Diphtheria Toxin-Murine Granulocyte-Macrophage Colony-Stimulating Factor-Induced Hepatotoxicity Is Mediated By Kupffer Cells

DT(388)GMCSF, a fusion toxin composed of the NH2-terminal region of diphtheria toxin (DT) fused to human granulocyte-macrophage colony-stimulating factor (GMCSF) has shown efficacy in the treatment of acute myeloid leukemia. However, the primary dose-limiting side effect is liver toxicity. We have reproduced liver toxicity in rats using the rodent cell-tropic DT-murine GMCSF (DT(390)mGMCSF). Serum aspartate aminotransferase and alanine aminotransferase were elevated 15- and 4-fold, respectively, in DT(390)mGMCSF-treated rats relative to controls. Histologic analysis revealed hepatocyte swelling; however, this did not lead to hepatic necrosis or overt histopathologic changes in the liver. Immumohistochemical staining showed apoptotic cells in the sinusoids, and depletion of cells expressing the monocyte/macrophage markers, ED1 and ED2, indicating that Kupffer cells (KC) are targets of DT(390)mGMCSF. In contrast, sinusoidal endothelial cells seemed intact. In vitro, DT(390)mGMCSF was directly cytotoxic to primary KC but not hepatocytes. Two related fusion toxins, DT(388)GMCSF, which targets the human GMCSF receptor, and DT(390)mIL-3, which targets the rodent IL-3 receptor, induced a less than 2-fold elevation in serum transaminases and did not deplete KC in vivo. In addition, DTU2mGMCSF, a modified form of DT(390)mGMCSF with enhanced tumor cell specificity, was not hepatotoxic and was significantly less toxic to KC in vivo and in vitro. These results show that DT390 mGMCSF causes liver toxicity by targeting KC, and establish a model for studying how this leads to hepatocyte injury. Furthermore, alternative fusion toxins with potentially reduced hepatotoxicity are presented.