Triple blockade of HER2 by a cocktail of anti-HER2 scFv antibodies induces high antiproliferative effects in breast cancer cells

Dual therapy targeting human epidermal growth factor receptor 2 (HER2) by pertuzumab and trastuzumab (Herceptin) resulted in the significant survival of patients with HER2-positive breast cancers. However, a number of HER2-overexpressing breast cancers escape from this combination therapy. Due to several advantages of human single-chain antibodies (single chain variable fragments (scFvs)), these molecules were approved as valuable alternatives to entire IgGs for molecular targeting. In this study, our aim was to evaluate the growth inhibitory effects of three novel human anti-HER2 scFvs on breast cancer cells either alone or in combination and to assess their influence on HER2 expression in these cells. Flow cytometry was performed to show the cell binding ability of the scFvs to HER2-overexpressing cell lines, BT-474 and SKBR-3 cells, and HER2 low-expressing cell line, HeLa cells. The antiproliferative effects of the antibodies on the cancer cells were assessed by MTT assay. The amounts of HER2 gene and protein expression after antibody treatments were determined by quantitative real-time PCR and western blotting, respectively. FACS analysis showed that the anti-HER2 scFvs bound to BT-474 and SKBR-3 cells significantly higher than HeLa cells. Growth inhibitory assessment demonstrated that the triple blockade of HER2 by a cocktail of the three anti-HER2 scFvs significantly inhibited the proliferation of the both cancer cells to a greater extent than scFvs individually, in dual combination (scFv-I and scFv-III), and Herceptin. The percentages of growth inhibition of BT-474 and SKBR-3 cells after treatment with the cocktail were up to 77.4 and 76.5 %, respectively. The three scFv antibodies also reduced HER2 expression at both the gene and protein levels individually and in combination. Our results suggest that the cocktail of the three anti-HER2 scFv-I, scFv-II, and scFv-III, which induces high growth inhibition in breast cancer cells and downregulates HER2 gene and protein expression, can be considered as a new alternative for targeting of HER2-positive breast cancers.