RAFT-Derived Polymer-Drug Conjugates: Poly(hydroxypropyl methacrylamide) (HPMA)-7-Ethyl-10-hydroxycamptothecin (SN-38) Conjugates

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.

Efficient Self-Immolative RAFT End Group Modification for Macromolecular Immunodrug Delivery

The reversible addition-fragmentation chain-transfer (RAFT) polymerization provides access to a broad variety of biocompatible and functional macromolecules for diverse polymer-drug conjugates. Due to thiocarbonylthio groups at the ends of each growing polymer chain, they can straightforwardly be converted into disufilde-containing self-immolative motives for reversible drug conjugation by traceless linkers. This may be relevant for RAFT-polymerized poly(N,N-dimethylacrylamide) (pDMA), which has been demonstrated to provide similar properties as poly(ethylene glycol) (PEG) in terms of improving the drug's poor pharmacokinetic profile or enhancing its bioavailability. For that purpose, we established a highly efficient one-pot reaction procedure for introducing various functionalities including both primary and secondary amines and primary alcohols and demonstrated their reversible conjugation and traceless release from pDMA's polymer chain end. Next, a first polymer-drug conjugate with a Toll-like receptor agonist exhibited significantly increased activity in vitro compared to conventional irreversibly covalently fixed variants. Finally, α-ω-bifunctional dye or drug conjugates could be generated by a cholesterol-modified RAFT chain-transfer agent. It facilitated the polymer-drug conjugate's internalization at the cellular level monitored by flow cytometry and confocal imaging. This approach provides the basis for a variety of potentially impactful polymer-drug conjugates by combining versatile small molecular drugs with a plethora of available RAFT polymers through reductive-responsive self-immolative linkers.

Synthesis of a SN38 prodrug grafted to amphiphilic phosphorylcholine polymers and their prodrug miceller properties

Polymer prodrug micelles, combining the advantages of prodrugs and polymer micelles, can greatly improve the solubility, permeability and stability of drugs.

Degradable polymer prodrugs with adjustable activity from drug-initiated radical ring-opening copolymerization

Degradable polymer prodrugs based on gemcitabine (Gem) as an anticancer drug were synthesized by 'drug-initiated' nitroxide-mediated radical ring-opening copolymerization (NMrROP) of methacrylic esters and 2-methylene-4-phenyl-1,3-dioxolane (MPDL). Different structural parameters were varied to determine the best biological performances: the nature of the monomer [i.e., oligo(ethylene glycol) methacrylate (OEGMA) or methyl methacrylate (MMA)], the nature of the Gem-polymer linker (i.e., amide or amide and diglycolate) and the MPDL content in the copolymer. Depending on the nature of the methacrylate monomer, two small libraries of water-soluble copolymer prodrugs and nanoparticles were obtained (M n ∼10 000 g mol-1, Đ = 1.1-1.5), which exhibited tunable hydrolytic degradation under accelerated conditions governed by the MPDL content. Drug-release profiles in human serum and in vitro anticancer activity on different cell lines enabled preliminary structure-activity relationships to be established. The cytotoxicity was independently governed by: (i) the MPDL content - the lower the MPDL content, the greater the cytotoxicity; (ii) the nature of the linker - the presence of a labile diglycolate linker enabled a greater Gem release compared to a simple amide bond and (iii) the hydrophilicity of the methacrylate monomer-OEGMA enabled a greater anticancer activity to be obtained compared to MMA-based polymer prodrugs. Remarkably, the optimal structural parameters enabled reaching the cytotoxic activity of the parent (free) drug.

Fully synthetic macromolecular prodrug chemotherapeutics with EGFR targeting and controlled camptothecin release kinetics

