From Defined Reactive Diblock Copolymers to Functional HPMA-Based Self-Assembled Nanoaggregates

Access to Functionalized Materials by Metal-Free Ring-Opening Metathesis Polymerization of Active Esters and Divergent Postpolymerization Modification

Metal-free ring-opening metathesis polymerization (MF-ROMP) is an emerging polymerization strategy that provides access to ROMP materials by using organic initiators and photoredox catalysts. Unlike metal-mediated ROMP, MF-ROMP is not highly tolerant toward functionalized monomers. Herein, we report that pentafluorophenyl esters are polymerizable under MF-ROMP conditions to produce homopolymers, statistical copolymers, and block copolymers. Amine coupling agents were then used to install a range of functional groups via acyl substitution including alkynes, amino acid derivatives, fluorophores, and redox active moieties. Overall, these findings provide a framework to prepare functionalized ROMP polymers without the risk of metal contamination.

Electrochemically Synthesized Polyacrylamide Gel and Core-Shell Nanoparticles for 3D Cell Culture Formation

Biocompatible polyacrylamide gel and core-shell nanoparticles (NPs) were synthesized using a one-step electrochemically initiated gelation. Constant-potential electrochemical decomposing of ammonium persulfate initiated the copolymerization of N-isopropyl acrylamide, methacrylic acid, and N,N'-methylenebisacrylamide monomers. This decomposing potential and monomers' concentrations were optimized to prepare gel NPs and thin gel film-grafted core-shell NPs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging confirmed the gel NP formation. The lyophilized gel NPs and core-shell NPs were applied to support the three-dimensional (3D) cell culture. In all, core-shell NPs provided superior support for complex 3D tissue structures.

Sulfoxide-functionalized nanogels inspired by the skin penetration properties of DMSO

Among polymeric nanocarriers, nanogels are especially promising non-irritating delivery vehicles to increase dermal bioavailability of therapeutics. However, accurately tailoring defined interactions with the amphiphilic skin barrier is still challenging. To address this limited specificity, we herein present a new strategy to combine biocompatible nanogels with the outstanding skin interaction properties of sulfoxide moieties. These chemical motifs are known from dimethyl sulfoxide (DMSO), a potent chemical penetration enhancer, which can often cause undesired skin damage upon long-term usage. By covalently functionalizing the nanogels' polymer network with such methyl sulfoxide side groups, tailor-made dermal delivery vehicles are developed to circumvent the skin disrupting properties of the small molecules. Key to an effective nanogel-skin interaction is assumed to be the specific nanogel amphiphilicity. This is examined by comparing the delivery efficiency of sulfoxide-based nanogels (NG-SOMe) with their corresponding thioether (NG-SMe) and sulfone-functionalized (NG-SO2Me) analogues. We demonstrate that the amphiphilic sulfoxide-based NG-SOMe nanogels are superior in their interaction with the likewise amphipathic stratum corneum (SC) showing an increased topical delivery efficacy of Nile red (NR) to the viable epidermis (VE) of excised human skin. In addition, toxicological studies on keratinocytes and fibroblasts show good biocompatibility while no perturbation of the complex protein and lipid distribution is observed via stimulated Raman microscopy. Thus, our NG-SOMe nanogels show high potential to effectively emulate the skin penetration enhancing properties of DMSO without its negative side effects.

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.

Sequential post-polymerization modification of a pentafluorophenyl ester-containing homopolymer: a convenient route to effective pH-responsive nanocarriers for anticancer drugs

Recently, pH-responsive polymeric micelles have gained significant attention as effective carriers for anti-cancer drug delivery. Herein, pH-responsive polymeric micelles were constructed by a simple post-polymerization modification of a single homopolymer, poly(pentafluorophenyl acrylate) (PPFPA). The PPFPA was first subjected to modification with 1-amino-2-propanol yielding the amphiphilic copolymer of poly(pentafluorophenyl acrylate)-ran-poly(N-(2-hydroxypropyl acrylamide)). A series of amphiphilic random copolymers of different compositions could self-assemble into spherical micelles with a unimodal size distribution in aqueous solution. Then, 1-(3-aminopropyl)imidazole (API), a reagent to introduce charge conversional entities, was reacted with the remaining PPFPA segment in the micellar core resulting in API-modified micelles which can encapsulate doxorubicin (DOX), a hydrophobic anti-cancer drug. As monitored by dynamic light scattering, the API-modified micelles underwent disintegration upon pH switching from 7.4 to 5.0, presumably due to imidazolyl group protonation. This pH-responsiveness of the API-modified micelles was responsible for the faster and greater in vitro DOX release in an acidic environment than neutral pH. Cellular uptake studies revealed that the developed carriers were internalized into MDA-MB-231 cells within 30 min via endocytosis and exhibited cytotoxicity in a dose-dependent manner.

