On the alleged high sensitivity of mouse Ehrlich-Lettre ascites tumor cells to diphtheria toxin.

It was recently reported by Iglewski and Rittenberg in THESE PROCEEDINGS (71, 2707-2710, 1974) that low doses of purified diphtheria toxin inhibit protein synthesis in mouse Ehrlich-Lettre ascites carcinoma cells cultured in vitro. These observations could not be confirmed by us nor could the authors' further claim that toxin can cause regression of well-established ascites tumors in preimmunized mice be confirmed. Although temporary regression of such tumors can be demonstrated in unimmunized mice following intraperitoneal injection of diphtheria toxin, the amounts of toxin required are high and approach the lethal dose. About the same amount of CRM45, a tox gene product serologically related to diphtheria toxin but only 1/10,000th as toxic for guinea pigs, will also cause temporary regression in tumor-bearing mice.