Pediatric Erythroid Sarcoma Diagnostically Confirmed by Identification of a Recurrent NFIA::CBFA2T3 Fusion.

Erythroid sarcoma (ES) is exceedingly rare in the pediatric population with only a handful of reports of de novo cases, mostly occurring in the central nervous system (CNS) or orbit. It is clinically and pathologically challenging and can masquerade as a nonhematopoietic small round blue cell tumor. Clinical presentation of ES without bone marrow involvement makes diagnosis particularly difficult. We describe a 22-month-old female with ES who presented with a 2-cm mass involving the left parotid region and CNS. The presence of crush/fixation artifact from the initial biopsy made definitive classification of this highly proliferative and malignant neoplasm challenging despite an extensive immunohistochemical workup. Molecular studies including RNA-sequencing revealed a NFIA::CBFA2T3 fusion. This fusion has been identified in several cases of de novo acute erythroid leukemia (AEL) and gene expression analysis comparing this case to other AELs revealed a similar transcriptional profile. Given the diagnostically challenging nature of this tumor, clinical RNA-sequencing was essential for establishing a diagnosis.

Genomic and global gene expression profiling in pediatric and young adult acute leukemia with PICALM::MLLT10 Fusion.

PICALM: MLLT10 fusion is a rare but recurrent genetic driver in acute leukemias. To better understand the genomic landscape of PICALM::MLLT10 (PM) positive acute leukemia, we performed genomic profiling and gene expression profiling in twenty PM-positive patients, including AML (n = 10), T-ALL/LLy (n = 8), Mixed-phenotype acute leukemia (MPAL), T/B (n = 1) and acute undifferentiated leukemia (AUL) (n = 1). Besides confirming the known activation of HOXA, differential gene expression analysis compared to hematopoietic stem cells demonstrated the enrichment of genes associated with cell proliferation-related pathways and relatively high expression of XPO1 in PM-AML and PM-T-ALL/LLy. Our study also suggested PHF6 disruption as a key cooperating event in PICALM::MLLT10-positive leukemias. In addition, we demonstrated differences in gene expression profiles as well as remarkably different spectra of co-occurring mutations between PM-AML and PM-T-ALL/LLy. Alterations affecting TP53 and NF1, hallmarks of PM-AML, are strongly associated with disease progression and relapse, whereas EZH2 alterations are highly enriched in PM-T-ALL/LLy. This comprehensive genomic and transcriptomic profiling provides insights into the pathogenesis and development of PICALM::MLLT10 positive acute leukemia.

Functional characterization of cooperating MGA mutations in RUNX1::RUNX1T1 acute myeloid leukemia.

MGA (Max-gene associated) is a dual-specificity transcription factor that negatively regulates MYC-target genes to inhibit proliferation and promote differentiation. Loss-of-function mutations in MGA have been commonly identified in several hematological neoplasms, including acute myeloid leukemia (AML) with RUNX1::RUNX1T1, however, very little is known about the impact of these MGA alterations on normal hematopoiesis or disease progression. We show that representative MGA mutations identified in patient samples abolish protein-protein interactions and transcriptional activity. Using a series of human and mouse model systems, including a newly developed conditional knock-out mouse strain, we demonstrate that loss of MGA results in upregulation of MYC and E2F targets, cell cycle genes, mTOR signaling, and oxidative phosphorylation in normal hematopoietic cells, leading to enhanced proliferation. The loss of MGA induces an open chromatin state at promoters of genes involved in cell cycle and proliferation. RUNX1::RUNX1T1 expression in Mga-deficient murine hematopoietic cells leads to a more aggressive AML with a significantly shortened latency. These data show that MGA regulates multiple pro-proliferative pathways in hematopoietic cells and cooperates with the RUNX1::RUNX1T1 fusion oncoprotein to enhance leukemogenesis.

5G2 mutant mice model loss of a commonly deleted segment of chromosome 7q22 in myeloid malignancies.

