Prasad Dande

A systematic study on the effect of 2'-sugar modifications (2'-F (2'-F-2'-deoxy-nucleoside residues), 2'-O-Me (2'-O-methyl-nucleoside residues), and 2'-O-MOE [2'-O-(2-methoxyethyl)]-nucleoside residues) in the antisense and sense strands of short interference RNA (siRNA) was performed in HeLa cells. The study of the antisense strand of siRNAs demonstrated that activity depends on the position of the modifications in the sequence. The siRNAs with modified ribonucleotides at the 5'-end of the antisense strand were less active relative to the 3'-modified ones. The 2'-F sugar was generally well-tolerated on the antisense strand, whereas the 2'-O-Me showed significant shift in activity depending on the position of modification. The 2'-O-MOE modification in the antisense strand resulted in less active siRNA constructs regardless of placement position in the construct. The incorporation of the modified residues, e.g., 2'-O-Me and 2'-O-MOE, in the sense strand of siRNA did not show a strong positional preference. These results may provide guidelines to design effective and stable siRNAs for RNA interference mediated therapeutic applications.

Hepatitis C virus infection constitutes a significant health problem in need of more effective therapies. We have recently identified 2'-C-methyladenosine and 2'-C-methylguanosine as potent nucleoside inhibitors of HCV RNA replication in vitro. However, both of these compounds suffered from significant limitations. 2'-C-Methyladenosine was found to be susceptible to enzymatic conversions by adenosine deaminase and purine nucleoside phosphorylase, and it displayed limited oral bioavailability in the rat. 2'-C-Methylguanosine, on the other hand, was neither efficiently taken up in cells nor phosphorylated well. As part of an attempt to address these limitations, we now report upon the synthesis and evaluation of a series of heterobase-modified 2'-C-methyl ribonucleosides. The structure-activity relationship within this series of nucleosides reveals 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine as potent and noncytotoxic inhibitors of HCV RNA replication. Both 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine display improved enzymatic stability profiles as compared to that of 2'-C-methyladenosine. Consistent with these observations, the most potent compound, 4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidine ribonucleoside, is orally bioavailable in the rat. Together, the potency of the 2'-C-methyl-4-amino-pyrrolo[2,3-d]pyrimidine ribonucleosides and their improved pharmacokinetic properties relative to that of 2'-C-methyladenosine suggests that this class of compounds may have clinical utility.

A systematic structure-activity relationship study of 4'-thioribose containing small interfering RNAs (siRNAs) has led to the identification of highly potent and stable antisense constructs. To enable this optimization effort for both in vitro and in vivo applications, we have significantly improved the yields of 4'-thioribonucleosides by using a chirally pure (R)-sulfoxide precursor. siRNA duplexes containing strategically placed regions of 4'-thio-RNA were synthesized and evaluated for RNA interference activity and plasma stability. Stretches of 4'-thio-RNA were well tolerated in both the antisense and sense strands. However, optimization of both the number and placement of 4'-thioribonucleosides was necessary for maximal potency. These optimized siRNAs were generally equipotent or superior to native siRNAs and exhibited increased thermal and plasma stability. Furthermore, significant improvements in siRNA activity and plasma stability were achieved by judicious combination of 4'-thioribose with 2'-O-methyl and 2'-O-methoxyethyl modifications. These optimized 4'-thio-siRNAs may be valuable for developing stable siRNAs for therapeutic applications.

From the Walter Reed Army Institute of Research (WRAIR) inventory, thirteen 8-aminoquinoline analogs of primaquine were selected for screening against a panel of seven Plasmodium falciparum clones and isolates. Six of the 13 8-aminoquinolines had average 50% inhibitory concentrations between 50 and 100 nM against these P. falciparum clones and were thus an order of magnitude more potent than primaquine. However, excluding chloroquine-resistant clones and isolates, these 8-aminoquinolines were all an order of magnitude less potent than chloroquine. None of the 8-aminoquinolines was cross resistant with either chloroquine or mefloquine. In contrast to the inactive primaquine prototype, 8 of the 13 8-aminoquinolines inhibited hematin polymerization more efficiently than did chloroquine. Although alkoxy or aryloxy substituents at position 5 uniquely endowed these 13 8-aminoquinolines with impressive schizontocidal activity, the structural specificity of inhibition of both parasite growth and hematin polymerization was low.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTControl over the Localization of Positive Charge in DNA: The Effect on Duplex DNA and RNA StabilityLauren E. Heystek, Hui-qiang Zhou, Prasad Dande, and Barry GoldView Author Information Eppley Institute for Research in Cancer Department of Pharmaceutical Sciences University of Nebraska Medical Center 600 South 42 Street, Omaha, Nebraska 68198-6805 Cite this: J. Am. Chem. Soc. 1998, 120, 46, 12165–12166Publication Date (Web):November 5, 1998Publication History Received11 June 1998Published online5 November 1998Published inissue 1 November 1998https://pubs.acs.org/doi/10.1021/ja982039yhttps://doi.org/10.1021/ja982039yrapid-communicationACS PublicationsCopyright © 1998 American Chemical SocietyRequest reuse permissionsArticle Views282Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Chemical structure,Genetics,Oligomers,Salts,Stability Get e-Alerts