No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Polymeric Carriers for Anticancer Drugs
Abstract
Chemotherapy together with debulking surgery is a major treatment for cancer. There are, however, major limitations of conventional
cytotoxic drugs that result from their nonspecific toxicity (e.g., the lack of selectivity) in the body and the intrinsic
or acquired multidrug resistance (MDR) of cancer cells. To this end, polymeric drug carriers have been developed to address
this nonspecificity and MDR [1]. It is believed that these drug carriers alter the biodistribution and increase the bioavailability
of incorporated anticancer agents to the target cells [2].
Folate-protein conjugates can be nondestructively delivered into a cell's cytoplasm via folate receptor-mediated endocytosis if (i) the target cells express a folate-binding protein, and (ii) if the folate is linked to its attached protein at a site that does not interfere with receptor recognition. Because such conjugates have been observed to remain in endosomal compartments for extended periods following cellular uptake, we decided to evaluate whether release into the cytoplasm might be expedited by inclusion of a translocation domain in the folate-protein construct. To test this possibility, momordin-folate and truncated Pseudomonas exotoxin-folate conjugates (LysPE38 and CysPE35), i.e. protein synthesis inhibitors either lacking or containing the desired translocation domain, respectively, were examined for their abilities to block protein synthesis in a variety of cell types. The translocation competent LysPE38-folate construct was found to kill cells six times more rapidly with 10-fold greater potency than the permeation-incompetent momordin-folate. Further, cells expressing low levels of folate receptors could only be exterminated by the translocation competent Pseudomonas exotoxin-folate conjugates. When the translocation capability of CysPE35-folate was inactivated by modification of Cys287, the construct also lost most of its cytotoxicity. These data suggest that autocatalysis of transport from an internal vesicular compartment into the cytoplasm can greatly augment the cytotoxicity of a protein toxin entering cells via the folate endocytosis pathway. Because the folate ligand can selectively target a protein conjugate to cancer cells in the presence of normal cells, such translocatable toxin-folate constructs warrant further study as a possible treatment for some malignancies.
Novel anti-neoplastic agents such as gene targeting vectors and encapsulated carriers are quite large (approximately 100–300
nm in diameter). An understanding of the functional size and physiological regulation of transvascular pathways is necessary
to optimize delivery of these agents. Here we analyze the functional limits of transvascular transport and its modulation
by the microenvironment. One human and five murine tumors including mammary and colorectal carcinomas, hepatoma, glioma, and
sarcoma were implanted in the dorsal skin-fold chamber or cranial window, and the pore cutoff size, a functional measure of
transvascular gap size, was determined. The microenvironment was modulated: (i) spatially, by growing tumors in subcutaneous or cranial locations and (ii) temporally, by inducing vascular regression in hormone-dependent tumors. Tumors grown subcutaneously exhibited a characteristic
pore cutoff size ranging from 200 nm to 1.2 μm. This pore cutoff size was reduced in tumors grown in the cranium or in regressing
tumors after hormone withdrawal. Vessels induced in basic fibroblast growth factor-containing gels had a pore cutoff size
of 200 nm. Albumin permeability was independent of pore cutoff size. These results have three major implications for the delivery
of therapeutic agents: (i) delivery may be less efficient in cranial tumors than in subcutaneous tumors, (ii) delivery may be reduced during tumor regression induced by hormonal ablation, and (iii) permeability to a molecule is independent of pore cutoff size as long as the diameter of the molecule is much less than
the pore diameter.
Internalization of exogenous macromolecules by live cells provides a powerful approach for studying cellular functions. Understanding the mechanism of transfer from the extracellular milieu to the cytoplasm and nucleus could also contribute to the development of new therapeutic approaches. This article summarizes the unexpected properties of penetratins, a class of peptides with translocating properties and capable of carrying hydrophilic compounds across the plasma membrane. This unique system allows direct targeting of oligopeptides and oligonucleotides to the cytoplasm and nucleus, is non-cell-type specific and highly efficient, and therefore has several applications of potential cell-biology and clinical interest.
Polymersomes are self-assembled shells of amphiphilic block copolymers that are currently being developed by many groups for fundamental insights into the nature of self-assembled states as well as for a variety of potential applications. While recent reviews have highlighted distinctive properties - particularly stability - that are strongly influenced by both copolymer type and polymer molecular weight, here we first review some of the more recent developments in computational molecular dynamics (MD) schemes that lend insight into assembly. We then review polymersome loading, in vivo stealthiness, degradation-based disassembly for controlled release, and even tumor-shrinkage in vivo. Comparisons of polymersomes with viral capsids are shown to encompass and inspire many aspects of current designs.
The formation of spherical, cylindrical, and bilayered vesicle structures from dispersions of polyethylene oxide)-b-poly(γ-methyl-ε-caprolactone) (OMCL) in water, is discussed. These structures were generated at moderate temperatures without the use of a cosolvent and are comprised of a hydrophilic, biocompatible poly(ethylene oxide) block and an amorphous poly(γ-methyl-ε-caprolactone) (PMCL). Aqueous solutions of OMCL diblocks were prepared by a thin-film hydration protocol in which OMCL was initially dissolved in methylene chloride and the solution was added to tared vials. Solution morphologies were characterized with cryogenic transmission electron microscopy (cryo-TEM) which allows direct visualization of the aggregate structures formed in water. The results of the study identify a promising approach for producing biocompatible and biodegradable dispersions under physiological conditions.
