Figure 3.

(a) Structure of matrix metalloproteinase (MMP)-targeted tumour-activated prodrug incorporating the cytotoxic agent doxorubicin (Albright et al., 2005). Doxorubicin is attached to a heptapeptide incorporating an MMP-selective cleavage site. The prodrug is endcapped by acetylation to prevent nonspecific exopeptidase activation and promote in vivo drug stability. (b) Schematic representation of prodrug activation by MMP with expected cleavage products. The cleavage site for MMP within the peptide is indicated by the arrow. Following the initial cleavage by MMP, the remaining amino-acid residues are removed rapidly by exopeptidases.