Inhibitor potency varies widely among tumor-relevant human isocitrate dehydrogenase 1 mutants.

Mutations in isocitrate dehydrogenase 1 (IDH1) drive most low-grade gliomas and secondary glioblastomas and many chondrosarcomas and acute myeloid leukemia cases. Most tumor-relevant IDH1 mutations are deficient in the normal oxidization of isocitrate to α-ketoglutarate (αKG), but gain the neomorphic activity of reducing αKG to D-2-hydroxyglutarate (D2HG), which drives tumorigenesis. We found previously that IDH1 mutants exhibit one of two reactivities: deficient αKG and moderate D2HG production (including commonly observed R132H and R132C) or moderate αKG and high D2HG production (R132Q). Here, we identify a third type of reactivity, deficient αKG and high D2HG production (R132L). We show that R132Q IDH1 has unique structural features and distinct reactivities towards mutant IDH1 inhibitors. Biochemical and cell-based assays demonstrate that while most tumor-relevant mutations were effectively inhibited by mutant IDH1 inhibitors, R132Q IDH1 had up to a 16 300-fold increase in IC50 versus R132H IDH1. Only compounds that inhibited wild-type (WT) IDH1 were effective against R132Q. This suggests that patients with a R132Q mutation may have a poor response to mutant IDH1 therapies. Molecular dynamics simulations revealed that near the NADP+/NADPH-binding site in R132Q IDH1, a pair of α-helices switches between conformations that are more wild-type-like or more mutant-like, highlighting mechanisms for preserved WT activity. Dihedral angle changes in the dimer interface and buried surface area charges highlight possible mechanisms for loss of inhibitor affinity against R132Q. This work provides a platform for predicting a patient's therapeutic response and identifies a potential resistance mutation that may arise upon treatment with mutant IDH inhibitors.

Activity of Selected Nucleoside Analogue ProTides against Zika Virus in Human Neural Stem Cells.

Zika virus (ZIKV), an emerging flavivirus that causes neurodevelopmental impairment to fetuses and has been linked to Guillain-Barré syndrome continues to threaten global health due to the absence of targeted prophylaxis or treatment. Nucleoside analogues are good examples of efficient anti-viral inhibitors, and prodrug strategies using phosphate masking groups (ProTides) have been employed to improve the bioavailability of ribonucleoside analogues. Here, we synthesized and tested a small library of 13 ProTides against ZIKV in human neural stem cells. Strong activity was observed for 2'-C-methyluridine and 2'-C-ethynyluridine ProTides with an aryloxyl phosphoramidate masking group. Substitution of a 2-(methylthio) ethyl phosphoramidate for the aryloxyl phosphoramidate ProTide group of 2'-C-methyluridine completely abolished antiviral activity of the compound. The aryloxyl phosphoramidate ProTide of 2'-C-methyluridine outperformed the hepatitis C virus (HCV) drug sofosbuvir in suppression of viral titers and protection from cytopathic effect, while the former compound's triphosphate active metabolite was better incorporated by purified ZIKV NS5 polymerase over time. These findings suggest both a nucleobase and ProTide group bias for the anti-ZIKV activity of nucleoside analogue ProTides in a disease-relevant cell model.