Pharmacokinetics and tissue distribution of a DNA-methyltransferase antisense (MT-AS) oligonucleotide and its catabolites in tumor-bearing nude mice.

The pharmacokinetics of a 20-mer phosphorothioate antisense oligodeoxynucleotide was investigated in nude mice bearing a s.c. human lung carcinoma. The oligodeoxynucleotide, referred to as DNA-methyltransferase antisense (MT-AS) was designed to bind to the mRNA that coded for DNA-methyltransferase, an enzyme that controls the extent of methylation of 5'-cytosine. MT-AS was administered at four different doses (10, 30, 100 and 300 mg/kg) as an i.v. bolus in a composite study design. A maximum of four blood samples were collected from any single animal, followed by sacrifice to obtain tissues. The plasma and tissue samples were collected from 5 min to 48 h after dosing and were processed by anion-exchange HPLC (high performance liquid chromatography) and by capillary gel electrophoresis. On the basis of total (i.e., 15-mer to 20-mer species) MT-AS plasma concentrations as determined by HPLC, total clearance ranged from 7.9 ml/min/kg at the 30-mg/kg dose level to 15.2 ml/min/kg at 10 mg/kg; however, there were no definitive dose-dependent changes in clearance. The volume of distribution at steady state increased from a low value of 379 ml/kg at 30 mg/kg to a high of 1983.0 ml/kg at 300 mg/kg, a result that suggests saturable protein binding. In vitro plasma protein binding data supported this possibility, because the percentage of MT-AS bound decreased at high MT-AS concentrations. MT-AS distributed into most tissues, with a general rank order of kidney > liver > tumor > lung > muscle > brain. Analysis of plasma samples by capillary gel electrophoresis from 2 h to 8 h revealed that about 50% of the total oligodeoxynucleotides were due to the parent 20-mer MT-AS; the remainder consisted of 15-mer to 19-mer catabolites. Of particular interest was the relatively high tumor uptake of MT-AS. These results will support future studies designed to characterize the pharmacological action of MT-AS and its efficacy in preclinical models.