Monosomy 7 and del(7q) are among the most common and poorly understood genetic alterations in myelodysplastic neoplasms and acute myeloid leukemia. Chromosome band 7q22 is a minimally deleted segment in myeloid malignancies with a del(7q). However, the rarity of "second hit" mutations supports the idea that del(7q22) represents a contiguous gene syndrome. We generated mice harboring a 1.5 Mb germline deletion of chromosome band 5G2 syntenic to human 7q22 that removes Cux1 and 27 additional genes. Hematopoiesis is perturbed in 5G2+/del mice but they do not spontaneously develop hematologic disease. Whereas alkylator exposure modestly accelerated tumor development, the 5G2 deletion did not cooperate with KrasG12D, NrasG12D, or the MOL4070LTR retrovirus in leukemogenesis. 5G2+/del mice are a novel platform for interrogating the role of hemopoietic stem cell attrition/stress, cooperating mutations, genotoxins, and inflammation in myeloid malignancies characterized by monosomy 7/del(7q).

UBTF tandem duplications in pediatric myelodysplastic syndrome and acute myeloid leukemia: implications for clinical screening and diagnosis.

Recent genomic studies in adult and pediatric acute myeloid leukemia (AML) demonstrated recurrent in-frame tandem duplications (TD) in exon 13 of upstream binding transcription factor (UBTF). These alterations, which account for ~4.3% of AMLs in childhood and about 3% in adult AMLs under 60, are subtype-defining and associated with poor outcomes. Here, we provide a comprehensive investigation into the clinicopathological features of UBTF-TD myeloid neoplasms in childhood, including 89 unique pediatric AML and 6 myelodysplastic syndrome (MDS) cases harboring a tandem duplication in exon 13 of UBTF. We demonstrate that UBTF-TD myeloid tumors are associated with dysplastic features, low bone marrow blast infiltration, and low white blood cell count. Furthermore, using bulk and single-cell analyses, we confirm that UBTF-TD is an early and clonal event associated with a distinct transcriptional profile, whereas the acquisition of FLT3 or WT1 mutations is associated with more stem celllike programs. Lastly, we report rare duplications within exon 9 of UBTF that phenocopy exon 13 duplications, expanding the spectrum of UBTF alterations in pediatric myeloid tumors. Collectively, we comprehensively characterize pediatric AML and MDS with UBTF-TD and highlight key clinical and pathologic features that distinguish this new entity from other molecular subtypes of AML.

Peptide-scFv antigen recognition domains effectively confer CAR T cell multiantigen specificity.

The emergence of immune escape is a significant roadblock to developing effective chimeric antigen receptor (CAR) T cell therapies against hematological malignancies, including acute myeloid leukemia (AML). Here, we demonstrate feasibility of targeting two antigens simultaneously by combining a GRP78-specific peptide antigen recognition domain with a CD123-specific scFv to generate a peptide-scFv bispecific antigen recognition domain (78.123). To achieve this, we test linkers with varying length and flexibility and perform immunophenotypic and functional characterization. We demonstrate that bispecific CAR T cells successfully recognize and kill tumor cells that express GRP78, CD123, or both antigens and have improved antitumor activity compared to their monospecific counterparts when both antigens are expressed. Protein structure prediction suggests that linker length and compactness influence the functionality of the generated bispecific CARs. Thus, we present a bispecific CAR design strategy to prevent immune escape in AML that can be extended to other peptide-scFv combinations.

A new genomic framework to categorize pediatric acute myeloid leukemia.

Recent studies on pediatric acute myeloid leukemia (pAML) have revealed pediatric-specific driver alterations, many of which are underrepresented in the current classification schemas. To comprehensively define the genomic landscape of pAML, we systematically categorized 887 pAML into 23 mutually distinct molecular categories, including new major entities such as UBTF or BCL11B, covering 91.4% of the cohort. These molecular categories were associated with unique expression profiles and mutational patterns. For instance, molecular categories characterized by specific HOXA or HOXB expression signatures showed distinct mutation patterns of RAS pathway genes, FLT3 or WT1, suggesting shared biological mechanisms. We show that molecular categories were strongly associated with clinical outcomes using two independent cohorts, leading to the establishment of a new prognostic framework for pAML based on these updated molecular categories and minimal residual disease. Together, this comprehensive diagnostic and prognostic framework forms the basis for future classification of pAML and treatment strategies.

