 9a-9c associated with plasmid DNA (pDNA) and formed complexes (polyplexes) at N/P ratios dependent on the amine number. TEM experiments revealed that 9a-9c polyplexes were small (50-120 nm) and had morphologies (spherical and rodlike) associated with the polymer chain stiffness. Dynamic light scattering studies in the presence of media containing serum demonstrated that 9c polyplexes had a low degree of flocculation, whereas 9a and 9b polyplexesd aggregate rapidly. Further biological studies revealed that these structures were biocompatible and deliver pDNA into HeLa cells. Particularly, 9c polyplexes promoted high delivery efficacy and gene expression profiles in the presence of serum.

Synthesis and characterization of antiseptic-based poly(anhydride-esters)

Poly(anhydride-esters) were prepared from catechol, fenticlor and hexachlorophene. The molecular weights (M_w) of the polymers were typically > 10,000 Da with glass transition temperatures (T_g) ranging from 23 to 84 °C. The thermal characteristics of the polymers paralleled the melting temperatures of the chemically incorporated antiseptic molecules. The in vitro release of the chemically incorporated antiseptic molecules were monitored over a 12 week period. For comparison, the in vitro release of physically admixed antiseptic molecules were also observed. After 12 weeks, the polymers were not completely degraded with drug release ranging from less than 1 to 55 %. Sessile-drop contact angles indicated that the polymers were relatively hydrophobic, contributing to the slow polymer degradation rates.

Novel Copolyanhydrides Combining Strong Inherent Fluorescence and a Wide Range of Biodegradability: Synthesis, Characterization and in vitro Degradation

In this work, a novel diacid monomer was synthesized in a very convenient scheme. The monomer is derived from naturally occurring products and emits strong fluorescence when polymerized to polyanhydride. The chemical structure of the monomer dCPS is as follows: HOC(O)ArOC(O)(CH2)2C(O)O--Ar--COOH. Copolyanhydrides composed of dCPS and sebacic acid were further prepared by melt copolycondensation, and characterized by IR, NMR, UV-Vis, DSC and fluorometry. The emission wavelength (lambda(em)) of the copolymers could be tuned by the excitation wavelength (lambda(ex)). Fluorescence intensity increased with the increase of dCPS content. The microspheres fabricated from the copolymer with dCPS content as low as 10% could be clearly visualized with fluorescence microscopy. Either blue or green images of the microspheres could be captured with an excitation of UV and visible light. The degradation rate of the copolyanhydrides decreased as the dCPS fraction increased, and the degradation duration could be modulated from several days to more than three months. In addition, it was found that the copolyanhydrides displayed surface degradation characteristics. In view of the advantages of the novel copolyanhydrides, such as easy preparation, unique inherent luminescent properties, and widely adjustable degradation rate, they might be useful for biomedical engineering.

Late metal salicylaldimine complexes derived from 5-aminosalicylic acid — Molecular structure of a zwitterionic mono Schiff base zinc complex

Condensation of salicylaldehyde (2-HOC6H4C(O)H) with 5-aminosalicylic acid (5-H2NC6H3-2-(OH)-CO2H) afforded the Schiff base 2-HOC6H4C(H)=NC6H3-2-(OH)-5-CO2H (a). Similar reactivity with 5-bromosalicylaldehyde was also observed to give 5-Br-2-HOC6H3C(H)=NC6H3-2-(OH)-5-CO2H (b). Reaction of these salicylaldehydes with Pd(II), Cu(II), and Zn(II) salts gave the corresponding bis(N-arylsalicylaldiminato)metal complexes (M = Pd (1), Cu (2), Zn (3)). The molecular structure of the Schiff base compound a has been confirmed by an X-ray diffraction study. Crystals of a were monoclinic, space group P2(1)/c, a = 7.0164(7) Å, b = 11.0088(11) Å, c = 14.8980(15) Å, β = 102.917(2)°, Z = 4. The molecular structure of a novel zwitterionic conformer of 3a was also characterized by an X-ray diffraction study. Crystals of 4 were monoclinic, space group P2(1)/c, a = 9.5284(5) Å, b = 19.5335(11) Å, c = 8.6508(5) Å, β = 90.596(1)°, Z = 4. All new compounds have been tested for their antifungal activity against Aspergillus niger and Aspergillus flavus. Key words: 5-aminosalicylic acid (5-ASA), antifungal, copper, palladium, salicylaldimines, Schiff base, zinc.

