Decreased binding to proteins and cells of polymeric gene delivery vectorssurface modified with a multivalent hydrophilic polymer and retargeting through attachment of transferrin

Binding of serum proteins to polyelectrolyte gene delivery complexes is tho ught to be an important factor limiting bloodstream circulation and restric ting access to target tissues. Protein binding can also inhibit transfectio n activity in vitro. In this study a multivalent reactive hydrophilic polym er has been used to inhibit protein binding. This polymer is based on poly- [N-(2-hydroxypropyl)methacrylamide] (pHPMA) bearing pendent oligopeptide (G ly-Phe-Leu-Gly) side chains terminated in reactive 4-nitrophenoxy groups (8 .6 mol%). The polymer reacts with the primary amino groups of poly(L-lysine ) (pLL) and produces a hydrophilic coating on the surface of pLL DNA comple xes (as measured by fluorescamine). The resulting pHPMA-coated complexes sh ow a decreased surface charge (from +14 mV for pLL DMA complexes to -25 mV for pHPMA-modified complexes) as measured by zeta potential analysis, The p HPMA-coated complexes also show a slightly increased average diameter (appr oximately 90 nm compared with 60 nm for pLL DNA complexes) as viewed by ato mic force and transmission electron microscopy and around 100 nm as viewed by photon correlation spectroscopy, They are completely resistant to protei n interaction, as determined by turbidometry and SDS-polyacrylamide gel ele ctrophoresis analysis of complexes isolated from plasma, and show significa ntly decreased nonspecific uptake into cells in vitro. Spare reactive ester groups can be used to conjugate targeting ligands (e.g. transferrin) on to the surface of the complex to provide a means of tissue-specific targeting and transfection. The properties of these complexes therefore make them pr omising candidates for targeted gene delivery, both in vitro and potentiall y in vivo.