Shiga-like toxin-VEGF fusion proteins are selectively cytotoxic to endothelial cells overexpressing VEGFR-2

Growing endothelial cells at sites of angiogenesis may be more sensitive than quiescent endothelial cells to toxin-VEGF fusion proteins, because they express higher numbers of VEGF receptors. We have constructed, expressed and purified a protein containing the catalytic A-subunit of Shiga-like toxin I fused to VEGF(121) (SLT-VEGF/L). SLT-VEGF/L inhibits protein synthesis in a cell-free translation system and induces VEGFR-2 tyrosine autophosphorylation in cells overexpressing VEGFR-2 indicating that both SLT and VEGF moieties are properly folded in the fusion protein. SLT-VEGF/L selectively inhibits growth of porcine endothelial cells expressing 2-3 x 10(5) VEGFR-2/cell with an IC50 of 0.1 nM, and rapidly induces apoptosis at concentrations > 1 nM. Similar results are observed with human transformed embryonic kidney cells, 293, engineered to express 2.5 x 10(6) VEGFR-2/cell. In contrast, SLT-VEGF/L does not affect three different types of endothelial cells (PAE/KDRlow, HUVE, MSI) expressing between 5 x 10(3) and 5 x 10(4) VEGFR-2/cell, and quiescent endothelial cells overexpressing VEGFR-2. Growth inhibition and induction of apoptosis by SLT-VEGF/L require intrinsic N-glycosidase activity of the SLT moiety, but occur without significant inhibition of protein synthesis, The selective cytotoxicity of SLT-VEGF proteins against growing endothelial cells overexpressing VEGFR-2 suggests that they may be useful in targeting similar cells at sites of angiogenesis. (C) 2001 Elsevier Science BY. All rights reserved.