Andrzej Grajkowski

Use of thermolytic protective groups to prevent G-tetrad formation in CpG ODN type D: structural studies and immunomodulatory activity in primates

CpG oligodeoxynucleotides (ODN) show promise as immunoprotective agents and vaccine adjuvants. CpG ODN type D were shown to improve clinical outcome in rhesus macaques challenged with Leishmania major. These ODN have a self-complementary core sequence and a 3′ end poly(G) track that favors G-tetrad formation leading to multimerization. Although multimerization appears necessary for localization to early endosomes and signaling via Toll-like receptor 9 (TLR-9), it can result in product polymorphisms, aggregation and precipitation, thereby hampering their clinical applications. This study shows that functionalizing the poly(G) track of D ODN with thermolytic 2-(N-formyl-N-methyl)aminoethyl (fma) phosphate/thiophosphate protecting groups (pro-D ODN) reduces G-tetrad formation in solution, while allowing tetrad formation inside the cell where the potassium concentration is higher. Temperature-dependent cleavage of the fma groups over time further promoted formation of stable G-tetrads. Peripheral blood cells internalized pro-D ODN efficiently, inducing high levels of IFNα, IL-6, IFNγ and IP-10 and triggering dendritic cell maturation. Administration of pro-D35 to macaques challenged with L.major significantly increased the number of antigen-specific IFNγ-secreting PBMC and reduced the severity of the skin lesions demonstrating immunoprotective activity of pro-D ODN in vivo. This technology fosters the development of more efficient immunotherapeutic oligonucleotide formulations for the treatment of allergies, cancer and infectious diseases.

Thermolytic CpG-containing DNA oligonucleotides as potential immunotherapeutic prodrugs

A CpG-containing DNA oligonucleotide functionalized with the 2-(N-formyl-N-methyl)aminoethyl thiophosphate protecting group (CpG ODN fma1555) was prepared from phosphoramidites 1a–d using solid-phase techniques. The oligonucleotide behaved as a prodrug by virtue of its conversion to the well-studied immunomodulatory CpG ODN 1555 through thermolytic cleavage of the 2-(N-formyl-N-methyl)aminoethyl thiophosphate protecting group. Such a conversion occurred at 37°C with a half-time of 73 h. The immunostimulatory properties of CpG ODN fma1555 were evaluated in two in vivo assays, one of which consisted of mice challenged in the ear with live Leishmania major metacyclic promastigotes. Local intradermal administration of CpG ODN fma1555 was as effective as that of CpG ODN 1555 in reducing the size of Leishmania lesions over time. In a different infectious model, CpG ODN 1555 prevented the death of Tacaribe-infected mice (43% survival) when administered between day 0 and 3 post infection. Administration of CpG ODN fma1555 three days before infection resulted in improved immunoprotection (60–70% survival). Moreover, co-administration of CpG ODN fma1555 and CpG ODN 1555 in this model increased the window for therapeutic treatment against Tacaribe virus infection, and thus supports the use of thermolytic oligonucleotides as prodrugs in the effective treatment of infectious diseases.

The 4-oxopentyl group as a labile phosphate/thiophosphate protecting group for synthetic oligodeoxyribonucleotides

Abstract An efficient and economical method for the solid-phase synthesis of oligodeoxyribonucleotides and their phosphorothioate analogues is described. The method entails the use of the 4-oxopentyl group for phosphate/thiophosphate protection. Post-synthesis removal of the protecting group is easily and rapidly achieved under mild conditions at ambient temperature using either pressurized gaseous amines or concentrated ammonium hydroxide.

Permanent or reversible conjugation of 2′-O- or 5′-O-aminooxymethylated nucleosides with functional groups as a convenient and efficient approach to the modification of RNA and DNA sequences

2′-O-Aminooxymethyl ribonucleosides are prepared from their 3′,5′-disilylated 2′-O-phthalimidooxymethyl derivatives by treatment with NH4F in MeOH. The reaction of these novel ribonucleosides with 1-pyrenecarboxaldehyde results in the efficient formation of stable and yet reversible ribonucleoside 2′-conjugates in yields of 69–82%. Indeed, exposure of these conjugates to 0.5 M tetra-n-butylammonium fluoride (TBAF) in THF results in the cleavage of their iminoether functions to give the native ribonucleosides along with the innocuous nitrile side product. Conversely, the reaction of 5-cholesten-3-one or dansyl chloride with 2′-O-aminooxymethyl uridine provides permanent uridine 2′-conjugates, which are left essentially intact upon treatment with TBAF. Alternatively, 5′-O-aminooxymethyl thymidine is prepared by hydrazinolysis of its 3′-O-levulinyl-5′-O-phthalimidooxymethyl precursor. Pyrenylation of 5′-O-aminooxymethyl thymidine and the sensitivity of the 5′-conjugate to TBAF further exemplify the usefulness of this nucleoside for modifying DNA sequences either permanently or reversibly. Although the versatility and uniqueness of 2′-O-aminooxymethyl ribonucleosides in the preparation of modified RNA sequences is demonstrated by the single or double incorporation of a reversible pyrenylated uridine 2′-conjugate into an RNA sequence, the conjugation of 2′-O-aminooxymethyl ribonucleosides with aldehydes, including those generated from their acetals, provides reversible 2′-O-protected ribonucleosides for potential applications in the solid-phase synthesis of native RNA sequences. The synthesis of a chimeric polyuridylic acid is presented as an exemplary model.

