The Comparison of In Vivo Properties of Water-Soluble HPMA-Based Polymer Conjugates with Doxorubicin Prepared by Controlled RAFT or Free Radical Polymerization

The transmission and toxicity of polymer-bound doxorubicin-containing exosomes derived from human adenocarcinoma cells

Background: Exosomes are extracellular vesicles with the ability to encapsulate bioactive molecules, such as therapeutics. This study identified a new exosome mediated route of doxorubicin and poly(N-(2-hydroxypropyl)methacrylamide) (pHPMA)-bound doxorubicin trafficking in the tumor mass. Materials & methods: Exosome loading was achieved via incubation of the therapeutics with an adherent human breast adenocarcinoma cell line and its derived spheroids. Exosomes were characterized using HPLC, nanoparticle tracking analysis (NTA) and western blotting. Results: The therapeutics were successfully loaded into exosomes. Spheroids secreted significantly more exosomes than adherent cells and showed decreased viability after treatment with therapeutic-loaded exosomes, which confirmed successful transmission. Conclusion: To the best of our knowledge, this study provides the first evidence of pHPMA-drug conjugate secretion by extracellular vesicles.

Simultaneous Delivery of Doxorubicin and Protease Inhibitor Derivative to Solid Tumors via Star-Shaped Polymer Nanomedicines Overcomes P-gp- and STAT3-Mediated Chemoresistance

The derivative of protease inhibitor ritonavir (5-methyl-4-oxohexanoic acid ritonavir ester; RD) was recently recognized as a potent P-gp inhibitor and cancerostatic drug inhibiting the proteasome and STAT3 signaling. Therefore, we designed high-molecular-weight HPMA copolymer conjugates with a PAMAM dendrimer core bearing both doxorubicin (Dox) and RD (Star-RD + Dox) to increase the circulation half-life to maximize simultaneous delivery of Dox and RD into the tumor. Star-RD inhibited P-gp activity, potently sensitizing both low- and high-P-gp-expressing cancer cells to the cytostatic and proapoptotic activity of Dox in vitro. Star-RD + Dox possessed higher cytostatic and proapoptotic activities compared to Star-Dox and the equivalent mixture of Star-Dox and Star-RD in vitro. Star-RD + Dox efficiently inhibited STAT3 signaling and induced caspase-3 activation and DNA fragmentation in cancer cells in vivo. Importantly, Star-RD + Dox was found to have superior antitumor activity in terms of tumor growth inhibition and increased survival of mice bearing P-gp-expressing tumors.

Synthesis, Morphology, and Rheological Evaluation of HPMA (N-2-Hydroxypropyl Methacrylamide)-PCL (Polycaprolactone) Conjugates

The design, synthesis, and physicochemical characterization of conjugates are arduous and tedious processes. Several synthetic pathways for polymeric conjugation have been reported; however, conjugation through monomers with suitable reaction conditions can be a simple and robust approach. In the present study, three different conjugates of hydrophilic N-2-hydroxypropyl methacrylamide (HPMA) and hydrophobic polycaprolactone (PCL) were synthesized. The followed synthetic pathway not only was simple and robust but also reduced the overall synthetic steps as well as harsh reaction conditions significantly. In a nutshell, three conjugates, i.e., N-2-hydroxypropyl methacrylamide and polycaprolactone (HP-PCL), n-butanol-polycaprolactone-N-2-hydroxypropyl methacrylamide (nBu-PCL-HP), and isoamyl alcohol-polycaprolactone-N-2-hydroxypropyl methacrylamide (ISAL-PCL-HP), were synthesized through this simple synthetic strategy following the monomer conjugation approach along with exhaustive spectroscopic and rheological characterization. The conjugates HP-PCL, nBu-PCL-HP, and ISAL-PCL-HP were characterized by Fourier transform infrared (FT-IR) and NMR (¹³C and ¹H) spectroscopies. The size and ζ potential of conjugates were determined through the dynamic light scattering (DLS) method. The nBu-PCL-HP conjugate displayed a hexagonal-like shape, as evidenced by scanning electron microscopy (SEM) with an obtained size of 237.9 ± 0.21 nm. X-ray diffraction (XRD) analysis proved the crystalline nature of nBu-PCL-HP conjugates. The results of smartly synthesized conjugates intrigued us to study their flow properties in detail. Rheological evaluation resulted in their non-Newtonian type of flow with the best-fit behavior for all of the conjugates followed as per the Herschel-Bulkley and power-law models applied herein. Conclusively, the synthesized HPMA and PCL conjugates may have applications in the preparation of blends, fibers, etc. in the future. The study portrayed that the explored synthetic scheme using monomers and initiators could be a suitable approach for the synthesis of HPMA and PCL conjugates.

