Starlike vs. classic macromolecular prodrugs: two different antibody-targeted HPMA copolymers of doxorubicin studied in vitro and in vivo as potential anticancer drugs

Polymer-ritonavir derivate nanomedicine with pH-sensitive activation possesses potent anti-tumor activity in vivo via inhibition of proteasome and STAT3 signaling

Drug repurposing is a promising strategy for identifying new applications for approved drugs. Here, we describe a polymer biomaterial composed of the antiretroviral drug ritonavir derivative (5-methyl-4-oxohexanoic acid ritonavir ester; RD), covalently bound to HPMA copolymer carrier via a pH-sensitive hydrazone bond (P-RD). Apart from being more potent inhibitor of P-glycoprotein in comparison to ritonavir, we found RD to have considerable cytostatic activity in six mice (IC₅₀ ~ 2.3-17.4 μM) and six human (IC₅₀ ~ 4.3-8.7 μM) cancer cell lines, and that RD inhibits the migration and invasiveness of cancer cells in vitro. Importantly, RD inhibits STAT3 phosphorylation in CT26 cells in vitro and in vivo, and expression of the NF-κB p65 subunit, Bcl-2 and Mcl-1 in vitro. RD also dampens chymotrypsin-like and trypsin-like proteasome activity and induces ER stress as documented by induction of PERK phosphorylation and expression of ATF4 and CHOP. P-RD nanomedicine showed powerful antitumor activity in CT26 and B16F10 tumor-bearing mice, which, moreover, synergized with IL-2-based immunotherapy. P-RD proved very promising therapeutic activity also in human FaDu xenografts and negligible toxicity predetermining these nanomedicines as side-effect free nanosystem. The therapeutic potential could be highly increased using the fine-tuned combination with other drugs, i.e. doxorubicin, attached to the same polymer system. Finally, we summarize that described polymer nanomedicines fulfilled all the requirements as potential candidates for deep preclinical investigation.

Poly(Ethylene Glycol)-Doxorubicin Conjugates with pH-Controlled Activation

The synthesis and physico-chemical characterisation of a biodegradable multiblock polymer drug carrier based on poly(ethylene glycol) (PEG) is described. The blocks of PEG ( Mw 2,000) are connected by an enzymatically degradable tripeptide derivative consisting of one lysine and two glutamic acid residues. Doxorubicin (Dox), was attached to the polymer carrier via a hydrazone bond susceptible to acid hydrolysis at pH 5.0. Human immunoglobulin (IgG) was covalently linked to the polymer-Dox conjugate by the reaction of 2-pyridyldisulfanyl groups of the polymer with thiol groups of the antibody modified with 2-iminothiolane. The resulting antibody-polymer-drug conjugates were characterised by size-exclusion chromatography, UV/VIS spectrophotometry, electrophoresis and amino acid analysis. All polymers studied (both with and without IgG) showed high anti-proliferative activity against concanavalin A-stimulated murine splenocytes and various cancer cell lines in vitro. The polymer-Dox conjugate (without IgG) exhibited a significant anti-tumor efficacy against murine EL4 T-cell lymphoma and human colorectal carcinoma SW620 in vivo.

Recent Developments in Active Tumor Targeted Multifunctional Nanoparticles for Combination Chemotherapy in Cancer Treatment and Imaging

Nanotechnology and combination therapy are two major fields that show great promise in the treatment of cancer. The delivery of drugs via nanoparticles helps to improve drug's therapeutic effectiveness while reducing adverse side effects associated wifh high dosage by improving their pharmacokinetics. Taking advantage of molecular markers over-expressing on tumor tissues compared to normal cells, an "active" molecular marker targeted approach would be-beneficial for cancer therapy. These actively targeted nanoparticles would increase drug concentration at the tumor site, improving efficacy while further reducing chemo-resistance. The multidisciplinary approach may help to improve the overall efficacy in cancer therapy. This review article summarizes recent developments of targeted multifunctional nanoparticles in the delivery, of various drugs for a combinational chemotherapy approach to cancer treatment and imaging.

