Citations

Abstract Pseudouridine (Ψ) is the most prevalent RNA modification in human cells. Although Ψ was among the first post-transcriptional modifications discovered (1951), its biological functions remain poorly understood. More recently, Ψ was incorporated into COVID-19 mRNA vaccine, where it enhances RNA stability and reduces innate immune sensing. However, the precise roles of RNA Ψ in cancer, including leukemia, are largely unknown. Here, we identify RNA Pseudouridine Synthase D4 (RPUSD4) as a novel vulnerability in acute myeloid leukemia (AML) via directly catalyzing mitochondrial RNA (mt-RNA) Ψ formation. We further provide proof-of-concept evidence that targeting RPUSD4 suppresses leukemogenesis and stimulates anti-leukemia immunity. To investigate whether RNA Ψ dysregulation is involved in leukemia, we first compared RNA Ψ levels between primitive CD34+ cells (LSC-enriched) and CD34- bulk cells from multiple primary AML specimens. CD34+ AML cells exhibited significantly elevated RNA Ψ levels. We also examined Ψ levels across various RNA types in AML cells, identifying that mt-RNA contained much higher Ψ levels than other RNA types. These findings imply that RNA Ψ, particularly mt-RNA Ψ, may play a role in LSC biology and leukemogenesis. Further unbiased CRISPR screening revealed RPUSD4 as the most critical Ψ synthase for LSC maintenance. Large-scale transcriptomic and patient data analyses showed that RPUSD4 is highly expressed in AML specimens (P = 3.5 × 10-9), particularly within LSCs (P = 1.4 × 10-18). RPUSD4 knockout (KO) significantly suppressed AML proliferation, reduced mitochondrial OxPhos, and decreased LSC frequency in vitro and substantially delayed AML progression in vivo (MLL-r and FLT3ITD models). Of note, RPUSD4 KO-mediated anti-leukemia effects could be fully rescued by wild-type but not catalytically inactive RPUSD4 both in vitro and in vivo, demonstrating that Ψ synthase activity is essential for its function in leukemia. To profile RPUSD4-dependent Ψ sites, we applied two orthogonal technologies, direct nanopore sequencing and PRAISE sequencing (PMID: 36997645), both capable of detecting Ψ at single-base resolution. These approaches converged on a single RPUSD4-dependent Ψ at position 3,067 on mt-16S rRNA. This Ψ site is essential for maintaining rRNA stability. RPUSD4 KO induced mt-16S rRNA decay, thereby suppressing mitochondrial translation. This led to OxPhos inhibition, growth suppression, and LSC eradication in AML. Mechanistically, RPUSD4 is exclusively localized in mitochondria, where it directly interacts with the mt-RNA exonuclease PNPase. Under physiological conditions, PNPase resides within mitochondria and degrades mt-RNA to prevent accumulation of mitochondrial double-stranded RNA (mt-dsRNA). Upon RPUSD4 depletion, PNPase translocates from mitochondria to the cytosol, resulting in two major consequences: (i) mRNA decay:Cytosolic PNPase degrades mRNAs, particularly the nuclear-encoded mitochondrial mRNAs, such as DHODH(Dihydroorotate dehydrogenase). By retrogradely upregulating DHODH, RPUSD4 promotes de novo pyrimidine synthesis in AML. (ii) Aberrant mt-dsRNA accumulation: The buildup and cytoplasmic release of mt-dsRNA activates “viral mimicry” response that sensitizes AML cells to T cell cytotoxicity. Finally, to therapeutically target RPUSD4, we developed an RNA-based inhibitor, CpG-siRNARPUSD4, by conjugating a specific RPUSD4 siRNA to a Toll-like receptor (TLR9) ligand. CpG-siRNARPUSD4 is specifically internalized by TLR9+ cells, including AML cells, thereby maximizing selectivity and minimizing toxicity. Preclinical studies demonstrate that pharmacologically targeting RPUSD4 significantly prolonged survival across multiple AML models, including patient-derived xenograft (PDX) models, and rendered AML cells more susceptible to T cell–mediated cytotoxicity. Furthermore, the RPUSD4 inhibitor exhibited a promising synergistic effect with DHODH inhibitor in treating relapsed AML in vivo. For instance, in a representative relapsed PDX model, median survival times (in days) were: Ctrl – 28, RPUSD4 inhibitor – 36, DHODH inhibitor – 39, and combination – over 60. In conclusion, our findings uncover a previously unrecognized role of RPUSD4 and mt-RNA Ψ in leukemic metabolism, anti-leukemia immunity, and LSC maintenance. This study also bridges a critical knowledge gap regarding the role of RNA Ψ in leukemogenesis.

