Risk assessment of adverse pulmonary effects induced by adrenaline beta-receptor antagonists and rational drug dosage regimen based on receptor occupancy

Theoretical method for evaluation of therapeutic effects and adverse effects of epidermal growth factor receptor tyrosine kinase inhibitors in clinical treatment

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are used for non-small cell lung cancer patients with an EGFR gene mutation. However, skin disorders are known as adverse events. In the present study, we investigated whether EGFR-TK occupancy is useful as an index for assessing clinical efficacy and adverse events for the proper use and development of EGFR-TKIs. Average binding occupancies (Φ _ss) of EGFR-TKIs, gefitinib and erlotinib, for the EGFR-TK of cancer or skin cells were calculated. The relationships of Φ _ss with response rate (RR) or frequency of rash were analyzed using the ternary complex model. Then, the relationships between the dose of EGFR-TKIs and RR or frequency of rash were examined. Gefitinib showed a greater difference for Φ _ss value for both wild-type and mutant EGFR as compared to erlotinib at usual dose. The RR increased in a nonlinear manner rapidly rising when Φ _ss exceeded 95%. It was thought that a very high Φ _ss value might be needed to obtain the therapeutic effect of EGFR-TKIs. Meanwhile, the frequency of rash increased in a linear manner along with elevation of Φ _ss. It was shown that the K _d ratio (K _d for mutant/K _d for wild type) was less than 0.001, when the high RR and low frequency of rash were obtained simultaneously. The results showed that the therapeutic effects and skin disorder can be assessed by using Φ _ss. Furthermore, it is likely that a proper choice of drug and dose can be made by using Φ _ss in EGFR-TKI therapy.

Analysis of Clinical Efficacy and Adverse Effects of β-Blocking Agents Used Clinically for Chronic Heart Failure

Clinical efficacy and adverse effects of the β-blocking agents, carvedilol, bisoprolol, and metoprolol were analyzed theoretically, and then compared quantitatively, for the purpose of determining their proper use for chronic heart failure. Initially, we evaluated occupancy binding to the β₁ and β₂ receptors (Фss^β₁ and Фss^β₂) by these drugs. Thereafter, we examined the relationship between Фss^β₁ values and left ventricular ejection fraction (LVEF) increase rate to determine efficacy. The result showed that the efficacy with carvedilol could be attained with a lower Фss^β₁ value than the others. Therefore, we constructed a model under the assumption that β-blocking agents exert both indirect action of LVEF increase through the β₁ receptor and direct action on ryanodine receptor 2. Using the model, it was suggested that these drugs have no differences in regard to the efficacy, while it was clarified theoretically that only carvedilol produces an effect that directly involves ryanodine receptor 2 at clinical doses. We also investigated decreases in heart rate and forced expiratory volume in 1 s as adverse effects of β-blocking agents using a ternary complex model. It was indicated that carvedilol is less likely to induce a heart rate decrease. Meanwhile, it was also suggested that the risk of an asthmatic attack was higher for carvedilol at clinical doses. Our results are considered useful for selection of a proper β-blocking agent and its administration at a reasonable dose for successful heart failure therapy.

Novel selective β1-adrenoceptor antagonists for concomitant cardiovascular and respiratory disease

β-Blockers reduce mortality and improve symptoms in people with heart disease; however, current clinically available β-blockers have poor selectivity for the cardiac β₁-adrenoceptor (AR) over the lung β₂-AR. Unwanted β₂-blockade risks causing life-threatening bronchospasm and reduced efficacy of β₂-agonist emergency rescue therapy. Thus, current life-prolonging β-blockers are contraindicated in patients with both heart disease and asthma. Here, we describe NDD-713 and -825, novel highly β₁-selective neutral antagonists with good pharmaceutical properties that can potentially overcome this limitation. Radioligand binding studies and functional assays that use human receptors expressed in Chinese hamster ovary cells demonstrate that NDD-713 and -825 have nanomolar β₁-AR affinity >500-fold β₁-AR vs. β₂-AR selectivity and no agonism. Studies in conscious rats demonstrate that these antagonists are orally bioavailable and cause pronounced β₁-mediated reduction of heart rate while showing no effect on β₂-mediated hindquarters vasodilatation. These compounds also have good disposition properties and show no adverse toxicologic effects. They potentially offer a truly cardioselective β-blocker therapy for the large number of patients with heart and respiratory or peripheral vascular comorbidities.—Baker, J. G., Gardiner, S. M., Woolard, J., Fromont, C., Jadhav, G. P., Mistry, S. N., Thompson, K. S. J., Kellam, B., Hill, S. J., Fischer, P. M. Novel selective β₁-adrenoceptor antagonists for concomitant cardiovascular and respiratory disease.

