Synthetic, implantable polymers for local delivery of IUdR to experimental human malignant glioma

PURPOSE: Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We evaluated whether we could similarly deliver halogenated pyrimidines to experimental intracranial human malignant glioma. To address this issue we studied the in vitro release from polymers and the in vivo drug delivery of IUdR to experimental human U251 glioblastoma xenografts. METHODS AND MATERIALS: In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local versus systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. versus flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry. RESULTS: In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 + 0.1, 70.0 + 0.2, and 90.2 + 0.2 (p < 0.001 ANOVA) for the 10%, 30%, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors versus time. For the ipsilateral IUdR polymers, the percentage of tumor cellular labeling after 4 days versus 8 days was 45.8 +/- 7.0 versus 40.6 +/- 3.9 (p = NS). For the contralateral polymer implants, the percentage of tumor cellular labeling were 43.9 +/- 10.1 versus 35.9 +/- 5.2 (p = NS) measured 4 days versus 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentage of tumor cellular labeling was low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentage labeling was comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling versus distance from the implanted IUdR polymer showed that labeling was highest closest to the polymer disc. CONCLUSION: Synthetic, implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.     

Peripheral pain mechanisms

A promising new treatment for glioma involves Auger electron emitters such as 125I or 123I conjugated to deoxyuridine (IUdR). However, the presence in tumour deposits of non-proliferating cells with clonogenic potential poses a major limitation to this cycle-specific therapy. We have used multicellular tumour spheroids derived from the human glioma cell line UVW to study [125I]IUdR-targeted radiotherapy in aggregates containing cells in different proliferative states. Autoradiographic identification of labelled cells indicated that nuclear incorporation of [125I]IUdR decreased markedly with increasing size of spheroid. IUdR incorporation was maximal in the surface layer of cells and decreased with depth within spheroids. Radiopharmaceutical uptake corresponded closely to the regions of cell cycling as indicated by staining for the nuclear antigen Ki67. The uptake of drug was enhanced by increasing the duration of incubation from 52 h to 104 h. These observations suggest that significant sparing of non-cycling malignant cells would result from treatment delivered as a single injection of radiolabelled IUdR. To achieve maximal therapeutic effect. IUdR should be administered by multiple injections, by slow release from biodegradable implants or by slow-pump delivery.     

Prolonged release of tegafur from S/O/W multiple emulsion

To develop a prolonged and sustained release preparation, we prepared an albumin microsphere-in-oil-in-water emulsion (S/O/W) and examined sustained release from it in comparison with other control preparations such as water-in-oil (W/O) emulsions and microspheres in vitro and in vivo, respectively. Tegafur was used as a model drug. A microsphere-in-oil emulsion was prepared by adding albumin microspheres to soybean oil containing 20% Span 80. To prepare an S/O/W emulsion, the microsphere-in-oil emulsion was added into an aqueous solution of hydroxypropyl methylcellulose containing Pluronic F68. The mean particle size of the albumin microspheres was 3 microns, and the ratio of entrapment of tegafur into albumin microspheres was about 25%. In an in vitro release test, the t75 of the S/O/W emulsion was fourfold greater and in an in vivo release test the mean residence time of tegafur from the S/O/W emulsion was more than twofold that from a W/O emulsion or microsphere system. The mean residence time of 5-fluorouracil (5-FU) from an S/O/W emulsion was also greater than with other dosage forms. These results suggest the possible usefulness of an S/O/W emulsion for the sustained and prolonged release of tegafur.     

Towards personal health record: current situation, obstacles and trends in implementation of electronic healthcare record in Europe

