A Randomized, Double-blind, Placebo-controlled Clinical Study of the Oral IL-12/23 Inhibitor, STA-5326 Mesylate, Administered to Patients With Rheumatoid Arthritis to Determine Safety, Tolerability, Pharmacokinetic and Synovial Tissue Outcomes

Inclusion Criteria: * Male or female 18 years of age or older. * Has a diagnosis of RA in conformance with the American College of Rheumatology (ACR) criteria for at least 6 months. * Has at least one knee, wrist, or ankle that has active synovitis and is amenable to arthroscopic procedures for the acquisition of synovial tissue via biopsy. * Must be taking methotrexate for a minimum of 4 months prior to Day 1, with a stable dose regimen for at least 2 months, and * have plans to remain on the stable dose regimen of methotrexate for the duration of this study. * If female of childbearing potential, must be neither pregnant nor breast feeding, and * must have a negative pregnancy test (serum β-hCG) within 1 week of Day 1. Must be willing to use "double-barrier" contraception methods for the duration of the study. Exclusion Criteria: * Is taking any disease-modifying anti-rheumatic drug (DMARD) other than MTX concomitantly or within 1 month prior to Day 1. * A positive (≥10 mm) tuberculin (PPD) skin test, unless the patient has had prior BCG immunization or has received prior suppressive treatment such as 1 year of INH. * Has received any investigational drug or experimental procedure for the treatment of RA within 3 months of Day 1 for a biologic compound or within 1 month of Day 1 for a non-biologic compound. * Has any clinically significant disease (e.g., renal, hepatic, neurological, cardiovascular, pulmonary, endocrine, psychiatric, hematologic, urologic, or other acute or chronic illness) that, in the opinion of the investigator, would make the patient an unsuitable candidate for this trial.