Melatonin enhances sorafenib actions in human hepatocarcinoma cells by inhibiting mTORC1/p70S6K/HIF-1α and hypoxia-mediated mitophagy
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Néstor Prieto-Domínguez1,2,*, Carolina Méndez-Blanco1,2,*, Sara Carbajo-Pescador1,2, Flavia Fondevila1,2, Andrés García-Palomo1,3, Javier González-Gallego1,2,** and José L. Mauriz1,2,**
1Institute of Biomedicine (IBIOMED), University of León, León, Spain
2Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd), Instituto de Salud Carlos III, Madrid, Spain
3Service of Oncology, Complejo Asistencial Universitario de León, León, Spain
*These authors have contributed equally to this work
**JLM and JGG share senior authorship
José L. Mauriz, email: firstname.lastname@example.org
Keywords: hepatocarcinoma, hypoxia-inducible factor-1α, hypoxia-mediated mitophagy, melatonin, sorafenib
Received: July 22, 2017 Accepted: August 09, 2017 Published: August 24, 2017
The antiangiogenic effects of sustained sorafenib treatment in hepatocellular carcinoma (HCC) lead to the occurrence of hypoxia-mediated drug resistance resulting in low therapy efficiency and negative outcomes. Combined treatments with coadjuvant compounds to target the hypoxia-inducible factor-1α (HIF-1α) represent a promising therapeutic approach through which sorafenib efficiency may be improved. Melatonin is a well-documented oncostatic agent against different cancer types. Here, we evaluated whether melatonin could enhance sorafenib cytotoxicity and overcome the hypoxia-mediated resistance mechanisms in HCC. The pharmacological melatonin concentration (2 mM) potentiated the oncostatic effects of sorafenib (5 μM) on Hep3B cells even under hypoxia. Melatonin downregulated the HIF-1α protein synthesis through the inhibition of the mammalian target of rapamycin complex 1 (mTORC1)/ribosomal protein S6 kinase beta-1 (p70S6K)/ribosomal protein S6 (RP-S6) pathway, although the indole enhanced Akt phosphorylation by the mTORC1/C2 negative feedback. Furthermore, melatonin and sorafenib coadministration reduced the HIF-1α-mitophagy targets expression, impaired autophagosome formation and subsequent mitochondria and lysosomes colocalization. Together, our results indicate that melatonin improves the Hep3B sensitivity to sorafenib, preventing HIF-1α synthesis to block the cytoprotective mitophagy induced by the hypoxic microenvironment, an important element of the multifactorial mechanisms responsible for the chemotherapy failure.
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