Biodistribution properties of nanoparticles based on mixtures of PLGA with PLGA-PEG diblock copolymers.

The basic characteristics and the biodistribution properties of nanoparticles prepared from mixtures of poly(lactide-co-glycolide) (PLGA) with poly(lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) copolymers were investigated. A PLGA(45)-PEG(5) copolymer of relatively low PEG content and a PLGA(5)-PEG(5) copolymer of relatively high PEG content were included in the study. Increasing the PLGA-PEG content of the PLGA/PLGA-PEG mixture, or when PLGA(45)-PEG(5) was replaced by PLGA(5)-PEG(5), a decrease in the size of the nanoparticles and an increase in the rate of PEG loss from the nanoparticles were observed. The blood residence of the PLGA/PLGA(45)-PEG(5) nanoparticles increased as their PLGA-PEG content was increased, reaching maximum blood longevity at 100% PLGA(45)-PEG(5). On the contrary, the blood residence of PLGA/PLGA(5)-PEG(5) nanoparticles exhibited a plateau maximum in the range of 80-100% PLGA(5)-PEG(5). At PLGA-PEG proportions lower than 80%, the PLGA/PLGA(45)-PEG(5) nanoparticles exhibited lower blood residence than the PLGA/PLGA(5)-PEG(5) nanoparticles, whereas at PLGA-PEG proportions higher than 80%, the PLGA/PLGA(45)-PEG(5) nanoparticles exhibited higher blood residence than the PLGA/PLGA(5)-PEG(5) nanoparticles. These findings indicate that apart from the surface PEG content, the biodistribution properties of the PLGA/PLGA-PEG nanoparticles are also influenced by the size of the nanoparticles and the rate of PEG loss from the nanoparticles.

Immune responses in mice of beta-galactosidase adsorbed or encapsulated in poly(lactic acid) and poly(lactic-co-glycolic acid) microspheres.

The immune response induced in mice by beta-galactosidase (beta-gal) adsorbed or encapsulated on poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) microspheres was investigated. The encapsulated protein elicited higher antibody response than the protein adsorbed on the microspheres in the case of the PLA microspheres. However, the encapsulated protein elicited weaker antibody response than the adsorbed protein in the case of the PLGA (50:50) microspheres, probably because, in this case, the encapsulation process adversely affected protein immunogenicity. In the case of adsorbed beta-gal, higher antibody response was obtained with the PLA microspheres than with the PLGA (50:50) microspheres. This may be related to the lower rate of beta-gal desorption from the PLA microspheres. Based on the immunoglobulin G1/immunoglobulin G2a ratios and the stimulation indices for interferon-gamma and interleukin-4, beta-gal encapsulated or adsorbed on PLA microspheres induced a Th(1)-biased immune response whereas beta-gal encapsulated or adsorbed on PLGA (50:50) microspheres induced a Th(2)-biased immune response. The results obtained indicate that more potent immune responses are obtained when the protein is encapsulated than adsorbed on the microspheres, providing that the encapsulation process does not adversely affect protein immunogenicity. Also, the type of polymer used to prepare the microspheres, but not the method of protein association with the microspheres, may affect the type of immune response.

PLA and PLGA microspheres of beta-galactosidase: Effect of formulation factors on protein antigenicity and immunogenicity.

The entrapment of beta-galactosidase (Escherichia coli) in PLA and PLGA microspheres using a double emulsion technique resulted to significant reduction of protein antigenicity. The extent of antigenicity loss depended on the conditions of microsphere preparation. Most of antigenicity loss occurred on the first emulsification step. Only the effects of microsphere preparation factors having an important influence on protein antigenicity, such as the type of organic phase (polymer solvent) and homogenization, could be predicted (on a qualitative basis) by antigenicity data obtained after the first emulsification step. The type of polymer and polymer solvent used to prepare the microspheres affected beta-galactosidase immunogenicity. The PLA microspheres prepared using ethyl acetate was the most immunogenic microsphere formulation, eliciting similar total antibody responses as the alum formulation of beta-gal. This formulation was the only microsphere formulation that induced an IgG1/IgG2a ratio lower than 1, indicating an immune response biased towards a Th1 type. The results obtained indicate that large protein molecules with complex tertiary structure such as beta-galactosidase can be entrapped in PLA and PLGA microspheres with retention of protein immunogenic potential, providing that appropriate conditions of microsphere preparation are applied, and that the formulation of microspheres might influence the Th1/Th2 type of immune response against the encapsulated antigen.

Effect of copolymer composition on the physicochemical characteristics, in vitro stability, and biodistribution of PLGA-mPEG nanoparticles.