Herein, we developed a fully polymerizable, peptide-targeted, camptothecin polymeric prodrug system. Two prodrug monomers were synthesized via esterification of campothecin (20Cam) and 10-hydroxycamptothecin (10Cam) with mono-2-(methacryloyloxy)ethyl succinate (SMA) resulting in polymerizable forms of the aliphatic ester- and aromatic ester-linked drugs respectively. These monomers were then incorporated into zwitterionic polymers via RAFT copolymerization of the prodrug monomers with a tert-butyl ester protected carboxy betaine monomer. Subsequent deprotection of the tert-butyl residues with TFA yielded carboxy betaine methacrylate (CBM) scaffolds with controlled prodrug incorporation. Reverse phase HPLC was then employed to establish drug release kinetics in human serum at 37 ^oC for the resultant polymeric prodrugs. Copolymers containing 10Cam residues linked via aromatic esters showed faster hydrolysis rates with 59 % drug released at 7 days, while copolymers with Cam residues linked via aliphatic esters showed only 28 % drug release over the same time period. These differences in drug release kinetics were then shown to correlate with large differences in cytotoxic activity in SKOV3 ovarian cancer cell cultures. At 72 hours, the IC50s of aromatic- and aliphatic- ester linked prodrugs were 56 nM and 4776 nM, respectively. An EGFR-targeting peptide sequence, GE11, was then directly incorporated into the polymeric prodrugs via RAFT copolymerization of the polymeric prodrugs with a peptide macronomer. The GE11-targeted polymeric prodrugs showed enhanced targeting and cytotoxic activity in SKOV3 cell cultures relative to untargeted polymers containing the negative control sequence HW12. Following pulse-chase treatment (15 min, 37 °C), the 72 hour IC50 of GE11 targeted prodrug was determined to be 1597 nM, in contrast to 3399 nM for the non-targeted control.

RAFT polymer cross-coupling with boronic acids

The ability to modify the thiocarbonylthio end-groups of RAFT polymers is important for applications where an inert or highly functionalised material is required. Here we report a copper promoted cross-coupling reaction between RAFT polymer end-groups and aryl boronic acids. This method gives high conversion to the modified polymers, and is compatible with a wide variety of functional molecules.

SN38-loaded <100 nm targeted liposomes for improving poor solubility and minimizing burst release and toxicity: in vitro and in vivo study

Background

SN38 (7-ethyl-10-hydroxycamptothecin) is a camptothecin derivative acts against various tumors. However, SN38 is hydrolyzed in the physiological environment (pH 7.4), and this instability interferes with its potential therapeutic effect. Our objective was to investigate SN38-loaded liposomes to overcome the poor solubility of SN38 and its biodistribution, which further diminish its toxicity.

Materials and methods

The sub-100 nm targeted liposomes was employed to deliver SN-38 and evaluate the characterization, release behaviors, cytotoxicity, in vivo pharmacokinetics and biochemical assay.

Results

The SN38-loaded targeted liposomes consisted of small (100.49 nm) spherical nanoparticles with negative charge (−37.93 mV) and high entrapment efficiency (92.47%). The release behavior of the SN38-loaded targeted liposomes was fitted with Higuchi kinetics (R²=0.9860). Free SN38 presented initial burst release. The IC₅₀ for the SN38-loaded targeted liposomes (0.11 μM) was significantly lower than for the SN38 solution (0.37 μM) in the MCF7 cell line (P<0.01). Confocal laser scanning microscopy also confirmed highly efficient accumulation in the MCF7 cells. Pharmacokinetics demonstrated that the SN38-loaded targeted liposomes had a slightly increased half-life and mean residence time and decreased area under the concentration–time curve and maximum concentration. The results suggested that retention was achieved while the exposure of SN38 was significantly decreased. A noninvasive in vivo imaging system also showed that the targeted liposomes selectively targeted MCF7 tumors. In vivo toxicity data demonstrated that the decrease in platelets was significantly improved by SN38-loaded targeted liposomes, and diarrhea was not observed in BALB/c mice.

Conclusion

In summary, SN38-loaded targeted liposomes could be a good candidate for application in human breast cancer.

Designing Smart Polymer Conjugates for Controlled Release of Payloads

Incorporating labile bonds inside polymer backbone and side chains yields interesting polymer materials that are responsive to change of environmental stimuli. Drugs can be conjugated to various polymers through different conjugation linkages and spacers. One of the key factors influencing the release profile of conjugated drugs is the hydrolytic stability of the conjugated linkage. Generally, the hydrolysis of acid-labile linkages, including acetal, imine, hydrazone, and to some extent β-thiopropionate, are relatively fast and the conjugated drug can be completely released in the range of several hours to a few days. The cleavage of ester linkages are usually slow, which is beneficial for continuous and prolonged release. Another key structural factor is the water solubility of polymer-drug conjugates. Generally, the release rate from highly water-soluble prodrugs is fast. In prodrugs with large hydrophobic segments, the hydrophobic drugs are usually located in the hydrophobic core of micelles and nanoparticles, which limits the access to the water, hence lowering significantly the hydrolysis rate. Finally, self-immolative polymers are also an intriguing new class of materials. New synthetic pathways are needed to overcome the fact that much of the small molecules produced upon degradation are not active molecules useful for biomedical applications.

