Macromolecular Prodrugs Research Articles

Drug Delivery: Macromolecular Prodrugs of Ribavirin: Concerted Efforts of the Carrier and the Drug (Adv. Healthcare Mater. 9/2014)

Automated parallel synthesis is applied by A. Postma, A. Zelikin, and team on page 1404 to obtain libraries of macromolecular prodrugs of ribavirin. Polymers differ in their average molar mass and drug content, the two parameters independently vary in broad respective ranges. Screening the libraries for intracellular activity identifies at least 10 formulations with efficacy matching that of the drug and at the same time significantly reducing toxicity.

Imaging of doxorubicin release from theranostic macromolecular prodrugs via fluorescence resonance energy transfer.

Herein we present a FRET-based theranostic macromolecular prodrug (TMP) composed of (a) dendritic polyglycerol (PG) as polymeric nanocarrier, (b) doxorubicin (Dox) linked via a pH-sensitive hydrazone to (c) a tri-functional linker, and (d) an indodicarbocyanine dye (IDCC) attached in close proximity to Dox. The drug fluorescence is quenched via intramolecular FRET until the pH-sensitive hydrazone bond between the TMP and Dox is cleaved at acidic pH. By measuring its fluorescence, we characterized the TMP cleavage kinetics at different pH values in vitro. The intracellular release of Dox from the carrier was monitored in real time in intact cancer cells, giving more insight into the mode of action of a polymer drug conjugate.

Highly active macromolecular prodrugs inhibit expression of the hepatitis C virus genome in the host cells.

Efficacious, potent, and at the same time nontoxic macromolecular prodrugs of ribavirin are designed taking advantage over prodrug activation by the intracellular milieu. Activity of these prodrugs is illustrated in the cells hosting hepatitis C virus replication and also in the cells implicated in the inflammatory response to the viral infection.

Prodrug applications for targeted cancer therapy.

Prodrugs are widely used in the targeted delivery of cytotoxic compounds to cancer cells. To date, targeted prodrugs for cancer therapy have achieved great diversity in terms of target selection, activation chemistry, as well as size and physicochemical nature of the prodrug. Macromolecular prodrugs such as antibody-drug conjugates, targeted polymer-drug conjugates and other conjugates that self-assemble to form liposomal and micellar nanoparticles currently represent a major trend in prodrug development for cancer therapy. In this review, we explore a unified view of cancer-targeted prodrugs and highlight several examples from recombinant technology that exemplify the prodrug concept but are not identified as such. Recombinant "prodrugs" such as engineered anthrax toxin show promise in biological specificity through the conditionally targeting of multiple cellular markers. Conditional targeting is achieved by structural complementation, the spontaneous assembly of engineered inactive subunits or fragments to reconstitute functional activity. These complementing systems can be readily adapted to achieve conditionally bispecific targeting of enzymes that are used to activate low-molecular weight prodrugs. By leveraging strengths from medicinal chemistry, polymer science, and recombinant technology, prodrugs are poised to remain a core component of highly focused and tailored strategies aimed at conditionally attacking complex molecular phenotypes in clinically relevant cancer.

Macromolecular (pro)drugs in antiviral research

Macromolecular (pro)drugs are a sub-discipline of medicinal and polymer chemistries aiming to optimize the delivery of drugs to their site of action. In recent decades, this field of science has undergone a tremendous development, with the soundest achievements registered in the delivery of anticancer drugs. Surprisingly, the development of these tools for applications in antiviral treatment lags significantly behind – despite the fact that the first in vivo successes of polymers in fighting viruses were reported half a century ago. Furthermore, the unique scope and utility of polymers in antiviral research is that macromolecules themselves exhibit highly potent activity against diverse viruses. Herein, in an attempt to revive the research interest in this field, we aim to provide an overview of successes (and failures) of polymers as antiviral agents and macromolecular prodrugs. Specifically, we discuss inhibition of the entry of the virus into mammalian cells by polymers, give an overview of the synthetic schemes applied for the conjugation of drugs to carrier polymers, and also present guidance with regard to potential reporter systems which can be used for the characterization of novel drug delivery systems in virus-free cell cultures.

