An antimelanoma immunotoxin containing recombinant human tumor necrosis factor: tissue disposition, pharmacokinetic, and therapeutic studies in xenograft models

The ability of monoclonal antibody conjugates to re-direct plant or bacterial toxins, chemotherapeutic agents and radionuclides to selected target cells has been well-documented. Recombinant human tumor necrosis factor (TNF) is a macrophage-derived, non-glycosylated (17 kDa) peptide with a broad range of biological and immunological effects including antiviral activity, cytotoxic and cytostatic effects. A conjugate of the antimelanoma antibody ZME-018 and TNF in previous studies has shown melanoma-selective cytotoxic effects in vitro. Pharmacokinetic studies of the ZME-TNF immunotoxin showed that the agent cleared from plasma biphasically with α-and β-phase half-lives similar to that of ZME itself (72 min and 36 h compared to 84 min and 41 h respectively). In contrast, TNF itself was cleared rapidly from plasma with a terminalphase half-life of only 2.7 h. The clearance rate of ZME-TNF from plasma (Cl_p) was almost tenfold more rapid than for ZME (1.1 versus 0.16 ml/kg x min) but was threefold slower than the clearance for TNF itself (3.4 ml/kg x min). Tissue distribution studies in nude mice bearing human melanoma xenografts showed similar tumor localization of the immunotoxin compared to the free antibody and slightly higher concentrations in liver and kidney compared to ZME itself. Treatment of nude mice bearing well-developed A375 tumors with the immunotoxin resulted in a statistically significant (P<0.002) suppression in tumor growth rate (fivefold increase) compared to saline-treated controls, which increased 20-fold over the same period. These studies demonstrate the feasibility of this approach and suggest that TNF may represent a non-antigenic alternative to immunotoxins containing plant and bacterial toxins.