Abstract
1691
Phosphatidylinositol 3-kinase (PI3K) is a promising molecular target of cancer therapy since it is a key enzyme playing important roles in various biological pathways such as cell survival, vesicle transport and cytoskeletal rearrangement and is also known to be involved in tumorigenesis. However, little anticancer agents targeting PI3K have been developed yet. We synthesized thousands of s-triazine derivatives and found by cell-based screening 2-(2-difluoromethylbenzoimidazol-1-yl)-4, 6-dimorpholino-1, 3, 5-triazine (ZSTK474) with potent antiproliferative activity. To predict the mode of action of ZSTK474, we exploited the COMPARE analysis based on the chemosensitivity database of a panel of 39 human cell lines. It revealed that ZSTK474 significantly correlated with LY294002 and wortmannin, suggesting that ZSTK474 inhibits PI3K. Then, we biochemically confirmed that ZSTK474 inhibited PI3K at concentrations of 10-100 nM. The inhibition was reversible as was the case of LY294002. Concerning the structure activity relationship, the difluoromethyl group of ZSTK474 was important for inhibiting both cell growth and PI3K. Furthermore, PI3K-inhibitory activities of several s-triazine derivatives significantly correlated with their growth-inhibitory activities. These results suggested that ZSTK474 inhibited cell proliferation through inhibiting PI3K activity. The computer-aided molecular modeling of PI3K-ZSTK474 complex revealed that ZSTK474 could bind to the ATP-binding site of PI3K, and that overall arrangement of ZSTK474 at the site was similar to that of ATP, but not of LY294002. We investigated the effects of ZSTK474 on the cellular signaling pathways and examined its anti tumor activity. ZSTK474 decreased the PDGF-dependent membrane ruffling of murine embryonic fibroblast cells, in which the PDGF-dependent generation of phosphatidylinositol-3,4,5-triphosphate was also reduced. ZSTK474 inhibited the phosphorylation of PI3K-downstream components, Akt and glycogen synthase kinase-3beta, and it decreased the cyclin D1 level. ZSTK474 showed potent antitumor activity by oral administration against murine solid tumors and human cancer xenografts. Severe body weight loss or serious bone marrow toxicity was not observed during the daily oral administrations for more than 10 days. The reduction of the Akt-phosphorylation and the cyclin D1 level in the tumor following ZSTK474 administration was confirmed. In conclusion, we found a novel PI3K inhibitor ZSTK474, and demonstrated its potent antitumor efficacy by oral administration without serious toxicity. ZSTK474 could be orally administered and showed favorable pharmacokinetic properties, which can be great advantages for clinical cancer treatment. ZSTK474 is a promising new anticancer agent for development toward clinical investigation.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]