Characteristics of AZD9708, a novel, selective ß2-adrenoceptor agonist with rapid onset and long duration of action.

Here we describe the pre-clinical pharmacological profile of AZD9708, a novel long-acting ß(2)-adrenoceptor agonist that has potential as a once-daily therapy for asthma and chronic obstructive pulmonary disease (COPD). AZD9708 is a potent and selective agonist at the human ß(2)-adrenoceptor, with selectivity over human ß(1)- and ß(3)-adrenoceptors of >500 and >24 fold, respectively. AZD9708 relaxes carbachol-induced contraction of human bronchial rings with a time to 90% of maximal relaxation of 13-20 min, similar to that seen with formoterol and quicker than salmeterol. In anesthetized guinea pigs, AZD9708 provides significant protection against histamine-induced airway constriction at 24 h after intratracheal and nebulized doses. This is longer than with intratracheal salmeterol, which is bronchoprotective for approximately 8 h, and formoterol, which is bronchoprotective for 8 and 12 h following nebulized and intratracheal dosing, respectively. AZD9708 also shows the potential for a greater therapeutic margin than widely used ß(2)-adrenoceptor agonists such as formoterol. At a defined efficacy dose that provides 80% bronchoprotection (ED(80)), formoterol leads to a decrease in blood potassium levels in guinea pigs, whilst AZD9708 is not associated with significant reductions in potassium levels at doses up to 7 times the ED(80). [(14)C]AZD9708 is associated with extensive protein binding in both human (mean 1.0% free) and rat (mean 2.6% free) plasma. This pharmacological profile indicates the potential of AZD9708 to become an important addition to the range of bronchodilators available for the treatment of patients with obstructive airways disease.

Evaluation of human pharmacokinetics, therapeutic dose and exposure predictions using marketed oral drugs.

In this article approaches to predict human pharmacokinetics (PK) are discussed and the capability of the exemplified methodologies to estimate individual PK parameters and therapeutic dose for a set of marketed oral drugs has been assessed. For a set of 63 drugs where the minimum efficacious concentration (MEC) and human PK were known, the clinical dose was shown to be well predicted or in some cases over-estimated using a simple one-compartment oral PK model. For a subset of these drugs, in vitro potency against the primary human targets was gathered, and compared to the observed MEC. When corrected for plasma protein binding, the MEC of the majority of compounds was < or=3 fold over the respective in vitro target potency value. A series of in vitro and in vivo experiments were conducted to predict the human PK parameters. Metabolic clearance was generally predicted well from human hepatocytes. Interestingly, for this compound set, allometry or glomerular filtration rate (GFR) ratio methods appeared to be applicable for renal CL even where CL(renal) > GFR. For approximately 90% of compounds studied, the predicted CL using in vitro-in vivo (IVIV) extrapolation together with a CL(renal) estimate, where appropriate, was within 2-fold of that observed clinically. Encouragingly volume of distribution at steady state (V(ss)) estimated in preclinical species (rat and dog) when corrected for plasma protein binding, predicted human V(ss) successfully on the majority of occasions--73% of compounds within 2-fold. In this laboratory, absorption estimated from oral rat PK studies was lower than the observed human absorption for most drugs, even when solubility and permeability appeared not to be limiting. Preliminary data indicate absorption in the dog may be more representative of human for compounds absorbed via the transcellular pathway. Using predicted PK and MEC values estimated from in vitro potency assays there was a good correlation between predicted and observed dose. This analysis suggests that for oral therapies, human PK parameters and clinical dose can be estimated from a consideration of data obtained from in vitro screens using human derived material and in vivo animal studies. The benefits and limitations of this holistic approach to PK and dose prediction within the drug discovery process are exemplified and discussed.

A unified model for predicting human hepatic, metabolic clearance from in vitro intrinsic clearance data in hepatocytes and microsomes.

The aim of this study was to evaluate a unified method for predicting human in vivo intrinsic clearance (CL(int, in vivo)) and hepatic clearance (CL(h)) from in vitro data in hepatocytes and microsomes by applying the unbound fraction in blood (fu(b)) and in vitro incubations (fu(inc)). Human CL(int, in vivo) was projected using in vitro data together with biological scaling factors and compared with the unbound intrinsic clearance (CL(int, ub, in vivo)) estimated from clinical data using liver models with and without the various fu terms. For incubations conducted with fetal calf serum (n=14), the observed CL(int, in vivo) was modeled well assuming fu(inc) and fu(b) were equivalent. CL(int, ub, in vivo) was predicted best using both fu(b) and fu(inc) for other hepatocyte data (n=56; r(2)=0.78, p=3.3 x 10(-19), average fold error=5.2). A similar model for CL(int, ub, in vivo) was established for microsomal data (n=37; r(2)=0.77, p=1.2 x 10(-12), average fold error=6.1). Using the model for CL(int, ub, in vivo) (including a further empirical scaling factor), the CL(h) in humans was also calculated according to the well stirred liver model for the most extensive dataset. CL(int, in vivo) and CL(h) were both predicted well using in vitro human data from several laboratories for acidic, basic, and neutral drugs. The direct use of this model using only in vitro human data to predict the metabolic component of CL(h) is attractive, as it does not require extra information from preclinical studies in animals.

Lung cancer mortality among chromate production workers.

