STA-5326 is an oral experimental drug that has been shown to block the release of interleukin-12 from peripheral blood mononuclear cells. Given this activity on the immune system, STA-5326 mesylate is a potential treatment for various autoimmune diseases, such as Crohn's disease, that are mediated by the inappropriate expression of Th1 cytokines.

This study is evaluating the use of STA-5326 mesylate in patients with moderate to severe, active Crohn's disease. Study visits include a screening visit, 4 treatment period visits over 4 weeks and a follow-up visit that will occur 7 days following the end of treatment. Subjects may continue treatment for an additional 4 weeks of open label STA-5326 mesylate administration that includes an additional 2 treatment period visits. Subjects will undergo a colonoscopy with biopsy collection at baseline, at the end of the 4 week blinded phase and at the end of the 4 week open label phase.

Inclusion Criteria:

• Is male or female aged 18 through 75 years.
• Has Crohn's disease diagnosed definitively prior to Screening (based upon clinical, endoscopic, radiologic imaging, or histological assessments).
• Has a CDAI score of 220 to 450, inclusive at Baseline.

Exclusion Criteria:

• Has any clinically significant disease (eg, renal, hepatic, neurological, cardiovascular, pulmonary, endocrinologic, psychiatric, hematologic, urologic, or other acute or chronic illness) that in the opinion of the investigator would make the subject an unsuitable candidate for this study.
• Is a woman who has a positive pregnancy test, who is breast-feeding, or who is sexually active without using birth control during the course of the study and Follow-up period.
• Is a woman of childbearing potential or a man who does not agree to use 2 forms of contraception during the course of the study and Follow-up period.
• Has clinically significant hematologic, hepatic or renal laboratory abnormalities.