So that you can determine the molecular mechanism of KRIBB3dependent growth inhibition, we examined mGluR cell cycle progression in a time dependent manner. Sixty percent of cells were arrested at the G2/M phase 12 h after KRIBB3 treatment. Cell cycle arrest at the G2/M phase was further confirmed by finding the G2/M phase distinct protein Cyclin B1 and phosphorylation of Histone H3. There are many possible KRIBB3 targets accountable for a KRIBB3dependent G2/M cycle arrest. Accumulation of Cyclin B1 shows that its degradation process could be blocked by KRIBB3. Cyclin B1 is degraded by the proteasome in a cycle dependent manner after APC/C dependent ubiquitination. Therefore,we decided to check whether KRIBB3 inhibits APC/ H dependent activity. APC/C dependent ubiquitination is dependent on CDC20 to recognize its substrate. That substrate recognition protein is associated with its inhibitory protein Mad2. For that reason, we analyzed the forming of the inhibitory complex p55CDC/ Mad2 in an occasion dependent manner after KRIBB3 treatment. Not surprisingly, KRIBB3 therapy induced affiliation of p55CDC with the Dalcetrapib CETP Inhibitors inhibitory protein Mad2. Dependent Cyclin B1 degradation may be blocked APC/C by this inhibitory complex. This leads to the question of how KRIBB3 triggers the complex of p55CDC/Mad2. Since microtubule poisons such as vinca alkaloids cause all kinetochores to become unattached, thereby generating a mitotic checkpoint indication, we decided to check whether KRIBB3 could restrict microtubule structure. We carried out indirect immunofluorescence microscopy to check the microtubule cytoskeleton in vivo. Cells treated with KRIBB3 showed short microtubule fragments Cellular differentiation in the cytoplasm. This construction is similar to microtubules in cells treated with nocodazole. Moreover, in vitro, purified tubulin polymerization was inhibited in the presence of KRIBB3 or nocodazole, and improved in the presence of paclitaxel. Out of this, we concluded that KRIBB3 inhibited tubulin polymerization. The inhibitory activity of KRIBB3 on tubulin polymerization resembles that of nocodazole. tubulin polymerization nevertheless, KRIBB2, a lazy structural analogue of KRIBB3, did not show any inhibitory effect. Consistent with this, KRIBB2 didn’t inhibit proliferation of HCT 116 cells. These results support our conclusion that inhibition of tubulin polymerization by KRIBB3 caused mitotic phase arrest and growth inhibition. Since p53 has been proven to be involved in apoptosis and more than 50% of human cancers have mutated p53, it’s essential for drugs to help you to induce apoptosis in a p53independent manner. Thus, we examined whether KRIBB3 can inhibit the growth of p53 null cancer cell lines. Luckily, KRIBB3 surely could cause cell Flupirtine cycle arrest at the mitotic phase, and apoptosis of both HCT 116 and DU 145 cells.