PEGylated lysine dendrimers for tumor-selective targeting after intravenous injection in tumor-bearing mice.

In this study, we synthesized a sixth generation lysine dendrimer (KG6) and two PEGylated derivatives thereof and evaluated their biodistribution characteristics in both normal and tumor-bearing mice. The intact KG6 showed a rapid clearance from the blood stream and non-specific accumulation in the liver and kidney. In contrast, the PEGylated derivatives showed a better retention in blood and low accumulativeness in organs dependent of the rate of PEGylation. In addition, PEGylated KG6 with a high modification rate was accumulated effectively in tumor tissue via the enhanced permeability and retention (EPR) effect. Moreover, we clarified that multiple administrations did not affect the biodistribution characteristics of a second dose of PEGylated KG6. PEGylated lysine dendrimer would be a useful material for a clinically applicable tumor-targeting carrier.     

Long circulation of intravenously administered plasmid DNA delivered with dendritic poly(L-lysine) in the blood flow.

We previously showed that dendritic poly(L-lysine) of the 6th generation (KG6) had high transfection ability without significant cytotoxicity in vitro. Here, to evaluate the potential of KG6 as a nonviral gene carrier that works in vivo, we investigated the biodistribution of plasmid DNA delivered with KG6 in mice after intravenous administration, in comparison with DOTAP/Chol liposomes and PEI. Southern blotting analysis revealed that plasmid DNA complexes with KG6 at a C/A ratio of 8.0 circulated in the blood for 3 h after intravenous injection. The amounts of plasmid DNA in the liver gradually decreased. In tumor-bearing mice, plasmid DNA injected with KG6 was observed in the tumor at 60 min after the intravenous injection, while no DNA was present in the tumor using DOTAP/Chol liposomes. The stealth character of DNA complexes with KG6 in the blood would cause an enhanced permeability and retention (EPR) effect in the tumor. KG6 is expected to be a promising candidate that enables functional gene delivery in vivo.     

Dendrimers: relationship between structure and biocompatibility in vitro, and preliminary studies on the biodistribution of 125I-labelled polyamidoamine dendrimers in vivo.

Dendrimers are highly branched macromolecules of low polydispersity that provide many exciting opportunities for design of novel drug-carriers, gene delivery systems and imaging agents. They hold promise in tissue targeting applications, controlled drug release and moreover, their interesting nanoscopic architecture might allow easier passage across biological barriers by transcytosis. However, from the vast array of structures currently emerging from synthetic chemistry it is essential to design molecules that have real potential for in vivo biological use. Here, polyamidoamine (PAMAM, Starburst), poly(propyleneimine) with either diaminobutane or diaminoethane as core, and poly(ethylene oxide) (PEO) grafted carbosilane (CSi-PEO) dendrimers were used to study systematically the effect of dendrimer generation and surface functionality on biological properties in vitro. Generally, dendrimers bearing -NH(2) termini displayed concentration- and in the case of PAMAM dendrimers generation-dependent haemolysis, and changes in red cell morphology were observed after 1 h even at low concentrations (10 microg/ml). At concentrations below 1 mg/ml CSi-PEO dendrimers and those dendrimers with carboxylate (COONa) terminal groups were neither haemolytic nor cytotoxic towards a panel of cell lines in vitro. In general, cationic dendrimers were cytotoxic (72 h incubation), displaying IC(50) values=50-300 microg/ml dependent on dendrimer-type, cell-type and generation. Preliminary studies with polyether dendrimers prepared by the convergent route showed that dendrimers with carboxylate and malonate surfaces were not haemolytic at 1 h, but after 24 h, unlike anionic PAMAM dendrimers they were lytic. Cationic 125I-labelled PAMAM dendrimers (gen 3 and 4) administered intravenously (i.v.) to Wistar rats ( approximately 10 microg/ml) were cleared rapidly from the circulation (<2% recovered dose in blood at 1 h). Anionic PAMAM dendrimers (gen 2.5, 3.5 and 5.5) showed longer circulation times ( approximately 20-40% recovered dose in blood at 1 h) with generation-dependent clearance rates; lower generations circulated longer. For both anionic and cationic species blood levels at 1 h correlated with the extent of liver capture observed (30-90% recovered dose at 1 h). 125I-Labelled PAMAM dendrimers injected intraperitoneally were transferred to the bloodstream within an hour and their subsequent biodistribution mirrored that seen following i.v. injection. Inherent toxicity would suggest it unlikely that higher generation cationic dendrimers will be suitable for parenteral administration, especially if they are to be used at a high dose. In addition it is clear that dendrimer structure must also be carefully tailored to avoid rapid hepatic uptake if targeting elsewhere (e.g. tumour targeting) is a primary objective.     

