Review article
HPMA copolymer–anticancer drug conjugates: design, activity, and mechanism of action

https://doi.org/10.1016/S0939-6411(00)00075-8Get rights and content

Abstract

The design, synthesis and properties of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers as carriers of anticancer drugs are reviewed. Macromolecular therapeutics based on HPMA copolymers are biocompatible, preferentially accumulate in tumors, and possess a higher anticancer efficacy than low molecular weight drugs. Novel designs of HPMA copolymer carriers resulted in long-circulating conjugates and gene and oligonucleotide delivery systems. HPMA copolymer based macromolecular therapeutics were active against numerous cancer models and are in clinical trials. The data obtained indicated that macromolecular therapeutics activated different signaling pathways and possessed a different mechanism of action than free drugs. This bodes well for the success of future research aimed at identification of new intracellular molecular targets as a basis for the design of the second generation of macromolecular therapeutics.

Introduction

The idea of using macromolecules as carriers of (anticancer) drugs developed continuously over the last 90 years. Ehrlich in 1906 coined the phrase ‘magic bullet’, recognizing the importance of biorecognition [1]. DeDuve discovered that many enzymes are localized in the lysosomal compartment and the lysosomotropism of macromolecules [2]. The conjugation of drugs to synthetic and natural macromolecules was initiated nearly 50 years ago. Jatzkewitz used a dipeptide spacer to attach a drug to polyvinylpyrrolidone in the early fifties [3] and Ushakov's group synthesized numerous water-soluble polymer–drug conjugates in the sixties and seventies (see, for example, Ref. [4]). Mathé et al. [5] pioneered conjugation of drugs to immunoglobulins, setting the stage for targeted delivery. Finally, Ringsdorf [6] presented the first clear concept of the use of polymers as targetable drug carriers.

The development of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers as anticancer drug carriers was the result of systematic research on hydrophilic biomedical polymers performed in one of the author's (J.K.) laboratory at the Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences (IMC) in Prague. In the late sixties and seventies, the IMC was a unique place to study hydrophilic biomedical polymers. Hydrogels were designed there by Wichterle and Lı́m [7] as well as soft contact lenses [8]. This was the driving force behind a detailed study of the relationship between the structure of soluble and cross-linked hydrophilic polymers and their biocompatibility [9], [10], [11], [12], [13], [14]. Based on these investigations, hydrogels have been used successfully in human medicine [15] and basic data on the structure–properties relationship were obtained, which permitted the design of new water-soluble polymeric drug carriers [16], [17].

A new hydrophilic, biocompatible polymer, based on N-(2-hydroxypropyl)methacrylamide (HPMA) [18], [19] was chosen as a candidate for a soluble polymeric drug carrier. The α-carbon substitution and the N-substituted amide bond ensured hydrolytic stability of the side-chains [13]. In addition, the crystallinity of the monomer guaranteed the absence of divinyl compounds (a problem with hydrophilic esters of the 2-hydroxyethyl methacrylate type) and the linearity of the macromolecules. The possibility to control the molecular weight distribution of macromolecular therapeutics is a prerequisite for their elimination from the organism. Oligopeptide side-chains were designed as drug attachment sites [20]. The important observation that oligopeptide sequences attached to HPMA copolymers were degradable in vivo and thus had potential as drug attachment/release sites was encouraging and crucial for the further development of HPMA copolymer based macromolecular therapeutics [21]. The chemistry of the synthesis of HPMA copolymer based macromolecular therapeutics was studied in detail [22], [23], [24]. Insulin [25] and ampicillin [26] were attached to HPMA copolymers by aminolysis of reactive polymeric precursors, whereas polymer conjugates containing N-(4-aminobenzensulfonyl)-N′-butylurea were prepared by copolymerization of HPMA and polymerizable derivatives of the drug [27].

The above mentioned initial studies resulted in numerous collaborations and indeed in an independent interest of other laboratories to pursue the potential of HPMA based therapeutics. This review attempts to present the state of the art developments of HPMA copolymer based macromolecular therapeutics and indicate the directions to be taken for the discovery of novel molecular targets and the design, synthesis, and evaluation of second generation conjugates. The review concentrates on HPMA copolymer conjugates only, however, the conclusions may be valid for other water-soluble macromolecular therapeutics.

