Metformin produces growth inhibitory effects in combination with nutlin-3a on malignant mesothelioma through a cross-talk between mTOR and p53 pathways

Our plain-English summary of Metformin produces growth inhibitory effects in combination with nutlin-3a on malignant mesothelioma through a cross-talk between mTOR and p53 pathways, by K. Shimazu, Y. Tada, T. Morinaga, et al (BMC Cancer, 2017).

The study

• Authors: K. Shimazu, Y. Tada, T. Morinaga, M. Shingyoji, I. Sekine, H. Shimada, K. Hiroshima, T. Namiki, K. Tatsumi, M. Tagawa
• Journal: BMC Cancer
• Published: 2017;17(1):309
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Mesothelioma is resistant to conventional treatments and is often defective in p53 pathways. We then examined anti-tumor effects of metformin, an agent for type 2 diabetes, and combinatory effects of metformin and nutlin-3a, an inhibitor for ubiquitin-mediated p53 degradation, on human mesothelioma.

Methods: We examined the effects with a colorimetric assay and cell cycle analyses, and investigated molecular events in cells treated with metformin and/or nutlin-3a with Western blot analyses. An involvement of p53 was tested with siRNA for p53.

Results: Metformin suppressed cell growth of 9 kinds of mesothelioma including immortalized cells of mesothelium origin irrespective of the p53 functional status, whereas susceptibility to nutlin-3a was partly dependent on the p53 genotype. We investigated combinatory effects of metformin and nutlin-3a on, nutlin-3a sensitive MSTO-211H and NCI-H28 cells and insensitive EHMES-10 cells, all of which had the wild-type p53 gene. Knockdown of p53 expression with the siRNA demonstrated that susceptibility of MSTO-211H and NCI-H28 cells to nutlin-3a was p53-dependent, whereas that of EHMES-10 cells was not. Nevertheless, all the cells treated with both agents produced additive or synergistic growth inhibitory effects. Cell cycle analyses also showed that the combination increased sub-G1 fractions greater than metformin or nutlin-3a alone in MSTO-211H and EHMES-10 cells. Western blot analyses showed that metformin inhibited downstream pathways of the mammalian target of rapamycin (mTOR) but did not activate the p53 pathways, whereas nutlin-3a phosphorylated p53 and suppressed mTOR pathways. Cleaved caspase-3 and conversion of LC3A/B were also detected but it was dependent on cells and treatments. The combination of both agents in MSTO-211H cells rather suppressed the p53 pathways that were activated by nutrin-3a treatments, whereas the combination rather augmented the p53 actions in NCI-H28 and EHMES-10 cells.

Conclusion: These data collectively indicated a possible interactions between mTOR and p53 pathways, and the combinatory effects were attributable to differential mechanisms induced by a cross-talk between the pathways.

