The effects of intraurethral or i.p. administration of a mouse skin tumor promoter phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), on rodent urinary bladder transitional epithelium were studied. TPA, when instilled into the urinary bladder of inbred rats (female Fischer, F344) or mice (C3H, ICR, C57BL × DBA/2 F1) at a dose as low as 0.16 nmol, led to a significant (about 10-fold) increase in bladder ornithine decarboxylase (EC 126.96.36.199) (ODC) activity. Peak ODC activity was observed at about 6 hr, and enzyme activity retumed to base levels about 14 hr after intravesical TPA. Administration of TPA i.p. in dimethyl sulfoxide also induced vesical ODC at 4 hr after treatment. The magnitude of vesical ODC induction correlated well with the ability of a series of phorbol esters to promote mouse skin tumor formation (TPA > phorbol didecanoate > phorbol dibenzoate, and phorbol diacetate or phorbol did not induce bladder ODC activity). Mezerein, a second stage mouse skin tumor promoter, induced urinary bladder ODC as much as TPA did. Increased ODC activity by TPA was the result of an increased amount of ODC protein localized mostly (>60%) in urinary bladder mucosa. Intraurethrally administered TPA induced transitional cell hyperplasia starting at Day 2, and it persisted for about 7 days. The urothelium regained normal histology 13 days after TPA treatment. TPA bound specifically and with high affinity to murine bladder mucosa and muscularis particulate preparations. Scatchard analysis of mucosal binding revealed a Kd of 0.82 nm; at saturation, 2.43 pmol were bound per mg protein. Since TPA binds specifically to urinary bladder epithelium, and the induction of ODC activity is one of the properties of tumor promoters, one may conclude that TPA may promote urinary bladder carcinogenesis. Intravesical saccharin also induced urinary bladder ODC activity, but TPA at equimolar quantity was far more potent than saccharin. Thus TPA, being a structurally well-defined molecule, may be a useful compound to study the phenomenon of the tumor promotion stage in urinary bladder carcinogenesis.
Supported in part by Grants CA 14520 and CA 14524 from the National Cancer Institute, the latter grant through the National Bladder Cancer Project, and by Grant IN-35V from the American Cancer Society.