HPMA-based polymer conjugates with drug combination

Nanotechnology-based combinational drug delivery: an emerging approach for cancer therapy

Combination therapy for the treatment of cancer is becoming more popular because it generates synergistic anticancer effects, reduces individual drug-related toxicity and suppresses multi-drug resistance through different mechanisms of action. In recent years, nanotechnology-based combination drug delivery to tumor tissues has emerged as an effective strategy by overcoming many biological, biophysical and biomedical barriers that the body stages against successful delivery of anticancer drugs. The sustained, controlled and targeted delivery of chemotherapeutic drugs in a combination approach enhanced therapeutic anticancer effects with reduced drug-associated side effects. In this article, we have reviewed the scope of various nanotechnology-based combination drug delivery approaches and also summarized the current perspective and challenges facing the successful treatment of cancer.

Combination drug delivery approaches in metastatic breast cancer

Disseminated metastatic breast cancer needs aggressive treatment due to its reduced response to anticancer treatment and hence low survival and quality of life. Although in theory a combination drug therapy has advantages over single-agent therapy, no appreciable survival enhancement is generally reported whereas increased toxicity is frequently seen in combination treatment especially in chemotherapy. Currently used combination treatments in metastatic breast cancer will be discussed with their challenges leading to the introduction of novel combination anticancer drug delivery systems that aim to overcome these challenges. Widely studied drug delivery systems such as liposomes, dendrimers, polymeric nanoparticles, and water-soluble polymers can concurrently carry multiple anticancer drugs in one platform. These carriers can provide improved target specificity achieved by passive and/or active targeting mechanisms.

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.

Nanoscale delivery systems for multiple drug combinations in cancer

Although drug-delivery systems have been developed to improve drug biodistribution and efficiency in cancer therapy, some limitations still hinder successful drug targeting and delivery. Multiple drugs in combination seems a promising strategy for cancer therapy. It enables drugs to be delivered to multiple targets and exhibits the additive or synergistic effects of drugs. Physiological barriers are known to be the main obstacles of insufficient drug efficacy and delivery in tumors, but they are likely to be potential targets in combination therapy as well. This article discusses some general considerations for optimizing multiply drug delivery, including drug-release profiles and loading strategies.

Novel star HPMA-based polymer conjugates for passive targeting to solid tumors

Novel star polymer-doxorubicin conjugates designed for passive tumor targeting have been developed and their potential for treatment of cancer has been investigated. In the present study the synthesis, physico-chemical characterization, drug release, bio-distribution and preliminary data of in vivo efficacy of the conjugates are described. In the water-soluble conjugates the core of a molecule formed by poly(amido amine) (PAMAM) dendrimers was grafted with semitelechelic N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers bearing doxorubicin (Dox) attached by hydrazone bonds enabling intracellular pH-controlled hydrolytic drug release, or by GFLG sequence susceptible to enzymatic degradation. The controlled synthesis utilizing semitelechelic copolymer precursors facilitated preparation of polymer conjugates in a broad range of molecular weights (1.1-3.0·10(5) g/mol). In contrast to free drug or linear conjugates the star polymer-Dox conjugates exhibited prolonged blood circulation and enhanced tumor accumulation in tumor-bearing mice indicating important role of the EPR effect. The star polymer-Dox conjugates showed significantly higher anti-tumor activity in vivo than Dox?HCl or its linear or graft polymer conjugates, if treated with a single dose 15 or 5 mg Dox eq./kg. Method of tumor initialization (acute or chronic experimental tumor models) significantly influenced effectiveness of the treatment with much lower success in treatment of mice bearing chronic tumors.

Synergistic effect of HPMA copolymer-bound doxorubicin and dexamethasone in vivo on mouse lymphomas

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer—drug conjugates bearing the antiinflammatory and anti-proliferative drug dexamethasone (DEX) and the anti-cancer drug doxorubicin (DOX) bound to either the polymer carrier separately or in combination, were synthesized. Both the in vitro and in vivo anti-cancer activity on mouse B-cell (38C13) and T-cell (EL4) lymphoma was studied. The conjugates were fairly stable in model buffers at pH 7.4, simulating blood pH, and the drug was released by chemical hydrolysis at pH values based on the endosomal and lysosomal environments in the target cells (pH 5—6). As a control, polymer conjugates containing only a single-drug (DOX or DEX) attached to the HPMA copolymer carrier were synthesized and tested. Contrary to the treatment with either single drug conjugate, where no significant long-term survival was observed, a synergistic effect of the two drugs was manifested in vivo. Treatment of mice bearing B-cell lymphoma 38C13 formulated as a mixture of both single drug-containing conjugates or a as a conjugate with both drugs in combination gave long-term survivors.

