Tumor necrosis factor‐α augmented tumor response in B16BL6 melanoma‐bearing mice treated with stealth liposomal doxorubicin (Doxil®) correlates with altered Doxil® pharmacokinetics

The application of tumor necrosis factor‐α (TNF) for the treatment of solid tumors is limited by its severe, life‐threatening, toxicity. Therefore, only low dosages of this cytokine can be applied systemically, which results in poor tumor response. It has been demonstrated previously that administration of high‐dose TNF in a so‐called isolated perfusion system markedly improved tumor response when combined with chemotherapy. It appeared that TNF had a major impact specifically on the tumor‐associated vasculature. At these high concentrations, endothelial cell death is induced by TNF, resulting in complete collapse of the tumor vascular bed. Strikingly, this effect alone is not enough to induce a tumor response, but addition of a chemotherapeutic drug is mandatory to obtain an anti‐tumor effect. We showed that TNF has no anti‐tumor effect by itself but augmented drug accumulation mainly in the tumor, most likely by enhancing vascular leakage. It seems that enhanced vascular leakage, but not endothelial cell death, explains the interaction between TNF and the co‐administered drug. We hypothesized that in a low‐dose setting TNF could induce tumor accumulation of chemotherapeutic drugs and consequently improve tumor response. We demonstrate that free TNF has a strong effect on the pharmacokinetics of co‐administered Doxil® in B16BL6 melanoma‐bearing mice, resulting in strongly augmented drug accumulation in the tumor and improved tumor response. Co‐injection of Stealth® liposomal TNF with Doxil® resulted in comparable or less pronounced tumor responses as compared to free TNF. These results imply that systemic application of clinically tolerable doses of TNF may improve drug distribution and tumor response and could be useful in a number of anti‐cancer therapies. © 2004 Wiley‐Liss, Inc.