Such probes can target cancer-associated enzymes including cathepsin-B, cathepsin-L [14, 15], matrix metalloproteinases-2 (MMP-2) [16, 17], β-galactosidase (β-Gal) [18–20] and γ-glutamyltransferase (GGT) (Figure 1) [9, 21, 22]. The gene discussed is MMP2; the disease is cancer.