Report of IRF2BP1 as a novel partner of RARA in variant acute promyelocytic leukemia.

IRF2BP1 breaked in the middle of exon 1 at the c.322 position and fused with RARA intron 2 which is located at 3717 bp upstream of its exon 3. The fusion produced a new intron by forming a paired splicing donor GT at 9 bp downstream of RARA breakpoint and acceptor AG at the 5' end of RARA exon 3. The IRF2BP1::RARA fusion gene leads a fusion transcript involving IRF2BP1 exon 1 and RARA exon 3, linked by a 9-bp fragment derived from RARA intron 2. The patient with IRF2BP1::RARA has same clinical features of APL.

Cellular hierarchy insights reveal leukemic stem-like cells and early death risk in acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) represents a paradigm for targeted differentiation therapy, with a minority of patients experiencing treatment failure and even early death. We here report a comprehensive single-cell analysis of 16 APL patients, uncovering cellular compositions and their impact on all-trans retinoic acid (ATRA) response in vivo and early death. We unveil a cellular differentiation hierarchy within APL blasts, rooted in leukemic stem-like cells. The oncogenic PML/RARα fusion protein exerts branch-specific regulation in the APL trajectory, including stem-like cells. APL cohort analysis establishes an association of leukemic stemness with elevated white blood cell counts and FLT3-ITD mutations. Furthermore, we construct an APL-specific stemness score, which proves effective in assessing early death risk. Finally, we show that ATRA induces differentiation of primitive blasts and patients with early death exhibit distinct stemness-associated transcriptional programs. Our work provides a thorough survey of APL cellular hierarchies, offering insights into cellular dynamics during targeted therapy.

High-Fat Diet Induced PPARδ Promotes Self-renewal of Preleukemic Progenitors in Development of Acute Promyelocytic Leukemia.

From risk association between acute promyelocytic leukemia (APL) and obese-overweight individuals, Mazzarella and colleagues hypothesized that a high-fat diet (HFD) promotes development of APL. Using mouse APL model (PML-RARα knock-in), the authors demonstrated that linoleic acid drives activation of PPARδ in hematopoietic progenitors, and that activation of PPARδ increases proliferation of progenitor cells with PML-RARA expression toward APL. Involvements of PPARδ on regulation of stem cell renewal and proliferation were shown in colorectal cancers earlier, but this study newly demonstrates in hematopoietic progenitors, while suggesting use of diet rich in linoleic acid with caution. See related article by Mazzarella et al., p. 59.

Identification of a novel fusion gene, RARA::ANKRD34C, in acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is a specific subtype of acute myeloid leukemia that is distinguished by the chromosomal translocation t(15;17)(q24;q21), which leads to the fusion of the promyelocytic leukemia (PML) gene with the retinoic acid receptor alpha (RARA). Recently, we identified a novel fusion gene in APL, RARA::ankyrin repeat domain 34C (ANKRD34C), identified its functions by morphological, cytogenetic, molecular biological and multiplex fluorescence in situ hybridization analyses, and demonstrated the potential therapeutic effect clinically and experimentally of all-trans retinoic acid (ATRA); the findings have important implications for the diagnosis and treatment of atypical APL.

High-Fat Diet Promotes Acute Promyelocytic Leukemia through PPARδ-Enhanced Self-renewal of Preleukemic Progenitors.

Risk and outcome of acute promyelocytic leukemia (APL) are particularly worsened in obese-overweight individuals, but the underlying molecular mechanism is unknown. In established mouse APL models (Ctsg-PML::RARA), we confirmed that obesity induced by high-fat diet (HFD) enhances leukemogenesis by increasing penetrance and shortening latency, providing an ideal model to investigate obesity-induced molecular events in the preleukemic phase. Surprisingly, despite increasing DNA damage in hematopoietic stem cells (HSC), HFD only minimally increased mutational load, with no relevant impact on known cancer-driving genes. HFD expanded and enhanced self-renewal of hematopoietic progenitor cells (HPC), with concomitant reduction in long-term HSCs. Importantly, linoleic acid, abundant in HFD, fully recapitulates the effect of HFD on the self-renewal of PML::RARA HPCs through activation of peroxisome proliferator-activated receptor delta, a central regulator of fatty acid metabolism. Our findings inform dietary/pharmacologic interventions to counteract obesity-associated cancers and suggest that nongenetic factors play a key role. PREVENTION RELEVANCE: Our work informs interventions aimed at counteracting the cancer-promoting effect of obesity. On the basis of our study, individuals with a history of chronic obesity may still significantly reduce their risk by switching to a healthier lifestyle, a concept supported by evidence in solid tumors but not yet in hematologic malignancies. See related Spotlight, p. 47.

