This will be a single centre, randomised, double-blind, placebo-controlled, 2-period crossover study to investigate the effect of treatment with repeat inhaled doses of GSK256066 on bronchial hyper-reactivity to adenosine monophosphate.

Inclusion: (All must Apply)

• Males and females aged 18 to 55 years inclusive.
• Documented history of bronchial asthma, first diagnosed at least 6 months prior to the screening visit and currently being treated only with intermittent short-acting beta -agonist therapy by inhalation.
• Pre-bronchodilator FEV1 >75% of predicted at screening.
• Documented sensitivity to AMP with a provocative concentration of AMP resulting in a 20% fall in FEV1 (PC20 AMP) of <80 mg/ml at the screening visit.
• Demonstrate stable bronchoconstriction in response to inhaled AMP at the run-in visit. 'Stable bronchoconstriction' is a term to define a population of asthmatics who have a repeatable and reproducible response to a challenge agent that induces bronchoconstriction. The run-in PC20 needs to be within 1.25DD of the screening PC20.
• Non-smoking status as verified by urinary cotinine levels below 300 ng/mL cotinine at the screening visit. This can include ex-smokers who have given up smoking for >6 months and have less than a 5 pack-year smoking history.
• Able and willing to give written informed consent to take part in the study.
• Available to complete all study measurements.

Exclusion:

• Pregnant or nursing females.
• Past or present disease, which as judged by the investigator, may affect the outcome of this study.
• Subject has known history of hypertension or is hypertensive at screening.
• Respiratory tract infection and/or exacerbation of asthma within 4 weeks prior to the first dose of study medication.
• History of life-threatening asthma, defined as an asthma episode that required intubation and/or was associated with hypercapnoea, respiratory arrest and/or hypoxic seizures.
• Unable to abstain from prescription medication, other than short acting inhaled beta-agonists and paracetamol for the treatment of minor ailments eg headache from 48h before the first dose until the follow-up visit.
• The subject has participated in a clinical trial during the previous 3 months.
• History of blood donation (450 mL) within 2 months of starting the clinical study.
• The subject regularly drinks more than 28 units of alcohol in a week if male, or 21 units per week if female.
• The subject has tested positive for hepatitis C antibody or hepatitis B surface antigen or HIV antibodies.
• The subject has positive drugs of abuse test.
• Subjects weighing less than 50kg are to be excluded from participating in the study.