Monoclonal antibodies to antitumor Vinca alkaloids: thermodynamics and kinetics

In vivo and in vitro pharmacokinetics and metabolism of vincaalkaloids in rat. II. Vinblastine and vincristine

Vinblastine and Vincristine pharmacokinetics, including tissue distribution, metabolism and biliary excretion, were investigated, using both "in vitro" and "in vivo" models, after i.v. injections in rats. Plasma kinetic curves were best fitted to a two-compartment open model. The average terminal half-lives of VLB and VCR were 14.3 h and 7.5 h, respectively. The systemic clearance and apparent distribution volume for VLB, respectively 1.49 l/h/kg and 11.46 l/kg, were significantly greater than those of VCR, 0.12 l/h/kg and 0.41 l/kg. VCR was found to be widely distributed in tissues after i.v. injections in rats. The highest drug accumulation site was the intestine (122.0 ng/g wet tissue at 24 h). Liver and kidneys also retained high proportions of drug (respectively, 47.0 ng/g and 44.4 ng/g at 24 h). Biliary excretion was more rapid for VCR (42.7% of total radioactivity excreted over 24 h) than VLB (28.2% of total dose over 24 h). For both molecules, the percentage of radioactivity excreted in bile over 30-48 h ranged between 40-50% of total dose. At high doses, either biliary excretion rate or cumulated excretion was reduced. High performance liquid chromatography analysis of bile samples revealed four biotransformation products for VLB and three for VCR. When incubated in freshly isolated rat hepatocytes, VLB penetrated more rapidly and intensely into the cells (more than 90% of total dose taken up over 20 min) than VCR (only about 40% accumulated), probably through a passive diffusion mechanism followed by tight cellular binding. "In vitro" metabolism patterns were similar to those found "in vivo", except for the most polar metabolites observed "in vitro". Two anti-Vinca monoclonal antibodies with different specificities were used to test VCR metabolite immunoreactivities. The results suggested that some structural modifications occurred in the catharantine moiety of the molecule but that the dimeric structure seemed to be well conserved after biotransformation.

In vivo and in vitro pharmacokinetics and metabolism of vincaalkaloids in rat. I. Vindesine (4-deacetyl-vinblastine 3-carboxyamide)

Vindesine (VDS) pharmacokinetics, including tissue distribution, metabolism and elimination, were investigated in rats using both in vivo and in vitro models. VDS was found to be intensively distributed in tissues after i.v. injection in rat. The most important drug accumulation site was the spleen (615.0 ng/g at 24 h). Liver and kidneys also retained VDS in significant amounts (respectively 170.1 +/- 11.0 ng/g and 145.0 +/- 17.0 ng/g at 24 h). Urine excretion of drug over 7 days was low (10.1 +/- 1.8% of total dose) and consisted mainly of unchanged drug (more than 85%). The major excretion route for VDS was the feces (69.6 +/- 2.5% of total dose) via the bile (50% of total dose excreted in 72 h). High performance liquid chromatography analysis (HPLC) of collected bile samples revealed the excretion of three VDS biotransformation products. These results were confirmed in vitro using freshly isolated rat hepatocytes in suspension. Rapid and high VDS uptake by liver cells, probably through a passive diffusion mechanism followed by a tight cellular binding, was demonstrated. Moreover, VDS was intensively converted, in vitro, into four metabolites which were rapidly excreted into the extracellular medium. In contrast, the intracellular medium contained almost exclusively unchanged drug, presumably fixed to tubulin proteins. Two anti-VDS monoclonal antibodies with different specificities were used to test metabolite immunoreactivities. The results suggested that some structural modifications occurred in the catharantine moiety of the molecule but that the VDS dimeric structure seemed well conserved after biotransformation.

Analysis of protein-protein interaction by simulation of small-zone size exclusion chromatography. Stochastic formulation of kinetic rate contributions to observed high-performance liquid chromatography elution characteristics

High-performance liquid chromatography (HPLC) procedures provide size-exclusion chromatography with sufficient speed that the elution characteristics of mixtures of interacting macromolecules are potentially determined by the kinetics of association and dissociation. However, few studies have yet addressed the consequences of interaction kinetics on HPLC analyses or evaluated the potential application of HPLC methods for the qualitative and quantitative interpretation of macromolecular interaction kinetics. An earlier simulation of small-zone chromatography of interacting molecules (Stevens, F. J. 1986. Biochemistry. 25:981-993) has been modified to incorporate the effects of association/dissociation kinetics on elution behavior. The previous assumption of instantaneous equilibration has been replaced by explicit calculation of partial relaxation of complexed and free constituent mixtures during each iteration of the simulation. In addition, a stochastically based formulation has been introduced to determine a velocity probability distribution that emulates the partial intermixing of free and complexed pools during the iteration cycle. The simulation generates bimodal elution profiles representing stable complexed and free components of mixtures for which interaction is characterized by slow kinetics relative to chromatography run times. For mixtures with rapid kinetics, a single-asymmetric peak results. When tested with a large-zone sample such that a plateau of stable concentration is generated, the simulation reproduces previous characterizations based on evaluations of solute continuity equations. Therefore, HPLC may, in many cases be an appropriate basis for techniques by which to evaluate kinetic and affinity characteristics of interacting biomolecules.

