Motexafin Gadolinium Upregulates pAkt Levels and Synergizes with Inhibitors of Akt Phosphorylation.

Motexafin gadolinium (MGd, Xcytrin^®) is a tumor-selective expanded porphyrin that targets oxidative stress related proteins. MGd treatment of the follicular lymphoma-derived cell line HF-1 resulted in growth suppression and apoptosis, whereas MGd treatment of the Burkitt’s lymphoma-derived cell line Ramos resulted in growth suppression but not apoptosis. Since phosphorylation status of Akt/PKB kinase is regulated by oxidative stress, we monitored total and phosphorylated Akt (pAkt) in MGd treated HF-1 and Ramos cells. Levels of total and pAkt increased within 30 min after MGd treatment of HF-1 but within 4 hrs began to show a progressive decline to below baseline levels prior to cells undergoing apoptosis. Levels of total Akt did not increase in MGd treated Ramos cells but pAkt increased about 2 fold within 8 h and remained persistently elevated. Since pAkt activates survival pathways, we determined if MGd-induced cell death could be enhanced by inhibiting phosphorylation of Akt. The addition of specific inhibitors of Akt phosphorylation (SH-5 or Akt inhibitor 1) reduced pAkt levels in MGd treated HF-1 and Ramos cells and synergistically enhanced MGd-induced cell death. MGd was also evaluated in combination with celecoxib, an inhibitor of Akt phosphorylation, or docetaxel, a microtubule inhibitor which can decrease Akt phosphorylation. The combination of MGd/celecoxib or MGd/docetaxel resulted in decreased Akt phosphorylation and in synergistic cytotoxicity compared to either agent alone. These data point to a potential protective role for pAkt in MGd-induced apoptosis and suggest that MGd activity may be enhanced by combining it with agents that inhibit Akt phosphorylation.