Discovery of a small molecule dihydroquinolinone inhibitor with potent antiproliferative and antitumor activity results in catastrophic cell division
Christadore, Lisa M
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A family of dihydroquinolinones that inhibited the proliferation of a number of cancer cell lines and targeted the oncogenic activities of the late simian virus 40 factor (LSF) was discovered. The lead quinolinone inhibitors, 8-(2-propoxyphenyl)-7,8-dihydro-[1,3]dioxolo[4,5-g]quinolin-6(5H)-one, FQI1, and 8-(2-propoxyphenyl)-[1,3]dioxolo[4,5-g]quinolin-6(5H)-one, FQI2, were determined by a comprehensive SAR study. The lead compounds had low micromolar to nanomolar Gi50S and IC50S (concentrations that induced 50% inhibition) in cell growth and LSF-directed luciferase reporter assays, respectively. A distinct correlation between the GI50 and IC50 values indicated antiproliferative effects resulted from inhibition of LSF activity. FQI1 had no growth effects on immortalized human hepatocytes or primary mouse hepatocytes. Overall, FQI1 proved a good drug candidate for hepatocellular carcinoma (HCC). It possessed a low molecular weight and moderate solubility, which was improved by substitution of the amide with a triazole bioisostere. FQI1 showed excellent microsomal stability, high in vivo volume of distribution and half-life in rodents, and was a potent inhibitor of HCC tumorigenesis in immunocompromised mice. FQI1 induced mitotic catastrophe in the HCC cell line, QGY-7703, the cervical carcinoma cell line, HeLa, and the NIH-3T3 fibroblasts, as evidenced by widespread multinucleated cell morphologies. Excessive micronucleation in NIH-3T3 cells treated with higher FQI1 concentrations further supported severe chromosome segregation defects. Mitotic slippage into interphase and subsequent endoreduplication was also induced by FQI1 in NIH-3T3 cells. These phenotypes have been seen with chemicals such as the microtubulin poisons and Aurora B kinase inhibitors. Together these results suggested that FQI1-induced evasion or adaptation of the spindle assembly checkpoint and abnormal chromosome segregation resulted in mitotic catastrophe, and in the case of NIH-3T3 cells, polyploid cell progeny. Expression profiling in QGY-7703 cells with FQI1 cells revealed an upregulation of multiple genes along the TGF-β/SMAD signaling cascade compared to the untreated cell population. This supported a model where the induction of p21Cip1 activity as a result of mitotic slippage activated the G1/S checkpoint in response to aberrant exit out of mitosis in QGY-7703 cells. These results together elucidated FQI1's mechanism of action in mitosis and also strongly suggested that LSF regulated genes required for the proper execution of mitosis.
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