ALBERT

Description: Syk kinase is central to FcR and B-cell signaling in inflammatory cells. By inhibiting syk, and thereby IgG signaling, R788 (a small molecule prodrug for biologically active R406), inhibits the downstream activation of mast cells, macrophages and B-cells. (Braselmann S. Pharm Exp Ther. 2006). Preclinical study showed that R788 minimized thrombocytopenia in mice treated with anti-platelet antibodies (Crow, A.R. Blood 2005). In this study, adult, refractory ITP patients (pts) were treated with escalating doses of R788 in cohorts of ≥3 pts to evaluate safety and efficacy. After a cohort completed four weeks, the next cohort could be initiated. Pts completed 2 weeks of dosing before the dose could be increased (by 25 mg twice daily). Dosing was initiated at 75mg PO BID to 150 mg PO BID. Pts who responded and then had their platelet (plt) counts (cts) decline, could have their dose increased to a maximum of 175mg bid. Safety: 14 pts entered the study, 10 after failed splenectomy and 5 who were 〉70 yo. Six pts withdrew due to failure to respond (4) or gastrointestinal (GI) symptoms (2). GI symptoms (vomiting & diarrhea) were seen in 5 of 14 pts with mild elevations in ALT in 2 pts (2 〉2XULN, one of whom had pre-existing hepatitis). Two pts were hospitalized for GI side effects (dehydration) and one developed an unrelated UTI with subsequent diagnosis of DVT. R788 also elevated blood pressure in some pts but appeared to not have a significant effect on neutrophil counts. Efficacy: By protocol standards, 9/14 pts are considered responders with stable platelet counts 〉 30,000/ul (30k). Six pts had peak counts 〉 100k. The mean change from pre treatment to the peak count in the 8 on study pts was 125k. Two pts, who previously had failed a wide range of other treatments, have maintained counts generally above 20k completing 〉 20 weeks of study with 0 and 1 IVIG treatments respectively, in each for the first time in 〉 10 years that they achieved prolonged avoidance of IVIG. Five had not responded to a thrombopoietic agent, 2 of whom responded to R788. Two responders discontinued the study because of nausea and vomiting at the dose that provided a response. Conclusions: The effects of R788 treatment are preliminary but, despite GI toxicity in certain patients, nonetheless impressive in this very refractory ITP population. Certain pts have had important clinical although numerically unimpressive benefit. Further studies are ongoing including studies of FcR expression before and after treatment. Patients Currently On Study Patient Baseline Plt Count x 109/L Peak Plt Count x 109/L (w/o IVIG) Most Recent Plt Count x 109/L Total Wks On Study Current Dose 001 14 49 20 30 175mg BID 002 22 222 18 24 175mg BID 003 32 158 37 24 150mg BID 007 20 111 40 21 100mg BID 008 22 205 205 19 125mg BID 009 46 329 329 14 100mg BID 011 45 124 124 11 125mg BID 014 107 107 36 6 125mg BID Mean 38 163 Patients Withdrawn From Study Patients Baseline Plt Count x 109/L Peak Plt Count x 109/L (w/o IVIG) End Of Study Plt Count x 109/L Total Wks On Study Highest Dose 004 12 11 11 19 175mg BID 005 12 66 11 14 150mg BID 010 18 13 21 11 175mg BID 012 17 17 14 3 125mg BID 013 25 159 97 5 150mg BID 015 3 13 13 4 125mg BID Mean 14 46

Description: Immune Thrombocytopenic Purpura (ITP) is an autoimmune disease characterised by the destruction of platelets by pathogenic autoantibodies. Clearance of platelets by phagocytic cells such as macrophages occurs through activating receptors for the Fc portion of IgG (FcγR). A central tyrosine kinase in this activation pathway is Syk, which is required for FcγR-mediated phagocytosis; thus, we questioned whether inhibition of Syk would ameliorate ITP. R406 is an orally bioavailable Syk-kinase inhibitor which is well tolerated by human volunteers. Using a well-described murine model of ITP, we tested the ability of R788 (the prodrug of R406) to ameliorate thrombocytopenia. Mice injected with an antibody directed to integrin αIIβ were profoundly thrombocytopenic when platelets were enumerated 24 hr post injection. However, mice pre-treated with 25 or 40 mg/kg R788 were protected from thrombocytopenia. Mice pre-treated with the vehicle alone displayed no protection. It has been demonstrated that chimeric Syk deficient mice display a bleeding diathesis; it was therefore questioned whether treatment of mice would demonstrate prolonged tail vein bleeding time. In independent experiments, mice treated with the with the bioavailable inhibitor R406 had no significant difference in bleeding time compared to untreated mice or mice treated with vehicle alone. Syk is also involved in collagen-induced platelet secretion and aggregation. To further the potential use of this drug in humans, the ability of platelets derived from human volunteers treated with R788 to respond to in vitro collagen-induced aggregation was analysed. Platelets from volunteers treated with the drug displayed normal collagen (as well as ADP)-induced platelet aggregation compared to untreated volunteers or those treated with the vehicle alone. These data suggest that future investigation of Syk inhibition in autoimmune diseases such as ITP is warranted.