Biodegradable star HPMA polymer–drug conjugates: Biodegradability, distribution and anti-tumor efficacy

Polymer-drug conjugates: Design principles, emerging synthetic strategies and clinical overview

Adagen, an enzyme replacement treatment for adenosine deaminase deficiency, was the first protein-polymer conjugate to be approved in early 1990s. Post this regulatory approval, numerous polymeric drugs and polymeric nanoparticles have entered the market as advanced or next-generation polymer-based therapeutics, while many others have currently been tested clinically. The polymer conjugation to therapeutic moiety offers several advantages, like enhanced solubilization of drug, controlled release, reduced immunogenicity, and prolonged circulation. The present review intends to highlight considerations in the design of therapeutically effective polymer-drug conjugates (PDCs), including the choice of linker chemistry. The potential synthetic strategies to formulate PDCs have been discussed along with recent advancements in the different types of PDCs, i.e., polymer-small molecular weight drug conjugates, polymer-protein conjugates, and stimuli-responsive PDCs, which are under clinical/preclinical investigation. Current impediments and regulatory hurdles hindering the clinical translation of PDC into effective therapeutic regimens for the amelioration of disease conditions have been addressed.

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

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

pH-Responsive Polymer Nanomaterials for Tumor Therapy

The complexity of the tumor microenvironment presents significant challenges to cancer therapy, while providing opportunities for targeted drug delivery. Using characteristic signals of the tumor microenvironment, various stimuli-responsive drug delivery systems can be constructed for targeted drug delivery to tumor sites. Among these, the pH is frequently utilized, owing to the pH of the tumor microenvironment being lower than that of blood and healthy tissues. pH-responsive polymer carriers can improve the efficiency of drug delivery in vivo, allow targeted drug delivery, and reduce adverse drug reactions, enabling multifunctional and personalized treatment. pH-responsive polymers have gained increasing interest due to their advantageous properties and potential for applicability in tumor therapy. In this review, recent advances in, and common applications of, pH-responsive polymer nanomaterials for drug delivery in cancer therapy are summarized, with a focus on the different types of pH-responsive polymers. Moreover, the challenges and future applications in this field are prospected.

A Review of Nanotechnology for Treating Dysfunctional Placenta

The placenta plays a significant role during pregnancy. Placental dysfunction contributes to major obstetric complications, such as fetal growth restriction and preeclampsia. Currently, there is no effective treatment for placental dysfunction in the perinatal period, and prophylaxis is often delivered too late, at which point the disease manifestation cannot be prevented. However, with recent integration of nanoscience and medicine to perform elaborate experiments on the human placenta, it is expected that novel and efficient nanotherapies will be developed to resolve the challenge of managing placental dysfunction. The advent of nanomedicine has enabled the safe and targeted delivery of drugs using nanoparticles. These smart nanoparticles can load the necessary therapeutic substances that specifically target the placenta, such as drugs, targeting molecules, and ligands. Packaging multifunctional molecules into specific delivery systems with high targeting ability, diagnosis, and treatment has emerged as a novel theragnostic (both therapeutic and diagnostic) approach. In this review, the authors discuss recent advances in nanotechnology for placental dysfunction treatment. In particular, the authors highlight potential candidate nanoparticle-loaded molecules that target the placenta to improve utero-placental blood flow, and reduce reactive oxygen species and oxidative stress. The authors intend to provide basic insight and understanding of placental dysfunction, potential delivery targets, and recent research on placenta-targeted nanoparticle delivery systems for the potential treatment of placental dysfunction. The authors hope that this review will sensitize the reader for continued exploration of novel nanomedicines.

Ginsenosides emerging as both bifunctional drugs and nanocarriers for enhanced antitumor therapies