Section snippets

Biological rationale

The rationale for the use of water-soluble polymers as carriers of anticancer drugs is based on the mechanism of cell entry. Whereas the majority of low molecular weight drugs enter the cell interior by diffusion via the plasma membrane, the entry of macromolecules is restricted to endocytosis [2]. Macromolecules captured by this mechanism are channeled to the lysosomal compartment of the cell. Endocytosis is a common term encompassing phagocytosis and pinocytosis. Phagocytosis describes the

Design of HPMA copolymer based macromolecular therapeutics

The design of macromolecular therapeutics must be based on a sound biological rationale. The HPMA copolymer–drug conjugate should be biorecognizable at two levels: at the plasma membrane to increase the recognition and internalization by a subset of target cells and intracellularly by lysosomal enzymes to release the drug from the carrier. The latter is a prerequisite for transport of the drug into the cytoplasm and nucleus resulting in biological activity [33], [34], [35], [36].

Biocompatibility of macromolecular therapeutics

Binding of anticancer drugs and targeting moieties such as antibodies to polymeric carriers improves their biocompatibility [36]. Using a non-toxic and non-immunogenic polymeric carrier, the decrease of non-specific toxicity of an attached drug (when compared to an unbound drug) may be mainly attributed to the change in body distribution. For example, anthracycline antibiotics have a non-specific cardiotoxicity and bone marrow toxicity, limiting the dose which can be administered. Binding of

Enhanced permeability and retention effect

It is now well accepted that the enhanced permeability and retention (EPR) effect is the predominant mechanism by which soluble macromolecular anticancer drugs exhibit their therapeutic effect on solid tumors. The phenomenon is attributed to high vascular density of the tumor, increased permeability of tumor vessels, defective tumor vasculature, and defective or suppressed lymphatic drainage in the tumor interstitium [74], [75]. Other factors, however, may have an opposite effect. For example,

New targeting strategies

There is a possibility of applying concepts of cell biology in targeted drug delivery. The incorporation of certain chemical features (targeting moieties) into a macromolecule can enormously enhance its rate of uptake by cells, by causing it to adhere to the plasma membrane being internalized [36], [98]. New developments in the design of targetable macromolecular therapeutics are discussed below.

Experimental cancer

HPMA copolymer conjugates have shown activity toward various tumor models. HPMA copolymer–daunomycin conjugate was active in the treatment of experimental Walker sarcoma [78] and L1210 leukemia [116], [117]. HPMA copolymer–doxorubicin conjugates were active against L1210 leukemia [118], B16F10 melanoma [119], M5076 [67], LS174T human colorectal carcinoma xenografts [67] and sensitive and resistant human ovarian carcinoma models [77], [94], [95], [97], [120]. HPMA copolymer platinates have shown

Gene and oligonucleotide delivery

Many laboratories are studying strategies to deliver genes or antisense oligonucleotides into somatic cells of patients [163]. With increasing interest in non-viral delivery systems, ways to overcome membrane barriers for gene delivery into the cytoplasm and/or nucleus are being evaluated [164]. Antisense oligonucleotides have been covalently bound to HPMA copolymers via disulfide [165] and amide [166] bonds.

Novel vectors, block and graft copolymers of HPMA, and comonomers containing quaternary

Mechanism of action of macromolecular therapeutics

Data on the mechanism of action of HPMA copolymer–DOX conjugates on human ovarian carcinomas in vitro and in vivo seem to support our hypothesis that macromolecular therapeutics activate different signaling pathways and possess different anticancer effects than free drugs. As a result of different pathways of internalization and subcellular trafficking, the HPMA copolymer–DOX conjugate might be more protected from cell detoxification mechanisms, resulting in an enhanced activation of apoptosis,

Conclusions and future directions

HPMA copolymers [18] and their conjugates with drugs (reviewed in Ref. [36]) have been one of the most extensively studied systems [176]. HPMA copolymer–anticancer drug conjugates have been found to be active against numerous cancer models and are in clinical trials. The scientific evidence as well as the results of clinical trials seem to indicate the great potential of macromolecular therapeutics in cancer treatment. The fact that the maximum tolerated dose of DOX in patients was several