A Novel Function of RNAs Arising From the Long Terminal Repeat of Human Endogenous Retrovirus 9 in Cell Cycle Arrest

ABSTRACT The human genome contains approximately 50 copies of the replication-defective human endogenous retrovirus 9 (ERV-9) and thousands of copies of its solitary long term repeat (sLTR) element. While some sLTRs are located upstream of critical genes and have enhancer activity, other sLTRs are located within introns and may be transcribed as RNAs. We found that intronic RNAs arising from U3 sLTRs of ERV-9 were expressed as both sense (S) and antisense (AS) transcripts in all human cells tested but that expression levels differed in malignant versus nonmalignant cells. In nonmalignant cells, AS was expressed at higher levels than S and at higher levels than in malignant cells; in malignant cells, AS was expressed at amounts equivalent to those of S RNA. Critically, U3 AS RNA was found to physically bind to key transcription factors for cellular proliferation, including NF-Y, p53, and sp1, indicating that such RNA transcripts may function as decoy targets or traps for NF-Y and thus inhibit the growth of human cancer cells. Indeed, short U3 oligodeoxynucleotides (ODNs) based on these RNA sequences ably inhibited proliferation of cancer cell lines driven by cyclins B1/B2, the gene targets of NF-Y.

Hydroxyalkylated phosphoramidate, phosphoramidothioate and phosphorodiamidothioate derivatives as thiophosphate protecting groups in the development of thermolytic DNA prodrugs

The hydroxyalkylated phosphoramidate 4a, phosphoramidothioates 4b, 4e–j, and phosphorodiamidothioates 4c and 4d have been identified as a new class of heat-sensitive thiophosphate protecting groups in the development of thermolytic immunomodulatory DNA prodrugs. These alcohols are converted to their deoxyribonucleoside phosphoramidite derivatives 6a–j, which are then used in the preparation of the thermosensitive dinucleoside phosphorothioates 7a–j. The negatively charged thiophosphate protecting groups of 7a–b and 7e–j presumably undergo thermolytic cyclodeesterification at elevated temperature under essentially neutral conditions. The thiophosphate protecting groups of 7e and 7f show relatively rapid deprotection kinetics at 37 °C (t½ = 20 and 42 h, respectively) and are therefore suitable for the protection of phosphodiester functions flanking the CpG motifs of immunomodulatory DNA sequences, whereas the thiophosphate protecting groups of 7g–j with thermolytic deprotection half-lives in the range of 94–265 h at 37 °C are more appropriate for the thiophosphate protection of CpG motifs. Furthermore, the thermostability of the group protecting the thiophosphate function of 7a (t½ = 82 min at 90 °C) should offer adequate protection of the 5′- and/or 3′-terminal phosphodiester functions of DNA prodrugs against ubiquitous extracellular and intracellular exonucleases.

Design and Development of Thermolytic DNA Oligonucleotide Prodrugs

Deoxyribonucleoside phosphoramidites functionalized with the thermolytic 2‐(N‐formyl‐N‐methyl)aminoethyl group for phosphorus protection (1a‐d) have been prepared and employed in the solid‐phase synthesis of CpG ODN fma1555. Given that this modified oligonucleotide can be converted to the immunomodulatory CpG ODN 1555 under neutral conditions at 37°C, its biologic activity was demonstrated in vivo by studies showing that intraperitoneal administration of CpG ODN fma1555 in mice resulted in the activation of cytokine‐secreting splenocytes. Furthermore, administration of CpG ODN fma1555 to mice that were challenged intradermally in the ear with live L. major metacyclic promastigotes, reduced the severity of Leishmania skin lesions over time to an extent similar to that obtained with CpG ODN 1555. In another infectious model experiment, CpG ODN fma1555 protected newborn mice from death (65% survival) when administered 3 days before infection with the aggressive Tacaribe (TCRV) virus. A comparable immunoprotection was obtained by treatment of TCRV‐infected mice with CpG ODN 1555 administered on the same day of infection (45% survival). However, when TCRV‐infected mice were treated with CpG ODN fma1555 on the day of infection, they died as a consequence of the relatively slow conversion of the oligonucleotide prodrug to the bioactive CpG ODN 1555. Co‐administration of both CpG ODN 1555 and CpG ODN fma1555 to mice 3 days prior to TCRV infection or on the day of infection provided protection from death (45‐65% survival) and thus widened the immunoprotection window against TCRV‐infection.

Release of DNA oligonucleotides and their conjugates from controlled-pore glass under thermolytic conditions.

The sequential functionalization of long‐chain alkylamine controlled‐pore glass (CPG) with a 3‐hydroxypropyl‐(2‐cyanoethyl)thiophosphoryl linker and a dinucleoside phosphorotetrazolide leads to a uniquely engineered support for solid‐phase synthesis. Unlike conventional succinylated‐CPG supports, this support is designed to allow oligonucleotide deprotection and elimination of deprotection side‐products to proceed without release of the oligonucleotide. When needed, the DNA oligonucleotide can be thermolytically released in 2 hr under essentially neutral conditions. The modified CPG support has been successfully employed in the synthesis of both native and fully phosphorothioated DNA 20‐mers. On the basis of reversed‐phase HPLC and electrophoretic analyses, the purity of the released oligonucleotides is comparable to that of identical oligonucleotides synthesized from succinylated‐CPG supports, in terms of both shorter‐than‐full‐length oligonucleotide contaminants and overall yields. The detailed preparation of DNA oligonucleotides conjugated with exemplary reporter or functional groups, either at the 3′‐terminus or at both 3′‐ and 5′‐termini, is also described. Curr. Protoc. Nucleic Acid Chem. 35:3.17.1‐3.17.21.