Abstract A systematic approach to identifying novel therapeutic strategies is essential for expanding curative options in hematopoietic malignancies such as acute myeloid leukemia (AML). We have recently established a high-resolution genetic platform that enables de novo therapeutic development through the CRISPR-Tiling Instructed Computer-Aided (CRISPR-TICA) workflow (Nat Struct Mol Biol 2024, PMID: 38316881). Using this approach, we further identified a new therapeutic pocket and its lead compound for AML treatment (Sci Adv 2024, PMID: 38394203). Here, we present an integrative pipeline, CRISPR-TICA.ai, which combines CRISPR-based functional genomics with generative artificial intelligence (GenAI)-driven ligand modeling to perform high-throughput evaluation of the top 100 leukemia-essential genes and their therapeutic potential in AML. We first used the CRISPR screen dataset published by Novartis (Cancer Discov 2016, PMID: 27260157), which tile-scanned 68 genes in three cancer cell lines, as the initial training dataset to establish the CRISPR-TICA.ai pipeline. Structurally, ligandable protein surface pockets were identified by employing the P2Rank algorithm (J Cheminform 2018, PMID: 30109435). For each pocket, we used the structure-guided diffusion model DiffSBDD (Nat Comput Sci 2024, PMID: 39653846) to generate previously unseen chemical structures that differ substantially from existing drugs, thereby enabling the exploration of novel chemical space. The model was further fine-tuned using direct preference optimization (NeurIPS 2023) against a curated dataset of known inhibitors to enrich for favorable binding profiles (low binding free energy, ΔG) and calibrated against drug-likeness (QED), synthetic accessibility (SA), lipophilicity (logP), and Lipinski's rule compliance. Additionally, our pipeline integrates ligand–protein contact maps with CRISPR-hypersensitive positions to assess spatial interactions, prioritizing ligands that effectively mask biologically essential residues with high affinity. The utility of CRISPR-TICA.ai in AML drug discovery was evaluated- we selected the top 100 leukemia-essential genes from the DepMap database (https://depmap.org/portal/) and generated custom CRISPR libraries for high-resolution gene tiling screens. These libraries comprised 20,233 sgRNAs to tile-scan all 100 genes (47,901 amino acid residues) in Molm13 AML cells at an average resolution of 2.4 amino acids per sgRNA. This dataset provided in-depth structural and functional input for CRISPR-TICA.ai to examine AI-enabled ligand design for over 300 high-confidence druggable pockets in AML. We further developed a user-friendly, web-based 3D visualization platform that interactively maps functional CRISPR hotspots alongside predicted pockets and ligands to enhance accessibility and reproducibility. This tool allows visualization of CRISPR tiling scores, predicted binding pockets, and ligand prioritization, enabling interactive exploration and application. To annotate therapeutically relevant sites, we incorporated data from multiple genomic and proteomic resources, including AlphaFold protein models, Pfam domain annotations, post-translational modification (PTM) sites, and COSMIC leukemia mutational data. Exportable files and GitHub integration are also provided for advanced users to deploy CRISPR-TICA.ai within their facilities.In summary, our study introduces a scalable, leukemia-focused framework for de novo therapeutic discovery. By integrating high-density CRISPR mutagenesis with diffusion-based GenAI modeling, CRISPR-TICA.ai provides a rational roadmap for compound design targeting residues essential for leukemia maintenance. Importantly, the CRISPR-TICA.ai pipeline is adaptable to CRISPR tiling datasets from solid tumors (e.g., the Novartis dataset), highlighting its versatility across diverse cancer types. This approach is especially promising for addressing historically undruggable and resistance-prone targets in AML and beyond.

