In Vitro/in Vivo Correlation for14C-Methylated Lysozyme Release from Poly(Ether-Ester) Microspheres

Impact of IGF-I release kinetics on bone healing: a preliminary study in sheep

Spatiotemporal release of growth factors from a delivery device can profoundly affect the efficacy of bone growth induction. Here, we report on a delivery platform based on the encapsulation of insulin-like growth factor I (IGF-I) in different poly(D,L-lactide) (PLA) and poly(D,L-lactide-co-glycolide) (PLGA) microsphere (MS) formulations to control IGF-I release kinetics. In vitro IGF-I release profiles generally exhibited an initial burst (14-36% of total IGF-I content), which was followed by a more or less pronounced dormant phase with little release (2 to 34 days), and finally, a third phase of re-increased IGF-I release. The osteoinductive potential of these different IGF-I PL(G)A MS formulations was tested in studies using 8-mm metaphyseal drill hole bone defects in sheep. Histomorphometric analysis at 3 and 6 weeks after surgery showed that new bone formation was improved in the defects locally treated with IGF-I PL(G)A MS (n=5) as compared to defects filled with IGF-I-free PL(G)A MS (n=4). The extent of new bone formation was affected by the particular release kinetics, although a definitive relationship was not evident. Local administration of IGF-I resulted in down-regulation of inflammatory marker genes in all IGF-I treated defects. The over-expression of growth factor genes in response to IGF-I delivery was restricted to formulations that produced osteogenic responses. These experiments demonstrate the osteoinductive potential of sustained IGF-I delivery and show the importance of delivery kinetics for successful IGF-I-based therapies.

Development of meloxicam in situ implant formulation by quality by design principle

OBJECTIVE

The focus of this study was to develop and optimize in situ implant formulation of meloxicam by quality by design (QbD) principle for long-term management of musculoskeletal inflammatory disorders.

METHODS

The formulation was optimized by Box-Behnken design with polylactide-co-glycolide (PLGA) level (X1), N-methyl pyrrolidone level (X2) and PLGA intrinsic viscosity (X3) as the independent variables and initial burst release of drug (Y1), cumulative release (Y2), and dissolution efficiency (Y3) as the dependent variables. The formulation was physicochemically characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (PXRD). Pharmacokinetic studies of the optimized formulation were performed on Sprague-Dawley rats.

RESULTS

Y1 was significantly affected by X2 and X3. Y2 was affected by X1 and X3 while Y3 was affected by all three independent variables employed in the formulations. Responses for the optimized formulation were in close agreement with the values predicted by the model. SEM photomicrographs indicated uniform gel formulation. No chemical interaction between the components of formulation was observed by FT-IR and meloxicam was found to be present in the amorphous form in the gel matrix as revealed by PXRD. The maximum plasma concentration (Cmax), time to achieve Cmax and area under plasma concentration curve were significantly different from those of the solution formulation used as the control. Plasma concentration of meloxicam was maintained above its IC50 concentration required for COX-2 inhibition for 23 days.

CONCLUSION

Meloxicam in situ implant may provide long-term management of inflammatory conditions with improved patient compliance and better therapeutic index.

Recent advances in polymeric microspheres for parenteral drug delivery--part 2

INTRODUCTION

Currently marketed microsphere products are manufactured with the use of organic solvents which have a negative impact on the environment and stability of biological molecules. With recent advances in fabrication technologies, solvent free methods have demonstrated potential for the preparation of microspheres.

AREAS COVERED

New technical advances recently achieved in solvent based microsphere manufacturing processes have allowed for major improvement in product quality and properties. Novel solvent free fabrication methods combined with newly functionalized biodegradable polymers have been explored for their application in the preparation of microspheres containing biological molecules.

EXPERT OPINION

Novel fabrication methods for microspheres have been recently reported but technical challenges and development risks remain high for scale up from bench to industrial commercialization. While the applications of microspheres for delivery of proteins, genes and vaccines have shown promise for clinical use, the approval of newly functionalized polymers as carriers may still face scrutiny on safety and biocompatibility, which can be key factors in securing the regulatory approval of the product.

Pharmacokinetic and pharmacodynamic profiles of recombinant human erythropoietin-loaded poly(lactic-co-glycolic acid) microspheres in rats

AIM

To characterize the pharmacokinetic and pharmacodynamic profiles of the recombinant human erythropoietin (rhEPO)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres in rats.

METHODS

The rhEPO-loaded microspheres were prepared using a solid-in-oil-in-water emulsion method. Pharmacokinetics and pharmacodynamics of the rhEPO-loaded microspheres were evaluated in male Sprague-Dawley rats. The serum rhEPO level was determined with ELISA. The level of anti-rhEPO antibody in the serum was measured to assess the immunogenicity of rhEPO released from the microspheres.