Biodegradable star HPMA polymer conjugates of doxorubicin for passive tumor targeting

New biodegradable star polymer-doxorubicin (Dox) conjugates designed for passive tumor targeting were investigated and the present study described their synthesis, physico-chemical characterization, drug release and biodegradation. In the conjugates the core formed by poly(amido amine) (PAMAM) dendrimers was grafted with semitelechelic N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers bearing doxorubicin attached by hydrazone bonds, which enabled intracellular pH-controlled drug release, or by a GFLG sequence, which was susceptible to enzymatic degradation. The controlled synthesis utilizing semitelechelic copolymer precursors facilitated preparation of biodegradable polymer conjugates in a broad range of molecular weights (110-295 kDa) while still maintaining low polydispersity (∼1.7). The polymer grafts were attached to the dendrimers either through stable amide bonds or enzymatically or reductively degradable spacers, which enabled intracellular degradation of the high molecular weight polymer carrier to products that were able to be excreted from the body by glomerular filtration. Biodegradability tests showed that the rate of degradation was much faster for reductively degradable conjugates (completed within 4 h) than the degradation of conjugates linked via an enzymatically degradable oligopeptide GFLG sequence (within 72 h). This finding was likely due to the difference in steric hindrance for the small molecule glutathione and the enzyme cathepsin B. As for drug release, the conjugates were fairly stable in buffer at pH 7.4 (model of blood stream) but released doxorubicin either under mild acidic conditions or in the presence of lysosomal enzyme cathepsin B, both of which modeled the tumor cell microenvironment.

Drug delivery systems for differential release in combination therapy

INTRODUCTION

Combination therapy with multiple therapeutic agents has wide applicability in medical and surgical treatment, especially in the treatment of cancer. Thus, new drug delivery systems that can differentially release two or more drugs are desired. Utilizing new techniques to engineer the established drug delivery systems and synthesizing new materials and designing carriers with new structures are feasible ways to fabricate proper multi-agent delivery systems, which are critical to meet requirements in the clinic and improve therapeutic efficacy.

AREAS COVERED

This paper aims to give an overview about the multi-agent delivery systems developed in the last decade for differential release in combination therapy. Multi-agent delivery systems from nanoscale to bulk scale, such as liposomes, micelles, polymer conjugates, nano/microparticles and hydrogels, developed over the last 10 years, have been collected and summarized. The characteristics of different delivery systems are described and discussed, including the structure of drug carriers, drug-loading techniques, release behaviors and consequent evaluation in biological assays.

EXPERT OPINION

The chemical structure of drug delivery systems is the key to controlling the release of therapeutic agents in combination therapy, and the differential release of multiple drugs could be realized by the successful design of a proper delivery system. Besides biological evaluation in vitro and in vivo, it is important to speed up practical application of the resulting delivery systems.

The reaction of cyanoacetylhydrazine with omega-bromo(4-methyl)acetophenone: synthesis of heterocyclic derivatives with antitumor activity

New approaches for the synthesis of hydrazide-hydrazone derivatives were demonstrated as well as some heterocyclizations of such derivatives to afford 1,3,4-triazine, pyridine and 1,3,4-oxadiazine derivatives. The antitumor evaluation of the newly synthesized products against three cancer cell lines, namely breast adenocarcinoma (MCF-7), non-small cell lung cancer (NCI-H460) and CNS cancer (SF-268) were recorded. Most of the synthesized compounds showed high inhibitory effects.

Combination therapy: opportunities and challenges for polymer-drug conjugates as anticancer nanomedicines

The discovery of new molecular targets and the subsequent development of novel anticancer agents are opening new possibilities for drug combination therapy as anticancer treatment. Polymer-drug conjugates are well established for the delivery of a single therapeutic agent, but only in very recent years their use has been extended to the delivery of multi-agent therapy. These early studies revealed the therapeutic potential of this application but raised new challenges (namely, drug loading and drugs ratio, characterisation, and development of suitable carriers) that need to be addressed for a successful optimisation of the system towards clinical applications.