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

Abstract

BackgroundMesothelioma 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.MethodsWe 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.ResultsMetformin 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.ConclusionThese 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-017-3300-y) contains supplementary material, which is available to authorized users.

mTOR Cross-Talk in Cancer and Potential for Combination Therapy

“…Moreover, the same group showed that a simultaneous inhibition of the PI3K/mTOR pathway and Mdm2-p53 complex assembly (by nutlin-3) is potentially effective in AML ( Table 2 ) [ 82 ]. Even in mesothelioma, p53 pathway is often defective, thus leading to conventional treatments resistance, and Shimazu and his group investigated a possible mechanism of the combinatory effects between up-regulation of p53 levels and inhibition of the mTOR pathways, by nutlin-3 and metformin respectively [ 103 ]. Nevertheless, in this work the authors demonstrated that combination of metformin and nutlin-3a results in both additive and synergistic effects, probably due to heterogeneity of mesothelioma cells.…”

Glucose starvation induces resistance to metformin through the elevation of mitochondrial multidrug resistance protein 1

“…HMM patients present poor therapeutic response due to traditional anticancer drug resistance, such as cisplatin and pemetrexed . Metformin, which is commonly used for the management of type II diabetes mellitus, has been suggested as an alternative anticancer drug . Recent studies have shown the potential therapeutic value of metformin in HMM cells, which is exerted through the inhibition of mTOR and cell cycle arrest .…”

“…20 Metformin, which is commonly used for the management of type II diabetes mellitus, has been suggested as an alternative anticancer drug. 21,22 Recent studies have shown the potential therapeutic value of metformin in HMM cells, which is exerted through the inhibition of mTOR and cell cycle arrest. 21 However, metformin treatment causes resistance in human breast cancer cells, although the precise mechanism has not been elucidated.…”

“…21,22 Recent studies have shown the potential therapeutic value of metformin in HMM cells, which is exerted through the inhibition of mTOR and cell cycle arrest. 21 However, metformin treatment causes resistance in human breast cancer cells, although the precise mechanism has not been elucidated. 23 Metformin treatment has shown no evidence to relieve HMM patients, which may be due to the tumor microenvironment.…”

Targeting the Hippo Pathway Is a New Potential Therapeutic Modality for Malignant Mesothelioma

“…However, a retrospective study of 300 patients with type 2 diabetes and MPM did not shown any improvement to patient survival [ 105 ]. Meanwhile, metformin has been recently shown to inhibit MM cell proliferation when administered in combination with nutlin-3a (an inhibitor of ubiquitin-mediated p53 degradation) [ 106 ].…”