Schremmer B, Manevich Y, Feinstein SI, Fisher AB.

Institute for Environmental Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.

Abstract

All six mammalian peroxiredoxins are expressed in the lung. Peroxiredoxin (Prx) VI is the isoform expressed at the highest level and its lung expression exceeds that for other organs. The predominant location of Prx VI is the cytosol and acidic organelles of Clara cells of the conducting airways and type II epithelial cells and macrophages in the alveoli. Prx I and VI show developmental induction of transcription at birth. PrxVI shares structural homology with other peroxiredoxins exhibiting a thioredoxin fold and a conserved catalytic Cys residue in the N-terminus of the protein. This enzyme is highly inducible by oxidative stress in both the neonatal and adult lung consistent with a role in antioxidant defense. Prx VI has several properties that distinguish its peroxidase activity from other peroxiredoxins: it can reduce phospholipid hydroperoxides in addition to other organic hydroperoxides and H2O2; the electron donor that serves to reduce the oxidized peroxidatic cysteine is not thioredoxin but GSH; instead of homodimerization, heterodimerization with pi-glutathione S-transferase is required for regeneration of the active enzyme. Prx VI also expresses a phospholipase A2 activity that is Ca2+-independent, maximal at acidic pH, and dependent on a serine-based catalytic triad and nucleophilic elbow at the surface of the protein. Models of altered Prx VI expression at the cellular, organ and whole animal levels have demonstrated that Prx VI functions as an important anti-oxidant enzyme with levels of protection that exceed those ascribed to GSH peroxidase (GPx1). The phospholipase A2 activity plays an important role in lung surfactant homeostasis and is responsible for the bulk of the degradation of internalized phosphatidylcholine and its resynthesis by the reacylation pathway. Expression of peroxiredoxins is elevated in several lung diseases including lung cancer, mesothelioma and sarcoidosis, although the mechanism for these alterations is not known. The unique properties of Prx VI enable it to play an important role in lung cell function.

Ramasamy Jagadeeswaran¹, Patrick C. Ma¹, Tanguy Y. Seiwert¹, Sujatha Jagadeeswaran¹, Osvaldo Zumba¹, Vidya Nallasura¹, Salman Ahmed¹, Rosangela Filiberti², Michela Paganuzzi², Riccardo Puntoni², Robert A. Kratzke³, Gavin J. Gordon⁴, David J. Sugarbaker⁴, Raphael Bueno⁴, Varalakshmi Janamanchi¹, Vytas P. Bindokas¹, Hedy L. Kindler¹ and Ravi Salgia¹

¹ Section of Hematology/Oncology, Department of Medicine, University of Chicago Cancer Research Center, University of Chicago Medical Center, Pritzker School of Medicine, Chicago, Illinois; ² Environmental Epidemiology and Biostatistics, National Cancer Research Institute, Largo Rosanna Benzi, Genoa, Italy; ³ Department of Surgery, Division of Cardiovascular and Thoracic Surgery, University of Minnesota Medical School, Minneapolis, Minnesota; and ⁴ Department of Surgery, Division of Thoracic Surgery, Brigham and Women’s Hospital, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts

