Multipoint targeting of the PI3K/mTOR pathway in mesothelioma.
BACKGROUND
Mesothelioma is a notoriously chemotherapy-resistant neoplasm, as is evident in the dismal overall survival for patients with those of asbestos-associated disease. We previously demonstrated co-activation of multiple receptor tyrosine kinases (RTKs), including epidermal growth factor receptor (EGFR), MET, and AXL in mesothelioma cell lines, suggesting that these kinases could serve as novel therapeutic targets. Although clinical trials have not shown activity for EGFR inhibitors in mesothelioma, concurrent inhibition of various activated RTKs has pro-apoptotic and anti-proliferative effects in mesothelioma cell lines. Thus, we hypothesised that a coordinated network of multi-RTK activation contributes to mesothelioma tumorigenesis.


METHODS
Activation of PI3K/AKT/mTOR, Raf/MAPK, and co-activation of RTKs were evaluated in mesotheliomas. Effects of RTK and downstream inhibitors/shRNAs were assessed by measuring mesothelioma cell viability/growth, apoptosis, activation of signalling intermediates, expression of cell-cycle checkpoints, and cell-cycle alterations.


RESULTS
We demonstrate activation of the PI3K/AKT/p70S6K and RAF/MEK/MAPK pathways in mesothelioma, but not in non-neoplastic mesothelial cells. The AKT activation, but not MAPK activation, was dependent on coordinated activation of RTKs EGFR, MET, and AXL. In addition, PI3K/AKT/mTOR pathway inhibition recapitulated the anti-proliferative effects of concurrent inhibition of EGFR, MET, and AXL. Dual targeting of PI3K/mTOR by BEZ235 or a combination of RAD001 and AKT knockdown had a greater effect on mesothelioma proliferation and viability than inhibition of individual activated RTKs or downstream signalling intermediates. Inhibition of PI3K/AKT was also associated with MDM2-p53 cell-cycle regulation.


CONCLUSIONS
These findings show that PI3K/AKT/mTOR is a crucial survival pathway downstream of multiple activated RTKs in mesothelioma, underscoring that PI3K/mTOR is a compelling target for therapeutic intervention.
1] Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China [2] Department of Bioengineering, College of Biology and Chemical Engineering, Jiaxing University, Jiaxing, China.
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S
Zhou
Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China.
L
L
Liu
Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China.
H
H
Li
Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
G
G
Eilers
Department of Biochemistry and Molecular Biology, College of Life Sciences, Zhejiang Sci-Tech University, Hangzhou, China.
Y
Y
Kuang
Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China.
S
S
Shi
Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China.
Z
Z
Yan
Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China.
X
X
Li
Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
J M
JM
Corson
Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China.
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F
Meng
Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China.
H
H
Zhou
Department of Biochemistry and Molecular Biology, College of Life Sciences, Zhejiang Sci-Tech University, Hangzhou, China.
Q
Q
Sheng
Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
J A
JA
Fletcher
1] Zhejiang Provincial Key Laboratory of Applied Enzymology, Department of Biotechnology and Biomedicine, Yangtze Delta Region Institute of Tsinghua University, Jiaxing, China [2] Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA [3] Department of Biochemistry and Molecular Biology, College of Life Sciences, Zhejiang Sci-Tech University, Hangzhou, China.
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Ou
D000970:Antineoplastic Agents / Q000494:pharmacology*; D002070:Butadienes / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology; D004354:Drug Screening Assays, Antitumor; D004789:Enzyme Activation / Q000187:drug effects; D000068338:Everolimus; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007191:Indazoles / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D008654:Mesothelioma / Q000201:enzymology* / Q000473:pathology; D058990:Molecular Targeted Therapy; D009025:Morpholines / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology; D009570:Nitriles / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011804:Quinolines / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000494:pharmacology; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects*; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology; D048490:raf Kinases / Q000502:physiology
D000970:Antineoplastic Agents; D002070:Butadienes; D002867:Chromones; D000068338:Everolimus; D007093:Imidazoles; D007191:Indazoles; D009025:Morpholines; D009363:Neoplasm Proteins; D009570:Nitriles; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D011804:Quinolines; D034741:RNA, Small Interfering; D020794:Receptor Protein-Tyrosine Kinases; D020123:Sirolimus; D013449:Sulfonamides; D058570:TOR Serine-Threonine Kinases; D048490:raf Kinases; C532162:2-(1H-indazol-4-yl)-6-(4-methanesulfonylpiperazin-1-ylmethyl)-4-morpholin-4-ylthieno(3,2-d)pyrimidine; C113580:U 0126; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human; C531198:dactolisib