Targeted long-read sequencing of the Ewing sarcoma 6p25.1 susceptibility locus identifies germline-somatic interactions with EWSR1-FLI1 binding

Ewing sarcoma (EwS) is a rare bone and soft tissue malignancy driven by chromosomal translocations encoding chimeric transcription factors, such as EWSR1-FLI1, that bind GGAA motifs forming novel enhancers that alter nearby expression. We propose that germline microsatellite variation at the 6p25.1 EwS susceptibility locus could impact downstream gene expression and EwS biology. We performed targeted long-read sequencing of EwS blood DNA to characterize variation and genomic features important for EWSR1-FLI1 binding. We identified 50 microsatellite alleles at 6p25.1 and observed that EwS-affected individuals had longer alleles (>135 bp) with more GGAA repeats. The 6p25.1 GGAA microsatellite showed chromatin features of an EWSR1-FLI1 enhancer and regulated expression of RREB1, a transcription factor associated with RAS/MAPK signaling. RREB1 knockdown reduced proliferation and clonogenic potential and reduced expression of cell cycle and DNA replication genes. Our integrative analysis at 6p25.1 details increased binding of longer GGAA microsatellite alleles with acquired EWSR-FLI1 to promote Ewing sarcomagenesis by RREB1-mediated proliferation.

In-utero exposure to zidovudine-containing antiretroviral therapy and clonal hematopoiesis in HIV-exposed uninfected newborns

OBJECTIVE

Zidovudine (ZDV) has been extensively used in pregnant women to prevent vertical transmission of HIV but few studies have evaluated potential mutagenic effects of ZDV during fetal development.

DESIGN

Our study investigated clonal hematopoiesis in HIV-exposed uninfected (HEU) newborns, 94 of whom were ZDV-exposed and 91 antiretroviral therapy (ART)-unexposed and matched for potential confounding factors.

METHODS

Utilizing high depth sequencing and genotyping arrays, we comprehensively examined blood samples collected during the first week after birth for potential clonal hematopoiesis associated with fetal ZDV exposure, including clonal single nucleotide variants (SNVs), small insertions and deletions (indels), and large structural copy number or copy neutral alterations.

RESULTS

We observed no statistically significant difference in the number of SNVs and indels per person in ZDV-exposed children (adjusted ratio [95% confidence interval, CI] for expected number of mutations = 0.79 [0.50--1.22], P = 0.3), and no difference in the number of large structural alterations. Mutations in common clonal hematopoiesis driver genes were not found in the study population. Mutational signature analyses on SNVs detected no novel signatures unique to the ZDV-exposed children and the mutational profiles were similar between the two groups.

CONCLUSION

Our results suggest that clonal hematopoiesis at levels detectable in our study is not strongly influenced by in-utero ZDV exposure; however, additional follow-up studies are needed to further evaluate the safety and potential long-term impacts of in-utero ZDV exposure in HEU children as well as better investigate genomic aberrations occurring late in pregnancy.

Incident disease associations with mosaic chromosomal alterations on autosomes, X and Y chromosomes: insights from a phenome-wide association study in the UK Biobank

BACKGROUND

Mosaic chromosomal alterations (mCAs) are large chromosomal gains, losses and copy-neutral losses of heterozygosity (LOH) in peripheral leukocytes. While many individuals with detectable mCAs have no notable adverse outcomes, mCA-associated gene dosage alterations as well as clonal expansion of mutated leukocyte clones could increase susceptibility to disease.

RESULTS

We performed a phenome-wide association study (PheWAS) using existing data from 482,396 UK Biobank (UKBB) participants to investigate potential associations between mCAs and incident disease. Of the 1290 ICD codes we examined, our adjusted analysis identified a total of 50 incident disease outcomes associated with mCAs at PheWAS significance levels. We observed striking differences in the diseases associated with each type of alteration, with autosomal mCAs most associated with increased hematologic malignancies, incident infections and possibly cancer therapy-related conditions. Alterations of chromosome X were associated with increased lymphoid leukemia risk and, mCAs of chromosome Y were linked to potential reduced metabolic disease risk.

CONCLUSIONS

Our findings demonstrate that a wide range of diseases are potential sequelae of mCAs and highlight the critical importance of careful covariate adjustment in mCA disease association studies.