Optimizing synthetic nucleic acid and protein nanocarriers: The chemical evolution approach

Optimizing synthetic nanocarriers is like searching for a needle in a haystack. How to find the most suitable carrier for intracellular delivery of a specified macromolecular nanoagent for a given disease target location? Here, we review different synthetic 'chemical evolution' strategies that have been pursued. Libraries of nanocarriers have been generated either by unbiased combinatorial chemistry or by variation and novel combination of known functional delivery elements. As in natural evolution, definition of nanocarriers as sequences, as barcode or design principle, may fuel chemical evolution. Screening in appropriate test system may not only provide delivery candidates, but also a refined understanding of cellular delivery including novel, unpredictable mechanisms. Combined with rational design and computational algorithms, candidates can be further optimized in subsequent evolution cycles into nanocarriers with improved safety and efficacy. Optimization of nanocarriers differs for various cargos, as illustrated for plasmid DNA, siRNA, mRNA, proteins, or genome-editing nucleases.

Synthesis and Postpolymerization Modification of Fluorine-End-Labeled Poly(Pentafluorophenyl Methacrylate) Obtained via RAFT Polymerization

Chain-end-labeled polymers are interesting for a range of applications. In polymer nanomedicine, chain-end-labeled polymers are useful to study and help understand cellular internalization and intracellular trafficking processes. The recent advent of fluorescent label-free techniques, such as nanoscale secondary ion mass spectrometry (NanoSIMS), provides access to high-resolution intracellular mapping that can complement information obtained using fluorescent-labeled materials and confocal microscopy and flow cytometry. Using poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA) as a prototypical polymer nanomedicine, this paper presents a synthetic strategy to polymers that contain trace element labels, such as fluorine, which can be used for NanoSIMS analysis. The strategy presented in this paper is based on reversible addition fragmentation chain transfer (RAFT) polymerization of pentafluorophenyl methacrylate (PFMA) mediated by two novel chain-transfer agents (CTAs), which contain either one (α) or two (α,ω) fluorine labels. In the first part of this study, via a number of polymerization experiments, the polymerization properties of the fluorinated RAFT CTAs were established. 19F NMR spectroscopy revealed that these fluorinated RAFT agents possess unique spectral signatures, which allow to directly monitor RAFT agent conversion and measure end-group fidelity. Comparison with 4-cyanopentanoic acid dithiobenzoate, which is a standard CTA for the RAFT polymerization of PFMA, revealed that the introduction of one or two fluorine labels does not significantly affect the polymerization properties of the CTA. In the last part of this paper, a proof-of-concept study is presented that demonstrates the feasibility of the fluorine-labeled poly(pentafluorophenyl methacrylate) polymers as platforms for the postpolymerization modification to generate PHPMA-based polymer nanomedicines.

A versatile synthetic platform for amphiphilic nanogels with tunable hydrophobicity

Functionalization of reactive precursor particles allows the preparation of amphiphilic nanogel libraries with tunable network hydrophobicity and comparable colloidal features.

Immunomodulatory Therapy of Inflammatory Liver Disease Using Selectin-Binding Glycopolymers

