Chun-Wei Chen

De novo purine synthesis is required to maintain tumor growth; however, its impact on therapy resistance remains unclear. Here, through a dynamic BH3-priming-based CRISPR screen, we found that deletion of ADSS2, which encodes the adenylosuccinate synthase 2 enzyme essential for adenosine monophosphate (AMP) synthesis, re-sensitizes drug-resistant acute myeloid leukemia cells to venetoclax and a myeloid cell leukemia-1 (MCL1) inhibitor. Single-cell sequencing analysis of patient-derived xenograft samples revealed a positive association of high ADSS2 activity in TP53-mutant cells with poor responsiveness to venetoclax. We developed an ADSS2 antagonist, which synergized with BH3 mimetics to promote apoptosis in preclinical models. Mechanistically, sensitization mediated by ADSS2 targeting correlated with downregulated AMP-activated protein kinase activity, which in resistant cells promotes mitophagy to eliminate damaged mitochondria after BH3 mimetic treatment. These data show that AMP synthesis promotes BH3 mimetic resistance and that combining ADSS2 targeting with BH3 mimetics represents a promising anti-cancer approach.

N7-methylguanosine (m7G), a prevalent modification in transfer RNAs (tRNAs), is primarily catalyzed by the methyltransferase METTL1. Although growing evidence supports a role for METTL1 in various tumors, its therapeutic potential and precise function in leukemia stem cell (LSC) homeostasis remain largely unexplored. Here, we identify METTL1 as a key regulator of LSC self-renewal and homing within bone marrow (BM) microenvironment through catalyzing m7G formation on a specific tRNA, tRNAPheGAA, thereby promoting leukemogenesis. Mechanistically, METTL1 loss significantly reduces m7G abundance and steady-state levels of tRNAPheGAA, leading to translation suppression and degradation of transcripts enriched with tRNAPheGAA-related codons, such as hematopoietic cell kinase (HCK). Decreased HCK expression disrupts CXCR4 signaling, impairing LSC self-renewal and BM homing. Therapeutically, we characterized a small-molecule METTL1 inhibitor (M1i; NSC137443), through high-throughput screening. Pharmacological inhibition of METTL1 demonstrated potent antitumor efficacy by reducing tRNA m7G levels and disrupting the tRNAPheGAA/HCK/CXCR4 cascade. Notably, targeting METTL1 significantly reduces LSC frequency, delays leukemogenesis, and prolongs survival in multiple acute myeloid leukemia models. Together, our findings establish a previously unrecognized role for METTL1 and its target tRNAPheGAA in LSC homeostasis and provide compelling proof-of-concept evidence that METTL1 is a druggable epitranscriptomic target for antileukemia therapy.

Table S1. Read normalized ratios of ChIPseq signal of untreated versus dTAG-13 treated OCI-AML3-NPM1c-FKBP12 cells.Table S2. Summary of NPM1c and NPM1 Chromatin Binding Targets.Table S3. Patient info for patient derived xenograft (PDX) models used.Table S4. ChIPseq reads per kilobase (rpk) data summary of PDX samples with NPM1c-Ab and NPM1-Ab.Table S5. RNAseq differential expression data of OCI-AML3-NPM1c-FKBP12 treated with dTag-13 for 3 or 24 h and OCI-AML3 cells treated with Selinexor for 6 h.Table S6. SLAMseq differential expression data of OCI-AML3-NPM1c-FKBP12 cells treated with dTag-13 for 15, 30, 60, 120 or 180 minutes.Table S7. PROseq differentially transcribed genes in OCI-AML3-NPM1c-FKBP12 cells treated with dTag-13 for 30 or 60 minutes and OCI-AML3 cells treated with VTP-50469 for 48 hours.Table S8. CRISPR tiling screen with NPM1 WT specific guides (blue) and NPM1c specific guides (red).Table S9. ChIPseq rpk values for CRM1 and HA ChIPs in 293T cells.Table S10. RNAseq differential gene expression analysis in 293T cells after overexpression of NPM1c-HA compared to all other samples (MIG, NPM1wt-HA and AS1-HA).Table S11. Fold change in ChIPseq differential peak interval signal in OCI-AML3 cells treated with Selinexor (100 nM, 6 hours) or VTP-50469 (330 nM, 96 hours).Table S12. Oligos used in this study.Table S13. Antibodies used in this study.Table S14. Summary of total and mapped reads of ChIPseq samples.

