[36] Baricitinib is currently in phase 3 trials for RA. VX-509 is a selective JAK3 inhibitor currently in phase 2 and 3 investigation in the treatment of RA. Phase 2 studies compared 12 weeks of VX-509 monotherapy to placebo in patients who had failed a non-biologic DMARD. A significant response based on ACR20 and DAS28-CRP was seen with VX-509 dosed above 50 mg twice daily. Serious infections were noted, including a case of tuberculosis and pneumonia. As seen with tofacitinib and JAK3 inhibition, elevations in LDL,

HDL and transaminases were reported. No effect was seen on hemoglobin, neutrophils or creatinine.[37] GLPG0634 is a selective JAK1 inhibitor. Conceptually, this might lead to anti-inflammatory effects of IL-6 reduction without the side-effect profile of JAK2 and JAK3 inhibition. A 4-week phase 2a trial was performed buy GDC-0941 on 36 RA patients comparing GLPG0634 to placebo in those with inadequate response to MTX. A statistically significant response was seen in ACR20, DAS28 and CRP. Mild decreases in neutrophils and platelets counts were reported

without see more effects on hemoglobin, LDL, creatinine or transaminases.[38] A larger phase 2a study confirmed the efficacy previously seen as well as the safety profile.[39] Phase 2b trials were scheduled to start in 2013. Spleen tyrosine kinase (Syk) is another intracellular cytoplasmic tyrosine kinase. Syk has generated interest in the rheumatology community because it is downstream

from the B cell receptor and Fc receptors, which have integral roles in immunoreceptor signaling for macrophages, neutrophils, mast cells and B cells.[40, 41] Additionally, Syk plays an important role in osteoclast development and bone remodeling, adding to its attraction as a target for inhibition in RA treatment.[42] Syk is expressed in the RA synovial tissue and mediates TNF-α-induced production of cytokines such as IL-6 and metalloproteinase.[43] Fostamatinib (R788) is a Syk inhibitor that showed superiority over placebo in attaining ACR20, ACR50, ACR70 and DAS28 responses in a phase 2a trial of patients failing MTX.[44] Calpain In a second, 6-month phase 2 trial, fostamatinib continued to show efficacy over placebo in RA patients on background MTX, with statistically significant improvements in ACR20, ACR50, ACR70 and DAS28 responses at 100 mg twice daily and 150 mg daily dosing regimens. Side-effects included diarrhea, neutropenia and transaminitis. Hypertension was also noted as an adverse event, although patients responded to anti-hypertensive therapy with subsequent normalization of blood pressure.[45] A subsequent phase 2 study of fostamatinib 100 mg twice daily in patients with an incomplete response to biologic therapy failed to demonstrate efficacy based on ACR response criteria. A difference was reported on CRP levels and magnetic resonance imaging synovitis score despite the lack of clinical response.