Ginsenosides, the main components isolated from Panax ginseng, can play a therapeutic role by inducing tumor cell apoptosis and reducing proliferation, invasion, metastasis; by enhancing immune regulation; and by reversing tumor cell multidrug resistance. However, clinical applications have been limited because of ginsenosides' physical and chemical properties such as low solubility and poor stability, as well as their short half-life, easy elimination, degradation, and other pharmacokinetic properties in vivo. In recent years, developing a ginsenoside delivery system for bifunctional drugs or carriers has attracted much attention from researchers. To create a precise treatment strategy for cancer, a variety of nano delivery systems and preparation technologies based on ginsenosides have been conducted (e.g., polymer nanoparticles [NPs], liposomes, micelles, microemulsions, protein NPs, metals and inorganic NPs, biomimetic NPs). It is desirable to design a targeted delivery system to achieve antitumor efficacy that can not only cross various barriers but also can enhance immune regulation, eventually converting to a clinical application. Therefore, this review focused on the latest research about delivery systems encapsulated or modified with ginsenosides, and unification of medicines and excipients based on ginsenosides for improving drug bioavailability and targeting ability. In addition, challenges and new treatment methods were discussed to support the development of these new tumor therapeutic agents for use in clinical treatment.

Enhanced Delivery of Thermoresponsive Polymer-Based Medicine into Tumors by Using Heat Produced from Gold Nanorods Irradiated with Near-Infrared Light

Simple Summary

To establish a therapy targeting scattered tumors throughout the body, we propose a novel drug delivery system using a thermoresponsive polyoxazoline (POZ) as a drug carrier in combination with gold nanorods (GNR), which produce heat when irradiated with near-infrared (NIR) light. After the tumor was irradiated with NIR light, where GNR was accumulated in advance, the radiolabeled POZ was intravenously injected. As a result, a marked tumor uptake was achieved via self-aggregation of POZ by sensing heat yielded from the GNR. Because the POZ would be chemically modified with various anti-tumor drugs including therapeutic radionuclides, remarkable anti-tumor effects can be expected by enhancing delivery of POZ-based medicine into scattered tumors throughout the body.

Abstract

The aim of this study was to establish a drug delivery system (DDS) for marked therapy of tumors using a thermoresponsive polymer, polyoxazoline (POZ). The effectiveness of the following was investigated: (i) the delivery of gold nanorods (GNRs) to tumor tissues, (ii) heat production of GNR upon irradiation with near-infrared (NIR) light, and (iii) high accumulation of an intravenously injected radiolabeled POZ as a drug carrier in tumors by sensing heat produced by GNRs. When the GNR solution was irradiated with NIR light (808 nm), the solution temperature was increased both in a GNR-concentration-dependent manner and in a light-dose-dependent manner. POZ, with a lower critical solution temperature of 38 °C, was aggregated depending on the heat produced by the GNR irradiated by NIR light. When it was intratumorally pre-injected into colon26-tumor-bearing mice, followed by NIR light irradiation (GNR+/Light+ group), the tumor surface temperature increased to approximately 42 °C within 5 min. Fifteen minutes after irradiation with NIR light, indium-111 (¹¹¹In)-labeled POZ was intravenously injected into tumor-bearing mice, and the radioactivity distribution was evaluated. The accumulation of POZ in the tumor was significantly (approximately 4-fold) higher than that in the control groups (GNR+/without NIR light irradiation (Light–), without injection of GNR (GNR–)/Light+, and GNR–/Light– groups). Furthermore, an in vivo confocal fluorescence microscopy study, using fluorescence-labeled POZ, revealed that uptake of POZ by the tumor could be attributed to the heat produced by GNR. In conclusion, we successfully established a novel DDS in which POZ could be efficiently delivered into tumors by using the heat produced by GNR irradiated with NIR light.

Acid-responsive HPMA copolymer-bradykinin conjugate enhances tumor-targeted delivery of nanomedicine

Obstructed blood flow and erratic blood supply in the tumor region attenuate the distribution and accumulation of nanomedicines in the tumor. Therefore, improvement of these conditions is crucial for efficient drug delivery. In this study, we designed and synthesized a novel N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymer conjugate of BK, which possessed adequate systemic stability and tumor-selective action required to improve the accumulation of nanomedicines in the tumor. Levulinoyl-BK (Lev-BK) was conjugated to an HPMA-based polymer via an acid-cleavable hydrazone bond (P-BK). An acid-responsive release of Lev-BK from P-BK was observed, and P-BK alone after intradermal application showed below 10% of the BK activity, thus proving a reduction in the vascular permeability activity of BK when attached to the polymer carrier. P-BK pre-treatment improved blood flow in the tumor tissue by 1.4-1.7-fold, which was maintained for more than 4 h. In addition, P-BK pre-treatment increased the tumor accumulation of pegylated liposomal doxorubicin (PLD) by approximately 3-fold. Furthermore, P-BK pre-treatment led to superior antitumor activity of PLD and significantly improved the survival of tumor-bearing mice. The release of BK from P-BK in the acidic milieu of the tumor was a prerequisite for P-BK to exert its effect, as the vascular permeability enhancing activity of P-BK was negligible. Collectively, P-BK pre-treatment improved intratumoral blood flow and augmented tumor accumulation of nanomedicine, thereby resulting in a significant suppression of tumor growth. Therefore, these findings demonstrate that P-BK is a potential concomitant drug for improving the tumor delivery of nanomedicines.