Stealth PEGylated polycyanoacrylate nanoparticles for intravenous administration and splenic targeting.

The aim of the present work was to investigate the biodistribution characteristics of PEG-coated polycyanoacrylate nanoparticles prepared by the nanoprecipitation/solvent diffusion method using the previously synthesized poly(MePEGcyanoacrylate-hexadecylcyanoacrylate) copolymer. It was observed that [14C]-radiolabeled PEGylated nanoparticles remained for a longer time in the blood circulation after intravenous administration to mice, compared to the non-PEGylated poly(hexadecylcyanoacrylate) (PHDCA) nanoparticles. Furthermore, hepatic accumulation was dramatically reduced, whereas a highly increased spleen uptake was shown. The PEGylation degree of the polymer seemed not to affect the in vivo behavior of the nanoparticles, whereas previously obtained in vitro data have shown a modification of plasma protein adsorption depending on the density of PEG at the surface of the particles. Moreover, the study of the in vitro cytotoxicity of the nanoparticles revealed that the PEGylation of the cyanoacrylate polymer reduced its toxicity. These results open up interesting perspectives for the targeting of drugs to other tissues than the liver.     

Synthesis and characterization of guanidinylated poly(propylene imine) dendrimers as gene transfection agents.

Fourth generation poly(propylene imine) dendrimer has been completely or partially functionalized with guanidinium groups. In the second case, the remaining toxic primary amino groups of the dendrimers were reacted with propylene oxide affording the corresponding hydroxylated derivatives. Five derivatives have been prepared bearing 0, 6, 12, 24 or 32 guanidinium groups. These guanidinylated dendrimers were interacted with plasmid DNA affording the corresponding dendriplexes. The complexes were physicochemically characterized by dynamic light scattering, zeta-potential measurements and AFM, while the extent of complexation was evaluated by agarose gel electrophoresis. Furthermore, their transfection efficiency was assessed employing HEK 293 and COS-7 cell lines, while the serum effect was studied in HEK 293 cells. It was found that complete replacement of primary amino groups with the hydroxylated moieties resulted in complete loss of transfection efficiency. On the contrary, guanidinylation of the parent dendrimer resulted to significant enhancement of its transfection efficiency, this enhancement being dependent on the number of guanidinium groups per dendrimer, the cell line used and the presence or absence of FBS. The fully guanidinylated dendrimer exhibited the best transfection efficiency under all the conditions studied. This efficiency has been attributed to the enhanced penetrating ability of the guanidinylated dendrimers due to the accumulation of the guanidinium group at the dendrimeric surface. It was also found that the derivative with 12 guanidinium groups exhibited the lowest toxicity. The reduction of toxicity was apparently attributed to the decrease of the external primary amino groups coupled with the presence of hydroxylated moieties located at the dendrimeric surface. The functionalization strategy employed leads to dendrimeric derivatives that combine satisfactory transfection efficiency and cytotoxicity.     

Cisplatin delivery from poly(acrylic acid-co-methyl methacrylate) microparticles.

