CEP-33779 is a selective JAK2 inhibitor (IC50 of 1.8 nM) developed by Cephalon, Inc for treating autoimmune disease (rheumatoid arthritis, lupus nephritis) and cancer. CEP-33779 orally administrated with 55 mg/kg inhibits phosphorylation of STAT5 in HEL92 tumor extracts from HEL92 xenograft mice. CEP33779 orally administered twice daily at the dose of 55 mg/kg reduces mean paw edema and clinical scores in mice with collagen-antibody-induced arthritis (CAIA) or collagen-induced arthritis (CIA). CEP-33779 orally administered twice daily at the dose of 55 mg/kg totally inhibits paw phospho-STAT3 expression in CAIA or CIA mice, associated with decreased cytokines including IL-12, IFNγ, IL-2, IL-1β, TNFα, and GM-CSF. CEP33779 results in reduced bone degradation, reduced tissue destruction, and reduced osteoarthritis in a dose-dependent manner in CAIA or CIA mice. CEP33779 orally administrated at 100 mg/kg extends survival and reduces splenomegaly/lymphomegaly in MRL/lpr systemic lupus erythematosus mice, thus protect mice from developing glomerulonephritis. CEP-33779 orally administrated at 100 mg/kg decreases several SLE-associated proinflammatory cytokines and reduces levels of a bone resorption biomarker associated with increased osteoclast activity in MRL/lpr systemic lupus erythematosus mice. CEP33779 orally administered twice daily at the dose of 55 mg/kg induces regression of established colorectal tumors, reduces angiogenesis, and reduces proliferation of tumor cells in a mouse model of colitis-induced colorectal cancer. Tumor regression correlated with inhibition of STAT3 and NF-κB (RelA/p65) activation, and decreased the expression of proinflammatory, tumor-promoting cytokines interleukin (IL)-6 and IL-1β