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BON cells, a human gastrointestinal carcinoid cell line, were obtained from Drs. B. Mark Evers and Courtney M. Townsend, Jr. (University of Texas Medical Branch, Galveston, TX) and were maintained in Dulbecco's modified Eagle medium‐nutrient mixture Ham's F‐12 K 1:1 (Invitrogen, Carlsbad, CA). H727 cells, a human bronchopulmonary carcinoid cell line, were purchased from American Type Culture Collection (Manassas, VA) and were maintained in RPMI1640 (Life Technologies, Grand Island, NY). MZ‐CRC‐1 cells, a human medullary thyroid cancer cell line, were provided by Dr. Barry Nelkin (Johns Hopkins, Baltimore, MD) and were maintained in DMEM/F‐12 medium (Life Technologies). All media were supplemented with 10% fetal bovine serum (Sigma‐Aldrich, St Louis, MO), 100 IU/mL penicillin (Invitrogen), and 100 μg/mL streptomycin (Invitrogen). All cell lines were grown in a humidified atmosphere of 5% CO₂ at 37°C.