To develop a platform for tumor chemotherapy, poly(acrylic acid-co-methyl methacrylate) microparticles have been synthesized. Carboxylate containing monomers were included to complex therapeutic agents, specifically cisplatin. Microparticles were prepared by free radical emulsion polymerization in aqueous media. Particle diameter, zeta-potential, in vitro cytotoxicity, and in vivo acute toxicity were characterized for both cisplatin-loaded microparticles and unloaded microparticles. In vitro cytotoxicity and FT-IR were used to characterize cisplatin released from cisplatin-loaded microparticles. Acrylic acid feed mole fraction determined several key microparticle properties, including particle size, zeta-potential, and yield. A burst release of cisplatin (40%) in the first day was followed by a zero-order release phase. The interaction between cisplatin and microparticles allowed approximately 20% additional cisplatin release in the next five days. Cisplatin-loaded and unloaded microparticles are non-toxic (LC50>15 mM) to the cell line used in in vitro tests. Cisplatin released from cisplatin-loaded microparticles retained activity, but that activity was slightly lower than freshly prepared cisplatin. Other than a slight reduction in cisplatin activity, microparticles exhibited low in vivo acute toxicity (LD50>170 mg/kg), which suggests that this hydrogel particulate system and the hydrogel complexation mechanism should further be studied for drug delivery.     

Transepithelial transport of poly(amidoamine) dendrimers across Caco-2 cell monolayers.

The objective of this study was to investigate the influence of physiochemical parameters (such as size, molecular weight, molecular geometry, and number of surface amine groups) of poly (amidoamine) (PAMAM) dendrimers, on their permeability across Caco-2 cell monolayers. The permeability of a series of PAMAM dendrimers, generations 0-4 (G0-G4), was investigated across Caco-2 cell monolayers in both the apical to basolateral (AB) and basolateral to apical (BA) directions. The influence of PAMAM dendrimers on the integrity, paracellular permeability, and viability of Caco-2 cell monolayers was also monitored by measuring the transepithelial electrical resistance (TEER), mannitol permeability, and leakage of lactate dehydrogenase (LDH) enzyme, respectively. G0, G1 and G2 demonstrated similar AB permeabilities, which were moderate several fold higher than the AB permeability of higher generations. The AB and BA permeability of G0-G4 typically increased with the increase in donor concentration and incubation time. Permeability values are not reported at generations, concentrations or incubation times that the dendrimers were toxic to Caco-2 cells. TEER values decreased and mannitol permeability increased as a function of donor concentration, incubation time, and generation number. LDH results for G3 and G4 indicate that Caco-2 cell viability was reduced with increasing donor concentration, incubation time, and generation number. The appreciable permeability of G0-G2, coupled with their nontoxic effects on Caco-2 cells, suggest their potential as water-soluble polymeric drug carriers for controlled oral drug delivery.     

Effect of the physicochemical properties of initially injected liposomes on the clearance of subsequently injected PEGylated liposomes in mice.

Using mice as a model, we recently reported that the long-circulating properties of polyethylene glycol (PEG) (M.W. 2000)-modified liposomes (mPEG(2000)-liposomes) disappeared when they were intravenously injected at certain intervals [referred to as the "accelerated blood clearance (ABC) phenomenon"]. Herein, we report on a study of issue of whether physicochemical properties of a prior dose of liposomes such as degree of PEGylation, PEG chain length, lipid dose, surface charge, size, play a role in inducing this phenomenon. The injection of conventional liposomes (without a PEG-coating) significantly induced the phenomenon. The PEGylation of conventional liposomes attenuated the induction of the phenomenon somewhat with increasing molar content of PEG derivative and PEG chain length. These findings clearly suggest that the PEGylation of liposomes are not the major cause of the ABC phenomenon but, rather, played a role in preventing it. In addition, increasing the lipid dose in a prior dose of mPEG(2000)-liposomes (0-25 micromol/kg) increased the induction of the phenomenon in a sigmoid manner. The surface charge and size of the liposomes were not critical for the induction of the phenomenon, although generally these serve as determinants in the biodistribution of liposomes. The results reported here clearly indicate that the physicochemical properties of a prior dose of liposomes strongly affect the pharmacokinetic behavior of a subsequent injection of mPEG(2000)-liposomes: The extent of PEGylation and the lipid dose had an effect, but the surface charge and size did not. The results reported herein have a considerable impact on the design and engineering of liposomal formulations for use in multiple drug therapy as well as in therapy that involves the use of liposomal drugs.     