Selective CK1α degraders exert antiproliferative activity against a broad range of human cancer cell lines.

Molecular-glue degraders are small molecules that induce a specific interaction between an E3 ligase and a target protein, resulting in the target proteolysis. The discovery of molecular glue degraders currently relies mostly on screening approaches. Here, we describe screening of a library of cereblon (CRBN) ligands against a panel of patient-derived cancer cell lines, leading to the discovery of SJ7095, a potent degrader of CK1α, IKZF1 and IKZF3 proteins. Through a structure-informed exploration of structure activity relationship (SAR) around this small molecule we develop SJ3149, a selective and potent degrader of CK1α protein in vitro and in vivo. The structure of SJ3149 co-crystalized in complex with CK1α + CRBN + DDB1 provides a rationale for the improved degradation properties of this compound. In a panel of 115 cancer cell lines SJ3149 displays a broad antiproliferative activity profile, which shows statistically significant correlation with MDM2 inhibitor Nutlin-3a. These findings suggest potential utility of selective CK1α degraders for treatment of hematological cancers and solid tumors.

SJPedPanel: A pan-cancer gene panel for childhood malignancies.

Background: Large scale genomics projects have identified driver alterations for most childhood cancers that provide reliable biomarkers for clinical diagnosis and disease monitoring using targeted sequencing. However, there is lack of a comprehensive panel that matches the list of known driver genes. Here we fill this gap by developing SJPedPanel for childhood cancers. Results: SJPedPanel covers 5,275 coding exons of 357 driver genes, 297 introns frequently involved in rearrangements that generate fusion oncoproteins, commonly amplified/deleted regions (e.g., MYCN for neuroblastoma, CDKN2A and PAX5 for B-/T-ALL, and SMARCB1 for AT/RT), and 7,590 polymorphism sites for interrogating tumors with aneuploidy, such as hyperdiploid and hypodiploid B-ALL or 17q gain neuroblastoma. We used driver alterations reported from an established real-time clinical genomics cohort (n=253) to validate this gene panel. Among the 485 pathogenic variants reported, our panel covered 417 variants (86%). For 90 rearrangements responsible for oncogenic fusions, our panel covered 74 events (82%). We re-sequenced 113 previously characterized clinical specimens at an average depth of 2,500X using SJPedPanel and recovered 354 (91%) of the 389 reported pathogenic variants. We then investigated the power of this panel in detecting mutations from specimens with low tumor purity (as low as 0.1%) using cell line-based dilution experiments and discovered that this gene panel enabled us to detect ∼80% variants with allele fraction of 0.2%, while the detection rate decreases to ∼50% when the allele fraction is 0.1%. We finally demonstrate its utility in disease monitoring on clinical specimens collected from AML patients in morphologic remission. Conclusions: SJPedPanel enables the detection of clinically relevant genetic alterations including rearrangements responsible for subtype-defining fusions for childhood cancers by targeted sequencing of ∼0.15% of human genome. It will enhance the analysis of specimens with low tumor burdens for cancer monitoring and early detection.

Acute myeloid leukemias with UBTF tandem duplications are sensitive to menin inhibitors.

ABSTRACT: UBTF tandem duplications (UBTF-TDs) have recently emerged as a recurrent alteration in pediatric and adult acute myeloid leukemia (AML). UBTF-TD leukemias are characterized by a poor response to conventional chemotherapy and a transcriptional signature that mirrors NUP98-rearranged and NPM1-mutant AMLs, including HOX-gene dysregulation. However, the mechanism by which UBTF-TD drives leukemogenesis remains unknown. In this study, we investigated the genomic occupancy of UBTF-TD in transformed cord blood CD34+ cells and patient-derived xenograft models. We found that UBTF-TD protein maintained genomic occupancy at ribosomal DNA loci while also occupying genomic targets commonly dysregulated in UBTF-TD myeloid malignancies, such as the HOXA/HOXB gene clusters and MEIS1. These data suggest that UBTF-TD is a gain-of-function alteration that results in mislocalization to genomic loci dysregulated in UBTF-TD leukemias. UBTF-TD also co-occupies key genomic loci with KMT2A and menin, which are known to be key partners involved in HOX-dysregulated leukemias. Using a protein degradation system, we showed that stemness, proliferation, and transcriptional signatures are dependent on sustained UBTF-TD localization to chromatin. Finally, we demonstrate that primary cells from UBTF-TD leukemias are sensitive to the menin inhibitor SNDX-5613, resulting in markedly reduced in vitro and in vivo tumor growth, myeloid differentiation, and abrogation of the UBTF-TD leukemic expression signature. These findings provide a viable therapeutic strategy for patients with this high-risk AML subtype.