Immunotherapies have the potential to significantly advance treatment of inflammatory disease and cancer, which are in large part driven by immune cells. Selectins control the first step in immune cell adhesion and extravasation, thereby guiding leukocyte trafficking to tissue lesions. We analyzed four different highly specific selectin-binding glycopolymers, based on linear poly(2-hydroxypropyl)-methacrylamide (PHPMA) polymers. These glycopolymers contain either the tetrasaccharide sialyl-Lewis^X (SLe^X) or the individual carbohydrates fucose, galactose, and sialic acids mimicking the complex SLe^X binding motive. The glycopolymers strongly bind to primary human macrophages, without activating them, and also to primary human blood leukocytes, but poorly to fibroblasts and endothelial cells in vitro. After intravenous injection in mice, all glycopolymers accumulated in the liver without causing hepatotoxicity. The glycosylated binder most potently targeted resident hepatic macrophages (Kupffer cells) and protected mice from acute toxic liver injury in the two different experimental models, carbon tetrachloride (CCl₄) or Concanavalin A (ConA)-based hepatitis. Its sulfated counterpart, on the other hand, induced a decrease in infiltrating and resident macrophages, increased T helper cells, and aggravated immune-mediated liver injury. We demonstrate that, in the context of selectin-binding glycopolymers, minor modifications strongly impact leukocyte influx and macrophage activation, thereby ameliorating or aggravating liver inflammation depending on the underlying immunopathology. The nonsulfated random glycopolymer is a promising candidate for the treatment of inflammatory disease. The modulation of hepatic immune cells by selectin-binding glycopolymers might breach the immunosuppressive hepatic microenvironment and could improve efficacy of immunotherapies for inflammatory disease and cancer.

High-molecular-weight HPMA-based polymer drug carriers for delivery to tumor

In this work, design and synthesis of high-molecular-weight N-(2-hydroxypropyl)methacrylamide-based polymer drug delivery systems tailored for cancer therapy is summarized. Moreover, the influence of their architecture on tumor accumulation and in vivo anti-cancer efficacy is discussed. Mainly, the high-molecular-weight delivery systems, such as branched, grafted, multi-block, star-like or micellar systems, with molecular weights greater than the renal threshold are discussed and reviewed in detail.

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.

Targeting cells of the immune system: mannosylated HPMA–LMA block-copolymer micelles for targeting of dendritic cells

Background: Successful tumor immunotherapy depends on the induction of strong and sustained tumor antigen-specific immune responses by activated antigen-presenting cells (APCs) such as dendritic cells (DCs). Since nanoparticles have the potential to codeliver tumor-specific antigen and DC-stimulating adjuvant in a DC-targeting manner, we wanted to assess the suitability of mannosylated HPMA-LMA block polymers for immunotherapy. Materials & methods: Fluorescence-labeled block copolymer micelles derived from P(HPMA)-block-P(LMA) copolymers and according statistical copolymers were synthesized via RAFT polymerization, and loaded with the APC activator L18-MDP. Both types of copolymers were conjugated with D-mannose to target the mannose receptor as expressed by DCs and macrophages. The extent and specificity of micelle binding and activation of APCs was monitored using mouse spleen cells and bone marrow-derived DC (BMDC). Results: Nontargeting HPMA-LMA statistical copolymers showed strong unspecific cell binding. HPMA-LMA block copolymers bound DC only when conjugated with mannose, and in a mannose receptor-specific manner. Mannosylated HPMA-LMA block copolymers were internalized by DC. DC-targeting HPMA-LMA block copolymers mediated DC activation when loaded with L18-MDP. Conclusion: Mannosylated HPMA-LMA block copolymers are a promising candidate for the delvopment of DC-targeting nanovaccines.

Biodegradable Micellar HPMA-Based Polymer-Drug Conjugates with Betulinic Acid for Passive Tumor Targeting

Here, we present the synthesis, physicochemical, and preliminary biological characterization of micellar polymer-betulinic acid (BA) conjugates based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer carriers, enabling the controlled release of cytotoxic BA derivatives in solid tumors or tumor cells. Various HPMA copolymer conjugates differing in the structure of the spacer between the drug and the carrier were synthesized, all designed for pH-triggered drug release in tumor tissue or tumor cells. The high molecular weight of the micellar conjugates should improve the uptake of the drug in solid tumors due to the Enhanced permeability and retention (EPR) effect. Nevertheless, only the conjugate containing BA with methylated carboxyl groups enabled pH-dependent controlled release in vitro. Moreover, drug release led to the disassembly of the micellar structure, which facilitated elimination of the water-soluble HPMA copolymer carrier from the body by renal filtration. The methylated BA derivative and its polymer conjugate exhibited high cytostatic activity against DLD-1, HT-29, and HeLa carcinoma cell lines and enhanced tumor accumulation in HT-29 xenograft in mice.

