Search

Melittin is a cytolytic peptide derived from bee venom that inserts into lipid membranes and oligomerizes to form membrane pores. Although this peptide is an attractive candidate for treatment of cancers and infectious processes, its nonspecific cytotoxicity and hemolytic activity have limited its therapeutic applications. Several groups have reported the development of cytolytic peptide prodrugs that only exhibit cytotoxicity following activation by site-specific proteases. However, systemic administration of these constructs has proven difficult because of their poor pharmacokinetic properties. Here, we present a platform for the design of protease-activated melittin derivatives that may be used in conjunction with a perfluorocarbon nanoparticle delivery system. Although native melittin was substantially hemolytic (HD50: 1.9 μM) and cytotoxic (IC50: 2.4 μM), the prodrug exhibited 2 orders of magnitude less hemolytic activity (HD50: > 100 μM) and cytotoxicity (IC50: > 100 μM). Incubation with matrix metalloproteinase-9 (MMP-9) led to cleavage of the prodrug at the expected site and restoration of hemolytic activity (HD50: 3.4 μM) and cytotoxicity (IC50: 8.1 μM). Incubation of the prodrug with perfluorocarbon nanoparticles led to stable loading of 10,250 peptides per nanoparticle. Nanoparticle-bound prodrug was also cleaved and activated by MMP-9, albeit at a fourfold slower rate. Intravenous administration of prodrug-loaded nanoparticles in a mouse model of melanoma significantly decreased tumor growth rate (p = 0.01). Because MMPs and other proteases play a key role in cancer invasion and metastasis, this platform holds promise for the development of personalized cancer therapies directed toward a patient's individual protease expression profile.

As molecular dynamics simulations continue to grow in size and complexity, new techniques are needed to rapidly identify regions of data likely to benefit from further analysis. Audibilization, the conversion of data to sound, facilitates this task by taking advantage of the user's innate ability to identify anomalies in patterns of sound. Audibilization also complements visualization of a molecular simulation by allowing the user to easily correlate changes in numerical quantities with changes in the overall structure of the molecular system. Here we present three examples highlighting the utility of audibilization in the analysis of three different molecular simulations. First, we present a simulation of liquid water in which the lengths of the O-H bonds are calculated at each time step and audibilized. Interestingly, we find that anomalies in the pattern of bond vibration are due to intermolecular interactions but do not correlate with the formation of hydrogen bonds. Next, we present a simulation of the rupture of a gold nanowire. Here we audibilize the nanowire potential energy and illustrate that sharp changes in this value coincide with important structural events such as the formation of monatomic chains and dislocations. Finally, we present a simulation of single-stranded DNA passing through a nanogap. Here the bond angle is audibilized and used to illustrate the conformational changes of each base as it passes through the nanogap. This simulation also illustrates the use of more advanced audibilization techniques such as the multiplexing of audibilized signals and the weighting of certain segments of data relative to others.

When polymeric nanoparticles (NPs) are formed by nanoprecipitation, which is a nucleation-growth process, the control over size requires changing the polymer concentration or solvent composition. Here, we demonstrate that the NP size can be controlled independent of polymer variables by introducing a polyelectrolyte (PE) in the aqueous phase. PEs that exhibit hydrogen bonding (H-bonding) yield a reduction in NP size, whereas PEs that do not possess this characteristic promote the formation of larger NPs. The observed effect can be attributed to the formation of a diffusional barrier around the NP in the form of a dense shell. This principle of controlling NP size is not limited to polymers and can also be employed in the production of lipid NPs.