Friday, August 5th, 2005.

The Journal of Thoracic and Cardiovascular Surgery 2005 Aug;130 (2):393-400

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.

Glossary

platelet

a part of the blood that helps it "stick together" (clot) to promote healing after an injury. Chemotherapy can cause a drop in the platelet count--a condition called thrombocytopenia.

oncology

(on-call-o-jee) the branch of medicine concerned with the diagnosis and treatment of cancer.

cell

the basic unit of which all living things are made. Cells replace themselves by splitting and forming new cells (mitosis). The processes that control the formation of new cells and the death of old cells are disrupted in cancer.

cancer

malignancy; a group of diseases typified by abnormal, generally out-of-control, cell growth.

tumor

an abnormal lump or mass of tissue. Tumors can be benign (not cancerous) or malignant (cancerous).

mesothelioma

a tumor derived from mesothelial tissue, such as the peritoneum (lining the abdomen) or pleura (lining the lungs). More on mesothelioma.

apoptosis

a type of cell death in which the cell basically commits suicide; scientists believe some types of cancer may originate from an interruption of this programmed cell death, allowing cells to grow out of control.

epidermal growth factor receptor

The process of cell division, growth, differentiation and death is a highly regulated process. Several class of trans membrane receptors play a pivot role in this process, of these, epidermal growth factor receptor (EGFR) a member of Receptor Tyrosine Kinase (RTK) family are best known. These comprises of four receptors Erb B1/HER 1, Erb B2 / HER 2, Erb B3/ HER 3, and Erb B4 / HER 4. Of these HER 2 is the most favoured target. (Source: Manoj Pandey and K Chandramohan)

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