Certain amphiphilic water-soluble polymers including amphiphilic derivatives of polyvinyl pyrrolidone (PVP) were found to be efficient steric protectors for liposomes in vivo. In this study, we have tried to develop synthetic pathways for preparing amphiphilic PVP and to investigate the influence of the hydrophilic/hydrophobic blocks on some properties of resulting polymers and polymer-coated liposomes. To prepare amphiphilic PVP with the end stearyl (S) or palmityl (P) residues, amino- and carboxy-terminated PVP derivatives were first synthesized by the free-radical polymerization of vinyl pyrrolidone in the presence of amino- or carboxy-mercaptans as chain transfer agents, and then modified by interaction of amino-PVP with stearoyl chloride or palmitoyl chloride, or by dicyclohexyl carbodiimide coupling of stearylamine with carboxy-PVP. ESR-spectra of the hydrophobic spin-probe, nitroxyl radical N-oxyl-2-hexyl-2-(10-methoxycarbonyl)decyl-4,4′-dimethyl oxazoline, in the presence of amphiphilic PVP demonstrated good accessibility of terminal P- and S-groups for the interaction with other hydrophobic ligands. Spontaneous micellization and low CMC values (in a low μmolar range) were found for amphiphilic PVP derivatives using the pyrene method. In general, S-PVP forms more stable micelles than P-PVP (at similar MW, CMC values for S-PVP are lower than for P-PVP). It was found that amphiphilic PVP incorporated into negatively charged liposomes effectively prevents polycation(poly-ethylpyridinium-4-vinylchloride)-induced liposome aggregation, completely abolishing it at ca. 10mol% polymer content in liposomes. Additionally, the liposome-incorporated PVP prevents the fluorescence quenching of the membrane-incorporated hydrophobic fluorescent label [N-(4-fluoresceinthiocarbamoyl)dipalmitoyl-PE] by the free polycation. PVP-modified liposomes were loaded with a self-quenching concentration of carboxyfluorescein, and their destabilization in the presence of mouse serum was investigated following the release of free dye. Amphiphilic PVP with MW between 1500 and 8000 provides good steric protection for liposomes. The degree of this protection depends on both polymer concentration and molecular size of the PVP block.
The paper discusses general problems in using PEG for conjugation to high or low molecular weight molecules. Methods of binding PEG to different functional groups in macromolecules is reported together with their eventual limitations. Problems encountered in conjugation, such as the evaluation of the number of PEG chains bound, the localisation of the site of conjugation in polypeptides and the procedure to direct PEGylation to the desired site in the molecule are discussed. Finally, the paper reports on more specific methods regarding reversible PEGylation, cross-linking reagents with PEG arms, PEG for enzyme solubilization in organic solvent and new polymers as alternative to PEG.
Daan J.A. Crommelin – Department of Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands
Gerrit Borchard – Enzon Pharmaceuticals, Piscataway, NJ, USA
Micellization of poly(ethylene glycol-b-(DL-lactic acid-co-glycolic acid)-b-ethylene glycol), PEG-PLGA-PEG, triblock copolymers in water was studied by 13C-NMR (nuclear magnetic resonance), dye solubilization method, and light scattering. Critical micelle concentration was decreased by half by increasing temperature from 20 to 50°C. Enthalpy of micellization was calculated to be 10–20 KJ/mole. Apparent aggregation number, diameter of a micelle abruptly increased while second viral coefficient decreased at ≈30°C suggesting that micellar growth as well as an increase in polymer–polymer attraction occur at this temperature. These findings might suggest that the sol to gel transition at high concentration of aqueous solutions of this polymer is driven by conformational changes of micelles.
In spite of the enormous possibilities presented by macromolecules for the development of advanced materials with increased functionality, the achievement of functionality is often limited by the randomness associated with polymer synthesis and the exponential increase in technical difficulties encountered in attaining a desired degree of complexity in the molecular design. This paper describes an increasingly important approach to the design of complex and highly functional macromolecules, i.e. the genetic engineering of protein-based macromolecules. The exploitation of the efficient machinery of protein synthesis in living cells opens a route to precisely defined and complex macromolecules.A series of molecular designs with increasing complexity are presented to show how this controlled increase yields materials with increasingly selective and sophisticated multifunctionality. The simplest designs already show interesting mechanical properties, but the adequate introduction of given chemical functions along the polymer chain provides an opportunity to expand the range of properties to smart behavior and self-assembly. Finally, examples are given where the molecular designs further incorporate selected bioactivities in order to develop materials for the most cutting-edge applications in f biomedicine and nanobiotechnology.
Experimental and computational approaches to estimate solubility and permeability in discovery and development settings are described. In the discovery setting `the rule of 5' predicts that poor absorption or permeation is more likely when there are more than 5 H-bond donors, 10 H-bond acceptors, the molecular weight (MWT) is greater than 500 and the calculated Log P (CLogP) is greater than 5 (or MlogP>4.15). Computational methodology for the rule-based Moriguchi Log P (MLogP) calculation is described. Turbidimetric solubility measurement is described and applied to known drugs. High throughput screening (HTS) leads tend to have higher MWT and Log P and lower turbidimetric solubility than leads in the pre-HTS era. In the development setting, solubility calculations focus on exact value prediction and are difficult because of polymorphism. Recent work on linear free energy relationships and Log P approaches are critically reviewed. Useful predictions are possible in closely related analog series when coupled with experimental thermodynamic solubility measurements.
