Oncogenic transcription factor Myc deregulates the cell cycle and simultaneously reprograms cellular metabolism to meet the biosynthetic and bioenergetic needs of proliferation. Myc also sensitizes cells to mitochondria-dependent apoptosis. Although metabolic reprogramming has been circumstantially connected to vulnerability to apoptosis, the connecting molecular pathways have remained poorly defined. Our recent studies revealed that Myc-dependent ATP depletion activates the energy sensor AMP-activated protein kinase (AMPK), which induces stabilizing phosphorylation of p53 at Ser15. AMPK-stabilized tumor suppressor protein p53 then accumulates in the mitochondria and interacts with the protein complex comprised of Bak and Bcl-xL, to sensitize cells to apoptosis. These results reveal an unexpected pro-apoptotic function of AMPK in context of Myc transformed cells.

We have explored possibilities to therapeutically exploit the Myc-AMPK facilitated apoptosis pathway. We show that a BH3-mimetic small molecule ABT-737, which neutralizes Bcl-2 and Bcl-xL, sensitizes to Myc-dependent apoptosis ex vivo and in vivo WAP-Myc tumours. ABT-737 also reduced WAP-Myc driven primary tumor growth and lung metastases in transgenic and syngrafted mice. Nevertheless, ABT-737 only delayed but did not prevent the formation of Wap-Myc tumors.

In a drug combination screen designed to identify small molecules that potentiate the efficacy of ABT-737, we found several compounds influencing the status of AMPK activity. The synergistic apoptotic action between ABT-737 and AMPK modulating agents has been validated in explant 3D cultures from patient derived Myc positive breast cancers. The mechanisms behind the proapoptotic AMPK function will be discussed. Our results provide evidence that AMPK has a context-dependent pro-apoptotic function that can be therapeutically exploited as a tumour cell-specific vulnerability.

Citation Format: Heidi M. Haikala, Elsa Marques, Vilja Eskelinen, Anni Viheriäranta-Nieminen, Sirkku Saarikoski, Liina Nevalaita, Panu Kovanen, Päivi Heikkilä, Marjut Leidenius, Daniel Laajala, Tero Aittokallio, Pauliina Munne, Juha Klefström. Pro-apoptotic functions of AMPK revealed by Myc. [abstract]. In: Proceedings of the AACR Special Conference on Myc: From Biology to Therapy; Jan 7-10, 2015; La Jolla, CA. Philadelphia (PA): AACR; Mol Cancer Res 2015;13(10 Suppl):Abstract nr B32.