Biodegradable microspheres containing recombinant human Erythropoietin (EPO) were prepared from ABA triblock copolymers, consisting of hydrophobic poly(l-lactic-co-glycolic acid) A blocks and hydrophilic polyethylenoxide (PEO) B blocks. Different polymer compositions were studied for the microencapsulation of EPO using a modified double-emulsion process (W/O/W). The encapsulation efficiency for EPO, ranging from 72% to 99% was quite acceptable. The formation of high molecular weight EPO aggregates, however, was higher than in poly(d,l-lactide-co-glycolide) (PLG) microparticles. Using different excipients with known protein stabilizing properties, such as Bovine Serum Albumin (BSA), Poly-l-Histidine (PH), Poly-l-Arginine (PA) or a combination of PA with Dextran 40 (D40), the EPO aggregate content was significantly reduced to <5% of the encapsulated EPO. In contrast to PLG, ABA triblockcopolymers containing >7 mol % PEO, allowed a continuous release of EPO from microspheres for up to 2 weeks under in-vitro conditions. The release profile was comparable to FITC-Dextran 40 kDa (FD 40) loaded microspheres in the initial release phase, while EPO release was leveling off at later time points. BSA additionally prolonged the EPO release, while blends of PLG and PEO did not generate continuous EPO release profiles. LPLG-PEO-LPLG triblock-copolymers (35 mol % PEO; 30 kDa) in combination with 5% BSA yielded both an acceptable level of EPO aggregates and a continuous release profile under in-vitro conditions for up to 2 weeks. The formation of EPO aggregates at later time points is probably induced by acidic cleavage products of the biodegradable polymer and requires further optimization of the ABA polymer composition.     

Vascular Parkinson syndromes: a controversial concept]

Development of a Sustained-Release Biodegradable Polymer Delivery System for Site-Specific Delivery of Oligonucleotides: Characterization of P(LA-GA) Copolymer Microspheres In Vitro Antisense oligodeoxynucleotides (ODNs) can selectively inhibit individual gene expression provided they gain access to and remain stable at the target site for a sufficient period of time. Biodegradable sustained-release delivery systems may facilitate site-specific delivery and also prevent degradation of ODNs by nucleases whilst delivering the nucleic acid in a controlled manner to the desired site of action. In this study, we have characterized biodegradable poly (lactide-co-glycolide) (P(LA-GA)) 50:50 microspheres for the potential delivery of antisense oligonucleotides in vivo. Phosphodiester (PO) oligonucleotides complementary to either c-myc proto-oncogene or the tat gene in HIV-RNA were adequately incorporated within P(LA-GA) microspheres with entrapment efficiencies up to 60% depending on particles size. In vitro release profiles of antisense nucleic acids from 10-20 microm size microspheres over 56 days in physiological buffer were triphasic. Profiles were characterised by an initial burst effect during the first 48 hours (phase 1) of release followed by a more sustained release (phase 2) with an additional increased release (phase 3) being observed after 25 days which corresponded with bulk degradation of the copolymer matrix. The release profiles were influenced by microsphere size, copolymer molecular weight, ODN loading, ODN length and by the pH of release medium used. The serum stability of PO ODNs was significantly improved when entrapped within P(LA-GA) microspheres and the hybridization capability, as assessed by duplex melting (Tm) measurements, of released ODN was not impaired by the double-emulsion microsphere fabrication procedure used. Thus, P(LA-GA) microspheres appear to be promising candidates for improving site-specific delivery profiles for ODNs and are worthy of further evaluation in vivo.     

Detection of abscisic-acid-binding proteins in the microsomal protein fraction of Arabidopsis thaliana with abscisic-acid-protein conjugates used as affinity probes

Radioiodinated iododeoxyuridine (IUdR) is a novel, cycle-specific agent that has potential for the treatment of residual malignant glioma after surgery. As only cells in S-phase incorporate IUdR into DNA, a major limitation to this therapy is likely to be proliferative heterogeneity of the tumour cell population. Using a clonogenic end point, we have compared the toxicities of three radioiodoanalogues of IUdR--[123I]IUdR, [125I]IUdR and [131I]IUdR--to the human glioma cell line UVW, cultured as monolayers in the exponential and the plateau phase of growth and as multicellular spheroids. Monolayers treated in the exponential growth phase were most efficiently sterilized by [125I]IUdR (concentration resulting in 37% survival (C37) = 2.36 kBq ml(-1)), while [123I]IUdR and [131I]IUdR were less effective eradicators of clonogens (C37 = 9.75 and 18.9 kBq ml(-1) respectively). Plateau-phase monolayer cultures were marginally more susceptible to treatment with [123I]IUdR and [125I]IUdR (40% clonogenic survival) than [131I]IUdR (60% clonogenic survival). In cells derived from glioma spheroids, both [125I]IUdR and [123I]IUdR were again more effective than [131I]IUdR at concentrations up to and including 20 kBq ml(-1). However, the survival curve for [131I]IUdR crossed the curves for the other agents, resulting in lower survival for [131I]IUdR than [123I]IUdR and [125I]IUdR at concentrations of 40 kBq ml(-1) and higher, the clonogenic survival values at 100 kBq ml(-1) were 13%, 45% and 28% respectively. It was concluded that IUdR incorporating the Auger electron emitters 123I and 125I killed only cells that were in S-phase during the period of incubation with the radiopharmaceutical, whereas the superior toxicity to clonogenic cells in spheroids of [131I]IUdR at higher concentration was due to cross-fire beta-irradiation. These findings suggest that [131I]IUdR or combinations of [131I]IUdR and [123I]IUdR or [125I]IUdR may be more effective than Auger electron emitters alone for the treatment of residual glioma, if proliferative heterogeneity exists.     

