In vitro activity: FX1 profoundly reduces recruitment of BCOR and SMRT to all 3 BCL6 target genes, but not at a negative control locus. There is little presence of SMRT at these loci in the BCL6-negative DLBCL cell line, which is not affected by FX1. The superior potency of FX1 versus 79-6 in disrupting BCL6 binding to SMRT is evident when these small molecules are compared head to head in quantitative ChIP assays in DLBCL cells after treatment with 50 μM FX1 for 6 hours. DLBCL cells are exposed to FX1 and mRNA is collect at 4 serial time points. FX1 almost invariantly induces significant derepression of these genes as compare with vehicle in 2 independent DLBCL cell lines

Kinase Assay: FX1 disrupted formation of the BCL6 repression complex, reactivated BCL6 target genes, and mimicked the phenotype of mice engineered to express BCL6 with corepressor binding site mutations. FX1 suppressed ABC-DLBCL cells in vitro and in vivo, as well as primary human ABC-DLBCL specimens ex vivo. FX1 is specific to BCL6 and binds with a greater affinity than the natural BCL6 ligand SMRT. FX1 almost invariantly induced significant derepression of these genes(BCL6 target genes CASP8, CD69, CXCR4, CDKN1A, and DUSP5) as compared with vehicle in 2 independent DLBCL cell lines. FX1 was more than 100-fold more powerful than the previous generation of BCL6 inhibitors represented by 79-6, and 300-fold more potent than the recently reported binding of the antibiotics rifamycin and rifabutin (KD ~1 mM).

Cell Assay: Cell viability is determined with the fluorescent redox dye. Fluorescence is determined for 3 replicates per treatment condition or vehicle with the microplate reader. Cell viability of the drug-treated cells is normalized to their vehicle-treated controls, and the results are expressed as percentage viability. The drug effect as 100-percentage viability is calculated. Through dose-effect curves the drug concentration that inhibits the growth of cell lines by 50% compare with vehicle (GI50) is determined. Experiments are performed in triplicate. For combination treatments, cells are exposed to a dose curve of each drug alone or their combination in constant ratio, and cell viability is determined. To compare different schedules of treatments, the cells are treated in triplicate as follows: FX1 and doxorubicin simultaneously and cells treated for 48 hours; FX1 first and 24 hours after doxorubicin is added and treats for an extra 48 hours; doxorubicin first and 24 hours after FX1 is added and treats for an extra 48 hours. Then, the software is used to plot dose-effect curves and calculate the dose-reduction index.