Nanoparticle mediated functional delivery of plasmid DNA (pDNA) in vivo typically requires the formulation of pDNA-nanoparticles with a surface layer of stealth/biocompatibility polymer (usually poly(ethylene glycol) [PEG]). This PEG layer ensures the colloidal stability of pDNA-nanoparticles in biological fluids and minimizes nanoparticle interactions with the reticulo-endothelical system. Unfortunately, the presence of the PEG layer appears to contribute to a reduction in efficiency of functional delivery of pDNA once target cells are reached. For this reason, we have focused recent research efforts on "triggerable" nanoparticle systems. These are designed to be stable from the point of administration until a target site of interest is reached, then triggered for the controlled release of therapeutic agent payload(s) at the target site by changes in local endogenous conditions or through the application of some exogenous stimulus. Here, we describe investigations into the potential use of enzymes to trigger pDNA-mediated therapy through a process of enzyme-assisted nanoparticle triggerability. Our approach is to use PEG(2000)-peptidyl lipids with peptidyl moieties sensitive to tumor-localized elastase or matrix metalloproteinase-2 digestion, and from these prepare putative enzyme-triggered PEGylated pDNA-nanoparticles. Our results provide initial proof of concept in vitro. From these data, we propose that this concept should be applicable for functional delivery of therapeutic nucleic acids to tumor cells in vivo, although the mechanism for enzyme-assisted nanoparticle triggerability remains to be fully characterized.