Tumor-specific targeting of polymer drug delivery systems with recombinant proteins bound via tris(nitrilotriacetic acid).

Antibody-mediated targeting is an efficient strategy to enhance the specificity and selectivity of polymer nanomedicines towards the target site, typically a tumor. However, direct covalent coupling of an antibody with a polymer usually results in a partial damage of the antibody binding site accompanied with a compromised biological activity. Here, an original solution based on well-defined non-covalent interactions between tris-nitrilotriacetic acid (trisNTA) and hexahistidine (His-tag) groups, purposefully introduced to the structure of each macromolecule, is described. Specifically, trisNTA groups were attached along the chains of a hydrophilic statistical copolymer based on N-(2-hydroxypropyl)methacrylamide (HPMA), and at the end or along the chains of thermo-responsive di-block copolymers based on N-isopropylmethacrylamide (NIPMAM) and HPMA; His-tag was incorporated to the structure of a recombinant single chain fragment of an anti-GD2 monoclonal antibody (scFv-GD2). Static and dynamic light scattering analyses confirmed that mixing of polymer with scFv-GD2 led to the formation of polymer/scFv-GD2 complexes; those prepared from thermo-responsive polymers formed stable micelles at 37 °C. Flow cytometry and fluorescence microscopy clearly demonstrated antigen-specific binding of the prepared complexes to GD2 positive murine T-cell lymphoma cells EL-4 and human neuroblastoma cells UKF-NB3, while no interaction with GD2 negative murine fibroblast cells NIH-3T3 was observed. These non-covalent polymer protein complexes represent a new generation of highly specific actively targeted polymer therapeutics or diagnostics.

Polymer-Antimicrobial Peptide Constructs with Tailored Drug-Release Behavior.

Microbial resistance is one of the main problems of modern medicine. Recently, antimicrobial peptides have been recognized as a novel approach to overcome the microbial resistance issue, nevertheless, their low stability, toxicity, and potential immunogenic response in biological systems have limited their clinical application. Herein, we present the design, synthesis, and preliminary biological evaluation of polymer-antibacterial peptide constructs. The antimicrobial GKWMKLLKKILK-NH2 oligopeptide (PEP) derived from halictine, honey bee venom, was bound to a polymer carrier via various biodegradable spacers employing the pH-sensitive or enzymatically-driven release and reactivation of the PEP's antimicrobial activity. The antibacterial properties of the polymer-PEP constructs were assessed by a determination of the minimum inhibitory concentrations, followed by fluorescence and transmission electron microscopy. The PEP exerted antibacterial activity against both, gram-positive and negative bacteria, via disruption of the bacterial cell wall mechanism. Importantly, PEP partly retained its antibacterial efficacy against Staphylococcus epidermidis, Escherichia coli, and Acinetobacter baumanii even though it was bound to the polymer carrier. Indeed, to observe antibacterial activity similar to the free PEP, the peptide has to be released from the polymer carrier in response to a pH decrease. Enzymatically-driven release and reactivation of the PEP antimicrobial activity were recognized as less effective when compared to the pH-sensitive release of PEP.

Polymer nanomedicines with enzymatically triggered activation: A comparative study of in vitro and in vivo anti-cancer efficacy related to the spacer structure.

Polymer nanomedicines with anti-tumor activity should exhibit sufficient stability during systemic circulation to the target tissue; however, they should release the active drug selectively in the tumor. Thus, choice of a tumor-specific stimuli-sensitive spacer between the drug and the carrier is critical. Here, a series of polymer conjugates of anti-cancer drugs doxorubicin and pirarubicin covalently bound to copolymers based on N-(2-hydroxypropyl)methacrylamide via various enzymatically cleavable oligopeptide spacers were prepared and characterized. The highest rate of the drug release from the polymer carriers in presence of the lysosomal protease cathepsin B was determined for the copolymers with Val-Cit-Aba spacer. Copolymers containing pirarubicin were more cytotoxic and showed higher internalization rate than the corresponding doxorubicin counterparts. The conjugates containing GFLG and Val-Cit-Aba spacers exhibited the highest anti-tumor efficacy in vivo against murine sarcoma S-180, the highest rate of the enzymatically catalyzed drug release, and the highest cytotoxicity in vitro.

