– H3B8800 is an orally available splicing modulator that targets spliceosome SF3b complex containing either WT or mutant SF3B1 (binding IC50 of 0.3-2 nM),demonstrates dose-dependent inhibition of both canonical splicing and aberrant splicing induced by mutant SF3B1 in in vitro assays of biochemical splicing, induces lethality in spliceosome-mutant cancer cells.. H3B-8800 potently and preferentially kills spliceosome-mutant epithelial and hematologic tumor cells.