The objective of the present work was to investigate the existence of an
oxytocin (OT)-mediated autocrine/paracrine signaling upon
small cell carcinoma of the lung (SCCL) cell growth. In that view, OT receptor (OTR) expression, concomitant with OT synthesis and secretion, was evidenced on three different SCCL cell lines (DMS79, H146, and H345) and related to the
vasopressin (VP) system. Specific OT, VP, OTR, V1a VP receptor (V1aR), and V1b/V3 VP receptor (V1bR/V3R) transcripts were identified by reverse transcription-PCR in all cell lines studied. Binding of 125I-(d(CH2)(5)(1), Tyr(Me)(2),Thr(4),Orn(8),Tyr(9)-NH2)-vasotocin (
OVTA) was observed on all SCCL cell lines, with a K(d) (dissociation constant) ranging from 0.025-0.089 nM, depending on the cell line and the analytical method. Selectivity of 125I-OVTA binding was confirmed by displacement curves obtained with various OTR and VP receptor agonists and antagonists (OT,
OVTA, L-371,257, VP, F180). Immunocytochemistry identified cellular OT and VP, and
peptide secretion was measured in supernatants of SCCL cultures. [3H]
Thymidine incorporations, applied on H345 cells, demonstrated a dose-dependent mitogenic effect of exogenous OT (1 and 100 nM) that was abolished by the OTR antagonist
OVTA. A decrease of proliferation was also observed with
OVTA alone, showing a functional mitogenic effect of
tumor-derived OT. Taken together, these observations demonstrate the existence of a functional OT-mediated autocrine/paracrine signaling actively implicated in growth and development of SCCL
tumors. Furthermore, these findings point to the potential of OT antagonists for development as therapeutic agents for the treatment of SCCL.