HPMA Copolymer Mebendazole Conjugate Allows Systemic Administration and Possesses Antitumour Activity In Vivo.

Mebendazole and other benzimidazole antihelmintics, such as albendazole, fenbendazole, or flubendazole, have been shown to possess antitumour activity, primarily due to their microtubule-disrupting activity. However, the extremely poor water-solubility of mebendazole and other benzimidazoles, resulting in very low bioavailability, is a serious drawback of this class of drugs. Thus, the investigation of their antitumour potential has been limited so far to administering repeated high doses given peroral (p.o.) or to using formulations, such as liposomes. Herein, we report a fully biocompatible, water-soluble, HPMA copolymer-based conjugate bearing mebendazole (P-MBZ; Mw 28-33 kDa) covalently attached through a biodegradable bond, enabling systemic administration. Such an approach not only dramatically improves mebendazole solubility but also significantly prolongs the half-life and ensures tumour accumulation via an enhanced permeation and retention (EPR) effect in vivo. This P-MBZ has remarkable cytostatic and cytotoxic activities in EL-4 T-cell lymphoma, LL2 lung carcinoma, and CT-26 colon carcinoma mouse cell lines in vitro, with corresponding IC50 values of 1.07, 1.51, and 0.814 µM, respectively. P-MBZ also demonstrated considerable antitumour activity in EL-4 tumour-bearing mice when administered intraperitoneal (i.p.), either as a single dose or using 3 intermittent doses. The combination of P-MBZ with immunotherapy based on complexes of IL-2 and anti-IL-2 mAb S4B6, potently stimulating activated and memory CD8+ T cells, as well as NK cells, further improved the therapeutic effect.

HPMA-Based Polymer Conjugates for Repurposed Drug Mebendazole and Other Imidazole-Based Therapeutics.

Recently, the antitumor potential of benzimidazole anthelmintics, such as mebendazole and its analogues, have been reported to have minimal side effects, in addition to their well-known anti-parasitic abilities. However, their administration is strongly limited owing to their extremely poor solubility, which highly depletes their overall bioavailability. This study describes the design, synthesis, and physico-chemical properties of polymer-mebendazole nanomedicines for drug repurposing in cancer therapy. The conjugation of mebendazole to water-soluble and biocompatible polymer carrier was carried out via biodegradable bond, relying on the hydrolytic action of lysosomal hydrolases for mebendazole release inside the tumor cells. Five low-molecular-weight mebendazole derivatives, differing in their inner structure, and two polymer conjugates differing in their linker structure, were synthesized. The overall synthetic strategy was designed to enable the modification and polymer conjugation of most benzimidazole-based anthelmintics, such as albendazole, fenbendazole or albendazole, besides the mebendazole. Furthermore, the described methodology may be suitable for conjugation of other biologically active compounds with a heterocyclic N-H group in their molecules.

Polymer-ritonavir derivate nanomedicine with pH-sensitive activation possesses potent anti-tumor activity in vivo via inhibition of proteasome and STAT3 signaling.

Drug repurposing is a promising strategy for identifying new applications for approved drugs. Here, we describe a polymer biomaterial composed of the antiretroviral drug ritonavir derivative (5-methyl-4-oxohexanoic acid ritonavir ester; RD), covalently bound to HPMA copolymer carrier via a pH-sensitive hydrazone bond (P-RD). Apart from being more potent inhibitor of P-glycoprotein in comparison to ritonavir, we found RD to have considerable cytostatic activity in six mice (IC50 ~ 2.3-17.4 µM) and six human (IC50 ~ 4.3-8.7 µM) cancer cell lines, and that RD inhibits the migration and invasiveness of cancer cells in vitro. Importantly, RD inhibits STAT3 phosphorylation in CT26 cells in vitro and in vivo, and expression of the NF-κB p65 subunit, Bcl-2 and Mcl-1 in vitro. RD also dampens chymotrypsin-like and trypsin-like proteasome activity and induces ER stress as documented by induction of PERK phosphorylation and expression of ATF4 and CHOP. P-RD nanomedicine showed powerful antitumor activity in CT26 and B16F10 tumor-bearing mice, which, moreover, synergized with IL-2-based immunotherapy. P-RD proved very promising therapeutic activity also in human FaDu xenografts and negligible toxicity predetermining these nanomedicines as side-effect free nanosystem. The therapeutic potential could be highly increased using the fine-tuned combination with other drugs, i.e. doxorubicin, attached to the same polymer system. Finally, we summarize that described polymer nanomedicines fulfilled all the requirements as potential candidates for deep preclinical investigation.

