Effect of Inocula of Benzo[a]pyrene-Treated Sarcoma Cells on Growth of Primary Tumors in Rats

Summary

Primary fibrosarcomas were induced in rats with benzo-[a]pyrene. When the tumors were between 1.5–2.5 cm in diameter, most of the tumor was removed at biopsy and a tumor cell suspension was prepared. The tumor cells were exposed in vitro to a benzo[a]pyrene-caffeine solution so that the carcinogen was incorporated into the cell membranes. The cells were then washed and injected subcutaneously into autologous or homologous recipients. The effect of this inoculation on the subsequent growth of the residual primary tumor was determined by regular measurements of the tumor diameter. Of the 39 rats treated in this way, 7 showed unequivocal evidence of retarded tumor growth and in 5 of these the tumors regressed completely. This effect was not observed when the inocula of tumor cells were treated with caffeine solution alone, or when the rats were inoculated with nonmalignant mammalian cells or bacterial cells that had been coated with benzo[a]pyrene. Clearly, the carcinogen did not act by increasing the strength of the tumor-specific antigen, since inocula of homologous tumor cells, treated with benzo[a]pyrene, were almost as effective in causing retardation of tumor growth as inocula of treated autologous tumor cells.