Macromolecular Prodrug That Provides the Irinotecan (CPT-11) Active-Metabolite SN-38 with Ultralong Half-Life, Low Cmax , and Low Glucuronide Formation

We have recently reported a chemical approach for half-life extension that utilizes β-eliminative linkers to attach amine-containing drugs or prodrugs to macromolecules. The linkers release free drug or prodrug over periods ranging from a few hours to over 1 year. We adapted these linkers for use with phenol-containing drugs. Here, we prepared PEG conjugates of the irinotecan (CPT-11) active metabolite SN-38 via a phenyl ether that release the drug with predictable long half-lives. Pharmacokinetic studies in the rat indicate that, in contrast to other SN-38 prodrugs, the slowly released SN-38 shows a very low C(max), is kept above target concentrations for extended periods, and forms very little SN-38 glucuronide (the precursor of enterotoxic SN-38). The low SN-38 glucuronide is attributed to low hepatic uptake of SN-38. These macromolecular prodrugs have unique pharmacokinetic profiles that may translate to less intestinal toxicity and interpatient variability than the SN-38 prodrugs thus far studied.

A macromolecular prodrug‐type injectable polymer composed of poly(depsipeptide‐co‐lactide)‐g‐PEG for sustained release of drugs

We propose a macromolecular prodrug strategy of an injectable polymer (IP) system for continuous and sustained release of water‐soluble low‐molecular‐weight drugs. A biodegradable graft copolymer‐type IP covalently immobilizing model drugs via hydrolyzable ester bonds was synthesized through the coupling reaction of poly(depsipeptide‐co‐dl‐lactide), P(DG‐dl‐LA), having reactive carboxylic acid side‐chain groups with the amino derivative of a model drug (levofloxacin [LEV]) and monomethoxy‐poly(ethylene glycol) (PEG). The solution of the obtained graft copolymer‐type IP/model drug conjugate exhibited a temperature‐responsive sol‐to‐gel transition between room temperature and body temperature in phosphate buffer solution, similar to P(GD‐dl‐LA)‐g‐PEG without LEV. The immobilization of the LEV molecule onto P(DG‐dl‐LA)‐g‐PEG did not have a significant influence on the sol‐to‐gel transition behavior, physical properties, or in vitro degradation rates of the hydrogels. The in vitro release of LEV derivatives from the P(DG‐dl‐LA)‐g‐PEG/LEV hydrogel in phosphate buffer solution was continuous for 11 weeks, which corresponded to the degradation period of the hydrogel, and slower than that from the control hydrogels prepared from P(DG‐dl‐LA)‐g‐PEG and PLGA‐b‐PEG‐b‐PLGA that physically entrapped LEV molecules. These results suggest that the covalent attachment strategy is effective in achieving sustained release of low‐molecular‐weight drugs in IP systems and can be applied to drug delivery devices for highly bioactive drugs. Copyright © 2014 John Wiley & Sons, Ltd.

Macromolecular Prodrugs of Ribavirin: Concerted Efforts of the Carrier and the Drug

Polymers in tune. Automated parallel polymer synthesis is developed to obtain libraries of macromolecular prodrugs of ribavirin, a broad-spectrum antiviral agent. As many as 10 identified lead polymer conjugates exhibit therapeutic efficacy matching that of the pristine drug and at the same time suppressed the origin of the main side effect of ribavirin.

Macromolecular prodrug of dexamethasone prevents particle-induced peri-implant osteolysis with reduced systemic side effects

Aseptic implant loosening related to implant wear particle-induced inflammation is the most common cause of failure after joint replacement. Modulation of the inflammatory reaction to the wear products represents a rational approach for preventing aseptic implant failure. Long-term treatment using anti-inflammatory agents, however, can be associated with significant systemic side effects due to the drugs' lack of tissue specificity. To address this issue, N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer–dexamethasone conjugate (P–Dex) was developed and evaluated for prevention of wear particle-induced osteolysis and the loss of fixation in a murine prosthesis failure model. Daily administration of free dexamethasone (Dex) was able to prevent wear particle-induced osteolysis, as assessed by micro-CT and histological analysis. Remarkably, monthly P–Dex administration (dose equivalent to free Dex treatment) was equally effective as free dexamethasone, but was not associated with systemic bone loss (a major adverse side effect of glucocorticoids). The reduced systemic toxicity of P–Dex is related to preferential targeting of the sites of wear particle-induced inflammation and its subcellular sequestration and retention by local inflammatory cell populations, resulting in sustained therapeutic action. These results demonstrate the feasibility of utilizing a macromolecular prodrug with reduced systemic toxicity to prevent wear particle-induced osteolysis.