New multimodal stationary phases prepared by Ugi multicomponent approach.

Eight different stationary phases based on two aminopropyl silicas of different brands suitable for multimodal chromatography applications have been prepared by a four-component Ugi reaction. The intention was to synthesize stationary phases significantly differing in their properties hereby demonstrating flexibility of the Ugi synthetic protocol. Diverse functional groups including a nonpolar long aliphatic chain, phenyl moiety, cholic acid scaffold, phenylboronic and monosaccharide units, charged betaine, and arginine moieties were immobilized on a silica surface. The novel sorbents were extensively characterized by elemental analysis, Raman spectroscopy, and chromatography. Considering the anchored chemical structures covalently bonded to the silica surface, reversed-phase, hydrophilic, and ion-exchange separation modes were expected. The chromatographic evaluation was performed directed to map the potential of the individual columns specifically in the mentioned chromatographic modes. The Ugi synthetic protocol has proven to be a simple, feasible, and versatile tool for the synthesis of sorbents of variable properties. The newly prepared stationary phases differed considerably in hydrophobicity and ion-exchange ability. A significant influence of the supporting aminopropyl silica on the final chromatographic behavior was observed. Finally, one practical example confirming applicability of the newly prepared sorbents was demonstrated in separation of cytarabine.

Highly effective anti-tumor nanomedicines based on HPMA copolymer conjugates with pirarubicin prepared by controlled RAFT polymerization.

Here, we describe innovative synthesis of well-defined biocompatible N-(2-hydroxypropyl) methacrylamide (HPMA)-based polymer carriers and their drug conjugates with pirarubicin intended for controlled drug delivery and pH-triggered drug activation in tumor tissue. Polymer carrier synthesis was optimized to obtain well-defined linear HPMA-based polymer precursor with dispersity close to 1 and molar mass close to renal threshold with minimal synthesis steps. The developed synthesis enables preparation of tailored polymer nanomedicines with highly enhanced biological behavior in vivo, especially the biodistribution, urine elimination, tumor accumulation and anticancer activity. STATEMENT OF SIGNIFICANCE: The manuscript reports on novel synthesis and detailed physicochemical characterization and in vivo evaluation of well-defined biocompatible hydrophilic copolymers based on N-(2-hydroxypropyl)methacrylamide (HPMA) and their drug conjugates with pirarubicin enabling controlled drug delivery and pH-triggered drug activation in tumor tissue. Polymer carrier synthesis was optimized to obtain well-defined linear HPMA-based polymer precursor with minimal synthesis steps using controlled polymerization. Compared to previously published HPMA-based polymer drug conjugates whose polymer carriers were prepared by classical route via free radical polymerization, the newly prepared polymer drug conjugates exhibited enhanced biological behavior in vivo, especially the prolonged blood circulation, urine elimination, tumor accumulation and excellent anticancer activity. We believe that the newly prepared well-defined polymer conjugates could significantly enhance tumor therapy in humans.

Polymer donors of nitric oxide improve the treatment of experimental solid tumours with nanosized polymer therapeutics.

Polymer carriers based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers with incorporated organic nitrates as nitric oxide (NO) donors were designed with the aim to localise NO generation in solid tumours, thus highly increasing the enhanced permeability and retention (EPR) effect. The NO donors were coupled to the polymer carrier either through a stable bond or through a hydrolytically degradable, pH sensitive, bond. In vivo, the co-administration of the polymer NO donor and HPMA copolymer-bound cytotoxic drug (doxorubicin; Dox) resulted in an improvement in the treatment of murine EL4 T-cell lymphoma. The polymer NO donors neither potentiated the in vitro toxicity of the cytotoxic drug nor exerted any effect on in vivo model without the EPR effect, such as BCL1 leukaemia. Thus, an increase in passive accumulation of the nanomedicine carrying cytotoxic drug via NO-enhanced EPR effect was the operative mechanism of action. The most significant improvement in the therapy was observed in a combination treatment with such a polymer conjugate of Dox, which is characterised by increased circulation in the blood and efficient accumulation in solid tumours. Notably, the combination treatment enabled the development of an anti-tumour immune response, which was previously demonstrated as an important feature of HPMA-based polymer cytotoxic drugs.