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.

Factors affecting the dynamics and heterogeneity of the EPR effect: pathophysiological and pathoanatomic features, drug formulations and physicochemical factors

INTRODUCTION

The enhanced permeability and retention (EPR) effect serves as the foundation of anticancer nanomedicine design. EPR effect-based drug delivery is an effective strategy for most solid tumors. However, the degree of efficacy depends on the pathophysiological conditions of tumors, drug formulations, and other factors.

AREAS COVERED

Vascular mediators including nitric oxide, bradykinin , and prostaglandins are vital for facilitating and maintaining EPR effect dynamics. Progression to large, advanced cancers may induce activated blood coagulation cascades, which lead to thrombus formation in tumor vasculature. Rapidly growing tumors cause obstructed or suppressed blood flow in tumor vasculature related to embolism or occluded blood vessels. The resulting limited tumor blood flow leads to less drug delivered to tumors, i.e. no or poor EPR effect. High stromal content also suppresses vascular permeability and drug diffusion. Restoring obstructed tumor blood flow and improving tumor vascular permeability via vascular mediators will improve drug delivery and the EPR effect. Physicochemical features of nanomedicines also influence therapeutic outcomes and are vital for the EPR effect.

EXPERT OPINION

The tumor microenvironment, especially tumor blood flow, is critical for a potent EPR effect. A rational strategy for circumventing EPR effect barriers must include restoring tumor blood flow.

Nanoparticles in pregnancy: the next frontier in reproductive therapeutics

BACKGROUND

Nanotechnology involves the engineering of structures on a molecular level. Nanomedicine and nano-delivery systems have been designed to deliver therapeutic agents to a target site or organ in a controlled manner, maximizing efficacy while minimizing off-target effects of the therapeutic agent administered. In both reproductive medicine and obstetrics, developing innovative therapeutics is often tempered by fears of damage to the gamete, embryo or developing foetus or of negatively impacting a woman's reproductive potential. Thus, nanomedicine delivery systems may provide alternative targeted intervention strategies, treating the source of the disease and minimizing long-term consequences for the mother and/or her foetus.

OBJECTIVE AND RATIONALE

This review summarizes the current state of nanomedicine technology in reproductive medicine and obstetrics, including safety, potential applications, future directions and the hurdles for translation.

SEARCH METHODS

A comprehensive electronic literature search of PubMed and Web of Science databases was performed to identify studies published in English up until February 2020. Relevant keywords were used to obtain information regarding use of nanoparticle technology in fertility and gene therapy, early pregnancy complications (ectopic pregnancy and gestational trophoblastic disease) and obstetric complications (preeclampsia, foetal growth restriction, preterm birth and gestational diabetes) and for selective treatment of the mother or foetus. Safety of specific nanoparticles to the gamete, embryo and foetus was also investigated.

OUTCOMES

Pre-clinical research in the development of nanoparticle therapeutic delivery is being undertaken in many fields of reproductive medicine. Non-hormonal-targeted nanoparticle therapy for fibroids and endometriosis may provide fertility-sparing medical management. Delivery of interventions via nanotechnology provides opportunities for gene manipulation and delivery in mammalian gametes. Targeting cytotoxic treatments to early pregnancy tissue provides an alternative approach to manage ectopic pregnancies and gestational trophoblastic disease. In pregnancy, nanotherapeutic delivery offers options to stably deliver silencing RNA and microRNA inhibitors to the placenta to regulate gene expression, opening doors to novel genetic treatments for preeclampsia and foetal growth restriction. Restricting delivery of teratogenic drugs to the maternal compartment (such as warfarin) may reduce risks to the foetus. Alternatively, targeted delivery of drugs to the foetus (such as those to treat foetal arrythmias) may minimize side effects for the mother.

