Peptide nucleic acids targeted to the neurotensin receptor and administered i.p. cross the blood-brain barrier and specifically reduce gene expression

Intraperitoneal injection of an unmodified antisense peptide nucleic acid ( PNA) complementary to mRNA of the rat neurotensin (NT) receptor (NTR1) was demonstrated by a gel shift assay to be present in brain, thus indicating t hat the PNA had in fact crossed the blood-brain barrier. An i.p. injection of this antisense PNA specifically inhibited the hypothermic and antinocice ptive activities of NT microinjected into brain. These results were associa ted with a reduction in binding sites for NT both in brain and the small in testine. Additionally, the sense-NTR1 PNA, targeted to DNA, microinjected d irectly into the brain specifically reduced mRNA levels by 50% and caused a loss of response to NT, To demonstrate the specificity of changes in behav ioral, binding, and mRNA studies, animals treated with NTR1 PNA were tested for behavioral responses to morphine and their mu receptor levels were det ermined. Both were found to be unaffected in these NTR1 PNA-treated animals . The effects of both the antisense and sense PNAs were completely reversib le. This work provides evidence that any antisense strategy targeted to bra in proteins can work through i.p. delivery by crossing the normal blood-bra in barrier. Equally important was that an antigene strategy, the sense PNA, was shown in vivo to be a potentially effective therapeutic treatment.