A micelle-forming polymeric drug was synthesized using adriamycin (an anti-cancer drug) and poly(ethylene glycol)-poly(aspartic acid) block copolymers. The micelle had a narrow and unimodal size distribution, and its diameter was observed to be ca. 50 nm, the range corresponding to viruses. This micelle-forming polymeric drug exhibited good water solubility and good stability against precipitation irrespective of the large quantity of incorporated hydrophobie adriamycin. In vivo anti-cancer activity of this polymeric drug against P-388 mouse leukemia was studied by changing the length of the poly(aspartic acid) chain of the block copolymer. The polymeric drug showed excellent in vivo anti-cancer activity, judged from the ratio of the survival period of the treated mice to that of the control (T/C), with lower toxicity than that of adriamycin. These results point to a promising figure of polymeric micelles as novel drug carriers.
The protective effect of poly(ethylene glycol) and some other polymers on nanoparticulate carriers including liposomes is considered in terms of statistical behavior of macromolecules in solution, when polymer flexibility plays a key role. According to the mechanism proposed, surface-grafted chains of flexible and hydrophilic polymers form dense “conformational clouds” preventing other macromolecules from the interaction with the surface even at low concentration of protecting polymer. Using liposomes as an example, experimental evidence is presented of the importance of protecting polymer flexibility in liposome steric protection. Further possible applications of the suggested model are discussed. The possibility of using protecting polymers other than poly(ethylene glycol) is analyzed, and examples of such polymers are given based on polymer-coated liposome biodistribution data. General requirements for protecting polymers are formulated, and differences in steric protection of liposomes and particles are discussed. The scale of protective effect is interpreted as the balance between the energy of hydrophobic anchor interaction with the liposome membrane core or with the particle surface and the energy of polymer chain free motion in solution.
There is a wide-spread consensus that characteristics of drug vehicles determine the applicability of the site-specific delivery of drugs. This article focused on the promising features of block copolymer micelles as drug vehicles mimicking the natural carrier-systems with supramolecular structures (i.e. viruses and lipoproteins). Considerable discussions are made on the physicochemical characteristics of polymeric micelles in aqueous milieu with shedding light on earlier works done in the field. Advantageous features of polymeric micelles as drug vehicles are summarized as: (1) formation of environmentally-separated microcontainer of drugs through supramolecular assemblage, (2) installation of anchoring moiety on the surface, (3) duration in the biological compartment and (4) programmable chronological stability. Then, our recent work concerning polymeric micelles with anti-tumor activity is presented to demonstrate these advantageous features of polymeric micelles. Worth noticing is that higher anti-tumor activity was achieved by adriamycin-conjugated micelles compared with parental adriamycin, indicating that a considerable improvement in cancer chemotherapy is feasible by the use of appropriate vehicle systems.
Nephrotoxicity is an inherent adverse effect of certain anticancer drugs. Renal dysfunction can be categorised as prerenal uraemia, intrinsic damage or postrenal uraemia according to the underlying pathophysiological process. Renal hypoperfusion promulgates prerenal uraemia. Intrinsic renal damage results from prolonged hypoperfusion, exposure to exogenous or endogenous nephrotoxins, renotubular precipitation of xenobiotics or endogenous compounds, renovascular obstruction, glomerular disease, renal microvascular damage or disease, and tubulointerstitial damage or disease. Postrenal uraemia is a consequence of clinically significant urinary tract obstruction. Clinical signs of nephrotoxicity and methods used to assess renal function are discussed.
Mechanisms of chemotherapy-induced renal dysfunction generally include damage to vasculature or structures of the kidneys, haemolytic uraemic syndrome and prerenal perfusion deficits. Patients with cancer are frequently at risk of renal impairment secondary to disease-related and iatrogenic causes.
This article reviews the incidence, presentation, prevention and management of anticancer drug-induced renal dysfunction. Dose-related nephrotoxicity subsequent to administration of certain chloroethylnitrosourea compounds (carmustine, semustine and streptozocin) is commonly heralded by increased serum creatinine levels, uraemia and proteinuria. Additional signs of streptozocin-induced nephrotoxicity include hypophosphataemia, hypokalaemia, hypouricaemia, renal tubular acidosis, glucosuria, aceturia and aminoaciduria. Cisplatin and carboplatin cause dose-related renal dysfunction. In addition to increased serum creatinine levels and uraemia, electrolyte abnormalities, such as hypomagnesaemia and hypokalaemia, are commonly reported adverse effects. Rarely, cisplatin has been implicated as the underlying cause of haemolytic uraemic syndrome. Pharmaceutical antidotes to cisplatin-induced nephrotoxicity include amifostine, sodium thiosulfate and diethyldithiocarbamate. Dose- and age-related proximal tubular damage is an adverse effect of ifosfamide. In addition to renal wasting of electrolytes, glucose and amino acids, Fanconi syndrome, rickets and osteomalacia have occurred with ifosfamide treatment.
