Gold Nanocrystal Therapeutics: Treatment of Multidrug Resistant Pathogens and Disrupting Protein/Protein Interactions

Research with gold nanoparticles has exploded since the development of the Brust synthesis in 1994. Since that time, gold nanoparticles have been shown to be biologically inert, tunable in core size and monolayer, comparable in size to protein therapeutics and utilized as multivalent scaffolds. Attracted by the versatility of the gold nanoparticle, we investigated gold nanoparticles for combating multidrug resistance and enhancing the binding affinity of a known small molecule to a protein target.;The design and synthesis of multivalent gold nanoparticle antibiotics is presented. The thiolated penicillin derivatives KDK-1022 and EAK-223 were synthesized and conjugated to 2.0 nm diameter gold nanoparticles. Free KDK-1022 and EAK-223 were effective at inhibiting the growth of methicillin-susceptible Staphylococcus aureus (MSSA), but had little inhibitory effect on methicillin-resistant Staphylococcus aureus (MRSA). In contrast, KDK-1022 and EAK-223 conjugated to gold nanoparticles were active toward both MSSA and MRSA growth inhibition. Thus, when conjugated to gold nanoparticles, these lactam derivatives appear to be less susceptible to the resistance mechanisms that render the free molecules less effective. The results presented here suggest that multivalent display of small molecules on gold nanoparticles can convert resistance-compromised small-molecule drugs into potent nanoscale therapeutics.;We also describe the size comparability of a 2.0 nm gold nanoparticle to a 15 kDa protein and illustrate the conjugation and binding assays used to prove binding affinity can be enhanced with the use of a multivalent scaffold. The multivalent character has the ability to turn a weak binding molecule into a stronger one through multiple contact points. In addition to this, increasing the size of the therapeutic could improve its ability to inhibit two proteins interacting via large surface area contacts (sterics). Specifically, the total footprint of the nanoparticle will be large enough to disrupt all contact points between the protein targets. To examine our hypothesis we employ the Interleukin-2/Interleukin---2 receptor interaction and a known small molecule that binds to Interleukin-2. We describe synthesis of drug/gold nanoparticle conjugates, quantitation of drugs per particle, and demonstrate that drug coated nanoparticles bind interleukin-2 using Biacore, and Biacore evaluation to determine binding affinity.