UBTF Tandem Duplications in Pediatric MDS and AML: Implications for Clinical Screening and Diagnosis.

Recent genomic studies in adult and pediatric acute myeloid leukemia (AML) demonstrated recurrent in-frame tandem duplications (TD) in exon 13 of upstream binding transcription factor (UBTF). These alterations, which account for ~4.3% of AMLs in childhood and up to 3% in adult AMLs under 60, are subtype-defining and associated with poor outcomes. Here, we provide a comprehensive investigation into the clinicopathological features of UBTF-TD myeloid neoplasms in childhood, including 89 unique pediatric AML and 6 myelodysplastic syndrome (MDS) cases harboring a tandem duplication in exon 13 of UBTF. We demonstrate that UBTF-TD myeloid tumors are associated with dysplastic features, low bone marrow blast infiltration, and low white blood cell count. Furthermore, using bulk and single-cell analyses, we confirm that UBTF-TD is an early and clonal event associated with a distinct transcriptional profile, whereas the acquisition of FLT3 or WT1 mutations is associated with more stem cell-like programs. Lastly, we report rare duplications within exon 9 of UBTF that phenocopy exon 13 duplications, expanding the spectrum of UBTF alterations in pediatric myeloid tumors. Collectively, we comprehensively characterize pediatric AML and MDS with UBTF-TD and highlight key clinical and pathologic features that distinguish this new entity from other molecular subtypes of AML.

CBFA2T3::GLIS2-positive acute leukemia with RAM and mixed T/megakaryocytic phenotype.

Herein, we present a rare case of acute myeloid leukemia (AML) with CBFA2T3-rearrangement and the expression of megakaryocytic and lymphoid markers, highlighting the need for a high suspicion index in differential diagnosis and applying adequate workup to avoid misdiagnosing this entity. CBFA2T3::GLIS2-positive AML is primarily found in infants with non-down syndrome acute megakaryoblastic leukemia (non-DSAMKL). Flow cytometry immunophenotyping plays an important role in recognizing the unique immunophenotype of bright CD56 expression with dim/negative expression of HLA-DR, CD38, and CD45 termed the RAM immunophenotype in this entity. Still, CBFA2T3::GLIS2-positive acute leukemia with T/megakaryocytic markers could be misdiagnosed as T-lymphoblastic leukemia/lymphoma, early T-cell precursor acute lymphoblastic leukemia/lymphoma, NK lymphoblastic leukemia, AML with minimal differentiation, or AML with myelodysplasia-related changes.

Proposal of a new genomic framework for categorization of pediatric acute myeloid leukemia associated with prognosis.

Recent studies on pediatric acute myeloid leukemia (pAML) have revealed pediatric-specific driver alterations, many of which are underrepresented in the current classification schemas. To comprehensively define the genomic landscape of pAML, we systematically categorized 895 pAML into 23 molecular categories that are mutually distinct from one another, including new entities such as UBTF or BCL11B, covering 91.4% of the cohort. These molecular categories were associated with unique expression profiles and mutational patterns. For instance, molecular categories characterized by specific HOXA or HOXB expression signatures showed distinct mutation patterns of RAS pathway genes, FLT3, or WT1, suggesting shared biological mechanisms. We show that molecular categories were strongly associated with clinical outcomes using two independent cohorts, leading to the establishment of a prognostic framework for pAML based on molecular categories and minimal residual disease. Together, this comprehensive diagnostic and prognostic framework forms the basis for future classification of pAML and treatment strategies.

