Early neoplastic commitment of hamster buccal pouch epithelium exposed biweekly to 7,12-dimethylbenz[a]anthracene

Experiments were performed to determine the rate at which hamster buccal pouch epithelium (HBPE) is committed to neoplastic development during a regimen of biweekly topical applications of 7,12-dimethylbenz[a]anthracene (DMBA) in mineral oil, administered for 1, 2, 3, 5 or 10 weeks. Evaluated indices of neoplastic commitment were: (i) primary tumor formation, (ii) passageability of HBPE cells in surface culture, (iii) anchorage-independent growth in soft agar and (iv) induction of the transformed phenotype in NIH3T3 cells following transfection with HBPE DNA. Groups of 12-15 hamsters, exposed to DMBA for 1, 2 and 3 weeks, developed buccal pouch tumor incidences of 13%, 42% and 71% respectively within 44 weeks. Buccal pouches of ten control hamsters treated for three weeks with mineral oil did not develop buccal pouch neoplasms during an observation period of 44 weeks. Whereas cultured HBPE cells obtained following three weeks of in vivo DMBA exposure were negative in assays for anchorage-independent growth, passageability in surface culture and induction of NIH3T3 transformants following DNA transfection, similarly cultured cells obtained following five and ten weeks of in vivo exposure were positive, or marginally positive, in each of these assays. These results indicate that (i) the regimen of biweekly DMBA applications commits HBPE to neoplastic development within three weeks and that (ii) subsequent cellular or molecular changes occurring during greater than or equal to 2 succeeding weeks of DMBA treatment are necessary to manifest the transformation associated phenotypes of continuous passageability, anchorage-independent growth, and induction of NIH3T3 transformants following DNA transfection.