Effect of Chain-End Chemistries on the Efficiency of Coupling Antibodies to Polymers Using Unnatural Amino Acids

Novel conjugates that incorporate strategies for increasing the therapeutic payload, such as targeted polymeric delivery vehicles, have great potential in overcoming limitations of conventional antibody therapies that often exhibit immunogenicity and limited drug loading. Click chemistry has significantly expanded the toolbox of effective strategies for developing hybrid polymer-biomolecule conjugates, however, effective systems require orthogonality between the polymer and biomolecule chemistries to achieve efficient coupling. Here, three cycloaddition-based strategies for antibody conjugation to polymeric carriers are explored and show that a purely radical-based method for polymer synthesis and subsequent biomolecule attachment has a trade-off between coupling efficiency of the antibody and the ability to synthesize polymers with controlled chemical properties. It is shown that careful consideration of both coupling chemistries as well as the potential effect of how this modulates the chemical properties of the polymer nanocarrier should be considered during the development of such systems. The strategies described offer insight into improving conjugate development for therapeutic and theranostic applications. In this system, polymerization using conventional and established reversible addition fragmentation chain transfer (RAFT) agents, followed by multiple post-modification steps, always leads to systems with more defined chemical architectures compared to strategies that utilize alkyne-functional RAFT agents.

Understanding the Uptake of Nanomedicines at Different Stages of Brain Cancer Using a Modular Nanocarrier Platform and Precision Bispecific Antibodies

Increasing accumulation and retention of nanomedicines within tumor tissue is a significant challenge, particularly in the case of brain tumors where access to the tumor through the vasculature is restricted by the blood-brain barrier (BBB). This makes the application of nanomedicines in neuro-oncology often considered unfeasible, with efficacy limited to regions of significant disease progression and compromised BBB. However, little is understood about how the evolving tumor-brain physiology during disease progression affects the permeability and retention of designer nanomedicines. We report here the development of a modular nanomedicine platform that, when used in conjunction with a unique model of how tumorigenesis affects BBB integrity, allows investigation of how nanomaterial properties affect uptake and retention in brain tissue. By combining different in vivo longitudinal imaging techniques (including positron emission tomography and magnetic resonance imaging), we have evaluated the retention of nanomedicines with predefined physicochemical properties (size and surface functionality) and established a relationship between structure and tissue accumulation as a function of a new parameter that measures BBB leakiness; this offers significant advancements in our ability to relate tumor accumulation of nanomedicines to more physiologically relevant parameters. Our data show that accumulation of nanomedicines in brain tumor tissue is better correlated with the leakiness of the BBB than actual tumor volume. This was evaluated by establishing brain tumors using a spontaneous and endogenously derived glioblastoma model providing a unique opportunity to assess these parameters individually and compare the results across multiple mice. We also quantitatively demonstrate that smaller nanomedicines (20 nm) can indeed cross the BBB and accumulate in tumors at earlier stages of the disease than larger analogues, therefore opening the possibility of developing patient-specific nanoparticle treatment interventions in earlier stages of the disease. Importantly, these results provide a more predictive approach for designing efficacious personalized nanomedicines based on a particular patient's condition.

Targeted and modular architectural polymers employing bioorthogonal chemistry for quantitative therapeutic delivery

There remain several key challenges to existing therapeutic systems for cancer therapy, such as quantitatively determining the true, tissue-specific drug release profile in vivo, as well as reducing side-effects for an increased standard of care. Hence, it is crucial to engineer new materials that allow for a better understanding of the in vivo pharmacokinetic/pharmacodynamic behaviours of therapeutics. We have expanded on recent “click-to-release” bioorthogonal pro-drug activation of antibody-drug conjugates (ADCs) to develop a modular and controlled theranostic system for quantitatively assessing site-specific drug activation and deposition from a nanocarrier molecule, by employing defined chemistries. The exploitation of quantitative imaging using positron emission tomography (PET) together with pre-targeted bioorthogonal chemistries in our system provided an effective means to assess in real-time the exact amount of active drug administered at precise sites in the animal; our methodology introduces flexibility in both the targeting and therapeutic components that is specific to nanomedicines and offers unique advantages over other technologies. In this approach, the in vivo click reaction facilitates pro-drug activation as well as provides a quantitative means to investigate the dynamic behaviour of the therapeutic agent.