Somatic mutational landscape of hereditary hematopoietic malignancies caused by germline variants in RUNX1, GATA2, and DDX41.

Individuals with germ line variants associated with hereditary hematopoietic malignancies (HHMs) have a highly variable risk for leukemogenesis. Gaps in our understanding of premalignant states in HHMs have hampered efforts to design effective clinical surveillance programs, provide personalized preemptive treatments, and inform appropriate counseling for patients. We used the largest known comparative international cohort of germline RUNX1, GATA2, or DDX41 variant carriers without and with hematopoietic malignancies (HMs) to identify patterns of genetic drivers that are unique to each HHM syndrome before and after leukemogenesis. These patterns included striking heterogeneity in rates of early-onset clonal hematopoiesis (CH), with a high prevalence of CH in RUNX1 and GATA2 variant carriers who did not have malignancies (carriers-without HM). We observed a paucity of CH in DDX41 carriers-without HM. In RUNX1 carriers-without HM with CH, we detected variants in TET2, PHF6, and, most frequently, BCOR. These genes were recurrently mutated in RUNX1-driven malignancies, suggesting CH is a direct precursor to malignancy in RUNX1-driven HHMs. Leukemogenesis in RUNX1 and DDX41 carriers was often driven by second hits in RUNX1 and DDX41, respectively. This study may inform the development of HHM-specific clinical trials and gene-specific approaches to clinical monitoring. For example, trials investigating the potential benefits of monitoring DDX41 carriers-without HM for low-frequency second hits in DDX41 may now be beneficial. Similarly, trials monitoring carriers-without HM with RUNX1 germ line variants for the acquisition of somatic variants in BCOR, PHF6, and TET2 and second hits in RUNX1 are warranted.

Clinical and genomic characterization of an ATRA-insensitive acute promyelocytic leukemia variant with a FNDC3B::RARB fusion.

The promyelocytic leukemia-retinoic acid receptor-α (PML::RARA) fusion is the hallmark of acute promyelocytic leukemia (APL) and is observed in over 95% of APL cases. RARA and homologous receptors RARB and RARG are occasionally fused to other gene partners, which differentially affect sensitivity to targeted therapies. Most APLs without RARA fusions have rearrangements involving RARG or RARB, both of which frequently show resistance to all-trans-retinoic acid (ATRA) and/or multiagent chemotherapy for acute myeloid leukemia (AML). We present a 13-year-old male diagnosed with variant APL with a novel FNDC3B::RARB in-frame fusion that showed no response to ATRA but responded well to conventional AML therapy. While FNDC3B has been identified as a rare RARA translocation partner in ATRA-sensitive variant APL, it has never been reported as a fusion partner with RARB and it is only the second known fusion partner with RARB in variant APL. We also show that this novel fusion confers an RNA expression signature that is similar to APL, despite clinical resistance to ATRA monotherapy.

Etiology of oncogenic fusions in 5,190 childhood cancers and its clinical and therapeutic implication.

Oncogenic fusions formed through chromosomal rearrangements are hallmarks of childhood cancer that define cancer subtype, predict outcome, persist through treatment, and can be ideal therapeutic targets. However, mechanistic understanding of the etiology of oncogenic fusions remains elusive. Here we report a comprehensive detection of 272 oncogenic fusion gene pairs by using tumor transcriptome sequencing data from 5190 childhood cancer patients. We identify diverse factors, including translation frame, protein domain, splicing, and gene length, that shape the formation of oncogenic fusions. Our mathematical modeling reveals a strong link between differential selection pressure and clinical outcome in CBFB-MYH11. We discover 4 oncogenic fusions, including RUNX1-RUNX1T1, TCF3-PBX1, CBFA2T3-GLIS2, and KMT2A-AFDN, with promoter-hijacking-like features that may offer alternative strategies for therapeutic targeting. We uncover extensive alternative splicing in oncogenic fusions including KMT2A-MLLT3, KMT2A-MLLT10, C11orf95-RELA, NUP98-NSD1, KMT2A-AFDN and ETV6-RUNX1. We discover neo splice sites in 18 oncogenic fusion gene pairs and demonstrate that such splice sites confer therapeutic vulnerability for etiology-based genome editing. Our study reveals general principles on the etiology of oncogenic fusions in childhood cancer and suggests profound clinical implications including etiology-based risk stratification and genome-editing-based therapeutics.