Multi-responsive polymer micelles as ellipticine delivery carriers for cancer therapy.

In the present study, we describe the synthesis and physicochemical properties of a novel pH- and thermoresponsive micellar drug delivery system for an anticancer ellipticinium derivative based on the triblock copolymer poly(ethylene oxide)-block-[tert-butylacrylamide-co-6-(N-methacryloylamino)hexanoic acid hydrazide]-block-poly(ethylene oxide). The system was designed to meet the basic criteria required for drug carrier systems, namely, solubility in water (overcoming the insolubility of ellipticine), satisfactory drug loading, particle size suitable for an efficient enhanced permeability and retention effect and adequate stability in blood plasma (pH 7.4) followed by rapid drug release in tumors or tumor cell endosomes (pH<6.5). The copolymer in the form of a unimer can be eliminated by kidneys because the weight-average molecular weight of 21 kDa is sufficiently below the renal threshold. The half-life of drug release in a pH 5.0 buffer solution (pH of a late endosome) was ~45 h, but a negligible amount of the free ellipticine derivative was detected at pH 7.4 (pH of blood). Consequently, this supramolecular polymer conjugate is a good candidate for the delivery of ellipticine-based drugs and will therefore be subjected to more detailed studies.

Multistage-targeted pH-responsive polymer conjugate of Auger electron emitter: optimized design and in vivo activity.

Auger electrons-emitting radioisotopes (such as iodine-125) are a potentially effective cancer treatment. They are extremely biologically effective, but only within a short range (nanometers). Their use as an effective cancer therapy requires that they will be transported within close proximity of DNA by an intercalator, where they induce double-strand breaks leading to cell death. This type of therapy may be even more beneficial when associated with drug delivery systems. In this report, we describe an optimized triple-targeted polymer delivery system for the intercalator ellipticine, which contains radioisotope iodine-125 with high specific radioactivity (63.2 GBq/mg). This compound is linked to an N-(2-hydroxypropyl)methacrylamide copolymer via an optimized acid-sensitive hydrazone linker. The system is stable at pH 7.4 (representing the pH of blood plasma), and the radioiodine-containing biologically active intercalator is released upon a decrease in pH (44% of the intercalator is released after 24h of incubation in pH 5.0 buffer, which mimics the pH in late endosomes). The active compound is a potent intercalator, as shown with direct titration with a DNA solution, and readily penetrates into cell nuclei, as observed by confocal microscopy. Its polymer conjugate is internalized into endosomes and releases the radioactive intercalator, which accumulates in the cell nuclei. In vivo experiments on mice with 4T1 murine breast cancer resulted in a statistically significant increase in the survival of mice treated with the polymer radioconjugate. The free radiolabeled intercalator was also shown to be effective, but it was less potent than the polymer conjugate.

Fine tuning of the pH-dependent drug release rate from polyHPMA-ellipticinium conjugates.

Polymer conjugates of anticancer drugs have shown high potential for assisting in cancer treatments. The pH-labile spacers allow site-specific triggered release of the drugs. We synthesized and characterized model drug conjugates with hydrazide bond-containing poly[N-(2-hydroxypropyl)methacrylamide] differing in the chemical surrounding of the hydrazone bond-containing spacer to find structure-drug release rate relationships. The conjugate selected for further studies shows negligible drug release in a pH 7.4 buffer but released 50% of the ellipticinium drug within 24h in a pH 5.0 phosphate saline buffer. The ellipticinium drug retained the antiproliferative activity of the ellipticine.

Polymer carriers for anticancer drugs targeted to EGF receptor.