High dose azacitidine causes renal dysfunction manifested by tubular acidosis, polyuria and increased urinary excretion of electrolytes, glucose and amino acids. Haemolytic uraemia is a rare adverse effect of gemcitabine. Methotrexate can cause increased serum creatinine levels, uraemia and haematuria. Acute renal failure is reported following administration of high dose methotrexate. Urinary alkalisation and hydration confer protection against methotrexate-induced renal dysfunction. Dose-related nephrotoxicity, including acute renal failure, are reported subsequent to treatment with pentostatin and diaziquone. Acute renal failure is a rare adverse effect of treatment with interferon-α. Haemolytic uraemic syndrome occurs with mitomycin administration. A mortality rate of 50 to 100% is reported in patients developing mitomycin—induced haemolytic uraemic syndrome. Capillary leak syndrome occurring with aldesleukin therapy can cause renal dysfunction. Infusion-related hypotension during infusion of high dose carmustine can precipitate renal dysfunction.
Dynamic light scattering measurements have been performed for aqueous solutions of linear poly(vinylcaprolactam) (PVCa) at several polymer concentrations and over a wide range of ionic surfactant concentration. The intermolecular aggregation of PVCa accompanied by a sharp increase of the light scattering intensity is observed in pure water at 33 °C. The effect of ionic surfactants (cetylpyridinium chloride (CPC) and sodium dodecyl sulfate (SDS)) on the behavior of solutions of linear PVCa was studied as a function of temperature. For polymer concentrations below the overlap concentration (2.5 mg/mL) a decrease of the macromolecular hydrodynamic diameter is observed upon the addition of ionic surfactant (SDS, CPC) at low surfactant concentrations. This effect is in contrast to the behavior of the complexes of surfactant with another thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPA). A further increase of the surfactant concentration leads to the reentrant swelling of macromolecules. In the presence of ionic surfactant the temperature increase results in the sharp drop of the hydrodynamic diameter of the particles at some critical temperature. This critical temperature becomes higher with increasing surfactant concentration. For higher polymer concentrations (5 mg/mL) the particle size always increases upon the addition of ionic surfactants, because of intermolecular aggregation.
We describe the preparation of a new set of amphiphilic block copolymers with well-defined molecular weights and block volume fractions. The synthesis of a variety of polyalkane−poly(ethylene oxide) block copolymers was accomplished by a new polymerization−hydrogenation sequence. Initially, anionic polymerization of either butadiene or isoprene was performed followed by end capping with ethylene oxide. The resulting hydroxyl-terminated polydienes were catalytically hydrogenated to give the corresponding hydroxyl-terminated polyalkanes. These polymeric alcohols were then titrated with potassium naphthalenide to yield the analogous potassium alkoxides. This type of macroinitiator was employed in the polymerization of ethylene oxide. Seventeen polyalkane−poly(ethylene oxide) block copolymers were prepared in near quantitative yields with molecular weights ranging from (1.4 to 8.7) × 103 and poly(ethylene oxide) volume fractions ranging from 0.29 to 0.73. These polymers are model materials for block copolymer phase behavior studies.
A new strategy for the synthesis of a soluble and well-defined dioctylpoly(thienylenevinylene) (DO-PTV), a low band-gap semiconducting polymer, via Horner−Wadsworth−Emmons condensation is presented. The chain length of the DO-PTV can be tuned by varying the amount of end-capping agent employed. This polymer was characterized by 1H NMR, UV−vis absorbance spectroscopy, and GPC. Finally, the DO-PTV was transformed into macroinitiator for nitroxide mediated radical polymerization. A preliminary experiment of polymerization of a mixture of styrene and chloromethylstyrene with this macroinitiator led to a low band gap rod−coil conjugated block copolymer which is a precursor for a donor−acceptor self-organized material.
Vesicles prepared in water from a series of diblock copolymers“polymersomes”are physically characterized. With increasing molecular weight M̄n, the hydrophobic core thickness for self-assembled bilayers of poly(ethylene oxide)−polybutadiene increases up to 20 nm, which is considerably greater than any previously studied lipid or polymersome system. Micromanipulation of vesicles demonstrates an interface-dominated elasticity that is independent of M̄n. Furthermore, membrane stability as defined by the maximal areal strain increases with M̄n, approaching a universal limit predicted by mean-field ideas and set by the interfacial tension. Nonlinear responses and memory effects also emerge with increasing M̄n, indicating the onset of chain entanglements at higher M̄n. The results highlight the interfacial limits and transitions to bulk responses of self-assemblies.
http://pubs.acs.org/doi/abs/10.1021/ja00011a057
This Progress Report describes the latest advances in vesicles and liposomes. Recent work on the self-assembly of complex polymer systems shows that the formation of polymer vesicles or closed hull structures is archetypal, leading to fascinating new possibilities and applications in materials science. A general view of the underlying self-assembly mechanisms leading to vesicles and the control of size, shape, and other vesicular properties by physicochemical means is presented, as background. This is followed by an overview of the recently described new classes of polymer and supramolecular tectons that make vesicle formation a more general phenomenon going beyond just lipids. Finally, the potential applications of vesicles, including non-lipid vesicles, are outlined.