New approaches for encapsulation of peptides into poly(lactic/glycolic acid) microspheres

The aim of the work was to develop small microspheres made from a biodegradable polymer, poly(lactide-co-glycolide), in order to entrap small peptides. Microspheres prepared by a water-in-oil-in-water emulsion solvent evaporation technique displayed a mean diameter below than 10 microns and showed high encapsulation efficiency of a 33 amino acid peptide (V3 BRU). In vitro release kinetics studies showed that such microparticles could be employed for both oral immunization and controlled release. The encapsulation of a seven aminoacid peptide in the same conditions, led to a very low encapsulation efficiency. In order to increase the entrapment efficiency, two strategies were adopted: taking into account the solubility of pBC 264 at different pH, a pH gradient was created to prevent the leakage of the encapsulated peptide into the outer aqueous phase. The inner aqueous phase was maintained at basic pH where the peptide was soluble, while the external aqueous phase was acidic: ovalbumin was added during preparation to stabilize the inner emulsion. These two strategies allowed to increase significantly the encapsulation rate of pBC 264. Nevertheless, the in vitro release kinetics of the peptide were strongly influenced by the presence of ovalbumin which seems to form pores in the microsphere structure (80% of the total peptide content was released after 30 minutes). By contrast, when ovalbumin was replaced by Pluronic F 68 microspheres did not have pores, thus the release profile and the extent of the burst were much smaller. When microspheres were stereotactically implanted in the rat brain, in vivo release profiles were in good agreement with the release observed in vitro. In conclusion, these microspheres are well suited for the slow delivery of neuropeptides in the brain, a feature expected to facilitate the study of long term effects of these compounds.     

Novel mucosal immunization with polysaccharide-protein conjugates entrapped in alginate microspheres

A novel mucosal immunization was examined using biocompatible and biodegradable alginate microspheres containing a conjugate of polysaccharide antigen and cholera toxin B subunit (CTB). In order to prepare the alginate microspheres with diameters of less than 5 microm, a new diffusion-controlled interfacial gelation technique was developed. Also, in order to improve the mucosal immune response, a pneumococcal capsular polysaccharide type 19 (PS19) was conjugated to the CTB (PS19-CTB). This conjugate was subsequently encapsulated into the alginate microspheres. The loading content of PS19-CTB to the alginate microspheres was 60%. An in vitro sustained release pattern was observed with the antigen-loaded microspheres, showing 80% antigen release within one day. Mucosal and systemic immunities following oral immunization with the alginate microspheres were studied. Balb/c mice were immunized perorally three times at intervals of two weeks. Peroral immunization with 25 microg of PS19-CTB entrapped in the alginate microspheres evoked both the mucosal IgA and systemic IgM responses to PS19 in small intestine and in sera, respectively. The results suggest that both the mucosal and systemic antibody responses could be induced by oral administration of the PS19-CTB antigen entrapped in alginate microspheres.     

Progress in the design of DNA sequence-specific lexitropsins

Polymeric microparticles containing two ceftiofur salts as antimicrobial agents for intramammary application in dry cows were prepared by modified o/w-solvent evaporation methods (dispersion or cosolvent method) or by a w/o/w-multiple emulsion solvent evaporation method. The microspheres were characterized with respect to drug loading, drug release, and morphological properties. The three methods resulted in high encapsulation efficiencies. The choice of organic solvent/solvent mixture strongly affected the structure of the microparticles; both matrix and reservoir-type structures with different porosities were obtained. Scaling up to larger batch sizes resulted in microspheres with a faster drug release. The addition of water-miscible cosolvents to the water-immiscible polymer solution allowed the preparation of microparticles from a drug solution rather than a drug dispersion. Microparticles prepared by the cosolvent method could be separated after shorter time intervals from the aqueous phase; the microspheres had a denser matrix with finely dispersed drug crystals and a slower drug release when compared with microspheres prepared by the dispersion method, which had a more porous structure with larger embedded drug crystals. The cosolvent and dispersion methods present a simple alternative to the w/o/w-solvent evaporation method for the encapsulation of water-soluble drugs with an external water phase.     

