Team:Penn/Targeting

Testing the Displayed HER2 DARPin on Cancer Cells

After verifying that the DARPin was displayed on the cell surface, we sought to test whether it could allow binding to HER2-overexpressing cancer cells. We were generously provided SKBR3 cells by the lab of Matthew Lazzara. These cells are derived from breast cancer cells and over-express HER2. We also obtained Human Embryonic Kidney (HEK) 293T cells, which express a low amount of HER2, to act as controls.

To verify that our SKBR3 cells overexpressed HER2, we immunostained for HER2 (primary anti-Neu Mouse Igg, Santa Cruz Biotechnology and secondary donkey anti-mouse Alexa-Fluor 647 conjugate, Jackson Immunoresearch) and visualized the cells on a confocal microscope. As expected, HER2 was overexpressed in SKBR3 cells (Figure 1).

To assay whether our DARPin-displaying E. coli bound to SKBR3 cells preferentially, we conducted experiments in which our bacteria were co-incubated with SKBR3 or HEK293T cells. The DARPin-displaying bacteria were co-transformed with constitutively expressed eGFP (pACBB-eGFP plasmid) for easy visualization. The goal was to show SKBR3-specific binding of eGFP labeled bacteria, and only when they were induced with IPTG to produce INPNC-DARPin. Preliminary results are exciting and show preferential binding to SKBR3 cells. In culture plates with low-HER2 HEK293T cells, no green bacteria were observed bound to the cells. IPTG-induced bacteria bound selectively to SKBR3 cells and we visualized this binding by confocal microscopy (Figure 3).

Taking a closer look at the SKBR3 + Induced Bacteria group, one can observe our eGFP labeled bacteria bound directly to the HER2 on SKBR3 cells (Figure 4)



In summary, we demonstrated surface display of DARPin H10-2-G3 for the first time and have preliminary evidence showing our DARPin-displaying bacteria can target cancer cells. We also developed a generalized surface display BioBrick for any iGEM team to use.