Genome-wide association studies (GWAS) have discovered thousands of risk loci for common, complex diseases, each of which could point to genes and gene programs that influence disease. For some diseases, it has been observed that GWAS signals converge on a smaller number of biological programs, and that this convergence can help to identify causal genes. However, identifying such convergence remains challenging: each GWAS locus can have many candidate genes, each gene might act in one or more possible programs, and it remains unclear which programs might influence disease risk. Here, we developed a new approach to address this challenge, by creating unbiased maps to link disease variants to genes to programs (V2G2P) in a given cell type. We applied this approach to study the role of endothelial cells in the genetics of coronary artery disease (CAD). To link variants to genes, we constructed enhancer-gene maps using the Activity-by-Contact model. To link genes to programs, we applied CRISPRi-Perturb-seq to knock down all expressed genes within +/-500 Kb of 306 CAD GWAS signals and identify their effects on gene expression programs using single-cell RNA-sequencing. By combining these variant-to-gene and gene-to-program maps, we find that 43 of 306 CAD GWAS signals converge onto 5 gene programs linked to the cerebral cavernous malformations (CCM) pathway, which is known to coordinate transcriptional responses in endothelial cells, but has not been previously linked to CAD risk. The strongest regulator of these programs is TLNRD1, which we show is a new CAD gene and novel regulator of the CCM pathway. TLNRD1 loss-of-function alters actin organization and barrier function in endothelial cells in vitro, and heart development in zebrafish in vivo. Together, our study identifies convergence of CAD risk loci into prioritized gene programs in endothelial cells, nominates new genes of potential therapeutic relevance for CAD, and demonstrates a generalizable strategy to connect disease variants to functions.

Amplification of MYCN is a poor prognostic feature in neuroblastoma (NBL) indicating aggressive disease. We and others have shown BET bromodomain inhibitors (BETi) target MYCN indirectly by downregulating its transcription. Here we sought to identify agents that synergize with BETi and to identify biomarkers of resistance. We previously performed a viability screen of ∼1,900 oncology-focused compounds combined with BET bromodomain inhibitors against MYCN -amplified NBL cell lines. Reanalysis of our screening results prominently identified inhibitors of aurora kinase A (AURKAi) to be highly synergistic with BETi. We confirmed the anti-proliferative effects of several BETi+AURKAi combinations in MYCN -amplified NBL cell lines. Compared to single agents, these combinations cooperated to decrease levels of N-myc. We treated both TP53 -wild type and mutant, MYCN -amplified cell lines with the BETi JQ1 and the AURKAi Alisertib. The combination had improved efficacy in the TP53 -WT context, notably driving apoptosis in both genetic backgrounds. JQ1+Alisertib combination treatment of a MYCN -amplified, TP53 -null or TP53 -restored genetically engineered mouse model of NBL prolonged survival better than either single agent. This was most profound with TP53 restored, with marked tumor shrinkage and apoptosis induction in response to combination JQ1+Alisertib. BETi+AURKAi in MYCN -amplified NBL, particularly in the context of functional TP53 , provided anti-tumor benefits in preclinical models. This combination should be studied more closely in a pediatric clinical trial.

Somatic mutations are rare in pediatric AML (pAML), indicating alternate strategies are needed to identify targetable dependencies. We performed the first enhancer mapping of 3 pAML in 22 patient samples. Generally, pAML samples were distinct from adult AML 4 samples, and MLL (KMT2A)-rearranged samples were also distinct from non-KMT2A-5 rearranged samples. Focusing specifically on super-enhancers (SEs), we identified SEs 6 associated with many known leukemia regulators. The retinoic acid receptor alpha 7 (RARA) gene was differentially regulated in our cohort, and a RARA associated SE was 8 detected in 64% our cohort across all cyto/molecular subtypes tested. RARA SE-positive 9 pAML cell lines and samples demonstrated high RARA mRNA levels. These samples 10 were specifically sensitive to the synthetic RARA agonist tamibarotene in vitro, with 11 slowed proliferation, apoptosis induction, differentiation, and upregulated retinoid target 12 gene expression, compared to RARA SE-negative samples. Tamibarotene prolonged 13 survival and suppressed the leukemia burden of a RARA SE-positive pAML patient-14 derived xenograft (PDX) mouse model compared to a RARA SE-negative PDX. Our work 15 demonstrates that examining chromatin regulation can identify new, druggable 16 dependencies in pAML and provides rationale for a pediatric tamibarotene trial in children 17 with RARA-high AML.