5-[125I]iodo-2'-deoxyuridine in the radiotherapy of brain tumors in rats

Glial neoplasms of the human central nervous system have defied treatment, in part because of the limited selectivity of available cytotoxic agents. The thymidine analog 5-iodo-2'-deoxyuridine radiolabeled with the Auger electron emitter 125I (125IUdR) is highly toxic to dividing cells when it is deoxyribonucleic acid incorporated, but it is relatively innocuous when located outside the nucleus. Previous studies have shown that 125IUdR has significant antineoplastic potential against mammalian cells in vitro and direct administration of 125IUdR is effective therapy for ovarian ascites tumors in mice and neoplastic meningitis in rats. Studies using external gamma imaging and autoradiography have also shown that direct intratumoral administration of 123IUdR/125IUdR into intracerebral 9L gliosarcomas in rats results in selective uptake of the radionuclide into tumor cells. Based on these encouraging results, we have evaluated the therapeutic potential of 125IUdR in rats bearing intracerebral 9L gliosarcomas. METHODS: Iodine-125-IUdR was infused intracerebrally over a 2-day period into rats bearing 1-day-old 9L tumors and over a 6-day period into animals with 9-day-old 9L tumors; equimolar concentrations of 127IUdR were infused into control animals. Tumor growth was monitored by contrast-enhanced 1H MRI and animal survival was followed over time. RESULTS: Intracerebral tumors (3-7 mm) were readily detected by MRI. Tumor-bearing rats treated with 127IUdR succumbed within 17-24 days, whereas tumor-bearing animals treated with 125IUdR survived significantly longer, and 10%-20% of the animals were cured of tumors. CONCLUSION: These data substantiate the antineoplastic potential of 5-[125I]iodo-2'-deoxyuridine and indicate that it may be a useful agent for the therapy of solid tumors that are accessible to direct radiopharmaceutical administration.     

Differential in vitro hepatic and intestinal metabolism of ifosfamide in the rat

Influence of chitosan molecular weight on drug loading and drug release of drug-loaded chitosan microspheres was studied. Chitosans of 70,000 (LC), 750,000 (MC), and 2,000,000 (HC) molecular weight were employed alone or as mixtures (HC/LC 1:1-1:2 w/w). Ketoprofen (ket) was chosen as the model drug to be encapsulated. Microspheres characterized by different theoretical polymer/drug ratios were prepared (2:1, 1:1, 1:2 w/w). Satisfactory ket contents were obtained for all batches of chitosan microspheres with the theoretical polymer/drug ratio 1:2 w/w; microspheres made of HC/LC (1:2 w/w) were characterized by good drug content and encapsulation efficiency independent by polymer/drug ratio. Prepared chitosan microparticulate delivery systems can modulate ket release within 48 hr. Microspheres consisting of HC/LC (1:2 w/w) were the most suitable formulation in controlling drug release.     

Female fifteen-spined sticklebacks prefer better fathers

PURPOSE: Due to the cytotoxicity of DNA-bound iodine-125, 5-[125I]Iodo-2'-deoxyuridine ([125I]IUdR), an analog of thymidine, has long been recognized as possessing therapeutic potential. In this work, the feasibility and potential effectiveness of hepatic artery infusion of [125I]IUdR is examined. METHODS: A mathematical model has been developed that simulates tumor growth and response to [125I]IUdR treatment. The model is used to examine the efficacy and potential toxicity of prolonged infusion therapy. Treatment of kinetically homogeneous tumors with potential doubling times of either 4, 5, or 6 days is simulated. Assuming uniformly distributed activity, absorbed dose estimates to the red marrow, liver and whole-body are calculated to assess the potential toxicity of treatment. RESULTS: Nine to 10 logs of tumor-cell kill over a 7- to 20-day period are predicted by the various simulations examined. The most slowly proliferating tumor was also the most difficult to eradicate. During the infusion time, tumor-cell loss consisted of two components: A plateau phase, beginning at the start of infusion and ending once the infusion time exceeded the potential doubling time of the tumor; and a rapid cell-reduction phase that was close to log-linear. Beyond the plateau phase, treatment efficacy was highly sensitive to tumor activity concentration. CONCLUSIONS: Model predictions suggest that [125I]IUdR will be highly dependent upon the potential doubling time of the tumor. Significant tumor cell kill will require infusion durations that exceed the longest potential doubling time in the tumor-cell population.     

