Antitumor activity of miR-34a in peritoneal mesothelioma relies on c-MET and AXL inhibition: persistent activation of ERK and AKT signaling as a possible cytoprotective mechanism

Our plain-English summary of Antitumor activity of miR-34a in peritoneal mesothelioma relies on c-MET and AXL inhibition: persistent activation of ERK and AKT signaling as a possible cytoprotective mechanism, by R. El Bezawy, M. De Cesare, M. Pennati, et al (Journal of Hematology & Oncology, 2017).

The study

• Authors: R. El Bezawy, M. De Cesare, M. Pennati, M. Deraco, P. Gandellini, V. Zuco, N. Zaffaroni
• Journal: Journal of Hematology & Oncology
• Published: 2017;10(1):19
• Cited by: 43 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The value of microRNAs (miRNAs) as novel targets for cancer therapy is now widely recognized. However, no information is currently available on the expression/functional role of miRNAs in diffuse malignant peritoneal mesothelioma (DMPM), a rapidly lethal disease, poorly responsive to conventional treatments, for which the development of new therapeutic strategies is urgently needed. Here, we evaluated the expression and biological effects of miR-34a-one of the most widely deregulated miRNAs in cancer and for which a lipid-formulated mimic is already clinically available-in a large cohort of DMPM clinical samples and a unique collection of in house-developed preclinical models, with the aim to assess the potential of a miR-34a-based approach for disease treatment.

Methods: miR-34a expression was determined by qRT-PCR in 45 DMPM and 7 normal peritoneum specimens as well as in 5 DMPM cell lines. Following transfection with miR-34a mimic, the effects on DMPM cell phenotype, in terms of proliferative potential, apoptotic rate, invasion ability, and cell cycle distribution, were assessed. In addition, three subcutaneous and orthotopic DMPM xenograft models were used to examine the effect of miR-34a on tumorigenicity. The expression of miRNA targets and the activation status of relevant pathways were investigated by western blot.

Results: miR-34a was found to be down-regulated in DMPM clinical specimens and cell lines compared to normal peritoneal samples. miR-34a reconstitution in DMPM cells significantly inhibited proliferation and tumorigenicity, induced an apoptotic response, and declined invasion ability, mainly through the down-regulation of c-MET and AXL and the interference with the activation of downstream signaling. Interestingly, a persistent activation of ERK1/2 and AKT in miR-34a-reconstituted cells was found to counteract the antiproliferative and proapoptotic effects of miRNA, yet not affecting its anti-invasive activity.

Conclusions: Our preclinical data showing impressive inhibitory effects induced by miR-34a on DMPM cell proliferation, invasion, and growth in immunodeficient mice strongly suggest the potential clinical utility of a miR-34a-replacement therapy for the treatment of such a still incurable disease. On the other hand, we provide the first evidence of a potential cytoprotective/resistance mechanism that may arise towards miRNA-based therapies through the persistent activation of RTK downstream signaling.

In plain English

This laboratory study looked at an RNA molecule called miR-34a in diffuse malignant peritoneal mesothelioma (DMPM), a cancer of the abdominal lining. It did not study asbestos or other causes of the disease. The authors measured miR-34a in tumor samples from 45 patients treated in Milan, Italy, between 1997 and 2013, in 7 normal peritoneum samples and in 5 DMPM cell lines. miR-34a was significantly lower in the tumors than in normal tissue. Its level was not significantly linked to 5-year disease-free survival (hazard ratio 1.85, 95% confidence interval 0.86–4.01). Adding synthetic miR-34a slowed growth in four of five cell lines and reduced invasion. Cells given miR-34a before injection under the skin of mice formed smaller tumors, with maximum volume reductions of 57 to 98% versus control cells. In the abdomen, 1 of 5 mice given treated STO cells developed tumors, versus 5 of 5 controls. The authors concluded that these preclinical results suggest possible clinical use of miR-34a replacement therapy. They also concluded that persistent ERK and AKT signaling may protect some cells against its growth-slowing and cell-killing effects.

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 study combining measurement of miR-34a in patient tumor samples, experiments in DMPM cell lines, and mouse xenograft experiments (human tumor cells grown in mice)
• Who was studied: 45 DMPM specimens (40 epithelioid, 1 sarcomatoid, 4 biphasic) from patients treated with cytoreductive surgery plus hyperthermic intraperitoneal chemotherapy at the Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, from October 1997 to February 2013; 7 normal peritoneum specimens from patients operated on for non-cancer disease; 5 DMPM cell lines (STO, MP4, MesoII, MP8, MP115); 8-week-old female SCID mice, five to six per group
• Exposure: No asbestos or fiber exposure was studied. The experimental treatment was transfection of cells with a synthetic miR-34a mimic, compared with a negative-control mimic. For the mouse experiments, cells were transfected before being injected. Some experiments also used siRNAs against AXL and c-MET, and AKT and MEK inhibitor drugs.
• Main results:
  • miR-34a levels were significantly lower in the 45 DMPM tumor samples than in the 7 normal peritoneum samples, and were also down-regulated in all 5 DMPM cell lines
  • In patients, miR-34a level did not significantly affect 5-year disease-free survival: 36% for high expressers versus 20% for low expressers (hazard ratio 1.85; 95% confidence interval 0.86–4.01; p = 0.11)
  • miR-34a reconstitution significantly inhibited proliferation of four of the five DMPM cell lines; in MP115 cells it caused only a weak inhibition (about 30%)
  • miR-34a reconstitution inhibited invasion of the DMPM cell lines in a Matrigel-based assay
  • STO, MesoII and MP8 cells were transfected with miR-34a and then injected under the skin of mice. The resulting tumors had maximum tumor volume inhibitions of 57 to 98% compared with tumors from negative-control-transfected cells (57% STO, 96% MesoII, 98% MP8). Already established tumors were not treated.
  • Cells were injected into the abdomen after transfection. With miR-34a-treated STO cells, 1 of 5 mice developed tumors, versus 5 of 5 controls (p = 0.0476). With MP8 cells, tumors took in all mice, but average tumor weight was lower: 88 mg versus 210 mg in controls, a 58% inhibition (p = 0.0071).
  • In the less sensitive MesoII cells, blocking both the AKT and the MEK/ERK pathways with low-dose inhibitors made their response to miR-34a similar to that of the sensitive STO cell line
• The authors' conclusion: The authors concluded that their preclinical data suggest potential clinical utility of miR-34a-replacement therapy for DMPM. They also concluded that they provide first evidence of a possible cytoprotective or resistance mechanism, through persistent activation of signaling downstream of receptor tyrosine kinases (ERK1/2 and AKT).
• Limitations the authors state:
  • MP115, the only biphasic DMPM cell line in the panel, could not grow in mice. The authors therefore could not test whether miR-34a's effect on it in the laboratory would translate into reduced tumor growth.

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: Peritoneal Mesothelioma, Peritoneum.

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