Svejda et al.: The 5-HT2B Receptor Plays a Key Regulatory Role in Both Neuroendocrine Tumor Cell Proliferation and the Modulation of the Fibroblast Component of the Neoplastic Microenvironment

Svejda, B; Kidd, M; Giovinazzo, F; Eltawil, K; Gustafsson, BI; Pfragner, R; Modlin, IM

The 5-HT2B Receptor Plays a Key Regulatory Role in Both Neuroendocrine Tumor Cell Proliferation and the Modulation of the Fibroblast Component of the Neoplastic Microenvironment

CANCER. 2010; 116(12): 2902-2912. full text full text MUG-login

Abstract:
BACKGROUND: Fibrosis is a cardinal feature of small intestinal neuroendocrine tumors (SI-NETs) both in local peritumoral tissue and systemic sites (cardiac). 5-HT, a commonly secreted NET amine, is a known inducer of fibrosis, although the mechanistic basis for it and growth factors regulating fibrosis and proliferation in the tumor microenvironment are unclear. We hypothesized that targeting 5-HT2B receptors on tumor cells would inhibit SI-NET 5-HT release and, thereby, fibroblast activation in the tumor microenvironment. METHODS: We studied the 5-HT2B receptor antagonist PRX-08066 in NET cell lines (KRJ-I, H720) and in the coculture system (KRJ-I cells: fibroblastic HEK293 cells) using real time polymerase chain reaction, ELISA, Ki67 immunostaining, and flow cytometry-based caspase 3 assays to assess antiproliferative and profibrotic signaling pathways. RESULTS: In the 5-HT2B expressing SI-NET cell line, KRJ-I, PRX-08066 inhibited proliferation (IC50 4.6x10(-9)M) and 5-HT secretion (6.9 x 10(-9)M) and decreased ERK1/2 phosphorylation and profibrotic growth factor synthesis and secretion (transforming growth factor beta 1 [TGF beta 1], connective tissue growth factor [CTGF] and fibroblast growth factor [FGF2]). In the KRJ-I:HEK293 coculture system, PRX-08066 significantly decreased 5-HT release (>60%), Ki67 (transcript and immunostaining: 20%-80%), TGF beta 1, CTGF and FGF2 transcription (20%-50%) in the KRJ-I cell line. 5-HT itself stimulated HEK293 proliferation (25%) and synthesis of TGF beta 1, CTGF and FGF2. PRX-08066 inhibition of KRJ-I function reversed these effects in the coculture system. CONCLUSIONS: Targeting the 5-HT2B receptor may be an effective antiproliferative and antifibrotic strategy for SI-NETs because it inhibits tumor microenvironment fibroblasts as well as NET cells. Fibrosis and proliferation appear to be biologically interfaced neuroendocrine neoplasia domains. Cancer 2010;116:2902-12. (C) 2010 American Cancer Society



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