qHTS for Inhibitors of mutant isocitrate dehydrogenase 1 (IDH1): Cherrypicks Autofluorescence Interference
Malignant glioblastomas (WHO grade IV), including primary and secondary glioblastomas, are among the most lethal with a median survival of one year, and unfortunately they are also the most prevalent type of brain tumors . By and large the standard of care of gliomas remains the use of the oral alkylating agent temozolomide and radiotherapy following surgical tumor resection . There is an urgent unmet medical need for novel therapeutics for gliomas. ..more
Depositor Specified Assays
Readout Interference Assay for Inhibitors of IDH1 R132H and WT IDH1
Malignant glioblastomas (WHO grade IV), including primary and secondary glioblastomas, are among the most lethal with a median survival of one year, and unfortunately they are also the most prevalent type of brain tumors . By and large the standard of care of gliomas remains the use of the oral alkylating agent temozolomide and radiotherapy following surgical tumor resection . There is an urgent unmet medical need for novel therapeutics for gliomas.
IDH mutations occur in up to 70% of grade II-IV secondary glioblastomas, and IDH1 R132H is the most prevalent mutation . Interestingly, IDH mutations are also present in ~10% of AML (acute myeloid leukemia) patients . Wild-type (WT) IDH1 catalyzes the conversion of isocitrate to a-ketoglutarate with the concomitant reduction of NADP+ to NADPH. In contrast, IDH1 R132H catalyzes the conversion of -ketoglutarate to 2-hydroxyglutarate (2-HG) with the concomitant oxidation of NADPH to NADP+ . Recently, a second significant advancement for the field was the finding that IDH is an oncogene, and that its metabolic product 2-HG may contribute to the pathogenesis of IDH-mutated cancers. Indeed, unbiased metabolite profiling of a U87MG stable cell line engineered to express IDH1 R132H mutant protein demonstrated that mutated IDH1 confers a gain-of-function to produce the onco-metabolite 2-HG, and in effect classifying IDH1 as an oncogene . These studies demonstrated the power of utilizing 2-HG as a biomarker for IDH-mutated cancers, as well as adding to the wealth of data linking the metabolite 2-HG to cancer. Although this link to cancer is tantalizing, the direct evidence of how 2-HG drives pathogenesis of gliomas and AML remains a subject of further research.
The goal of this detection interference assay is to identify whether the potential small-molecule inhibitors of IDH1 R132H or WT IDH1 confound the fluorescence readout by interfering with the detection reagent. Inhibition of the detection reagent would lead to a decrease in observed fluorescence of the product resorufin relative to the DMSO control. Compounds were screened as concentration-titration series that ranged from 76 uM to 0.15 uM.
NIH Molecular Libraries Probe Production Network [MLPCN]
NIH Chemical Genomics Center [NCGC]
MLSCN Grant: R03 DA032129
PI Name: Dr. Lenny Dang
Detection reagent buffer was dispensed into black, solid 1536-well plates at 9 microL/well in 20 mM Tris buffer, pH 7.5, containing final concentrations of 10 mM MgCl2, 20 mM NaCl, 0.05% BSA, 2 mM beta-ME, 0.008 mM NADPH, 1 mM alpha-ketoglutarate, and 0.008 mM resorufin. Then, 23 nL of compounds or DMSO were delivered to each well using a pin tool. The fluorescence intensity was monitored on an Envision plate reader at 590 nm (Ex 540, Em 590, bodipy mirror, 10 flashes). The %Activity was determined from the corrected fluorescence values. Resorufin at 0x was included to normalize %Activity of identified inhibitors; 0x resorufin values corresponded to 100%Activity (full inhibition), while 1x resorufin values were used to normalize 0%Activity (no inhibition).
Concentration-response curves were fitted to the signals arising from the resulting fluorescence. The concentration-response curves were then classified based on curve quality (r2), response magnitude and degree of measured activity, and compounds were subsequently categorized based on their curve class. Inactive compounds showed no effect on fluorescence signal increase relative to the DMSO control.
Keywords: Isocitrate dehydrogenase, IDH1, IDH1 R132H, 2-HG, 2-hydroxyglutarate, AML, glioma, MLSMR, MLPCN, NIH Roadmap, qHTS, NCGC
1. Compounds are first classified as having full titration curves, partial modulation, partial curve (weaker actives), single point activity (at highest concentration only), or inactive. See data field "Curve Description". For this assay, apparent activators are ranked higher than compounds that showed apparent inhibition.
2. For all inactive compounds, PUBCHEM_ACTIVITY_SCORE is 0. For all active compounds, a score range was given for each curve class type given above. Active compounds have PUBCHEM_ACTIVITY_SCORE between 40 and 100. Inconclusive compounds have PUBCHEM_ACTIVITY_SCORE between 1 and 39. Fit_LogAC50 was used for determining relative score and was scaled to each curve class' score range.
* Activity Concentration. ** Test Concentration.
Data Table (Concise)