Polymers are used as carriers for the delivery of drugs, proteins, targeting moieties, and imaging agents. Several polymers, poly(ethylene glycol) (PEG), N-(2-hydroxypropyl)methacrylamide (HPMA), and poly(lactide-co-glycolide) (PLGA) copolymers have been successfully utilized in clinical research. Recently, interest in polymer conjugation with biologically active components has increased remarkably as such conjugates are preferably accumulated in solid tumors and can reduce systemic toxicity. Based on the site and the mode of action, polymer conjugates possess either 'tuned' degradable or non-degradable bonds. In order to obtain such bonds, most of the strategies involve incorporation of amino acids, peptides or small chains as spacer molecules through multiple steps to include protections and deprotections. There is a need to design efficient synthetic methods to obtain polymeric conjugates with drugs and other bioactive components. Designs should aim to decrease the steric hindrance exhibited by polymers and the biocomponents. In addition, the reactivity of polymer and drug must be enhanced. This is especially true for the use of high molecular weight linear polymers and bulkier unstable drugs such as steroids and chemotherapeutic agents. Further, it is essential to elucidate the structure activity relationship (SAR) of a drug when it is conjugated with a polymer using different conjugation sites, as this can vary the efficacy and mechanism of action when compared with its free form. This review will discuss the current synthetic advances in polymer-conjugation with different bioactive components of clinical importance. In addition, the review will describe the strategies for reduction of steric hindrance and increase in reactivity of the polymers, drugs and bioactive agents and highlight the requisite structure activity relationship in polymer–drug bioconjugates. Finally, we will focus on passive and active targeting of polymeric drug delivery systems to specific site of drug action.
Different polymeric transport systems for biologically active substances are presented. In the past, most of the reviews on polymeric drugs dealt with pharmaca, fixed to conventional water-soluble polymers. Naturally occuring transport proteins with their complex features have recently been imitated by micellar solubilized polymers. Polymerized liposomes from polymerizable lipids can be regarded as vesicular solubilized polymers and are discussed as stable models for biomembranes. By insertion of glycolipids, these liposomes are rendered susceptible to specific recognition by proteins. When natural or cleavable synthetic lipids are incorporated into polymerizable membranes, phase-separation of the different lipid fractions may occur. The unpolymerized components can then be degraded or solubilized and thereby can be removed from the polymerized matrix, allowing a selective opening of stable compartments.Verschiedene polymere Transportsysteme für biologisch aktive Substanzen werden diskutiert. Die bislang erschienenen Arbeiten und Zusammenfassungen behandelten fast ausnahmslos normal (isotrop) gelöste Polymere. Den natürlichen Transportproteinen mit ihren vielfältigen Aufgaben nachempfunden sind micellar gelöste Polymere. Auf der Basis polymerer Liposomen ist kürzlich auch der Aufbau vesikulär gelöster Polymerer und damit stabiler Membran- und Zellmodelle möglich geworden. Der Einbau von Glycolipiden, von funktionellen Lipiden und aktiven Enzymen ermöglicht Oberflächenreaktionen, die für eine Reihe von Zellfunktionen von Bedeutung sind. Baut man diese stabilen Liposomen außerdem aus Mischungen von natürlichen und bzw. spaltbaren und polymerisierbaren Lipiden auf, so sind sie gezielt öffenbar - und etwa so, wie man eine Flasche entkorkt.
cis-Diamminedichloroplatinum (II) (cisplatin, CDDP), a potent anticancer agent, was bound to the aspartic acid residues of poly(ethylene glycol)-poly(aspartic acid) (PEG-P(ASP)) block copolymer by ligand substitution reaction at the platinum atom of CDDP. The polymeric drug thus obtained was observed to form a micelle structure in aqueous medium, showing excellent water solubility. In the present study, in vitro and in vivo antitumor activity against several human tumor cell lines, toxicity and pharmacokinetic characteristics in rodents of CDDP-incorporated polymeric micelles (CDDP/m) were evaluated in comparison with those of CDDP. In vitro, CDDP/m exhibited 10-17% of the cytotoxicity of CDDP against human tumor cell lines. CDDP/m given by intravenous (i.v.) injection yielded higher and more sustained serum levels than CDDP. In vivo CDDP/m treatment resulted in higher and more sustained levels in tumor tissue than CDDP, and showed similar antitumor activity to CDDP against MKN 45 human gastric cancer xenograft. CDDP/m treatment caused much less renal damage than CDDP. These results indicate that CDDP/m treatment can reduce CDDP-induced nephrotoxicity without compromising the anticancer cytotoxicity of CDDP.
The success of most advanced drug delivery strategies requires development of sophisticated new site-specific carriers. Several new targeting methods use physical and chemical signals such as magnetic fields or changes in pH or temperature as targeting and triggering tools. In addition to site-specificity, the carrier should achieve passive targeting to evade the body's reticulo-endothelial system (RES) and exhibit long blood circulation times in order to efficiently distribute active drug to the site of action (active targeting). To fulfil these requirements, thermo-responsive polymeric micelles have been prepared from amphiphilic block copolymers composed of N-isopropylacrylamide (IPAAm) (a thermo-responsive outer shell) and styrene (St) (hydrophobic inner core). The polymeric micelle which is very stable in aqueous media was formed by the dialyzed method from DMF solution against water. The micelles have a unimodal size distribution (24±4 nm) and CMC was around 10 mg/l (ml→l). These micelles have a small diameter with a low critical micelle concentration, providing a carrier that may have long blood circulation times and a low RES uptake. When the temperature is increased above the transition temperature of the thermo-responsive block chains (32°C), the outer shell chains dehydrate and collapse, allowing aggregation between micelles and favoring binding interactions with cell membrane surfaces. Moreover, these changes are reversible. Hydrophobic molecules are shown to be incorporated into the inner hydrophobic core of the thermo-responsive micelles. Consequently, these micelles are valuable for site-specific delivery of drugs using changes in temperature as a trigger.