There remain several key challenges to existing therapeutic systems for cancer therapy, such as quantitatively determining the true, tissue-specific drug release profile in vivo, as well as reducing side-effects for an increased standard of care.

Effects of Surface Charge of Hyperbranched Polymers on Cytotoxicity, Dynamic Cellular Uptake and Localization, Hemotoxicity, and Pharmacokinetics in Mice

Nanoscaled polymeric materials are increasingly being investigated as pharmaceutical products, drug/gene delivery vectors, or health-monitoring devices. Surface charge is one of the dominant parameters that regulates nanomaterial behavior in vivo. In this paper, we demonstrated how control over chemical synthesis allowed manipulation of nanoparticle surface charge, which in turn greatly influenced the in vivo behavior. Three methacrylate/methacrylamide-based monomers were used to synthesize well-defined hyperbranched polymers (HBP) by reversible addition-fragmentation chain transfer (RAFT) polymerization. Each HBP had a hydrodynamic diameter of approximately 5 nm as determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Incorporation of a fluorescent moiety within the polymeric nanoparticles allowed determination of how charge affected the in vivo pharmacokinetic behavior of the nanomaterials and the biological response to them. A direct correlation between surface charge, cellular uptake, and cytotoxicity was observed, with cationic HBPs exhibiting higher cellular uptake and cytotoxicity than their neutral and anionic counterparts. Evaluation of the distribution of the differently charged HBPs within macrophages showed that all HBPs accumulated in the cytoplasm, but cationic HBPs also trafficked to, and accumulated within, the nucleus. Although cationic HBPs caused slight hemolysis, this was generally below accepted levels for in vivo safety. Analysis of pharmacokinetic behavior showed that cationic and anionic HBPs had short blood half-lives of 1.82 ± 0.51 and 2.34 ± 0.93 h respectively, compared with 5.99 ± 2.30 h for neutral HBPs. This was attributed to the fact that positively charged surfaces are more readily covered with opsonin proteins and thus more visible to phagocytic cells. This was supported by in vitro flow cytometric and qualitative live cell imaging studies, which showed that cationic HBPs tended to be taken up by macrophages more effectively and rapidly than neutral and anionic particles.

Stability of Trithiocarbonate RAFT Agents Containing Both a Cyano and a Carboxylic Acid Functional Group

The hydrolytic degradation of widely used cyano-containing, acid-bearing trithiocarbonate reversible addition-fragmentation chain-transfer (RAFT) agents has been identified and shown to effect the RAFT polymerization and end-group fidelity of PMMA polymers. The hydrolysis occurred when the RAFT agents were stored under the recommended conditions. Degradation was identified in both commercially available and popular synthetic RAFT agents. ¹H and ¹³C NMR as well as mass spectroscopy show that the cyano functionality hydrolyzes to the amide adduct. Doping of this amide degradation product into RAFT polymerizations of MMA results in increased dispersities and changes in expected end-group fidelities. The ability to identify this degradation product and remove it from the RAFT agent before use will allow better control over polymer properties and postmodification processes commonly used in complex polymer systems, nanomedicines, and bioconjugates.

Overcoming Instability of Antibody-Nanomaterial Conjugates: Next Generation Targeted Nanomedicines Using Bispecific Antibodies

Targeted nanomaterials promise improved therapeutic efficacy, however their application in nanomedicine is limited due to complexities associated with protein conjugations to synthetic nanocarriers. A facile method to generate actively targeted nanomaterials is developed and exemplified using polyethylene glycol (PEG)-functional nanostructures coupled to a bispecific antibody (BsAb) with dual specificity for methoxy PEG (mPEG) epitopes and cancer targets such as epidermal growth factor receptor (EGFR). The EGFR-mPEG BsAb binds with high affinity to recombinant EGFR (KD : 1 × 10(-9) m) and hyperbranched polymer (HBP) consisting of mPEG (KD : 10 × 10(-9) m) and demonstrates higher avidity for HBP compared to linear mPEG. The binding of BsAb-HBP bioconjugate to EGFR on MDA-MB-468 cancer cells is investigated in vitro using a fluorescently labeled polymer, and in in vivo xenograft models by small animal optical imaging. The antibody-targeted nanostructures show improved accumulation in tumor cells compared to non-targeted nanomaterials. This demonstrates a facile approach for tuning targeting ligand density on nanomaterials, by modulating surface functionality. Antibody fragments are tethered to the nanomaterial through simple mixing prior to administration to animals, overcoming the extensive procedures encountered for developing targeted nanomedicines.

