Apogossypolone acts as a metastasis inhibitor via up-regulation of E-cadherin dependent on the GSK-3/AKT complex

Malignant pheochromocytoma is exactly diagnosed only upon the occurrence of metastatic foci. At that point, however, patients are less likely to experience many benefits from traditional chemotherapy. Therefore, a strategy worthy of consideration is inhibition or delay of metastasis with drugs. Recently, numerous studies have indicated that epithelial-to-mesenchymal transition (EMT) is involved in malignant pheochromocytoma, where there is over-expression of metastatic promoting genes and low expression of metastatic suppressor genes. In previous research, we confirmed that apogossypolone (ApoG2) could effectively inhibit tumor movement capabilities, but potential mechanisms for the inhibition were unknown. Here, we initially corroborated that ApoG2 could induce GSK-3/AKT complex formation to down-regulate phosphorylation of the PI3K/AKT pathway. Subsequently, ApoG2 inhibited cell mobilities via promotion of E-cadherin and β-catenin translocation from cytoplasm to membrane dependent on down-regulate of the PI3K/AKT pathway. Unexpectedly, ApoG2 seemed to promote tumor progression, instead of suppression when there were circulating tumor cells in vivo. Our results indicated that ApoG2 might be an effective target agent early in the disease rather than at the advanced stage where there are a majority of circulating tumor cells. Those cells rely on the mesenchymal-epithelial transition (MET) process to anchor to distant new sites. Hence, the so-called anti-tumor drugs with inhibition of migration and invasion should be carefully distinguished as to whether they are involved in EMT and MET processes or not. Most importantly, we identified that GSK-3 is not only a downstream effector but also an upstream regulator of the PI3K/AKT pathway.