Binding of vinca alkaloid analogues to human serum albumin and to alpha 1-acid glycoprotein

Synthesis and pharmacological activity of vinpocetine derivatives

Vinpocetine and its derivatives were extensively employed in the treatment of ischemic stroke, serving as effective cerebrovascular vasodilators. They could also be utilized for neuroprotection, anti-inflammatory purposes, anti-aging interventions, insomnia treatment, and antidepressant effects. However, due to issues such as hepatic first-pass effect, low bioavailability, and poor patient compliance with multiple dosing, the secondary development of Vinpocetine to address these limitations became a prominent area of research. Five primary methodologies were employed for the synthesis of Vinpocetine derivatives. These included substitution on the A ring to modify the 14-ester group, alteration of the 16-ethyl group, simplification of the D and E rings, and modification of the conformation of Vinpocetine. This paper summarized the current synthesis and activity studies of Vinpocetine and its derivatives, with the aim of providing a reference for the discovery of more potent derivatives of Vinpocetine.

Dimeric binding of plant alkaloid ellipticine to human serum proteins

Induced exciton circular dichroism signals reveal the accommodation of a pair of ellipticine molecules to the subdomain IB of human serum albumin and the β-barrel of α₁-acid glycoprotein.

Lipophilicity of vinpocetine and related compounds characterized by reversed-phase thin-layer chromatography

A reversed-phase thin-layer chromatographic method was developed and applied to quantitate the lipophilicity of sparingly water-soluble eburnane alkaloids of therapeutic interest. Our method development included calibration, optimization and validation procedures, using also sets of auxiliary compounds. The log P(TLC) values of five relatively hydrophilic eburnanes were verified by stir-flask studies. The alkaloids were found to have lipophilicity values in the 2.9-4.8 log P(TLC) range. Conclusions on structure-lipophilicity relationships were drawn in terms of ring anellation, character and length of side chain, conformational preferences and moiety-solvent interactions, also supported by molecular mechanics studies.

Human alpha-1-glycoprotein and its interactions with drugs

For about half a century, the binding of drugs to plasma albumin, the "silent receptor," has been recognized as one of the major determinants of drug action, distribution, and disposition. In the last decade, the binding of drugs, especially but not exclusively basic entities, to another plasma protein, alpha 1-acid glycoprotein (AAG), has increasingly become important in this regard. The present review points out that hundreds of drugs with diverse structures bind to this glycoprotein. Although plasma concentration of AAG is much lower than that of albumin, AAG can become the major drug binding macromolecule in plasma with significant clinical implications. Also, briefly reviewed are the physiological, pathological, and genetic factors that influence binding, the role of AAG in drug-drug interactions, especially the displacement of drugs and endogenous substances from AAG binding sites, and pharmacokinetic and clinical consequences of such interactions. It can be predicted that in the future, rapid automatic methods to measure binding to albumin and/or AAG will routinely be used in drug development and in clinical practice to predict and/or guide therapy.

Mechanisms of retention of pyrrolidinyl norephedrine on immobilized alpha(1)-acid glycoprotein

The HPLC separation of the R,S and S,R enantiomers of pyrrolidinyl norephedrine on immobilized alpha-1 glycoprotein (AGP) was investigated. Conditions for the separation were varied using a premixed mobile phase containing an ammonium phosphate buffer and an organic modifier. The influence of mobile phase pH, ionic strength, organic modifier composition, modifier type, and temperature on the chiral selectivity and retention were investigated. The presented data demonstrate that independent phenomena govern the enantioselectivity and retention. Retention is a function of both ion exchange equilibria and hydrophobic adsorption. Thermodynamic data derived from van't Hoff plots illustrates that while enantioselectivity is also enthalpically driven, the magnitude of the enthalpy term is governed by pH. Enantioselectivity has little dependence on ionic strength. Hydrophobic interactions appear to foster hydrogen bonding interactions; the two appear to be mutually responsible for chiral selectivity. The chiral selectivity decreases as the pH is decreased and increases with mobile phase buffer strength.

Drug-protein binding sites. New trends in analytical and experimental methodology

In the last few years, continuous progress in instrumental analytical methodology has been achieved with a substantial increase in the number of new, more specific and more flexible methods for ligand-protein assays. In general, the methods used for drug-protein binding studies can be divided into two main groups: separation methods (enabling the calculation of binding parameters, i.e. the number of binding sites and their respective affinity constants) and non-separation methods (describing predominantly qualitative parameters of the ligand-protein complex). This review will be focussed particularly on recent trends in the development of drug-protein binding methods including stereoselective and non-stereoselective aspects using chromatography, capillary electrophoresis and microdialysis as compared to the "conventional approach" using equilibrium dialysis, ultrafiltration or size exclusion chromatography. The advantages and limitations of various methods will be discussed including a focus on "optimal" experimental strategies taking into account in vitro, ex vivo and/or in vivo studies. Furthermore, the importance of some particular aspects concerning the drug binding to proteins (covalent binding of drugs and metabolites, stereoselective interactions and evaluation of binding data) will be outlined in more detail.

