Targeted
therapy is a new type of
cancer treatment that most often uses biologically active drugs attached to a
monoclonal antibody. This so called
antibody-drug conjugate strategy allows the use of highly toxic substances that target
tumor cells specifically, leaving healthy tissues largely unaffected. Over the last few years,
antibody-drug conjugates have become a powerful tool in
cancer treatment. We developed and characterized a novel cytotoxic conjugate against HER2
tumors in which the antibody has been substituted with a much smaller molecule: the affibody. The conjugate is composed of the ZHER2:2891 affibody that recognizes HER2 and a highly potent cytotoxic drug
auristatin E. The ZHER2:2891 molecule does not contain
cysteine(s) in its amino acid sequence. We generated 3 variants of ZHER2:2891, each containing a single
cysteine to allow conjugation through the
maleimide group that is present in the cytotoxic component. In 2 variants, we introduced single S46C and D53C substitutions. In the third variant, a short Drug Conjugation Sequence (DCS) containing a single
cysteine was introduced at the C-terminus of ZHER2:2891, resulting in ZHER2:2891-DCS. The latter variant exhibited a significantly higher conjugation yield, and therefore its cytotoxicity has been studied more thoroughly. The ZHER2:2891-DCS-MMAE conjugate killed the HER2-overexpressing SK-BR-3 and MDA-MB-453 cells efficiently (IC50 values of 5.2 and 24.8 nM, respectively). The T-47-D and MDA-MB-231 cells that express normal levels of HER2 were significantly less sensitive to the conjugate (IC50 values of 135.6 and 161.5 nM, respectively). Overall, we have demonstrated for the first time that
proteins other than
antibodies/
antibody fragments can be successfully combined with a linker-drug module, resulting in conjugates that eliminate
cancer cells selectively.