The physicochemical properties, the colloidal stability in vitro and the biodistribution properties in mice of different PLGA-mPEG nanoparticle compositions were investigated. The nanoparticles were prepared by a precipitation-solvent evaporation technique. The physical characteristics and the colloidal stability of the PLGA-mPEG nanoparticles were significantly influenced by the composition of the PLGA-mPEG copolymer used to prepare the nanoparticles. PLGA-mPEG nanoparticles prepared from copolymers having relatively high mPEG/PLGA ratios were smaller and less stable than those prepared from copolymers having relatively low mPEG/PLGA ratios. All PLGA-mPEG nanoparticle compositions exhibited prolonged residence in blood, compared to the conventional PLGA nanoparticles. The composition of the PLGA-mPEG copolymer affected significantly the blood residence time and the biodistribution of the PLGA-mPEG nanoparticles in liver, spleen and bones. The in vivo behavior of the different PLGA-mPEG nanoparticle compositions did not appear to correlate with their in vitro stability. Optimum mPEG/PLGA ratios appeared to exist leading to long blood circulation times of the PLGA-mPEG nanoparticles. This may be associated with the effects of the mPEG/PLGA ratio on the density of PEG on the surface of the nanoparticles and on the size of the nanoparticles.

PLGA-mPEG nanoparticles of cisplatin: in vitro nanoparticle degradation, in vitro drug release and in vivo drug residence in blood properties.

The in vitro nanoparticle degradation, in vitro drug release and in vivo drug residence in blood properties of PLGA-mPEG nanoparticles of cisplatin were investigated. The nanoparticles were prepared by a double emulsion method and characterized with regard to their morphology, size, zeta potential and drug loading. The rate of in vitro degradation of the PLGA-mPEG nanoparticles in PBS (pH 7.4) depended on their composition, increasing when the mPEG content (mPEG:PLGA ratio) of the nanoparticles increased. Sustained cisplatin release over several hours from the PLGA-mPEG nanoparticles in vitro (PBS) was observed. The composition of the nanoparticles affected drug release: the rate of release increased when the mPEG content of the nanoparticles increased. Within the range of drug loadings investigated, the drug loading of the nanoparticles did not have any significant effect on drug release. The loading efficiency was low and needs improvement in order to obtain PLGA-mPEG nanoparticles with a satisfactory cisplatin content for therapeutic application. The i.v. administration of PLGA-mPEG nanoparticles of cisplatin in BALB/c mice resulted in prolonged cisplatin residence in systemic blood circulation. The results appear to justify further investigation of the suitability of the PLGA-mPEG nanoparticles for the controlled i.v. delivery and/or targeting of cisplatin.

Effect of dose on the biodistribution and pharmacokinetics of PLGA and PLGA-mPEG nanoparticles.

The effect of nanoparticle dose on the biodistribution and pharmacokinetics of conventional PLGA and stealth poly(Lactide-co-glycolide)-monomethoxypoly(ethyleneglycol) (PLGA-mPEG) nanoparticles was investigated. The precipitation-solvent diffusion method was used to prepare PLGA and PLGA-mPEG nanoparticles labeled with 125I-cholesterylaniline. These were administered intravenously (i.v.) in mice and at predetermined time intervals the animals were sacrificed and their tissues were excised and assayed for radioactivity. Within the dose range applied in this study, blood clearance and mononuclear phagocyte system (MPS) uptake of the PLGA nanoparticles depended on dose whereas they were independent of dose in the case of the PLGA-mPEG nanoparticles. Increasing the dose, decreased the rates of blood clearance and MPS uptake of the PLGA nanoparticles, indicating a certain degree of MPS saturation at higher doses of PLGA nanoparticles. The dose affected the distribution of PLGA nanoparticles between blood and MPS (liver) but it did not affect the nanoparticle levels in the other tissues. Within the range of doses applied here, the PLGA nanoparticles followed non-linear and dose-dependent pharmacokinetics whereas the PLGA-mPEG nanoparticles followed linear and dose-independent pharmacokinetics. In addition to the prolonged blood residence, the dosage-independence of the pharmacokinetics of the PLGA-mPEG nanoparticles would provide further advantages for their application in controlled drug delivery and in drug targeting.

Effect of preparative variables on the properties of poly(dl-lactide-co-glycolide)-methoxypoly(ethyleneglycol) copolymers related to their application in controlled drug delivery.

The effect of certain preparative variables, such as the composition of the feed, the reaction time and the reaction temperature, on the properties of prepared poly(dl-lactide-co-glycolide)-methoxypoly(ethyleneg lycol) (PLGA-mPEG) copolymers and on the yield of the reaction was investigated. The results with regard the molecular weight and yield were discussed in relation to a polymerization mechanism proposed recently (Du et al., 1995. Macromolecules 28, 2124-2132). The higher the PEG content of the feed the lower the molecular weight of the copolymer and the yield of the reaction. The breadth of the molecular weight distribution decreased initially with time, but appeared to stabilize later at low values. Both the ethylene oxide content and the lactide to glycolide molar ratio in the copolymer depended on the reaction temperature and varied with the reaction time. PLGA and mPEG appeared to be partially miscible, and copolymers containing approximately 40% mol or higher ethylene oxide exhibited crystallinity.