RESULTS

rhEPO was almost completely released from the PLGA microspheres in vitro, following zero-order release kinetics over approximately 30 d. After intramuscular injection (10,000 or 30,000 IU rhEPO/kg) in the rats, the serum rhEPO concentration reached maximum levels on d 1, then decreased gradually and was maintained at nearly steady levels for approximately 4 weeks. Furthermore, the release of rhEPO from the PLGA microspheres was found to be controlled mainly by a dissolution/diffusion mechanism. A good linear correlation (R(2)=0.98) was obtained between the in vitro and in vivo release data. A single intramuscular injection of the rhEPO-loaded PLGA microspheres (10,000 or 30,000 IU rhEPO/kg) in the rats resulted in elevated hemoglobin and red blood cell concentrations for more than 28 d. Moreover, the immunogenicity of rhEPO released from the PLGA microspheres was comparable with that of the unencapsulated rhEPO.

CONCLUSION

The results prove the feasibility of using the PLGA-based microspheres to deliver rhEPO for approximately 1 month.

Role of in vitro release models in formulation development and quality control of parenteral depots

This review article provides an assessment of advantages/limitations of the use of current in vitro release models to predict in vivo performance of parenteral sustained release products (injectable depots). As highlighted, key characteristics influencing the in vivo drug fate may vary with the route of administration and the type of sustained release formulation. To this end, an account is given on three representative injection sites (intramuscular, subcutaneous and intra-articular) as well as on in vitro release mechanism(s) of drugs from five commonly investigated depot principles (suspensions, microspheres, hydrogels, lipophilic solutions, and liposomes/other nano-size formulations). Current in vitro release models are, to a different extent, able to mimic the rate, transport and equilibrium processes that the drug substance may experience in the environment of the administration site. Their utility for the purpose of quality control including in vitro-in vivo correlations and formulation design is discussed.

Rheological behaviour of thermoplastic poly(ester-siloxane)s

Two series of thermoplastic elastomers (TPES) based on poly(dimethylsiloxane), (PDMS) as the soft segment and poly(butylene terephthalate) (PBT) as the hard segment, were analyzed by dynamic mechanical spectroscopy. In the first TPES series the lengths of both hard and soft segments were varied while the mass ratio of the hard to soft segments was nearly constant (about 60 mass%). In the second series, the mass ratio of hard and soft segments was varied in the range from 60/40 to 40/60, with a constant length of soft PDMS segments. The influence of the structure and composition of TPESs on the rheological properties, such as complex dynamic viscosity, ?*, the storage, G?, and loss, G?, shear modulus as well as the microphase separation transition temperature, TMST, was examined. The obtained results showed that the storage modulus of the TPESs increased in a rubbery plateau region with increasing degree of crystallinity. The rheological measurements of TPESs also showed that a microphase reorganization occurred during the melting process. The microphase separation transition temperatures were in the range from 220 to 234 ?C. In the isotropic molten state, the complex dynamic viscosity increased with increasing both the content and lenght of hard PBT segments.

Tailored release of TGF-β1 from porous scaffolds for cartilage tissue engineering

In view of cartilage tissue engineering, the possibility to prepare porous scaffolds releasing transforming growth factor-beta(1) (TGF-beta(1)) in a well controlled fashion was investigated by means of an emulsion-coating method. Poly(ether-ester) multiblock copolymers were used to prepare emulsions containing TGF-beta(1) which were subsequently applied onto prefabricated scaffolds. This approach resulted in defined porous structures (66%) with interconnected porosity, suitable to allow tissue ingrowth. The scaffolds were effectively associated with TGF-beta(1) and allowed to tailor precisely the release of the growth factor from 12 days to more than 50 days by varying the copolymer composition of the coating. An incomplete release was measured by ELISA, possibly linked to the rapid concentration decrease of the protein in solution. The released growth factor retained its biological activity as was assessed by a cell proliferation assay and by the ability of the released protein to induce chondrogenic differentiation of bone marrow-derived mesenchymal stem cells. However, exact bioactivity quantification was rendered difficult by the protein concentration decrease during storage. Therefore, this study confirms the interest of poly(ether-ester) multiblock copolymers for controlled release of growth factors, and indicates that emulsion-coated scaffolds are promising candidates for cartilage tissue engineering applications requiring precise TGF-beta(1) release rates.

