Streptovitacin A was shown to induce a lag phase in KB human epidermoid carcinoma cells which lasted approximately 24 hours. The cells then grew out at the normal rate.

At the time when KB cells overcame the streptovitacin A inhibition, cytotoxic activity was still present in the medium, and the culture was still sensitive to subsequent treatment with this agent. A possible mechanism to explain these results in presented.

The inhibition pattern of streptovitacin A on KB cells which were treated in vitro under conditions simulating those found in vivo was determined.

No reversal of streptovitacin A cytotoxicity to KB cells was observed when mixtures of purines, pyrimidines, nucleosides, vitamins, amino acids, co-factors, Krebs' cycle intermediates, glucose, metals, or versene were added to the tissue culture medium.

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This work was supported in part by Contract No. SA-43-ph-1933, Cancer Chemotherapy National Service Center, National Institutes of Health.

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