An in vitro model of pancreas carcinogenesis: two-stage MNU--TPA effect.

Organ-cultured embryonic rat pancreata were exposed to either single or multiple doses of methylnitrosourea (MNU), a single dose of MNU followed by 12-O-tetradecanoyl-phorbol-13-acetate (TPA), or TPA alone and cultured for up to 6 weeks. Both single and multiple doses of MNU caused similar alterations during the first 10 days; ie, for 4 days the explants grew and differentiated as untreated explants, forming acini and ductules; thereafter the presence of MNU induced ductular proliferation and hyperplasia. Explants exposed to a single dose of MNU failed to proliferate beyond the 10th day of culture, showed progressive cell necrosis, and became almost completely necrotic in 6 weeks. Cells prepared from these explants on Day 10 and injected subcutaneously into nude mice also failed to grow and degenerated after 2 weeks. Multiple doses of MNU in vitro, however, produced further proliferation with an atypical cribriform pattern by the 15th day. In the absence of MNU, treatment with TPA alone had no histologic effect; but TPA treatment after a single dose of MNU promoted abnormal growth similar to that produced by multiple doses of MNU. Cells prepared from 10-day explants treated with a single dose of MNU followed by TPA grew subcutaneously in nude mice and formed nodules of atypical growth within 2 weeks. This system constitutes a simple model of short-latency chemical carcinogenesis.