Reversible activation of pH-sensitive cell penetrating peptides attached to gold surfaces

pH-sensitive viral fusion protein mimics are widely touted as a promising route towards site-specific delivery of therapeutic compounds across lipid membranes. Here, we demonstrate that a fusion protein mimic, designed to achieve a reversible, pH-driven helix-coil transition mechanism, retains its functionality when covalently bound to a surface.

The in vivo fate of nanoparticles and nanoparticle-loaded microcapsules after oral administration in mice: Evaluation of their potential for colon-specific delivery

Anti-cancer drug loaded-nanoparticles (NPs) or encapsulation of NPs in colon-targeted delivery systems shows potential for increasing the local drug concentration in the colon leading to improved treatment of colorectal cancer. To investigate the potential of the NP-based strategies for colon-specific delivery, two formulations, free Eudragit® NPs and enteric-coated NP-loaded chitosan-hypromellose microcapsules (MCs) were fluorescently-labelled and their tissue distribution in mice after oral administration was monitored by multispectral small animal imaging. The free NPs showed a shorter transit time throughout the mouse digestive tract than the MCs, with extensive excretion of NPs in faeces at 5h. Conversely, the MCs showed complete NP release in the lower region of the mouse small intestine at 8h post-administration. Overall, the encapsulation of NPs in MCs resulted in a higher colonic NP intensity from 8h to 24h post-administration compared to the free NPs, due to a NP 'guarding' effect of MCs during their transit along mouse gastrointestinal tract which decreased NP excretion in faeces. These imaging data revealed that this widely-utilised colon-targeting MC formulation lacked site-precision for releasing its NP load in the colon, but the increased residence time of the NPs in the lower gastrointestinal tract suggests that it is still useful for localised release of chemotherapeutics, compared to NP administration alone. In addition, both formulations resided in the stomach of mice at considerable concentrations over 24h. Thus, adhesion of NP- or MC-based oral delivery systems to gastric mucosa may be problematic for colon-specific delivery of the cargo to the colon and should be carefully investigated for a full evaluation of particulate delivery systems.

Utilising polymers to understand diseases: advanced molecular imaging agents

This review describes how the highly tuneable size, shape and chemical functionality of polymeric molecular imaging agents provides a means to intimately probe the various mechanisms behind disease formation and behaviour.

Enzyme cleavable nanoparticles from peptide based triblock copolymers

A solid-phase synthesis based approach towards protease cleavable polystyrene-peptide-polystyrene triblock copolymers and their formulation to nanoparticulate systems is presented. These nanoparticles are suitable for the optical detection of an enzyme and have the potential for application as a drug delivery system. Two different peptide sequences, one cleaved by trypsin (GFF), the other by hepsin (RQLRVVGG), a protease overexpressed in early stages of prostate cancer, are used as the central part of the triblock. For optical detection a fluorophore-quencher pair is introduced around the cleavage sequence. The solid phase synthesis is conduced such that two identical sequences are synthesized from one branching point. Eventually, carboxy-terminated polystyrene is introduced into the peptide synthesizer and coupled to the amino-termini of the branched sequence. Upon cleavage, a fragment is released from the triblock copolymer, which has the potential for use in drug delivery applications. Conducting the whole synthesis on a solid phase in the peptide synthesizer avoids solubility issues and post-synthetic purification steps. Due to the hydrophobic PS-chains, the copolymer can easily be formulated to form nanoparticles using a nanoprecipitation process. Incubation of the nanoparticles with the respective enzymes leads to a significant increase of the fluorescence from the incorporated fluorophore, thereby indicating cleavage of the peptide sequence and decomposition of the particles.

