Coactivation of receptor tyrosine kinases in malignant mesothelioma as a rationale for combination targeted therapy

Our plain-English summary of Coactivation of receptor tyrosine kinases in malignant mesothelioma as a rationale for combination targeted therapy, by M. Brevet, S. Shimizu, M.J. Bott, et al (Journal of Thoracic Oncology, 2011).

The study

• Authors: M. Brevet, S. Shimizu, M.J. Bott, N. Shukla, Q. Zhou, A.B. Olshen, V. Rusch, M. Ladanyi
• Journal: Journal of Thoracic Oncology
• Published: 2011;6(5):864-74
• Cited by: 55 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: To identify new therapeutic approaches in malignant mesothelioma (MM), we examined the expression and activation of receptor tyrosine kinases (RTKs) and the effects of specific RTK inhibitors and the mammalian target of rapamycin (mTOR) inhibitor rapamycin; the latter being of special interest in MM given the recent linkage between NF2 loss and mTOR activation.

Methods: We performed a screen for mutated or activated RTKs in 14 MM cell lines and 70 primary tumors. Expression of phosphorylated RTKs was analyzed by Western blotting and a membrane-based antibody array in normal growth conditions and after treatment by specific inhibitors. MET and epidermal growth factor receptor (EGFR) mutations were screened by sequencing. MET, hepatocyte growth factor, insulin-like growth factor 1 receptor, and EGFR expression were studied by Western blotting, immunohistochemistry, enzyme-linked immunosorbent assay, and by Affymetrix expression microarrays.

Results: Profiling of the phosphorylation status of 42 RTKs showed prominent coactivation of MET and EGFR in 8 of 14 (57%) MM cell lines. MET, EGFR, and insulin-like growth factor 1 receptor were the main RTKs activated after mTOR inhibition and contributed to AKT feedback activation. Knockdown of MET by RNA interference inhibited not only the phosphorylation of MET but also that of EGFR. Conversely, stimulation with hepatocyte growth factor increased both phospho-MET and phospho-EGFR. The combination of PHA-665752 and the EGFR inhibitor, erlotinib, suppressed cell growth more than either agent alone in three of six cell lines tested. Finally, combinations of rapamycin and different RTK inhibitors were more active than either drug alone in 12 of 13 cell lines.

Conclusion: Combination targeting of kinase signaling pathways is more effective than single agents in most MM.

In plain English

This laboratory study of malignant mesothelioma cell lines and tumor samples examined signaling proteins called receptor tyrosine kinases. It did not study asbestos exposure. In 10 of 14 cell lines, activated EGFR was higher than in controls, and 6 of 14 (43%) showed both activated MET and activated EGFR; the abstract instead gives 8 of 14 (57%). Blocking MET, by drug or gene knockdown, also reduced activated EGFR. Strong staining for both HGF and MET appeared in 13 of 118 (11%) tumor cases. The authors concluded from sequencing that somatic mutations could not explain the frequent MET and EGFR activation; at most 2 of 70 tumors had possible somatic MET mutations, and these could not be confirmed. In medium with 10% fetal calf serum, rapamycin activated a protein called AKT in 10 of 13 cell lines; this disappeared without serum. PHA-665752 (a MET drug) plus erlotinib (an EGFR drug) inhibited growth more than PHA-665752 alone in 3 of 6 lines tested. Rapamycin combined with different kinase drugs was more active than either drug alone in 12 of 13 lines. The authors concluded that combining inhibitors may be necessary in mesothelioma.

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 of mesothelioma cell lines and tumor samples, including drug-treatment experiments and gene sequencing
• Who was studied: 14 malignant mesothelioma cell lines and two immortalized human mesothelial cell lines. Tumor samples were also studied: 70 sequenced for mutations, 99 examined by gene-expression arrays, and 118 cases stained (IHC) on tissue microarrays. All work was done at Memorial Sloan-Kettering Cancer Center, New York.
• Exposure: No asbestos exposure was studied. The exposures were laboratory drug treatments of cell lines: erlotinib (EGFR inhibitor), PHA-665752 (MET inhibitor), MK-0646 (IGF-1R inhibitor) and rapamycin (mTOR inhibitor), alone and in combination.
• Main results:
  • In the cell lines, 10 of 14 showed higher phosphorylated (activated) EGFR than controls.
  • In the cell lines, 6 of 14 (43%) showed both phosphorylated MET and phosphorylated EGFR. The abstract gives 8 of 14 (57%).
  • In tumor cases, 13 of 118 (11%) showed strong immunostaining for both HGF and MET. In the gene-expression data, 6 of 99 (6%) showed raised HGF and MET transcripts.
  • In three cell lines, the MET inhibitor PHA-665752 also reduced EGFR phosphorylation. In two other cell lines, switching off MET with siRNA reduced phosphorylated EGFR.
  • Sequencing found MET sequence alterations in 6 of 70 tumor samples, and four of these were germline polymorphisms. The authors stated that MET somatic mutations occur in at most 3% (2 of 70) of cases and therefore cannot account for the high frequency of MET activation. For those two variants, they could not confirm a somatic origin. No EGFR kinase-domain mutations were found in the 14 cell lines.
  • Rapamycin 0.1 nM induced AKT activation in 10 of 13 cell lines grown in 10% FCS (fetal calf serum). This feedback activation disappeared in medium lacking FCS.
  • Erlotinib plus PHA-665752 significantly shifted the IC50 compared with PHA-665752 alone in 3 of the 6 cell lines tested (JMN, Meso 10, Meso 9). In these three lines the combination inhibited cell growth more than PHA-665752 alone.
  • Combinations of rapamycin and different RTK inhibitors were more active than either drug alone in 12 of 13 cell lines. H-Meso was the only line resistant to all combinations.
• The authors' conclusion: The authors concluded that because several RTKs are activated together in mesothelioma, combinations of RTK inhibitors may be necessary. They also concluded that combining mTOR and specific RTK inhibitors more effectively decreased cell growth in the cell lines.
• Limitations the authors state:
  • The Met5A cell line, used as a non-tumor comparison, shows widespread genomic copy number aberrations.
  • For two novel MET alterations, the authors could not confirm a somatic origin because matching normal DNA was unavailable.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Targeted Therapy, EGFR, Immunohistochemistry.

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