An engineered antibody–interleukin‐12 fusion protein with enhanced tumor vascular targeting properties

The antibody‐mediated targeted delivery of interleukin‐12 (IL12) to the EDB domain of fibronectin, a marker of angiogenesis, is a promising avenue for enhancing the therapeutic index of this anti‐cancer cytokine. Previous experiments, based on sequential fusion of a single‐chain IL12 derivative to the anti‐EDB antibody fragment scFv(L19) had yielded a therapeutic fusion protein [IL12‐scFv(L19)‐FLAG], which displayed an impressive therapeutic activity in murine models of cancer, in spite of a tumor uptake, which was less efficient compared to the parental unmodified scFv(L19). In this article, we describe the comparative analysis of 3 recombinant fusion proteins comprising the scFv(L19) and IL12 moieties. One of them, in which the p40 and p35 form a covalent heterodimer and in which each subunit is fused to a molecule of scFv(L19), displays an excellent tumor targeting performance in vivo , as assessed by quantitative biodistribution analysis, and a potent anti‐tumor effect, superior to the one of IL12‐scFv(L19)‐FLAG. These results may have a clinical impact, considering the fact that the tumor targeting ability of scFv(L19) in patients with cancer has been demonstrated using scintigraphic methods, and that 2 scFv(L19)‐based antibody‐cytokine fusion are currently entering clinical trials. © 2006 Wiley‐Liss, Inc.