Acknowledgements

Thanks to our Prague coworkers (Drs K. Ulbrich, B. Řı́hová, J. Strohalm, V. Chytrý, and V. Šubr) – that is the place where everything started; thanks to our coworkers at the University of Utah (Drs C.M. Peterson, J. Spikes, V. Omelyanenko, J.-G. Shiah, N.L. Krinick, D. Putnam, M. Demoy, J. Callahan, K. Fowers, A. Tang, M. Tijerina, C. Wang, and D. Wang) and in the United Kingdom (Drs J.B. Lloyd, R. Duncan, and L.C. Seymour) – those are the places where, in addition to Prague and Milan, the HPMA

References (178)

  • P. Rejmanová et al.

    Stability in rat plasma and serum of lysosomally degradable oligopeptide sequences in N-(2-hydroxypropyl)methacrylamide copolymers

    Biomaterials

    (1985)
  • D. Putnam et al.

    Intracellularly biorecognizable derivatives of 5-fluorouracil: implications of targetable delivery in the human condition

    Biochem. Pharmacol.

    (1996)
  • V. Chytrý et al.

    Insulin bound to chiral polymer with N-acetyl-D-glucosaminyl units. Lack of mitogenic activity on rat aorta smooth muscle cell proliferation

    J. Controll Release

    (1998)
  • B. Řı́hová et al.

    Antibody directed affinity therapy applied to the immune system: in vivo effectiveness and limited toxicity of daunomycin conjugates to HPMA copolymers and targeting antibody

    Clin. Immunol. Immunopathol.

    (1988)
  • L. Korčáková et al.

    A simple test for immunogenicity of colloidal infusion solutions – the draining lymph node activation

    Z. Immun. Forsch.

    (1976)
  • B. Řı́hová et al.

    Effect of the chemical structure of N-(2-hydroxypropyl)methacrylamide copolymers on their ability to induce antibody formation in inbred strains of mice

    Biomaterials

    (1984)
  • B. Řı́hová et al.

    Biocompatibility of N-(2-hydroxypropyl)methacrylamide copolymers containing adriamycin

    Biomaterials

    (1989)
  • R. Duncan et al.

    Preclinical evaluation of polymer-bound doxorubicin

    J. Control. Release

    (1992)
  • B. Crepon et al.

    Enzymatic degradation and immunogenic properties of derivatized dextrans

    Biomaterials

    (1991)
  • J. Cassidy et al.

    Activity of N-(2-hydroxypropyl)methacrylamide copolymers containing daunomycin against a rat tumor model

    Biochem. Pharmacol.

    (1989)
  • J.-G. Shiah et al.

    Biodistribution of free and N-(2-hydroxypropyl)methacrylamide copolymer-bound meso, chlorin e6 and adriamycin in nude mice bearing human ovarian carcinoma OVCAR-3 xenografts

    J. Control. Release

    (1999)
  • T. Yamaoka et al.

    Distribution and tissue uptake of poly(ethylene glycol) with different molecular weights after intravenous administration to mice

    J. Pharm. Sci.

    (1994)
  • P.S. Steyger et al.

    Intratumoural distribution as a determinant of tumor responsiveness to therapy using polymer-based macromolecular prodrugs

    J. Control. Release

    (1996)
  • S.A. Cartlidge et al.

    Soluble, crosslinked N-(2-hydroxypropyl)methacrylamide copolymers as potential drug carriers. 1. Pinocytosis by rat visceral yolk sacs and rat intestine cultured in vitro. Effect of molecular weight on uptake and intracellular degradation

    J. Control. Release

    (1986)
  • S.A. Cartlidge et al.

    Soluble, crosslinked N-(2-hydroxypropyl)methacrylamide copolymers as potential drug carriers. 3. Targeting by incorporation of galactosamine residues. Effect of route of administration

    J. Control. Release

    (1987)
  • S.A. Cartlidge et al.

    Soluble, crosslinked N-(2-hydroxypropyl)methacrylamide copolymers as potential drug carriers. 2. Effect of molecular weight on blood clearance and body distribution in the rat after intraveneous administration. Distribution of unfractionated copolymer after intraperitoneal, subcutaneous or oral administration

    J. Control. Release

    (1987)
  • M. Dvořák et al.

