A systemic route for drug loading to lymphatic phagocytes.

Lymph nodes are primary germination and proliferation sites for many types of pathogens. Maintaining therapeutic levels of appropriate chemotherapeutic agents in the lymph node tissue is critical for the treatment of both infection and cancer. This study was intended to develop a systemic route for loading lymph node phagocytes with drugs, using a lymph node specific nanocarrier. The latter is assembled as a 10-15 nm particle with a drug-carrying core and a phagocyte-homing poly(1-->6)-alpha-d-glucose based interface. Biokinetics and microdistribution of the model carrier were investigated in vivo. Nanocarrier accumulation in lymph nodes reached 30-35% dose/g in central lymph nodes, with deposition in various phagocytic cell populations. The latter included cells harboring inhaled microparticles translocated to lymph nodes from the lungs. In view of the nanocarrier ability to transport and release significant amounts of various drug substances, the data suggests feasibility of systemic drug loading to lymphatic phagocytes and, through drug release, to the neighboring cells.

Synthesis of a macromolecular camptothecin conjugate with dual phase drug release.

A water soluble macromolecular conjugate of camptothecin (CPT) with a new, dual phase hydrolytic drug release mechanism was prepared on the basis of a 60 kDa biodegradable hydrophilic "stealth" polyacetal, poly(1-hydroxymethylethylene hydroxy-methyl formal). Succinamido-glycinate was used as a prodrug releasing group. A model preparation with 7.5% CPT content w/w was water soluble. The lipophilic camptothecin prodrug, camptothecin-(O20)-succinimidoglycinate, was released from the conjugate with t(1/2) = 2.2 +/- 0.1 h in rodent plasma. The blood clearance in a rodent model as measured by CPT was release limited, t(1/2) = 2.1 +/- 0.2 h, while the conjugate half-life was 14.2 +/- 1.7 h. In a xenograft tumor model, the conjugate demonstrated higher antineoplastic efficacy than CPT at a less than equitoxic dose. This improved therapeutic window is in line with the modified drug pharmacokinetics and with camptothecin release in a stabilized lipophilic prodrug form. Regulation of prodrug release and hydrolysis rates through linker structure modification will open the way to further improve both pharmacokinetics and pharmacodynamics.

Macromolecular intravenous contrast agent for MR lymphography: characterization and efficacy studies.

PURPOSE: To determine the pharmacokinetic and magnetic resonance (MR) imaging properties of diethylenetriaminepentaacetic acid (DTPA) conjugated with a polyglucose-associated macrocomplex (PGM), which accumulates in lymph nodes. MATERIALS AND METHODS: In 124 normal and 20 tumor-bearing rats, Gd-DTPA PGM was administered intravenously in doses of 2, 10, 20 mumol gadolinium per kilogram of tissue. RESULTS: Mean blood half-life was 2 hours. Maximum accumulation in peripheral (33.0% injected dose [ID]/g +/- 16.2 [standard deviation]) and central lymph nodes (63.2% ID/g +/- 16.5) was observed within 24 hours after administration. The optimum dose range was 10-20 mumol Gd/kg in rats. At 24 hours after administration of 20 mumol Gd/kg, the signal-to-noise ratio increased from 30.9 +/- 0.4 to 83.2 +/- 5.2 in normal lymph nodes (P < .001). Differentiation between normal and metastatic lymph nodes was improved. CONCLUSION: When labeled with Gd-DTPA, the PGM-based graft copolymer significantly increases signal intensity at MR imaging of normal but not metastatic lymph nodes without causing distortion artifacts.

MR lymphography with a lymphotropic T1-type MR contrast agent: Gd-DTPA-PGM.

A model system of a paramagnetic lymphotropic MR contrast agent (Gd-DTPA labeled polyglucose associated macrocomplex, PGM) for T1-weighted MR imaging of lymph nodes in rats and rabbits was evaluated. Pharmacokinetic (tissue accumulation) and MR imaging data (optimal dose and timing parameters) were obtained in normal rats (n = 88) after subcutaneous (SC) injection of paramagnetic, radiolabeled [111In]Gd-DTPA-PGM. A rabbit model of lymph node metastases (n = 8) was ultimately used to demonstrate the potential of MR imaging with Gd-DTPA-PGM for nodal tumor detection. Maximum concentrations of Gd-DTPA-PGM were found in popliteal and paraaortic lymph nodes within 24 h after SC administration, and highest lymph node SNR values were obtained by MR imaging at this time point. The optimum imaging dose was 6-12 mumol Gd/kg. Tumor-lymph node contrast increased from 0.0 +/- 1.2 precontrast to 19.2 +/- 6.5 (spoiled gradient echo sequence, TR 50/TE 7/flip angle 60 degrees) postcontrast and conspicuity of nodal metastases was improved. Gd-DTPA-PGM accumulates in lymph nodes after SC administration and significantly enhances lymph node signal intensity of normal animals but not metastatic lymph nodes.

