Molecular vehicle for target-mediated delivery of therapeutics and diagnostics

Selective targeting of therapeutic and diagnostic agents improves their efficacy and minimizes potentially adverse side effects. Existing methods for selective targeting are based on chemical conjugation of therapeutics and diagnostics, or their carriers, to cell-specific targeting molecules (e.g., growth factors, antibodies). These methods are limited by potential damage to targeting molecules that can be inflicted by the conjugation procedure. In addition, conjugation procedures have to be developed on a case-by-case basis. In order to avoid these problems we have developed a new approach to constructing molecular vehicles for target-mediated delivery of therapeutics and diagnostics. In this approach, the targeting molecule is expressed as a fusion protein containing a recognition tag. The recognition tag is defined as a peptide or protein that can bind non-covalently another peptide or protein (adapter). In turn, the adapter is chemically conjugated to a carrier of therapeutics or diagnostics. The assembled molecular delivery vehicle contains a carrier-adapter conjugate bound non-covalently to a recognition tag fused to the targeting protein. The advantages of this technology are: (i) no chemical modification of targeting molecules, and (ii) universal, 'off-the-shelf' carrier-adapter constructs that can be combined with different fusion targeting proteins. To obtain a proof-of-principle we have constructed VEGF fusion proteins containing a 15-aa S-peptide fragment of RNase A as a recognition tag. Using the S-protein fragment of RNase A as an adapter and polyethylenimine as a DNA carrier we have achieved selective gene delivery to cells overexpressing VEGFR-2.