Polymer-drug conjugates in inflammation treatment.

Inflammation is a vital defense mechanism of living organisms. However, persistent and chronic inflammation may lead to severe pathological processes and evolve into various chronic inflammatory diseases (CID), e.g. rheumatoid arthritis, multiple sclerosis, multiple sclerosis, systemic lupus erythematosus or inflammatory bowel diseases, or certain types of cancer. Their current treatment usually does not lead to complete remission. The application of nanotherapeutics may significantly improve CID treatment, since their accumulation in inflamed tissues has been described and is referred to as extravasation through leaky vasculature and subsequent inflammatory cell-mediated sequestration (ELVIS). Among nanotherapeutics, water-soluble polymer-drug conjugates may be highly advantageous in CID treatment due to the possibility of their passive and active targeting to the inflammation site and controlled release of active agents once there. The polymer-drug conjugate consists of a hydrophilic biocompatible polymer backbone along which the drug molecules are covalently attached via a biodegradable linker that enables controlled drug release. Their active targeting or bio-imaging can be achieved by introducing the cell-specific targeting moiety or imaging agents into the polymer conjugate. Here, we review the relationship between polymer conjugates and inflammation, including the benefits of the application of polymer conjugates in inflammation treatment, the anti-inflammatory activity of polymer drug conjugates and potential polymer-promoted inflammation and immunogenicity.

Intracellular fate of polymer therapeutics investigated by fluorescence lifetime imaging and fluorescence pattern analysis.

Nanocarriers bearing anticancer drugs are promising candidates to improve the efficacy of cancer therapy and minimize side effects. The most potent cytostatics used in the treatment of various cancers are anthracyclines, e.g. doxorubicin or pirarubicin. Recently, polymer therapeutics carrying anthracyclines have been intensively studied. The precise characterization of in vitro nanocarrier biological behavior brings a better understanding of the nanocarrier characteristics and enables prediction of the behavior of the nanocarrier during in vivo application. Advanced fluorescence detection methods, e.g. fluorescence lifetime imaging microscopy (FLIM), were successfully exploited to describe the properties of various polymeric nano-systems and contributed to a complex view of anthracyclines' intracellular transport and DNA intercalation. Here, we report the application of a specific technique for processing FLIM images, called fluorescence pattern decomposition, to evaluate early events after doxorubicin or pirarubicin treatment of cells. Moreover, we characterized changes in the intracellular localization and release of the anthracyclines during the incubation of cells with polymer nanotherapeutics based on poly[N-(2-hydroxypropyl)-methacrylamide] (pHPMA).

PCL-PEG graft copolymers with tunable amphiphilicity as efficient drug delivery systems.

The development of flexible drug delivery systems that can be tuned as a function of the drug to be delivered and of the target disease is crucial in modern medicine. For this aim, novel amphiphilic poly(ε-caprolactone)-g-poly(ethylene glycol) (PCL-g-PEG) copolymers with well-controlled design were synthesized by thiol-yne photochemistry. The grafting density and the copolymer amphiphilicity were easily controlled via the reaction parameters: concentration, reaction time, PEG length and the molar ratio between PCL and PEG or the photoinitiator in the reaction mixture. The self-assembling behavior of the copolymers was studied and a correlation between the composition of PCL-g-PEG and the nanoaggregate diameter sizes (28 to 73 nm) and critical aggregation concentrations (1.1 to 4.3 mg L-1) was found. The influence of copolymer amphiphilicity on the drug loading was evaluated with various drugs including anticancer drugs (paclitaxel, ABT-199), drugs to overcome multidrug resistance in cancer cells (curcumin, elacridar), an anti-inflammatory drug (dexamethasone) and an antibacterial drug (clofazimine). Finally, the influence of amphiphilicity on curcumin release and toxicity towards MCF-7 cancer cell lines was studied. The impact of the grafting density, PEG length and the overall EG/CL ratio is discussed in detail. Curcumin loaded PCL-g-PEG with lower EG/CL ratios and shorter PEG chains showed higher toxicity compared to their more hydrophilic counterparts.

Micelle-forming HPMA copolymer conjugates of ritonavir bound via a pH-sensitive spacer with improved cellular uptake designed for enhanced tumor accumulation.

We describe design, synthesis, physico-chemical characterization and preliminary biological evaluation of micelle-forming polymer drug conjugates with controlled drug release intended for tumor treatment. The structure of the conjugates was designed to enable tumor tissue- and cell-specific drug release and micelle disassembly to avoid side effects accompanying classic chemotherapy and guarantee safe elimination of the drug-free carrier from the organisms. The amphiphilic polymer conjugates consisted of a hydrophobic hexaleucine block and a hydrophilic block based on the N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer with an antiviral and cytostatic drug, ritonavir, bound through a pH-sensitive spacer. Diblock copolymers with low dispersity (D∼ 1.1) were prepared via reversible addition-fragmentation chain transfer (RAFT) copolymerization using a hexaleucine derivative as a chain transfer agent. The associative properties of the copolymers depend on the hydrophilic polymer block length and the hydrophobic ritonavir content. The micelles dissociated under mild acidic conditions mimicking the environment inside tumor tissue/cells, because of the decrease in polymer hydrophobicity after the rapid release of the hydrophobic drug from the polymer carrier. Unexpectedly, the polymer-ritonavir conjugates internalized into HeLa cells significantly more than the polymers without ritonavir. The enhanced cell penetration and pH-triggered micelle disassembly predetermine the polymer-ritonavir conjugates to become promising tumor-targeted drug carriers.