WIDER IMPLICATIONS

We expect that further development of targeted therapies using nanoparticles in a reproductive setting has promise to eventually allow safe and directed treatments for conditions impacting the health and reproductive capacity of women and for the management of pregnancy and serious pregnancy complications.

Glucose-Responsive Microspheres as a Smart Drug Delivery System for Controlled Release of Insulin

BACKGROUND AND OBJECTIVES

Diabetes mellitus, a disease of glucose regulation, has become one of the most common medical problems in the world. At present, alternative therapy for diabetes has, to a large extent, been widely concerned with the improvement of treatment efficacy. The aims of this study were to characterize and evaluate the surface morphology of the novel glucose-responsive injectable microspheres containing insulin, along with their in vitro release and in vivo efficacy.

METHODS

In this study, glucose-responsive microspheres as an emerging smart drug delivery system for controlled release of insulin were developed by an improved water-in-oil-in-water (W/O/W) double emulsion preparation method. Here, methoxypolyethylene glycol-hydrazone-4-methoxypolyethylene glycol benzoate (mPEG-Hz-mPEG4AB) was synthesized as a pH-responsive carrier.

RESULTS

The microspheres had a good spherical structure with a particle size of 5 ~ 10 μm. Approximately 61% of insulin was released in 15 h under a high glucose environment but was barely released within the normal glucose range in in vitro studies. After a subcutaneous injection of insulin microspheres in rats, blood glucose levels rapidly decreased within 2 h and could be maintained for 2 days in the normal range. Histopathological evaluation indicated that the microspheres were almost non-irritating.

CONCLUSIONS

The pH-responsive mPEG-Hz-mPEG4AB could be used as an efficient insulin microsphere carrier, and the optimized microspheres had good morphology and sustained hypoglycemic effect.

PEG Grafted Polymethacrylates Bearing Antioxidants as a New Class of Polymer Conjugates for Application in Cosmetology

The amphiphilic copolymers of poly(ethylene glycol) methyl ether methacrylate (MPEGMA) and alkyne functionalized 2-hydroxyethyl methacrylate (AlHEMA) were synthesized by controlled atom transfer radical polymerization (ATRP). The reactions were carried out using the standard ATRP initiator ethyl α-bromoisobutyrate, (EiBBr) and the “bio”initiator bromoester derivative of 4-n-butylresorcinol (4nBREBr₂). Two substances with antioxidant activity used in cosmetology, (±)-α-lipoic acid (LA) and ferulic acid (FA), were subjected to esterification reactions to introduce azide groups. The “click” reactions between the alkyne contained copolymers and functionalized acids (LA-N₃, FA-N₃) were performed to obtain polymer-antioxidant conjugates (P((HEMA-click-FA)-co-MPEGMA) and P((HEMA-click-LA)-co-MPEGMA)). The conjugation was performed with an efficiency of 20–75%. In vitro experiments in a phosphate buffer saline (PBS) solution at neutral conditions demonstrated that the sufficient release was reached after 2.5 h for FA and 1 h for LA. The rapid release kinetics as well as the polymer carriers, which were applied to regulate the delivery of antioxidant substances, are beneficial in cosmetology.

HPMA-based polymeric conjugates in anticancer therapeutics

Polymer therapeutics has gained prominence due to an attractive structural polymer chemistry and its applications in diseases therapy. In this review, we discussed the development and capabilities of N-(2-hydroxypropyl) methacrylamide (HPMA) and HPMA-drug conjugates in cancer therapy. The design, architecture, and structural properties of HPMA make it a versatile system for the synthesis of polymeric conjugations for biomedical applications. Research suggests that HPMA could be a possible alternative for polymers such polyethylene glycol (PEG) in biomedical applications. Although numerous clinical trials of HPMA-drug conjugates are ongoing, yet no product has been successfully brought to the market. Thus, further research is required to develop HPMA-drug conjugates as successful cancer therapeutics.

