Autoregulatory effects of serotonin on proliferation and signaling pathways in lung and small intestine neuroendocrine tumor cell lines.
BACKGROUND
: Survival rates for gastrointestinal (GI) and bronchopulmonary (BP) neuroendocrine tumors (NETs) have not altered significantly (5-year survival rate: GI NETs, 64.1%; BP NETs, 87%-89%) in 30 years (from 1973 to 2004). No effective or specific antineoplastic agents are available to date, although somatostatin analogs inhibit NET 5-hydroxytryptophan (5-HT) secretion. Given the expression of 5-HT receptors on NETs, the authors hypothesized that 5-HT autoregulated NET proliferation.


METHODS
: Proliferation was evaluated in 3 NET cell lines using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide uptake; in addition, real-time polymerase chain reaction analyses and enzyme-linked immunosorbent assay studies were performed to delineate 5-HT-mediated signaling pathways. To determine the receptor and role of endogenous 5-HT production, the effects of ketanserin (5-HT receptor subtypes 2A and 2C [5-HT(2A/2C)]); ondansetron (5-HT(3)); and the suicide inhibitor of the rate-limiting enzyme for 5-HT synthesis, tryptophan hydroxylase (7-HTP) were investigated.


RESULTS
: Exogenously added 5-HT stimulated proliferation in atypical BP NET NCI-H720 cells (+50%; half-maximal stimulatory concentration [EC(50)] = 10 nM), in typical BP NET NCI-H727 cells (+40%; EC(50) = 0.01 nM), and in GI NET KRJ-I cells (+60%; EC(50) = 25 nM). In NCI-H720 cells, proliferation was inhibited by ketanserin (half-maximal inhibitory concentration [IC(50)] = 0.06 nM) and ondansetron (IC(50) = 0.4 nM) and also was inhibited by 7-HTP (IC(50) = 0.3 nM). In NCI-H727 cells, ketanserin and 7-HTP inhibited proliferation (IC(50) = 0.3 nM and IC(50) = 2.3 nM, respectively), whereas ondansetron had no effect. In KRJ-I cells, ketanserin (IC(50) = 0.1 nM) and 7-HTP (IC(50) = 0.6 nM), but not ondansetron, inhibited proliferation. In all cell lines, 5-HT activated proliferation through extracellular signal-regulated kinase 1 (ERK1) and ERK2 phosphorylation and c-Jun N-terminal kinase (JNK)-mediated pathways (c-JUN and Ki-67 transcription). An autoregulatory effect was indicated by the 7-HTP-mediated inhibition of extracellular 5-HT and downstream effects on NET proliferation.


CONCLUSIONS
: Lung and GI NET proliferation was autoregulated by 5-HT through alterations in ERK and JNK signaling. Targeting NET cells with 5-HT(2) receptor antagonists and 7-HTP reversed proliferation. The current results indicated that 5-HT(2) receptor subtype-specific antagonists may represent a viable antiproliferative therapeutic strategy. Cancer 2009. (c) 2009 American Cancer Society.
Drozdov
Ignat
I
Gastrointestinal Pathobiology Research Group, Yale University School of Medicine, New Haven, Connecticut, USA. imodlin@optonline.net
Kidd
Mark
M
Gustafsson
Bjorn I
BI
Svejda
Bernhard
B
Joseph
Richard
R
Pfragner
Roswitha
R
Modlin
Irvin M
IM
D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D006706:Homeostasis; D006801:Humans; D007414:Intestinal Neoplasms / Q000378:metabolism* / Q000473:pathology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D007650:Ketanserin / Q000031:analogs & derivatives / Q000494:pharmacology; D008175:Lung Neoplasms / Q000378:metabolism* / Q000473:pathology; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D018358:Neuroendocrine Tumors / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*; D015398:Signal Transduction; D014364:Tryptophan / Q000031:analogs & derivatives / Q000494:pharmacology
C461139:7-hydroxytryptophan; D011985:Receptors, Serotonin; D012701:Serotonin; C039722:ketanserinol; D014364:Tryptophan; D007650:Ketanserin; D048031:JNK Mitogen-Activated Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3