A macromolecular prodrug strategy for combinatorial drug delivery

A novel macromolecular prodrug strategy was developed for the combinatorial delivery of two poorly water-soluble drugs, dexamethasone and doxorubicin. In this work, dexamethasone was firstly conjugated onto a water-soluble modified polysaccharide by an acid-labile hydrazone linkage. The resultant macromolecular prodrug had an amphiphilic character and could self-assemble into spherical polymeric micelles in aqueous system. With these micelles, doxorubicin was then encapsulated into their hydrophobic cores. For the conjugated dexamethasone and encapsulated doxorubicin, they could exhibit independent and acid-sensitive release characteristics. For the doxorubicin-loaded prodrug micelles, they were easily be internalized by living cells and showed obvious antitumor activity.

A Dexamethasone Prodrug Reduces the Renal Macrophage Response and Provides Enhanced Resolution of Established Murine Lupus Nephritis

We evaluated the ability of a macromolecular prodrug of dexamethasone (P-Dex) to treat lupus nephritis in (NZB × NZW)F1 mice. We also explored the mechanism underlying the anti-inflammatory effects of this prodrug. P-Dex eliminated albuminuria in most (NZB × NZW)F1 mice. Furthermore, P-Dex reduced the incidence of severe nephritis and extended lifespan in these mice. P-Dex treatment also prevented the development of lupus-associated hypertension and vasculitis. Although P-Dex did not reduce serum levels of anti-dsDNA antibodies or glomerular immune complexes, P-Dex reduced macrophage recruitment to the kidney and attenuated tubulointerstitial injury. In contrast to what was observed with free dexamethasone, P-Dex did not induce any deterioration of bone quality. However, P-Dex did lead to reduced peripheral white blood cell counts and adrenal gland atrophy. These results suggest that P-Dex is more effective and less toxic than free dexamethasone for the treatment of lupus nephritis in (NZB × NZW)F1 mice. Furthermore, the data suggest that P-Dex may treat nephritis by attenuating the renal inflammatory response to immune complexes, leading to decreased immune cell infiltration and diminished renal inflammation and injury.

Narrow Therapeutic Window of Ribavirin as an Inhibitor of Nitric Oxide Synthesis is Broadened by Macromolecular Prodrugs

Ribavirin (RBV), a broad-spectrum antiviral agent, is a standard medication against hepatitis C virus (HCV). However, despite the decades of clinical success, the mechanism of action of this drug against HCV remains a subject of debate. Furthermore, the appeal of this therapeutic agent is considerably lessened by unfavorable pharmacokinetics. This interdisciplinary study contributes to the understanding of intracellular effects exerted by RBV and presents a successful design of macromolecular prodrugs of RBV to achieve a safer treatment. Specifically, we demonstrate that RBV exhibits a pronounced anti-inflammatory activity in cultured macrophages as is evidenced by a 2-fold decrease in the levels of produced nitric oxide achieved using a clinically relevant concentration of this drug. However, this effect was characterized by a rather narrow therapeutic window with experimental values of EC50 and IC50 being 7 and 19 μM, respectively. Macromolecular prodrugs were obtained using an acrylate derivative of RBV, RAFT polymerization technique, and N-vinyl pyrrolidone as a partner monomer. The synthesized polymers were characterized with uniform molecular weights, relatively narrow polydispersities, and gradually increasing content of RBV. The resulting polymer therapeutics were effective in delivering their payload to the cultured macrophages and afforded a significantly wider therapeutic window, as much as >1000 μM (18-fold in relative values). Taken together, this work contributes significantly to the development of safer methods for delivery of RBV, as well as understanding the mechanism of action and origins of the side effects of this broad-spectrum antiviral agent.