Effects of ethylene glycol-based graft, star-shaped, and dendritic polymers on solubilization and controlled release of paclitaxel.

New methods and pharmaceutical compositions were developed to increase the aqueous solubility of paclitaxel (PTX), a poorly water-soluble drug. Graft and star-shaped graft polymers consisting of poly(ethylene glycol) (PEG400) graft chains increased the PTX solubility in water by three orders of magnitude. Polyglycerol dendrimers (dendriPGs) dissolved in water at high concentrations without significantly increasing the viscosity and, at 80 wt.%, were found to increase the solubility of PTX 10,000-fold. The solubilized PTX was released from graft polymers, star-shaped graft polymers, and the dendriPGs into the surrounding aqueous solution. The release rate was a function of the star shape and the dendrimer generation. The availability of the new graft, star and dendritic polymers having ethylene glycol units should permit development of novel delivery systems for other poorly water-soluble drugs.     

Dendritic PARACEST contrast agents for magnetic resonance imaging

MRI contrast agents based on chemical exchange‐dependent saturation transfer (CEST), such as Yb(III)DOTAM complexes, are highly suitable for pH mapping. In this paper, the synthesis of Yb(III)DOTAM‐functionalized poly(propylene imine) dendrimers is described. The applicability of these dendritic PARACEST MRI agents for pH mapping has been evaluated on a 7 T NMR spectrometer and on a 3 T clinical MRI scanner. As expected, based on the different numbers of exchangeable amide protons, the lowest detectable concentration of the first and third generation dendritic PARACEST agents is by a respective factor of about 4 and 16 lower than that of a mononuclear reference complex. The pH dependence of the CEST effect observed for these compounds depends on the generation of the poly(propylene imine) dendrimer. Upon going to higher generations of the Yb(III)DOTAM‐terminated dendrimer, a shift of the maximum CEST effect towards lower pH values was observed. This allows for a fine‐tuning of the responsive pH region by varying the dendritic framework. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface-Engineered Dendrimeric Nanoconjugates for Macrophage-Targeted Delivery of Amphotericin B: Formulation Development and In Vitro and In Vivo Evaluation

The present study aimed to develop an optimized dendrimeric delivery system for amphotericin B (AmB). Fifth-generation (5.0G) poly(propylene imine) (PPI) dendrimers were synthesized, conjugated with mannose, and characterized by use of various analytical techniques, including Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (¹H-NMR) spectroscopic analysis, and atomic force microscopy (AFM). Mannose-conjugated 5.0G PPI (MPPI) dendrimers were loaded with AmB and evaluated for drug loading efficiency, in vitro drug release profile, stability, hemolytic toxicity to human erythrocytes, cytotoxicity to and cell uptake by J774A.1 macrophage cells, antiparasitic activity against intracellular Leishmania donovani amastigotes, in vivo pharmacokinetic and biodistribution profiles, drug localization index, toxicity, and antileishmanial activity. AFM showed the nanometric size of the MPPI dendrimers, with a nearly globular architecture. The conjugate showed a good entrapment efficiency for AmB, along with pH-sensitive drug release. Highly significant reductions in toxicity toward human erythrocytes and macrophage cells, without compromising the antiparasitic activity of AmB, were observed. The dendrimeric formulation of AmB showed a significant enhancement of the parasiticidal activity of AmB toward intramacrophagic L. donovani amastigotes. In the in vitro cell uptake studies, the formulation showed selectivity toward macrophages, with significant intracellular uptake. Further pharmacokinetic and organ distribution studies elucidated the controlled delivery behavior of the formulation. The drug localization index was found to increase significantly in macrophage-rich organs. In vivo studies showed a biocompatible behavior of MPPIA, with negligible toxicity even at higher doses, and promising antileishmanial activity. From the results, we concluded that surface-engineered dendrimers may serve as optimized delivery vehicles for AmB with enhanced activity and low or negligible toxicity.     