Abstract Nucleophosmin mutations are among the most common aberrations in acute myeloid leukemia (AML). We previously uncovered a novel pivotal role for mutant NPM1 (NPM1c) in the nucleus, where it binds chromatin at key self-renewal gene loci, such as HOXA/B and MEIS1, directly regulating oncogenic transcription. How NPM1c regulates the transcriptional activity of its chromatin targets remains unclear. To identify potential nuclear cooperating partners of NPM1c, we employed TurboID proximity labeling of NPM1c and wild-type NPM1 (NPM1wt). Mass spectrometric analysis revealed an enrichment of nucleoporins in the NPM1c interactome, with Nucleoporin 98 (NUP98) emerging as a top candidate. NUP98, a key component of the nuclear pore complex (NPC), has been established as a critical oncogenic player in AML as part of oncogenic fusion proteins. In these oncofusions the N-terminal FG (phenylalanine-glycine) repeat domain of NUP98 is preserved and fused to a diverse set of partner genes. NUP98-fusion partners are believed to mediate the chromatin binding specificity of the oncoprotein while the NUP98 FG repeats have been shown to form biomolecular condensates that enhance transcriptional output. Interestingly, wild-type NUP98 (NUP98wt) itself has been linked to gene regulatory functions during embryonic development and normal hematopoiesis. However, the role of NUP98wt in transcriptional regulation in the context of leukemia remains unresolved. To explore a potential cooperation between NUP98wt and NPM1c we first validated their interaction by co-immunoprecipitation assays. We next wanted to determine whether NUP98 and NPM1c are recruited to the same chromatin sites. To this end, we performed ChIP-seq in an NPM1c endogenous degrader cell line. These experiments revealed co-occupancy of NUP98 at NPM1c target genes and a significant reduction of NUP98 binding upon degradation of NPM1c. These findings suggest that NPM1c is required for the recruitment of NUP98 to key oncogenic target loci. To dissect the functional role of NUP98wt in NPM1c AML, we performed loss of function studies. CRISPR mediated knock-out of NUP98 in NPM1 mutant (OCI-AML3) cells resulted in a significant repression of NPM1c target genes, including HOXA/B and MEIS1. Given the essential nature of NUP98, we also engineered an endogenous NUP98 degrader system in OCI-AML3 and NPM1wt (MV4-11) cells to allow for the study of the effects of rapid protein depletion. Upon degradation of NUP98, OCI-AML3 cells exhibited robust myeloid differentiation (~70% increase in CD11b) and increased apoptosis (~50% increase in Annexin V+). MV411 cells on the other hand did not show the same differentiation phenotype. To characterize the immediate transcriptional consequences of NUP98 depletion, we performed nascent RNAseq after 1 and 3 hours of degradation. In the first hours of degradation we observed a rapid and significant repression of NPM1c target genes such as HOXA/B cluster genes, MEIS1, SMC4, TNRC18, SATB1/2 and UNCX, thus demonstrating the strong dependency of the NPM1c-driven transcriptional program on the presence of NUP98. In contrast, in MV4-11 cells, NUP98 loss had no effect on HOXA/MEIS1 expression, suggesting a leukemia subtype-specific role of NUP98wt. To delineate the domains of NUP98 required for its chromatin function, we performed a CRISPR gene tiling screen of full-length NUP98 (635 sgRNAs) and based on this we generated several domain-deletion mutants for rescue experiments in the NUP98-degrader cell lines. Retroviral overexpression of the N-terminal FG-repeat containing domains of NUP98 was sufficient to rescue cell viability and prevent the differentiation phenotype typically observed upon NUP98 degradation. Strikingly, gene expression analysis showed that the NUP98 FG-repeats were sufficient to restore the expression of HOXA10, MEIS1, and HOXB9 expression. Overall, our study identifies NUP98wt as a critical cofactor for NPM1c-driven oncogenic transcription. NPM1c recruits NUP98 to its chromatin targets, functionally substituting for an oncogenic fusion partner to concentrate transcriptional condensates at oncogenic loci. This establishes a previously unrecognized, subtype-specific dependency on NUP98wt in leukemogenesis.