Introduction: New approaches to find and then drug pediatric acute myeloid leukemia (AML)-specific targets are clearly needed to help the nearly 35% of patients who still die from the disease. While RARA is a known druggable target in acute promyelocytic leukemia (APL), the utility of using retinoic acid agonists in non-APL AML has not proven consistently beneficial. Super enhancers (SEs), large regions of highly active chromatin, define cell state and cell identity by regulating oncogenes in many cancers. Recent enhancer profiling of 66 adult non-APL AML patient samples revealed SE-defined, prognostically relevant subgroups. An SE was detected at the retinoic acid receptor alpha (RARA) gene locus in 59% of the samples, which were sensitive to the second-generation retinoic acid agonist tamibarotene which has led to a phase II clinical trial. This study confirms that characterization of the chromatin-defined dependencies in specific cancers can pinpoint targets which can be drugged. We are delineating the transcriptional regulation of pediatric AML (pAML) by SE analysis, which has already elucidated deeper insights into pediatric leukemogenesis, as typified by strong RARA dependence in a majority of pAML. Methods: Three AML cell lines and 19 pAML primary samples were enhancer profiled by H3K27Ac chromatin immunoprecipitation followed by massively parallel sequencing (ChIP-seq). SEs were detected and assigned to genes using the rank ordering of super-enhancers (ROSE) algorithm. Tamibarotene treatment of cell lines and patient samples were assessed for gene and protein expression changes and phenotypic differences. For in vivo assessment, 200,000 cells of a RARA SE+ pAML patient sample were injected into each NSGS mouse by tail-vein injection. One week after injection, tamibarotene (6mg/kg) or vehicle treatment was initiated by gavage (n=7 each arm). Peripheral blood monitoring of leukemia burden was determined flow cytometry. Results: The primary pAML sample cohort encompassed the diverse pAML cytogenetic subtypes (Fig 1a), with an overrepresentation of KMT2A rearrangements (n=9, 47%). The number of unique enhancer regions was nearly saturated in the 19 samples. Median SE size was 3,780bp, much larger than the 511bp of typical enhancers. When SE regions across all samples were clustered together, a RARA SE was seen in two of the ten clusters (Fig 1b). Eleven of the 19 samples (58%) contained a RARA SE, crossing multiple cytogenetic subtypes (Fig 1c). Tamibarotene treatment of RARA SE+ pAML cell lines and patient samples suppressed proliferation and increased apoptosis (detected by annexin V+), with minimal effect in Kasumi, a pAML cell line without a RARA SE (Fig 2a). In the RARA SE+ cell lines and samples only, tamibarotene increased CD38 (a myeloid differentiation marker usually suppressed by ligand-unbound RARA) (Fig 2b). High RARA mRNA levels confirmed the SE assignments in both cell lines and patient samples (Fig 2c). Tamibarotene induced the transcription of DHRS3 (another RARA target gene used as a pharmacodynamic biomarker in the adult tamibarotene phase II trial) (Fig 2d). Tamibarotene suppressed colony formation ability in RARA SE+ cell lines. An ongoing RARA SE+ patient-derived pAML xenograft confirmed tamibarotene markedly suppressed disease progression (Fig 3), with vehicle mice requiring euthanasia 42 days after tail-vein injection for significant disease burden, while the tamibarotene treated mice continued to be well-appearing at the same timepoint. Conclusion: We have profiled the enhancer landscapes of 19 primary pAML samples, the largest dataset of its kind, and seen a high frequency of a RARA SE in pAML. Tamibarotene has anti-proliferative, proapoptotic, and on-target pro-differentiation effects in RARA SE+ pAML in vitro and marked anti-leukemia activity in vivo. Given these positive findings, we are evaluating combinations of other AML-active agents with tamibarotene. Additionally, as there is a range of sensitivity to tamibarotene in RARA SE+ samples, we are also interrogating other SE-regulated genes interacting with RARA that may predict degree of response or resistance to tamibarotene. Our studies confirm that studying the transcriptional regulation of pAML samples through SE analysis can identify druggable targets and also lay the preclinical foundation for a biomarker-defined tamibarotene trial in pediatric AML. Disclosures Wei: NHI NHLBI Grant: Other: received funding . Lin:Syros Pharmaceuticals: Equity Ownership, Patents & Royalties.

Genome editing of primary human cells with CRISPR‐Cas9 is a powerful tool to study gene function. For many cell types, there are efficient protocols for editing with optimized plasmids for Cas9 and sgRNA expression. Vascular cells, however, remain refractory to plasmid‐based delivery of CRISPR machinery for in vitro genome editing due to low transfection efficiency, poor expression of the Cas9 machinery, and toxic effects of the selection antibiotics. Here, we describe a method for high‐efficiency editing of primary human vascular cells in vitro using nucleofection for direct delivery of sgRNA:Cas9‐NLS ribonucleoprotein complexes. This method is more rapid and its high editing efficiency eliminates the need for additional selection steps. The edited cells can be employed in diverse applications, such as gene expression measurement or functional assays to assess various genetic perturbation effects in vitro. This method proves effective in vascular cells that are refractory to standard genome manipulation techniques using viral plasmid delivery. We anticipate that this technique will be applied to other non‐vascular cell types that face similar barriers to efficient genome editing. © 2021 Wiley Periodicals LLC. Basic Protocol: CRISPR‐Cas9 genome editing of primary human vascular cells in vitro

