Inhibition of neurotensin-induced pancreatic carcinoma growth by a nonpeptide neurotensin receptor antagonist, SR48692

BACKGROUND. Recently, a nonpeptide neurotensin (NT) receptor antagonist, SR48692, was developed that selectively antagonizes the high affinity, biologically active NT binding site. The effect of SR48692 on NT-mediated growth of a human pancreatic carcinoma, MIA PaCa-2, was determined both in vitro and in vivo. METHODS. ¹²⁵I-NT binding and Northern blot analyses were performed for evaluation of the NT receptor in MIA PaCa-2 cells. Intracellular calcium ([Ca²⁺l(i)) mobilization and inositol phosphate (IP₃) levels were measured. Cell growth studies were performed by counting cell numbers. Athymic nude mice were inoculated with MIA PaCa-2 cells and randomized into four groups to receive either vehicle (NT or SR48692) or NT + SR48692. RESULTS. MIA PaCa-2 cells possess both a high affinity, SR48692- sensitive and a levocabastine-insensitive NT binding site; Northern blot analysis demonstrated expression of the NT receptor. SR48692 inhibited [Ca²⁺](i) mobilization, IP₃ turnover, and MIA PaCa-2 cell growth induced by NT in a dose-dependent fashion. In in vivo experiments, NT significantly increased the size, weight, and DNA and protein content of xenografted MIA PaCa-2 tumors; SR48692 inhibited the effect of NT. CONCLUSIONS. The novel NT receptor antagonist SR48692 will be a valuable agent to delineate further the cellular mechanisms responsible for peptide-mediated growth of normal and neoplastic gut tissues.