The study drug, GSK356278, is a possible new medicine for the treatment of Huntington's disease. Huntington's disease, which is often called HD, is caused by a faulty gene that is passed down through families. HD causes damage to nerve cells in the brain which causes them to waste away. As the damage progresses patients develop symptoms that affect every aspect of life. HD reduces people's ability to walk, talk, think, communicate and causes uncontrolled movements. GSK356278 may slow down the progression of damage to nerve cells in people with HD and help with their ability to think.

GSK356278 was well tolerated when it was given as a single dose to healthy people. In this study we want to see what effects, both good and bad, GSK356278 has in people when it is taken every day. During the study we will look at about 3 different doses of GSK356278 in about 36 healthy people. The study will also look at how GSK356278 tablets behave in the body after it is swallowed (this is called pharmacokinetics). The study will also look at effects of GSK356278 on the body (this is called pharmacodynamics). The study will help to design future clinical studies with GSK356278.

Inclusion Criteria:

• AST, ALT, alkaline phosphatase and bilirubin less than and equal to 1.5xULN (isolated bilirubin greater than 1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin less than 35%).
• Healthy as determined by a responsible and experienced physician, based on a medical evaluation including medical history, physical examination, laboratory tests and cardiac monitoring. A subject with a clinically significant abnormality or laboratory parameters significantly outside the reference range for the population being studied may be included only if the Investigator and the GSK Medical Monitor agree that the finding is unlikely to introduce additional risk factors and will not interfere with the study procedures.
• Male or female between 18 and 65 years of age inclusive, at the time of signing the informed consent.
• A female subject is eligible to participate if she is of: Non-childbearing potential is defined as pre-menopausal females with a documented tubal ligation or hysterectomy; or postmenopausal defined as 12 months of spontaneous amenorrhea. In questionable cases a blood sample with simultaneous follicle stimulating hormone (FSH) greater than 40 MlU/ml and estradiol less than 40 pg/ml (less than 147 pmol/L) is confirmatory. Females on hormone replacement therapy (HRT) and whose menopausal status is in doubt will not be eligible for the study.
• Male subjects with female partners of child-bearing potential must agree to use one of the contraception methods listed in the protocol (contraception requirements). This criterion must be followed from the time of the first dose of study medication until the follow up visit.
• Body weight greater than and equal to 50 kg and BMI within the range 19 - 30 kg/m2 (inclusive).
• Capable of giving written informed consent, which includes compliance with the requirements and restrictions listed in the consent form.Average of triplicate QTcF less than 450 msec (on an average of triplicate values)
• Normal echocardiography, plasma troponin and BNP levels confirmed before first dose

Exclusion Criteria:

• A positive pre-study Hepatitis B surface antigen or positive Hepatitis C antibody result within 3 months of screening
• Chronic history of liver disease, or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones).
• A positive pre-study drug/alcohol screen.
• A positive test for HIV antibody.
• History of regular alcohol consumption within 6 months of the study defined as: An average weekly intake of greater than 21 units for males or greater than 14 units for females. One unit is equivalent to 8 g of alcohol: a half-pint (approximately 240 ml) of beer, 1 glass (125ml) of wine or 1 (25 ml) measure of spirits.
• The subject has participated in a clinical trial and has received an investigational product within the following time period prior to the first dosing day in the current study: 30 days, 5 half-lives or twice the duration of the biological effect of the investigational product (whichever is longer).
• Exposure to more than four new chemical entities within 12 months prior to the first dosing day.
• Use of prescription or non-prescription drugs, including vitamins, herbal and dietary supplements (including St John's Wort) within 7 days (or 14 days if the drug is a potential enzyme inducer) or 5 half-lives (whichever is longer) prior to the first dose of study medication, unless in the opinion of the Investigator and GSK Medical Monitor the medication will not interfere with the study procedures or compromise subject safety.
• History of sensitivity to any of the study medications, or components thereof or a history of drug or other allergy that, in the opinion of the investigator or GSK Medical Monitor, contraindicates their participation.
• Where participation in the study would result in donation of blood or blood products in excess of 500 mL within a 30 day period.
• Unwillingness or inability to follow the procedures outlined in the protocol.
• Urinary cotinine levels indicative of smoking or history or regular use of tobacco or nicotine-containing products within 6 months prior to screening.
• Unable to refrain from consumption of red wine, seville oranges, grapefruit or grapefruit juice and/or pummelos, exotic citrus fruits, grapefruit hybrids from 7 daysprior to the first dose of study medication.
• Any history of suicidal behaviours or any suicidal ideation of type 4 or 5 on the CSSR in the last six months.

Patient-level data for this study will be made available through www.clinicalstudydatarequest.com following the timelines and process described on this site.