Abstract

c-Met receptor tyrosine kinase (RTK) has not been extensively studied in malignant pleural mesothelioma (MPM). In this study, c-Met was overexpressed and activated in most of the mesothelioma cell lines tested. Expression in MPM tissues by immunohistochemistry was increased (82%) in MPM in general compared with normal. c-Met was internalized with its ligand hepatocyte growth factor (HGF) in H28 MPM cells, with robust expression of c-Met. Serum circulating HGF was twice as high in mesothelioma patients as in healthy controls. There was a differential growth response and activation of AKT and extracellular signal–regulated kinase 1/2 in response to HGF for the various cell lines. Dose-dependent inhibition (IC₅₀ < 2.5 µmol/L) of cell growth in mesothelioma cell lines, but not in H2052, H2452, and nonmalignant MeT-5A (IC₅₀ >10 µmol/L), was observed with the small-molecule c-Met inhibitor SU11274. Furthermore, migration of H28 cells was blocked with both SU11274 and c-Met small interfering RNA. Abrogation of HGF-induced c-Met and downstream signaling was seen in mesothelioma cells. Of the 43 MPM tissues and 7 cell lines, we have identified mutations within the semaphorin domain (N375S, M431V, and N454I), the juxtamembrane domain (T1010I and G1085X), and an alternative spliced product with deletion of the exon 10 of c-Met in some of the samples. Interestingly, we observed that the cell lines H513 and H2596 harboring the T1010I mutation exhibited the most dramatic reduction of cell growth with SU11274 when compared with wild-type H28 and nonmalignant MeT-5A cells. Ultimately, c-Met would be an important target for therapy against MPM.

Cardillo I, Spugnini EP, Verdina A, Galati R, Citro G, Baldi A.

SAFU Department, Center for Experimental Research, Regina Elena Cancer Institute, Rome, Italy.

Abstract

Cyclooxygenases catalyze the rate limiting step in the production of prostanoids. Accumulating data demonstrate that overexpression of these enzymes, and in particular of cyclooxygenases-2, promotes multiple events involved in tumorigenesis; in addition, numerous studies show that inhibition of cyclooxygenases-2 can delay or prevent certain forms of cancer. Malignant mesothelioma is a lethal pleural, peritoneal and pericardial neoplasia that actually lacks valid therapies and in which cyclooxygenases-2 is recognized as an important adverse prognostic factor. Hence, there is an increasing interest in the development of new treatments based on cyclooxygenases-2 inhibitors, to prolong survival and even potentially cure this neoplasia.

Altomare DA, You H, Xiao GH, Ramos-Nino ME, Skele KL, De Rienzo A, Jhanwar SC, Mossman BT, Kane AB, Testa JR.

Human Genetics Program, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA

Abstract

Malignant mesotheliomas (MMs) are very aggressive tumors that respond poorly to standard chemotherapeutic approaches. The phosphatidylinositol 3-kinase (PI3K)/AKT pathway has been implicated in tumor aggressiveness, in part by mediating cell survival and reducing sensitivity to chemotherapy. Using antibodies recognizing the phosphorylated/activated form of AKT kinases, we observed elevated phospho-AKT staining in 17 of 26 (65%) human MM specimens. In addition, AKT phosphorylation was consistently observed in MMs arising in asbestos-treated mice and in MM cell xenografts. Consistent with reports implicating hepatocyte growth factor (HGF)/Met receptor signaling in MM, all 14 human and murine MM cell lines had HGF-inducible AKT activity. One of nine human MM cell lines had elevated AKT activity under serum-starvation conditions, which was associated with a homozygous deletion of PTEN, the first reported in MM. Treatment of this cell line with the mTOR inhibitor rapamycin resulted in growth arrest in G1 phase. Treatment of MM cells with the PI3K inhibitor LY294002 in combination with cisplatin had greater efficacy in inhibiting cell proliferation and inducing apoptosis than either agent alone. Collectively, these data indicate that MMs frequently express elevated AKT activity, which may be targeted pharmacologically to enhance chemotherapeutic efficacy. These findings also suggest that mouse models of MM may be useful for future preclinical studies of pharmaceuticals targeting the PI3K/AKT pathway.

Philip A. Rascoe, MD^a, Xiaobo Cao, MD^b, Jonathan C. Daniel, MD^a, Steven D. Miller, MD^a, W. Roy Smythe, MD^b,_*

^a Department of Thoracic and Cardiovascular Surgery, Section of Thoracic Molecular Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Tex
^b Scott and White Medical Center, The Texas A&M University System Health Science Center, Temple, Tex

Read at the Eighty-fourth Annual Meeting of The American Association for Thoracic Surgery, Toronto, Ontario, Canada, April 25–28, 2004.

