C188-9 (TTI-101) is a Stat3 inhibitor with an IC50 of 4-7 μM.

STAT3:4-7 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

In an analysis of approximately 13,528 discernible genes, C188 influences the expression of 37 gene transcripts (17 downregulated and 20 upregulated, false discovery rate (fdr)<0.01, fold change≥1.5), including 7 known targets of STAT3. Conversely, C188-9 exhibits a broader impact, modifying the expression of 384 genes related to oncogenesis (95 down- and 289 up-regulated), 76 of which are regulated by STAT3 (38 down-regulated and 38 up-regulated). Notably, C188-9 treatment downregulates 24 out of 38 genes (63%) previously identified as upregulated by STAT3. Furthermore, C188-9 downregulates an additional 10 genes (fdr <0.01, fold change≥1.5) known to be upregulated by STAT1, suggesting that 83.3% (40 out of 48) of the genes downregulated by C188-9 are positively regulated by STAT1. This includes sixteen genes co-regulated by both STAT3 and STAT1. The findings suggest that C188-9's modulation of gene transcript levels in head and neck squamous cell carcinoma (HNSCC) tumors may be attributed to its dual influence on STAT3 and STAT1 pathways.