The limited solubility of hydrophobic drugs may hamper their potential investigation. Vehicles that can incorporate and effectively deliver such drugs are of interest. To this end, we have prepared micelles based on AB block copolymers of poly(ethylene oxide) (PEO) and poly(β-benzyl l-aspartate) (PBLA). The distribution of hydrophobic molecules into PEO-PBLA micelles was investigated by UV spectroscopy and the fluorescence probe technique using pyrene as a model drug. Further, the effects of temperature and sonication on pyrene partitioning into PEO-PBLA micelles were studied. The solubility of pyrene was enhanced in a linear fashion with respect to PEO-PBLA concentration. Weight-average partition coefficients of about 104 were determined for pyrene distribution in PEO-PBLA micellar solutions. The photophysical properties of pyrene, which are modified upon uptake within PEO-PBLA micelles, indicate a low polarity and pyrene mobility in the solubilization site (i.e. core region). The polarity of micellar cores (i.e. micropolarity) is apparently important for solute partitioning into polymeric micelles. PEO-PBLA micelles offer micropolarities slightly higher than those of the well-studied AB block copolymer micelles based on PEO and polystyrene (PS) on the pyrene scale. Nonetheless, block copolymer micelles, having cores consisting of a poly(amino acid), can be chemically tailored to adjust micropolarities for enhanced drug loading.
A growing body of literature describes the development and applications of novel targeting and/or contents release triggering schemes to improve the therapeutic index of drugs encapsulated within liposomes. This review focuses on literature appearing between January 1995–December 1997 that report 1) antibody and receptor-mediated targeting approaches for improving drug localization and 2) acid, enzymatic, thermal or photochemical triggering processes that destabilize membranes and improve drug bioavailability via cytoplasmic delivery of liposomal contents.
Polyethylene glycol (PEG) is widely used as a covalent modifier of biological macromolecules and particulates as well as a carrier for low molecular weight drugs. In the first two instances proteins and liposomes are of particular importance. Their conjugates with PEG often possess the ability to avoid quick recognition and clearance in vivo, that their unconjugated counterparts are suffering from. In this review (with 133 references) methods for preparation of PEG conjugates with various biologically active compounds are summarized. Since the bulk of the published work in this field involves proteins, drugs, and lipids, an appropriate emphasis is given to the conjugates of these compounds. While the first two types of PEG conjugates are usually intended for a direct use as therapeutics, PEG-lipids are mainly utilized for formation of long-circulating liposomes. Particular attention is paid to the comparative attributes of various reactive PEG derivatives, properties of the linkages formed, and possible side reactions. The relationships between various conjugation strategies and their influence on the relevant biological properties and/or on in vivo performance of the corresponding conjugates is also discussed.
The purpose of this study was to evaluate the functions of a modified polyvinyl alcohol (PVA-R), which has a hydrophobic moiety, as a coating material for liposomes to be loaded with the anticancer drug, doxorubicin. The size controlled liposomes (egg phosphatidylcholine: cholesterol=1:1 molar ratio) were prepared by the hydration method followed by extrusion. Drug encapsulation and surface modification with polymers (PVA and PVA-R) were carried out simultaneously using a modified pH gradient method. The existence of a thick polymer layer on the surface of the liposomes was confirmed by an increase in particle size and the amount of polymer on the liposomal surface, especially for the PVA-R-coated liposomes. The effects of polymer coating on the behavior of the liposomes in vivo were evaluated by measuring the circulation time and biodistribution of the drug after i.v. administration of the liposomal drug in rats. The PVA-R-coated liposomes showed a more prolonged circulating time for the drug with less uptake by the reticuloendothelial system after i.v. administration in rats, compared with non-coated liposomes. These results confirm that polymer possessing a hydrophobic anchor at its end, like PVA-R, is a suitable material for modifying the surface of doxorubicin-loaded liposomes to improve their stability in the circulating blood.
Naturally occurring peptides and protein domains with amphipathic sequences play a dominant role in physiological, lipid membrane-reorganizing processes like fusion, disruption, or pore formation. More recently this capacity to modulate membrane integrity has been exploited for drug delivery into cells. Incorporation of synthetic membrane-active peptides into delivery systems has been found to enhance intracellular delivery of drugs including oligonucleotides, peptides, or plasmid DNA. In the majority of applications, the amphipathic peptides are designed to act after uptake by endocytosis, releasing the delivered agent from intracellular vesicles to the cytoplasm. Alternatively, peptides might mediate direct drug transfer across the plasma membrane. Although encouraging results have been obtained with the use of synthetic peptides to enhance cellular delivery of various compounds, the naturally evolved mechanisms observed in the entry of viruses or protein toxins are still far more efficient. For the development of improved synthetic peptides and carrier systems a better understanding of the molecular details of membrane-destabilization and reorganization will be essential.