Abstract Menin, encoded by the MEN1 gene, is a chromatin adaptor critical in AML through its role in the MLL complex. Inhibiting the Menin–MLL interaction promotes differentiation and reduces leukemia burden in MLL-rearranged and NPM1c AMLs, leading to the approval of Menin inhibitors by FDA. However, acquired resistance remains a challenge, highlighting the need to understand long-term effects. To understand the Menin inhibitors' effect in the long-term treatment, we firstly treated the MLL-r and NPM1c AML cell lines for long term and then withdraw the inhibitors to observe the potential recovery of cells. We found the cell growth inhibition and viability decrease were not sustained and proliferation resumed after the withdrawal of 18-30 days treatment of Menin inhibitor both in MLL-r and NPM1c cell lines and NPM1c primary AML cells. In parallel, differentiation cannot be maintained after Menin inhibitor withdrawal. Differentiation marker CD11b expression also gradually lost after 10-day of withdrawal. To determine whether these regrown cells develop resistance, we compared the regrown cells to untreated cells and found that there was no significant difference in IC50 of Menin inhibitors between the regrown and untreated cells, showing the cells regrown due to the reversibility of Menin inhibitors but not resistance. Furthermore, due to the heterogeneous differentiation induced by Menin inhibitors, we compare the effect of differentiation on the cell growth. After 24 days of treatment, CD11bhi and CD11blo cells were sorted after inhibitor removal, we could observe a significant slower cell growth in CD11bhi than CD11blo cells. We also found a CD11bhi group gradually lost the differentiation marker and revert the grow rate as CD11blo. This indicates that these cells underwent dedifferentiation, suggesting that Menin inhibitors alone induce only reversible differentiation. Interestingly, we found the regrown cells silenced HOX/MEIS1 genes permanently showing the HOXA/MEIS1 genes are not playing a role in the long-term treatment of Menin inhibitors. To enhance and stabilize differentiation, we conducted a CRISPR screen targeting chromatin regulators in MOLM13 and OCI-AML3 cells treated with Menin inhibitor or DMSO for 2 weeks. CD11bhi and CD11blo cells were sorted by FACS. Hits included members of the SAGA, LSD1/CoREST, MBD2 NuRD complex, ING5, non-canonical BAF, and MLL/Menin complexes. Knockdown of RCOR1, LSD1, MBD2, MEAF6, KAT6A, and KAT2A enhanced Menin inhibitor–induced differentiation and stabilized it after withdrawal for up to 20 days. We futher screened pharmacological inhibitors of these targets and found that LSD1, KAT6A, and MBD2 inhibitors enhanced differentiation. In particular, combining the experimental MBD2 inhibitor KCC07 with the Menin inhibitor Revumenib accelerated differentiation as early as day 3 (vs. day 7 with Revumenib alone). Long-term co-treatment stabilized differentiation, induced cell death, and suppressed proliferation, indicating chromatin modulation can lock in terminal differentiation, lead to cell death, and potentiate Menin inhibitor effects. RNA-seq of OCI-AML3 cells treated with DMSO, Reumenib, KCC07, or their combination showed that the MBD2/Menin combination inhibition significantly upregulated differentiated monocytes and neutrophils signatures while reducing immature neutrophil signature. GO analysis revealed strong activation of monocyte differentiation and repression of PI3K-AKT signaling. HOXA and MEIS1 expression were only modestly changed, showing the combination mostly enhanced diffrentiation gene programs but not self-renewal maintaining HOX/MEIS1 axis. ATAC-seq revealed globally increased chromatin accessibility in the MBD2/Menin combination inhibition group in comparison with Revumenib only treatment group, with enhanced peaks located predominantly in myeloid differentiation genes, suggesting the MBD2 inhibition also leads to derepression of differentiation related genes repressed by MBD2-NuRD complexes. Our study is the first to demonstrate the reversibility of Menin inhibitor–induced growth inhibition and differentiation. More importantly, we identified differentiation associated chromatin complex targeting (such as MBD2 inhibition) as a low-toxicity strategy that enhances and stabilizes Menin inhibitor–induced differentiation, offering a promising approach to overcome durability limitations in AML therapy.