Radiolabeled nucleoside analogs in cancer diagnosis and therapy

Radiolabeled nucleosides, specifically 5-iodo-2'-deoxyuridine (IUdR) radioiodinated with the Auger-electronemitting 123I or 125I, have been shown to produce extensive DNA damage in mammalian cell systems in vitro. Such nucleosides are cycle-dependent agents that are taken up by mitotically dividing cells in the S phase of the cell cycle. The degree of damage that occurs is related to the fact that these nucleosides bind covalently to DNA bringing the decaying Augerelectron-emitting radionuclide in close proximity to the genome. The use of these radiohalogenated nucleosides in vivo is associated with several problems. The first relates to their extremely short biologic half-life in blood (T1/2 of minutes in humans). The second involves achieving therapeutic ratios in tumor cells in the face of efficient hepatic dehalogenation. The third concerns the uptake of these radiopharmaceuticals by actively proliferating normal cell renewal systems, thus potentially causing toxic side effects. The fourth, one shared with other cycle-dependent drugs, relates to the matter of labeling the whole tumor cell population. To facilitate targeting to tumors, investigators have been examining the direct introduction of these agents into the targeted area or into an arterial blood supply that immediately precedes the target. For example, radiopharmaceutical administration could be intracavitary (bladder, spinal fluid, peritoneum), intralesional (brain tumor, breast mass) or intra-arterial (liver, pancreas). In all these situations, the following conditions must be met: (a) once within the vicinity of the tumor the agent can freely diffuse through the tissues and is selectively taken up by cancerous cells; (b) once the agent has left the target area it is converted quickly into a nontoxic form and/or excreted from the body; and finally, (c) the biologic behavior of the agent is not altered by repeated injections. We report herein our experience and that of others with [123I/125I/131I]IUdR in cultured cells, animal tumor-model systems, and patients. In vitro, DNA incorporation of 123I- and 125I-labeled IUdR leads to an exponential decrease in cell survival (no shoulder on the survival curve). However, the total number of decays needed to produce a given lethal effect with [123I]IUdR is approximately twice that required with [125I]IUdR. In vivo, the scintigraphic and antineoplastic capabilities of radioiodinated IUdR have been demonstrated in an intraperitoneal murine ovarian tumor model following intraperitoneal injection; in an intracerebral rat gliosarcoma model after intracranial administration; in an intrathecal rat gliosarcoma model after intrathecal infusion; and in a rat transitional cell bladder cancer model following intravesicular infusion. [123I]IUdR, [125I]IUdR, and/or [131I]IUdR have been administered to patients with brain, breast, colorectal, or gastrointestinal cancers (intratumorally); ovarian cancer (intraperitoneally); bladder cancer (intravesically); liver metastases from colorectal cancer (through the hepatic artery, permanent intra-arterial catheter). These studies have confirmed the observations made in animal models. The data indicate that 5-iodo-2'-deoxyuridine radiolabeled with an Auger electron emitter (123I or 125I) may be a useful agent for the scintigraphic diagnosis and/or therapy of neoplastic diseases that are accessible to direct radiopharmaceutical administration. This radiopharmaceutical should serve as a prototype for, and facilitate the development of, other radiolabeled nucleoside analogs. Further investigations are certainly warranted.     

Colon-specific prodrugs of 5-radioiodo-2'-deoxyuridine

Two glycoside-based prodrugs, 125IUdR-5'-beta-D-glucopyranoside and 125IUdR-5'-beta-D-galactopyranoside, were synthesized. This selection was dictated by the abundance of appropriate enzymes in the GI tract of mice and similar levels of beta-D-glycosidases in human and rodent large intestine. Studies to establish the ability of colonic microflora to release 125IUdR were conducted in vitro and in Swiss Webster mice. Both prodrugs released 125IUdR in the presence of the corresponding enzymes or the GI content homogenates in vitro, and in vivo. Luminal enzymes in the proximal and distal small intestine in mice degraded less than 10% of each prodrug whereas enzymes from the colonic/caecal lumen of mice released nearly 100% of 125IUdR. 125IUdR freed by bacterial glycosidases was stable in the GI content. No significant amounts of other metabolites or deiodination products were observed. Total radioactivity recovered as by-products was less than 10%. The efflux of prodrugs from the GI tract after oral administration in mice was slow and limited. Unlike 125IUdR, prodrugs were not dehalogenated in vivo as indicated by biodistribution and imaging studies.     

