Synthesis of Well-Defined Semitelechelic Poly[N-(2-hydroxypropyl)methacrylamide] Polymers with Functional Group at the α-End of the Polymer Chain by RAFT Polymerization

Synthesis and Structure Optimization of Star Copolymers as Tunable Macromolecular Carriers for Minimal Immunogen Vaccine Delivery

Minimal immunogen vaccines are being developed to focus antibody responses against otherwise challenging targets, including human immunodeficiency virus (HIV), but multimerization of the minimal peptide immunogen on a carrier platform is required for activity. Star copolymers comprising multiple hydrophilic polymer chains ("arms") radiating from a central dendrimer unit ("core") were recently reported to be an effective platform for arraying minimal immunogens for inducing antibody responses in mice and primates. However, the impact of different parameters of the star copolymer (e.g., minimal immunogen density and hydrodynamic size) on antibody responses and the optimal synthetic route for controlling those parameters remains to be fully explored. We synthesized a library of star copolymers composed of poly[N-(2-hydroxypropyl)methacrylamide] hydrophilic arms extending from poly(amidoamine) dendrimer cores with the aim of identifying the optimal composition for use as minimal immunogen vaccines. Our results show that the length of the polymer arms has a crucial impact on the star copolymer hydrodynamic size and is precisely tunable over a range of 20-50 nm diameter, while the dendrimer generation affects the maximum number of arms (and therefore minimal immunogens) that can be attached to the surface of the dendrimer. In addition, high-resolution images of selected star copolymer taken by a custom-modified environmental scanning electron microscope enabled the acquisition of high-resolution images, providing new insights into the star copolymer structure. Finally, in vivo studies assessing a star copolymer vaccine comprising an HIV minimal immunogen showed the criticality of polymer arm length in promoting antibody responses and highlighting the importance of composition tunability to yield the desired biological effect.

Iridium-based Polymeric Multifunctional Imaging Tools for Biochemistry

Herein, we report the development of a macromolecular multifunctional imaging tool for biological investigations, which is comprised of an N-(2-hydroxypropyl)methacrylamide backbone, iridium-based luminescent probe, glutamate carboxypeptidase II (GCPII) targeting ligand, and biotin affinity tag. The iridium luminophore is a tris-cyclometalated complex based on [Ir(ppy)3] with one of its 2-phenylpyridine ligands functionalized to allow conjugation. Synthesized macromolecular probes differed in the structure of the polymer and content of the iridium complex. The applicability of the developed imaging tools has been tested in flow cytometry (FACS) based assay, laser confocal microscopy, and fluorescence lifetime imaging microscopy (FLIM). The FACS analysis has shown that the targeted iBodies containing the iridium luminophore exhibit selective labelling of GCPII expressing cells. This observation was also confirmed in the imaging experiments with laser confocal microscopy. The FLIM experiment has shown that the iBodies with the iridium label exhibit a lifetime greater than 100 ns, which distinguishes them from typically used systems labelled with organic fluorophores exhibiting short fluorescence lifetimes. The results of this investigation indicate that the system exhibits interesting properties, which supports the development of additional biological tools utilizing the key components (iridium complexes, iBody concept), primarily focusing on the longer lifetime of the iridium emitter.

Iron-based compounds coordinated with phospho-polymers as biocompatible probes for dual 31P/1H magnetic resonance imaging and spectroscopy

In this work, we present the synthesis and evaluation of magnetic resonance (MR) properties of novel phosphorus/iron-containing probes for dual 31P and 1H MR imaging and spectroscopy (MRI and MRS). The presented probes are composed of biocompatible semitelechelic and multivalent phospho-polymers based on poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) coordinated with small paramagnetic Fe3+ ions or superparamagnetic maghemite (γ-Fe2O3) nanoparticles via deferoxamine group linked to the end or along the polymer chains. All probes provided very short 1H T1 and T2 relaxation times even at low iron concentrations. The presence of iron had a significant impact on the shortening of 31P relaxation, with the effect being more pronounced for probes based on γ-Fe2O3 and multivalent polymer. While the water-soluble probe having one Fe3+ ion per polymer chain was satisfactorily visualized by both 31P-MRS and 31P-MRI, the probe with multiple Fe3+ ions could only be detected by 31P-MRS, and the probes consisting of γ-Fe2O3 nanoparticles could not be imaged by either technique due to their ultra-short 31P relaxations. In this proof-of-principle study performed on phantoms at a clinically relevant magnetic fields, we demonstrated how the different forms and concentrations of iron affect both the 1H MR signal of the surrounding water molecules and the 31P MR signal of the phospho-polymer probe. Thus, this double contrast can be exploited to simultaneously visualize body anatomy and monitor probe biodistribution.