Dendritic systems for drug delivery applications

Dendrimers are synthetic, highly branched and nanometer-sized macromolecules that offer potential application to various fields. They have uniform size and molecular weight, wide internal cavity and modifiable surface functionality that made them very attractive for biological and drug delivery applications. Commercially available PAMAM (polyamidoamine) dendrimers are most frequently used for construction of delivery system by modification of surface amino groups. One of the examples is anticancer drug-PAMAM conjugate with folic acid (FA) for targeting. DNA linked FA-PAMAM and FITC-PAMAM conjugates have been recently developed. Polyester dendrimers are expected to be biodegradable and less toxic to cells. An example is shown. Lastly, construction of a delivery system using caged compounds for photochemical release of drug is described.     

Peptide dendrimers as efficient and biocompatible gene delivery vectors: Synthesis and in vitro characterization

We report the synthesis and characterization of different generations of dendritic poly(l-lysine) vectors, and their use for in vitro gene transfection. Gel retardation assay revealed that the dendrimers could form complexes with plasmid DNAs (pDNAs), evident from the inhibition of the migration of pDNA at the N/P ratios of 0.5, 1 and 2 by G3, G4 and G5 dendritic generations, respectively. DNase I assay revealed the protection of pDNA acquired from the complexation with dendrimers from nuclease-catalyzed degradation, with the protection capacity of G5 being even stronger than poly(ethyleneimine) (PEI). Atomic force microscopy (AFM) revealed that all 4 generations of dendrimer/DNA complexes studied were of similar particle sizes within 100-200 nm. Zeta potential measurements showed that as the N/P ratio increased from 1 to 25, all dendrimer/pDNA complexes gradually changed from negative to positive charges. The higher generations tended to produce the greater positive potentials, indicating a stronger potency of the complexes to interact with negatively charged cell membranes. In vitro and in vivo cytotoxicity evaluations showed good biocompatibility of the dendrimers and their complexes over the different N/P ratios studied. In vitro gene transfection revealed higher efficiency of G5 than other dendrimers and insensitive variation to the presence of serum. Given its similar transfection efficiency to PEI but lower toxicity to cultured cells, dendrimer G5 could be a better candidate for gene delivery.     

Factors controlling the pharmacokinetics,biodistribution and intratumoral penetration of nanoparticles

Nanoparticle drug delivery to the tumor is impacted by multiple factors: nanoparticles must evade clearance by renal filtration and the reticuloendothelial system, extravasate through the enlarged endothelial gaps in tumors, penetrate through dense stroma in the tumor microenvironment to reach the tumor cells, remain in the tumor tissue for a prolonged period of time, and finally release the active agent to induce pharmacological effect. The physicochemical properties of nanoparticles such as size, shape, surface charge, surface chemistry (PEGylation, ligand conjugation) and composition affect the pharmacokinetics, biodistribution, intratumoral penetration and tumor bioavailability. On the other hand, tumor biology (blood flow, perfusion, permeability, interstitial fluid pressure and stroma content) and patient characteristics (age, gender, tumor type, tumor location, body composition and prior treatments) also have impact on drug delivery by nanoparticles. It is now believed that both nanoparticles and the tumor microenvironment have to be optimized or adjusted for optimal delivery. This review provides a comprehensive summary of how these nanoparticle and biological factors impact nanoparticle delivery to tumors, with discussion on how the tumor microenvironment can be adjusted and how patients can be stratified by imaging methods to receive the maximal benefit of nanomedicine. Perspectives and future directions are also provided.     

Preparation of a novel PEG-clay hybrid as a DDS material: dispersion stability and sustained release profiles.