Biomimetic silver-containing colloids of poly(2-methacryloyloxyethyl phosphorylcholine) and their film-formation properties

The synthesis of stable dispersions of hybrid colloids comprising copolymers of biocompatible 2-hydroxyethyl methacrylate (HEMA) and zwitterionic, biomimetic 2-methacryloyloxyethyl phosphorylcholine (MPC) incorporating antibacterial AgBF(4) by inverse miniemulsion is described. The prepared hybrid colloids were designed to provide both antibacterial and antifouling properties for the formation of interesting, multifunctional films. The obtained particles had sizes in the range of 130-160 nm with two different weight ratios of MPC to HEMA (1:10 and 2:5) and AgBF(4) contents between 0% and 15%. The silver salt takes on the role of the lipophobe in stabilizing the miniemulsion droplets against Ostwald ripening and is reduced after polymerization to Ag nanoparticles by gaseous hydrazine. Subsequently, the hybrid particles are transformed into smooth and stable films with thicknesses between 145 and 225 nm by simple drop casting and solvent annealing. The dispersions and films were thoroughly characterized by DLS, TEM, SEM, EDX, TGA, UV-vis spectroscopy, ICP-OES, XRD, AFM, and contact angle measurements. After immersion into water, the films did not show detectable leakage of silver, so they could be employed as dual-functional antifouling and antibacterial coatings.

Two-Dimensional Crystal Growth and Stacking of Bis(phthalocyaninato) Rare Earth Sandwich Complexes at the 1-Phenyloctane/Graphite Interface

Initial stages of two-dimensional crystal growth of the double-decker sandwich complex Lu(Pc*)2 [Pc* = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] have been studied by scanning tunneling microscopy at the liquid/solid interface between 1-phenyloctane and highly oriented pyrolytic graphite. High-resolution images strongly suggest alignment of the double-decker molecules into monolayers with the phthalocyanine rings parallel to the surface. Domains were observed with either hexagonal or quadrate packing motifs, and the growing interface of the layer was imaged. Molecular resolution was achieved, and the face of the phthalocyanine rings appeared as somewhat diffuse circular features. The alkyl chains are proposed to be interdigitating to maintain planar side-by-side packing.

[Cytomegalovirus (CMV) retinitis in AIDS. Gancilovir implantation in comparison with systemic therapy]

INTRODUCTION

Untreated CMV retinitis with AIDS leads to blindness; therefore, a life-long virostatic treatment is required. It can either be administered systemically or locally, as there are different advantages and disadvantages. When treating patients we aim at therapy that preserves vision without diminishing quality of life. It should induce as few drug-induced side effects as possible and not shorten the patient's life expectation.

METHODS AND RESULTS

A total of 111 patients (150 eyes) with systemic maintenance treatment were compared retrospectively with 33 patients (62 eyes) that received a ganciclovir implant only as maintainance therapy and no additional systemic treatment. Patients with an implant showed a prolonged interval of nonprogression of retinitis than patients receiving systemic treatment. Patients with unilateral retinitis are at higher risk of developing bilateral disease in the implant group than in the systemically treated group. Manifestation of extraocular disease was equal in both groups. Local treatment with the implant does not shorten patient survival time.

CONCLUSION

Local treatment with the ganciclovir implant means quality of life for patients and also safe protection of the affected eye. Extraocular disease and survival time are not influenced adversely by local treatment. However, primarily unilateral involved patients show higher risk for bilateral disease in the implant group than in the systemically treated group.

[Local therapy in treatment of cytomegalovirus (CMV) retinitis in AIDS. The ganciclovir implant (pellet)]

BACKGROUND

Cytomegalovirus (CMV) retinitis with AIDS has been treated either systemically or locally by weekly intravitreous injections. An intraocular device now offers a new therapeutic approach. We investigated its efficacy in preventing progression of CMV retinitis without additional systemic therapy. Conversely, we also studied the risks and disadvantages of this method of drug administration.

PATIENTS AND METHODS

In our study 46 devices were implanted in 28 patients. All patients were pretreated with systemic medication. Systemic treatment was stopped on the day of surgery.

RESULTS

Severe perioperative complications occurred in one patient, who developed retinal detachment after surgery. Most patients showed no relapse of retinitis with the implant, though they did not receive systemic treatment for 8.1 months on average. Only 20% of our patients presented with extraocular CMV disease. Thirty-five percent (n = 17) of patients with unilateral retinitis developed CMV retinitis in the primary uninvolved fellow eye. After implantation of a device into this eye also progression could be stopped without additional systemic treatment. Two patients showed progression of retinitis due to an empty ganciclovir reservoir. A second device was implanted without removal of the first.

CONCLUSIONS

The intraocular ganciclovir device appears to be an effective treatment for CMV retinitis with few disadvantages. Time to progression of retinitis tends to be prolonged compared to systemic treatment.