Clinical impact of minimal residual disease in blood and bone marrow of children with acute myeloid leukemia.

The prognostic significance of bone marrow minimal residual disease (MRD) in pediatric patients with acute myeloid leukemia (AML) is well characterized, but the impact of blood MRD is not known. We, therefore, used flow cytometric assessment of leukemia-specific immunophenotypes to measure levels of MRD in both the blood and bone marrow of patients treated in the AML08 (NCT00703820) clinical trial. Blood samples were obtained on days 8 and 22 of therapy, whereas bone marrow samples were obtained on day 22. Among patients who tested as having MRD-negative bone marrow on day 22, neither day-8 nor day-22 blood MRD was significantly associated with the outcome. However, day-8 blood MRD was highly predictive of the outcome among patients who tested as having MRD-positive bone marrow on day 22. Although the measurement of blood MRD on day 8 cannot be used to identify patients who have day-22 MRD-negative bone marrow who are likely to relapse, our findings suggest that day-8 blood MRD results can identify patients with MRD-positive bone marrow who have a dismal prognosis and may be candidates for the early use of experimental therapy.

From PROTAC to inhibitor: Structure-guided discovery of potent and orally bioavailable BET inhibitors.

An X-ray structure of a CLICK chemistry-based BET PROTAC bound to BRD2(BD2) inspired synthesis of JQ1 derived heterocyclic amides. This effort led to the discovery of potent BET inhibitors displaying overall improved profiles when compared to JQ1 and birabresib. A thiadiazole derived 1q (SJ1461) displayed excellent BRD4 and BRD2 affinity and high potency in the panel of acute leukaemia and medulloblastoma cell lines. A structure of 1q co-crystalised with BRD4-BD1 revealed polar interactions with the AZ/BC loops, in particular with Asn140 and Tyr139, rationalising the observed affinity improvements. In addition, exploration of pharmacokinetic properties of this class of compounds suggest that the heterocyclic amide moiety improves drug-like features. Our study led to the discovery of potent and orally bioavailable BET inhibitor 1q (SJ1461) as a promising candidate for further development.

SAMHD1 single nucleotide polymorphisms impact outcome in children with newly diagnosed acute myeloid leukemia.

Cytarabine arabinoside (Ara-C) has been the cornerstone of acute myeloid leukemia (AML) chemotherapy for decades. After cellular uptake, it is phosphorylated into its active triphosphate form (Ara-CTP), which primarily exerts its cytotoxic effects by inhibiting DNA synthesis in proliferating cells. Interpatient variation in the enzymes involved in the Ara-C metabolic pathway has been shown to affect intracellular abundance of Ara-CTP and, thus, its therapeutic benefit. Recently, SAMHD1 (SAM and HD domain-containing deoxynucleoside triphosphate triphosphohydrolase 1) has emerged to play a role in Ara-CTP inactivation, development of drug resistance, and, consequently, clinical response in AML. Despite this, the impact of genetic variations in SAMHD1 on outcome in AML has not been investigated in depth. In this study, we evaluated 25 single nucleotide polymorphisms (SNPs) within the SAMHD1 gene for association with clinical outcome in 400 pediatric patients with newly diagnosed AML from 2 clinical trials, AML02 and AML08. Three SNPs, rs1291128, rs1291141, and rs7265241 located in the 3' region of SAMHD1 were significantly associated with at least 1 clinical outcome: minimal residual disease after induction I, event-free survival (EFS), or overall survival (OS) in the 2 cohorts. In an independent cohort of patients from the COG-AAML1031 trial (n = 854), rs7265241 A>G remained significantly associated with EFS and OS. In multivariable analysis, all the SNPs remained independent predictors of clinical outcome. These results highlight the relevance of the SAMHD1 pharmacogenomics in context of response to Ara-C in AML and warrants the need for further validation in expanded patient cohorts.