J. Drobník

Hydrogels in endovascular embolization. III. Radiopaque spherical particles, their preparation and properties

The synthesis and properties of spherical radiopaque hydrogel particles designed for endovascular occlusion are reported. These particles were prepared by the hydroxyl acylation of low crosslinked poly (2-hydroxyethyl methacrylate) beads with a nontoxic radiopaque compound based on triiodobenzoic acid, without affecting their properties which are advantages in medical practice. The effect of the iodine content on the size of dry and swollen particles is discussed. It has been found that an iodine content of about 25-30 wt% is desirable in order to obtain an easily recognizable X-ray image. These particles make the immediate control of embolus application easy and enable periodical inspection of the polymer to check the successful blockage of the vessel. They also open up the method of endovascular occlusion to further improvement.

Soluble synthetic polymers in biological systems

This review summarizes facts and theories on the fate of a soluble polymer in an animal or human body, mainly from the point of view of therapeutic or diagnostic applications in medicine. Analytical methods which are the main source of our knowledge on this subject are discussed. A compartmental model is suggested and the importance of the individual compartmental barriers and the peculiarity of the polymer pharmacokinetics is documented: the molecular weight distribution changes with time in the circulating fraction; the various routes of parenteral administration are not equivalent. The main route of clearance from the body is the glomerular filtration, which is limited by the size and modified by the charge of the molecule. Polymers which pass through glomerulus may be reabsorbed in the tubulus by pinocytosis, which is largely dependent on the chemical nature of the polymer. Synthetic polymers may elicit antibody production, induce immunological tolerance, activate supressor cells, serve as a non-specific immunostimulator, particularity of the macrophage cytotoxicity, etc. Practical applications in medicine require more detailed knowledge of the fate of polymers in the body. Diagnostics is more a promising field for the immediate future.

Poly(N5-hydroxyalkylglutamines). IV. Enzymatic degradation of n5-(2-hydroxyethyl)-L-glutamine homopolymers and copolymers

Abstract Enzymatic degradation of water-soluble neutral synthetic polymers derived from poly[N5-(2-hydroxyethyl)- l -glutamine] (PHEG) was studied using proteolytic enzymes (papain, cathepsin B, pronase E, pepsin, chymotrypsin A and elastase). Endopeptidase and exopeptidase mechanisms were followed. GPC was used for a quantitative evaluation of the degradation in terms of mole amount of hydrolyzed peptide bonds in the main polymer chain. All proteases investigated in this study degraded PHEG and/or its derivatives by the endopeptidase mechanism. The exopeptidase activity was detected only with pronase E. In some cases degradation down to low molecular weight products was observed. The PHEG homopolymer is resistent to serine proteases, but the hydrophobie modification of glutamic acid side chains or the copolymerization with hydrophobic l -itamino acids render such derivatives susceptible to these enzymes. The kinetics of poly[N5-(2-hydroxyethyl)- l -glutamine-co- l -phenylalanine] degradation by chymotrypsin A showed that the degradation rate is dependent not only on the total concentration of Phe units in the reaction mixture but also on their frequency in the polymer chain.

Antitumor activity of platinum complexes

SummaryContemporary ideas about the mechanism of antitumor activity of platinum complexes are reviewed and discussed. The induction of SOS functions in bacteria is emphasized and an analogous mechanism in animal cells is suggested. The fate of the leaving ligand in the body is not known. Therefore the complex which reaches the target DNA may be very different from the applied compound. Even the amino ligand may be detached in the body, probably as part of the detoxication by binding to proteins. In the case of fast or medium-speed reactive complexes most of the platinum is inactivated by binding to proteins, whereas slow-reacting drugs are mostly excreted unchanged in the urine. Thus, the quantity of the complex which reaches the target ist also difficult to assess. Due to peculiar pharmacokinetics, the results obtained with poorly soluble compounds administered in the solid form cannot be compared with those obtained in true solutions. There are many reasons for believing that the study of a coordination anticancer drug may contribute to our understanding of cancer growth and its reversal.

The renal excretion and retention of macromolecules

Five derivatives of polyaspartamide were used as macromolecular models to study the effect of chemical structure of macromolecules on their renal excretion and retention. The parent polymer was formed solely by N(2-hydroxyethyl)aspartamide units (I) and in its derivatives about 20% of 2-hydroxyethyl groups were randomly replaced by either n-butyl- (II), 2(4-hydroxyphenyl)ethyl- (III), N-dimethylamino propyl- (IV) or the aspartamide unit was modified to free aspartic acid carboxyl (V). The rate of clearance from the serum, the deposition in the kidney tissue in comparison with the deposition in reticuloendothelial system organs — liver and spleen, as well as tissue and cellular localisation of deposites were studied on rabbits and mice taking advantage of fluorescence labelling. The clearance of macromolecular models from the serum compartment by the glomerular filtration is mainly molecular weight controlled, while the retention of macromolecules possessing the same molecular weight by the kidney tubular epithelium is strongly affected by chemical modification. About thirty and hundred times higher retentions due to reabsorption in proximal rubule were found with macromolecular models II and III respectively.