A novel actively targeted polymer carrier for anticancer drugs based on an N-(2-hydroxypropyl)methacrylamide copolymer (PHPMA) is proposed. An oligopeptide sequence GE7, attached to the polymer, is a specific ligand for the EGF receptor overexpressed on most tumor cells. Co-attachment of selected chemotherapeutics will therefore lead to formation of tumor-specific polymer therapeutics, further enhanced by the EPR effect. FACS measurements prove elevated binding activity of the fluorescently labeled PHPMA/GE7 conjugate in EGFR-rich cells (FaDu, MCF-7), compared to conjugates of scrambled peptides. Cell lines with low EGFR level (SW620, B16F10) bind the GE7 conjugate significantly less.

Polymer conjugates of acridine-type anticancer drugs with pH-controlled activation.

Acridines are potent DNA-intercalating anticancer agents with high in vivo anticancer effectiveness, but also severe side effects. We synthesized five 9-anilinoacridine-type drugs and their conjugates with biocompatible water-soluble hydrazide polymer carrier. All of the synthesized acridine drugs retained their in vitro antiproliferative properties. Their polymer conjugates were sufficiently stable at pH 7.4 (model of pH in blood plasma) while releasing free drugs at pH 5.0 (model of pH in endosomes). After internalization of the conjugates, the free drugs were released and are visible in cell nuclei by fluorescence microscopy. Their intercalation ability was proven using a competitive ethidium bromide displacement assay.

DNA interactions of 2-pyrrolinodoxorubicin, a distinctively more potent daunosamine-modified analogue of doxorubicin.

It was shown earlier that 2-pyrrolinodoxorubicin was 500-1000 times more active towards human and mouse cancer cells in vitro than parental doxorubicin. However, the biochemical factors responsible for such a large difference in potency between doxorubicin and 2-pyrrolinodoxorubicin are not clear at the molecular level. To provide this information, we have investigated in cell-free media by biochemical and biophysical methods interactions of both anthracyclines with DNA, effects of these interactions on activity of human topoisomerase II, human Bloom's syndrome helicase and prokaryotic T7 RNA polymerase, and the capability of these drugs to form DNA interstrand cross-links in formaldehyde-free medium. Experiments aimed at understanding the properties of double-helical DNA in the presence of doxorubicin and 2-pyrrolinodoxorubicin revealed only small differences in DNA modifications by these anthracyclines and resulting conformational alterations in DNA. Similarly, the ability of 2-pyrrolinodoxorubicin modifications of DNA to inhibit catalytic activity of topoisomerase II does not differ significantly from that of doxorubicin. On the other hand, we demonstrate that an important factor responsible for the markedly higher antiproliferative potency of DNA modifications by 2-pyrrolinodoxorubicin is capability of these modifications to inhibit downstream cellular processes which process DNA damaged by this drug and involve separation of complementary strands of DNA, such as DNA unwinding by helicases or RNA polymerases. In addition, the results are also consistent with the hypothesis that in particular the capability of 2-pyrrolinodoxorubicin to readily form DNA interstrand cross-links is responsible for inhibition of these processes in the cells treated with this analogue of doxorubicin.

Ellipticine-aimed polymer-conjugated auger electron emitter: multistage organelle targeting approach.

Radioactive decay of some radionuclides produces a shower of Auger electrons, potent ionizing radiation within a very short range in living tissue (typically ca. 100 nm). Therefore, they must be brought to DNA-containing cell compartments and preferentially directly to DNA to be fully biologically effective. They may be used for a triple-targeting approach (first targeting, polymer-based system targeting into tumor tissue due to EPR effect; second targeting, pH-controlled release of intercalator-bound Auger electron emitter in slightly acidic tumor tissue or endosome; third targeting, into DNA in cell nucleus by the intercalator) minimizing radiation burden of healthy tissues. We describe a first system of this type, an ellipticine derivative-bound iodine-125 attached to hydrazide moieties containing poly[N-(2-hydroxypropyl)methacrylamide]. The system is stable at pH 7.4 (0% intercalator released after 24 h incubation), while iodine-containing biologically active intercalator is released upon decrease of pH (25% intercalator released after 24 h incubation at pH 5.0-model of late endosomes). Both 2-N-(2-oxobutyl)-9-iodoellipticinium bromide and the noniodinated 2-N-(2-oxobutyl)ellipticinium bromide are potent intercalators, as proven by direct titration with DNA and ethidium displacement assay, and readily penetrate into cell nuclei, as proven by confocal microscopy. They retain chemotherapeutical antiproliferative properties of ellipticine against Raji, EL-4, and 4T1cells with IC(50) in the range 0.27-8.8 µmol/L. Polymer conjugate of 2-N-(2-oxobutyl)-9-iodoellipticinium bromide is internalized into endosomes, releases active drug, possesses cytotoxic activity, and the drug accumulates in cell nuclei.

