A subgroup of pleural mesothelioma expresses ALK protein and may be targetable by combined rapamycin and crizotinib therapy

Our plain-English summary of A subgroup of pleural mesothelioma expresses ALK protein and may be targetable by combined rapamycin and crizotinib therapy, by D. Mönch, S. Bode-Erdmann, J. Kalla, et al (Oncotarget, 2018).

The study

• Authors: D. Mönch, S. Bode-Erdmann, J. Kalla, J. Sträter, C. Schwänen, R. Falkenstern-Ge, S. Klumpp, G. Friedel, G. Ott, C. Kalla
• Journal: Oncotarget
• Published: 2018;9(29):20781-20794
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is a neoplasm with inferior prognosis and notorious chemotherapeutic resistance. Targeting aberrantly overexpressed kinases to cure MPM is a promising therapeutic strategy. Here, we examined ALK, MET and mTOR as potential therapeutic targets and determined the combinatorial efficacy of ALK and mTOR targeting on tumor cell growth in vivo. First, ALK overexpression, rearrangement and mutation were studied in primary MPM by qRT-PCR, FISH, immunohistochemistry and sequence analysis; mTOR and MET expression by qRT-PCR and immunohistochemistry. Overexpression of full-length ALK transcripts was observed in 25 (19.5%) of 128 primary MPM, of which ten expressed ALK protein. ALK overexpression was not associated with gene rearrangement, amplification or kinase-domain mutation. mTOR protein was detected in 28.7% MPM, co-expressed with ALK or MET in 5% and 15% MPM, respectively. The ALK/MET inhibitor crizotinib enhanced the anti-tumor effect of the mTOR-inhibitor rapamycin in a patient-derived MPM xenograft with co-activated ALK/mTOR: combined therapy achieved tumor shrinkage in 4/5 tumors and growth stagnation in one tumor. Treatment effects on proliferation, apoptosis, autophagy and pathway signaling were assessed using Ki-67 immunohistochemistry, TUNEL assay, LC3B immunofluorescence, and immunoblotting. Co-treatment significantly suppressed cell proliferation and induced autophagy and caspase-independent, necrotic cell death. Rapamycin/crizotinib simultaneously inhibited mTORC1 (evidenced by S6 kinase and RPS6 dephosphorylation) and ALK signaling (ALK, AKT, STAT3 dephosphorylation), and crizotinib suppressed the adverse AKT activation induced by rapamycin. In conclusion, co-treatment with rapamycin and crizotinib is effective in suppressing MPM tumor growth and should be further explored as a therapeutic alternative in mesothelioma.

In plain English

This laboratory study examined malignant pleural mesothelioma tumor tissue and then tested two drugs in mice. Of 128 tumors, 25 (19.5%) showed raised ALK gene expression; normal pleura samples did not express ALK. Ten of these 25 tumors made ALK protein. No ALK gene rearrangement, extra gene copies or activating kinase-domain mutations were found in these ten tumors. Of 101 tumors stained for protein, 5% showed high levels of both ALK and mTOR, and 15% of both MET and mTOR. Age, sex, asbestos exposure, metastasis at first presentation and growth pattern were not significantly associated with these proteins. In mice carrying one patient-derived tumor with active ALK and mTOR (five per group), crizotinib alone had no anti-tumor activity. Rapamycin alone shrank one of five tumors by 35% and stopped growth in two others. The combination shrank four of five tumors by 26-34% and stopped growth in the fifth. It also lowered dividing cells by 21.8% versus controls and caused necrotic rather than apoptotic cell death. The authors concluded that the combination should be further explored as a mesothelioma treatment.

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 tumor tissue samples (gene expression, FISH, gene sequencing and protein staining) combined with an animal experiment in mice carrying a patient-derived mesothelioma graft
• Who was studied: Preserved resection specimens from 144 patients diagnosed with malignant pleural mesothelioma, plus five normal pleura specimens. Gene expression testing was done on 128 tumors, and protein staining could be interpreted in 101. Eight patient-derived xenograft models were established. One of them (PDX680) was tested in nude mice, with 5 mice per treatment group. Dates and patient origin were not given.
• Exposure: The study did not examine asbestos fiber types or doses. Asbestos exposure appears only as a patient characteristic checked against the tumor findings. The exposures studied were drugs given to mice for 21 days: crizotinib (100 mg/kg per day by mouth), rapamycin (7.5 mg/kg every 2 days by injection into the abdomen), both together, or an inactive control.
• Main results:
  • Of 128 mesotheliomas, 25 (19.5%) showed upregulated balanced ALK transcript expression. ALK was not expressed in normal pleura. ALK protein was found in 10 of these 25 tumors.
  • All ALK protein-expressing tumors were negative for ALK gene rearrangement and amplification by FISH. No activating mutations were found in the ALK kinase domain.
  • Among 101 tumors with interpretable protein staining, 10 (9.9%) were ALK positive, 46 (45.5%) were moderately to strongly MET positive, and 29 (28.7%) were moderately to strongly mTOR positive. High-level co-expression of ALK and mTOR was seen in 5% of tumors, and of MET and mTOR in 15%.
  • ROS1 was not expressed in the 126 mesotheliomas analyzed.
  • Age, sex, asbestos exposure, metastasis at initial presentation and histological growth pattern were not significantly associated with ALK, MET or mTOR protein expression. Overall survival did not differ between kinase-positive and kinase-negative tumors.
  • In mice carrying the PDX680 graft, crizotinib alone showed no anti-tumor growth activity. Rapamycin alone was effective in three of five tumors: shrinkage of 35% in one and growth stagnation in two.
  • Rapamycin plus crizotinib was active in all five tumors: shrinkage of 26-34% in four and growth stagnation in one. All treatments were well tolerated, judged by stable body weights.
  • Only the combination reduced proliferating (Ki-67 positive) cells, by 21.8% compared with the control group (p=0.0065). Neither drug alone produced a significant change.
  • Apoptosis was low in all groups and not significantly different from control: 7.5% (crizotinib), 10.5% (rapamycin) and 8.5% (combination), versus 7.4% (control). The authors reported that the combination instead induced caspase-independent, necrotic cell death.
  • Autophagy-positive cells were 9.1% with rapamycin, 7.7% with crizotinib and 2.5% in controls. With both drugs together the figure was 17.5% (p=0.0156).
  • Rapamycin increased AKT activation, and adding crizotinib suppressed this increase. Crizotinib alone did not affect AKT activity.
• The authors' conclusion: The authors concluded that they had identified a subgroup of malignant pleural mesothelioma with ALK overexpression. They stated that co-treatment with crizotinib and rapamycin should be further explored as a targeted treatment option in mesothelioma.
• Limitations the authors state:
  • Suitable frozen tissue was not available to test whether MET was active in the patient tumors that expressed both ALK and MET.
  • The Ki-67 staining used to measure cell division cannot detect cell cycle arrest, so the authors could not exclude it with rapamycin.

Topics

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Neoplasm, Prognosis, Fluorescence In Situ Hybridization (FISH), Immunohistochemistry, Apoptosis, Ki-67, Mesothelioma.

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