Anti-Lymphoma Efficacy Comparison of Anti-Cd20 Monoclonal Antibody-Targeted and Non-Targeted Star-Shaped Polymer-Prodrug Conjugates

Here we describe the synthesis and biological properties of two types of star-shaped polymer-doxorubicin conjugates: non-targeted conjugate prepared as long-circulating high-molecular-weight (HMW) polymer prodrugs with a dendrimer core and a targeted conjugate with the anti-CD20 monoclonal antibody (mAb) rituximab (RTX). The copolymers were linked to the dendrimer core or to the reduced mAb via one-point attachment forming a star-shaped structure with a central antibody or dendrimer surrounded by hydrophilic polymer chains. The anticancer drug doxorubicin (DOX) was attached to the N-(2-hydroxypropyl)methacrylamide (HPMA)-based copolymer chain in star polymer systems via a pH-labile hydrazone linkage. Such polymer-DOX conjugates were fairly stable in aqueous solutions at pH 7.4, and the drug was readily released in mildly acidic environments at pH 5–5.5 by hydrolysis of the hydrazone bonds. The cytotoxicity of the polymer conjugates was tested on several CD20-positive or negative human cell lines. Similar levels of in vitro cytotoxicity were observed for all tested polymer conjugates regardless of type or structure. In vivo experiments using primary cell-based murine xenograft models of human diffuse large B-cell lymphoma confirmed the superior anti-lymphoma efficacy of the polymer-bound DOX conjugate when compared with the original drug. Targeting with RTX did not further enhance the anti-lymphoma efficacy relative to the non-targeted star polymer conjugate. Two mechanisms could play roles in these findings: changes in the binding ability to the CD-20 receptor and a significant loss of the immunological properties of RTX in the polymer conjugates.

Nanotherapeutics With Anthracyclines: Methods of Determination and Quantification of Anthracyclines in Biological Samples

Anthracyclines, e.g. doxorubicin, pirarubicin, are widely used as cytostatic agents in the polymer nanotherapeutics designed for the highly effective antitumor therapy with reduced side effects. However, their precise dosage scheme needs to be optimized, which requires an accurate method for their quantification on the cellular level in vitro during nanocarrier development and in body fluids and tissues during testing in vivo. Various methods detecting the anthracycline content in biological samples have already been designed. Most of them are highly demanding and they differ in exactness and reproducibility. The cellular uptake and localization is predominantly observed and determined by microscopy techniques, the anthracycline content is usually quantified by chromatographic analysis using fluorescence detection. We reviewed and compared published methods concerning the detection of anthracycline nanocarriers.

Smart branched polymer drug conjugates as nano-sized drug delivery systems

Branched polymers own special properties derived from their intrinsic characteristics. These properties make them ideal candidates to be used as carriers for an improved generation of polymer-drug conjugates.

GATG dendrimers and PEGylated block copolymers: from synthesis to bioapplications

Dendrimers are synthetic macromolecules composed of repetitive layers of branching units that emerge from a central core. They are characterized by a tunable size and precise number of peripheral groups which determine their physicochemical properties and function. Their high multivalency, functional surface, and globular architecture with diameters in the nanometer scale makes them ideal candidates for a wide range of applications. Gallic acid-triethylene glycol (GATG) dendrimers have attracted our attention as a promising platform in the biomedical field because of their high tunability and versatility. The presence of terminal azides in GATG dendrimers and poly(ethylene glycol) (PEG)-dendritic block copolymers allows their efficient functionalization with a variety of ligands of biomedical relevance including anionic and cationic groups, carbohydrates, peptides, or imaging agents. The resulting functionalized dendrimers have found application in drug and gene delivery, as antiviral agents and for the treatment of neurodegenerative diseases, in diagnosis and as tools to study multivalent carbohydrate recognition and dendrimer dynamics. Herein, we present an account on the preparation and recent applications of GATG dendrimers in these fields.