Natural tripeptide capped pH-sensitive gold nanoparticles for efficacious doxorubicin delivery both in vitro and in vivo

Nanobiotechnology has been gaining ever-increasing interest for the successful implementation of chemotherapy based treatment of cancer. Gold nanoparticles (AuNPs) capped with a natural pH-responsive short tripeptide (Lys-Phe-Gly or KFG) sequence are presented herein for significant intracellular delivery of an anti-cancer drug, doxorubicin (DOX). A particularly increased apoptotic response has been observed for DOX treatments mediated by KFG-AuNPs when compared with drug alone treatments in various cell lines (BT-474, HeLa, HEK 293 T and U251). Furthermore, KFG-AuNP mediated DOX treatment significantly decreases cell proliferation and tumor growth in a BT-474 cell xenograft model in nude mice. In addition, KFG-AuNPs demonstrate efficacious drug delivery in DOX-resistant HeLa cells (HeLa-DOXR).

Self-assembling poly(ethylene glycol)-block-polylactide-cabazitaxel conjugate nanoparticles for anticancer therapy with high efficacy and low in vivo toxicity

Traditional approaches used for transforming hydrophobic anticancer drugs into therapeutically available nanoparticles heavily rely on the noncovalent formulation of drugs within amphiphilic copolymers. However, these nanotherapies have not yet shown the expected favorable clinical outcomes in cancer patients, presumably due to their insufficient stability. To solve this dilemma, we conceive a new class of nanotherapies assembled with polymeric prodrugs that maintain pharmacological activity while substantially alleviate the drug toxicity in animals. By exploiting methoxypoly(ethylene glycol)-block-poly(D, L-lactic acid) (mPEG-PLA) as a promoiety, cabazitaxel is tethered to the terminus of the PLA fragment via a hydrolysable ester linkage. These conjugates recapitulate the self-assembly to produce colloidal stable nanotherapies. In a xenograft model of prostate cancer, this nanotherapy shows a durable inhibition of tumor progression upon the administration of a tolerable dose. Our results suggest that a hydrophobic and highly toxic drug can be rationally converted into a pharmacologically efficient and self-deliverable nanotherapy.

Dendritic Polyglycerol-Derived Nano-Architectures as Delivery Platforms of Gemcitabine for Pancreatic Cancer

Dendritic polyglycerol-co-polycaprolactone (PG-co-PCL)-derived block copolymers are synthesized and explored as nanoscale drug delivery platforms for a chemotherapeutic agent, gemcitabine (GEM), which is the cornerstone of therapy for pancreatic ductal adenocarcinoma (PDAC). Current treatment strategies with GEM result in suboptimal therapeutic outcome owing to microenvironmental resistance and rapid metabolic degradation of GEM. To address these challenges, physicochemical and cell-biological properties of both covalently conjugated and non-covalently stabilized variants of GEM-containing PG-co-PCL architectures have been evaluated. Self-assembly behavior, drug loading and release capacity, cytotoxicity, and cellular uptake properties of these constructs in monolayer and in spheroid cultures of PDAC cells are investigated. To realize the covalently conjugated carrier systems, GEM, in conjunction with a tertiary amine, is attached to the polycarbonate block grafted from the PG-co-PCL core. It is observed that pH-dependent ionization properties of these amine side-chains direct the formation of self-assembly of block copolymers in the form of nanoparticles. For non-covalent encapsulation, a facile "solvent-shifting" technique is adopted. Fabrication techniques are found to control colloidal and cellular properties of GEM-loaded nanoconstructs. The feasibility and potential of these newly developed architectures for designing carrier systems for GEM to achieve augmented prognosis for pancreatic cancer are reported.

Polymer-drug conjugate therapeutics: advances, insights and prospects

Polymer-drug conjugates have long been a mainstay of the drug delivery field, with several conjugates successfully translated into clinical practice. The conjugation of therapeutic agents to polymeric carriers, such as polyethylene glycol, offers several advantages, including improved drug solubilization, prolonged circulation, reduced immunogenicity, controlled release and enhanced safety. In this Review, we discuss the rational design, physicochemical characteristics and recent advances in the development of different classes of polymer-drug conjugates, including polymer-protein and polymer-small-molecule drug conjugates, dendrimers, polymer nanoparticles and multifunctional systems. Current obstacles hampering the clinical translation of polymer-drug conjugate therapeutics and future prospects are also presented.

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.

Drug carriers with star polymer structures

In this review we summarize several synthetic approaches to the advanced synthesis of star-like polymer-based drug carriers. Moreover, their application as nanomedicines for therapy or the diagnosis of neoplastic diseases and their biodistribution are reviewed in detail. From a broad spectrum of star-like systems, we focus only on fully water-soluble systems, mainly based on poly(ethylene glycol) or N-(2-hydroxypropyl)methacrylamide polymer and copolymer arms and polyamidoamine dendrimers serving as the core of the star-like systems.

