Combination of mTOR inhibitor PP242 and AMPK activator metformin exerts enhanced inhibitory effects on colorectal carcinoma cells in vitro by blocking multiple kinase pathways

Abstract

The second-generation mammalian target of rapamycin (mTOR) inhibitor PP242 has demonstrated limited success in some rapamycin-insensitive tumours. We examined the therapeutic potential of combining PP242 with adenosine 50- monophosphate-activated protein kinase (AMPK) activator metformin, using a panel of colorectal carcinoma (CRC) cell lines. We found that the PP242 and metformin combination enhanced the suppression of CRC cell proliferation, colony formation, and cancer cell apoptosis induction. The effect of this combination was observed on AMPK phosphorylation. Western blotting showed that PP242 inhibited mTORC1 activation, as indicated by the reduced expression of its major substrate p-S6K1 and the partially reduced phosphorylation of eIF4E-binding protein 1 (4E-BP1). The inhibition of mTORC2-mediated AKT phosphorylation at Ser 473 (AKT Ser473) was transient and occurred in the first few hours of PP242 treatment; metformin exposure decreased the PP242 activity, counteracting AKT activation. We further demonstrated that this was related to direct AMPK-mediated phosphorylation of IRS-1 at Ser789. Thus, the combination of PP242 and metformin completely blocked the activity of both mTORC1 and mTORC2 kinase. This study suggests that this combination could be a more effective strategy for the treatment of CRC.

Keywords:

• PP242
• metformin
• mTOR inhibitor
• AMPK activator
• colorectal cancer
• combination therapy

Acknowledgment

This project was supported by Research Institute of McGill University Health Centre.

Consent to publish

All the authors agree with the publication of the present paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethics approval and consent to participate

Not applicable.

Data availability statement

The data of this study is available from the corresponding author on reasonable request.

Additional information

Funding

This project was supported by Research Institute of McGill University Health Centre and Natural Science Foundation of Shandong Province (Grant No. ZR2020QH361).