To improvethe MMP selectivity, the authors conducted a metabolic analysis andidentified that the replacement of l-lysine by d-lysine reduced nonspecific cleavage and improved the tumor-to-backgroundratios of initial constructs when employed for in vivo imaging.85 Interestingly, these probes have also been usedto image MMP-9 expression in vivo in mouse models of diabetic stroke,demonstrating potential clinical utility across several diseases.86 The gene discussed is MMP9; the disease is neoplasm.