PHARMACOKINETICS AND ORGAN CLEARANCE OF A 3'-BIOTINYLATED, INTERNALLY[P-32] LABELED PHOSPHODIESTER OLIGODEOXYNUCLEOTIDE COUPLED TO A NEUTRAL AVIDIN MONOCLONAL-ANTIBODY CONJUGATE

The pharmacokinetics and organ uptake of a 3'-biotinylated, [P-32] int ernally labeled 36-mer phosphodiester oligodeoxynucleotide (PO-ODN) we re measured after intravenous injection in the anesthetized adult rat. The PO-ODN was antisense to the fat gene of the human immunodeficienc y virus, and was 3'-biotinylated to a) protect against serum and tissu e 3'-exonuclease activity, and b) facilitate coupling to a neutral avi din-based transcellular drug delivery vector, The latter was comprised of a covalent conjugate of neutral avidin (NLA) and the OX26 murine m onoclonal antibody to the rat transferrin receptor. The PO-ODN was int ernally labeled at the 21-nucleotide position to prevent rapid hydroly sis [P-32] label by serum and tissue 5'-phosphatases. The uptake of th e 3'-bio[P-32(21)]PO-ODN by brain, heart, kidney, lung, and liver was measured, The studies show that the unconjugated 3'-bio-[P-32(21)]PO-O DN was rapidly removed from plasma, with a mean residence time of 22 /- 1 min and a systemic clearance of 9.2 +/- 0.5 ml/min/kg. Large amou nts of [P-32] radioactivity were recovered in the urine following the injection of the PO-ODN, and when this fraction was included in the ca lculation of the renal clearance parameter, the renal clearance was 20 -fold higher, indicating the principal site of organ clearance of the unconjugated PO-ODN was the kidney, Conjugation of the 3'-bio-PO-ODN t o the NLA-OX26 vector reduced the systemic clearance 50%, owing to a > 10-fold reduction in renal clearance. Following conjugation of the 3'- bio-PO-ODN to the NLA-OX26 vector, the major clearance organ was the l iver. Despite the 3'-biotinylation, the PO-ODN was rapidly degraded in vivo, based on trichloroacetic acid precipitation of plasma radioacti vity. In conclusion, these studies demonstrate that PO-ODNs are rapidl y removed from the plasma compartment following intravenous injection, and PO-ODN clearance is redirected from kidney to liver following con jugation to the NLA-OX26 transport vector.