Codendrimer from polyamidoamine (PAMAM) and oligoethylene dendron as a thermosensitive drug carrier

The efficient synthesis of codendrimer PAMAM-co-OEG (PAG) and its properties in aqueous solution, including particle size and thermosensitivity, are described. PAG is synthesized with well-defined structure through the "attach to" route. In the aqueous solutions, PAG forms unimer and multimolecular aggregates with the respective particle sizes of approximately 8 and 200 nm, depending on the concentration. PAG shows thermosensitive behavior with sharp and fast transition, and the lower critical solution temperature is 38.2 °C. The suitability of codendrimer PAG as the thermosensitive carrier is evaluated with methotrexate (MTX) as the model drug. MTX is encapsulated in PAG with the drug-loading capacity of 39%, among which 30% of MTX is encapsulated in PAMAM core. The release behavior of MTX mediated by temperature is investigated with focus on the effects around the LCST of PAG.

Amphiphilic starlike dextran wrapped superparamagnetic iron oxide nanoparticle clsuters as effective magnetic resonance imaging probes

Starlike polymers have been widely used in various fields, such as tissue engineering, imaging, gene and drug delivery because of their unique structures and properties. Dextran has long been used as a temporary plasma substitute because of its excellent biocompatibility. In this study, starlike polysaccharide with multiple dextran arms was designed and developed by attaching dextran to a β-cyclodextrin core through click chemistry. Next, starlike dextran was modified with aliphatic chains and these amphiphilic polymers can self-assemble into nanoscale micelles in water, and their critical micelle concentration values (3.7 × 10(-8) M) are much lower comparing to its linear analogs (1.7 × 10(-7) M), resulting in more stable nanostructures in aqueous environment. These micelles can encapsulate multiple superparamagnetic iron oxide nanoparticles and forming clustering particle nanostructures in water, and the resulting nanocomposites have a high T(2) relaxivity of 436.8 Fe mm(-1) s(-1) under a 1.5T clinical magnetic resonance imaging (MRI) scanner. Further, dual functional probes were developed by loading both superparamagnetic iron oxide nanoparticles and small molecule anticancer drug doxorubicin into polymeric micelles. Multidrug-resistant breast cancer cells MCF-7/Adr treated with these probes can be characterized under MRI.

Polymeric conjugates for drug delivery

The field of polymer therapeutics has evolved over the past decade and has resulted in the development of polymer-drug conjugates with a wide variety of architectures and chemical properties. Whereas traditional non-degradable polymeric carriers such as poly(ethylene glycol) (PEG) and N-(2-hydroxypropyl methacrylamide) (HPMA) copolymers have been translated to use in the clinic, functionalized polymer-drug conjugates are increasingly being utilized to obtain biodegradable, stimuli-sensitive, and targeted systems in an attempt to further enhance localized drug delivery and ease of elimination. In addition, the study of conjugates bearing both therapeutic and diagnostic agents has resulted in multifunctional carriers with the potential to both "see and treat" patients. In this paper, the rational design of polymer-drug conjugates will be discussed followed by a review of different classes of conjugates currently under investigation. The design and chemistry used for the synthesis of various conjugates will be presented with additional comments on their potential applications and current developmental status.

Possibility of Using Embolizing Preparation Derived from Poly(2-Hydroxyethyl Methacrylate) (Poly-HEMA) for Chemoemobolization

The principal opportunity of uptaking weakly crosslinked hydrogel emboli is shown by Doxorubicin at different temperatures. The optimal process time is 1.5–2.5 h. It is revealed that Doxorubicin is capable to diffuse from a polymeric matrix, having targeted medical effect on surrounding tissue and reducing side impacts on other organs.

Active targeting schemes for nanoparticle systems in cancer therapeutics

The objective of this review is to outline current major cancer targets for nanoparticle systems and give insight into the direction of the field. The major targeting strategies that have been used for the delivery of therapeutic or imaging agents to cancer have been broken into three sections. These sections are angiogenesis-associated targeting, targeting to uncontrolled cell proliferation markers, and tumor cell targeting. The targeting schemes explored for many of the reported nanoparticle systems suggest the great potential of targeted delivery to revolutionize cancer treatment.

Past and future evolution in colloidal drug delivery systems

Colloidal drug delivery systems have been providing alternative formulation approaches for problematic drug candidates, and improved delivery for existing compounds for decades. Colloidal systems for drug delivery have all evolved down a similar pathway, almost irrespective of the delivery system, from conception, to the use of safer excipients, PEGylation for passive targeting and attachment of ligands for active targeting. The recent emergence of truly biologically interactive systems represents the latest step forward in colloidal delivery systems. In this article, the maturation pathway and recent advances for the major classes of colloidal delivery systems are reviewed, and the paper poses the question of whether the nanotechnology boom will create a revolution in colloidal delivery, or just the next natural stage in evolution.

