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

Background: 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.

Study design and methods: 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.

Results: 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.

Conclusion: 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.