N-(2, 6-dimethoxypyridine-3-yl)-9-methylcarbazole-3-sulfonamide (IG-105) As A Novel Tubulin Ligand Against Human Cancer

We have synthesized a new tubulin ligand N-(2,6-dimethoxypyridine-3-yl)-9-methyl-carbazole-3-sulfonamide(IG-105) showing potent activity against a variety of human cancer cells with low IC₅₀ values ranging from 0.01 to 0.3μmol/L.Interestingly,it was also very active in tumor cells that were resistant to the known tubulin-active anticancer drugs,such as paclitaxel and vincristine.Pgp ATPase activity assay showed that IG-105 was not a P-glycoprotein substrate.The primary action of IG-105 was to inhibit microtubule assembly from intracellular tubulin pool.In the cell free system,IG-105 inhibited tubulin polymerization with an ICs0 of 3μmol/L.In the live cell system,IG-105 caused wild microtubule de-polymerization and whole cytoskeleton network disruption.Using computational molecular docking as well as tubulin competition binding assay we identified colchicine pocket on tubulin as the IG-105's selective binding site.Further,IG-105 can induce M-phase arrest and following cell death characterized with the fragmented DNA in Bel-7402 cells.Accordingly,the up-regulated expression of Cyclin B1 as well as the down-regulation of Cyclin D1 by IG-105 was detected in the arrested cells. IG-105 induced programmed cell death via the mitochondrial pathways mediated through Bcl-2 phosphorylation,p53 up-regulation and Caspase-3/8/9 activity increase.DNA microarray analysis was performed on the IG-105-treated cells to learn the global change of the expression of 22,000 human genes,and suggested that IG-105 might be considerably specific for the tubutin-related cascade described above,rather than for other important life-determining pathways.Animal studies showed that IG-105 monotherapy yielded 81%inhibition of tumor growth for Bel-7402 human hepatoma in nude mice at 100 mg/kg(i.p.,q2d),and completely inhibited the growth of Bel-7402 hepatoma at 275 mg/kg(i.p.,q2d).MCF-7 human breast cancer demonstrated a similar response to IG-105.In combination with oxaliplatin or doxorubicin,IG-105 converted each of these subcurative compounds into a curative treatment with a complete inhibition of tumor growth of Bel-7402 hepatoma.The combination was more efficient than either drug.In no experiment was toxicity increased by combination chemotherapy.IG-105 showed a good safety in mice even when the dose of IG-105 was over 1000 mg/kg(i.p.).No evidence of histopathological damage was found in liver,kidney,heart,lung and spleen.In addition,the human plasma protein binding rate of IG-105 was also investigated in the study.In summary,IG-105(1) inhibits microtubule assembly by selectively binding at colchicine pocket,(2) shows a potent anticancer activity in the naive and drug-resistant tumors,and(3) completely inhibits human tumor growth in mice with good safety.We consider IG-105 merits further investigation.