Antibody-drug conjugates (ADCs) represent a promising class of
biopharmaceuticals with the potential to localize at the
tumor site and improve the therapeutic index of cytotoxic drugs. While it is generally believed that ADCs need to be internalized into
tumor cells in order to display optimal therapeutic activity, it has recently been shown that non-internalizing
antibodies can efficiently liberate
disulfide-linked drugs at the extracellular
tumor site, leading to potent anti-
cancer activity in preclinical animal models. Here, we show that engineered variants of the F16 antibody, specific to a splice
isoform of
tenascin-C, selectively localize to the subendothelial
tumor extracellular matrix in three mouse models of human
cancer (U87, A431, MDA-MB-231). A site-specific coupling of F16 in
IgG format with a
monomethyl auristatin E (MMAE) derivative, featuring a
valine-
citrulline dipeptide linker equipped with a self-immolative spacer, yielded an ADC product, which cured
tumor-bearing mice at a dose of 7 mg/Kg. The observation of an efficient extracellular proteolytic cleavage of the
valine-
citrulline linker was surprising, as it has generally been assumed that this peptidic structure would be selectively cleaved by
cathepsin B in intracellular compartments. The products described in this article may be useful for the treatment of human
malignancies, as their cognate
antigen is strongly expressed in the majority of human solid
tumors,
lymphomas and aggressive
leukemias, while being virtually undetectable in most normal adult tissues.