Chemosensitization of tumors via simultaneous delivery of STAT3 inhibitor and doxorubicin through HPMA copolymer-based nanotherapeutics with pH-sensitive activation

We synthesized three novel STAT3 inhibitors (S3iD1-S3iD3) possessing oxoheptanoic residue enabling linkage to HPMA copolymer carrier via a pH-sensitive hydrazone bond. HPMA copolymer conjugates bearing doxorubicin (Dox) and our STAT3 inhibitors were synthesized to evaluate the anticancer effect of Dox and STAT3 inhibitor co-delivery into tumors. S3iD1-3 and their copolymer-bound counterparts (P-S3iD1-P-S3iD3) showed considerable in vitro cytostatic activities in five mouse and human cancer cell lines with IC50 ~0.6-7.9 μM and 0.7-10.9 μM, respectively. S3iD2 and S3iD3 were confirmed to inhibit the STAT3 signaling pathway. The combination of HPMA copolymer-bound Dox (P-Dox) and P-S3iD3 at the dosage showing negligible toxicity demonstrated significant antitumor activity in B16F10 melanoma-bearing mice and completely cured 2 out of 15 mice. P-Dox alone had a significantly lower therapeutic activity with no completely cured mice. Thus, polymer conjugates bearing STAT3 inhibitors may be used for the chemosensitization of chemorefractory tumors.

Adaptable polymerization platform for therapeutics with tunable biodegradability

Biodegradable polymer-based therapeutics have recently become essential drug delivery biomaterials for various bioactive compounds. Biodegradable and biocompatible polymer-based biomaterials fulfill the requirements of these therapeutics because they enable to obtain polymer biomaterials with optimized blood circulation, pharmacokinetics, biodegradability, and renal excretion. Herein, we describe an adaptable polymerization platform employed for the synthesis of long-circulating, stimulus-sensitive and biodegradable biomaterials, therapeutics, or theranostics. Four chain transfer agents (CTA) were designed and successfully synthesized for the reversible addition-fragmentation chain transfer polymerization, allowing the straightforward synthesis of hydrolytically biodegradable structures of block copolymers-based biomaterials. The controlled polymerization using the CTAs enables controlling the half-life of the hydrolytic degradation of polymer precursors in a wide range from 5 h to 21 days. Moreover, the antitumor drug pirarubicin (THP) was successfully conjugated to the polymer biomaterials via a pH-sensitive hydrazone bond for in vitro and in vivo experiments. Polymer conjugates demonstrated superior antitumor efficacy compared to basic linear polymer-based conjugates. Notably, the biodegradable systems, even though those with degradation in the order of hours were selected, increased the half-life of THP in the bloodstream almost two-fold. Indeed, the presented platform design enables the main chain-end specific attachment of targeting ligands or diagnostic molecules. The adaptable polymerization platform design allows tuning of the biodegradability rate, stimuli-sensitive drug bonding, and optimized pharmacokinetics to increase the therapy outcome and system targeting, thus allowing the preparation of targeted or theranostic polymer conjugates. STATEMENT OF SIGNIFICANCE: Biodegradable and biocompatible polymer-based biomaterials are recognized as potential future bioactive nanomedicines. To advance the development of such biomaterials, we developed polymerization platforms utilizing tailored chain transfer agents allowing the straightforward synthesis of hydrolytically degradable polymer biomaterials with tuned biodegradability from hours to several days. The platform allows for the synthesis of long-circulating, stimulus-sensitive and biodegradable biomaterial serving as drug carriers or theranostics. The therapeutic potential was validated by preparation of polymer biomaterials containing pirarubicin, anticancer drug, bound via pH sensitive bond and by showing prolonged blood circulation and increased antitumor activity while keeping the drug side effects low. This work paves the way for future development of biodegradable polymer biomaterials with advanced properties in drug delivery.