Pharmacokinetics and in vitro and in vivo correlation of huperzine A loaded poly(lactic-co-glycolic acid) microspheres in dogs

The purpose of this study was to investigate the pharmacokinetics and in vitro/in vivo correlation (IVIVC) of huperzine A loaded poly(lactic-co-glycolic acid) (PLGA) microspheres in dogs. Several huperzine A loaded PLGA microspheres were prepared by an O/W method and three of them (single dose) were injected intramuscularly (i.m.) or subcutaneously (s.c.) to five beagle dogs, respectively. With the increase of the molecular weight of PLGA and the particle size of microspheres, the in vitro and in vivo release periods of huperzine A were prolonged. After s.c. injection, the release of huperzine A from microspheres was faster than that after i.m. injection. The IVIVC models of huperzine A loaded PLGA microspheres were established successfully and after i.m. administration the linear relationship between the in vitro and the in vivo releases was better than that after s.c. administration. It was also found when the particle size of the microspheres was smaller; the values of correlation coefficient were higher.

Controlled release of proteins from degradable poly(ether-ester) multiblock copolymers

A new series of multiblock poly(ether-ester)s based on poly(ethylene glycol) (PEG), butylene terephthalate (BT) and butylene succinate (BS) segments were introduced as matrices for controlled release applications. The release of two model proteins, lysozyme and bovine serum albumin (BSA), from poly(ether-ester) films were evaluated and correlated to the swelling and degradation characteristics of the polymer matrices. First- and zero-order profiles were found for the release of lysozyme, depending on the composition of the polymer matrix. The initial diffusion coefficient was correlated to the swelling of the matrix, which increased with longer PEG segments and lower BT/BS ratios of the polymer. High swelling matrices released the lysozyme according to diffusion-controlled first-order release profiles. Zero-order release profiles were obtained from less swollen matrices due to a combination of diffusion and degradation of the matrix. In contrast to the release of lysozyme, BSA was released from the poly(ether-ester) matrices via delayed release profiles. Both the delay time and the release rate could be tailored by varying the matrix composition. The BSA release rate was mainly determined by the degradation, whereas the delay time was determined by a combination of the swelling and the degradation rate of the polymer matrix.

A new approach to the in vivo and in vitro investigation of drug release from locoregionally delivered microspheres

The purpose of this work was to determine the in vivo release profile of doxorubicin (Dox) delivered locoregionally by dextran-based microspheres (MS) and to develop an in vitro method for predicting in vivo drug release from MS-- in vitro-in vivo correlation (IVIVC). For the determination of in vivo Dox release, drug-loaded MS were placed into hollow fibers (HF) and implanted subcutaneously into C3H mice. Samples were retrieved at various times following implantation, MS removed from HF, and the amount of Dox remaining determined via ultraviolet/visible (UV/Vis) spectrophotometry. Various in vitro systems were designed and investigated for their ability to link in vivo and in vitro release profiles, including an open system (e.g. a column) with continuous flow of release medium at different flow rates and closed systems (e.g. a cuvette) using different release media and conditions. About 34% of loaded Dox was released from MS in vivo at 48 h. Only an incremental release was observed over the ensuing 72 h. The release kinetics of Dox from MS using three of the investigated in vitro systems, column system and HF immersed in a buffer solution or growth medium gave release profiles that were highly correlated with the in vivo release profile (r(2)>0.9). The relationships, both linear and non-linear, suggest that Level A IVIVC models can be developed for Dox release from locoregionally delivered MS using specially designed release systems.

Biodegradable poly(ether-ester) multiblock copolymers for controlled release applications: Anin vivoevaluation

Multiblock poly(ether-ester)s based on poly(ethylene glycol), butylene terephthalate, and butylene succinate segments were evaluated for their in vivo degradation and biocompatibility in order to establish a correlation with previously reported in vitro results. Porous polymer sheets were implanted subcutaneously for 32 weeks in rats. The degradation was monitored visually (histology), by molecular weight (GPC), and by copolymer composition (NMR). Substitution of the aromatic terephthalate units by aliphatic succinate units was shown to accelerate the degradation rate of the copolymers. Direct correlation of the in vivo and in vitro degradation of the porous implants showed a slightly faster initial molecular weight decrease in vivo. Besides hydrolysis, oxidation occurs in vivo due to the presence of radicals produced by inflammatory cells. In addition, the higher molecular weight plateau of the residue found in vivo indicated a higher solubility of the oligomers in the extracellular fluid compared to a phosphate buffer. Minor changes in the poly(ether-ester) compositions were noted due to degradation. Microscopically, fragmentation of the porous implants was observed in time. At later stages of degradation, macrophages were observed phagocytozing small polymer particles. Both in vitro cytotoxicity studies and histology on in vivo samples proved the biocompatibility of the poly(ether-ester)s.