Abstract Background: Partial tandem duplications of the histone methyltransferase KMT2Agene(KMT2A-PTD) are the most common KMT2A-aberration in adult acute myeloid leukemia (AML). KMT2A-PTD AML represents a high-risk disease subset with a poor prognosis. However, KMT2A-PTD leukemia is under studied, likely due to a lack of experimental models, and therefore the underlying mechanisms of leukemogenesis remain elusive. Since KMT2A-PTD leukemias possess high-level expression of HOXAgenes, similar to KMT2A-rearranged (KMT2A-r) and NPM1c AML, patients with this type of AML are currently enrolled into several phase I/II trials assessing menin inhibitors (MIs). However, mechanistic or clinical evidence for treatment response is lacking. To date, no targeted therapeutic approaches for KMT2A-PTD leukemia are available. Results: To better understand KMT2A-PTD mediated leukemogenesis, we endogenously tagged the KMT2A-PTD or KMT2A-wildtype (WT) allele in EOL-1 cells with a dTAG that can be degraded with PROTACs. Targeted protein degradation showed that the KMT2A-PTD, but not the KMT2A-WT protein, is critical to maintain leukemia cell growth. We identified KMT2A-PTD specific genome-wide chromatin binding sites and direct target genes as assessed by changes in nascent RNA production that started to occur within 30 minutes of KMT2A-PTD degradation. KMT2A-PTD target genes identified in this study included HOXA9, HMX2, HMX3, CDKN2C, MYC and CDK6 among others. Having defined the KMT2A-PTD target gene program, we assessed the effect of MI on KMT2A-PTD function. In KMT2A-PTD cell lines, PDXs and cells from a published murine KMT2A-PTD/FLT3-ITD knockin model, we observed intrinsic resistance to revumenib characterized by retained chromatin binding of KMT2A-PTD, but not KMT2A-WT after MI treatment. We next defined critical domains for KMT2A-PTD function via a KMT2A domain scan. This revealed the CXXC domain and AT hooks as critical dependencies in EOL-1 cells. Overexpression of KMT2A or mutants with duplicated domains in 293T cells showed that a duplication of the CXXC domain or the AT hooks is sufficient to mediate retained KMT2A chromatin binding under MI. Therefore, the resistance to MIs is likely due to the duplicated protein of KMT2A subverting menin function at critical target loci. Given that KMT2A-PTD remains chromatin-bound upon menin inhibition, we focused on ENL as a potential regulator of leukemia gene expression programs. In KMT2A-r and NPM1c leukemia, the ENL protein has been shown to be a critical dependency as it associates with acetyl lysine via its YEATS domain. ENL/AF9 YEATS inhibitors reverse ENL-dependent gene expression including HOXA9 and MYC. Using the small molecules TDI-11055 and TM-7, we show that YEATS inhibition leads to loss of members of the super-elongation complex and DOT1L from KMT2A-PTD driven loci and downregulation of target gene expression. Treatment of KMT2A-PTD PDXs with YEATS inhibitors induced differentiation and significantly reduced leukemia burden in vivo. Interestingly, we show that in contrast to previous findings in KMT2A-r leukemia, loss of ENL alone is insufficient to abrogate leukemic proliferation of EOL-1 cells. Instead, by combining ENL degradation with CRISPR-Cas9 mediated knockdown of AF9, we find that both YEATS proteins, ENL and its paralogue AF9, support aberrant gene expression in KMT2A-PTD leukemia. Finally, we show that the novel combination of MI and YEATS inhibition (revumenib plus TDI-11055) synergistically affects proliferation and induces differentiation in cell line and PDX models of KMT2A-PTD leukemia, which in turn prolongs survival of mice with KMT2A-PTD leukemia. Conclusions: KMT2A-PTD