HPMA Copolymer-Based Nanomedicines in Controlled Drug Delivery

Recently, numerous polymer materials have been employed as drug carrier systems in medicinal research, and their detailed properties have been thoroughly evaluated. Water-soluble polymer carriers play a significant role between these studied polymer systems as they are advantageously applied as carriers of low-molecular-weight drugs and compounds, e.g., cytostatic agents, anti-inflammatory drugs, antimicrobial molecules, or multidrug resistance inhibitors. Covalent attachment of carried molecules using a biodegradable spacer is strongly preferred, as such design ensures the controlled release of the drug in the place of a desired pharmacological effect in a reasonable time-dependent manner. Importantly, the synthetic polymer biomaterials based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers are recognized drug carriers with unique properties that nominate them among the most serious nanomedicines candidates for human clinical trials. This review focuses on advances in the development of HPMA copolymer-based nanomedicines within the passive and active targeting into the place of desired pharmacological effect, tumors, inflammation or bacterial infection sites. Specifically, this review highlights the safety issues of HPMA polymer-based drug carriers concerning the structure of nanomedicines. The main impact consists of the improvement of targeting ability, especially concerning the enhanced and permeability retention (EPR) effect.

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 Cancerostatics Targeted by Recombinant Antibody Fragments to GD2-Positive Tumor Cells

A water-soluble polymer cancerostatic actively targeted against cancer cells expressing a disialoganglioside antigen GD2 was designed, synthesized and characterized. A polymer conjugate of an antitumor drug doxorubicin with a N-(2-hydroxypropyl)methacrylamide-based copolymer was specifically targeted against GD2 antigen-positive tumor cells using a recombinant single chain fragment (scFv) of an anti-GD2 monoclonal antibody. The targeting protein ligand was attached to the polymer-drug conjugate either via a covalent bond between the amino groups of the protein using a traditional nonspecific aminolytic reaction with a reactive polymer precursor or via a noncovalent but highly specific interaction between bungarotoxin covalently linked to the polymer and the recombinant scFv modified with a C-terminal bungarotoxin-binding peptide. The GD2 antigen binding activity and GD2-specific cytotoxicity of the targeted noncovalent polymer-scFv complex proved to be superior to the covalent polymer-scFv conjugate.

Biodistribution, Clearance, and Long-Term Fate of Clinically Relevant Nanomaterials

Realization of the immense potential of nanomaterials for biomedical applications will require a thorough understanding of how they interact with cells, tissues, and organs. There is evidence that, depending on their physicochemical properties and subsequent interactions, nanomaterials are indeed taken up by cells. However, the subsequent release and/or intracellular degradation of the materials, transfer to other cells, and/or translocation across tissue barriers are still poorly understood. The involvement of these cellular clearance mechanisms strongly influences the long-term fate of used nanomaterials, especially if one also considers repeated exposure. Several nanomaterials, such as liposomes and iron oxide, gold, or silica nanoparticles, are already approved by the American Food and Drug Administration for clinical trials; however, there is still a huge gap of knowledge concerning their fate in the body. Herein, clinically relevant nanomaterials, their possible modes of exposure, as well as the biological barriers they must overcome to be effective are reviewed. Furthermore, the biodistribution and kinetics of nanomaterials and their modes of clearance are discussed, knowledge of the long-term fates of a selection of nanomaterials is summarized, and the critical points that must be considered for future research are addressed.

A tumor-targeted polymer theranostics platform for positron emission tomography and fluorescence imaging

Here, we describe a novel polymer platform suitable for efficient diagnostics and potential theranostics based on ⁸⁹Zr-labeled N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymer conjugates. A set of polymers differing in molecular weight with either low dispersity or high dispersity were designed and synthesized and their biodistribution in vivo was successfully and precisely observed over 72 h. Moreover, the feasibility of two imaging techniques, fluorescence imaging (FI) and positron emission tomography (PET), was compared using labeled polymer conjugates. Both methods gave comparable results thus showing the enhanced diagnostic potential of the prepared polymer-dye or polymer-chelator-⁸⁹Zr constructs. The in vivo and ex vivo PET/FI studies indicated that the dispersity and molecular weight of the linear HPMA polymers have a significant influence on the pharmacokinetics of the polymer conjugates. The higher molecular weight and narrower distribution of molecular weights of the polymer carriers improve their pharmacokinetic profile for highly prolonged blood circulation and enhanced tumor uptake. Moreover, the same polymer carrier with the anticancer drug doxorubicin bound by a pH-sensitive hydrazone bond showed higher cytotoxicity and cellular uptake in vitro. Therefore, HPMA copolymers with low dispersity and a molecular weight near the limit of renal filtration can be used as highly efficient polymer carriers of tumor-targeted therapeutics or for theranostics with minimal side effects.

