The primary objective of this study is to evaluate the efficacy (ACR20) of Rob 803 administered orally once daily for 12 weeks in combination with a stable dose of methotrexate in subjects with moderate or severe active RA.

Rheumatoid arthritis (RA) is a common, chronic, disabling systemic autoimmune disease in which inflammation of the joint lining (synovium) occurs when the body's tissues are attacked by the immune system. The joint inflammation begins in the synovium and slowly destroys the cartilage, narrowing the joint and eventually damaging the bone. A large amount of inflammatory mediators or rheumatoid factors are synthesised in the joint which accelerate proliferation and differentiation of immune cells further to amplify the autoimmune reaction. A widely accepted model has emerged in which the presence of inflammation in established RA is driven by interactions between T cells, macrophages, and fibroblasts in an abnormal microenvironment.

Rheumatoid arthritis has an annual incidence of approximately 0.2 per 1000 in males and 0.4 per 1000 in females. In general, higher rates have been reported in the USA than in European populations. The incidence of RA increases with age until the mid 70s. A prevalence of 0.5-1% is reported in diverse populations world-wide.

Treatments for RA focus on relieving pain, reducing inflammation, slowing or stopping joint damage, and improving patients' well being and ability to function. Current therapies include non-steroidal anti-inflammatory drugs (NSAIDs) which target the clinical features of the disease to alleviate the pain and swelling that accompany RA, disease-modifying anti-rheumatic drugs (DMARDs) which target the actual cause of the disease and biological agents which are genetically engineered to target and modify the autoimmune response. Non-steroidal anti-inflammatory drugs are effective in managing the symptoms of RA, but are limiting as they cannot suppress progression of the disease. First line treatment on confirmation of RA is the use of DMARDs, supported by pain relief medication.

Biologic agents (TNF antagonists, anti B-cell agents and anti-interleukins) have proven effective in RA symptoms management. TNF antagonists have become an important therapeutic option in the treatment of advanced RA.

Inclusion Criteria:

• Diagnosed with RA based on the ARA 1987 revised criteria at least 16 weeks prior to study enrolment, Day 0
• Have an ACR global functional status class of 1 to 3
• Have active disease, defined as the presence of 6 swollen joints and 6 tender joints in a 44 joint examination
• Have a CRP level at screening of ≥ 1.5 mg/dL
• Have been taking oral or parenteral methotrexate (15 mg weekly or above), have been using methotrexate for at least 16 weeks (up to Day 0 of study), and have been on a stable dose for at least 8 weeks, up to Day 0.

Exclusion Criteria:

• Arthritis onset prior to 16 years old
• Any of the following infections:
• Known or acute infection that may affect CRP levels
• Active tuberculosis
• Known chronic infection with human immunodeficiency virus (HIV), hepatitis C virus (HCV) or hepatitis B virus (HBV) including positive serology
• Ongoing systemic inflammatory condition which may interfere with the results of clinical or laboratory tests planned in the study (eg, systemic lupus erythematosus or any other systemic rheumatic disease other than RA)