Macromolecular Prodrugs for Controlled Delivery of Ribavirin

Ribavirin (RBV)-containing polymers are synthesized based on poly(N-vinylpyrrolidone) and poly(acrylic acid), two polymers with extensive characterization in biomedicine. The copolymers are shown to exhibit a minor to negligible degree of association with erythrocytes, thus effectively eliminating the origin of the main side effects of RBV. The therapeutic benefit of macromolecular RBV prodrugs is illustrated by matched efficacy in suppressing production of nitric oxide by stimulated cultured macrophages as compared to pristine RBV with no associated cytotoxicity, which is in stark contrast to an RBV-based treatment which results in a significant decrease in cell viability. These results contribute to the development of antiviral polymer therapeutics and delivery of RBV in particular.

Polymer Prodrug Nanoparticles Based on Naturally Occurring Isoprenoid for Anticancer Therapy

The synthesis of a novel class of polymer prodrug nanoparticles with anticancer activity is reported by using squalene, a naturally occurring isoprenoid, as a building block by the reversible addition-fragmentation (RAFT) technique. The RAFT agent was functionalized by gemcitabine (Gem) as anticancer drug, and the polymerization of squalenyl-methacrylate (SqMA) led to well-defined macromolecular prodrugs comprising one Gem at the extremity of each polymer chain. The amphiphilic nature of the resulting Gem-PSqMA conjugates allowed them to self-assemble into long-term stable and narrowly dispersed nanoparticles with significant anticancer activity in vitro on various cancer cell lines. To confer stealth properties on these nanoparticles, their PEGylation was successfully performed, as confirmed by X-ray photoelectron spectroscopy (XPS) and complement activation assay. It was also shown that the PEGylated nanoparticles could be internalized in cancer cells to a greater extent than their non-PEGylated counterparts.

Antimyeloma activity of NK012, a micelle‐forming macromolecular prodrug of SN‐38, in an orthotopic model

NK012 is a micelle-forming macromolecular prodrug of 7-ethyl-10-hydroxy camptothecin (SN-38), an active metabolite of irinotecan. It is accumulated and retained in tumor tissues and gradually releases SN-38 in an enzyme-independent manner. NK012 was previously demonstrated to have stronger antitumor activity than irinotecan in a broad range of human solid-tumor xenograft models. In our study, we used an orthotopic multiple myeloma (MM) model created by injecting CD138-positive U266B1, a myeloma cell line that produces human IgE lambda light chain (monoclonal protein, M protein), into immunodeficient NOD/Shi-scid, IL-2Rγc (null) mice. This model shows typical bone marrow infiltration by the human myeloma cells. We evaluated the antimyeloma activity of intravenously administered NK012 in this model and showed that it suppressed the M protein concentration in the plasma and proliferation of myeloma cells in the bone marrow in a dose-dependent manner. NK012 suppressed the progression of hind-leg paralysis and prolonged the survival time of the mice compared to the untreated control group. In combination with bortezomib (BTZ), NK012 increased the median survival time compared to that with BTZ alone. In conclusion, these results suggest that NK012 is a potential candidate for use-alone and in combination-in the treatment of MM in humans.

Fabrication, characterization, thermal stability and nanoassemblies of novel pullulan-aspirin conjugates

Present study deals with homogeneous and one-pot synthesis of novel macromolecular prodrugs (MPDs) of aspirin onto naturally occurring hydrophilic biopolymer pullulan. Pullulan-aspirin conjugates were synthesized by using green carboxylic acid activating reagent 1,1′-carbonyldiimidazole (CDI). The aspirin was first reacted with CDI to prepare aspirin-imidazolide at RT for 24h which in situ reacted with pre-dissolved pullulan and the reaction preceded further for 24h at 80°C under nitrogen. Degree of substitution (DS 0.32–0.40) of aspirin onto pullulan was calculated from 1H NMR spectroscopy. Spectroscopic techniques confirmed the high covalent drug loading and purity. Thermal analysis has revealed that new MPDs of aspirin are thermally more stable than pure aspirin. The activation energy, order and frequency factor of the degradation reactions were calculated using Broido, Friedman and Chang models. The amphiphilic pullulan-aspirin conjugates self-assembled in nanoparticles without further structural modifications at solvent interface in the range of 500–680nm as examined by transmission electron microscopy. These novel pullulan-aspirin conjugates with masked COOH functional group could be potentially safe prodrugs for the stomach.

