A multikinase inhibitor of the Raf/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway, sorafenib, is increasingly being used in the management of hepatocellular carcinoma, and its combination with conventional chemotherapeutics has stimulated particular interest. Although the combination of sorafenib with doxorubicin (DOX) is presently being investigated in a phase III randomized trial, little is known about the molecular mechanisms of their interaction. Because DOX causes cell death through upregulation of the MEK/ERK pathway, and sorafenib has an opposite influence on the same cascade, we hypothesized that co-treatment with these drugs may lead to an antagonistic effect. DOX treatment arrested proliferation and induced autophagic cell death in Hep3B cells, whereas apoptotic changes were not conspicuous. Sorafenib alone affected viability and caused massive mitochondrial degradation. However, when added together with DOX, sorafenib facilitated cell cycle progression, increased survival, and reduced autophagy. To evaluate the molecular mechanisms of this phenomenon, we examined the expression of ERK1/2, protein kinase B (Akt), and cyclin D1, as well as the members of Bcl-2 family. ERK1/2 activation induced by DOX was suppressed by sorafenib. Similarly, ERK targeting with the selective inhibitor U0126 impaired DOX-induced toxicity. Treatment with sorafenib, either alone or in combination with DOX, resulted in Akt activation. The role of sorafenib-induced degradation of cyclin D1 in the suppression of DOX efficiency is discussed. In conclusion, MEK/ERK counteraction, stimulation of survival via Akt and dysregulation of cyclin D1 could contribute to the escape from DOX-induced autophagy and thus promote cancer cell survival. The use of MEK/ERK inhibitors in combination with chemotherapeutics, intended to enhance anticancer efficacy, requires the consideration of possible antagonistic effects.
© 2011 The Authors Journal compilation © 2011 FEBS.