Enabling in vivo Analysis Via Nanoparticle-mediated Intracellular Assay Probe Delivery: Using RAS as the Prototype
Many experimental protocols must be executed in vitro due to a lack of cell-permeable analysis probes. For instance, the cellular signaling moderator RAS proteins alternate between the active GTP-binding and the inactive GDP-binding states. Though many GTP analogs can serve as probes for RAS activity analysis, their cell impermeability renders in vivo analysis impossible. On the other hand, the lipid/calcium/phosphate (LCP) nanoparticle has enabled efficient intracellular delivery of a nucleotide analog as a chemotherapy agent. Thus, using RAS analysis and LCP nanoparticle as the prototype, we tackled the cell-impermeability issue via nanoparticle-mediated intracellular delivery of the analysis probe. Briefly, BODIPY-FT-GTP-{gamma}-S, a GTP analog that becomes fluorescent only upon protein binding, was chosen as the analysis probe, so that GTP binding can be quantified by fluorescent activity. BODIPY-FT-GTP-{gamma}-S-loaded LCP-nanoparticle was synthesized for efficient intracellular BODIPY-FT-GTP-{gamma}-S delivery. Binding of the delivered BODIPY-FT-GTP-{gamma}-S to the RAS proteins were consistent with previously reported observations; the RAS GTP binding activity was reduced in serum-starved cells; and a transient activation peak of the binding activity was observed upon subsequent serum reactivation of the cells. In a word, nanoparticle-mediated probe delivery enabled an in vivo RAS analysis method. The approach should be applicable to a wide variety of analysis protocols.