TY - JOUR
T1 - Single-chain antibody-based immunotoxins targeting her2/neu
T2 - Design optimization and impact of affinity on antitumor efficacy and off-target toxicity
AU - Cao, Yu
AU - Marks, James D.
AU - Huang, Qian
AU - Rudnick, Stephen I.
AU - Xiong, Chiyi
AU - Hittelman, Walter N.
AU - Wen, Xiaoxia
AU - Marks, John W.
AU - Cheung, Lawrence H.
AU - Boland, Kim
AU - Li, Chun
AU - Adams, Gregory P.
AU - Rosenblum, Michael G.
PY - 2012/1
Y1 - 2012/1
N2 - Recombinant immunotoxins, consisting of single-chain variable fragments (scFv) genetically fused to polypeptide toxins, represent potentially effective candidates for cancer therapeutics. We evaluated the affinity of various anti-Her2/neu scFv fused to recombinant gelonin (rGel) and its effect on antitumor efficacy and off-target toxicity.Aseries of rGel-based immunotoxins were created from the human anti-Her2/neu scFv C6.5 and various affinity mutants (designated ML3-9, MH3-B1, and B1D3) with affinities ranging from 10 -8 to 10 -11 mol/L. Against Her2/neu-overexpressing tumor cells, immunotoxins with increasing affinity displayed improved internalization and enhanced autophagic cytotoxicity. Targeting indices were highest for the highest affinity B1D3/rGel construct. However, the addition of free Her2/neu extracellular domain (ECD) significantly reduced the cytotoxicity of B1D3/rGel because of immune complex formation. In contrast,ECDaddition had little impact on the lower affinity constructs in vitro. In vivo studies against established BT474M1xenografts showed growth suppression by all immunotoxins. Surprisingly, therapy with the B1D3-rGel induced significant liver toxicity because of immune complex formation with shed Her2/neu antigen in circulation. The MH3-B1/rGel construct with intermediate affinity showed effective tumor growth inhibition without inducing hepatotoxicity or complex formation. These findings show that while high-affinity constructs can be potent antitumor agents, they may also be associated with mistargeting through the facile formation of complexes with soluble antigen leading to significant off-target toxicity. Constructs composed of intermediate-affinity antibodies are also potent agents that are more resistant to immune complex formation. Therefore, affinity is an exceptionally important consideration when evaluating the design and efficacy of targeted therapeutics.
AB - Recombinant immunotoxins, consisting of single-chain variable fragments (scFv) genetically fused to polypeptide toxins, represent potentially effective candidates for cancer therapeutics. We evaluated the affinity of various anti-Her2/neu scFv fused to recombinant gelonin (rGel) and its effect on antitumor efficacy and off-target toxicity.Aseries of rGel-based immunotoxins were created from the human anti-Her2/neu scFv C6.5 and various affinity mutants (designated ML3-9, MH3-B1, and B1D3) with affinities ranging from 10 -8 to 10 -11 mol/L. Against Her2/neu-overexpressing tumor cells, immunotoxins with increasing affinity displayed improved internalization and enhanced autophagic cytotoxicity. Targeting indices were highest for the highest affinity B1D3/rGel construct. However, the addition of free Her2/neu extracellular domain (ECD) significantly reduced the cytotoxicity of B1D3/rGel because of immune complex formation. In contrast,ECDaddition had little impact on the lower affinity constructs in vitro. In vivo studies against established BT474M1xenografts showed growth suppression by all immunotoxins. Surprisingly, therapy with the B1D3-rGel induced significant liver toxicity because of immune complex formation with shed Her2/neu antigen in circulation. The MH3-B1/rGel construct with intermediate affinity showed effective tumor growth inhibition without inducing hepatotoxicity or complex formation. These findings show that while high-affinity constructs can be potent antitumor agents, they may also be associated with mistargeting through the facile formation of complexes with soluble antigen leading to significant off-target toxicity. Constructs composed of intermediate-affinity antibodies are also potent agents that are more resistant to immune complex formation. Therefore, affinity is an exceptionally important consideration when evaluating the design and efficacy of targeted therapeutics.
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U2 - 10.1158/1535-7163.MCT-11-0519
DO - 10.1158/1535-7163.MCT-11-0519
M3 - Article
C2 - 22090420
AN - SCOPUS:84862907829
SN - 1535-7163
VL - 11
SP - 143
EP - 153
JO - Molecular cancer therapeutics
JF - Molecular cancer therapeutics
IS - 1
ER -