AIMS: To assess mortality in 1997 among 493 former workers of a US chromate production plant employed for at least one year between 1940 and 1972. METHODS: Cohort members were followed for mortality to 31 December 1997. Standardised mortality ratios (SMRs) were calculated for selected cause specific categories of death including lung cancer. Lung cancer mortality was investigated further by calculation of SMRs stratified by year of hire, duration of employment, time since hire, and categories of cumulative exposure to Cr(VI). RESULTS: Including 51 deaths due to lung cancer, 303 deaths occurred. SMRs were significantly increased for all causes combined (SMR = 129), all cancers combined (SMR = 155), and lung cancer (SMR = 241). A trend test showed a strong relation between lung cancer mortality and cumulative hexavalent exposure. Lung cancer mortality was increased for the highest cumulative exposure categories (> or =1.05 to <2.70 mg/m(3)-years, SMR = 365; > or =2.70 to 23 mg/m(3)-years, SMR = 463), but not for the first three exposure groups. Significantly increased SMRs were also found for year of hire before 1960, 20 or more years of exposed employment, and latency of 20 or more years. CONCLUSIONS: The finding of an increased risk of lung cancer mortality associated with Cr(VI) exposure is consistent with previous reports. Stratified analysis of lung cancer mortality by cumulative exposure suggests a possible threshold effect, as risk is significantly increased only at exposure levels over 1.05 mg/m(3)-years. Though a threshold is consistent with published toxicological evidence, this finding must be interpreted cautiously because the data are also consistent with a linear dose response.

Historical cohort study of 10 109 men in the North American vinyl chloride industry, 1942-72: update of cancer mortality to 31 December 1995.

OBJECTIVES: To update and assess mortality from neoplasms to 31 December 1995 among 10 109 men employed in a job exposed to vinyl chloride for at least 1 year between 1942 and 1972 at any of 37 North American factories. Previous analyses indicated associations between employment in vinyl production and increased mortality risk from cancers of the liver and biliary tract, due to increased mortality from angiosarcoma of the liver, and brain cancer. METHODS: Standardised mortality ratio (SMR) analyses, overall and stratified by several work related variables, were conducted with United States and state reference rates. Cox's proportional hazards models and stratified log rank tests were used to further assess occupational factors. RESULTS: 895 of 3191 deaths (28%) were from malignant neoplasms, 505 since the previous update to the end of 1982. Mortality from all causes showed a deficit (SMR 83, 95% confidence interval (95% CI) 80 to 86), whereas mortality from all cancers combined was similar to state referent rates. Mortality from cancers of the liver and biliary tract was clearly increased (SMR 359, 95% CI 284 to 446). Modest excesses of brain cancer (SMR 142, 95% CI 100 to 197) and cancer of connective and soft tissue (SMR 270, 95% CI 139 to 472) were found. Stratified SMR and Cox's proportional hazard analyses supported associations with age at first exposure, duration of exposure, and year of first exposure for cancers of the liver and soft tissues, but not the brain. CONCLUSIONS: Excess mortality risk from cancer of the liver and biliary tract, largely due to angiosarcoma, continues. Risk of mortality from brain cancer has attenuated, but its relation with exposure to vinyl chloride remains unclear. A potentially work related excess of deaths from cancer of connective and soft tissue was found for the first time, but was based on few cancers of assorted histology.

The effect of ionic strength on liposome-buffer and 1-octanol-buffer distribution coefficients.

The distribution of salmeterol and proxicromil between unilamellar vesicles of dioleoylphosphatidylcholine (DOPC) and aqueous buffer at pH 7.4 has been studied, using an ultrafiltration method, as a function of compound concentration, DOPC concentration, and buffer ionic strength. The binding of these ionized lipophilic compounds to neutral DOPC vesicles induces a surface charge, which causes the observed membrane distribution coefficient D(mem)obs to vary significantly with bound compound to DOPC ratio and with ionic strength. This variability is shown to be well-described with use of the Gouy-Chapman theory of the ionic double layer and is contrasted with the ideal behavior shown by the neutral compound clofibrate. Increasing ionic strength is also shown to increase the observed 1-octanol-buffer distribution coefficients D(o/w)obs of proxicromil but through a very different mechanism involving the extraction of ion pairs. This study highlights the experimental difficulty in determining concentration-independent liposome distribution coefficients of ionized lipophilic compounds and describes when deviations will be significant and how observed values may be corrected for such effects. The general effect of ionic strength on membrane-buffer distribution and 1-octanol-buffer distribution is discussed with particular reference to the very different propensity for ion pair formation shown by the two systems, and the most suitable experimental conditions that should be used with each system.

Partitioning of ionizing molecules between aqueous buffers and phospholipid vesicles.

The distribution of four ionizing molecules between small unilamellar vesicles of dimyristoylphosphatidylcholine (DMPC) and aqueous buffers has been studied as a function of pH using an ultrafiltration method. The results show that pH-distribution behavior observed in the standard 1-octanol-water system does not always apply in model membrane systems, since the charged form of some molecules are able to partition into a phospholipid bilayer. It was further shown that the partitioning of these charged species into the bilayer is not as a consequence of ion pairing. The results clarify reports suggesting that protonated amines have a surprisingly high membrane affinity, and the implications of these findings for drug design are discussed.