[Polymer nanoparticles for the delivery of anticancer drug]

Nanocarriers based on polymers are currently attracting much attention to perform efficient drug delivery, especially in cancer therapy. Over the last decades, different kinds of polymer nanoparticulate systems have been developed (e.g., simple, stealth, targeted, stimuli-responsive and prodrug) to propose novel, better and safer cancer therapies. This article will give a brief overview of the different classes of polymer nanoparticles that have been reported and discuss some key achievements deriving from their use in the field of cancer therapy.

Camptothecin-based nanodrug delivery systems

The drug camptothecin has a wide range of antitumor effects in cancers including gastric cancer, rectal and colon cancer, liver cancer, and lung cancer. Camptothecin-based drugs inhibit topoisomerase 1 (Topo 1), leading to destruction of DNA, and are currently being used as important chemotherapeutic agents in clinical antitumor treatment. However, the main obstacle associated with cancer therapy is represented by systemic toxicity of conventional anticancer drugs and their low accumulation at the tumor site. In addition, low bioavailability, poor water solubility, and other shortcomings hinder their anticancer activity. Different from traditional pharmaceutical preparations, nanotechnology-dependent nanopharmaceutical preparations have become one of the main strategies for different countries worldwide to overcome drug development problems. In this review, we summarized the current hotspots and discussed a variety of camptothecin-based nanodrugs for cancer therapy. We hope that through this review, more efficient drug delivery systems could be designed with potential applications in clinical cancer therapy.

Advances in oral delivery of anti-cancer prodrugs

INTRODUCTION

Most anticancer drugs have poor aqueous solubility and low permeability across the gastrointestinal tract. Furthermore, extensive efflux by P-glycoproteins (P-gp) in the small intestine also limits the efficient delivery of anticancer drugs via oral route. Area covered: This review explores the prodrug strategy for oral delivery of anticancer drugs. Different categories of oral anticancer prodrugs along with recent clinical studies have been comprehensively reviewed here. Furthermore, novel anticancer prodrugs such as polymer-prodrugs and lipid-prodrugs have been discussed in detail. Finally, various nanocarrier-based approaches employed for oral delivery of anticancer prodrugs have also been discussed. Expert opinion: Premature degradation of anticancer prodrugs in the gastrointestinal tract could lead to variable pharmacokinetics and undesired toxicity. Despite their increased aqueous solubility, the oral bioavailability of several anticancer prodrugs are limited by their poor permeability across the gastrointestinal tract. These limitations can be overcome by the use of functional excipients (polymers, lipids, amino acids/dipeptides), which are specifically absorbed via transporters and receptor-mediated endocytosis. Oral delivery of anticancer prodrugs using nanocarrier-based drug delivery system is a recent development; however it should be justified based on the comparative advantages of encapsulating prodrug in a nanocarrier versus the use of anticancer prodrug molecule itself.

The influence of mPEG-PCL and mPEG-PLGA on encapsulation efficiency and drug-loading of SN-38 NPs

The influence of mPEG-PCL and mPEG-PLGA on encapsulation efficiency and drug-loading of nanoparticles was very important. SN-38 NPs were prepared from a series of diblock copolymers: mPEG1000-PLGA2000, mPEG2000-PCLs, mPEG5000-PCLs, mPEG2000-PLGAs, and mPEG5000-PLGAs by the thin film-hydration method. The prepared nanoparticles were characterized by morphology, size, encapsulation efficiency, drug-loading, and in vitro release behavior. This experiment suggested that the encapsulation efficiency and drug-loading of SN-38 NPs were attained the maximum values when the ratio of hydrophilic to hydrophobic block was between 1:2 and 1:3.

