transforming-growth-factor-alpha and Carcinoma--Medullary

Oncogenic conversion of the RET tyrosine kinase is a frequent feature of medullary thyroid carcinoma (MTC). ZD6474 (vandetanib) is an ATP-competitive inhibitor of RET, epidermal growth factor receptor (EGFR), and vascular endothelial growth factor receptors kinases. In this study, we have studied ZD6474 mechanism of action in TT and MZ-CRC-1 human MTC cell lines, carrying cysteine 634 to tryptophan (C634W) and methionine 918 to threonine (M918T) RET mutation respectively. ZD6474 blunted MTC cell proliferation and RET, Shc and p44/p42 mitogen-activated protein kinase (MAPK) phosphorylation. Single receptor knockdown by RNA interference showed that MTC cells depended on RET for proliferation. Adoptive expression of the ZD6474-resistant V804M RET mutant rescued proliferation of TT cells under ZD6474 treatment, showing that RET is a key ZD6474 target in these MTC cells. Upon RET inhibition, adoptive stimulation of EGFR partially rescued TT cell proliferation, MAPK signaling, and expression of cell-cycle-related genes. This suggests that simultaneous inhibition of RET and EGFR by ZD6474 may overcome the risk of MTC cells to escape from RET blockade through compensatory over-activation of EGFR.

Topics: Carcinoma, Medullary; Cell Line, Tumor; Cell Proliferation; ErbB Receptors; Humans; Mutation; Piperidines; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-ret; Quinazolines; Signal Transduction; Thyroid Neoplasms; Transforming Growth Factor alpha; Vascular Endothelial Growth Factor Receptor-2

In 20 patients with sporadic medullary thyroid carcinoma (MTC), immuno-histochemistry was used to localize the expression of the c-Myc oncoprotein, transforming growth factor alpha (TGF-alpha) and epidermal growth factor receptor (EGFR) and these three markers were analysed regarding their relation to histopathological and histochemical variables of the tumours. The detection rates of c-Myc, TGF-alpha and EGFR were 90%, 90% and 95% respectively. Concomitant demonstration of the markers was reflected in significant associations (correlation factor between TGF-alpha and EGFR was 0.93, p < 0.001). The markers were almost invariably located within the cytoplasm, which might suggest their crucial role in growth regulation and cell differentiation; this seems especially true of TGF-alpha and EGFR. The different markers showed no relation to either histopathological or histochemical variables (tumour behaviour, tumour size, tumour cell type). The prominent co-expression of c-Myc, TGF-alpha and EGFR proteins indicates that in MTC these factors might be of importance for tumour cell proliferation via autocrine growth stimulation.

Topics: Adolescent; Adult; Aged; Aged, 80 and over; Biomarkers, Tumor; Carcinoma, Medullary; Cell Differentiation; Cell Division; Cell Membrane; Coloring Agents; Cytoplasm; Disease-Free Survival; ErbB Receptors; Female; Follow-Up Studies; Gene Expression Regulation, Neoplastic; Humans; Immunohistochemistry; Inclusion Bodies; Male; Middle Aged; Nuclear Envelope; Proto-Oncogene Proteins c-myc; Survival Rate; Thyroid Neoplasms; Transforming Growth Factor alpha

Transforming growth-factor-alpha (TGF-alpha) is a 50-amino-acid polypeptide that binds to the epidermal growth factor (EGF) receptor and stimulates cell growth. It has been suggested that enhanced production of TGF-alpha and EGF receptors by tumour cells promote tumour-cell growth by autocrine mechanisms. In the present study we have investigated the expression of TGF-alpha and EGF receptors in human neuroendocrine tumours, including midgut carcinoid tumours, phaeochromocytomas and medullary thyroid carcinomas. TGF-alpha expression was demonstrated in biopsies of all tumours examined (n = 30) and EGF receptors in a majority of tumours by Northern analysis and/or immunocytochemistry. Expression of TGF-alpha and EGF receptors was also demonstrated in primary cultures of tumour cells. Carcinoid tumours and phaeochromocytomas in culture secreted detectable amounts of TGF-alpha into the culture medium (400-700 pM). The amount of secreted TGF-alpha could be suppressed by octreotide treatment in individual tumours. Administration of exogenous TGF-alpha stimulated carcinoid tumour growth in vitro as determined by the DNA contents of cell cultures. The growth-stimulatory effect of TGF-alpha could be partially blocked by the use of neutralizing anti-EGF receptor monoclonal antibodies (MAbs). In conclusion, several human neuroendocrine tumours express both TGF-alpha and EGF receptors in in vivo and in vitro, suggesting that TGF-alpha may regulate tumour-cell growth by autocrine mechanisms.

Topics: Adrenal Gland Neoplasms; Aged; Antibodies, Monoclonal; Autoreceptors; Carcinoid Tumor; Carcinoma, Medullary; Cell Division; DNA, Neoplasm; ErbB Receptors; Female; Gene Expression Regulation, Neoplastic; Humans; Liver Neoplasms; Lymphatic Metastasis; Male; Middle Aged; Neoplasm Proteins; Neuroendocrine Tumors; Paraganglioma; Pheochromocytoma; Retroperitoneal Neoplasms; RNA, Messenger; RNA, Neoplasm; Thyroid Neoplasms; Transforming Growth Factor alpha; Tumor Cells, Cultured