A novel small molecule phagocytosis inhibitor, KB‐208, ameliorates ITP in mouse models with similar efficacy as IVIG.

Background Study Design and Methods Results Conclusion The characteristic feature of immune cytopenias involves the process of extravascular phagocytosis, wherein macrophages in the spleen and/or liver engage in the destruction of blood cells that have been opsonized by auto‐ or alloantibodies. Therefore, new treatments that prevent phagocytosis will be advantageous, especially for short‐term usage along with alternative options.KB‐208, a small molecule drug, previously shown to be efficacious for the in vitro inhibition of phagocytosis was synthesized. A passive antibody mouse model of immune thrombocytopenia (ITP) was used. Three different mouse strains (BALB/c, C57BL/6, CD1) were used to determine the efficacy of KB‐208 compared with IVIG to ameliorate the ITP. Toxicity was investigated after 60‐day chronic administration of KB‐208 by a biochemistry panel, gross necroscopy and histopathology.KB‐208 showed similar efficacy to ameliorate the thrombocytopenia compared with IVIG in all three mouse strains. This small molecule drug was effective at 1 mg/kg in ameliorating ITP, in comparison with IVIG at 1000–2500 mg/kg. KB‐208 did not affect other blood parameters or elevate serum biochemistry markers of toxicity nor were any abnormal histopathological findings found.KB‐208 is similar to IVIG for the amelioration of ITP in multiple mouse strains. Chronic administration of KB‐208 for 60 days did not demonstrate in vivo toxicity. These findings indicate that KB‐208 is efficacious, without significant in vivo toxicities in mice, and is a potential small molecule candidate for further evaluation to be used in the treatment of ITP and possibly all immune cytopenias where phagocytosis is responsible for the pathophysiology. [ABSTRACT FROM AUTHOR]