Mutations at proximal cysteine residues in PML impair ATO binding by destabilizing the RBCC domain.

Acute promyelocytic leukemia (APL) is characterized by the fusion gene promyelocytic leukemia-retinoic acid receptor-alpha (PML-RARA) and is conventionally treated with arsenic trioxide (ATO). ATO binds directly to the RING finger, B-box, coiled-coil (RBCC) domain of PML and initiates degradation of the fusion oncoprotein PML-RARA. However, the mutational hotspot at C212-S220 disrupts ATO binding, leading to drug resistance in APL. Therefore, structural consequences of these point mutations in PML that remain uncertain require comprehensive analysis. In this study, we investigated the structure-based ensemble properties of the promyelocytic leukemia-RING-B-box-coiled-coil (PML-RBCC) domains and ATO-resistant mutations. Oligomeric studies reveal that PML-RBCC wild-type and mutants C212R, S214L, A216T, L217F, and S220G predominantly form tetramers, whereas mutants C213R, A216V, L218P, and D219H tend to form dimers. The stability of the dimeric mutants was lower, exhibiting a melting temperature (Tm) reduction of 30 °C compared with the tetrameric mutants and wild-type PML protein. Furthermore, the exposed surface of the C213R mutation rendered it more prone to protease digestion than that of the C212R mutation. The spectroscopic analysis highlighted ATO-induced structural alterations in S214L, A216V, and D219H mutants, in contrast to C213R, L217F, and L218P mutations. Moreover, the computational analysis revealed that the ATO-resistant mutations C213R, A216V, L217F, and L218P caused changes in the size, shape, and flexibility of the PML-RBCC wild-type protein. The mutations C213R, A216V, L217F, and L218P destabilize the wild-type protein structure due to the adaptation of distinct conformational changes. In addition, these mutations disrupt several hydrogen bonds, including interactions involving C212, C213, and C215, which are essential for ATO binding. The local and global structural features induced by these mutations provide mechanistic insight into ATO resistance and APL pathogenesis.

Leukemia cells accumulate zinc for oncofusion protein stabilization.

Acute promyelocytic leukemia (APL) and chronic myeloid leukemia (CML) are both hematological malignancies characterized by genetic alterations leading to the formation of oncofusion proteins. The classical chromosomal aberrations in APL and CML result in the PML-RARα and BCR-ABL1 oncofusion proteins, respectively. Interestingly, our flow cytometric analyses revealed elevated free intracellular zinc levels in various leukemia cells, which may play a role in stabilizing oncofusion proteins in leukemia and thus support cell proliferation and malignancy. Long-term zinc deficiency resulted in the degradation of PML-RARα in NB4 cells (APL cell line) and of BCR-ABL1 in K562 cells (CML cell line). This degradation may be explained by increased caspase 3 activity observed in zinc deficient cells, whereas zinc reconstitution normalized the caspase 3 activity and abolished zinc deficiency-induced oncofusion protein degradation. In NB4 cells, fluorescence microscopic images further indicated enlarged and enriched lysosomes during zinc deficiency, suggesting increased rates of autophagy. Moreover, NB4 cells exhibited increased expression of the zinc transporters ZIP2, ZIP10 and ZnT3 during zinc deficiency and revealed excessive accumulation of zinc in contrast to healthy peripheral blood mononuclear cells (PBMCs), when zinc was abundantly available extracellularly. Our results highlight the importance of altered zinc homeostasis for some characteristics in leukemia cells, uncover potential pathways underlying the effects of zinc deficiency in leukemia cells, and provide potential alternative strategies by which oncofusion proteins can be degraded.

Prognosis influence of additional chromosome abnormalities in newly diagnosed acute promyelocytic leukemia with t(15;17)(q24;q21).

