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The Specificity of Inhibition of L1210 Tumor Growth by Mouse Thymus Deoxyribonucleic Acid¹

Roswell Park Memorial Institute, Buffalo, New York

Growth of L1210 tumor cells in vivo was inhibited by incubation of the cells with mouse thymus DNA prior to s.c. injection in mice. Incubation of L1210 cells with L1210 DNA had no effect on subsequent tumor growth, whereas incubation of L1210 cells with Escherichia coli DNA resulted in enhanced tumor growth. The growth inhibitory effect of the thymus DNA was abolished by pretreatment of the DNA with either DNase, ultraviolet irradiation, or heat at 100°C. Pretreatment of thymus DNA with either RNase or heat at 60°C did not affect its activity.

Various conditions concerning the interaction of L1210 cells with thymus DNA were explored: DNA concentration, length of incubation, temperature of incubation, and effect of DNA on cell viability. The temperature studies indicated that the inhibitory action of thymus DNA on L1210 cells was an energy-dependent process. Cell viability was not affected by thymus DNA during any of the incubations but was subsequently impaired if the DNA-treated cells were reincubated in DNA-free medium. L1210 DNA and E. coli DNA did not cause losses of cell viability, even when the cells were reincubated in DNA-free medium.

¹ Supported in part by Grants 1-F2-CA-24245-01 and AI-04409 from the USPHS.

Received 5/17/66. Accepted 8/19/66.