Poly(ethylene glycol) on the liposome surface: on the mechanism of polymer-coated liposome longevity.

The hypothetical model is built explaining the molecular mechanism of protective action of poly(ethylene glycol) on liposomes in vivo. The protective layer of the polymer on the liposome surface is considered as a statistical 'cloud' of polymer possible conformations in solution. Computer simulation was used to demonstrate that relatively a small number of liposome-grafted molecules of hydrophilic and flexible polymer can create a dense protective conformational cloud over the liposome surface preventing opsonizing protein molecules from contacting liposome. A more rigid polymer fails to form this dense protective cloud, even when hydrophilic. Computer simulation was also used to reveal possible heterogeneity of reactive sites on a polymer-coated liposome surface, and to estimate the optimal polymer-to-lipid ratio for efficient liposome protection. Experiments have been performed with the quenching of liposome-associated fluorescent label (nitrobenzoxadiazole or fluorescein) with protein (rhodamine-ovalbumin or anti-fluorescein antibody) from solution. It was shown that poly(ethylene glycol) grafting to liposomes hinders protein interaction with the liposome surface, whereas liposome-grafted dextran (more rigid polymer) in similar quantities does not affect protein-liposome interaction. Highly-reactive and low-reactive populations of chemically identical reactive sites have been found on polymer-coated liposomes. Experimental data satisfactory confirm the suggested mechanism for the longevity of polymer-modified liposome.

MR lymphography: study of a high-efficiency lymphotrophic agent.

PURPOSE: To investigate the utility of a monocrystalline iron oxide nanoparticle (MION) as a contrast agent in magnetic resonance (MR) imaging of lymph nodes. MATERIALS AND METHODS: Pharmacokinetic data were obtained in rats after intravenous, subcutaneous, and intraarterial injection of indium-111-MION-46. MR imaging was performed to determine optimal dosages and pulse sequences in rats. Models of lymph node metastasis in rabbits and lymph node hyperplasia in rats were used to demonstrate the efficacy of MION in differentiation of malignant and benign adenopathies. RESULTS: Biokinetic data indicate that nodal accumulation occurs primarily after extravasation of agent into the interstitial space (slow component) and subsequent trapping by lymph node macrophages (fast component). Relatively low concentrations (15-25 mumol Fe per kilogram for peripheral nodes after intraarterial injection) decrease signal intensity of nodes at MR imaging. CONCLUSIONS: Lymph node accumulation of MION-46 is high. Modification of injection techniques that alter capillary permeability allows use of systemically administered agent at doses as low as 15-25 mumol Fe per kilogram.

A new macromolecule as a contrast agent for MR angiography: preparation, properties, and animal studies.

The authors developed and evaluated a polymer as a contrast agent for magnetic resonance (MR) angiography. The agent consists of a monomethoxy ether of poly(ethylene glycol) covalently attached to poly(L-lysine) (PL), with PL serving as the carrier of gadolinium diethylenetriaminepentaacetic acid (DTPA). Immunogenicity and toxicity studies were performed in mice, and biokinetic and metabolic studies were performed in rats. Dose response studies were performed with a three-dimensional time-of-flight sequence in eight rats. No permanent immune response was elicited against Gd-DTPA or the carrier molecule, and accumulation in organs of the reiculoendothelial system was minimal. The blood half-life of the agent was 14 hours. A dose of 20 mumol of gadolinium per kilogram of body weight was sufficient to increase the vessel-muscle ratio by four- to fivefold. Contrast was substantially improved and remained unchanged 2 hours after contrast medium administration, and good visualization of four orders of vasculature was allowed.

[Biokinetics of magnetic carriers for directed transport of drugs]. / Biokinetika magnitnykh nositelei dlia napravlennogo transporta lekarstv.

Localization of intravenously injected magnetic drug carriers in the affected areas of the host is complicated by the carrier capture in the liver and other nonaffected organs and tissues. In vivo kinetics of radiolabeled magnetically targeted drug carriers was studied and one-exponent kinetics was shown. A mathematical model of the carrier capture in animal tissues based on the capture mechanism and mass transfer processes in circulating blood was proposed. Biodistribution and capture intensity of carbohydrate-and albumin-coated magnetic microparticles of different sizes were compared. A one-animal biokinetic test based on the model proposed proved to be effective in detecting insignificant differences in the magnetic carrier biokinetics usually hidden by individual differences of the animals.

