Effect of mithramycin on HeLa cells

Mithramyin is an antibiotic that produces objective improvement in metastatic embryonal cell carcinoma of the testis, hypernephroma and glioblastoma multiforme. Its cytotoxic effect appears to be due to inhibition of RNA synthesis with little or no immediate effect on DNA. Mithramycin was added to tissue cultures of HeLa cells. In low concentrations mithramycin retarded the generation time of cells and at higher concentrations it caused an absolute decrease in the total cell count. The addition of DNA to mithramycin-treated HeLa cells resulted in significantly less retardation of cell growth. The synthesis of RNA and DNA by the HeLa cells, as measured by the incorporation of 32P, was inhibited after 24 hours of treatment with mithramycin.