Targeted inhibition of multiple receptor tyrosine kinases in mesothelioma

Our plain-English summary of Targeted inhibition of multiple receptor tyrosine kinases in mesothelioma, by W.B. Ou, C. Hubert, J.M. Corson, et al (Neoplasia, 2011).

The study

• Authors: W.B. Ou, C. Hubert, J.M. Corson, R. Bueno, D.L. Flynn, D.J. Sugarbaker, J.A. Fletcher
• Journal: Neoplasia
• Published: 2011;13(1):12-22
• Cited by: 59 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The receptor tyrosine kinases (RTKs) epidermal growth factor receptor (EGFR) and MET are activated in subsets of mesothelioma, suggesting that these kinases might represent novel therapeutic targets in this notoriously chemotherapy-resistant cancer. However, clinical trials have shown little activity for EGFR inhibitors in mesothelioma. Despite the evidence for RTK activation in mesothelioma pathogenesis, it is unclear whether transforming activity is dependent on an individual kinase oncoprotein or the coordinated activity of multiple kinases. Using phospho-RTK and immunoblot assays, we herein demonstrate activation of multiple RTKs (EGFR, MET, AXL, and ERBB3) in individual mesothelioma cell lines but not in normal mesothelioma cells. Inhibition of mesothelioma multi-RTK signaling was accomplished using combinations of RTK direct inhibitors or by inhibition of the RTK chaperone, heat shock protein 90 (HSP90). Multi-RTK inhibition by the HSP90 inhibitor 17-allyloamino-17-demethoxygeldanamycin (17-AAG) had a substantially greater effect on mesothelioma proliferation and survival compared with inhibition of individual activated RTKs. HSP90 inhibition also suppressed phosphorylation of downstream signaling intermediates (AKT, mitogen-activated protein kinase, and S6); upregulated the p53, p21, and p27 cell cycle checkpoints; induced G(2) phase arrest; induced caspase 3/7 activity; and led to an increase in the sub-G(1) apoptotic population. These compelling proapoptotic and antiproliferative responses indicate that HSP90 inhibition warrants clinical evaluation as a novel therapeutic strategy in mesothelioma.

In plain English

This was a laboratory study of human mesothelioma cells grown in culture. It did not study asbestos exposure or treat patients. The authors established ten mesothelioma cell lines from untreated patients' surgical tissue and compared them with normal mesothelial cells. In mesothelioma cells, the growth-signal proteins EGFR, MET, AXL and ERBB3 (receptor tyrosine kinases) were active together. EGFR, MET and AXL were present in most mesothelioma lines at two- to five-fold higher levels than in normal cells. Drugs blocking EGFR or MET, alone or together, had little effect on cell viability. The largest reductions (more than 40%) came from blocking several kinases at once, with drug combinations or with 17-AAG, which blocks a helper protein called HSP90. The 17-AAG concentration that halved cell viability (IC50) was lower in two lines with spindle-cell components (69 and 72 nM) than in two epithelioid lines (192 and 266 nM). 17-AAG also increased the share of dying cells. The authors concluded that HSP90 inhibition warrants evaluation as a treatment strategy. They said further studies are needed to see whether these responses can be achieved in living (in vivo) models.

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 mesothelioma cell lines treated with kinase-inhibitor drugs
• Who was studied: Ten mesothelioma cell lines established at Brigham and Women's Hospital from surgical material of previously untreated patients (2 epithelial-type, 6 mixed-histology, 2 spindle cell). They were compared with normal mesothelial cells from a nonneoplastic pleural effusion and from nonneoplastic peritoneum. Drug experiments used four lines: MESO924, MESO257, MESO296 and MESO428.
• Exposure: No asbestos or fiber exposure was studied. The cells were treated with drugs: gefitinib (EGFR inhibitor), PHA-665752 (MET inhibitor) and DP-3975 (AXL inhibitor), each at 1 μM, alone or in combination. They were also treated with the HSP90 inhibitor 17-AAG at 0.1 to 1 μM.
• Main results:
  • In MESO924 mesothelioma cells, EGFR, ERBB3, AXL and MET were activated together. In normal mesothelial cells the array showed only apparent EGFR activation, which the authors judged a false-positive result after immunoblot testing.
  • EGFR, MET and AXL were co-expressed in most mesothelioma cell lines at levels two- to five-fold higher than in normal mesothelial cells.
  • In all mesothelioma cell lines tested, the greatest reduction in cell viability (more than 40%) came from combined inhibition of EGFR, MET and AXL. This was achieved either with multiple kinase inhibitors or with HSP90 inhibition.
  • EGFR and MET inhibition, singly or in combination, had little effect on mesothelioma cell viability.
  • The 17-AAG half maximal inhibitory concentration (IC50) values for cell viability were 69 nM in MESO296 and 72 nM in MESO428, the lines with spindle-cell components.
  • The 17-AAG IC50 values were 192 nM in MESO257 and 266 nM in MESO924, the epithelioid lines.
  • 17-AAG inactivated EGFR, MET, ERBB3, AXL, EPHA7 and EPHB2 in MESO924 and MESO428. It also inactivated the downstream signals AKT and S6 in all lines.
  • The share of fragmented (apoptotic) cells with control (DMSO only) versus 0.5 μM 17-AAG was 0.1% versus 8.0% in MESO924, 1.7% versus 4.4% in MESO257, 1.7% versus 20% in MESO296, and 0.7% versus 2.6% in MESO428.
  • HSP90 inhibition raised levels of the cell cycle checkpoint proteins p27, p21 and p53. It also caused a dose-dependent G2 block (cells stalled before dividing).
• The authors' conclusion: The authors concluded that mesothelioma cell proliferation and survival require coactivation of multiple receptor tyrosine kinases, including EGFR, MET and AXL. They concluded that HSP90 inhibition, as a single agent or in combination therapy, warrants evaluation as a novel therapeutic strategy in mesothelioma.
• Limitations the authors state:
  • The findings are from cells in culture. The authors state that further studies are needed to determine whether the responses can be achieved in in vivo models.
  • The phospho-RTK array gave a false-positive EGFR signal in normal mesothelial cells.
  • The authors note that clinical use of 17-AAG has been hampered by its low water solubility.

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, EGFR, Chemotherapy, Clinical Trial.

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