Investigation of the enhancement of N-nitrosomethylbenzylamine-induced esophageal tumorigenesis by 6-phenylhexyl isothiocyanate

Previous studies in our laboratory have shown that 6-phenylhexyl isothiocya nate (PHITC), enhances N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis in F344 rats while the shorter chain analogs, phenylethyl is othiocyanate (PEITC), and 3-phenylpropyl isothiocyanate (PPITC), inhibit NM BA-induced esophageal tumorigenesis. To test the hypothesis that PHITC infl uences the promotional stage of esophageal tumorigenesis, groups of 22-27 r ats were dosed with vehicle or NMBA three times a week for 5 week, and fed a modified AIN-76A diet containing PHITC at concentrations of 0.0, 1.0, and 2.5 mu mol/g. At the 25th week, the rats were killed, esophagi harvested a nd tumors counted. In the groups that received NMBA + PHITC, apparent but s tatistically insignificant increases in tumor multiplicity of 32 and 42% we re found in comparison to rats treated with NMBA alone. A higher frequency of dysplastic lesions was found in rats treated with NMBA + 2.5 mu mol/g PH ITC (71%) when compared to rats treated with NMBA only (12%). To test wheth er PHITC increased cellular proliferation, we evaluated proliferating cell nuclear antigen (PCNA) expression by immunohistochemistry. While there were no significant increases in PCNA staining in rats treated with NMBA + PHIT C compared to rats treated with NMBA only, rats treated with PHITC only had a significantly higher PCNA index compared to untreated controls. Expressi on of cyclin D1, another biomarker of proliferation, was analyzed by semi-q uantitative reverse transcription-polymerase chain reaction. There were no significant increases in cyclin D1 expression in groups treated with NMBA PHITC compared to the group treated with NMBA only. Thus, while the data s uggest a promotional effect by PHITC as manifested by a significant increas e in dysplastic leukoplakia by the high dose of PHITC and an increase in th e PCNA index by PHITC alone, PHITC does not appear to have a significant ef fect on esophageal cell proliferation. (C) 2001 Elsevier Science Ireland Lt d. All rights reserved.