Evaluating liver uptake and distribution of different poly(2-methyl-2-oxazoline) modified lysine dendrimers following intravenous administration

Residual charge and drug modification determine the cellular distribution in the liver for poly(2-methyl-2-oxazoline) modified lysine dendrimers.

Biodegradable Simvastatin-Containing Polymeric Prodrugs with Improved Drug Release

Simvastatin was previously converted to a polymeric prodrug with higher drug loading, but the hydrophobic nature of the poly(simvastatin) component of the block copolymer led to slow release of the drug in vitro. In this study, we hypothesized that degradation could be accelerated by chemically modifying the polymer backbone by introducing glycolide and lactide comonomers. Copolymers were formed by ring-opening polymerization using 5 kDa monomethyl ether poly(ethylene glycol) as the microinitiator in presence of triazabicyclodecene catalyst. In addition to simvastatin, modified reaction mixtures contained lactide or glycolide. Incorporation of the less hydrophobic glycolide comonomer led to in vitro degradation of up to two times greater mass loss, release of up to ~7 times more simvastatin, and a 2-3 times increase in compressive modulus compared to the lactide-containing and parent polymers.

An effective "three-in-one" screening assay for testing drug and nanoparticle toxicity in human endothelial cells

Evaluating nanoparticle (NP) toxicity in human cell systems is a fundamental requirement for future NP biomedical applications. In this study, we have designed a screening assay for assessing different types of cell death induced by NPs in human umbilical vein endothelial cell (HUVEC) culture. This assay consists of WST-8, LDH and Hoechst 33342 staining, all performed in one well, which enables an evaluation of cell viability, necrosis and apoptosis, respectively, in the same cell sample. The 96-well format and automated processing of fluorescent images enhances the assay rapidity and reproducibility. After testing the assay functionality with agents that induced different types of cell death, we investigated the endothelial toxicity of superparamagnetic iron oxide nanoparticles (SPIONs, 8 nm), silica nanoparticles (SiNPs, 7-14 nm) and carboxylated multiwall carbon nanotubes (CNTCOOHs, 60 nm). Our results indicated that all the tested NP types induced decreases in cell viability after 24 hours at a concentration of 100 μg/ml. SPIONs caused the lowest toxicity in HUVECs. By contrast, SiNPs induced pronounced necrosis and apoptosis. A time course experiment showed the gradual toxic effect of all the tested NPs. CNTCOOHs inhibited tetrazolium derivatives at 100 μg/ml, causing false negative results from the WST-8 and LDH assay. In summary, our data demonstrate that the presented "three-in-one" screening assay is capable of evaluating NP toxicity effectively and reliably. Due to its simultaneous utilization of two different methods to assess cell viability, this assay is also capable of revealing, if NPs interfere with tetrazolium salts.

PEGylated Multistimuli-Responsive Dendritic Prodrug-Based Nanoscale System for Enhanced Anticancer Activity

A PEGylated multistimuli-responsive dendritic copolymer-doxorubicin (DOX) prodrug-based nanoscale system was developed as a delivery model for hydrophobic drugs. In this system, PEGylation did not only prolong circulation of the nanoscale system in the body (average half-life of 14.6 h, four times longer than that of the free drug), but also allowed the system to aggregate into nanoparticles (NPs) because of interactions between hydrophilic (polyethylene glycol) and hydrophobic (dendritic prodrug) moieties for better uptake through endocytosis (around 150 nm of particle size with a neutrally charged surface for the PEGylated dendritic prodrug with 12.1 wt % of DOX). The dendritic structure was built by bridging poly[ N-(2-hydroxypropyl)methacrylamide] segments with enzyme-responsive GFLG (Gly-Phe-Leu-Gly tetrapeptide) linkers. DOX was released by hydrolyzing the hydrazone bond between DOX and the copolymer framework in the acidic endosomes/lysosomes. In vitro studies on DOX released from the NPs induced mitochondrial dysfunction during apoptosis. By imaging the main organs and tumor tissues from mice treated with the NPs, boosted accumulation of this nanoscale medicine was found in tumor tissues, leading to a decrease in toxicity and side effects to normal tissues and enhancement in drug tolerance. In the 4T1 breast cancer model, these NPs exhibited a superior antitumor efficacy confirmed by inhibiting angiogenesis, proliferation of tumor tissues, and inducing procedural apoptosis of tumor cells. The highest tumor growth inhibition value mediated by the NPs was up to 86.5%. Therefore, this PEGylated multistimuli-responsive dendritic copolymer-DOX prodrug-based nanoscale system may be further explored as an alternative to traditional chemotherapy for breast cancer treatment.

