Development of a Cytosolic DNA Sensor Agonist Using GALA Peptide-Conjugated DNA and Long Single-Stranded DNA

Cytosolic DNA sensors (CDSs) recognize DNA molecules that are abnormally located in the cytosol, thus leading to the activation of the stimulator of interferon genes (STING) and the induction of type 1 interferon. In turn, type 1 interferon evokes defensive reactions against viral infections and activates the immune system; therefore, the use of agonists of CDSs as cancer therapeutics and vaccine adjuvants is expected. Double-stranded DNA molecules with dozens to thousands of bases derived from bacteria and viruses are agonists of CDSs. However, DNA is a water-soluble molecule with a high molecular weight, resulting in poor cellular uptake and endosomal escape. In contrast, long single-stranded DNA (lssDNA) obtained by rolling circle amplification is efficiently taken up and localized to endosomes. Here we constructed a CDS-targeting lssDNA via the facilitation of its intracellular transport from endosomes to the cytosol. An endosome-disrupting GALA peptide was used to deliver the lssDNA to the cytosol. A peptide–oligonucleotide conjugate (POC) was successfully obtained via the conjugation of the GALA peptide with an oligonucleotide complementary to the lssDNA. By hybridization of the POC to the complementary lssDNA (POC/lssDNA), the CDS–STING pathway in dendritic cells was efficiently stimulated. GALA peptide-conjugated DNA seems to be a helpful tool for the delivery of DNA to the cytosol.