Lysine-deficient lymphotoxin-α mutant for site-specific PEGylation

The cytokine lymphotoxin-alpha (LT alpha) is a promising anticancer agent; however, its instability currently limits its therapeutic potential. Modification of proteins with polyethylene glycol (PEGylation) can improve their in vivo stability, but PEGylation occurs randomly at lysine residues and the N-terminus. Therefore, PEGylated proteins are generally heterogeneous and have lower bioactivity than their non-PEGylated counterparts. Previously, we created phage libraries expressing mutant LT alpha s in which the lysine residues of wild-type LT alpha (wtLT alpha) were substituted for other amino acids. Here, we attempted to create a lysine-deficient mutant LT alpha with about the same bioactivity as wtLT alpha by using these libraries and site-specific PEGylation of the N-terminus. We isolated a lysine-deficient mutant LT alpha, LT-KO, with almost identical bioactivity to that of wtLT alpha against mouse LM cells. The bioactivity of wtLT alpha decreased to 10% following random PEGylation, whereas that of LT-K0 decreased to 50% following site-specific PEGylation; PEGylated LT-K0 retained five times the bioactivity of randomly PEGylated wtLT alpha. These results suggest that site-specific PEGylated LT-KO may be useful in cancer therapy. (C) 2011 Elsevier Ltd. All rights reserved.