Inhibition of CD44v3 and CD44v6 function blocks tumor invasion and metastatic colonization

The prevention of cancer cell dissemination and secondary tumor formation are major goals of cancer therapy. Here, we report on the development of a new CD44-targeted copolymer carrying multiple copies of the A5G27 peptide, known for its ability to bind specifically to CD44v3 and CD44v6 on cancer cells and inhibit tumor cell migration, invasion, and angiogenesis. We hypothesized that conjugation of A5G27 to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer would enhance tumor tissue accumulation, promote selective binding to cancer cells, with concomitant increased inhibition of cancer cell invasiveness and migration. Fluorescein-5-isothiocyanate or the near-infrared fluorophore IR783 were attached to the copolymer backbone through a non-cleavable linkage to assess in vitro binding to cancer cells and biodistribution of the polymer in 4T1 murine mammary adenocarcinoma-bearing mice, respectively. The anti-migratory activity was evaluated both in vitro and in vivo. The binding of the targeted copolymer to cancer cells correlated well with the level of CD44 expression, with the polymer being internalized more efficiently by cancer cells. Pre-treatment of mice with polymer-bound A5G27 significantly inhibited lung colonization of migrating 4T1 cells in vivo, with the targeted copolymer accumulating preferentially in subcutaneous 4T1 tumors, when compared to a non-targeted system. As such, the HPMA copolymer-A5G27 conjugate is a promising candidate for inhibiting cancer cell migration and can also be used as a drug or imaging probe carrier for detection and treatment of cancer.

Dual-sensitive and biodegradable core-crosslinked HPMA copolymer–doxorubicin conjugate-based nanoparticles for cancer therapy

The nanoplatform of biosafe crosslinked copolymer-NPs efficiently delivers anticancer drugs to tumor cellsviablood circulation.

Tumor-targeted micelle-forming block copolymers for overcoming of multidrug resistance

New amphiphilic diblock polymer nanotherapeutics serving simultaneously as a drug delivery system and an inhibitor of multidrug resistance were designed, synthesized, and evaluated for their physico-chemical and biological characteristics. The amphiphilic character of the diblock polymer, containing a hydrophilic block based on the N-(2-hydroxypropyl)methacrylamide copolymer and a hydrophobic poly(propylene oxide) block (PPO), caused self-assembly into polymer micelles with an increased hydrodynamic radius (R_h of approximately 15nm) in aqueous solutions. Doxorubicin (Dox), as a cytostatic drug, was bound to the diblock polymer through a pH-sensitive hydrazone bond, enabling prolonged circulation in blood, the delivery of Dox into a solid tumor and the subsequent stimuli-sensitive controlled release within the tumor mass and tumor cells at a decreased pH. The applicability of micellar nanotherapeutics as drug carriers was confirmed by an in vivo evaluation using EL4 lymphoma-bearing C57BL/6 mice. We observed significantly higher accumulation of micellar conjugates in a solid tumor because of the EPR effect compared with similar polymer-drug conjugates that do not form micellar structures or with the parent free drug. In addition, highly increased anti-tumor efficacy of the micellar polymer nanotherapeutics, even at a sub-optimal dose, was observed. The presence of PPO in the structure of the diblock polymer ensured, during in vitro tests on human and mouse drug-sensitive and resistant cancer cell lines, the inhibition of P-glycoprotein, one of the most frequently expressed ATP-dependent efflux pump that causes multidrug resistance. In addition, we observed highly increased rate of the uptake of the diblock polymer nanotherapeutics within the cells. We suppose that combination of unique properties based on MDR inhibition, stimuli sensitiveness (pH sensitive activation of drug), improved pharmacokinetics and increased uptake into the cells made the described polymer micelle a good candidate for investigation as potential drug delivery system.

Overcoming multidrug resistance in Dox-resistant neuroblastoma cell lines via treatment with HPMA copolymer conjugates containing anthracyclines and P-gp inhibitors

Water-soluble N-(2-hydroxypropyl)methacrylamide copolymer conjugates bearing the anticancer drugs doxorubicin (Dox) or pirarubicin (THP), P-gp inhibitors derived from reversin 121 (REV) or ritonavir (RIT)), or both anticancer drug and P-gp inhibitor were designed and synthesized. All biologically active molecules were attached to the polymer carrier via pH-sensitive spacer enabling controlled release in mild acidic environment modeling endosomes and lysosomes of tumor cells. The cytotoxicity of the conjugates against three sensitive and Dox-resistant neuroblastoma (NB) cell lines, applied alone or in combination, was studied in vitro. All conjugates containing THP displayed higher cytotoxicity against all three Dox-resistant NB cell lines compared with the corresponding Dox-containing conjugates. Furthermore, the cytotoxicity of conjugates containing both drug and P-gp inhibitor was up to 10 times higher than that of the conjugate containing only drug. In general, the polymer-drug conjugates showed higher cytotoxicity when conjugates containing inhibitors were added 8 or 16h prior to treatment compared with conjugates bearing both the inhibitor and the drug. The difference in cytotoxicity was more pronounced at the 16-h time point. Moreover, higher inhibitor:drug ratios resulted in higher cytotoxicity. The cytotoxicity of the polymer-drug used in combination with polymer P-gp inhibitor was up to 84 times higher than that of the polymer-drug alone.