OBJECTIVES: In patients with acute promyelocytic leukemia (APL), additional chromosomal abnormalities (ACAs) are prognostic indicators. However, the clinical features of ACAs were not systematically reported in Chinese patients. Therefore, we enrolled a large cohort of APLs to demonstrate the clinical characteristics and prognostic value of ACAs. METHODS: 268 patients with newly diagnosed APL with t(15;17)(q24;q21) were retrospectively enrolled, and their clinical characteristics and the predictive value of ACAs were assessed between patients with the presence and absence of ACAs. RESULTS: APL patients with and without ACAs did not differ significantly in their clinical features or treatment response and clinical outcomes like overall survival (OS) and disease-free survival (DFS). It appeared to be substantially associated with worse OS in APL patients with trisomy 8, which was the most common ACA, although DFS was unaffected. Interestingly, the presence of ACAs or trisomy 8 affected OS and DFS in the subgroup of patients aged ≥60 years; by contrast, ACAs had no effect on OS or DFS in any treatment subgroup (ATRA + ATO/RIF or ATRA + ATO/RIF + CH or ATRA + CH), except for the ATRA + ATO/RIF + CH treatment subgroup, where their impact on DFS was less favorable. CONCLUSIONS: Our results suggested that OS and DFS were unaffected by ACAs. Nonetheless, in the subgroup of patients older than 60, the existence of ACAs or trisomy 8 appeared to impact OS and DFS negatively. Individuals with t(15;17) alone had a higher DFS and were more susceptible to ATRA + ATO/RIF + CH than individuals with t(15;17) ACAs.

Venetoclax overcomes resistance to all-trans retinoic acid in a variant acute promyelocytic leukemia with TNRC18::RARA fusion.

Acute promyelocytic leukemia (APL) is generally driven by PML::RARA, but approximately 2% of variant APL patients do not contain this fusion gene and pose challenges in diagnosis and treatment. Here, we reported an aggressive APL patient with variant TNRC18::RARA fusion gene, who was resistant to standard differentiation induction therapy consisting of all-trans retinoic acid (ATRA) and arsenic trioxide but achieved complete remission with venetoclax plus ATRA. Mechanistically, venetoclax possesses synergistic effects in ATRA-induced TNRC18::RARA-positive cell differentiation.

Effective treatment with Gilteritinib-based regimens for FLT3-mutant extramedullary relapse in acute promyelocytic leukemia.

OBJECTIVE: Extramedullary relapse (EMR) is rare in acute promyelocytic leukemia (APL) and, there is a lack of information on its management. Current practices for EMR in APL are always to adopt strategies from other subtypes of Acute lymphoblastic leukemia (ALL) and Acute myeloid leukemia (AML). Gilteritinib, a highly selective FLT3 inhibitor, has demonstrated a remarkable effect on EMR in FLT3-mutant AML. Therefore, it is worthwhile exploring if FLT3 mutation can be a therapeutic target and assessing the efficacy of Gilteritinib on FLT3-mutant EMR in APL. METHODS: We described three cases of FLT3-mutant EMR in APL, comprising two isolated EMR cases and one systemic relapse. The patients underwent treatment with Gilteritinib-based regimens based on FLT3 mutation. RESULTS: All three patients achieved complete regression of EMR, and no signs of tumor lysis syndrome during Gilteritinib-based therapy, only patient 1 showed mild granulocytopenia. They all maintained molecular complete remission (mCR) during the follow-up period. CONCLUSIONS: The Gilteritinib-based regimen shows a high and sustained therapeutic effect with minimal adverse effects, and provides a valuable experience for further evaluation in EMR APL patients.

Identification of concurrent STAT3::RARA and RARA::STAT5b fusions in a variant APL case.

Acute promyelocytic leukemia (APL) with typically PML::RARA fusion gene caused by t (15;17) (q22; q12) was distinguished from other types of acute myeloid leukemia. In a subset of patients with APL, t (15;17) (q22;q21) and PML::RARA fusion cannot be detected. In this report, we identified the coexistence of STAT3::RARA and RARA::STAT5b fusions for the first time in a variant APL patient lacking t (15;17)(q22;q21)/PML::RARA fusion. Then, this patient was resistant to all-trans retinoic acid combined arsenic trioxide chemotherapy. Accurate detection of RARA gene partners is crucial for variant APL, and effective therapeutic regime is urgently needed.

Transformation from acute promyelocytic leukemia in pregnancy to acute myeloid leukemia with MLL-AF9 fusion gene: A case report and literature review.