Phosphorus-Containing Polymers as Sensitive Biocompatible Probes for 31P Magnetic Resonance

The visualization of organs and tissues using ³¹P magnetic resonance (MR) imaging represents an immense challenge. This is largely due to the lack of sensitive biocompatible probes required to deliver a high-intensity MR signal that can be distinguished from the natural biological background. Synthetic water-soluble phosphorus-containing polymers appear to be suitable materials for this purpose due to their adjustable chain architecture, low toxicity, and favorable pharmacokinetics. In this work, we carried out a controlled synthesis, and compared the MR properties, of several probes consisting of highly hydrophilic phosphopolymers differing in composition, structure, and molecular weight. Based on our phantom experiments, all probes with a molecular weight of ~3-400 kg·mol^-1, including linear polymers based on poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), poly(ethyl ethylenephosphate) (PEEP), and poly[bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)]phosphazene (PMEEEP) as well as star-shaped copolymers composed of PMPC arms grafted onto poly(amidoamine) dendrimer (PAMAM-g-PMPC) or cyclotriphosphazene-derived cores (CTP-g-PMPC), were readily detected using a 4.7 T MR scanner. The highest signal-to-noise ratio was achieved by the linear polymers PMPC (210) and PMEEEP (62) followed by the star polymers CTP-g-PMPC (56) and PAMAM-g-PMPC (44). The ³¹P T₁ and T₂ relaxation times for these phosphopolymers were also favorable, ranging between 1078 and 2368 and 30 and 171 ms, respectively. We contend that select phosphopolymers are suitable for use as sensitive ³¹P MR probes for biomedical applications.

Coating Persistent Luminescence Nanoparticles With Hydrophilic Polymers for in vivo Imaging

Persistent luminescence nanoparticles (PLNPs) are innovative nanomaterials highly useful for bioimaging applications. Indeed, due to their particular optical properties, i.e., the ability to store the excitation energy before slowly releasing it for a prolonged period of time, they allow in vivo imaging without auto-fluorescence and with a high target to background ratio. However, as for most nanoparticles (NPs), without any special surface coating, they are rapidly opsonized and captured by the liver after systemic injection into small animals. To overcome this issue and prolong nanoparticle circulation in the bloodstream, a new stealth strategy was developed by covering their surface with poly(N-2-hydroxypropyl)methacrylamide (pHPMA), a highly hydrophilic polymer widely used in nanomedicine. Preliminary in vivo imaging results demonstrated the possibility of pHPMA as an alternative strategy to cover ZnGa₂O₄:Cr NPs to delay their capture by the liver, thereby providing a new perspective for the formulation of stealth NPs.

A radioligand binding assay for the insulin-like growth factor 2 receptor

Insulin-like growth factors 2 and 1 (IGF2 and IGF1) and insulin are closely related hormones that are responsible for the regulation of metabolic homeostasis, development and growth of the organism. Physiological functions of insulin and IGF1 are relatively well-studied, but information about the role of IGF2 in the body is still sparse. Recent discoveries called attention to emerging functions of IGF2 in the brain, where it could be involved in processes of learning and memory consolidation. It was also proposed that these functions could be mediated by the receptor for IGF2 (IGF2R). Nevertheless, little is known about the mechanism of signal transduction through this receptor. Here we produced His-tagged domain 11 (D11), an IGF2-binding element of IGF2R; we immobilized it on the solid support through a well-defined sandwich, consisting of neutravidin, biotin and synthetic anti-His-tag antibodies. Next, we prepared specifically radiolabeled [125I]-monoiodotyrosyl-Tyr2-IGF2 and optimized a sensitive and robust competitive radioligand binding assay for determination of the nanomolar binding affinities of hormones for D11 of IGF2. The assay will be helpful for the characterization of new IGF2 mutants to study the functions of IGF2R and the development of new compounds for the treatment of neurological disorders.

Graft copolymers with tunable amphiphilicity tailored for efficient dual drug delivery via encapsulation and pH-sensitive drug conjugation

Amphiphilic poly(ε-caprolactone)-graft-(poly-N-(2-hydroxypropyl) methacrylamide) copolymers with tunable solution properties form stable micelles with high drug payload via simultaneous encapsulation and pH-sensitive covalent conjugation.