Supplementary Figure 1. NPM1c degradation leads to differentiation of OCI-AML3 cells.Supplementary Figure 2. NPM1c chromatin targets identified in OCI-AML3-NPM1c-FKBP12 cells and validated by targeted degradation.Supplementary Figure 3. Motif analysis reveals developmental transcription factor binding sites at NPM1c bound regions.Supplementary Figure 4. NPM1c chromatin targets are highly expressed in patient samples of NPM1c AML.Supplementary Figure 5. NPM1c degradation has rapid effects on transcription at it target genes.Supplementary Figure 6. Transcriptional machinery is lost from NPM1c targets after 1 hour of NPM1c degradation.Supplementary Figure 7. CRIPSR domain scan reveals specific dependency of NPM1 mutant cells on the AS2 region.Supplementary Figure 8. The AS2 region affects NPM1c localization in 293T and OCI-AML3 cells.Supplementary Figure 9. Selinexor treatment disrupts NPM1c chromatin binding.Supplementary Figure 10. NPM1c cooperates with MLL1 to drive oncogenic gene expression.Supplementary Figure 11. NPM1c is selectively lost from chromatin in response to Menin inhibitor treatment.Supplementary Figure 12. Menin-MLL inhibition leads to selective loss of NPM1c target gene expression.

Stress granules (SGs) and processing bodies (PBs), assembled via liquid-liquid phase separation (LLPS), are critical for spatial regulation of gene expression in the cytoplasm. However, their roles in tumorigenesis remain poorly understood. Here, we show DEAD-box helicase 6 (DDX6) as the most promising vulnerability in acute myeloid leukemia (AML) through in vitro and in vivo CRISPR screenings using a specialized library targeting RNA-binding proteins enriched in SGs and PBs. Knockout (KO) of DDX6 significantly delays leukemogenesis with minimal impact on normal hematopoiesis. Importantly, the functions of DDX6 in AML depend largely on its ability to trigger LLPS and PB assembly. Mechanistically, PBs serve as “reservoirs” for the mRNAs interacting directly with DDX6 and having low GC content. DDX6 KO leads to rapid PB dissolution and release of PB-enriched mRNAs, such as BCAT1, into the cytosol, where these transcripts undergo degradation. By reducing BCAT1 levels, DDX6 KO reprograms amino acid metabolism and sensitizes AML cells to cytarabine chemotherapy.

Metabolic reprogramming of amino acids represents a vulnerability in cancer cells, yet the mechanisms underlying serine metabolism in acute myeloid leukemia (AML) and leukemia stem/initiating cells (LSCs/LICs) remain unclear. Here, we identify RNA N⁶-methyladenosine (m⁶A) modification as a key regulator of serine biosynthesis in AML. Using a CRISPR/Cas9 screen, we find that depletion of m⁶A regulators IGF2BP3 or METTL14 sensitizes AML cells to serine and glycine (SG) deprivation. IGF2BP3 recognizies m⁶A on mRNAs of key serine synthesis pathway (SSP) genes (e.g., ATF4, PHGDH, PSAT1), stabilizing these transcripts and sustaining serine production to meet the high metabolic demand of AML cells and LSCs/LICs. IGF2BP3 silencing combined with dietary SG restriction potently inhibits AML in vitro and in vivo, while its deletion spares normal hematopoiesis. Our findings reveal the critical role of m⁶A modification in the serine metabolic vulnerability of AML and highlight the IGF2BP3/m⁶A/SSP axis as a promising therapeutic target.

