Human
monoclonal antibodies are promising agents for the development of more selective anticancer
therapeutics. However, the
tumor-targeting efficiency of most anticancer
antibodies is severely limited by their poor penetration into the
tumor mass. Recent studies have shown that a
peptide derived from the
HIV TAT protein could improve the distribution of cytoplasmic reporter
proteins when administered systemically as fusion
proteins or cross-linked chimeras. In this article, we tested by quantitative biodistribtution analysis whether conjugation to TAT
peptides could improve the
tumor targeting properties of scFv(L19)-Cys: an engineered human
antibody fragment specific for the ED-B domain of
fibronectin, a marker located in the modified extracellular matrix surrounding
tumor neovasculature. Our results show that TAT
peptides, consisting either of L-
amino acids or D-
amino acids, can efficiently transduce target cells when conjugated to fluorophores and/or
antibody fragments, suggesting a receptor-independent cell entry mechanism. However, conjugation of scFv(L19)-Cys to TAT
peptides resulted in a severely reduced
tumor targeting performance compared to the unconjugated antibody, as measured in murine F9
teratocarcinoma-bearing mice, after
intravenous injection of the radiolabeled antibody preparations. Our results outline the usefulness of TAT
peptides for the efficient in vitro transduction of cells with globular
proteins. In particular, the use of TAT
peptides composed of D-
amino acids may significantly reduce proteolytic degradation. At the same time, the poor biodistribution properties of antibody-TAT conjugates cast doubts over the applicability of this methodology for the delivery of
biopharmaceuticals in vivo.