Induction of apoptosis by the formation of self-assemblies of polycyclic aromatic compounds Riku Umemura , Natsumi Shimizu, Kenta Morita and Tatsuo Maruyama Graduate School of Engineering, Kobe University Currently, chemotherapy using anti-cancer drugs is commonly used as a treatment for cancer. However, anti- cancer drugs also affect normal cells, causing side effects that are problematic. In this study, we focused on apoptosis, which is one of mechanisms of cell death, and attempted to develop a new molecule that induces cell apoptosis. A previous study reported by another group demonstrated that a molecule called 1541B self- assembled to form nanofibers and that procaspase-3 was adsorbed on the nanofibers and activated to produce caspase-3 [1] . The activation of caspase-3 is known to be closely related to apoptosis. The objective of this study was to develop novel self-assembling molecules with a simpler chemical structure inspired by 1541B. We synthesized a series of compounds that had a part of the molecular structure of 1541B and evaluated their induction of apoptosis in cancer cells. We conjugated an alkyl chain (C 10 ~C 16 ) with the partial structure of 1541B (termed IPP-C n ). The induction of apoptosis by 1541B and IPP-C n was investigated using human liver cancer cells (HepG2 cells). Among the synthesized compounds, IPP-C 14 was the most cytotoxic, with sufficient toxicity at 30 μM. The differences in the cytotoxicity of IPP-C n were thought to be due to differences in their intracellular localization and their self- assembling ability caused by the lengths of the aklyl chains. We examined whether IPP-C 14 and 1541B led to apoptosis of HepG2 cells. Apoptosis was detected using Annexin V-FITC, a fluorescently labeled protein that specifically binds to phosphatidylserine (PS) exposed on the membrane surface in apoptosis. As a result, we found that IPP-C 14 and 1541B induced apoptosis of HepG2 cells. To explore the apoptosis pathway, we used various caspase substrates to detect caspase activation in HepG2 cells. The caspase-3 activation was examined in the induction of apoptosis. The results showed that IPP-C 14 and 1541B induced caspase-3 activation in HepG2 cells. However, no activation of purified procaspase-3 (without living cells) was observed using 1541B and IPP-C 14 . These suggested that, in contrast to the previous study [1] , IPP-C 14 and 1541B were not directly related to the activation of caspase-3 in the cells. Then, we looked at the activation of caspase-10, which is upstream of caspase-3. Activation assays using the caspase-10 substrate suggested that IPP-C 14 and 1541B induced the activation of caspase-10 in HepG2 cells. These results suggest that IPP-C 14 and 1541B indirectly induced the activation of caspase-3 by activating caspase-10 in HepG2 cells, finally leading to their apoptosis. In future, we would like to examine how IPP-C 14 acts on HepG2 cells to induce the activation of these caspases. References 1. Zorn et al., J. Am. Chem. Soc, 133, 19630 (2011)
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