Rapid in Vivo Assay for Oral Cancer Chemoprevention

Northwestern University, Evanston IL

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Abstract

The long range objective of this research is to develop a rapid in vivo assay for oral cancer chemopreventive agents(OCCAs), based on the hypothesis that effective agents(or combinations of agents) will impede or prevent oral cancer formation by inhibiting or blocking the induction, expansion, and persistence of the key cells and cell populations participating in each step in the carcinogenic process. In the hamster buccal pouch epithelial (HBPE) model of oral carcinogenesis, focal populations of basal cells exhibiting gamma-glutamyl transpeptidase histochemical activity(GGT foci), and patches of basal cells exhibiting nuclear p53 immunohistochemical staining (p53 foci) appear to be two such relevant populations. Specific Aim 1 is to quantify the extent to which a group of known anticarcinogens inhibit the induction of early (i.e., 4 or 10 days) GGT foci, as detected in HBPE whole mounts, when the agents are applied to the mucosal surfaces prior to and concurrent with the potent chemical carcinogens 7,12- dimethylbenz(a)anthracene(DMBA) and N-methyl-N- benzylnitrosamine(MBN). Specific Aim 2 is to quantify the extent to which three presumptive OCCAs, selected from among those shown to inhibit GGT foci induction in SA1, also inhibit the expansion of GGT foci, during a 21-day regimen of exposure to the either DMBA or MBN,. The feasibility of identifying early p53 foci in standard sections of hamster pouch, and thus of quantifying anticarcinogen-mediated inhibition in the formation of these lesions will also be evaluated using the SA2 protocol. Specific Aim 3 will employ a complete carcinogenesis protocol to quantify the extent to which three chemopreventive agents examined in SA2, also inhibit: (1) induction of GGT foci and p53 foci(observed at 7 weeks), (2) induction of dysplastic lesions, both p53 positive and p53 negative(observed at 7 weeks), (3) induction and expansion of persistent p53 foci(observed at 12 and 21 weeks), (4) induction of persistent dysplastic lesions, both p53 positive and p53 negative(observed at 12 and 21 weeks), (5) development of dysplastic cells (including persistent dysplastic cells, and both p53 positive and p53 negative cells) detectable in cytologic smears at 12 weeks, and (6) HBPE cancer formation. (7) Anticarcinogen- mediated inhibition of forestomach papillomas will also be assessed in hamsters sacrificed at 7 weeks in the SA3 protocol. The research outlined also suggests a rational strategy for the identification of combinations of efficacious OCCAs which are likely to exhibit an additive or synergistic effect in clinical trials -specifically, combinations of agents which individually exhibit maximal inhibition of various surrogate end points of cancer relating to induction, expansion, and persistence of the key participating cell populations.