Role of polyanhydrides as localized drug carriers

Many drugs that are administered in an unmodified form by conventional systemic routes fail to reach target organs in an effective concentration, or are not effective over a length of time due to a facile metabolism. Various types of targeting delivery systems and devices have been tried over a long period of time to overcome these problems. Targeted delivery or localized drug delivery offers an advantage of reduced body burden and systemic toxicity of the drugs, especially useful for highly toxic drugs like anticancer agents. Local drug delivery via polymer is a simple approach and hypothesized to avoid the above stated problems. Polyanhydrides are a unique class of polymer for drug delivery because some of them demonstrate a near zero order drug release and relatively rapid biodegradation in vivo. Further, the release rate of polyanhydride fabricated device can be altered over a thousand fold by simple changes in the polymer backbone. Hence, these are one of the best-suited polymers for drug delivery, with biodegradability and biocompatibility. The review focuses on the advantages of polyanhydride carriers in localized drug delivery along with their degradability behavior, toxicological profile and role in various disease conditions.

Synthesis and Cytotoxicity of Salicylate-Based Poly(anhydride esters)

This paper describes the synthesis and cytotoxicity of poly(anhydride esters) that are composed of several salicylate derivatives, including halogenated salicylates, aminosalicylates, salicylsalicylic acid, and thiolsalicylic acid. The incorporation of these nonsteroidal antiinflammatory drugs (NSAIDs) into a biodegradable polymer backbone yields drug-based polymers that have potential for a variety of applications. The poly(anhydride esters) were synthesized by melt condensation polymerization. The halogenated salicylate derivatives yielded the highest molecular polymers as well as the highest glass transition temperatures. All polymers displayed in vitro degradation lag times from 1 to 3 days, depending on the water solubility of the salicylate derivative. Cell viability and proliferation were determined with L929 fibroblast cells in serum-containing medium to assess the polymer cytotoxicities, which varied as a function of the saliyclate chemistry. Cell morphology was normal for most of the polymers evaluated.

Poly(anhydride-ester) fibers: Role of copolymer composition on hydrolytic degradation and mechanical properties

Poly(anhydride-esters), based on carboxyphenoxydecanoate (CPD), are biocompatible polymers that hydrolytically degrade. The mechanical properties of the poly(anhydride-esters) can be altered by copolymerization with para-carboxyphenoxyhexane (pCPH). Mechanical properties of three CPD:pCPH compositions (30:70, 40:60, and 50:50) are reported as a function of hydrolytic degradation. The mechanical characteristics evaluated were tensile modulus at 1% strain (E(1%)), tensile strength (sigma(B)), ultimate elongation (epsilon(B)), and toughness (E(r)). The 30:70 CPD:pCPH fibers maintained higher values for tensile modulus at all time points than the two other fiber compositions. In addition, the 30:70 CPD:pCPH fibers maintained lower values for both tensile strength and toughness than the two other fiber compositions. These phenomena resulted from the brittle nature of pCPH, the major component of the 30:70 CPD:pCPH fibers; increasing the pCPH concentration in the polymer lowers both tensile strength and toughness of the polymer by decreasing ductility. With increasing amounts of pCPH, the hydrolytic degradation occurred more slowly, as reflected in the copolymers' improved ability to retain their mechanical properties. Therefore, copolymerization is useful for controlling the mechanical properties of the fibers as well as the polymer degradation rate, which ultimately determines the rate at which physically or chemically encapsulated drugs can be released.