Comparative pharmacokinetics, tissue distribution, and tumor accumulation of phosphorothioate, phosphorodithioate, and methylphosphonate oligonucleotides in nude mice.

The goals of this study were to systematically compare the pharmacokinetics and tissue distribution of phosphorothioate (PS), methylphosphonate (MP), and phosphorodithioate (PS2) oligonucleotide analogs; 15-mers of sequence d-TAC GCC AAC AGC TCC (5'-3') complementary to the AUG region of K-ras were radiolabeled with carbon-14. Oligomers were administered as a single dose in the tail vein of nude mice harboring a K-ras-dependent human pancreatic tumor (CFPAC1). The kinetics of PS, PS2, and MP oligomer availability in the bloodstream was followed. Concentration versus time profiles for all oligomers were biphasic, indicative of a two-compartment model. A rapid distribution phase with t1/2 alpha values of 1 minute or less and an elimination phase with average t1/2 beta values of 24-35 minutes were observed. Volumes of distribution (Vd) were 3.2, 4.8, and 6.3 ml for PS2, MP, and PS, respectively, in comparison to 3.6 ml for sucrose, a fluid-phase marker. Relative tissue drug levels obtained at 1 and 24 hours after administration were kidney > liver > spleen > tumor > muscle. Total kidney and liver oligonucleotide accumulation was approximately 7%-15% of the initial dose, with tumor accumulating 2%-3%. Intact compound was recovered from all tissues, including tumor, as assessed by high-pressure reversed-phase HPLC coupled to radiometric detection. Integrity of the oligonucleotides ranged from 73% in blood to 43%-46% in kidney and liver. Kidney and liver appear to be the primary sites of metabolism. These results demonstrate widespread tissue availability of these compounds and suggest their development as potential antitumor agents.

Interactions between single-stranded DNA binding protein and oligonucleotide analogs with different backbone chemistries.

Chemical modification of backbone structures has been an important strategy in designing oligonucleotides capable of improved antisense effects. However, altered backbone chemistry may also affect the binding of oligonucleotides to key cellular proteins, and thus may impact on the overall biological action of antisense agents. In this study we have examined the binding of oligonucleotides having four different backbone chemistries to single-strand binding protein (SSB), a protein having a key role in DNA repair and replication. The oligomers tested had the same sequence, while the internucleoside linkages were phosphodiester (PO), phosphorothioate (PS), phosphorodithioate (PS2), or methylphosphonate (MP). We found that both PS and PS2 oligomers bound to SSB with higher affinity than PO oligonucleotides, while MP oligonucleotides did not bind appreciably at the concentrations tested. Oligonucleotide length was also an important factor in binding to SSB, but sequence was less critical. These observations indicate that backbone chemistry is an important factor in interactions between oligonucleotides and critical cellular proteins, and thus may be a key determinant of the biological effects of antisense oligonucleotides.

Prevention of tumor formation in a mouse model of Burkitt's lymphoma by 6 weeks of treatment with anti-c-myc DNA phosphorothioate.

BACKGROUND: Transgenic mice bearing a murine immunoglobulin enhancer/c-myc fusion transgene (Emu-myc) provide a useful model for Burkitt's lymphoma. MATERIALS AND METHODS: Groups of 12 Emu-myc mice were treated prophylactically for 6 weeks after weaning with anti-c-myc DNA phosphorothioate (20 mg/kg/day), scrambled control DNA, or saline, delivered by micro-osmotic pumps. RESULTS: Half of the mice treated with saline or scrambled control DNA displayed palpable tumors by 8-9 weeks after birth, and 95% of them did so by 16 weeks, but 75% of the mice treated with antisense DNA were still free of tumors at the age of 26 weeks. Antisense therapy ablated MYC antigen in the spleens of tumor-bearing mice. Plasma physiological parameters indicated no acute toxicity. CONCLUSIONS: Long-term tumor resistance after anti-c-myc DNA therapy implies induction of a host response. Prophylactic anti-c-myc DNA therapy might prevent lymphoma in asymptomatic individuals displaying c-myc translocations.