Previous studies in our laboratory have shown that
6-phenylhexyl isothiocyanate (
PHITC), enhances
N-nitrosomethylbenzylamine (NMBA)-induced esophageal
tumorigenesis in F344 rats while the shorter chain analogs,
phenylethyl isothiocyanate (
PEITC), and
3-phenylpropyl isothiocyanate (
PPITC), inhibit NMBA-induced esophageal
tumorigenesis. To test the hypothesis that
PHITC influences the promotional stage of esophageal
tumorigenesis, groups of 22-27 rats 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 micromol/g. At the 25th week, the rats were killed, esophagi harvested and
tumors counted. In the groups that received NMBA+PHITC, apparent but statistically insignificant increases in
tumor multiplicity of 32 and 42% were found in comparison to rats treated with NMBA alone. A higher frequency of dysplastic lesions was found in rats treated with NMBA+2.5 micromol/g
PHITC (71%) when compared to rats treated with NMBA only (12%). To test whether
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+PHITC compared to rats treated with NMBA only, rats treated with
PHITC only had a significantly higher
PCNA index compared to untreated controls. Expression of
cyclin D1, another
biomarker of proliferation, was analyzed by semi-quantitative 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 suggest a promotional effect by
PHITC as manifested by a significant increase in dysplastic
leukoplakia by the high dose of
PHITC and an increase in the
PCNA index by
PHITC alone,
PHITC does not appear to have a significant effect on esophageal cell proliferation.