C188-9

C188-9 (TTI-101) is a STAT3 inhibitor, with a K_d of 4.7 nM. C188-9 inhibits G-CSF-induced STAT3 activation and STAT3-dependent gene expression. C188-9 induces apoptosis in AML cell lines and primary samples and inhibits colony formation by primary AML blasts^[1][2][3][4]. IC50 & Target: Kd: 4.7 nM (Stat3)^[1]. In Vitro: C188-9 is a Stat3 inhibitor, with a K_d of 4.7 nM^[1]. The IC₅₀s of C188-9 to inhibit Stat3 activation in AML cell lines are in the range of 4-7 μM, and in primary AML samples the IC₅₀s are in the range of 8-18 μM. For apoptosis studies, AML cell lines and primary samples are treated for 24 hours with C188-9, then apoptotic cells are quantified by FACS analysis for annexin V-labeled cells. The EC₅₀s for apoptosis induction are quite variable, ranging from 6 μM to over 50 μM^[2]. In Vivo: Of the approximately 13,528 discernible genes, levels of 37 gene transcripts are altered by C188 (17 down and 20 up-regulated, fdr <0.01, fold change≥1.5), of which 7 are known STAT3 gene targets. In comparison, C188-9 affects a much greater number of genes involved in oncogenesis (384 total, 95 down- and 289 up-regulated), including 76 genes previously reported as regulated by STAT3 (38 down-regulated and 38 up-regulated). Among the 38 genes previously shown to be upregulated by STAT3, 24 (63%) genes are downregulated by C188-9 treatment, as expected. Additionally, 10 more genes downregulated by C188-9 (fdr <0.01, fold change≥1.5) that previously are shown to be upregulated by STAT1. Thus, 40 of 48 (83.3%) genes downregulated by C188-9 previously are shown to be positively regulated by STAT1, including sixteen genes shown to be co-regulated by STAT3 and STAT1. This analysis raises the possibility that the effect of C188-9 on gene transcript levels in HNSCC tumors is mediated by its effects on both STAT3 and STAT1^[3].