In Situ In Vivo radiolabeling of polymer-coated hydroxyapatite nanoparticles to track their biodistribution in mice

The imaging of healthy tissues and solid tumors benefits from the application of nanoparticle probes with altered pharmacokinetics, not available to low molecular weight compounds. However, the distribution and accumulation of nanoprobes in vivo typically take at least tens of hours to be efficient. For nanoprobes bearing a radioactive label, this is contradictory to the requirement of minimizing the radiation dose for patients by using as-short-as-feasible half-life radionuclides in diagnostics. Thus, we developed a two-stage diagnostic concept for monitoring long-lasting targeting effects with short-lived radioactive labels using bone-mimicking biocompatible polymer-coated and colloidally fully stabilized hydroxyapatite nanoparticles (HAP NPs) and bone-seeking radiopharmaceuticals. Within the pretargeting stage, the nonlabeled nanoparticles are allowed to circulate in the blood. Afterward, ^99mTc-1-hydroxyethylidene-1.1-diphosphonate (^99mTc-HEDP) is administered intravenously for in situ labeling of the nanoparticles and subsequent single-photon emission computed tomography/computed tomography (SPECT/CT) visualization. The HAP NPs, stabilized with tailored hydrophilic polymers, are not cytotoxic in vitro, as shown by several cell lines. The polymer coating prolongs the circulation of HAP NPs in the blood. The nanoparticles were successfully labeled in vivo with ^99mTc-HEDP, 1 and 24 h after injection, and they were visualized by SPECT/CT over time in healthy mice.

Synthesis of water-soluble star polymers based on cyclodextrins

Novel star polymers based on the water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer and cyclodextrin were synthesized and the physico-chemical behavior of these precursors was studied. Semitelechelic HPMA copolymers were grafted onto the cyclodextrin core, thus forming star-like structure. Both prepared systems were designed as possible polymer carriers for the controlled release of cytostatic drugs, which after the drug release and degradation will be eliminated from the organism. Two synthesis approaches were used to obtain similar polymer carriers with different degradation rates. All the polymers were prepared by reversible addition-fragmentation chain-transfer polymerization, which guarantees low dispersity of the prepared systems.

Synthesis and self-seeding behavior of oligo(p-phenylene vinylene)-b-poly(N-(2-hydroxypropyl)methacrylamide)

This article reports the preparation of uniform fiber- and ribbon-like nanostructures via the self-seeding of OPV₅-b-PHPMA diblock copolymers.

Optimizing the Cu-RDRP ofN-(2-hydroxypropyl) methacrylamide toward biomedical applications

Aqueous Cu-RDRP ofN-(2-hydroxypropyl) methacrylamide was optimized to achieve co(polymers) of low dispersity and controlled molecular weight at high conversions.

Intended and Unintended Targeting of Polymeric Nanocarriers: The Case of Modified Poly(glycerol adipate) Nanoparticles

Biodegradable nanoparticles based on stearic acid-modified poly(glycerol adipate) (PGAS) are promising carriers for drug delivery. In order to investigate the impact of the particle interface characteristics on the biological fate, PGAS nanoparticles are covalently and noncovalently coated with N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers. HPMA copolymer-modified PGAS nanoparticles have similar particle sizes, but less negative zeta-potentials. Nanoparticles are double labeled with the fluorescent dyes DiR (noncovalently) and DYOMICS-676 (covalently bound to HPMA copolymer), and their biodistribution is investigated noninvasively by multispectral optical imaging. Both covalent and noncovalent coatings cause changes in the pharmacokinetics and biodistribution in healthy and tumor-bearing mice. In addition to the intended tumor accumulation, high signals of both fluorescent dyes are also observed in other organs, including liver, ovaries, adrenal glands, and bone. The unintended accumulation of nanocarriers needs further detailed and systematic investigations, especially with respect to the observed ovarian and adrenal gland accumulation.

HPMA Copolymer-Drug Conjugates with Controlled Tumor-Specific Drug Release

Over the past few decades, numerous polymer drug carrier systems are designed and synthesized, and their properties are evaluated. Many of these systems are based on water-soluble polymer carriers of low-molecular-weight drugs and compounds, e.g., cytostatic agents, anti-inflammatory drugs, or multidrug resistance inhibitors, all covalently bound to a carrier by a biodegradable spacer that enables controlled release of the active molecule to achieve the desired pharmacological effect. Among others, the synthetic polymer carriers based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers are some of the most promising carriers for this purpose. This review focuses on advances in the development of HPMA copolymer carriers and their conjugates with anticancer drugs, with triggered drug activation in tumor tissue and especially in tumor cells. Specifically, this review highlights the improvements in polymer drug carrier design with respect to the structure of a spacer to influence controlled drug release and activation, and its impact on the drug pharmacokinetics, enhanced tumor uptake, cellular trafficking, and in vivo antitumor activity.