Abstract

Objective: The phosphoinositide-3 kinase signaling pathway is implicated in the development of malignancy and promotes cell-cycle progression and resistance to apoptosis. Malignant mesothelioma tumor specimens demonstrate high levels of the phosphoinositide-3 kinase downstream mediator phosphorylated Akt. Exposure of mesothelioma cell lines to LY294002, a phosphoinositide-3 kinase inhibitor, results in apoptotic cell death and decreased phosphorylated Akt in vitro and tumor burden reduction in vivo. Phosphoinositide-3 kinase is activated by cell-surface receptor tyrosine kinases. We sought to determine which receptors are present in mesothelioma and their role in cellular survival and phosphoinositide-3 kinase signaling.

Methods: Western blot analysis was performed to determine the relative expression of epidermal growth factor receptor, insulin-like growth factor receptor, and platelet-derived growth factor receptor in the mesothelioma cell lines I-45 and REN and the mesothelial line Met5a. After exposure of mesothelioma lines to kinase inhibitors, a cell viability assay was performed, cell-cycle analysis was performed to determine the percentage of apoptosis, and Western blot analysis was performed for phosphorylated Akt.

Results: Inhibition of epidermal growth factor receptor resulted in apoptotic cell death and Akt hypophosphorylation in mesothelioma cell lines. Insulin-like growth factor receptor inhibition led to apoptotic cell death without affecting Akt phosphorylation. Platelet-derived growth factor receptor inhibition did not affect cellular survival or phosphoinositide-3 kinase signaling.

Conclusion: In malignant mesothelioma constitutive activation of phosphoinositide-3 kinase/Akt results in cellular survival and contributes to the malignant phenotype. We have demonstrated that epidermal growth factor receptor inhibition leads to apoptotic cell death through downregulation of phosphoinositide-3 kinase signaling in mesothelioma cell lines, whereas insulin-like growth factor receptor inhibition leads to apoptosis independent of phosphoinositide-3 kinase. Epidermal growth factor receptor, insulin-like growth factor receptor, and phosphoinositide-3 kinase inhibition might be clinically relevant in malignant mesothelioma.

Toru Mukohara^a-c, Gabriel Civiello^a, Bruce E. Johnson^a-c, Pasi A. Jänne^a-c

^aLowe Center for Thoracic Oncology, Department of Medical Oncology, Dana-Farber Cancer Institute; Departments of Medicine, ^bBrigham and Women’s Hospital and ^cHarvard Medical School, Boston, Mass., USA

Abstract

The majority of malignant pleural mesotheliomas (MPMs) aberrantly express the epidermal growth factor receptor (ErbB1). We examined the efficacy of GW572016 (lapatinib), a dual inhibitor of ErbB1/ErbB2 with a panel of 10 MPM cell lines. Two of the 10 MPM cell lines, H2373 and H2452, underwent G1/S cell cycle arrest and growth inhibition with an IC₅₀ of 1 µM and 0.8 µM, respectively. There was no relationship between the presence or the amount of ErbB1, phospho-ErbB1, phospho-ErbB2, ErbB3, ErbB4, phospho-Akt, and Akt or the ability of lapatinib to inhibit phospho-ErbB1 in these cell lines compared to those that did not respond to lapatinib. The sensitive cell lines had a time-dependent decrease in phospho-Akt and/or ERK1/2, and an increase in p27 and when treated with lapatinib. The combination of lapatinib with U0126, LY294002 or rapamycin caused greater growth inhibition than either drug alone in the sensitive cell lines while this did not occur in the resistant cell lines. Our findings suggest that ErbB1 alone is a therapeutic target for the minority of mesotheliomas and that combining ErbB1 inhibitors with signal transduction inhibitors in mesothelioma will enhance their effectiveness. Furthermore, combinations of growth factor and signal transduction inhibitors may be needed to inhibit the growth of the majority of MPM cell lines, and therefore patients with MPM.