In order to direct antisense oligonucleotides to specific tissues or cell types in vivo, we are exploring the possibility to utilize lipoproteins as transport vehicles. A 16-mer oligonucleotide (ODN) was derivatized at the 5' prime through a 32P phosphate spacer with cholesterol, yielding a 32P-labeled amphiphatic cholesteryl-oligonucleotide (cholODN). Incubation of cholODN with low-density lipoprotein (LDL) for 2 hr at 37 degrees C resulted in the formation of a cholODN-LDL complex that migrates as a single peak on agarose gel electrophoresis. The cholODN was found to bind quantitatively to both high-density lipoproteins (HDL) and LDL, but not to albumin. Stable oligonucleotide-LDL particles with up to 50 molecules of cholODN per LDL particle could be obtained. In contrast, the control ODN did not show affinity for plasma lipoproteins. Upon injection into rats, cholODN became rapidly associated with plasma lipoproteins while control ODNs were recovered in the lipoprotein deficient serum fraction. The plasma half-life of cholODN (9-11 min) is considerably prolonged as compared with the control ODN (t1/2 less than 1 min). The cholODN-LDL was at least 5 min stable against degradation by rat plasma nucleases. It is concluded that derivatization of antisense oligonucleotides with cholesterol profoundly modifies their in vivo fate and opens possibilities for efficient and specific receptor-dependent targeting, mediated by lipoproteins coupled with specific recognition markers to various hepatic cell types.

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The endogenous Cbl uptake pathway can be exploited for oral peptide delivery as indicated by the specific and high (40-45%) uptake of metabolically stable Cbl-coupled octapeptides.

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