The main objective of this study was to synthesize novel folic acid-functionalized diblock copolymer micelles and evaluate their solubilization of two poorly water-soluble anti-tumor drugs, tamoxifen and paclitaxel, which suffer from low water solubility and/or poor hydrolytic stability. The diblock copolymer consisted of a permanently hydrophilic block comprising 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) residues and a pH-sensitive hydrophobic block comprising 2-(diisopropylamino)ethyl methacrylate (DPA) residues. Folic acid (FA) was conjugated to the end of the MPC block so that this group was located on the micelle periphery. Tamoxifen- and paclitaxel-loaded micelles were prepared from FA–MPC–DPA copolymers prepared with two different block compositions that were designed to produce optimal solubilization of each drug. Their drug-loading capacities and aqueous stabilities were determined by high performance liquid chromatography. The hydrodynamic diameters of tamoxifen- and paclitaxel-loaded FA–MPC–DPA micelles ranged from 30 to 60 nm, as judged by dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies. Finally, tamoxifen and paclitaxel release profiles were evaluated in phosphate buffer solution at pH 7.4 and 5. These studies demonstrated that FA–MPC–DPA micelles acted as useful drug carriers, leading to relatively slow release of both tamoxifen and paclitaxel into aqueous solution over a period of 7 days. In addition, rapid release can be triggered by lowering the solution pH to 5, which leads to protonation of the DPA block and hence rapid micellar dissociation.
This review defines chemotherapeutic engineering as an engineering discipline that applies and further develops chemical engineering principles, techniques and devices for chemotherapy of cancer and other diseases. It provides new challenges as well as new opportunities for chemical engineering. Chemical engineering has substantially changed the human civilization through its services and products to improve the quality of life for human being. It is now time for chemical engineering to contribute to the most important aspect of the quality of life—human health care. Cancer and cardiovascular diseases are the leading causes for deaths. Chemotherapy is one of the most important treatments currently available for cancer and other diseases such as cardiovascular diseases. The present status of chemotherapy is far from being satisfactory. Its efficacy is limited and patients have to suffer from serious side effects, some of which are life-threatening. Chemotherapeutic engineering is emerging to help solving the problems in chemotherapy and to eventually develop an ideal way to conduct chemotherapy with the best efficacy and the least side effects. This review gives, from an engineering point of view, brief introductions to cancer and cancer treatment, chemotherapy and the problems involved in chemotherapy, and the possible roles of chemical engineering in solving the problems involved. Progress in developing various controlled and targeted drug delivery systems is reviewed with an emphasis on nanoparticles of biodegradable polymers and lipid bilayer vesicles (liposomes). Preparation, characterization, in vitro release, cell line experiments and animal testing of drug-loaded polymeric nanoparticles are described with paclitaxel as a prototype drug, which is one of the best anticancer drugs found in nature. A novel drug delivery system, liposomes-in-microspheres, is used as an example for possible combinations of the existing polymer- and lipid-based delivery systems. Research of molecular interactions between the drug and the cell membrane is also reviewed, with the lipid monolayer at the air–water or oil–water interface and bilayer vesicles as models for the cell membrane. Finally, mathematical modeling in chemotherapeutic engineering is discussed with typical examples in the literature. This review is a short introduction of chemotherapeutic engineering to chemical engineers, biomedical engineers, other engineers, clinical oncologists, and pharmaceutical scientists, who are interested in developing new dosage forms of drugs for chemotherapy of cancer and other diseases with the best efficacy and the least side effects.
Delivery of protein drugs is highly challenging due to the low permeability, short circulatory half-life, rapid proteolysis, low stability, and immunogenicity of the protein drugs. Studies using polysaccharide hydrogels to overcome these problems are reviewed. The different approaches are divided into four classes: (1) polysaccharide microspheres; (2) polysaccharide-conjugated protein drugs; (3) polysaccharide matrix in protein drug delivery; and (4) microencapsulation of protein drugs. Polysaccharide hydrogels will be useful in the development of controlled release formulations for protein drugs.
The possibility of using biodegradable polymers as drug carriers was brought to the attention of many scientists when bioresorbable sutures entered the market two decades ago. Since that time, researchers in pharmacy, chemical engineering, and other disciplines have striven to design biodegradable polymers with desired degradation mechanisms and mechanical properties. Biodegradable polymers have advantages over other carrier systems in that they need not be surgically removed when drug delivery is completed and that they can provide direct drug delivery to the systemic circulation. The drug and polymer may be combined in a number of different ways depending upon the application of interest. Microparticulate formulations have the widest applicability to the widest variety of formulation needs: oral delivery, intramuscular injection, subcutaneous injection, and targeted delivery. This review addresses recent work utilizing biodegradable polymers for controlled drug delivery, focusing on micro- and nanoparticulate delivery systems containing poly(lactic acid), poly(glycolic acid) or their copolymers.
Multidrug resistance is a generic term for the variety of strategies that tumor cells develop to evade the cytotoxic effects of anticancer drugs. It is characterized by decreased cellular sensitivity, not only to the drug(s) employed in chemotherapy but also to a broad spectrum of drugs with neither obvious common targets nor structural homology. It is one of the major obstacles to the successful treatment of tumors. This review concentrates on some of the physiological changes observed in drug-sensitive and drug-resistant tumor cell lines that could account for their relative sensitivities to chemotherapeutics. These changes suggest alternative strategies for combating tumor cells in general and multidrug-resistant cells in particular.
This review presents the most outstanding contributions in the field of biodegradable polymeric nanoparticles used as drug delivery systems. Methods of preparation, drug loading and drug release are covered. The most important findings on surface modification methods as well as surface characterization are covered from 1990 through mid-2000.