Abstract 5704: Pan-cancer genomic characterization of patient-matched primary, extracranial, and brain metastases

Brain metastases (BM) occur in 10-30% of patients with cancer. Approximately 200,000 new cases of brain metastases are diagnosed in the United States annually, with median survival after diagnosis ranging from 3 to 27 months. Recently, studies have identified significant genetic differences between BM and their corresponding primary tumors. It has been shown that BM harbor clinically actionable mutations that are distinct from those in the primary tumor samples. Additional genomic profiling of BM will provide deeper understanding of the pathogenesis of BM and suggest new therapeutic approaches.

We performed whole-exome sequencing of BM and matched tumors from 41 patients collected from renal cell carcinoma (RCC), breast cancer, lung cancer, and melanoma, which are known to be more likely to develop BM. We profiled total 126 fresh-frozen tumor samples and performed subsequent analyses of BM in comparison to paired primary tumor and extracranial metastases (ECM). We found that lung cancer shared the largest number of mutations between BM and matched tumors (83%), followed by melanoma (74%), RCC (51%), and Breast (26%), indicating that cancer type with high tumor mutational burden share more mutations with BM. Mutational signatures displayed limited differences, suggesting a lack of mutagenic processes specific to BM. However, point-mutation heterogeneity revealed that BM evolve separately into different subclones from their paired tumors regardless of cancer type, and some cancer driver genes were found in BM-specific subclones. These models and findings suggest that these driver genes may drive prometastatic subclones that lead to BM. 32 curated cancer gene mutations were detected and 71% of them were shared between BM and primary tumors or ECM. 29% of mutations were specific to BM, implying that BM often accumulate additional cancer gene mutations that are not present in primary tumors or ECM. Co-mutation analysis revealed a high frequency of TP53 nonsense mutation in BM, mostly in the DNA binding domain, suggesting TP53 nonsense mutation as a possible prerequisite for the development of BM. Copy number alteration analysis showed statistically significant differences between BM and their paired tumor samples in each cancer type (Wilcoxon test, p < 0.0385 for all). Both copy number gains and losses were consistently higher in BM for breast cancer (Wilcoxon test, p =1.307e-5) and lung cancer (Wilcoxon test, p =1.942e-5), implying greater genomic instability during the evolution of BM.

Our findings highlight that there are more unique mutations in BM, with significantly higher copy number alterations and tumor mutational burden. These genomic analyses could provide an opportunity for more reliable diagnostic decision-making, and these findings will be further tested with additional transcriptomic and epigenetic profiling for better characterization of BM-specific tumor microenvironments.

Citation Format: Olivia W. Lee, Akash Mitra, Won-Chul Lee, Kazutaka Fukumura, Hannah Beird, Miles Andrews, Grant Fischer, John N. Weinstein, Michael A. Davies, Jason Huse, P. Andrew Futreal. Pan-cancer genomic characterization of patient-matched primary, extracranial, and brain metastases [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5704.

Identification of Activators of Human Fumarate Hydratase by Quantitative High-Throughput Screening

Fumarate hydratase (FH) is a metabolic enzyme that is part of the Krebs cycle and reversibly catalyzes the hydration of fumarate to malate. Mutations of the FH gene have been associated with fumarate hydratase deficiency (FHD), hereditary leiomyomatosis and renal cell cancer (HLRCC), and other diseases. Currently, there are no high-quality small-molecule probes for studying human FH. To address this, we developed a quantitative high-throughput screening (qHTS) FH assay and screened a total of 57,037 compounds from in-house libraries in dose-response. While no inhibitors of FH were confirmed, a series of phenyl-pyrrolo-pyrimidine-diones were identified as activators of human FH. These compounds were not substrates of FH, were inactive in a malate dehydrogenase counterscreen, and showed no detectable reduction-oxidation activity. The binding of two compounds from the series to human FH was confirmed by microscale thermophoresis. The low hit rate in this screening campaign confirmed that FH is a "tough target" to modulate, and the small-molecule activators of human FH reported here may serve as a starting point for further optimization and development into cellular probes of human FH and potential drug candidates.

