IN-VITRO CARCINOGENESIS OF HAMSTER PANCREATIC DUCT CELLS - CELLULAR AND MOLECULAR ALTERATIONS

Neoplastic transformation of Syrian golden hamster (SGH) pancreatic du ct cells was induced by in vitro treatment with the direct-acting carc inogens N-methylnitrosourea (MNU) and N-(2-hydroxypropyl)nitrosourea ( HPNU), with subsequent selection by sustained culture in serum- and ep idermal growth factor (EGF)-deprived medium. The present study examine s the efficacy of serum and EGF deprivation as a selection pressure an d the effect of the carcinogen dose, frequency and interval of exposur e on tumorigenesis and K-ras mutation. Selection of carcinogen-initiat ed duct cells by serum and EGF deprivation is highly reproducible and effective, increasing the incidence of tumors from 26 to 93% for MNU o r from 0 to 100% for HPNU. SGH pancreatic duct cells exposed to 0.5 mM MNU for 13 weeks (long-treatment schedule) produced K-ras mutations a t codon 12 in six of six tumors. However, when cells were exposed to 0 .125, 0.25 or 0.5 mM MNU daily for 5 days (short-treatment schedule), mutations of K-ras at codon 13 were identified in four of 16 tumors, t he remaining 12 showing no mutations. Duct cells exposed to 0.5 mM HPN U by the short-treatment schedule produced K-ras mutations in codon 13 in six of six tumors, as contrasted to 12 tumors that developed from cells exposed to 0.125 or 0.25 mM HFNU, which all contained K-ras codo n 12 mutations, The current experiments demonstrate that K-ras mutatio n in pancreatic carcinogenesis in vitro by MNU or HPNU can be modified by the nature and dose of the carcinogen as well as the frequency and duration of exposure.