[Prediction of the biological effect of magnetically regulated drugs]. / Prognozirovanie biologicheskogo éffekta magnitoupravliaemykh lekarstvennykh preparatov.

Kinetic aspects of magnetically targeted drug transport are discussed. The influence of the magnetic drug carrier properties, the transported drug and the target organ parameters on the biological effect of the drug was investigated. A mathematical model reflecting mass transfer processes in the circulatory system was used for estimating the influence of these factors on the therapeutic effect of the drug delivered to the target. The nature of the effect of the drug release parameters, inactivation rate of the released drug in the blood and intensity of the carrier capture out of the target organ on the drug therapeutic action was revealed. Mathematical modeling of magnetically targeted drug kinetics was shown to provide prognostication of the drug effect and increasing of the experiment informative capacity.

Magnetically driven thrombolytic preparation containing immobilized streptokinase-targeted transport and action.

Streptokinase was immobilized on the magnetic carrier at a concentration of 2,000-2,700 IU/ml of preparation. Thrombosis was induced in both canine carotid arteries by means of the vascular wall flap inverting into its lumen. The red, completely occluding thrombus was formed inside the vessel 4-5 h later. A samarium-cobalt magnet was secured externally to one of the arteries. After the clot formation the magnetically immobilized streptokinase was injected intravenously. The preparation concentrated in the region of the magnetic field action caused complete thrombus degradation and normal blood flow restoration; no effect on the clot in the control artery was observed.

[Drug preparations of immobilized enzymes with enhanced affinity for the site of action]. / Lekarstvennye preparaty immobilizovannykh fermentov s povyshennym srodstvom k mestu deistviia.

Several approaches to development of systems for directed transport of drugs are illustrated by an example of thrombolytic therapy. Preparation and properties of enzyme derivatives with increased tropism to the thrombus material due to modification of enzymes by fibrinogen or specific antibodies are discussed. The data on directed transport of drugs under the action of the magnetic field and on the selective action of drugs on culture cells are also presented.

Magnetic Sephadex as a carrier for enzyme immobilization and drug targeting.

Magnetic materials were suggested as carriers for protein immobilization about 10 years ago [1,2]. The main advantage of these carriers is their ability to be concentrated near magnetic terminals upon the application of the external magnetic field. This property is used in technological processes for selective catalyst removal from the reaction mixture [3], in immunological studies for the separation of cells to which magnetic particles are specifically bound modified with antibodies against cell surface components [4], in experiments for the drug targeting in vivo into appropriate tissues under the action of external magnetic field [5]. The properties of magnetic carriers are reviewed in [3]. There exist a number of methods to obtain porous magnetic carriers, containing immobilized matter not only on the surface, but also in the volume of a particle. Normally, these preparations are obtained by the granule formation from the suspension of ferromagnetic particles in the solution or melt of appropriate high-molecular-weight compound [5,6]. The drawback of the above-mentioned methods is the pronounced aggregation of ferromagnetic particles. The aggregation does not permit to use concentrated enough suspensions of magnetic particles and causes the formation of the product with a variety of sizes and magnetic properties. We made an attempt to synthesize the magnetic carrier for protein immobilization on the basis of commercial Sephadex porous spheres. Sephadex granules were made magnetic by adsorptional fixation of ferromagnetic particles in its pores. The properties of the "native" and "magnetic" Sephadexes as carriers for protein immobilization were compared by parallel immobilization on both carriers of alpha-chymotrypsin and 131I-albumin. In in vivo experiments we studied the ability of magnetic Sephadex to be concentrated in a desired region of the circulation under the action of external magnetic field.

[Possibilities of using ferromagnetic materials for targeted drug transport]. / Vozmozhnosti ispol'zovaniia ferromagnitnykh materialov dlia napravlennogo transporta lekarstv.

Possibilities of using particles containing ferromagnetic materials and magnetic concentrated colloids for targeted drug transport have been studied. Magnetic particles produced from Sephadex G-25 by ferromagnetic material fixation, polymer-modified iron particles 100 nm in diameter, and concentrated colloid solutions of Fe3O4 are retained in the marginal ear vein of the rabbit by magnetic field at H = 0.5 kHs/cm. The data on magnetic retention of the above-indicated agents in the vein, obtained by measuring 75Se and 131I activity, of labeled particles are presented.