RATIONALE: Because there are few evidence-based guidelines and an extremely low incidence rate, managing and treating patients who have transitioned from acute promyelocytic leukemia (APL), which was diagnosed during pregnancy, to acute myeloid leukemia (AML), can be difficult. PATIENT CONCERNS: In this case, a 34-year-old pregnant patient was diagnosed with APL in medium-risk group in June 2017. After the all-trans retinoic acid and arsenic trioxide-based full-course treatment, the patients achieved complete remission (CR) and were well-tolerated. After 5 years, the patient complained of fatigue for 3 months. DIAGNOSIS: Bone marrow examination revealed hypercellularity with approximately 50% immunophenotypic abnormal myeloblasts with MLL-AF9 fusion gene. Based on the AML diagnosis criteria of the World Health Organization, the patient was eventually diagnosed with a rare transformation from APL to AML. INTERVENTIONS: The patient was treated with two cycles of induction chemotherapy and an allogeneic hematopoietic stem cell transplantation (allo-HSCT). OUTCOMES: Until now, the patient is in continuous remission with no signs of APL and AML. LESSIONS: Despite the rarity of APL to AML transformation, it is crucial to track the disease's progress and administer treatment on time. It remains uncertain whether the risk stratification and clinical outcomes of secondary AML with MLL-AF9 are equivalent to those of de novo AML with MLL-AF9. The management and treatment of these patients should be personalized and require further observation.

Treating low- and intermediate-risk acute promyelocytic leukemia with and without chemotherapy: A comparison in a tertiary care center.

Background: Acute promyelocytic leukemia (APL) comprises approximately 10% of acute myeloid leukemia (AML) cases. Material and Methods: Both options of treatment (ATRA-ATO and ATRA-chemotherapy) were discussed with patients with low- and intermediate-risk APL, pros and cons explained in details, and treatment regimen selected after getting informed written consent. Results: Total 71 patients were included in the study; among these patients, 3 were negative for both FISH for t (15,17) and RT-PCR for promyelocytic leukemia retinoic acid receptor alpha, and 36 patients with APL had white blood cell count at diagnosis >10 × 109/l. Total 30 patients with newly diagnosed as low- and intermediate-risk-APL fulfilled all inclusion criteria, treated and followed for a minimum period of 2 years up to June, 2016. Fifteen patients liked to be treated with all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), while rest of the 15 patients preferred treatment with ATRA and chemotherapy. Conclusion: Combination of ATRA and ATO is equally effective, less toxic, and more feasible in comparison to ATRA and chemotherapy for patients with low- and intermediate-risk APL and is a viable option for this subset of patients, especially in countries with limited resources.

Integrated bioinformatics analysis and network pharmacology to explore the potential mechanism of Patrinia heterophylla Bunge against acute promyelocytic leukemia.

INTRODUCTION: Current treatment with arsenic trioxide and all-trans retinoic acid has greatly improved the therapeutic efficacy and prognosis of acute promyelocytic leukemia (APL), but may cause numerous adverse effects. Patrinia heterophylla Bunge (PHEB), commonly known as "Mu-Tou-Hui" in China, is effective in treating leukemia. However, no studies have reported the use of PHEB for APL treatment. In this study, we aimed to investigate the potential anticancer mechanism of PHEB against APL. METHODS: Public databases were used to search for bioactive compounds in PHEB, their potential targets, differentially expressed genes associated with APL, and therapeutic targets for APL. The core targets and signaling pathways of PHEB against APL were identified by the protein-protein interaction network, Kaplan-Meier curves, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway enrichment, and compound-target-pathway network analysis. Molecular docking was performed to predict the binding activity between the most active compounds and the key targets. RESULTS: Quercetin and 2 other active components of PHEB may exert anti-APL effects through proteoglycans in cancer, estrogen signaling, and acute myeloid leukemia pathways. We also identified 6 core targets of the bioactive compounds of PHEB, including protein tyrosine phosphatase receptor type C, proto-oncogene tyrosine-protein kinase Src, mitogen-activated protein kinase phosphatase 3 (MAPK3), matrix metalloproteinase-9, vascular endothelial growth factor receptor-2, and myeloperoxidase, most of which were validated to improve the 5-year survival of patients. Molecular docking results showed that the active compound bound well to key targets. CONCLUSION: The results not only predict the active ingredients and potential molecular mechanisms of PHEB against APL, but also help to guide further investigation into the anti-APL application of PHEB.