Cell signaling pathways are enriched for biological processes crucial for cellular communication, response to external stimuli, and metabolism. Here, a cell signaling‐focused CRISPR screen identified cytochrome c oxidase subunit 4 isoform 1 (COX4I1) as a novel vulnerability in acute myeloid leukemia (AML). Depletion of COX4I1 hindered leukemia cell proliferation and impacted in vivo AML progression. Mechanistically, loss of COX4I1 induced mitochondrial stress and ferroptosis, disrupting mitochondrial ultrastructure and oxidative phosphorylation. CRISPR gene tiling scans, coupled with mitochondrial proteomics, dissected critical regions within COX4I1 essential for leukemia cell survival, providing detailed insights into the mitochondrial Complex IV assembly network. Furthermore, COX4I1 depletion or pharmacological inhibition of Complex IV (using chlorpromazine) synergized with venetoclax, providing a promising avenue for improved leukemia therapy. This study highlights COX4I1, a nuclear encoded mitochondrial protein, as a critical mitochondrial checkpoint, offering insights into its functional significance and potential clinical implications in AML.

Reduced responsiveness of precursor B-acute lymphoblastic leukemia (BCP-ALL) to chemotherapy can be first detected in the form of minimal residual disease leukemia cells that persist after 28 days of initial treatment. The ability of these cells to resist chemotherapy is partly due to the microenvironment of the bone marrow, which promotes leukemia cell growth and provides protection, particularly under these conditions of stress. It is unknown if and how the glycocalyx of such cells is remodelled during the development of tolerance to drug treatment, even though glycosylation is the most abundant cell surface post-translational modification present on the plasma membrane. To investigate this, we performed omics analysis of BCP-ALL cells that survived a 30-day vincristine chemotherapy treatment while in co-culture with bone marrow stromal cells. Proteomics showed decreased levels of some metabolic enzymes. Overall glycocalyx changes included a shift from Core-2 to less complex Core-1 O-glycans, and reduced overall sialylation, with a shift from α2-6 to α2-3 linked Neu5Ac. Interestingly, there was a clear increase in bisecting complex N-glycans with a concomitant increased mRNA expression of MGAT3 , the only enzyme known to form bisecting N-glycans. These small but reproducible quantitative differences suggest that individual glycoproteins become differentially glycosylated. Glycoproteomics confirmed glycosite-specific modulation of cell surface and lysosomal proteins in drug-tolerant BCP-ALL cells, including HLA-DRA, CD38, LAMP1 and PPT1. We conclude that drug-tolerant persister leukemia cells that grow under continuous chemotherapy stress have characteristic glycotraits that correlate with and perhaps contribute to their ability to survive and could be tested as neoantigens in drug-resistant leukemia.

Epigenetic dysregulation has been reported in multiple cancers including leukemias. Nonetheless, the roles of the epigenetic reader Tudor domains in leukemia progression and therapy remain unexplored. Here, we conducted a Tudor domain–focused CRISPR screen and identified SGF29, a component of SAGA/ATAC acetyltransferase complexes, as a crucial factor for H3K9 acetylation, ribosomal gene expression, and leukemogenesis. To facilitate drug development, we integrated the CRISPR tiling scan with compound docking and molecular dynamics simulation, presenting a generally applicable strategy called CRISPR-Scan Assisted Drug Discovery (CRISPR-SADD). Using this approach, we identified a lead inhibitor that selectively targets SGF29’s Tudor domain and demonstrates efficacy against leukemia. Furthermore, we propose that the structural genetics approach used in our study can be widely applied to diverse fields for de novo drug discovery.

The plasma membrane is enriched for receptors and signaling proteins that are accessible from the extracellular space for pharmacological intervention. Here we conducted a series of CRISPR screens using human cell surface proteome and integrin family libraries in multiple cancer models. Our results identified ITGAV (integrin αV) and its heterodimer partner ITGB5 (integrin β5) as the essential integrin α/β pair for cancer cell expansion. High-density CRISPR gene tiling further pinpointed the integral pocket within the β-propeller domain of ITGAV for integrin αVβ5 dimerization. Combined with in silico compound docking, we developed a CRISPR-Tiling-Instructed Computer-Aided (CRISPR-TICA) pipeline for drug discovery and identified Cpd_AV2 as a lead inhibitor targeting the β-propeller central pocket of ITGAV. Cpd_AV2 treatment led to rapid uncoupling of integrin αVβ5 and cellular apoptosis, providing a unique class of therapeutic action that eliminates the integrin signaling via heterodimer dissociation. We also foresee the CRISPR-TICA approach to be an accessible method for future drug discovery studies.