iBodies: Modular Synthetic Antibody Mimetics Based on Hydrophilic Polymers Decorated with Functional Moieties

Antibodies are indispensable tools for biomedicine and anticancer therapy. Nevertheless, their use is compromised by high production costs, limited stability, and difficulty of chemical modification. The design and preparation of synthetic polymer conjugates capable of replacing antibodies in biomedical applications such as ELISA, flow cytometry, immunocytochemistry, and immunoprecipitation is reported. The conjugates, named “iBodies”, consist of an HPMA copolymer decorated with low‐molecular‐weight compounds that function as targeting ligands, affinity anchors, and imaging probes. We prepared specific conjugates targeting several proteins with known ligands and used these iBodies for enzyme inhibition, protein isolation, immobilization, quantification, and live‐cell imaging. Our data indicate that this highly modular and versatile polymer system can be used to produce inexpensive and stable antibody substitutes directed toward virtually any protein of interest with a known ligand.

Synthesis and Properties of Star HPMA Copolymer Nanocarriers Synthesised by RAFT Polymerisation Designed for Selective Anticancer Drug Delivery and Imaging

High-molecular-weight star polymer drug nanocarriers intended for the treatment and/or visualisation of solid tumours were synthesised, and their physico-chemical and preliminary in vitro biological properties were determined. The water-soluble star polymer carriers were prepared by the grafting of poly(amido amine) (PAMAM) dendrimers by hetero-telechelic N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers, synthesised by the controlled radical Reversible Addition Fragmentation chain Transfer (RAFT) polymerisation. The well-defined star copolymers with Mw values ranging from 2 · 10(5) to 6 · 10(5) showing a low dispersity (approximately 1.2) were prepared in a high yield. A model anticancer drug, doxorubicin, was bound to the star polymer through a hydrazone bond, enabling the pH-controlled drug release in the target tumour tissue. The activated polymer arm ends of the star copolymer carrier enable a one-point attachment for the targeting ligands and/or a labelling moiety. In this study, the model TAMRA fluorescent dye was used to prove the feasibility of the polymer carrier visualisation by optical imaging in vitro. The tailor-made structure of the star polymer carriers should facilitate the synthesis of targeted polymer-drug conjugates, even polymer theranostics, for simultaneous tumour drug delivery and imaging.

Synthesis of non-fouling poly[N-(2-hydroxypropyl)methacrylamide] brushes by photoinduced SET-LRP

Surface-initiated photoinduced SET-LRP of N-(2-hydroxypropyl)methacrylamide from an initiator-containing monolayer yields micropatterned brushes resistant to blood plasma fouling.

Reversible Addition-Fragmentation Chain Transfer Synthesis of a Micelle-Forming, Structure Reversible Thermosensitive Diblock Copolymer Based on the N-(2-Hydroxy propyl) Methacrylamide Backbone

A diblock copolymer composed of N-(2-hydroxy propyl) methacrylamide (HPMAm) as hydrophilic block and N-(2-hydroxy propyl) methacrylamide dilactate (HPMAm-Lac₂) as thermosensitive block was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. To this end, HPMAm was first polymerized with 4-cyano-4-[(dodecylsulfanylthiocarbonyl)-sulfanyl]pentanoic acid as the chain transfer agent and azobisisobutyronitrile (AIBN) as the initiator. The polymerization showed a linear increase in M_n as a function of monomer conversion. The living p(HPMAm) chain (7 kDa) was subsequently extended with HPMAm-Lac₂ yielding a diblock copolymer (total M_n of 22 kDa). The copolymer showed reversible thermosensitivity in aqueous solution and self-assembled into micelles with a size of 58 nm (PDI 0.13) above its critical micelle temperature (CMT, 2.1 °C) and concentration (CMC, 0.044 mg/mL) and was soluble below the CMT. Paclitaxel, a hydrophobic chemotherapeutic drug, was encapsulated in the micelles with a loading capacity of 16.1 ± 1.2%. Hydrolysis of the dilactate side groups of the p(HPMAm-Lac₂) block converted the copolymer to the fully hydrophilic p(HPMAm) homopolymer, resulting in dissociation of the micelles. In conclusion, the livingness and versatility of RAFT polymerization provide possibilities to synthesize block copolymers with HPMAm and derivatives thereof.