Localization and therapeutic potential of tritiated tetracycline in rodent tumors.

The reputed localization of tetracycline in human and animal tumors suggested that chemically stable, high-spe cific-activity tritiated tetracycline (TTC) might have antineoplastic therapeutic potential. Direct therapeutic effects were tested in two transplanted tumor lines in rats, and the localizing properties of TTC were measured in 30 trans planted tumor lines in rats and mice and in 23 spontaneous mammary tumors in rats. The therapeutic studies demonstrated that, while a signif icant reduction in the growth rates of transplanted tumors could be obtained through the administration of heavy doses of TTC, similar reductions were observed in the growth rates of tumors in animals receiving unlabeled tetracycline. In the localization studies the concentrations of TTC in normal tissues and tumors were compared and correlated with corresponding concentrations of [14C]thymidine, a measure of proliferative activity. Signifi cantly greater binding of TTC over normal tissue occurred only in areas that failed to incorporate [14C]thymidine.