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Oligomeric Regulation of Ribonucleotide Reductase (RNR) by Antileukemic Nucleotides
Author(s) -
Wisitpitthaya Somsinee,
Fu Yuan,
Li Minxing,
Weiss Robert,
Aye Yimon
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.721.36
Subject(s) - ribonucleotide reductase , prodrug , nucleotide , nucleoside analogue , nucleoside , cladribine , fludarabine , deoxycytidine kinase , biochemistry , chemistry , clofarabine , enzyme , gemcitabine , biology , leukemia , cancer , cytarabine , genetics , chemotherapy , deoxycytidine , gene , protein subunit , cyclophosphamide
Human RNR (hRNR) is the rate‐limiting enzyme for the de novo dNTP synthesis required for DNA replication and repair. hRNR activity is positively correlated with cancer cell proliferation and nucleotide analogs that can suppress hRNR activity such as gemcitabine and clofarabine (ClF) are proven effective in chemotherapy. However, the precise mechanisms by which many of the nucleoside prodrugs inhibit hRNR are unknown in most cases. The active hRNR is minimally an α 2 β 2 holocomplex. Leukemia drug ClF is shown to inhibit hRNR through persistent hexamerization of α (α 6 ) without requiring β. We hypothesize that α hexamerization is a universal mechanism by which antileukemic nucleotides inhibit hRNR, ultimately presenting a powerful small‐molecule approach to regulate hRNR. To test this hypothesis, I have sought to establish the mechanisms of hRNR inhibition by two additional clinically used nucleoside prodrugs—cladribine (CLA) and fludarabine (FLU). My studies have revealed that di‐ and triphosphates are active forms of both drugs that reversibly inhibit hRNR. CLA nucleotides [CLAD(T)P] are more potent than FLU nucleotides [FLUD(T)P] ( K i = 0.8, 0.1, 4.9 and 6.6 µM, respectively). In all cases, enzyme inhibition is coupled to α 6 formation. We further validate in NIH‐3T3 cells stably expressing wild type α and hexamerization‐defective mutant α that hRNR inhibition by these nucleosides is directly correlated with oligomeric deregulation in cellular environment.