Cellular effects of imatinib on medullary thyroid cancer cells harboring multiple endocrine neoplasia Type 2A and 2B associated RET mutations.
BACKGROUND
Activating mutations in the RET gene, which encodes a tyrosine kinase receptor, often cause medullary thyroid carcinoma (MTC). Surgical resection is the only curative treatment; no effective systemic treatment is available. We evaluated imatinib, a tyrosine kinase inhibitor currently used to treat chronic myelogenous leukemia and gastrointestinal stromal tumors, as a potential drug for systemic treatment of MTC, in 2 MTC-derived cell lines expressing multiple endocrine neoplasia-associated mutant RET receptors.


METHODS
We determined RET expression and Y1062 phosphorylation using Western blot analysis and quantitative polymerase chain reaction. We determined the effects on cell proliferation by a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay, and we used fluorescence-activated cell sorter analysis with annexin V/propidium iodide staining to study imatinib-induced cell-cycle arrest, apoptosis, and cell death.


RESULTS
Imatinib inhibited RET Y1062 phosphorylation in a dose-dependent manner after 1.5 hours of exposure. After 16 hours both RET Y1062 phosphorylation and protein expression levels were affected. Dose-dependent decreases in cell proliferation of both cell lines after exposure to imatinib with inhibitory concentration of 50% levels of 23 +/- 2 micromol/L and 25 +/- 4 micromol/L were seen. These values are high, compared with those for chronic myelogenous leukemia and gastrointestinal stromal tumors. We further could show that imatinib induced cell-cycle arrest, and apoptotic and nonapoptotic cell death.


CONCLUSIONS
Imatinib inhibits RET-mediated MTC cell growth affecting RET protein levels in vitro in a dose-dependent manner. The concentration of imatinib necessary to inhibit RET in vitro, however, makes it impossible to conclude that imatinib monotherapy will be a good option for systemic therapy of MTC.
de Groot
J W B
JW
Department of Surgical Oncology, University Medical Center Groningen, Groningen, The Netherlands.
Plaza Menacho
I
I
Schepers
H
H
Drenth-Diephuis
L J
LJ
Osinga
J
J
Plukker
J Th M
JT
Links
Th P
TP
Eggen
B J L
BJ
Hofstra
R M W
RM
D017209:Apoptosis / Q000187:drug effects; D001549:Benzamides; D018276:Carcinoma, Medullary / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D000068877:Imatinib Mesylate; D018813:Multiple Endocrine Neoplasia Type 2a / Q000235:genetics*; D018814:Multiple Endocrine Neoplasia Type 2b / Q000235:genetics*; D009154:Mutation; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology*; D051096:Proto-Oncogene Proteins c-ret / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology*; D013964:Thyroid Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology
D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human