Drug-Initiated Synthesis of Polymer Prodrugs: Combining Simplicity and Efficacy in Drug Delivery

In the field of nanomedicine, the global trend over the past few years has been toward the design of highly sophisticated drug delivery systems with active targeting and/or imaging capabilities, as well as responsiveness to various stimuli to increase their therapeutic efficacy. However, providing sophistication generally increases complexity that could be detrimental in regards to potential pharmaceutical development. An emerging concept to design efficient yet simple drug delivery systems, termed the "drug-initiated" method, consists of growing short polymer chains from drugs in a controlled fashion to yield well-defined drug-polymer prodrugs. These materials are obtained in a reduced amount of synthetic steps and can be self-assembled into polymer prodrug nanoparticles, be incorporated into lipid nanocarriers or be used as water-soluble polymer prodrugs. This Perspective article will capture the recent achievements from the "drug-initiated" method and highlight the great biomedical potential of these materials.

Designing of Biodegradable and Biocompatible Release and Delivery Systems of Selected Antioxidants Used in Cosmetology

Conjugates of antioxidants p-anisic (p-AA) and vanillic (VA) acids with nontoxic, biocompatible, and biodegradedable oligo-(R,S)-(3-hydoxybutyrate) carrier were synthesized, and their structural and biological characterization was performed. The molecular structure of the bioconjugates, in which antioxidants are covalently bonded with oligo(3-hydroxybutyrate) (OHB) chains, has been proven by mass spectrometry supported by NMR. The bioconjugate hydrolytic degradation studies allowed gaining thorough insight into the hydrolysis process and confirmed the release of p-AA and VA. In vitro studies demonstrated that all of the conjugates studied were well tolerated by KB and HaCaT cell lines, as they had no marked cytotoxicity, while conjugates with a relatively short OHB carrier are optimal to support keratinocyte function. The preliminary study of the biological activity confirmed the protective effect of VA-OHB conjugates against H2O2-induced lipid peroxidation in human keratinocytes (HaCaT). It was also demonstrated that the selected bioconjugates can penetrate all layers of the skin, which shows their functionality and opens up their potential application in cosmetology.

Biomedical applications of polymers derived by reversible addition - fragmentation chain-transfer (RAFT)

RAFT- mediated polymerization, providing control over polymer length and architecture as well as facilitating post polymerization modification of end groups, has been applied to virtually every facet of biomedical materials research. RAFT polymers have seen particularly extensive use in drug delivery research. Facile generation of functional and telechelic polymers permits straightforward conjugation to many therapeutic compounds while synthesis of amphiphilic block copolymers via RAFT allows for the generation of self-assembled structures capable of carrying therapeutic payloads. With the large and growing body of literature employing RAFT polymers as drug delivery aids and vehicles, concern over the potential toxicity of RAFT derived polymers has been raised. While literature exploring this complication is relatively limited, the emerging consensus may be summed up in three parts: toxicity of polymers generated with dithiobenzoate RAFT agents is observed at high concentrations but not with polymers generated with trithiocarbonate RAFT agents; even for polymers generated with dithiobenzoate RAFT agents, most reported applications call for concentrations well below the toxicity threshold; and RAFT end-groups may be easily removed via any of a variety of techniques that leave the polymer with no intrinsic toxicity attributable to the mechanism of polymerization. The low toxicity of RAFT-derived polymers and the ability to remove end groups via straightforward and scalable processes make RAFT technology a valuable tool for practically any application in which a polymer of defined molecular weight and architecture is desired.

Protein corona hampers targeting potential of MUC1 aptamer functionalized SN-38 core-shell nanoparticles

Nanoparticles have been considered to improve delivery and physicochemical characteristics of bioactive agents in recent years. In this study, a core-shell chitosan nanoparticulate system was prepared for the targeted delivery of SN-38. SN-38, an active metabolite of camptothecin, conjugated to hyaluronic acid (HA) was used as the shell of chitosan nanoparticles decorated with MUC1 aptamer. The conjugation was confirmed by UV and (1)H NMR techniques. Targeting efficiency was evaluated by confocal microscopy and flow cytometry. It was shown that MUC1 decoration increased the uptake of nanoparticles by HT29 cells, MUC1 positive cell line, while CHO as MUC1 negative cell line showed no enhanced uptake of decorated nanoparticles. Compared to non-targeted nanoparticles, flow cytometric annexin V/PI analyses showed that the nanoparticles exert cytotoxicity through apoptosis. It was, however, shown that protein corona adsorption at the surface of nanoparticles hampered the cytotoxicity of nanoparticles, as there was no difference between the cytotoxicity of targeted and non-targeted nanoparticles, when treated with bovine serum albumin prior to cytotoxicity study.

