Safety and Tolerability Study of GSK2586184 in Patients With Moderate to Severely Active Ulcerative Colitis.

Inclusion Criteria: * Male or female, between 18 and 75 years of age inclusive, at the time of signing the informed consent. * Moderate to severely active UC at least 6 months prior to Screening confirmed by colonoscopy or sigmoidoscopy with video recording, and biopsy. * A Mayo score of 6 to 12 points and endoscopy sub score of 2 to 3 at screening, despite concurrent treatment with at least 1 of the following (oral corticosteroids or any oral 5-aminosalicylic acid (ASA) or both as defined below): Oral 5-ASA at a stable dose (\>=2.4grams (g)/day) for at least 4 weeks from first dose. Must remain on a stable dose until end of treatment, Stable oral corticosteroid dose (prednisone of \<=20 mg/day or equivalent) for at least 14 days prior to Baseline (must remain on a stable dose until end of treatment). * Otherwise 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 clinical abnormality or laboratory parameters outside the reference range for the population being studied may be included only if the investigator agrees that the finding is unlikely to introduce additional risk factors and will not interfere with the study procedures * A female subject is eligible to participate if she is of: Non-childbearing potential 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) \>40 milliinternational units (MlU)/milliliter (mL) and estradiol \<40 picograms (pg)/mL (\<147 picomole \[pmol\]/liter \[L\]) is confirmatory). Females on hormone replacement therapy (HRT) must discontinue HRT to allow confirmation of post-menopausal status before study enrollment. For most forms of HRT, at least 2 to 4 weeks should elapse between the cessation of therapy and the blood draw; this interval depends on the type and dosage of HRT. Following confirmation of their post-menopausal status, they can resume use of HRT during the study without use of a contraceptive method. * Male subjects with female partners of child-bearing potential must agree to use acceptable contraception methods. This criterion must be followed during the study and for at least 2 weeks after their last dose. * Capable of giving written informed consent, which includes compliance with the requirements and restrictions listed in the consent form. Exclusion Criteria: * Subjects with fulminant UC, or UC limited to rectum. * Subjects with previous colonic surgery, histological evidence of colonic dysplasia, or bowel stricture. * Subjects who have received therapeutic enema or suppository, other than required for endoscopy, within 14 days prior to the Screening endoscopy and during the remainder of Screening Period. * Unable to refrain from the use of the prohibited drugs before the stated time before first dose of study medication until completion of the follow-up visit. * A live vaccination within 4 weeks before the first dose of study medication, or a live vaccination planned during the course of the study (until completion of the follow-up visit). * A major organ transplant (e.g. heart, lung, kidney, liver) or haematopoietic stem cell/marrow transplant. * Significant unstable or uncontrolled acute or chronic disease unrelated to UC (i.e. cardiovascular including uncontrolled hypertension, hypercholesterolemia, pulmonary, hematologic, gastrointestinal, hepatic, renal, neurological, malignancy or infectious diseases) which, in the opinion of the investigator, could confound the results of the study or put the subject at undue risk. * A planned surgical procedure that, in the opinion of the investigator, makes the subject unsuitable for the study. * A history of malignant neoplasm within the last 5 years, except for adequately treated cancers of the skin (basal or squamous cell) or carcinoma in situ of the uterine cervix. * Acute or chronic infections, as follows: Known previous, active or latent infection with Mycobacterium Tuberculosis, Currently on any suppressive therapy for a chronic infection (such as pneumocystis, cytomegalovirus, herpes simplex virus, herpes zoster and atypical mycobacteria), Hospitalisation for treatment of infection within 60 days before first dose, Use of parenteral (IV or intramuscular) antibiotics (antibacterials, antivirals, antifungals, or antiparasitic agents) within 60 days before first dose, Serologic evidence of Hepatitis B (HB) infection based on the results of testing for HBsAg, anti-HBc antibody as follows: subjects positive for HBsAg are excluded; and subjects positive for anti-HBc antibody (regardless of anti-HBs antibody status) are excluded, Positive test for Hepatitis C antibody confirmed on the same sample with a Hepatitis C third generation immunoassay or PCR. Subjects who are positive for Hepatitis C antibody, but negative when the Hepatitis C third generation immunoassay or PCR is performed on the same sample, will be eligible to participate, Subjects who are positive for Hepatitis C antibody and have a positive or indeterminate result when the Hepatitis C third generation immunoassay or PCR is performed on the same sample, will not be eligible to participate. * A positive test for HIV antibody. * Haemoglobin \<11 g/decilitre (dL) (6.83 millimoles\[mmol\]/L), haematocrit \<30%, white blood cells (WBC) count (absolute) \<3×10\^9/L, neutrophils \<1.5×10\^9/L, platelets \<100×10\^9/L, lymphocytes\<1×10\^9/L. * Current or history of renal disease, or estimated creatinine clearance \<60 mL/min/1.73m\^2 or serum creatinine \>1.5 upper limit of normal (ULN). * Single QT duration corrected (QTc) \>450 millisecond (msec); or QTc \>480 msec in subjects with Bundle Branch Block. * Current or chronic history of liver disease, or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones). * Alanine aminotransferase (ALT) \>2xULN; alkaline phosphatase and bilirubin ≥ 1.5xULN (isolated bilirubin \>1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin \<35%). * History of regular alcohol consumption within 6 months of the study defined as an average weekly intake of \>168g for males or \>112 g for females (8 g of alcohol is equivalent to 240mL of beer, 125mL of wine or 25mL 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). Or if the subject plans to take part in another clinical trial at the same time as participating in this clinical trial. * History of sensitivity to any components of the study medications, or a history of drug or other allergy that, in the opinion of the investigator, contraindicates their participation. * Where donation of blood or blood products, in addition to those required for the study, would be in excess of 500 mL within a 56 day period. * Exposure to more than four new chemical entities within 12 months prior to the first dosing day. * Unable to refrain from the consumption of grapefruit or grapefruit juice from 3 weeks before the first dose of study medication until 2 weeks after the last dose of study medication.