Antibody mimics, fibronectin domain III for EphA2-targeting as a probe in murine tumor model

Objectives Specific binder proteins are developed on diagnosis and therapy for in vitro and in vivo applications. As an antibody mimics, human fibronectin domain III (Fn3) of small, stable and single-domain is well studied as a scaffold protein which is capable to be easily engineered with specificity and affinity. EphA2 is well-known early detection marker of various tumors such as lung, breast and colon cancer.

Methods In this study, we isolated EphA2 targeting peptides (E1 and E10) with Fn3 scaffold through the screening of yeast surface display library. They showed high affinities (Kd~2nM) against recombinant human EphA2 (hEphA2).

Results In ELISA against EphA2 and their homologs, they only bound hEphA2 and mEphA, although binding to hEphA2 binding is 2-fold higher than mEphA2. Also they showed similar binding to the cells and tumor tissue with EphA expression on the cell surface. In vivo optical imaging showed a strong targeting of Cy5.5-labled E1 in EphA2 over-expressing xenograft models (PC3 cells).

Conclusions Fn3 proteins isolated from this study show specifically binding to EphA2 with enough affinity. Altogether, high affinity Fn3 against EphA2, E1 would be useful as a candidate for EphA2 probe for in vivo diagnosis and therapy.