Nanotherapeutics with anthracyclines: methods of determination and quantification of anthracyclines in biological samples.

Anthracyclines, e.g. doxorubicin, pirarubicin, are widely used as cytostatic agents in the polymer nanotherapeutics designed for the highly effective antitumor therapy with reduced side effects. However, their precise dosage scheme needs to be optimized, which requires an accurate method for their quantification on the cellular level in vitro during nanocarrier development and in body fluids and tissues during testing in vivo. Various methods detecting the anthracycline content in biological samples have already been designed. Most of them are highly demanding and they differ in exactness and reproducibility. The cellular uptake and localization is predominantly observed and determined by microscopy techniques, the anthracycline content is usually quantified by chromatographic analysis using fluorescence detection. We reviewed and compared published methods concerning the detection of anthracycline nanocarriers.

The comparison of in vivo properties of water-soluble HPMA-based polymer conjugates with doxorubicin prepared by controlled RAFT or free radical polymerization.

Two conjugates of anticancer drug doxorubicin (Dox) covalently bound by the hydrolytically degradable hydrazone bond to the polymer carrier based on water-soluble N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers were synthesized and their properties were compared, namely their behavior in vivo. The polymer carriers differed in dispersity due to different methods of synthesis; the carrier with relatively high dispersity (HD) was prepared by free radical polymerization (Mw=29,900 g/mol, D=1.75) and the carrier with low dispersity (LD) by controlled radical polymerization (Mw=30,000 g/mol, D=1.13). Both polymer-Dox conjugates showed prolonged blood circulation and tumor accumulation of the drug in comparison with the free drug; e.g. the tumor-to-blood ratio for the polymer-bound Dox was 3-5 times higher. The LD polymer-Dox conjugate exhibited moderately higher tumor accumulation than the HD one at a dose of 1x15 mg Dox (eq.)/kg. Also, their anti-tumor activity did not differ when injected at this dose. However, the increase of the dose to 1x25 mg Dox (eq.)/kg resulted in the enhanced therapeutic activity of the conjugates, especially of the LD one with 100% of long-term survivals. The dispersity of polymer drug carriers influenced the tumor accumulation rate, which affected the overall anti-cancer activity of polymer-drug conjugates.

Synthesis of poly[N-(2-hydroxypropyl)methacrylamide] conjugates of inhibitors of the ABC transporter that overcome multidrug resistance in doxorubicin-resistant P388 cells in vitro.

The effects of novel polymeric therapeutics based on water-soluble N-(2-hydroxypropyl)methacrylamide copolymers (P(HPMA)) bearing the anticancer drug doxorubicin (Dox), an inhibitor of ABC transporters, or both, on the viability and the proliferation of the murine monocytic leukemia cell line P388 (parental cell line) and its doxorubicin-resistant subline P388/MDR were studied in vitro. The inhibitor derivatives 5-methyl-4-oxohexanoyl reversin 121 (MeOHe-R121) and 5-methyl-4-oxohexanoyl ritonavir ester (MeOHe-RIT), showing the highest inhibitory activities, were conjugated to the P(HPMA) via the biodegradable pH-sensitive hydrazone bond, and the ability of these conjugates to block the ATP driven P-glycoprotein (P-gp) efflux pump was tested. The P(HPMA) conjugate P-Ahx-NH-N═MeOHe-R121 showed a dose-dependent increase in the ability to sensitize the P388/MDR cells to Dox from 1.5 to 24 µM, and achieved an approximately 50-fold increase in sensitization at 24 µM. The P(HPMA) conjugate P-Ahx-NH-N═MeOHe-RIT showed moderate activity at 6 µM (∼10 times higher sensitization) and increased sensitization by 50-fold at 12 µM. The cytostatic activity of the P(HPMA) conjugate P-Ahx-NH-N═MeOHe-R121(Dox) containing Dox and the P-gp inhibitor MeOHe-R121, both bound via hydrazone bonds to the P(HPMA) carrier, was almost 30 times higher than that of the conjugate P-Ahx-NH-N═Dox toward the P388/MDR cells in vitro. A similar result was observed for P-Ahx-NH-N═MeOHe-RIT(Dox), which exhibited almost 10 times higher cytostatic activity than P-Ahx-NH-N═Dox.