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Methods for determining plasma free drug concentration by direct measurement of binding affinity of protease inhibitors to plasma proteins

a protease inhibitor and plasma protein technology, applied in the field of isothermal titration calorimetry analysis of the binding affinity of protease inhibitors to plasma proteins, can solve the problems of % change in free drug concentration, toxic response, significant changes in clinical respons

Inactive Publication Date: 2006-09-14
TIBOTEC PHARMA
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  • Abstract
  • Description
  • Claims
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Benefits of technology

[0013] Furthermore, the present invention provides a method that can calculate the effect of plasma-proteins on the antiviral activity (EC50 values) of protease inhibitors from their binding affinities to plasma proteins. The present invention provides as well a method that can evaluate the in vivo anti-HIV efficacy of PIs in human plasma.
[0014] Often there may be competition between drugs in plasma protein binding, in which agents that are bound tightly, such as coumarin anticoagulants, macrolide or lincosamide antibiotics that bind tightly to alpha-1-acid Glycoprotein (AAG), are able to displace less tightly bound compounds from their binding sites and thus can increase the free form of the drug and improve the biological efficacy (Sommadossi, et al., 1998 U.S. Pat. No. 5,750,493). Therefore, the present invention provides as well a method for selecting compounds that competitively bind with plasma proteins, said selection being useful for co-administering agents to compete for plasma protein binding, so that an increase of the free plasma concentration of protease inhibitors can be achieved.

Problems solved by technology

Slight changes in the binding affinity of drugs to blood components can result in significant changes in clinical response or can even cause a toxic response.
Since it is the free-drug in plasma which equilibrates with the pharmacologically active site, a slight change in the binding affinity, such as from 99 to 98% binding, can result in an almost 100% change in free drug concentration, and, thus, can cause a significant alteration in response.
Also, the clinical significance of these effects in vitro was shown by the lack of clinical efficacy of the HIV PI SC-52151, which has potent antiretroviral activity in vitro but inactivity in vivo, because extensive protein binding prevented intracellular diffusion (Fischl et al.
While there are extensive data to address this problem, no general correlation between protein binding and anti-HIV activity can be made so far on the basis of these studies.
Therefore, the use of percentage of bound and free forms is not useful and cannot be generally applied.

Method used

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  • Methods for determining plasma free drug concentration by direct measurement of binding affinity of protease inhibitors to plasma proteins
  • Methods for determining plasma free drug concentration by direct measurement of binding affinity of protease inhibitors to plasma proteins
  • Methods for determining plasma free drug concentration by direct measurement of binding affinity of protease inhibitors to plasma proteins

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example 1

Thermodynamic Equilibrium Binding Assay Using ITC

[0049] Binding experiments were run using Isothermal Titration Calorimetry (ITC) to measure bound and unbound protease inhibitors.

[0050] Sample preparation: Solutions of AAG and its variants for ITC experiments were made up in 20 mM sodium borate buffer, pH7.4. All compounds were prepared as stock solution of 20 mM or 25 mM in DMSO and thereafter diluted to desired concentration in the same buffer. For all ITC experiments, the percentage of DMSQ is below 1%.

[0051] ITC Experiments: The isothermal titration measurements of the binding of various PIs to AAG can be typically carried out at 37° C. using a VP-ITC titration calorimeter (MicroCal, Northampton, Mass.). The instrument was electrically calibrated by means of a standard electric pulse as recommended by the manufacturer. For the PIs binding to AAG, solutions of PI (80˜100 μM) were used to titrate AAG (10˜12 μM). A 300 μL syringe was used for the titrant, mixing was effected by ...

example 2

Ka can be Utilized to Predict the Effect of AAG on EC50 Value in Cell-Based Antiviral Assays

[0054] In order to determine whether there is a strong correlation between the loss of activity of PIs in presence of AAG and their binding affinities measured directly by ITC, the antiviral EC50 of these PIs in the presence of 1 mg / mL of AAG from their binding constants Ka with AAG and their EC50 in the absence of AAG was calculated according to Equation 4. FIG. 3 shows the calculated and experimental EC50 of 7 PIs studied here in the presence of 1 mg / mL AAG and in the absence of AAG. As discussed above, the addition of 1 mg / mL AAG in the cell culture markedly decreased the EC50 of PIs except IDV, herein we consider the presence of AAG has no effect on EC50 of IDV. Comparison of the calculated and experimental EC50 of these PIs in the presence of AAG revealed that the calculated and experimental values were highly consistent (FIG. 3). FIG. 4 shows the calculated EC50 versus experimental EC5...

example 3

Comparative Evaluation of the In Vivo Antiviral Efficacy of PIs in the Presence of AAG

[0055] The evaluation of the relative in vivo efficacy of PIs in human plasma from their EC50 (Equation 5) is shown in FIG. 5. The validation of the correct equation was confirmed using published data for three PIs monotherapy trials.

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Abstract

Methods for isothermal titration calorimetry analysis of the binding affinity of protease inhibitors to plasma proteins. A method that can quantitatively calculate free drug concentrations of protease inhibitors in human plasma, as well as a method to calculate therapeutic amounts and dosage regimens. Furthermore, the present invention provides a method that can calculate the effect of plasma proteins on the antiviral activity (EC50 values) of protease inhibitors from their binding affinities to plasma proteins. The present invention provides as well a method that can evaluate the in vivo anti-HIV efficacy of PIs in human plasma.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 60 / 295,557, filed on Jun. 5, 2001.FIELD OF THE INVENTION [0002] The present invention relates to methods for isothermal titration calorimetry analysis of the binding affinity of protease inhibitors to plasma proteins. BACKGROUND OF THE INVENTION [0003] Following administration, drugs are transported in biological fluids (e.g. in blood) partly in solution as free drug and partly bound to blood components (e.g., plasma proteins, blood cells). The physiologically active substances are in equilibrium between a free form and a form bound to endogenous ligands present in the same fluids (see reviews by Kremer, et al. Pharmacol Rev. 1988, 40:1-47). Only free drug is available for passive diffusion to target tissue sites where the desired biological activity may take place. When compared to the total-substance level, the free drug concen...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C12Q1/70C12Q1/68C12Q1/18G01N33/566G01N33/94
CPCC12Q1/18G01N33/566G01N33/94G01N2500/02
Inventor XIE, DONGCAO, WEIERICKSON, JOHN W.
Owner TIBOTEC PHARMA
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