Charge transfer chromatographic study of the binding of commercial pesticides to various albumins

The interaction of 28 commercial pesticides with human and bovine serum albumin as well as with egg albumin was studied by charge-transfer reversed-phase thin-layer chromatography and the relative strength of the interaction was calculated. Only one pesticide interacted with egg albumin whereas the majority of pesticides bound both to bovine and human serum albumins. Stepwise regression analysis proved that the hydrophobicity parameters of pesticides exert a significant impact on their capacity to bind to serum albumins. These findings support the hypothesis that the binding of pesticides to albumins may involve hydrophilic forces occurring between the corresponding apolar substructures of pesticides and amino acid side chains. No linear correlation was found between the capacities of human and bovine serum albumins to bind pesticides.

Vinorelbine high-affinity binding to human platelets and lymphocytes: distribution in human blood

Using [3H]-vinorelbine, we demonstrated the presence of saturable and time-dependent high-affinity binding sites on human platelets and lymphocytes. The dissociation constant and binding-site values observed were 200 +/- 38 nM, 20.0 +/- 2.2 amol/platelet, and 155 +/- 20 amol/lymphocyte, respectively. Among other blood components, saturable low-affinity binding of vinorelbine to alpha 1-acid glycoprotein, serum albumin, and lipoproteins was observed. The binding to erythocytes was nonsaturable. Given the relative concentrations of these carriers, vinorelbine mainly distributes in the platelet compartment in blood (> 70%), and the amount of free vinorelbine in plasma relative to the total amount in blood is < 2%. It is suggested that because of the preferential retention of vinorelbine by platelets, variations in the platelet count are very likely to produce changes in the free blood fraction of vinorelbine.

Effect of D,L-verapamil, verapamil enantiomers and verapamil metabolites on the binding of vincristine to alpha 1-acid glycoprotein

Vincristine binding to solutions of alpha 1-acid glycoprotein (AGP, 2 mg/ml) and the effect of D,L-verapamil, verapamil enantiomers and the verapamil metabolites norverapamil and D617 were investigated in vitro using equilibrium dialysis and 3H-labelled vincristine. Vincristine binding to AGP (52.3 +/- 3.6%) was concentration independent over the range 0.002-2.0 micrograms/ml. The displacement of vincristine from AGP varied between 25.1 and 81.3% with D,L-verapamil and verapamil enantiomers added at concentrations in the range 5-50 micrograms/ml. In contrast, the displacement by D617 (5-100 micrograms/ml) was weaker and varied between 0 and 47%. The displacement at 20 micrograms/ml produced by D,L-verapamil, R-verapamil, S-verapamil and norverapamil was 53.1%, 56.8%, 58.9% and 53.9%, respectively, was more than double that for D617 (25%; P = 0.002). It is concluded that vincristine, D,L-verapamil and verapamil isomers and metabolites interact at binding sites on AGP. These interactions may be clinically important in multidrug resistance, for example in cancer patients with elevated levels of AGP undergoing treatment with verapamil and vinca alkaloids.

Binding of a new vinca alkaloid derivative, S12363, to human plasma proteins and platelets. Usefulness of an erythrocyte partitioning technique

The interactions of S12363 with human plasma proteins have been investigated in vitro by an erythrocyte partitioning technique that allows a quantitative estimation of the plasma and erythrocytes binding. S12363 was 85-95% plasma-bound and 97-98% blood-bound. The main binding protein in plasma was alpha-acid glycoprotein, with a binding constant of 0.6 x 10(6) M-1, accounting for 70% of total S12363 in plasma. Owing to extensive binding to platelets (40-50% of total blood amount), S12363 was mainly distributed in the non plasma blood compartment, with blood-to-plasma concentrations ratio of 1.2-1.4. These results indicate that, in vivo, the fraction of blood S12363 available for tissue diffusion, i.e., the free drug fraction in blood, should depend on both alpha 1-acid glycoprotein concentration in plasma and blood platelet count.

Chiral high-performance liquid chromatographic separations of vinca alkaloid analogues on alpha 1-acid glycoprotein and human serum albumin columns

Separations of the stereoisomers of a series of tetracyclic and pentacyclic vinca alkaloid analogues having two or three chiral centres were performed on Chiral-AGP and Chiral-HSA high-performance liquid chromatographic columns. Phosphate buffers with pH 5-7 containing 5-35% acetonitrile or 2-propanol were used as mobile phases. The results were in accordance with previous binding data obtained with native AGP and on an HSA-Sepharose column. Whereas on Chiral-AGP the retention of the trans isomers having 1(R),12b(S)-indolo[2,3-a]quinolizidine or the corresponding 3(S),16(R)-eburnane absolute configurations was exceedingly high, on Chiral-HSA the trans isomers, independently of their absolute configurations, were more retained. Eburnane-type compounds could also be separated according to the configuration of the chiral centre at position 14. A comparison of the chromatographic properties of the vinca alkaloids on the Chiral-AGP and Chiral-HSA columns demonstrates that these compounds are bound with higher affinity to the AGP phase. The AGP column resolves a very broad range of vinca alkaloids compared with the HSA column. Higher stereoselectivity and a much better chromatographic performance were also obtained on the Chiral-AGP column.