Prediction of alpha1-adrenoceptor occupancy in the human prostate from plasma concentrations of silodosin, tamsulosin and terazosin to treat urinary obstruction in benign prostatic hyperplasia

Alpha1-adrenoceptor antagonists are clinically useful for the improvement of urinary obstruction due to benign prostatic hyperplasia (BPH), and their therapeutic effects are mediated through the blockade of prostatic alpha(1)-adrenoceptors. The present study was undertaken to predict the magnitude and duration of alpha(1)-adrenoceptor occupancy in the human prostate after oral alpha(1)-adrenoceptor antagonists. Prostatic alpha(1)-adrenoceptor-binding parameters of silodosin were estimated by measuring specific [(3)H]prazosin binding in rat prostate after oral administration of this drug. The plasma concentration of silodosin after oral administration in rats and healthy volunteers was measured using a high-performance liquid chromatographic method. The alpha(1)-adrenoceptor-binding affinities (K(i)) of silodosin, tamsulosin, and terazosin in the human prostate and plasma concentrations of tamsulosin and terazosin were obtained from the literature. Using the alpha(1)-adrenoceptor binding parameters of silodosin in rat prostate, alpha(1)-adrenoceptor occupancy in the human prostate was estimated to be around 60-70% at 1-6 h after oral administration of silodosin at doses of 3.0, 8.1, and 16.1 micromol. Thereafter, the receptor occupancy was periodically decreased, to 24% (8.1 micromol) and 54% (16.1 micromol) 24 h later. A similar magnitude and time course of alpha(1)-adrenoceptor occupancy by silodosin in the human prostate were estimated using alpha(1)-adrenoceptor-binding affinities (K(i)) in the human prostate. Despite about two orders of differences in the plasma unbound concentrations after clinically effective oral dosages of silodosin, tamsulosin, and terazosin, there was a comparable magnitude of prostatic alpha(1)-adrenoceptor occupancy by these drugs. In conclusion, the prediction of alpha(1)-adrenoceptor occupancy in the human prostate by alpha(1)-adrenoceptor antagonists may provide the rationale for the optimum dosage regimen of these drugs in the therapy of BPH.

Quantitative estimation of myocardial fibrosis based on receptor occupancy for beta2-adrenergic receptor agonists in rats

To develop beta2-adrenergic receptor (AR) agonists with higher selectivity, it is essential to evaluate the cardiac side effects which are the most serious side effects of this class of drugs. We studied receptor occupancy of beta1-ARs in rats as a possible cause for the side effect of beta2-AR agonists, namely myocardial fibrosis. Myocardial fibrosis in rats was observed on Day 7 after the administration of salbutamol and terbutaline, both of which are selective beta2-AR agonists, at higher dose levels. To evaluate receptor occupancy, plasma concentrations of (R)-salbutamol and (R)-terbutaline, plasma protein binding and the EC50 for chronotropic effects in rats were determined. Based on the plasma concentrations, the plasma protein binding and EC50, receptor occupancy-time profiles were constructed. The relationship between the receptor occupancy-time profile under the curve, the AUCphi, and the degree of myocardial fibrosis was evaluated with a multiple correlation analysis. Myocardial fibrosis was significantly correlated (r2 > 0.78) to the AUCphi with the threshold above approximately 50%, but not to plasma concentrations. These results indicate that the receptor occupancy theory is also useful for the evaluation of the chronotropic side effects of beta2-AR agonists.

Ocular pharmacokinetic/ pharmacodynamic modeling for bunazosin after instillation into rabbits

PURPOSE

To develop a pharmacokinetic/pharmacodynamic (PK/PD) model for an alpha1-blocker (bunazosin) after instillation. The PK/PD model can predict both the drug concentrations in various ocular tissues and the hypotensive effect.