Facile Synthetic Procedure for ω, Primary Amine Functionalization Directly in Water for Subsequent Fluorescent Labeling and Potential Bioconjugation of RAFT-Synthesized (Co)Polymers

We describe a facile method to amine functionalize and subsequently fluorescently label polymethacrylamides synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. RAFT-generated poly(N-(2-hydroxypropyl) methacrylamide-b-N-[3-(dimethylamino)propyl] methacrylamide) (poly(HPMA-b-DMAPMA)), a water soluble biocompatible polymer, is first converted to a polymeric thiol and functionalized with a primary amine through a disulfide exchange reaction with cystamine and subsequently reacted with the amine-functionalized fluorescent dye, 6-(fluorescein-5-carboxamido)hexanoic acid, succinimidyl ester (5-SFX). Poly(HPMA258-b-DMAPMA13) (Mn = 39 700 g/mol, Mw/Mn = 1.06), previously synthesized by RAFT polymerization, was used to demonstrate this facile labeling method. The problem with labeling the omega-terminal chain end of a RAFT-synthesized polymethacrylamide is that the reduced end yields a tertiary thiol with low reactivity. The key to labeling poly(HPMA-b-DMAPMA) is to first reduce the dithioester chain end with a strong reducing agent such as NaBH4, and then functionalize the tertiary polymeric thiol with a primary amine through a disulfide exchange reaction with dihydrochloride cystamine. We show that the disulfide exchange reaction is efficient and that the amine-functionalized poly(HPMA-b-DMAPMA) can be easily labeled with the fluorescent dye, 5-SFX. This concept is proven by using a ninhydrin assay to detect primary amines and UV-vis spectroscopy to measure the degree of conjugation.

Cationic poly-L-lysine dendrimers: pharmacokinetics, biodistribution, and evidence for metabolism and bioresorption after intravenous administration to rats

Cationic poly-L-lysine 3H-dendrimers with either 16 or 32 surface amine groups (BHALys [Lys]4 [3H-Lys]8 [NH2]16 and BHALys [Lys]8 [3H-Lys]16 [NH2]32, generation 3 and 4, respectively) have been synthesized and their pharmacokinetics and biodistribution investigated after intravenous administration to rats. The species in plasma with which radiolabel was associated was also investigated by size exclusion chromatography (SEC). Rapid initial removal of radiolabel from plasma was evident for both dendrimers (t(1/2) < 5 min). Approximately 1 h postdose, however, radiolabel reappeared in plasma in the form of free lysine and larger (but nondendrimer) species that coeluted with albumin by SEC. Plasma and whole blood pharmacokinetics were similar, precluding interaction with blood components as a causative factor in either the rapid removal or reappearance of radioactivity in plasma. Administration of monomeric 3H L-lysine also resulted in the appearance in plasma of a radiolabeled macromolecular species that coeluted with albumin by SEC, suggesting that biodegradation of the dendrimer to L-lysine and subsequent bioresorption may explain the pharmacokinetic profiles. Capping the Lys8 dendrimer with D-lysine to form BHALys [Lys]4 [3H-Lys]8 [D-Lys]16 [NH2]32 resulted in similar, and very rapid, initial disappearance kinetics from plasma when compared to the L-lysine capped dendrimer. Since significant extravasation of these large hydrophilic molecules seems unlikely, this most likely reflects both elimination and extensive binding to vascular surfaces. Capping with "non-natural" D-lysine also appeared to render the dendrimer essentially inert to the biodegradation process. For the L-lysine capped dendrimers, radiolabel was widely distributed throughout the major organs, with no apparent selectivity for organs of the reticuloendothelial system. In contrast, a greater proportion of the administered radiolabel was recovered in the organs of the reticuloendothelial system for the D-lysine capped system, as might be expected for a nondegrading circulating foreign colloid. To our knowledge this is the first data to demonstrate the biodegradation/bioresorption of poly-L-lysine dendrimers and has significant implications for the utility of these systems as drugs or drug delivery systems.