MUC1 aptamer conjugated to chitosan nanoparticles, an efficient targeted carrier designed for anticancer SN38 delivery

Molecularly targeted therapy is of great interest for diagnosis and treatment of cancerous cells due to its low toxicity for normal cells. In this study, chitosan was utilized as a promising carrier for delivery, and aptamer (Apt) was employed for active targeting of SN38 to colon cancer. SN38 cannot be used clinically due to its poor solubility and high toxicity. Developing nanoparticles (NPs) of drug-polymer conjugates can be a good candidate for overcoming such problems. N-Carboxyethyl chitosan ester (CS-EA) was synthesized as an intermediate for conjugation of SN38 to chitosan. MUC1 DNA aptamer with 5'-NH2 functional group was conjugated to the self-assembled conjugate as a targeting agent. Prepared NPs had smooth and spherical morphology with 200 nm particle size. Conjugation of aptamer was confirmed by gel electrophoresis. In vitro cytotoxicity of NPs was assessed by HT-29 as MUC1 positive cell line through MTT assay. Aptamer conjugated NPs (Apt NPs) were more toxic than non-targeted NPs, however they were as toxic as free drug. Cellular uptake and targeting ability of prepared NPs were also confirmed via confocal microscopy. As a conclusion, prepared CS-SN38-Apt NPs can increase efficacy of drug SN38 through increasing solubility and specific delivery to the target tissue.

Prodrug and nanomedicine approaches for the delivery of the camptothecin analogue SN38

SN38 (7-ethyl-10-hydroxy camptothecin) is a prominent and efficacious anticancer agent. It is poorly soluble in both water and pharmaceutically approved solvents; therefore, the direct formulation of SN38 in solution form is limited. Currently, the water soluble prodrug of SN38, irinotecan (CPT-11), is formulated as a low pH solution and is approved for chemotherapy. However, CPT-11, along with most other water-soluble prodrugs shows unpredictable inter-patient conversion to SN38 in vivo, instability in the physiological environment and variable dose-related toxicities. More recently, macromolecular prodrugs (i.e. EZN-2208, IMMU-130) and nanomedicine formulations (i.e. nanoemulsions, polymeric micelles, lipid nanocapsule/nanoparticle, and liposomes) of SN38 have been investigated for improved delivery to cancer cells and tissues. Specifically, these carriers can take advantage of the EPR effect to direct drug preferentially to tumour tissues, thereby substantially improving efficacy and minimising side effects. Furthermore, oral delivery has been shown to be possible in preclinical results using nanomedicine formulations (i.e. dendrimers, lipid nanocapsules, polymeric micelles). This review summarizes the recent advances for the delivery of SN38 with a focus on macromolecular prodrugs and nanomedicines.

Advanced materials and processing for drug delivery: the past and the future

Design and synthesis of efficient drug delivery systems are of vital importance for medicine and healthcare. Materials innovation and nanotechnology have synergistically fueled the advancement of drug delivery. Innovation in material chemistry allows the generation of biodegradable, biocompatible, environment-responsive, and targeted delivery systems. Nanotechnology enables control over size, shape and multi-functionality of particulate drug delivery systems. In this review, we focus on the materials innovation and processing of drug delivery systems and how these advances have shaped the past and may influence the future of drug delivery.

Living Radical Polymerization by the RAFT Process – A Third Update

This paper provides a third update to the review of reversible deactivation radical polymerization (RDRP) achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition-fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669) and the second in December 2009 (Aust. J. Chem. 2009, 62, 1402). This review cites over 700 publications that appeared during the period mid 2009 to early 2012 covering various aspects of RAFT polymerization which include reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses, and a diverse range of applications. This period has witnessed further significant developments, particularly in the areas of novel RAFT agents, techniques for end-group transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.