    High-molecular weight HPMA copolymer–adriamycin conjugates

    J. Control. Release

    (1999)
  • T. Minko et al.

    HPMA copolymer bound adriamycin overcomes MDR1 gene encoded resistance in a human ovarian carcinoma cell line

    J. Control. Release

    (1998)
  • T. Minko et al.

    Chronic exposure to HPMA copolymer-bound adriamycin does not induce multidrug resistance in a human ovarian carcinoma cell line

    J. Control. Release

    (1999)
  • K. Kunath et al.

    HPMA copolymer–anticancer drug–OV-TL16 antibody conjugates. 3. The effect of free and polymer-bound adriamycin on the expression of some genes in the OVCAR-3 human ovarian carcinoma cell line

    Eur. J. Pharm. Biopharm.

    (2000)
  • R. Duncan et al.

    Fate of N-(2-hydroxypropyl)methacrylamide copolymers with pendent galactosamine residues after intravenous administration to rats

    Biochim. Biophys. Acta

    (1986)
  • P. Ehrlich

    Studies in Immunity

    (1906)
  • H. Jatzkewitz

    Peptamin (glycyl-L-leucyl-mescaline) bound to blood plasma expander (polyvinylpyrrolidone) as a new depot form of a biologically active primary amine (mescaline)

    Z. Naturforsch.

    (1955)
  • E.F. Panarin et al.

    Synthesis of polymer salts and amidopenicillines (in Russian)

    Khim. Pharm. Zhur.

    (1968)
  • G. Mathé et al.

    Effect sur la leucémie L1210 de la souris d'une combinaison par diazotation d'A méthoptérine et de γ-globulines de hamsters porteurs de cette leucémie par hétérogreffe

    Compte-rendus del'Académie des Sciences

    (1958)
  • H. Ringsdorf

    Structure and properties of pharmacologically active polymers

    J. Polym. Sci. Polym. Symp.

    (1975)
  • O. Wichterle et al.

    Hydrophilic gels for biological use

    Nature

    (1960)
  • O. Wichterle, Hydrogel contact lenses, US Patent 3,496,254...
  • L. Šprincl et al.

    Biological tolerance of poly(N-substituted methacrylamides)

    J. Biomed. Mater. Res.

    (1971)
  • L. Šprincl et al.

    Effect of porosity of heterogeneous poly(glycol monomethacrylate) gels on the healing-in of test implants

    J. Biomed. Mater. Res.

    (1971)
  • J. Kopeček et al.

    Biological tolerance of poly(N-substituted acrylamides)

    J. Biomed. Mater. Res.

    (1973)
  • L. Šprincl et al.

    Effect of the structure of poly(glycol monomethacrylate) gels on the calcification of implants

    Calcif. Tissue Res.

    (1973)
  • J. Kopeček et al.

    Relationship between the structure and biocompatibility of hydrophilic gels

    Polym. Med. (Wroclaw)

    (1974)
  • J. Kopeček et al.

    New types of synthetic infusion solutions. I. Investigation of the effect of solutions of some hydrophilic polymers on blood

    J. Biomed. Mater. Res.

    (1973)
  • Z. Voldřich et al.

    Long-term experience with the poly(glycol monomethacrylate) gel in plastic operations of the nose

    J. Biomed. Mater. Res.

    (1975)
  • J. Kopeček

    Soluble biomedical polymers

    Polym. Med. (Wroclaw)

    (1977)
  • J. Kopeček

    Soluble polymers in medicine

  • J. Drobnı́k et al.

    Enzymatic cleavage of side-chains of synthetic water-soluble polymers

    Makromol. Chem.

    (1976)
  • J. Kopeček et al.

    Polymers containing enzymatically degradable bonds. 4. Preliminary experiments in vivo

    Makromol. Chem.

    (1981)
  • P. Rejmanová et al.

    Aminolyses of monomeric and polymeric p-nitrophenyl esters of methacryloylated amino acids

    Makromol. Chem.

    (1977)
  • Cited by (0)

    View full text