Treatment with HPMA copolymer-based doxorubicin conjugate containing human immunoglobulin induces long-lasting systemic anti-tumour immunity in mice

Linkage of doxorubicin (Dox) to a water-soluble synthetic N-(2-hydroxypropyl)methacrylamide copolymer (PHPMA) eliminates most of the systemic toxicity of the free drug. In EL-4 lymphoma-bearing C57BL/6 mice, a complete regression of pre-established tumours has been achieved upon treatment with Dox-PHPMA-HuIg conjugate. The treatment was effective using a range of regimens and dosages, ranging from 62.5 to 100% cured mice treated with a single dose of 10-20 mg of Dox eq./kg, respectively. Fractionated dosages producing lower levels of the conjugate for a prolonged time period had substantial curative capacity as well. The cured mice developed anti-tumour protection as they rejected subsequently re-transplanted original tumour. The proportion of tumour-protected mice inversely reflected the effectiveness of the primary treatment. The treatment protocol leading to 50% of cured mice produced only protected mice, while no mice treated with early treatment regimen (i.e. starting on day 1 after tumour transplantation) rejected the re-transplanted tumour. Exposure of the host to the cancer cells was a prerequisite for developing protection. The anti-tumour memory was long lasting and specific against the original tumour, as the cured mice did not reject another syngeneic tumour, melanoma B16-F10. The immunity was transferable to naïve recipients in in vivo neutralization assay by spleen cells or CD8(+) lymphocytes derived from cured animals. We propose an effective treatment strategy which eradicates tumours without harming the protective immune anti-cancer responses.

Polymeric Conjugates of 9-[2-(Phosphonomethoxy)ethyl]purine with Potential Antiviral and Cytostatic Activity

Syntheses and characterization of polymer conjugates of 9-[2-(phosphonomethoxy)ethyl] (PME) derivatives of adenine (PMEA), 2,6-diaminopurine (PMEDAP) and guanine (PMEG) are described. The phosphonate group of these acyclic nucleotide analogues was activated by reaction with triphenylphosphine and di(2-pyridyl) disulfide (TPP-PDS). The activated phosphonate reacted with a random copolymer containing N-(2-hydroxypropyl)methacrylamide (HPMA) and N-(3-methacrylamidopropanoyl)ethane-1,2-diamine (Ma-AP-ED) units. The phosphonamide bond between the nucleotide and polymer carrier proved to be relatively stable at physiological pH 7.4 while at pH 5.0 (corresponding to endosomal or lysosomal compartments of cells) underwent slow hydrolysis. The rate of hydrolysis (drug release) was shown to depend on the detailed structure of the heterocyclic base. The polymer-drug conjugates described in the paper represent a new family of antiviral and cytostatic drugs with potentially improved pharmacokinetics, sustained drug release and diminished non-specific toxicity.

Essential properties of drug-targeting delivery systems

How, if at all, can drug delivery help to create ideal drugs? After four decades of trying, an effective site-specific drug-delivery system has not yet been developed. This review draws attention to the pharmacokinetic conditions that must be met to achieve a successful performance by site-selective drug-carrier delivery systems. In a drug-carrier approach, a drug is attached to a macromolecular carrier via a chemically labile linker. The carrier transports the drug to its site of action and releases it at the target site. For this simple approach to work, several fundamental conditions (nonspecific interactions, target site access, drug release and drug suitability) must be satisfied. The importance of these essential requirements, not always recognized in the development of drug-delivery systems, is discussed and illustrated by recent examples selected from the literature.

Polymer conjugates: nanosized medicines for treating cancer

Interdisciplinary research at the interface of polymer chemistry and the biomedical sciences has produced the first polymer-based nanomedicines for the diagnosis and treatment of cancer. These water-soluble hybrid constructs, designed for intravenous administration, fall into two main categories: polymer-protein conjugates or polymer-drug conjugates. Polymer conjugation to proteins reduces immunogenicity, prolongs plasma half-life and enhances protein stability. Polymer-drug conjugation promotes tumor targeting through the enhanced permeability and retention (EPR) effect and, at the cellular level following endocytic capture, allows lysosomotropic drug delivery. The successful clinical application of polymer-protein conjugates (PEGylated enzymes and cytokines) and promising results arising from clinical trials with polymer-bound chemotherapy (e.g. doxorubicin, paclitaxel, camptothecins) has provided a firm foundation for more sophisticated second-generation constructs that deliver the newly emerging target-directed anticancer agents (e.g. modulators of the cell cycle, signal transduction inhibitors and antiangiogenic drugs) in addition to polymer-drug combinations (e.g. endocrine- and chemo-therapy).