HPMA-based block copolymers promote differential drug delivery kinetics for hydrophobic and amphiphilic molecules

We describe a method how polymeric nanoparticles stabilized with (2-hydroxypropyl)methacrylamide (HPMA)-based block copolymers are used as drug delivery systems for a fast release of hydrophobic and a controlled release of an amphiphilic molecule. The versatile method of the miniemulsion solvent-evaporation technique was used to prepare polystyrene (PS) as well as poly-d/l-lactide (PDLLA) nanoparticles. Covalently bound or physically adsorbed fluorescent dyes labeled the particles' core and their block copolymer corona. Confocal laser scanning microscopy (CLSM) in combination with flow cytometry measurements were applied to demonstrate the burst release of a fluorescent hydrophobic drug model without the necessity of nanoparticle uptake. In addition, CLSM studies and quantitative calculations using the image processing program Volocity® show the intracellular detachment of the amphiphilic block copolymer from the particles' core after uptake. Our findings offer the possibility to combine the advantages of a fast release for hydrophobic and a controlled release for an amphiphilic molecule therefore pointing to the possibility to a 'multi-step and multi-site' targeting by one nanocarrier.

STATEMENT OF SIGNIFICANCE

We describe thoroughly how different components of a nanocarrier end up in cells. This enables different cargos of a nanocarrier having a consecutive release and delivery of distinct components. Most interestingly we demonstrate individual kinetics of distinct components of such a system: first the release of a fluorescent hydrophobic drug model at contact with the cell membrane without the necessity of nanoparticle uptake. Secondly, the intracellular detachment of the amphiphilic block copolymer from the particles' core after uptake occurs. This offers the possibility to combine the advantages of a fast release for a hydrophobic substance at the time of interaction of the nanoparticle with the cell surface and a controlled release for an amphiphilic molecule later on therefore pointing to the possibility to a 'multi-step and multisite' targeting by one nanocarrier. We therefore feel that this could be used for many cellular systems where the combined and orchestrated delivery of components is prerequisite in order to obtain the highest efficiency.

Synthesis of cyclic peptide disulfide–PHPMA conjugates via sequential active ester aminolysis and CuAAC coupling

A synthetic strategy for the preparation of cyclic peptide disulfide–polymer conjugates that does not require peptide protecting groups is reported.

Multiple strategies to produce lipophilic nanoparticles leaving water-soluble poly(HPMA)

N-(2-Hydroxypropyl) methacrylamide (HPMA) is used to produce water-soluble polymers with non-immumogenic properties that can be used in drug delivery applications.

Mammalian cell growth on gold nanoparticle-decorated substrates is influenced by the nanoparticle coating

In this work, we study epithelial cell growth on substrates decorated with gold nanorods that are functionalized either with a positively charged cytotoxic surfactant or with a biocompatible polymer exhibiting one of two different end groups, resulting in a neutral or negative surface charge of the particle. Upon observation of cell growth for three days by live cell imaging using optical dark field microscopy, it was found that all particles supported cell adhesion while no directed cell migration and no significant particle internalization occurred. Concerning cell adhesion and spreading as compared to cell growth on bare substrates after 3 days of incubation, a reduction by 45% and 95%, respectively, for the surfactant particle coating was observed, whereas the amino-terminated polymer induced a reduction by 30% and 40%, respectively, which is absent for the carboxy-terminated polymer. Furthermore, interface-sensitive impedance spectroscopy (electric cell-substrate impedance sensing, ECIS) was employed in order to investigate the micromotility of cells added to substrates decorated with various amounts of surfactant-coated particles. A surface density of 65 particles/µm(2) (which corresponds to 0.5% of surface coverage with nanoparticles) diminishes micromotion by 25% as compared to bare substrates after 35 hours of incubation. We conclude that the surface coating of the gold nanorods, which were applied to the basolateral side of the cells, has a recognizable influence on the growth behavior and thus the coating should be carefully selected for biomedical applications of nanoparticles.

