Abstract 3994: Perifosine, an AKT inhibitor, downregulates mTOR function and suppresses the growth of human gastric cancer cells in mice.
Authors: Takagi Akimitsu , Tsugane Momomi , Konishi Hiroaki , Ishii Satoru , Sata Ken-ichi , Kodaira Hiroshi , Matsuzaki Takeshi 
Published: August 2014

Background: Perifosine is an oral anticancer compound that inhibits the PH-domain of AKT, which is frequently activated in human cancers including gastric cancer. In this study, the mode of action of perifosine, especially in association with mTOR, and the antitumor activity in combination with paclitaxel were examined in human gastric cancer cell lines.

Materials and Methods: The following human gastric cancer cell lines were used in this study: MKN1, MKN45, MKN74, AGS, and NCI-N87. Monolayers of cultured cells were exposed to perifosine for 48 hours and the antiproliferative activity was measured. The phosphorylated (p-)AKT status and its downstream molecules (e.g., PRAS40, TSC2, mTOR, 4E-BP1, and p70S6K) were analyzed using immunoblotting. In perifosine-treated cells, the induction of autophagy-like cell death was detected using LC3. With or without perifosine, the p-AKT (S473) levels were examined in rapamycin-treated cells. In a drug combination study, perifosine was used in combination with paclitaxel, and the synergistic effects of these drugs were quantified using the median-effect method to estimate the Combination Index. The antitumor efficacy of daily oral perifosine alone or in combination with intravenous paclitaxel was evaluated at various doses for 4 weeks in xenografted mice. The tumors at the time of necropsy were immunohistochemically examined for TUNEL, Ki-67 and AKT signal-related molecules.

Results: Perifosine exhibited antiproliferative activity in the tested cell lines (GI50: 4.7-18.0 μmol/L), reducing p-AKT. The perifosine-induced inhibition of phosphorylation was also seen in molecules downstream of AKT, such as PRAS40, mTOR, and p70S6K. Perifosine also induced autophagy-like cell death, observed as the induction of type II LC3 along with cleaved PARP. The phosphorylation of AKT (S473) was induced by rapamycin treatment. While this phosphorylation was not induced by perifosine, the rapamycin-dependent phosphorylation of AKT was inhibited by perifosine. The Combination Index showed synergistic or additive effects when perifosine was used in combination with paclitaxel. The antitumor activities of perifosine were demonstrated in a dose-dependent manner in the 3 cell lines tested in mice. When perifosine was administered with paclitaxel to NCI-N87 cells in mice, the inhibitory ratio of the tumor increased to 78.8% from 61.7% for perifosine monotherapy and from 50.0% for paclitaxel monotherapy. The population of TUNEL-positive cells was higher in the combination therapy group than in the monotherapy group in the tumor tissues. This combination decreased the number of positive cells with Ki-67 and AKT signal molecules in the tissue.

Conclusion: These results demonstrated that perifosine downregulates the mTOR function. The combination of perifosine and paclitaxel appears to be a promising regimen for the treatment of gastric cancer.

Citation Format: Akimitsu Takagi, Momomi Tsugane, Hiroaki Konishi, Satoru Ishii, Ken-ichi Sata, Hiroshi Kodaira, Takeshi Matsuzaki. Perifosine, an AKT inhibitor, downregulates mTOR function and suppresses the growth of human gastric cancer cells in mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3994. doi:10.1158/1538-7445.AM2013-3994