Size-exclusion high-performance liquid chromatography in analysis of protein and peptide epitopes

Size-exclusion HPLC provides direct observation of antibody-antigen interactions in free solution without chemical modification of either component. HPLC data collection systems are now a routine resource in both academic and industrial research laboratories. Monoclonal antibodies are, in principle, homogeneous reagents whose interactions with epitope are suitable for unambiguous quantitative characterization. HPLC-based methods, therefore, have the potential to contribute significantly to efficient quantitative characterization of monoclonal antibodies in studies directed to the fundamental physiological roles of these molecules as well as to the optimized selection and quality control of these reagents in biotechnical applications such as represented by the immunodiagnostic industry. In many cases, HPLC-based methods may represent the simplest and most rapid approach for evaluation of relative epitope specificities and affinity/kinetic characteristics of interaction.

Size-exclusion HPLC analysis of epitopes

A size-exclusion chromatography method based on competition between intact antibodies and antigen-binding fragments (Fabs) is used to evaluate relative spatial location of epitopes recognized by monoclonal antibodies. If epitopes are spatially distinct, the presence of a potentially competitive Fab results in formation of complexes of higher molecular weight than those formed by antigen and intact IgG. Complexes of lower molecular weight are formed if the epitopes overlap, are identical, or if, upon formation of the antigen-antibody complex, conformational change occurs that results in loss of epitope. Size-exclusion chromatography of the relevant mixtures reveals these shifts in molecular weight distribution and, therefore, provides an unambiguous determination of spatially independent epitopes. In addition, chromatographic analysis of competition between IgG and its enzymatically prepared Fab is used to evaluate the dissociation rate constant of the antigen-antibody reaction in re-equilibrating mixtures.

Antibody recognition of substituted ammonium ions. Modulation by the counterion

Antibodies directed against elliptinium acetate, a quaternary ammonium compound with antineoplastic activity in man, were obtained in rabbits, after conjugation of the drug with haemocyanin. These antibodies are specific for the quaternary ammonium structure. However, the recognition of the drug can be markedly decreased (ten-fold) by changing the associated counterion. These observations were extended to other ellipticine derivatives that exist in two forms: acetate and chloride. In each case, the recognition of the acetate form was 7-11-fold higher than that of the chloride form. These results could be explained by high-energy strengths existing between the cation and the anion, resulting in a paired-ion antigen. This represents the first identification of antibodies directed to a paired-ion structure, with specificity for both the cation and anion used for immunization. Such results are relevant in the construction of immunoassays for quaternary ammonium compounds.

Comparative pharmacokinetics of antitumor Vinca alkaloids: intravenous bolus injections of navelbine and related alkaloids to cancer patients and rats

The kinetics of distribution and elimination in rats of the antitumor drug navelbine and of two of its analogues, Na-formyl navelbine and deacetyl navelbine amide, have been studied by radioimmunoassay and compared with the kinetics obtained with vinblastine and vincristine. Fitting to two-exponential curves was used to derive pharmacokinetic parameters. Clearance was found to parallel toxicity for all drugs: it increases from 0.19 1 h-1 kg-1 for vincristine to 0.41 for Na-formyl navelbine, 1.4 for vinblastine, 2.3 for navelbine, and 2.6 for deacetyl navelbine amide. Terminal half-lives were longer for the Na-formyl-substituted alkaloids (around 13 h) than for the others (8-10 h). We have also studied navelbine kinetics in cancer patients entered in recent navelbine clinical trials and found that navelbine pharmacokinetics are characterized by fast and extensive distribution, high clearance (0.92 +/- 0.27 1 h-1 kg-1), and a relatively long terminal half-life (31.2 +/- 4.4 h). Relationships between chemical structure, pharmacokinetic properties, and toxicity or therapeutic efficiency within the Vinca alkaloid series are discussed, together with the relevance of animal models such as the rat in the screening of new antitumor drugs.

An enzyme-linked immunosorbent assay for the antineoplastic agent vincristine

An enzyme-linked immunosorbent assay for vincristine was developed, based on a new procedure for synthesizing the hapten-protein conjugate. In both the immunogen and the enzyme tracer a spacer group was introduced between the hapten and protein, and the vincristine was coupled at a site far from its functional groups. The antibody produced proved to be exceptionally specific as compared with previous immunoassays for bis-indole alkaloids. Thousandfold antibody dilutions could be used and samples at the femtomole range were assayable. Applications of the method to patient plasma samples and to plant material are described.