Interference with PDK1-Akt survival signaling pathway by UCN-01 (7-hydroxystaurosporine)

3-Phosphoinositide-dependent protein kinase-1 (PDK1) plays a central role in activating the AGC subfamily of protein kinases. In particular, PDK1 plays an important role in the regulation of Akt/PKB survival pathway by phosphorylating Akt on Thr308. Here we show that UCN-01 (7-hydroxystaurosporine), a drug now in clinical trials and with a unique fingerprint pattern, induced dephosphorylation and inactivation of Akt, resulting in the turn-off of the survival signals and the induction of apoptosis. Further analysis revealed that UCN-01-mediated Akt inactivation was caused by inhibiting upstream Akt kinase PDK1 (IC50=33 nM) both in vitro and from cells, but not by suppressing Akt itself or phosphatidylinositide-3-OH kinase. UCN-01-induced PDK1 inhibition was also observed in in vivo murine and human tumor xenografts. Overexpression of active form of Akt diminished the cytotoxic effects of UCN-01, suggesting that UCN-01 may in part exert its cytotoxicity by inhibiting PDK1-Akt survival pathway. Because UCN-01 has already proved to have potent anti-tumor activity in vivo, PDK1-Akt survival pathway is a new, attractive target for cancer chemotherapy.