leukemia is dependent on the mutated, but not the WT KMT2A allele. It is characterized by a relative, intrinsic resistance to MI monotherapy, which is mediated by a duplication of the CXXC domain and AT hooks of KMT2A. Targeting both, the ENL and AF9 YEATS domain, is a possible treatment strategy and when combined with revumenib, YEATS inhibition has synergistic effects and overcomes intrinsic MI resistance. However, based on our studies, MI monotherapy may not be effective for most patients with KMT2A-PTD leukemia. Given that numerous compounds targeting the ENL (and AF9) YEATS domain are under study and MIs have recently obtained FDA approval, the combination of MI and YEATS inhibition could be translated into clinical trials for patients with KMT2A-PTD leukemia in the relatively near future.

Importance Despite treatment advances, metastatic recurrence continues to be a leading cause of morbidity and mortality. Empirical data on the incidence and survival after metastatic recurrence remain limited, as cancer registries historically do not collect data on recurrence. Objective To estimate the cumulative incidence (CMI) of metastatic recurrence among adolescents and young adults diagnosed with earlier-stage disease and compare survival to those with metastatic disease at diagnosis. Design, Setting, Participants This was a retrospective cohort study of adolescents and young adults aged 15 to 39 years who were diagnosed with nonmetastatic cancers from 2006 to 2018. Adolescents and young adults were identified from the California Cancer Registry linked with statewide hospitalization, emergency department, and ambulatory surgery encounters from the California Department of Health Care Access and Information. Data were analyzed from December 2023 to June 2025. Exposures Cancer types, including melanoma, sarcoma, and breast, cervical, colorectal, testicular, and thyroid cancers. Main Outcomes and Measures Metastatic recurrence was identified using International Classification of Diseases, Ninth Revision, Clinical Modification, and Tenth Revision, Clinical Modification, metastatic disease codes at least 6 months after cancer diagnosis or from an underlying cancer cause of death. Follow-up was through December 31, 2020. Results Of a total of 48 406 adolescents and young adults (median [IQR] age at diagnosis, 33.0 [28.0-37.0] years; 67.4% female), 9.2% had metastatic disease at diagnosis, and 9.5% had metastatic recurrence. Among 43 935 adolescents and young adults who presented with nonmetastatic disease, the 5-year CMI of metastatic recurrences was highest among patients with sarcoma (24.5%; 95% CI, 22.6%-26.6%) and colorectal cancer (21.8%; 95% CI, 20.3%-23.4%) and intermediate for cervical (16.3%; 95% CI, 15.0%-17.6%) and breast (14.7%; 95% CI, 14.0%-15.4%) cancers. The CMI for metastatic recurrence increased with increasing stage at diagnosis, with 5-year CMIs higher than 30% for all stage III cancers (except thyroid). The 5-year CMI of metastatic recurrence also increased over time for cervical cancer (2006-2009: 12.7% [95% CI, 10.8%-14.8%]; 2015-2018: 20.4% [95% CI, 17.5%-23.6%]) and decreased for colorectal cancer (2006-2009: 24.4% [95% CI, 21.3%-27.6%]; 2015-2018: 19.2% [95% CI, 16.4%-22.2%]). Survival after metastatic recurrence was worse than metastatic disease at diagnosis for all cancer types, except for testicular and thyroid cancers. Conclusions and Relevance The findings from this cohort study highlight the overall burden of metastatic disease in adolescents and young adults, expanding the knowledge of metastatic recurrences that help improve care for adolescent and young adult survivors throughout the cancer survivorship spectrum.