Effects of cholesterol incorporation on the physicochemical, colloidal, and biological characteristics of pH-sensitive AB₂ miktoarm polymer-based polymersomes

In our previous study, a histidine-based AB2 miktoarm polymer, methoxy poly(ethylene glycol)-b-poly(l-histidine)2 (mPEG-b-(PolyHis)2), was designed to construct pH-sensitive polymersomes that transform in acidic pH; the polymer self-assembles into a structure that mimics phospholipids. In this study, the polymersomes further imitated liposomes due to the incorporation of cholesterol (CL). The hydrodynamic radii of the polymersomes increased with increasing CLwt% (e.g., 70 nm for 0 wt% vs. 91 nm for 1 wt%), resulting in an increased capacity for encapsulating hydrophilic drugs (e.g., 0.92 μL/mg for 0 wt% vs. 1.42 μL/mg for 1 wt%). The CL incorporation enhanced the colloidal stability of the polymersomes in the presence of serum protein and retarded their payload release. However, CL-incorporating polymersomes still demonstrated accelerated release of a hydrophilic dye (e.g., 5(6)-carboxyfluorescein (CF)) below pH 6.8 without losing their desirable pH sensitivity. CF-loaded CL-incorporating polymersomes showed better cellular internalization than the hydrophilic CF, whereas doxorubicin (DOX)-loaded CL-incorporating polymersomes presented similar or somewhat lower anti-tumor effects than free hydrophobic DOX. The findings suggest that CL-incorporating mPEG-b-(PolyHis)2-based polymersomes may have potential for intracellular drug delivery of chemical drugs due to their improved colloidal stability, lower drug loss during circulation, acidic pH-induced drug release, and endosomal disruption.

Selective Postmodification of Copolymer Backbones Bearing Different Activated Esters with Disparate Reactivities

In this communication, we report an easy method for introducing functional groups into polymer structures by successively reacting two different activated ester functionalities (pentafluorophenyl (PFP) ester and azlactone (AZ)) with different functional amine compounds. By exploiting the difference in reactivity of the two activated esters (PFP and AZ) toward different amino compounds, we demonstrate, for the first time, a selective modification of the different activated ester groups, thereby introducing functional groups to the polymer backbone in a controlled manner. Statistical and block copolymers of vinyl dimethyl azlactone (VDM) and pentafluorophenyl acrylate (PFPA), i.e.,(p(VDM-stat-PFPA)) and (p(VDM-block-PFPA)), were prepared using reversible addition-fragmentation transfer (RAFT) polymerization and subsequently modified using a library of amino compounds, yielding macromolecules with bespoke functionality. In additional work, the functional macromolecules were self-assembled into nanoparticles.

Water-soluble polymers coupled with glycopeptide antigens and T-cell epitopes as potential antitumor vaccines

Highly decorated: Tumor-associated MUC1 glycopeptide and tetanus toxoid T-cell epitope P2 can be attached to water-soluble poly(N-(2-hydroxypropyl)methacrylamide) carriers by orthogonal ligation techniques. Fully synthetic vaccine A with additional nanostructure-promoting domains induced antibodies that exhibit high affinity to tumor cells.

PEGylation of HPMA-based block copolymers enhances tumor accumulation in vivo: a quantitative study using radiolabeling and positron emission tomography

This paper reports the body distribution of block copolymers (made by controlled radical polymerization) with N-(2-hydroxypropyl)methacrylamide (HPMA) as hydrophilic block and lauryl methacrylate (LMA) as hydrophobic block. They form micellar aggregates in aqueous solution. For this study the hydrophilic/hydrophobic balance was varied by incorporation of differing amounts of poly(ethylene glycol) (PEG) side chains into the hydrophilic block, while keeping the degree of polymerization of both blocks constant. PEGylation reduced the size of the micellar aggregates (Rh=113 to 38 nm) and led to a minimum size of 7% PEG side chains. Polymers were labeled with the positron emitter (18)F, which enables to monitor their biodistribution pattern for up to 4h with high spatial resolution. These block copolymers were investigated in Sprague-Dawley rats bearing the Walker 256 mammary carcinoma in vivo. Organ/tumor uptake was quantified by ex vivo biodistribution as well as small animal positron emission tomography (PET). All polymers showed renal clearance with time. Their uptake in liver and spleen decreased with size of the aggregates. This made PEGylated polymers--which form smaller aggregates--attractive as they show a higher blood pool concentration. Within the studied polymers, the block copolymer of 7% PEGylation exhibited the most favorable organ distribution pattern, showing highest blood-circulation level as well as lowest hepatic and splenic uptake. Most remarkably, the in vivo results revealed a continuous increase in tumor accumulation with PEGylation (independent of the blood pool concentration)--starting from lowest tumor uptake for the pure block copolymer to highest enrichment with 11% PEG side chains. These findings emphasize the need for reliable (non-invasive) in vivo techniques revealing overall polymer distribution and helping to identify drug carrier systems for efficient therapy.

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.