A Study of CH-4051 in Patients With Rheumatoid Arthritis (RA)

Inclusion Criteria: * Patients must be between the ages of 18 and 80; * Have diagnosed active rheumatoid arthritis according to ACR criteria functional class I-III; * Have at least 6 swollen joints (max = 66) and 6 tender joints (max = 68) at screening and baseline visits; * Patients must have at least one of the following: * C-reactive protein \> 1.0 mg/dl at screening; * erythrocyte sedimentation rate \> 28 mm/Hr; * Patients must have been taking methotrexate between 15 and 25 mg/week for at least 3 months and at a stable dose for at least 6 weeks; * Patients must be either Rheumatoid Factor (RF) or anti-cyclic citrullinated peptide (anti-CCP) positive; * Patients must have voluntarily signed the informed consent. Exclusion Criteria: * Patients who received previous therapy with any biologic agent; * Patients currently taking any disease modifying anti-rheumatic drug (DMARD) other than MTX; * Previous non-biologic DMARD therapy is permitted as long as their last dose was at least 30 days prior to baseline; * Female patients of child bearing potential who are pregnant or who are not using two methods of contraception (at least one barrier: i.e. condom) with their partner; * Male patients who are sexually active and not using two methods of contraception (at least one barrier: i.e. condom) with their partner; * Patients with any current active infection or infections requiring IV drug therapy within 30 days of baseline or oral therapy within 15 days of Baseline; * Patients that have had any surgical procedures within 30 days of baseline; * Patients with a history of HIV; * Patients with Hepatitis B surface antigen positive and/or Hepatitis C antibody positive; * Patients who consume more than 4 units of alcohol per week (1 unit = 5 ounces/150 ml of wine = 1.5 ounces/45 ml spirits = 12 ounces/360 ml of beer); * Patients currently receiving any investigational drug or have received an investigational drug within 30 days of baseline or 5 half-lives of the investigational drug (whichever is longer); * Patients with a history of cancer within the past 5 years other than a successfully treated, non-metastatic cutaneous squamous cell or basal cell carcinoma or cervical cancer in situ; * Patients with a history of, or any, disease associated with an inflammatory arthritis other than RA; * Patients with pulmonary fibrosis (Chest x-ray must be taken within 28 days of screening); * Patients receiving probenecid; * Patients who have received any steroid injections within 30 days of baseline; * Patients with concomitant diseases that are unstable (i.e. cardiac, pulmonary) or that may affect drug activity (i.e. absorption, reactions, change in kinetics); * Patients, in the investigator's opinion, that have any significant renal or hepatic impairment; * Patients with a serum creatinine level \> 1.5 mg/dl at screening; * Patients with an ALT \>1.5 ULN at screening; * Patients considered by the investigator to be an unsuitable candidate to receive CH-4051; * Wheelchair or bed-bound patients.