Multi-drug delivery system using streptavidin-transforming growth factor-alpha chimeric protein

Kinetic parameters for small-molecule drug delivery by covalent cell surface targeting

Human cells incubated with N-levulinoylmannosamine (ManLev) process this unnatural metabolic precursor into N-levulinoyl sialic acid (SiaLev), which is incorporated into cell surface glycoconjugates. A key feature of SiaLev is the presence of a ketone group that can be exploited in chemoselective ligation reactions to deliver small-molecule probes to the cell surface. A mathematical model was developed and tested experimentally to evaluate the prospects of using cell surface ketones as targets for covalent small-molecule drug delivery. We quantified the absolute number of ketone groups displayed on cell surfaces as a function of the concentration of ManLev in the medium. The apparent rate constants for the hydrolysis and disappearance of the cell surface conjugates were determined, as well as the apparent rate constant for the formation of covalent bonds with cell surface ketones. These values and the mathematical model confirm that chemoselective reactions on the cell surface can deliver to cells similar numbers of molecules as antibodies. Thus, cell surface ketones are a potential vehicle for a metabolically controlled small-molecule drug delivery system.

Targeted gene transfer system using a streptavidin-transforming growth factor-alpha chimeric protein

The previously reported streptavidin-TGFalpha chimeric protein-based delivery system (Ohno and Meruelo, DNA Cell Biol. 15:401-406, 1996) could efficiently transfer protein molecules into A431 cells via the epidermal growth factor (EGF) receptor. We have modified this delivery system for the transfer of DNA. For this purpose, we have linked the chimeric protein ST-TGFalpha to DNA through biotinylated polylysine molecules. We show with this system, in the presence of the endosome-destabilizing reagent chloroquine, an average of 50-fold increase in reporter gene expression in comparison with polylysine DNA complexes alone. This gene expression is specific for EGF receptor-expressing cells and is blocked by EGF-binding molecules. These results suggest that the ST-TGFalpha biotinylated polylysine system could be used to deliver DNA to targeted cells.