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Kinases have been studied as potential cancer targets because they play important roles in the cellular signaling of tumors. A number of small molecules targeting kinases are prescribed in clinics and many kinase inhibitors are being evaluated in the clinical phase. Previously, we discovered a series of aminopyridines substituted with benzoxazole as orally active c-Met kinase inhibitors. One of the compounds, KRC-108, has been evaluated as an anti-cancer agent in vitro and in vivo. A kinase panel assay exhibited that KRC-108 is a potent inhibitor of Ron, Flt3 and TrkA as well as c-Met. Moreover, KRC-108 inhibited oncogenic c-Met M1250T and Y1230D more strongly than wild type c-Met. The anti-proliferative activity of KRC-108 was measured by performing a cytotoxicity assay on a panel of cancer cell lines. The GI(50) values (i.e., 50% inhibition of cell growth) for KRC-108 ranged from 0.01 to 4.22 μM for these cancer cell lines. KRC-108 was also effective for the inhibition of tumor growth in human HT29 colorectal cancer and NCI-H441 lung cancer xenograft models in athymic BALB/c nu/nu mice. This molecule should serve as a useful lead for inhibitors targeting kinases and may lead to new therapeutics for the treatment of cancer.

SIRT1 and SIRT2 are deacetylase enzymes that belong to the sirtuin family and are involved in tumorigenesis. In our screen for small molecules inhibiting SIRT1/2 toxoflavin was identified. Toxoflavin potently inhibited SIRT1 activity in in vitro deacetylase assay using purified SIRT1 protein. SIRT2 activity was also inhibited by toxoflavin less potently than SIRT1 in deacetylase assay in vitro. Toxoflavin exhibited growth inhibition of various cancer cell lines including A549 lung cancer cells with a GI(50) of 48 nM. Toxoflavin treatment in A549 cells increased the acetylated form of p53, which is a substrate of SIRT1. The acetylation levels of α-tubulin, a SIRT2 substrate, were also increased by toxoflavin treatment dose-dependently. Several toxoflavin derivatives were synthesized to determine the preliminary structure-activity relationship of toxoflavin. Some of the toxoflavin derivatives showed highly selective inhibition against SIRT1. In conclusion, this study presented toxoflavin as a potent SIRT1/2 inhibitor with anticancer activity.