In plain English

This was a laboratory study of human cells grown in dishes. No patients, animals or asbestos exposure were studied. The authors tested metformin, a diabetes drug, and nutlin-3a, which raises p53 protein levels. They used 8 mesothelioma cell lines and one immortalized mesothelial line (Met-5A). Metformin reduced viability of all the cells regardless of p53 function. Average IC50 values were 8.5 mM (standard error 7.4) in the functional-p53 group and 8.2 mM (standard error 3.5) in the non-functional group (P = 0.93). Nutlin-3a was more potent on average in functional-p53 cells, though EHMES-10 was relatively insensitive despite wild-type p53. Three lines with wild-type p53 (MSTO-211H, NCI-H28, EHMES-10) were then given both agents. The combination produced additive or synergistic growth suppression in all three. In MSTO-211H and EHMES-10 it also raised the sub-G1 fraction more than either agent alone. Protein analyses differed by cell line. From these cell results, the authors suggested that combining an mTOR inhibitor with a p53-activating agent is a new therapeutic regimen for mesothelioma with characteristic genetic alterations. They noted the mechanism differed among the cells.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) study of human cell lines; no human specimens or animals
• Who was studied: 8 human mesothelioma cell lines (MSTO-211H, NCI-H28, NCI-H226, NCI-H2052, NCI-H2452, JMN-1B, EHMES-1, EHMES-10) and one line of mesothelial cells immortalized with SV40 T antigen (Met-5A). These were grouped by whether p53 was functional (MSTO-211H, NCI-H28, NCI-H226, NCI-H2052, EHMES-10) or non-functional (JMN-1B, EHMES-1, NCI-H2452, Met-5A).
• Exposure: Treatment of cells with metformin (a type 2 diabetes drug) and/or nutlin-3a (an inhibitor of MDM2-p53 interaction) at various concentrations. Asbestos exposure was not studied.
• Main results:
  • Metformin suppressed viability of all cells tested. Susceptibility did not depend on p53 function: average IC50 was 8.5 mM (SE 7.4) in the functional-p53 group and 8.2 mM (SE 3.5) in the non-functional-p53 group, P = 0.93.
  • Nutlin-3a was more potent in cells with functional p53. Average IC50 was 8.0 μM (SE 5.6) in the functional-p53 cells, including EHMES-10, and 24.5 (SE 2.7) in the non-functional-p53 cells, P less than 0.05. EHMES-10 cells were less sensitive despite wild-type p53.
  • Metformin plus nutlin-3a produced additive or synergistic growth suppression. This was seen at fraction-affected points between 0.35 and 0.8 in MSTO-211H and EHMES-10 cells, and between 0.2 and 0.6 in NCI-H28 cells.
  • Reducing p53 with siRNA did not change any cell line's sensitivity to metformin. It significantly reduced nutlin-3a cytotoxicity in MSTO-211H and NCI-H28 cells, but not in EHMES-10 cells.
  • In MSTO-211H and EHMES-10 cells, metformin 60 mM combined with nutlin-3a increased the sub-G1 fraction more than either agent alone. At 72 h in MSTO-211H cells it was 36.25% for the combination, versus 13.28% for metformin 60 mM and 11.38% for nutlin-3a 10 μM. In NCI-H28 cells the combination did not change the cell cycle beyond nutlin-3a alone.
  • Metformin inhibited downstream mTOR pathways but did not induce p53 phosphorylation in any of the cells. Combined with nutlin-3a, it suppressed p53 pathways in MSTO-211H cells but augmented them in NCI-H28 and EHMES-10 cells.
• The authors' conclusion: The authors concluded that both agents produced combinatory effects on mesothelioma cell growth, through mechanisms that differed among the cells. They suggested that combining an mTOR inhibitor with a p53-activating agent targets mesothelioma with characteristic genetic alterations and is a new therapeutic regimen.
• Limitations the authors state:
  • The mechanism of the combination differed among the cell lines tested, which the authors attributed probably to heterogeneity of mesothelioma.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Mesothelium.

Related studies

• Combination of a p53-activating CP-31398 and an MDM2 or a FAK inhibitor produces growth suppressive effects in mesothelioma with wild-type p53 genotype — B. Zhong, M. Shingyoji, et al. (2020)
• An MDM2 inhibitor achieves synergistic cytotoxic effects with adenoviruses lacking E1B55kDa gene on mesothelioma with the wild-type p53 through augmenting NFI expression — T.T.T. Nguyen, M. Shingyoji, et al. (2021)
• Combination of a third generation bisphosphonate and replication-competent adenoviruses augments the cytotoxicity on mesothelioma — Y. Jiang, B. Zhong, et al. (2016)
• Zoledronic acid produces combinatory anti-tumor effects with cisplatin on mesothelioma by increasing p53 expression levels — S. Okamoto, Y. Jiang, et al. (2013)
• Pharmacological targeting of p53 through RITA is an effective antitumoral strategy for malignant pleural mesothelioma — D. Di Marzo, I.M. Forte, et al. (2014)
• Zoledronic acid produces antitumor effects on mesothelioma through apoptosis and S-phase arrest in p53-independent and Ras prenylation-independent manners — S. Okamoto, K. Kawamura, et al. (2012)

Browse more research in BMC Cancer, or return to medical research.