Effect of chemical modifications of cytosine and guanine in a CpG-motif of oligonucleotides: structure-immunostimulatory activity relationships.
Oligodeoxynucleotides containing unmethylated CpG-motifs stimulate the innate immune system, including inducing B-cell proliferation and cytokine production. However, the mechanism of immunostimulation by CpG-oligonucleotides and the precise structural requirements and specific functional groups of cytosine and guanine necessary for recognition of and interaction with protein/receptor factors that are responsible for immune stimulation have not been elucidated. We sought to understand the critical role of each functional group of the cytosine and guanine moieties in a CpG-motif in inducing immunostimulatory activity. To this end, we examined structure-immunostimulatory activity relationships of phosphorothioate oligodeoxynucleotides (PS-oligos) containing YpG- and CpR-motifs (Y and R stand for pyrimidine and purine analogues, respectively). The PS-oligos containing a YpG-motif in which the natural deoxycytidine was replaced with deoxy-5-hydroxycytidine or deoxy-N4-ethylcytidine showed immunostimulatory activity. Substitution of deoxycytidine with a deoxy-5-methylisocytidine, deoxyuridine, or deoxy-P-base-nucleoside in the YpG-motif completely abolished the immunostimulatory activity, similar to the results observed with deoxy-5-methylcytidine. In the case of PS-oligos containing a CpR-motif, 7-deazaguanine substitution for natural guanine showed immunostimulatory activity similar to that of a parent PS-oligo. These studies suggest that the 2-keto, 3-imino and 4-amino groups of cytosine, and the 1-imino, 2-amino and 6-keto groups of guanine in a CpG-motif are important for the immunostimulatory activity of CpG-PS-oligos. The absence of N7 on guanine of the CpG-motif does not affect immunostimulatory activity significantly. These studies suggest that it is possible to develop YpG- and CpR-motifs as an alternative to CpG-motifs in PS-oligos for immunostimulatory studies.
Kandimalla
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Hybridon, Inc., Cambridge, MA 02139, USA.
Yu
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D
Zhao
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Agrawal
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D000818:Animals; D001483:Base Sequence; D003596:Cytosine / Q000737:chemistry; D015224:Dideoxynucleosides / Q000737:chemistry / Q000276:immunology; D015195:Drug Design; D005260:Female; D006147:Guanine / Q000737:chemistry; D007274:Injections, Intraperitoneal; D008213:Lymphocyte Activation / Q000187:drug effects*; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects; D051379:Mice; D008807:Mice, Inbred BALB C; D009841:Oligonucleotides / Q000737:chemistry / Q000276:immunology* / Q000494:pharmacology; D013154:Spleen / Q000166:cytology / Q000187:drug effects; D013163:Splenomegaly / Q000139:chemically induced; D013329:Structure-Activity Relationship
D015224:Dideoxynucleosides; D009841:Oligonucleotides; D006147:Guanine; D003596:Cytosine