Accentuating Death Signaling in Colon Cancer Cells: A Chemical Biology Approach

Colon cancers harbor a variety of mutations that result in uncontrolled proliferation and suppression of apoptotic pathways. The initial objective of our work was to understand how colon cancer cells survive their inflammatory micro-environment, including high levels of TNF and other death ligands. Towards this goal, we identified a series of mitotically acting piperazine-based compounds that sensitized colon cancer cells to TNF-dependent apoptosis. The most potent of these compounds, 1-(3-chlorophenyl)-4-(2-ethoxybenzoyl)piperazine or AK301, arrested cells in a mitotic state (EC50 ≈ 115 nM) in which the TNF receptor was efficiently coupled to caspase-8 activation. Our structure-activity relationship studies predicted AK301 binding to β-tubulin in a novel orientation that reduced the rate of tubulin polymerization. These data suggested that targeting mitosis may be an effective approach for sensitizing cancer cells to their inflammatory microenvironment. Further study of the activity of AK301 showed that p53-normal colon cancer cells efficiently underwent apoptosis in the absence of death ligands following release from their mitotic arrest. Study of this effect indicated that AK301-treated cells showed high levels of ATM signaling during mitotic arrest and exit from mitosis, following compound withdrawal, resulted in a p53-dependent apoptosis. Interestingly, the apoptotic activity of AK301 was more apparent in APC mutant cells, suggesting that AK301 exacerbated the mitotic defects associated with an APC mutation. This work details the identification and structure-activity relationship studies of a new class of small molecule compounds and explores their anti-mitotic activity and provides a paradigm for exploiting molecular alterations in mutated cells. These findings could serve as a basis for the development of agents that target the molecular alterations in mutated colon cancer cells and augment the apoptotic actions of their inflammatory microenvironment, for robust activation of apoptotic signaling. Understanding the mechanisms cancer cells use to suppress apoptosis may ultimately facilitate in the development of novel approaches to colon cancer treatment and prevention