An advanced hybrid drug carrier has been developed using porous nanocrystals of a swelling clay mineral conjugated with a block copolymer containing poly(ethylene glycol) and polyamine segments. Synthetic hectorite (Laponite) modified with (alpha-acetal-poly(ethylene glycol)-block-[poly(2-(N,N-dimethylamino) ethyl methacrylate)] (Acetal-PEG-b-PAMA) produced a homogeneous dispersion of organic-inorganic hybrid in an aqueous solution, which showed flocculation-resistive properties with an elevated ionic strength. The zeta-potential measurement revealed that nonionic PEG brush layers are formed on the surface of the clay nanocrystals since negative charge of the clay surface was completely neutralized by the positive charge of the cationic PAMA segment and the entire surface charge is successfully shielded by the effect of nonionic PEG segment in the block copolymer. This charge neutralization is in good agreement with the dispersion stability in solutions of high ionic strength. The average particle size of the PEG-modified hybrid particle was estimated to be 120 nm by a dynamic light scattering (DLS) method. When pyrene was used as the model compound of hydrophobic drug, it was incorporated into the nanopore in the clay mineral without showing any remarkable expansion of the basal spacings. Fluorescence spectra and powder X-ray diffraction patterns demonstrated that pyrene molecules are captured in an amorphous state in the range of low pyrene content (<5%), while excimer formation was seen at the higher pyrene concentration (>5%). The PEG-clay hybrid act as a carrier for sustained release of hydrophobic substances due to the high affinity (K = 1.52 x 10(4)) between the drug and clay surface.     

Efficient modification of PAMAM G1 dendrimer surface with β-cyclodextrin units by CuAAC: impact on the water solubility and cytotoxicity

The toxicity of the poly(amidoamine) dendrimers (PAMAM) caused by the peripheral amino groups has been a limitation for their use as drug carriers in clinical applications. In this work, we completely modified the periphery of PAMAM dendrimer generation 1 (PAMAM G1) with β-cyclodextrin (β-CD) units through the Cu(i)-catalyzed azide–alkyne cycloaddition (CuAAC) to obtain the PAMAM G1-β-CD dendrimer with high yield. The PAMAM G1-β-CD was characterized by ¹H- and ¹³C-NMR and mass spectrometry studies. Moreover, the PAMAM G1-β-CD dendrimer showed remarkably higher water solubility than native β-CD. Finally, we studied the toxicity of PAMAM G1-β-CD dendrimer in four different cell lines, human breast cancer cells (MCF-7 and MDA-MB-231), human cervical adenocarcinoma cancer cells (HeLa) and pig kidney epithelial cells (LLC-PK1). The PAMAM G1-β-CD dendrimer did not present any cytotoxicity in cell lines tested which shows the potentiality of this new class of dendrimers.

The toxicity of the poly(amidoamine) dendrimers (PAMAM) caused by the peripheral amino groups has been a limitation for their use as drug carriers in clinical applications.     

State of the art in PEGylation: the great versatility achieved after forty years of research

In the recent years, protein PEGylation has become an established and highly refined technology by moving forward from initial simple random coupling approaches based on conjugation at the level of lysine ε-amino group. Nevertheless, amino PEGylation is still yielding important conjugates, currently in clinical practice, where the degree of homogeneity was improved by optimizing the reaction conditions and implementing the purification processes. However, the current research is mainly focused on methods of site-selective PEGylation that allow the obtainment of a single isomer, thus highly increasing the degree of homogeneity and the preservation of bioactivity. Protein N-terminus and free cysteines were the first sites exploited for selective PEGylation but currently further positions can be addressed thanks to approaches like bridging PEGylation (disulphide bridges), enzymatic PEGylation (glutamines and C-terminus) and glycoPEGylation (sites of O- and N-glycosylation or the glycans of a glycoprotein). Furthermore, by combining the tools of genetic engineering with specific PEGylation approaches, the polymer can be basically coupled at any position on the protein surface, owing to the substitution of a properly chosen amino acid in the sequence with a natural or unnatural amino acid bearing an orthogonal reactive group. On the other hand, PEGylation has not achieved the same success in the delivery of small drugs, despite the large interest and several studies in this field. Targeted conjugates and PEGs for combination therapy might represent the promising answers for the so far unmet needs of PEG as carrier of small drugs. This review presents a thorough panorama of recent advances in the field of PEGylation.     

Synthesis and characterization of branched poly(L-glutamic acid) as a biodegradable drug carrier.