Cytotoxic Profiling of Annotated and Diverse Chemical Libraries Using Quantitative High-Throughput Screening

Cell-based phenotypic screening is a commonly used approach to discover biological pathways, novel drug targets, chemical probes, and high-quality hit-to-lead molecules. Many hits identified from high-throughput screening campaigns are ruled out through a series of follow-up potency, selectivity/specificity, and cytotoxicity assays. Prioritization of molecules with little or no cytotoxicity for downstream evaluation can influence the future direction of projects, so cytotoxicity profiling of screening libraries at an early stage is essential for increasing the likelihood of candidate success. In this study, we assessed the cell-based cytotoxicity of nearly 10,000 compounds in the National Institutes of Health, National Center for Advancing Translational Sciences annotated libraries and more than 100,000 compounds in a diversity library against four normal cell lines (HEK 293, NIH 3T3, CRL-7250, and HaCat) and one cancer cell line (KB 3-1, a HeLa subline). This large-scale library profiling was analyzed for overall screening outcomes, hit rates, pan-activity, and selectivity. For the annotated library, we also examined the primary targets and mechanistic pathways regularly associated with cell death. To our knowledge, this is the first study to use high-throughput screening to profile a large screening collection (>100,000 compounds) for cytotoxicity in both normal and cancer cell lines. The results generated here constitute a valuable resource for the scientific community and provide insight into the extent of cytotoxic compounds in screening libraries, allowing for the identification and avoidance of compounds with cytotoxicity during high-throughput screening campaigns.

A High-Throughput Screen of a Library of Therapeutics Identifies Cytotoxic Substrates of P-glycoprotein

The ATP-binding cassette transporter P-glycoprotein (P-gp) is known to limit both brain penetration and oral bioavailability of many chemotherapy drugs. Although US Food and Drug Administration guidelines require that potential interactions of investigational drugs with P-gp be explored, often this information does not enter the literature. In response, we developed a high-throughput screen to identify substrates of P-gp from a series of chemical libraries, testing a total of 10,804 compounds, most of which have known mechanisms of action. We used the CellTiter-Glo viability assay to test library compounds against parental KB-3-1 human cervical adenocarcinoma cells and the colchicine-selected subline KB-8-5-11 that overexpresses P-gp. KB-8-5-11 cells were also tested in the presence of a P-gp inhibitor (tariquidar) to assess reversibility of transporter-mediated resistance. Of the tested compounds, a total of 90 P-gp substrates were identified, including 55 newly identified compounds. Substrates were confirmed using an orthogonal killing assay against human embryonic kidney-293 cells overexpressing P-gp. We confirmed that AT7159 (cyclin-dependent kinase inhibitor), AT9283, (Janus kinase 2/3 inhibitor), ispinesib (kinesin spindle protein inhibitor), gedatolisib (PKI-587, phosphoinositide 3-kinase/mammalian target of rampamycin inhibitor), GSK-690693 (AKT inhibitor), and KW-2478 (heat-shock protein 90 inhibitor) were substrates. In addition, we assessed direct ATPase stimulation. ABCG2 was also found to confer high levels of resistance to AT9283, GSK-690693, and gedatolisib, whereas ispinesib, AT7519, and KW-2478 were weaker substrates. Combinations of P-gp substrates and inhibitors were assessed to demonstrate on-target synergistic cell killing. These data identified compounds whose oral bioavailability or brain penetration may be affected by P-gp. SIGNIFICANCE STATEMENT: The ATP-binding cassette transporter P-glycoprotein (P-gp) is known to be expressed at barrier sites, where it acts to limit oral bioavailability and brain penetration of substrates. In order to identify novel compounds that are transported by P-gp, we developed a high-throughput screen using the KB-3-1 cancer cell line and its colchicine-selected subline KB-8-5-11. We screened the Mechanism Interrogation Plate (MIPE) library, the National Center for Advancing Translational Science (NCATS) pharmaceutical collection (NPC), the NCATS Pharmacologically Active Chemical Toolbox (NPACT), and a kinase inhibitor library comprising 977 compounds, for a total of 10,804 compounds. Of the 10,804 compounds screened, a total of 90 substrates were identified of which 55 were novel. P-gp expression may adversely affect the oral bioavailability or brain penetration of these compounds.

