Activatable antibodies having non-binding steric moieties and methods of using the same

A method of treating an EGFR-expressing cancer, the method comprising administering a therapeutically effective amount of a composition comprising an activatable antibody to a subject in need thereof, the activatable antibody comprising:

• an antibody or antibody fragment (AB) that binds specifically to a target, wherein the target is an epidermal growth factor receptor (EGFR), wherein the AB comprises the six complementarity determining regions (CDRs) of cetuximab;
• a cleavable linker (CL) covalently linked to the AB, wherein the CL comprises a substrate (S) for an enzyme, wherein the enzyme is urokinase plasminogen activator (uPa);
• and
• a binding partner (BP) for a non-binding steric moiety (NB), wherein the BP is an albumin-binding polypeptide comprising the amino acid sequence of SEQ ID NO:
• 1 and the NB comprises a serum albumin, wherein the NB is covalently linked to the CL, wherein the NB does not bind specifically to the AB;
• and
• wherein
• when the activatable antibody is in an uncleaved state and the NB is bound to the BP, the NB interferes with binding of the AB to the target and when the activatable antibody is in a cleaved state, the NB does not interfere with binding of the AB to the target, and
• the activatable antibody in the uncleaved state has the structural arrangement from N-terminus to C-terminus as follows:
• BP-CL-AB or AB-CL-BP.