METHODS

Bunazosin concentrations were determined with High Performance Liquid Chromatography (HPLC) in tear fluid, the aqueous humor, cornea, and iris-ciliary body after instillation or ocular injection into the anterior chamber in rabbits. After instillation of bunazosin in rabbits, intraocular pressure (IOP) was also determined with a pneumatic tonometer. The PK/PD parameters were estimated by fitting the concentration-time profiles and the hypotensive effect-time profiles to the developed PK/PD models using the MULTI (RUNGE) program.

RESULTS

On the basis of the concentration-time profiles of bunazosin, a PK model, including seven compartments, was developed for examining the behavior of bunazosin after instillation. Then, two PK/ PD models for hypotensive effect of bunazosin were developed using an indirect response (model A) and the relationship between IOP and aqueous humor flow (model B). These models well described the concentration-time profiles and hypotensive effect-time profiles of bunazosin after instillation.

CONCLUSIONS

This study is the first trial to develop a PK/PD model for an antiglaucoma agent using an indirect response and the relationship between IOP and aqueous humor flow.

Prediction and assessment of extrapyramidal side effects induced by risperidone based on dopamine D(2) receptor occupancy

In the present study, we attempted to predict the risk of extrapyramidal side effects of a selective monoaminergic antagonist, risperidone, by analyzing the correlation between the dopamine D(2) receptor occupancy and the degree of extrapyramidal side effects of the drug. The occupancies of D(2) and 5-HT(2) receptors at various doses of risperidone were calculated by means of a receptor occupancy theory. The extrapyramidal side effects after administration of risperidone were attempted to predict by theoretical analysis of the correlation between the calculated occupancies and the evidence of extrapyramidal symptoms using a ternary complex model. The pharmacokinetic/pharmacodynamic analysis utilized the data concerning the pharmacokinetics of risperidone and 9-hydroxyrisperidone (active metabolite), their binding affinities with D(2) and 5-HT(2) receptors, and the clinical evidence of extrapyramidal symptoms (Extrapyramidal Symptom Rating Scale: ESRS), gathered from the literature. The mean occupancy of 5-HT(2) receptors after the administration of regular doses of risperidone was suggested to be more than 90%, whereas the mean occupancy of D(2) receptors varied between 50-80%, depending on the dose. The correlation between the occupancy of D(2) receptors and the extrapyramidal symptoms could be successfully analyzed with a ternary complex model, showing the predictability of the model for the extrapyramidal side effects of risperidone. Since the estimated risk of the extrapyramidal side effects varied with the dose, the present method of predicting the extrapyramidal side effects of risperidone may provide a basis for developing a rational dosing regimen for the drug.

Assessment of systemic adverse reactions induced by ophthalmic beta-adrenergic receptor antagonists

To assess quantitatively the risks of ophthalmic beta-blocking agents for cardiovascular and respiratory adverse reactions, we analyzed the binding kinetics of beta-blocking agents to the beta-1 and beta-2 adrenoceptors. The relationship between the occupancies for beta-1 and beta-2 adrenoceptors and the effects on the exercise pulse rate or the forced expiratory volume in one second (FEV1) after topical administration of carteolol, befunolol, timolol and betaxolol was analyzed using a ternary complex model. The beta-1 and beta-2 receptor occupancies after ophthalmic administration were calculated to be quite high as well as those after oral administration. The maximum occupancies for beta-1 and beta-2 receptors after ordinary ophthalmic administration were 52% and 88% for carteolol, 52% and 61% for befunolol, 62% and 82% for timolol, and 44% and 3% for betaxolol, respectively. Concave relationships were obtained between a decrease in exercise pulse rate and the beta-1 receptor occupancy and between a decrease in FEV1 and beta-2 receptor occupancy, respectively. Nasolacrimal occlusion was estimated to decrease the exercise pulse rate and FEV1 by 65% and 50%, respectively. The beta-1 and beta-2 adrenoceptor occupancies were proved to be the most appropriate indicators for cardiac and pulmonary adverse reactions evoked by ophthalmic beta-blocking agents.