Previously it has been shown that bioerodible poly (ortho ester) matrices can be synthesised to contain the anticancer drug 5-fluorouracil (5-FU) and, with adjustment of their suberic acid excipient content, designed to produce approximately zero order release of 5-FU in vitro over 15 days. This short study describes the first evaluation of such matrices against a human colorectal carcinoma model in vivo (a LS174T xenograft), colorectal cancer being the ultimate therapeutic target. First, in order to assess the potential general toxicity of the polymer, between one and four drug-free polymer matrices were implanted in the peritoneal cavity of DBA2 mice, and the animals subsequently monitored for 60 days. Following implantation of one to three matrices (a polymer dose equivalent to 8.4 g/kg) animals showed no weight loss, and no overt signs of toxicity. However, implantation of four matrices did produce visible signs of toxicity, even though these animals displayed no significant weight loss. To evaluate their antitumour activity, 5-FU-containing matrices (one to four matrices equivalent to 5-FU doses of 280, 560, 840 and 1120 mg/kg, respectively) were implanted into the peritoneal cavity of nude mice bearing established subcutaneous LS174T xenografts, and the antitumour activity compared with that seen following bolus administration of free 5-FU at a dose of 200 or 500 mg/kg). An increased survival relative to untreated controls was observed following implantation of one, two and three matrices, the values being 122, 178, and 155%, respectively. The animals receiving three 5-FU-containing matrices were eventually withdrawn due to drug toxicity rather than tumour growth, and those receiving four matrices showed very early signs of drug-related toxicity . Although 5-FU did suppress tumour growth, mice treated with free drug showed either no increase in survival (200 mg/kg), or a decreased lifespan due to drug-related toxicity (500 mg/kg). Dose-dependent control of xenograft growth, and prolongation of animal survival was seen following implantation of 5-FU-containing matrices.
Internalization of exogenous macromolecules by live cells provides a powerful approach for studying cellular functions. Understanding the mechanism of transfer from the extracellular milieu to the cytoplasm and nucleus could also contribute to the development of new therapeutic approaches. This article summarizes the unexpected properties of penetratins, a class of peptides with translocating properties and capable of carrying hydrophilic compounds across the plasma membrane. This unique system allows direct targeting of oligopeptides and oligonucleotides to the cytoplasm and nucleus, is non-cell-type specific and highly efficient, and therefore has several applications of potential cell-biology and clinical interest.
New biodegradable polymers with an aromatic ring in the main chain and with aromatic rings in both the main chain and the pendant group were synthesized by the direct polycondensation of L-lactic acid (LA) and aromatic hydroxy acids such as DL-mandelic (MA), p-hydroxybenzoic (HBA), p-hydroxyphenylacetic (HPAA), and p-hydroxyphenylpropionic (HPPA) acids, using polymer systems composed of LA/HBA, LA/HPAA, LA/HPPA, and LA/MA/HPPA, for example. In an LA copolymer, the degree of degradation in vivo markedly decreases with increasing proportion of aromatic hydroxy acid in the system, in which the degradation behavior resulted in either a linear or a parabolic profile according to the kind of copolymer and its composition. In contrast, an S-type degradation pattern was obtained in a ternary polymer system (e.g. poly(LA/MA/HPPA), 80:10:10 mol%). Estramustine was incorporated into the ternary polymer formulation in the form of small cylinders followed by subcutaneous implantation into male rats. The pharmacological effect of drug released in vivo from the formulation was examined by measuring the changes in weight of the accessory sex organs of male rats, the results demonstrating the maintenance of efficacious pharmacological action over a period of approx. 10 weeks.
To obtain liposomes with longer circulation times in vivo, we newly synthetized dipalmitoylphosphatidylpolyglycerol (DPP-PG). A series of DPP-PGs of different chain lengths was used in this study. The individual derivatives were incorporated into distearoylphosphatidylcholine/cholesterol liposomes (1:1, molar ratio). The effectiveness of DPP-PG derivatives was dependent on the amount and degree of polymerization. Low-polymerized PGs such as diglycerol and tetraglycerol needed a high incorporation rate of 8 mol%, while high-polymerized PGs such as octaglycerol required 4 mol%. The incorporation of 6 mol% of DPP-hexaglycerol was most effective in prolonging the circulation time of liposomes.
Sensitive polymers with external physical, chemical, and electrical stimuli are termed as ‘intelligent materials’ and currently have been used in variety fields of engineering, and medicine. Numerous research papers utilizing stimuli-responsive intelligent materials are found in the literature to date. In this manuscript, the authors described several applications of surfaces and interfaces modified with stimuli-responsive polymers for stimuli-responsive surface property alteration and their application for the separation sciences. The special attention is paid to the temperature responsive polymers, poly(N-isopropylacrylamide) (PIPAAm) and its derivatives as surface modifiers for novel ‘green’ chromatography in which only aqueous mobile phase was utilized for separation of bioactive compounds. Several factors were investigated and discussed the effects on separation of bioactive compounds; these include the effects of the temperature-responsive hydrophilic/hydrophobic changes, copolymer composition, graft polymer molecular architecture and the incorporation of charged groups. Furthermore, application of PIPAAm-grafted surfaces for affinity separation of proteins will be discussed. The technique has superior characteristics in reducing organic wastes and costs to run chromatographic separation, and thus must be an environmentally friendly separation tool.