A biocompatible and cathepsin B sensitive nanoscale system of dendritic polyHPMA-gemcitabine prodrug enhances antitumor activity markedly

In an attempt to improve the therapeutic indices of gemcitabine (GEM), a prodrug was designed by conjugating GEM with a stimuli-responsive dendritic polyHPMA copolymer (dendritic polyHPMA-GEM) and synthesized using the one-pot method of RAFT polymerization. The prodrug with dendritic architectures was able to aggregate and form stable nanoscale systems in the order of 46 nm. The high molecular weight (HMW, 168 kDa) dendritic prodrug could biodegrade into segments of low molecular weight (LMW, 29 kDa) for excretion. The prodrug demonstrates enzyme-responsive drug release features; over 95% GEM was released from the carrier in the presence of cathepsin B within 3 h. Investigation of the cellular mechanism underlying the dendritic prodrug suggests that cytotoxicity is associated with cellular uptake and cell apoptosis. The prodrug shows good hemocompatibility and in vivo biosafety. In particular, the dendritic polymer prodrug displays high accumulation within tumors and markedly improved in vivo antitumor activity in the 4T1 murine breast cancer model compared to free GEM. The in vivo antitumor activities are characterized by a marked suppression in tumor volumes indicating much higher tumor growth inhibition (TGI, 83%) than that in GEM treatment (TGI, 36%). In addition, some tumors were eliminated. The tumor xenograft immunohistochemistry study clearly indicates that tumor apoptosis occurs through antiangiogenic effects. These results suggest that the stimuli-responsive dendritic polymer-gemcitabine has great potential as an efficient anticancer agent.

Enzyme/pH-sensitive polyHPMA-DOX conjugate as a biocompatible and efficient anticancer agent

In this study, to enhance the therapeutic function and reduce the side-effects of doxorubicin (DOX), a biodegradable N-(2-hydroxypropyl) methacrylamide (HPMA) polymer-DOX conjugate has been prepared through reversible addition fragmentation chain transfer (RAFT) polymerization and conjugation chemistry, and the anticancer agent DOX was covalently linked to the polymeric vehicle through a pH-responsive hydrazone bond. The cellular mechanisms of the conjugate were explored, and the therapeutic indexes were studied as well. The high molecular weight (MW) polymeric conjugate (94 kDa) was degraded into products with low MW (45 kDa) in the presence of lysosomal cathepsin B and also showed pH-responsive drug release behavior. In vitro cellular mechanism studies revealed that the polymeric conjugate was uptaken by the 4T1 cells, leading to cell apoptosis and cytotoxicity to cancer cells, while the polymeric conjugate demonstrated excellent in vivo biosafety even at a high dose. Compared to free DOX, the conjugate has a much longer half-life in pharmacokinetics and accumulates in tumors with a much higher amount. The conjugate therefore has a much greater in vivo anticancer efficacy against 4T1 xenograft tumors and shows subtle side-effects, which were confirmed via tumor size and weight, immunohistochemistry and histological studies. Overall, this polymeric conjugate may be used as an enzyme/pH-sensitive anticancer agent.

Cleavable PEGylation: a strategy for overcoming the "PEG dilemma" in efficient drug delivery

To prolong the circulation time of drug, PEGylation has been widely used via the enhanced permeability and retention (EPR) effect, thereby providing new hope for better treatment. However, PEGylation also brings the "PEG dilemma", which is difficult for the cellular absorption of drugs and subsequent endosomal escape. As a result, the activity of drugs is inevitably lost after PEG modification. To achieve successful drug delivery for effective treatment, the crucial issue associated with the use of PEG-lipids, that is, “PEG dilemma” must be addressed. In this paper, we introduced the development and application of nanocarriers with cleavable PEGylation, and discussed various strategies for overcoming the PEG dilemma. Compared to the traditional ones, the vehicle systems with different environmental-sensitive PEG-lipids were discussed, which cleavage can be achieved in response to the intracellular as well as the tumor microenvironment. This smart cleavable PEGylation provides us an efficient strategy to overcome “PEG dilemma”, thereby may be a good candidate for the cancer treatment in future.