Antibody–cytotoxic agent conjugates for cancer therapy

Antibody-based delivery of cytotoxic agents, including toxins, to tumours can dramatically reduce systemic toxicity and increase therapeutic efficacy. The advantage of a monoclonal antibody (mAb) is superior selectivity towards antigens expressed on the surface of cancer cells. Recent advances in biotechnology accelerated progress in the pharmaceutical applications of mAbs. A cytotoxic warhead is attached to a mAb in an immunoconjugate via a linker, which is stable in circulation but efficiently cleaved in the tumour tissue. The warhead, mAb and linker play important roles in the successful design of potent and efficient immunoconjugates. To date, one mAb-cytotoxic agent conjugate has been approved by the FDA and several other candidates are in various stages of clinical trials. This review describes the recent progress in the design and development of mAb-based immunoconjugates of cytotoxic agents, and summarises the criteria for the critical choices of a suitable mAb, linker and cytotoxic agent to design an efficacious immunoconjugate.

Transferrin-oligomers as potential carriers in anticancer drug delivery

PURPOSE

To investigate if the cross-linking of transferrin receptor (TfR) induced by Tf-oligomers alters the endocytosis of receptor-ligand complexes in cultured tumor cells and hence increases intracellular drug release.

METHODS

An average of 3.5 Tf molecules per aggregate were cross-linked either by using homobifunctional linker (1, 11-bis-maleimidotetraethyleneglycol) [Tf(3.5-BM(PEO)4)] or heterobifunction linker [succinimidyl 4-(-p-maleimidophenyl)-butyrate] (Tf(3.5-SMPB)). Cell surface binding and competition experiments with 125I-Tf for TfR binding were studied to demonstrate that Tf-oligomers maintain specificity of the TfR-binding. To determine the degradation of Tf-oligomers in TfR-mediated endocytosis, cultured tumor cells were pulsed for 15 min with 125I-Tf-oligomers and chased for 2 h at 37 degrees C in the presence of excess unlabeled Tf. The chase medium was subjected to TCA precipitation to separate the intact and degraded Tf. To investigate if the alteration of TfR-trafficking facilitates the intracellular release of the drug from the Tf-conjugated form, methotrexate (MTX) was conjugated to Tf-oligomer (Agg-Tf-MTX) and its antiproliferative activity was compared with monomeric-Tf-MTX (Mono-Tf-MTX) in human colon carcinoma (Caco-2) cells, human breast adenocarcinoma (MCF-7) cells, wild-type Chinese hamster ovary (CHO) cells, and MTX-resistant CHO (CHO-MTX-RII) cells.

RESULTS

TfR-mediated degradation of Tf-oligomers was higher than that of monomeric Tf in both Caco-2 and MCF-7 cells. The IC50 of Agg-Tf-MTX was lower than that of Mono-Tf-MTX in both tumor cell lines. The IC50 of MTX and Mono-Tf-MTX in CHO-MTX-RII cells was higher than that in wild-type CHO cells, whereas the Agg-Tf-MTX was almost identical in both the resistant and wild-type cells.

CONCLUSIONS

Cross-linking of TfR induced by oligomeric Tf binding alters the intracellular trafficking of Tf-TfR complexes, redirects them out of the recycling pathway, and targets them to intracellular degradation in cultured tumor cells. The alteration of TfR-trafficking facilitates the intracellular release of the drug from the Tf-conjugated form. Consequently, Agg-Tf-MTX is more effective than Mono-Tf-MTX as a TfR-mediated antiproliferative agent in tumor cells, as well as in MTX-resistant transport deficient cells. Therefore, Tf-oligomers are potentially effective TfR-targeting carriers for intracellular delivery of anticancer drugs.