Biodegradable soluble macromolecules as drug carriers

Abstract Macromolecular drug forms are expected to prolong the drug residence time in the compartment of application due to their very limited passage across compartmental barriers. Second, the carrier may protect the active moiety from inactivation and may render it less immunogenic. Third, the macromolecular carrier provides the opportunity of attaching specific ligands with tissue or organ affinity which makes the control of drug biodistribution possible. Similar to many natural regulatory macromolecules, the onset of function is contingent on the cleavage of the drug-carrier bond. Any carrier polymers should be cleared from the body after fulfilment of its role, the safest way being degradation to metabolizable fragments. Most macromolecular drugs are processed in lysosomes, but drug release in the central compartment would be more favourable in some cases. It is necessary to check the degradation of the final drug form and assess the pharmacology and immunology of all intermediate fragments. Certain fragments may play an important role in biodistribution and antigen presentation. Some synthetic polymers are known as biodegradable in the environment, but their biodegradability in the body has never been checked and is doubtful. It is difficult to shape natural macromolecules to the needs of pharmacology; the future lies therefore in synthetic polymers degradable in the main chain, poly(amino acids) being the most promising type.

Synthetic model polymers in the study of protein immobilization on glycidyl methacrylate carriers

Abstract The reactive polymer polysuccinimide was aminolysed with the spin label 2,2,6,6-tetramethyl 4-aminopiperidine- N -toxide to obtain on average about 9 unpaired spins/macromolecule. The remaining monomeric units were partially converted (80–99.5 mol%) to the 2-hydroxyethyl aspartamide residues, partly substituted with functional groups modelling side chains of natural proteins: carboxyl, primary alkylamine, imidazole, indole and 4-hydroxyphenyl groups. These model water-soluble polymers were reacted with the macroporous spherical carrier formed by glycidyl methacrylate-ethylene dimethacrylate copolymer and with epoxy-activated Sepharose. The amount of immobilized model compound was estimated by e.s.r. measurement. Reaction kinetics were studied at pH 3.85, 6.7, 8.15 and 9.55 at 4, 37 and 65°C. Flurescent amine was used to visualize the penetration of aqueous reactant solution into the beads. The binding yield of carboxyl-containing models was low at all pHs. Models with amine react easily and the binding yield at various pH values was clearly determined by dissociation. A rather different pH dependence was obtained with imidazole-containing models. The binding of 4-hydroxyphenyl and indole groups proceeded over the whole pH range, being highest on the acid side. Only a minor portion of binding groups accessible to low molecular weight reactants is occupied by the model polymers, even at saturation. The results suggest that with the synthetic carrier the kinetics of immobilization are dominated by diffusion of the reactant into the carrier particle followed by fast sorption on the internal surface which increases its local concentration in the vicinity of the oxirane reactive groups and which is responsible for the rapid onset of immobilization. The effect of sorption is almost absent with epoxy-activated Sepharose.

Fluorescence labeling method for estimation of soluble polymers in the living material

Abstract The highly fluorescent derivatives of fluorescein, bearing the aliphatic primary amino groups, N -(2-aminoethylcarbonyl)-5(6)-aminofluorescein and 5-[ N′ -(2-aminoethyl)thioureido]fluorescein, were prepared for labeling of soluble polymers. The absorption and emission properties of these labels and polymers labeled with them were compared with properties of fluorescein and fluorescein isothiocyanate (FITC)-bovine serum albumin conjugate. Effects of the chemical structure of the polymer on the relative fluorescence quantum yield of a covalently attached label were evaluated using ionogenic, olefinic, or phenolic groups in side chains. The fluorescence of labeled polymers was adequate for their tracing in all the cases studied. The most pronounced quenching of fluorescence in the presence of phenolic groups is comparable with the quenching of fluorescence of FITC observed in FITC-protein conjugates. The long-term stability of the polymer-fluorochrome bond was checked in solutions of pH 2.10, 7.46, and 11.84; a higher stability of simple amide over amide plus the thiourea bond was found. The quantitative method of measurement of the concentration of labeled polymers in the biological material in a range of about 10 ng was developed; factors affecting the reproducibility are discussed.

Pharmacokinetics and plasma protein binding of two platinum cytostatics CHIP and CBDCA in rats.

SummaryPlasma protein binding and pharmacokinetic parameters of CHIP (cis-dichloro-trans-dihydroxy-bisisopropylamine platinum IV) and CBDCA (cis-diammine-1,1-cyclobutane dicarboxylate platinum II) were investigated in male Wistar rats. The plasma clearance of total and non-protein-bound platinum was determined and compared with that of 99mTc-DTPA. for binding experiments, a novel, simple, and quick method based on adsorption of non-protein-bound platinum species to charcoal was used. The clearance of total platinum after CHIP and CBDCA administration was markedly lower than the glomerular filtration rate (determined as the clearance of 99mTc-DTPA). The renal clearance of non-proteinbound platinum corresponded to 168% and 50% of the glomerular filtration rate for CHIP and CBDCA, respectively. These studies suggested that CHIP was excreted by the rat kidney.

The reaction of Pt-antitumor drugs with selected nucleophiles. I. The reaction of cis-[Pt(NH3)2Cl2] with glycine.

Various Pt(II)-glycine coordination compounds were characterized by 1H and 13C NMR spectroscopy, some of them also by electrophoretic and chromatographic behavior. The results were applied to the analysis of the reaction mixtures of cis-[Pt(NH3)2Cl2] and glycine obtained under various conditions. Cis-[Pt(NH3)2Cl2] reacts with glycine to give cis-diammine-(glycine-N,O)-Pt(II) and cis-diammine-bis(glycine-N-)Pt(II). Their ratio depends primarily on the pH of the reaction medium. Conformation of these compounds is discussed based on the observed Pt-C and Pt-H NMR coupling constants.