Valproic acid activates Notch1 signaling and induces apoptosis in medullary thyroid cancer cells.
OBJECTIVE
To examine the effects of valproic acid (VPA) on Notch1 expression and cancer cell proliferation in medullary thyroid cancer (MTC) cells.


BACKGROUND
Other than surgery, there are no effective treatments for MTC, a neuroendocrine malignancy that frequently metastasizes. We have previously shown that over-expression of Notch1 in MTC cells inhibits cell growth and hormone production. VPA, a drug long used for the treatment of epilepsy, has recently been identified as a potential Notch1 activator. We hypothesized that VPA might activate Notch1 signaling in MTC cells, with antiproliferative effects.


METHODS
Human MTC cells were treated with VPA (0-5 mM) and Western blotting was performed to measure levels of Notch1 pathway proteins and neuroendocrine tumor markers. After confirming that VPA is a Notch1 activator in MTC cells, we performed cell proliferation assay. Finally, to determine the mechanism of growth inhibition, we measured protein levels of various markers of apoptosis.


RESULTS
Notch1 was absent in MTC cells at baseline. VPA treatment resulted in an increase in both full-length and active Notch1 protein. Notch1 activation with VPA suppressed 2 neuroendocrine tumor markers, ASCL1 and chromogranin A. Importantly, VPA inhibited the growth of MTC cells in a dose-dependent manner. Immunoblot analysis demonstrated caspase activation and poly(ADP-ribose) polymerase cleavage, indicating the induction of apoptosis.


CONCLUSIONS
VPA activates Notch1 signaling in MTC cells and inhibits their growth by inducing apoptosis. As the safety of VPA in human beings is well established, a clinical trial using this drug to treat patients with advanced MTC could be initiated in the near future.
Endocrine Surgery Research Laboratories, Department of Surgery, University of Wisconsin, University of Wisconsin Paul P. Carbone Comprehensive Cancer Center, Madison, Wisconsin, USA.
David Yu
DY
Greenblatt
Max A
MA
Cayo
Joel T
JT
Adler
Li
L
Ning
Megan R
MR
Haymart
Muthusamy
M
Kunnimalaiyaan
Herbert
H
Chen
D000704:Analysis of Variance; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D014408:Biomarkers, Tumor / Q000378:metabolism; D015153:Blotting, Western; D018276:Carcinoma, Medullary / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D015536:Down-Regulation; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D051881:Receptor, Notch1 / Q000378:metabolism*; D015398:Signal Transduction; D013964:Thyroid Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D014407:Tumor Cells, Cultured; D014635:Valproic Acid / Q000494:pharmacology*
D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; C497761:NOTCH1 protein, human; D051881:Receptor, Notch1; D014635:Valproic Acid