Macromolecular Prodrug of 4-Aminosalicylic Acid for Targeted Delivery to Inflamed Colon

Macromolecular Prodrug of 4-Aminosalicylic Acid for Targeted Delivery to Inflamed Colon

Macromolecular Prodrug of 4-Aminosalicylic Acid for Targeted Delivery to Inflamed Colon

Sterically hindered esters or esters of drugs with macromolecular carriers like dextran and cyclodextrin find wide applicability in colon-targeted delivery. We report here synthesis, in vitro release kinetics of macromolecular prodrug of 4-aminosalicylic acid (4-ASA) with β-cyclodextrin and its extensive pharmacological evaluation in 2, 4, 6- trinitrobenzenesulphonic acid - induced colitis in rats. Formyl 4-ASA was conjugated with β-cyclodextrin by CDI coupling followed by deprotection of the final product which was then characterized by IR, 1H-NMR and LC-MS. In vitro stability and release were studied in buffers (pH 1.2 and 7.4), stomach/small intestinal homogenates and rat cecal/fecal matters. The prodrug resisted pH-dependent hydrolysis. In stomach and small intestinal homogenates 20-23% release was observed (t1/2: 1278 and 1103 min respectively) while 68% and 92% release was furnished in rat cecal and fecal matters (t1/2: 341 and 245 min respectively). Mitigating effect of 4-AβCyd on colitis was moderate when compared with sulfasalazine or 4/5-ASA administered rectally, but it was comparable to that of aminosalicylates administered orally, suggesting incomplete delivery of 4-ASA to colon due to partial hydrolysis of 4-AβCyd in the upper GIT. The histological assessment of pancreas and liver of the prodrug-treated group showed no pathological changes indicating its better safety profile than that of sulfasalazine or oral 5-ASA. The prodrug brought about significant lowering in ulcer index compared to aminosalicylates suggesting significant improvement in gastro-protective effect than oral aminosalicylates.

Hydroxypropylcellulose-aceclofenac conjugates: high covalent loading design, structure characterization, nano-assemblies and thermal kinetics

This article presents synthesis of novel macromolecular prodrugs of aceclofenac (an anti-inflammatory drug) onto hydroxypropylcellulose (HPC). The HPC-aceclofenac conjugates were prepared using an acylating agent 1,1′-carbonyldiimidazole (CDI) under homogenous reaction conditions. Aceclofenac was first activated by using CDI to form its N-acylimidazole. The N-acylimidazole of aceclofenac was then reacted with HPC polymer at 80 °C for 24 h. Highly pure prodrugs of aceclofenac were synthesized with a wide range of moderate to high degree of substitution (DS 0.41–2.12) as calculated by 1H NMR spectroscopy. The UV spectroscopic analysis has also revealed that the active drug aceclofenac was found in different conjugates from 28 to 67 mg/100 mg of HPC-aceclofenac conjugates which are in good agreement with DS calculated by 1H NMR spectroscopy. The gel permeation chromatography showed unimodal absorption that indicates no significant degradation in polymer chains during the reaction. The macromolecular prodrugs of aceclofenac were characterized using different spectroscopic and chromatographic techniques. The thermal analysis has revealed that HPC-aceclofenac conjugates (prodrugs) are 92 and 96 °C more stable than pure aceclofenac regarding their initial (Tdi) and maximum degradation temperatures (Tdm), respectively. The activation energy (Ea) and frequency factor (Z) of the degradation reactions were evaluated using Friedman, Broido and Chang methods. Degradation followed first order (n) kinetics. Transmission electron microscopy has revealed the formation of sponge like nano aggregates with population size distribution of around 80–150 nm.

Macromolecular prodrugs of ribavirin combat side effects and toxicity with no loss of activity of the drug

Chemi-enzymatic synthesis of ribavirin acrylate and subsequent RAFT co-polymerization with acrylic acid afforded a formulation of a broad spectrum antiviral drug which avoids accumulation in erythrocytes, the origin of the main side effect of ribavirin. In cultured macrophages the macromolecular prodrugs exhibited decreased toxicity while maintaining the anti-inflammatory action of ribavirin.