Definition

A bicyclic peptide targeting Ephrin receptor A2 (EphA2) and conjugated, through an inert sarcosine spacer chain and a valine-citrulline cleavable linker, to the cytotoxic agent monomethyl auristatin E (MMAE), an auristatin derivative and a potent inhibitor of microtubule polymerization, with potential antineoplastic activity. Upon administration of the EphA2-targeting bicycle toxin conjugate BT5528, this agent targets and binds to EphA2-expressing tumor cells. After internalization and enzymatic cleavage of the immunoconjugate within the tumor cell cytosol, free MMAE binds to tubulin and inhibits its polymerization, which may result in G2/M phase arrest and tumor cell apoptosis. The cell-surface receptor EphA2, a member of the ephrin family of receptor tyrosine kinases (RTKs) involved in mammalian development, is overexpressed by a variety of different cancer cell types. EphA2 expression is associated with poor prognosis.