Synthesis and Evaluation of Parenchymal Retention and Efficacy of a Metabolically Stable O-Phosphocholine-N-docosahexaenoyl-l-serine siRNA Conjugate in Mouse Brain

Bioconjug Chem. 2017 Jun 21;28(6):1758-1766. doi: 10.1021/acs.bioconjchem.7b00226. Epub 2017 May 10.

Abstract

Ligand-conjugated siRNAs have the potential to achieve targeted delivery and efficient silencing in neurons following local administration in the central nervous system (CNS). We recently described the activity and safety profile of a docosahexaenoic acid (DHA)-conjugated, hydrophobic siRNA (DHA-hsiRNA) targeting Huntingtin (Htt) mRNA in mouse brain. Here, we report the synthesis of an amide-modified, phosphocholine-containing DHA-hsiRNA conjugate (PC-DHA-hsiRNA), which closely resembles the endogenously esterified biological structure of DHA. We hypothesized that this modification may enhance neuronal delivery in vivo. We demonstrate that PC-DHA-hsiRNA silences Htt in mouse primary cortical neurons and astrocytes. After intrastriatal delivery, Htt-targeting PC-DHA-hsiRNA induces ∼80% mRNA silencing and 71% protein silencing after 1 week. However, PC-DHA-hsiRNA did not substantially outperform DHA-hsiRNA under the conditions tested. Moreover, at the highest locally administered dose (4 nmol, 50 μg), we observe evidence of PC-DHA-hsiRNA-mediated reactive astrogliosis. Lipophilic ligand conjugation enables siRNA delivery to neural tissues, but rational design of functional, nontoxic siRNA conjugates for CNS delivery remains challenging.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain / metabolism*
  • Brain / pathology
  • Docosahexaenoic Acids / chemistry
  • Drug Delivery Systems / methods*
  • Drug Stability
  • Gene Silencing
  • Huntingtin Protein / genetics
  • Mice
  • Parenchymal Tissue / metabolism*
  • Phosphorylcholine / chemistry
  • RNA Interference
  • RNA, Messenger
  • RNA, Small Interfering / administration & dosage
  • RNA, Small Interfering / chemical synthesis*
  • RNA, Small Interfering / therapeutic use
  • Serine / chemistry
  • Treatment Outcome

Substances

  • Huntingtin Protein
  • RNA, Messenger
  • RNA, Small Interfering
  • Phosphorylcholine
  • Docosahexaenoic Acids
  • Serine