Background Migraine is a highly prevalent neurological disorder with many treatment options, both pharmacological and non-pharmacological. Artificial intelligence (AI) has great potential to optimize treatment selection strategies for individual patients. This review provides an overview of AI models and the techniques used to predict migraine treatment outcomes. Methods We conducted a literature search in PubMed and examined studies that reported employing AI models to predict migraine preventive and acute treatment outcomes. We also explored incorporating AI/machine learning to enhance personalized migraine treatment strategies, including forecasting migraine attacks. Additionally, we summarized future research directions, including incorporating multimodality data, using AI frameworks for the discovery of novel treatment targets, and advancing the field with innovative AI techniques such as digital twins, conversational AI and virtual AI agents. Results Studies have employed ML and deep learning on a combination of clinical features and imaging data to predict acute or preventive migraine treatment outcomes with reported success. Continued model optimization, validation, and prospective assessment of the clinical utility of deploying ML models in real-world settings are crucial. Conclusions While AI has demonstrated success in predicting migraine treatment responses, future research incorporating novel AI techniques and diverse data sources could pave the way to advance personalized migraine treatment.

A 44-year-old recent heart transplant recipient supported by VA-ECMO presented to the operating room (OR) for left ventricular (LV) vent removal. She had a history of double-inlet LV with right atrioventricular valve atresia and transposition of great arteries, status post fenestrated Fontan complicated by end-stage heart failure. Three days ago, she underwent a fourth sternotomy and orthotopic heart transplant complicated by coagulopathy and severe bi-ventricular dysfunction necessitating initiation of central VA-ECMO. Due to massive blood product transfusion and ventricular dilatation, an apical LV vent was inserted. Postoperatively the arterial line waveform remained non-pulsatile. The patient was brought to the OR for mediastinal debridement and removal of the LV vent for the purpose of assessing ventricular function and improving arterial pulsatility. Pulse pressure remained negligible at an ECMO flow of 4.5 L/min. Transeosphageal echocardiography (TEE) demonstrated extensive thrombosis of the aortic root, particularly involving the right and non-coronary sinuses (Fig 1a). The aortic valve (AV) did not open. Patency of the left main coronary ostium was evident by color Doppler (Fig 1b) although no right coronary artery (RCA) flow could be visualized. The tip of LV vent was seen tenting the anterior leaflet of mitral valve (MV) causing significant regurgitation. (Fig. 2a-d) After vent removal, LV contraction gradually increased and the AV began to open. This progressively dislodged thrombus from the aortic root. At the conclusion of imaging, there was a highly mobile, bi-lobed thrombus attached to the sinotubular junction (Fig 1c-d). Right ventricular (RV) function remained severely reduced. Moderate mitral regurgitation persisted, arising from A2 leaflet prolapse. This patient subsequently underwent transcatheter thrombectomy and aspiration of the aortic root with cerebral protection device. Coronary angiogram confirmed proximal RCA occlusion (Fig. 3). Attempts to remove RCA thrombus were only partially successful. She eventually required a second heart transplant due to RV infarction. Discussion: This case illustrates a TEE-detected complication of excessive LV venting during VA-ECMO support, namely aortic root thrombosis associated with lack of AV opening. TEE also demonstrated the associated complications of RCA occlusion and iatrogenic mitral valve injury. Unfortunately, these complications were not detected soon enough to avoid RV infarction.