HPMA-copolymer conjugates targeted to tumor endothelium using synthetic oligopeptides.

Synthesis and characterization of N-(2-hydroxypropyl)methacrylamide (HPMA)-copolymer-based drug carriers targeted on specific receptors in the membrane of endothelial cells by oligopeptides (GRGDG, cyclo(RGDfK), and PHSCN) are described in this study. The copolymers containing targeting oligopeptides bound to the polymer via dodeca(ethylene glycol) spacer showed a receptor-specific time-dependent uptake with selected endothelial cell lines. The polymers were labeled with a fluorescent dye to enable monitoring of the interaction of the polymer conjugate with cells using fluorescence microscopy. Cellular uptake and apoptosis induction have been studied in vitro using various cell lines (EA.hy926, 3T3, SW620, and EL4). In vivo accumulation of the conjugate specifically targeted with cyclo(RGDfK) within the tumor vasculature was detected using fluorescence intravital microscopy in mice. The conjugate targeted by cyclo(RGDfK) was accumulated preferentially in the periphery of the growing tumor suggesting that the cyclo(RGDfK) peptide targets the polymer conjugate to the site of neoangiogenesis, rather than to the tumor mass.

New bioerodable thermoresponsive polymers for possible radiotherapeutic applications.

A new thermoresponsive system designed for local radiotherapy has been developed. In this system a radionuclide complex is entrapped in a thermoresponsive polymer locally precipitated at body temperature after injection of a polymer-complex solution into the tissue where a therapeutic effect is required. The lifetime of the system is controlled by the rate of polymer hydrolysis, its dissolution and elimination from the body. The thermoresponsive polymer with the cloud temperature (CT) below body temperature is based on copolymers of N-isopropylmethacrylamide with a methacrylamide-type comonomer containing hydrophobic n-alkyls of three different sizes (C(3), C(6) and C(12)) bonded by a hydrolytically labile hydrazone bond. Hydrolysis of hydrazone bond results in a copolymer soluble at body temperature. The copolymer containing 27.5 mole% of the comonomer with the C(6) moiety, which was chosen for further study, has the CT 22 degrees C and its phase separation is complete at 34 degrees C. Polymer dissolution is complete within 48 h at both pH 5.0 or 7.4. The model therapeutic radionuclide, (64)Cu, in the form of its hydrophobic chelate bis(quinolin-8-olato-N,O) [(64)Cu]copper, is efficiently kept hydrophobically entrapped in the phase-separated polymer until the dissolution by hydrolytic degradation is completed.

Characterization of molecular structures and properties of polyurethanes using molecular dynamics simulations.

Thermotropic polyurethanes with mesogenic groups in side chains were prepared from two diisocyanates and four diols with stoichiometric ratios of reactive isocyanate (NCO) and hydroxy (OH) groups. Their thermal behavior was determined by differential scanning calorimetry. The effect of structure modifications of the diisocyanates and diols, in particular changes in the mesogen, were investigated. Introduction of mesogenic segments into the polymers suppresses the ordering. Stiff end substituents (phenyl and alkoxy groups) of the mesogens stabilize the mesophases to such an extent that the negative influence of long polymer chains is compensated and the liquid-crystalline properties are recovered. All-atom molecular dynamics simulations in the Cerius2 modeling environment were carried out to characterize the structures of the polymers. Analysis of the dynamic trajectories at 20, 100, 120 and 170 degrees C revealed changes in conformation of macromolecules, which correlate with DSC measurements.