Antisense inhibition of delta-opioid receptor gene function in vivo by peptide nucleic acids

Peptide nucleic acids (PNA) are synthetic analogs of DNA that hybridize to complementary oligonucleotide sequences with exceptional affinity and targe t specificity. The stability of PNA in biological fluids together with the unique hybridization characteristics of these structures suggests that PNA may have considerable potential as antisense agents for experimental use in vivo. To test this hypothesis, we attempted to modulate supraspinal delta- opioid receptor function in rats using PNA sequences designed to be complem entary to a region of the rat delta-opioid receptor. Repeated i.c.v. admini stration of PNA over a period of 5 days significantly inhibited the antinoc iceptive response and locomotor response to selective delta-opioid receptor agonists. PNA attenuated delta-opioid receptor function in a sequence-spec ific, target-specific, and reversible manner characteristic of the function al inhibition caused by an antisense mechanism. There were no apparent toxi cities arising from the PNA treatment based on the behavior of the animals and inspection of the treated tissues. Saturation binding studies on brain homogenates did not reveal any significant difference in receptor B-max bet ween treatment groups. However, [S-35] guanosine-5'-O-(3-thio)triphosphate binding assays demonstrated a significant decrease in agonist efficacy in h omogenates prepared from antisense-treated rats. Taken together, these resu lts demonstrate that peptide nucleic acids are effective antisense agents i n vivo and suggest that PNA may be a useful alternative to phosphodiester o r phosphorothioate oligonucleotides, or variants thereof, for determination of gene function in vivo.