Interstitial delivery of carboplatin via biodegradable polymers is effective against experimental glioma in the rat

PURPOSE: Carboplatin has shown promise experimentally as an antineoplastic agent against both primary central nervous system (CNS) tumors and several solid tumors that frequently metastasize to the brain. Unfortunately, carboplatin is limited in its clinical use for tumors in the CNS by systemic toxicity and poor penetration through the blood brain barrier. Recent advances in polymer technology have made feasible the intracranial implantation of a biodegradable polymer capable of local sustained delivery of chemotherapy for brain neoplasms. This study assessed the toxicity and efficacy of carboplatin delivered from intracranial sustained release polymers in the treatment of experimental gliomas in rodents. METHODS: Two biodegradable anhydride polymer systems were tested: a copolymer of 1,3-bis-(p-carboxyphenoxy propane) and sebacic acid, and a copolymer of fatty acid dimer and sebacic acid. The polymers were loaded with carboplatin and dose escalation studies evaluating toxicity were performed by implanting carboplatin-loaded polymers into the brains of rats. Next, efficacy was tested. F-98 glioma cells were injected intracranially into rats, and 5 days later polymers containing the highest tolerated doses were implanted at the site of tumor growth. The survival of animals receiving carboplatin-loaded polymer was compared with that of animals receiving intraperitoneal doses of the same agent. RESULTS: Carboplatin-polymer was well tolerated at doses up to 5% loading in both polymer systems. Locally delivered carboplatin effectively prolonged survival of rats with F98 gliomas. Maximal treatment effect was seen with 5% loading of either polymer, with median survival increased threefold over control (P < 0.004). Systemic carboplatin also significantly prolonged survival, but the best intracranial polymer dose was significantly more effective than the best systemic dose tested. CONCLUSIONS: Carboplatin can be safely delivered intracranially by biodegradable sustained- release polymers. This treatment improves survival in rodents with experimental gliomas, with locally delivered carboplatin being more effective than systemic carboplatin.     

Analysis of commercial mini-bus accidents

The major challenge in liquid sustained-release oral suspensions is to minimize drug diffusion into the suspending medium and to retain the original properties of the microparticles during storage. Diclofenac wax microspheres prepared by the hydrophobic congealable disperse phase method were formulated as a sustained release suspension and stored at three different temperatures (25, 37 and 45 degrees C) for 3 months, to evaluate the physical and chemical stability of the suspended microspheres. Suspensions of microspheres stored at ambient temperatures were both physically and chemically stable, but at higher temperatures, up to 45 degrees C, there was a decrease in drug release due to scaling and melting on the microsphere surface as observed by scanning electron microscopy. However, on prolonged storage, up to 90 days, especially at 45 degrees C, temperature became a dominant factor causing an increase in drug release. The suspension of diclofenac microspheres was chemically stable for 3 months, while the plain drug suspension exhibited slight degradation.     

Preparation and in vitro characterization of gentamycin-impregnated biodegradable beads suitable for treatment of osteomyelitis

A new method for preparing poly(L-lactide) (PLA) biodegradable beads impregnated with an ionic aminoglycoside, gentamycin, is described. The process employs hydrophobic ion pairing to solubilize gentamycin in a solvent compatible with PLA, followed by precipitation with a compressed antisolvent (supercritical carbon dioxide). The resulting precipitate is a homogeneous dispersion of the ion-paired drug in PLA microspheres. The microspheres are approximately 1 microm in diameter and can be compressed into beads (3-6 mm in diameter) strung on surgical sutures for implantation. The bead strings exhibit no significant change in release kinetics upon sterilization with a hydrogen peroxide plasma (Ster-Rad). The kinetics of gentamycin release from the PLA beads are consistent with a matrix-controlled diffusion mechanism. While nonbiodegradable poly(methyl methacrylate) (PMMA) beads initially release gentamycin in a similar manner, the drug release from PMMA ceases after 8 or 9 weeks, while the PLA beads continue to release drug for over 4 months. Moreover, only 10% of the gentamycin is released from the PMMA beads, while PLA beads release more than 60% of their load, if serum is present in the release medium. The PLA system displays improved release kinetics relative to PMMA, is biodegradable, is unaltered by gas sterilization, can be used for a range of antibiotics, and can be manipulated without disintegration. These are all desirable properties for an implantable drug delivery system for the prevention or treatment of osteomyelitis.     