Discovery of novel inhibitors of human galactokinase by virtual screening

Classic Galactosemia is a potentially lethal autosomal recessive metabolic disorder caused by deficient galactose-1-phosphate uridyltransferase (GALT) that results in the buildup of galactose-1-phosphate (gal-1-p) in cells. Galactokinase (GALK1) is the enzyme responsible for converting galactose into gal-1-p. A pharmacological inhibitor of GALK1 is hypothesized to be therapeutic strategy for treating galactosemia by reducing production of gal-1-p. In this study, we report the discovery of novel series of GALK1 inhibitors by structure-based virtual screening (VS). Followed by an extensive structural modeling and binding mode analysis of the active compounds identified from quantitative high-throughput screen (qHTS), we developed an efficient pharmacophore-based VS approach and applied for a large-scale in silico database screening. Out of 230,000 compounds virtually screened, 350 compounds were cherry-picked based on multi-factor prioritization procedure, and 75 representing a diversity of chemotypes exhibited inhibitory activity in GALK1 biochemical assay. Furthermore, a phenylsulfonamide series with excellent in vitro ADME properties was selected for downstream characterization and demonstrated its ability to lower gal-1-p in primary patient fibroblasts. The compounds described herein should provide a starting point for further development of drug candidates for the GALK1 modulation in the Classic Galactosemia.

Abstract LB-066: A high-throughput screen of an annotated small molecule library identifies substrates of P-glycoprotein

A major difficulty in treating cancer is the development of cellular resistance to chemotherapeutics, a phenomenon known as multidrug resistance (MDR). MDR is primarily conferred by an upregulation of ATP-binding cassette (ABC) transporters, most notably P-glycoprotein (P-gp, MDR1, ABCB1), which are responsible for the active transport of drugs out of the cells thereby minimizing drug-target interactions. While numerous strategies to overcome transporter-mediated MDR have been explored, none have proved successful. An alternative approach is to exploit resistance by identifying drugs that target MDR cells over the nonresistant parental cells from which they were selected. As such, the development of MDR1-selective agents represents a novel and relatively unexplored strategy for resolving multidrug resistance. To identify such agents, we developed a series of robust, high-throughput assays to examine differential toxicity between drug-naïve cancer cell lines and their drug-selected, multidrug-resistant sublines. We performed high-throughput screens against several libraries of annotated compounds including the NCATS Pharmaceutical Collection (NPC), a comprehensive collection of all clinically approved drugs - to identify P-gp substrates, and classes of small molecules that exhibit selective toxicity against MDR tumor lines. Further mechanistic evaluation of these compounds has provided valuable insight into targets or pathways that appear to have been rendered more sensitive to inhibition in the course of multidrug resistance development.

Citation Format: Tobie D. Lee, Olivia W. Lee, Kyle R. Brimacombe, Min Shen, Lu Chen, Rajarshi Guha, Bethelihem Tebase, Robert W. Robey, Suresh V. Ambudkar, Michael M. Gottesman, Matthew D. Hall. A high-throughput screen of an annotated small molecule library identifies substrates of P-glycoprotein [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-066.

High-throughput screening with nucleosome substrate identifies small-molecule inhibitors of the human histone lysine methyltransferase NSD2

The histone lysine methyltransferase nuclear receptor-binding SET domain protein 2 (NSD2, also known as WHSC1/MMSET) is an epigenetic modifier and is thought to play a driving role in oncogenesis. Both NSD2 overexpression and point mutations that increase its catalytic activity are associated with several human cancers. Although NSD2 is an attractive therapeutic target, no potent, selective, and bioactive small molecule inhibitors of NSD2 have been reported to date, possibly due to the challenges of developing high-throughput assays for NSD2. Here, to establish a platform for the discovery and development of selective NSD2 inhibitors, we optimized and implemented multiple assays. We performed quantitative high-throughput screening with full-length WT NSD2 and a nucleosome substrate against a diverse collection of bioactive small molecules comprising 16,251 compounds. We further interrogated 174 inhibitory compounds identified in the primary screen with orthogonal and counter assays and with activity assays based on the clinically relevant NSD2 variants E1099K and T1150A. We selected five confirmed inhibitors for follow-up, which included a radiolabeled validation assay, surface plasmon resonance studies, methyltransferase profiling, and histone methylation in cells. We found that all five NSD2 inhibitors bind the catalytic SET domain and one exhibited apparent activity in cells, validating the workflow and providing a template for identifying selective NSD2 inhibitors. In summary, we have established a robust discovery pipeline for identifying potent NSD2 inhibitors from small-molecule libraries.