The effects of poly(zwitterions)s versus poly(ethylene glycol) surface coatings on the biodistribution of protein nanoparticles

Zwitterionic poly(carboxybetaine) (PCB), poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and non-ionic poly(ethylene glycol) (PEG), which have similar degrees of polymerization, were grafted to branched polyethyleneimine (PEI) to generate PCB-grafted PEI (PEI-PCB), PMPC-grafted PEI (PEI-PMPC) and PEG-grafted PEI (PEI-PEG) copolymers, respectively. These grafted PEI copolymers with almost the same grafting number were coated on the surface of 110 nm bovine serum albumin-poly(N-3-acrylamidophenylboronic acid) (BSA-PAPBA) nanoparticles to make a comparison of the surface decoration effect on the biodistribution of nanoparticles. Compared to the nanoparticles without surface decoration, surface decoration with the copolymers significantly prolonged the circulation time of BSA-PAPBA nanoparticles, leading to remarkable enhancement of tumor uptake of the nanoparticles. The drug accumulation at the tumor site reached more than 10% injected dose per gram of tumor. Among them, the PEI-PMPC-decorated nanoparticles exhibited the best performance in tumor accumulation and anticancer ability. Thus, these surface-decorated nanoparticles may serve as a strong candidate for high tumor accumulation of drug delivery systems.

Cyclic peptide-poly(HPMA) nanotubes as drug delivery vectors: In vitro assessment, pharmacokinetics and biodistribution

Size and shape have progressively appeared as some of the key factors influencing the properties of nanosized drug delivery systems. In particular, elongated materials are thought to interact differently with cells and therefore may allow alterations of in vivo fate without changes in chemical composition. A challenge, however, remains the creation of stable self-assembled materials with anisotropic shape for delivery applications that still feature the ability to disassemble, avoiding organ accumulation and facilitating clearance from the system. In this context, we report on cyclic peptide-polymer conjugates that self-assemble into supramolecular nanotubes, as confirmed by SANS and SLS. Their behaviour ex and in vivo was studied: the nanostructures are non-toxic up to a concentration of 0.5 g L^-1 and cell uptake studies revealed that the pathway of entry was energy-dependent. Pharmacokinetic studies following intravenous injection of the peptide-polymer conjugates and a control polymer to rats showed that the larger size of the nanotubes formed by the conjugates reduced renal clearance and elongated systemic circulation. Importantly, the ability to slowly disassemble into small units allowed effective clearance of the conjugates and reduced organ accumulation, making these materials interesting candidates in the search for effective drug carriers.

HPMA copolymer conjugate with pirarubicin: In vitro and ex vivo stability and drug release study

We have developed a tumor environment-responsive polymeric anticancer prodrug containing pirarubicin (THP) conjugated to N-(2-hydroxypropyl) methacrylamide copolymer (PHPMA), [P-THP], through a spacer containing pH-sensitive hydrazone bond, that showed remarkable therapeutic effect against various tumor models and in a human pilot study. Toward clinical development, here we report THP release profile from its HPMA copolymer conjugate, the conjugate stability, protein and cell-binding and solubility of P-THP. Size exclusion chromatography of P-THP (molecular weight 38 kDa) showed similar hydrodynamic volume as bovine serum albumin (BSA) in aqueous solution, with no apparent interactions with BSA, nor aggregation by itself. pH-responsive release of free THP was reconfirmed at pHs 6.5 and lower. The drug release was significantly affected by a type of used buffer. Phosphate buffer seems to facilitate faster hydrazone bond cleavage at pH 7.4 whereas higher stability was achieved in L-arginine solution which yielded only little cleavage and THP release, approx. 15% within 2 weeks at the same pH at 25 °C. Furthermore, ex vivo study using sera of different animal species showed very high stability of P-THP. Incubation with blood showed high stability of P-THP during circulation, without binding to blood cells. These findings revealed that L-arginine solution provides appropriate media for formulation of P-THP infusion solution as tumor-targeted polymeric anticancer drug based on EPR effect.