Introduction: Nearly 35% of children with acute myeloid leukemia (AML) die, despite aggressive but toxic and nonspecific therapies. New approaches to find and drug pediatric AML targets are clearly needed. Super enhancers (SEs), large regions of highly active chromatin, define cell state and cell identity by regulating oncogenes in many cancers. Recent enhancer profiling of 66 adult AML patient samples revealed SE-defined, prognostically relevant subgroups. An SE was at the retinoic acid receptor alpha (RARA) gene locus in 59% of the samples, which were sensitive to the RARA agonist tamibarotene. We are delineating the transcriptional regulation of pediatric AML (pAML) by SE analysis, which has already elucidated deeper insights into pediatric leukemogenesis, as typified by RARA regulation. Methods: Four AML/APL cell lines and 19 pAML primary samples were enhancer profiled by H3K27Ac chromatin immunoprecipitation followed by massively parallel sequencing (ChIP-seq). SEs were detected and assigned to genes using the rank ordering of super-enhancers (ROSE) algorithm. Tamibarotene treatment of cell lines and patient samples were assessed for gene and protein expression changes and phenotypic differences. Results: The primary pAML sample cohort encompassed the diverse pAML cytogenetic subtypes, with an over-representation of KMT2A rearrangements (n=9, 47%). The number of unique enhancer regions was nearly saturated in the 19 samples. Median SE size was 3,780bp, much larger than the 511bp of typical enhancers. When SE regions across all samples were clustered together, a RARA SE was seen in two of the ten clusters. Some of the highly correlated, SE-associated genes in these clusters encode proteins involved in inflammation. Eleven of the 19 samples (58%) contained a RARA SE, crossing multiple cytogenetic subtypes. Tamibarotene treatment of RARA SE+ pAML cell lines and patient samples reduced cell viability and increased apoptosis (detected by annexin V+ and activated caspase 3/7), with no effect in RARA SE- pAML samples. In the RARA SE+ samples, tamibarotene increased CD38 (a myeloid differentiation marker usually suppressed by ligand-unbound RARA) and DHRS3 (another RARA target gene used as a pharmacodynamic biomarker in the adult tamibarotene phase II trial). Conclusion: We have profiled the enhancer landscapes of 19 primary pAML samples, the largest dataset of its kind, and have seen a high frequency of a RARA SE in pAML. Tamibarotene has antiproliferative, proapoptotic, and prodifferentiation effects in RARA SE+ pAML. We are confirming these results in a RARA SE+ patient-derived xenograft mouse model, evaluating combinations, and interrogating other SE-regulated genes interacting with RARA that may predict degree of response or resistance to tamibarotene. Our studies confirm that studying the transcriptional regulation of pAML samples through SE analysis can identify druggable targets and also lay the preclinical foundation for a biomarker-defined tamibarotene trial in pediatric AML. Citation Format: Monika Perez, Alfred Daramola, Oscar Sias-Garcia, Helen Wei, Nikitha Cherayil, Charles Y. Lin, Joanna S. Yi. Defining the transcriptional regulation of pediatric AML as a new strategy to find potential druggable vulnerabilities [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A55.

Introduction: Phenotypic switching of vascular cells is a complex process associated with vascular disorders, including thoracic aortic aneurysm (TAA). Vascular smooth muscle cells (VSMCs) appear to switch from a contractile to synthetic phenotype in TAA. Single nuclear RNA-seq (snRNA-seq) of normal human and TAA aortas may be used to characterize cell heterogeneity of normal aortas, population shifts in disease, and the transcriptional profile of VSMC phenotypic switching. Hypothesis: snRNA-seq of normal and TAA aortas will identify the cell heterogeneity and transcriptional profiles of TAA. Methods: We performed snRNA-seq of 5 aortas from 2 normal and 3 TAA patients. We used a 10X-CellBender pipeline for profiling and analysis. Results: snRNA-seq identified 6 major cell types. The majority were VSMCs, exhibiting 4 sub-populations in all specimens (a). Cell distribution comparisons showed VSMC1 (ELN, PKD1, FLNA high) and VSMC2 (PRKG1, PDE3A, PCDH7 high) to be differentially-enriched in controls and TAA samples, respectively (b,c). Gene set and trajectory analyses confirmed prior observations of phenotypic switching (d,e). Genes associated with switching in VSMCs included TAA genes (PRKG1, PKD1, FLNA) with concordance of expression and putative function of Mendelian variants (i-k). Cell junction and regulation of muscle contraction pathways drove trajectory. We further assessed cell-type heritability of vascular GWAS variants (h). These gene sets were differentially-regulated between control and TAA. The strongest association was between VSMC2 and ascending aortic size (h). Conclusions: In this study, we demonstrated a dissociation bias-free method for snRNA-Seq of human vasculature. We confirmed enrichment of synthetic VSMCs in TAA and implicate phenotypic switching as a pathologic mechanism. Our study identifies a cell type-specific transcriptional profile of aortopathy genes, which may drive TAA and represent therapeutic targets.