Diminished kidney function and nephrocalcinosis in rats fed a magnesium-deficient diet

Microcapsules have been used as drug delivery systems in the pharmaceutical field for sustained or controlled release of drug, and for artificial cells and organs. Biodegradable polymers, especially polylactic acid, have been widely used in this field. In this study, an attempt was made to develop a new method to prepare polylactic acid microcapsules for drug delivery. The biodegradable polylactic acid microcapsules were made by the phase separation process: two types of polylactic acid, poly[(D,L)lactic acid] and poly[(L)lactic acid] were combined as the membrane material. Because of the difference of the crystal properties of the two polymers, the aggregation which happens frequently in the phase separation process was prevented. As a model drug, Ciprofloxacin was encapsulated in the polylactic acid microcapsules.     

The biologic effects of growth factor-toxin conjugates in models of vascular injury depend on dose, mode of delivery, and animal species

Toxin-conjugates, complexes designed from the fusion of tissue toxins and pathology-specific ligands, offer the potential for targeted cytotoxic therapy. Some have postulated that the recurrent failure of these conjugates to exhibit benefit in animal models of vascular injury arose because the timing and frequency of conjugate delivery were insufficient to meet the demands of the arterial wall. Previous data suggest that increasingly frequent dosing would lead to superior inhibition of intimal hyperplasia. We now report on the biological effects of the controlled release of a recombinant conjugate of basic fibroblast growth factor (bFGF) and the plant toxin saporin (SAP), bFGF-SAP. Alginate/heparin-Sepharose microspheres and films were designed as drug carriers to control release the bFGF-SAP conjugate or bFGF alone in small doses. When bFGF-SAP-incorporated microspheres or films were implanted adjacent to balloon angioplastied porcine carotid arteries, the controlled release of bFGF-SAP over the four-week study stimulated rather than inhibited hyperplasia. When these same devices were used in cell culture, unexpected findings were produced. bFGF-SAP reduced in vitro bovine vascular smooth muscle cell growth at high concentrations (1-10 microgram/mL) but increased smooth muscle cell growth at lower concentrations (up to 1 microgram/mL). Microsphere controlled-released bFGF-SAP ( approximately 60 ng/mL over 4 days) stimulated the growth of smooth muscle cells more than any of the tested bolus applications of the conjugate. These data provide cause to reconsider our acceptance of controlled release technology as the answer to all forms of drug delivery problems, and to apply more rigorous means of matching the kinetics of drug delivery to the kinetics of the vascular response to injury.     

Gonadal cell apoptosis: hormone-regulated cell demise

We have studied the release of nerve growth factor (NGF), a protein under consideration for treatment of Alzheimer's Disease, from polymer matrices and microspheres to characterize the stability of NGF, the dynamics of NGF release, and the distribution of NGF within the brain interstitium. Poly(ethylene-co-vinyl acetate) (EVAc) disks and poly(L-lactic acid) (PLA) microspheres were formed by codispersing NGF with one of a variety of molecules. The mass of mouse NGF (mNGF) detected following release from EVAc disks into buffered saline varied five-fold over the range of codispersants studied, with carboxymethyldextran providing optimal release, while the mass of recombinant human NGF (rhNGF) released varied four-fold from both EVAc disks and PLA microspheres, with albumin and carboxymethyldextran providing optimal release. Variation of the codispersant species significantly affected NGF release into buffered saline; it also had a noticeable, but small, effect of the amount of NGF found in the brain tissue following implantation of a polymer device. To improve NGF retention in tissue, NGF was conjugated to 70,000 molecular weight dextran and incorporated into a polymeric device. The distribution of NGF was enhanced by conjugation; comparison of NGF concentrations in the brain to a mathematical model of diffusion and elimination suggested that the elimination rate of NGF-dextran conjugate in the tissue was over seven times slower than the elimination rate of NGF. These results indicate that variation of the properties of the controlled release system may be useful in regulating the time course of NGF delivery to tissue, and that modification of the NGF itself can improve penetration and retention in the brain.