Polymeric drug delivery systems are used not only to improve aqueous solubility of drug molecules but also to achieve desirable pharmacokinetics and an enhanced therapeutic index. New biodegradable polymers are needed to improve the biodistribution and targeting-ability of polymeric carriers. In this study, the synthesis and characterization of branched poly(L-glutamic acid) (PG) containing multiple PG chains centered on a poly(amidoamine) (PAMAM) dendrimer or polyethyleneimine (PEI) cores were described. The branched PG polymers were obtained by ring-opening polymerization of benzyl ester of L-glutamic acid N-carboxyanhydride using PAMAM or PEI as the initiator. These polymers were degradable in the presence of the lysosomal enzyme cathepsin B, albeit more slowly than linear PG. Unlike conventional linear PG, each branched PG possessed multiple terminal amino groups. This made it possible to attach multiple targeting moieties selectively to the termini of branched PG. Conjugation of monofunctional or heterodifunctional polyethylene glycol to the chain ends of branched PG was demonstrated in the presence of side chain carboxyl groups. Furthermore, folic acid, a model targeting moiety, and the near-infrared dye indocyanine green, a model diagnostic agent, were successfully conjugated to the terminal amino groups and the side chain carboxyl groups of branched PG, respectively. The resulting conjugate had reduced nonspecific interaction and bound selectively to tumor cells expressing folate receptors. Thus, branched PG may be useful as a polymeric carrier for targeted drug delivery.     

PEGylation of HPMA-based block copolymers enhances tumor accumulation in vivo: A quantitative study using radiolabeling and positron emission tomography

This paper reports the body distribution of block copolymers (made by controlled radical polymerization) with N-(2-hydroxypropyl)methacrylamide (HPMA) as hydrophilic block and lauryl methacrylate (LMA) as hydrophobic block. They form micellar aggregates in aqueous solution. For this study the hydrophilic/hydrophobic balance was varied by incorporation of differing amounts of poly(ethylene glycol) (PEG) side chains into the hydrophilic block, while keeping the degree of polymerization of both blocks constant. PEGylation reduced the size of the micellar aggregates (R_h = 113 to 38 nm) and led to a minimum size of 7% PEG side chains. Polymers were labeled with the positron emitter ¹⁸F, which enables to monitor their biodistribution pattern for up to 4 h with high spatial resolution. These block copolymers were investigated in Sprague–Dawley rats bearing the Walker 256 mammary carcinoma in vivo. Organ/tumor uptake was quantified by ex vivo biodistribution as well as small animal positron emission tomography (PET).     

Camptothecin derivative-loaded poly(caprolactone-co-lactide)-b-PEG-b-poly(caprolactone-co-lactide) nanoparticles and their biodistribution in mice.

Triblock copolymers of poly(caprolactone-co-lactide)-b-PEG-b-poly(caprolactone-co-lactide) (PCLLA-PEG-PCLLA) were synthesized by ring opening copolymerization of caprolactone and lactide in the presence of poly(ethylene glycol) (PEG). With such triblock copolymers, PCLLA-PEG-PCLLA nanoparticles entrapping 10-hydroxycamptothecin-10,20-diisobutyl dicarbonate (HCPT-1), a derivative of the antitumor drug 10-hydroxycamptothecin (HCPT), were prepared by nano-precipitation method and characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The investigations on drug loading, in vitro release and body distribution in mice after intravenous (i.v.) administration were also carried out. It is found that the obtained nanoparticles showed smooth surface and spherical shape with the controllable size in the range of 70-180 nm, and drug loading content varied from 3.3% to 7.0% depending on the copolymer composition and preparation conditions. The in vitro release behavior exhibited a sustaining release manner and was affected by particle size as well as copolymer composition. The results of body distribution study in mice show that the blood concentration of HCPT-1 could be maintained for a long period and the tissue distribution was influenced by the particle size to some extent. These results suggest that the PCLLA-PEG-PCLLA nanoparticles seem to be a promising delivery system for poorly soluble antitumor drugs or their derivatives.