Dual origin of relapses in retinoic-acid resistant acute promyelocytic leukemia

History of Developing Acute Promyelocytic Leukemia Treatment and Role of Promyelocytic Leukemia Bodies

The story of acute promyelocytic leukemia (APL) discovery, physiopathology, and treatment is a unique journey, transforming the most aggressive form of leukemia to the most curable. It followed an empirical route fueled by clinical breakthroughs driving major advances in biochemistry and cell biology, including the discovery of PML nuclear bodies (PML NBs) and their central role in APL physiopathology. Beyond APL, PML NBs have emerged as key players in a wide variety of biological functions, including tumor-suppression and SUMO-initiated protein degradation, underscoring their broad importance. The APL story is an example of how clinical observations led to the incremental development of the first targeted leukemia therapy. The understanding of APL pathogenesis and the basis for cure now opens new insights in the treatment of other diseases, especially other acute myeloid leukemias.

A machine learning model identifies M3-like subtype in AML based on PML/RARα targets

The typical genomic feature of acute myeloid leukemia (AML) M3 subtype is the fusion event of PML/RARα, and ATRA/ATO-based combination therapy is current standard treatment regimen for M3 subtype. Here, a machine-learning model based on expressions of PML/RARα targets was developed to identify M3 patients by analyzing 1228 AML patients. Our model exhibited high accuracy. To enable more non-M3 AML patients to potentially benefit from ATRA/ATO therapy, M3-like patients were further identified. We found that M3-like patients had strong GMP features, including the expression patterns of M3 subtype marker genes, the proportion of myeloid progenitor cells, and deconvolution of AML constituent cell populations. M3-like patients exhibited distinct genomic features, low immune activity and better clinical survival. The initiative identification of patients similar to M3 subtype may help to identify more patients that would benefit from ATO/ATRA treatment and deepen our understanding of the molecular mechanism of AML pathogenesis.

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.

Retinoic acid signaling in development and differentiation commitment and its regulatory topology

Retinoic acid (RA), the derivative of vitamin A/retinol, is a signaling molecule with important implications in health and disease. It is a well-known developmental morphogen that functions mainly through the transcriptional activity of nuclear RA receptors (RARs) and, uncommonly, through other nuclear receptors, including peroxisome proliferator-activated receptors. Intracellular RA is under spatiotemporally fine-tuned regulation by synthesis and degradation processes catalyzed by retinaldehyde dehydrogenases and P450 family enzymes, respectively. In addition to dictating the transcription architecture, RA also impinges on cell functioning through non-genomic mechanisms independent of RAR transcriptional activity. Although RA-based differentiation therapy has achieved impressive success in the treatment of hematologic malignancies, RA also has pro-tumor activity. Here, we highlight the relevance of RA signaling in cell-fate determination, neurogenesis, visual function, inflammatory responses and gametogenesis commitment. Genetic and post-translational modifications of RAR are also discussed. A better understanding of RA signaling will foster the development of precision medicine to improve the defects caused by deregulated RA signaling.

Advances in acute myeloid leukemia differentiation therapy: A critical review

Acute myeloid leukemia (AML) is characterized by impaired differentiation and indefinite proliferation of abnormal myeloid progenitors. Although differentiating agents were deemed to revolutionize AML therapy, most treated non-APL AML patients are refractory or relapse. According to cancer stem cell model, leukemia-initiating cells are the root cause of relapse given their unidirectional potential to generate differentiated AML blasts. Nonetheless, accumulating evidences emphasize the de-differentiation plasticity and leukemogenic potential of mature AML blasts and the frailty of targeting leukemic stem cells per se. This review critically discusses the potential and challenges of (lessons learnt from) conventional and novel differentiating agents in AML therapy. Although differentiating agents might hold promise, they should be exploited within the context of a rationale combination regimen eradicating all maturation/differentiation states of AML cells. The results of the routinely used immunophenotypic markers and/or morphological analyses of differentiation should be carefully interpreted given their propensity to underestimate AML burden.

The PML hub: An emerging actor of leukemia therapies

PML assembles into nuclear domains that have attracted considerable attention from cell and cancer biologists. Upon stress, PML nuclear bodies modulate sumoylation and other post-translational modifications, providing an integrated molecular framework for the multiple roles of PML in apoptosis, senescence, or metabolism. PML is both a sensor and an effector of oxidative stress. Emerging data has demonstrated its key role in promoting therapy response in several hematological malignancies. While these membrane-less nuclear hubs can enforce efficient cancer cell clearance, their downstream pathways deserve better characterization. PML NBs are druggable and their known modulators may have broader clinical utilities than initially thought.

[Vitamins and Immune System Health]

Keeping the immune system healthy forms an effective way to fight infections. Past experience has shown that, in addition to effective interventions including vaccination, drug therapy, and non-pharmaceutical intervention (NPI), dietary nutrition and mental health are also key factors in maintaining immune system health and combating emerging and sudden outbreaks of infections. As the main dietary nutrients, vitamins are active regulators of the immune response and exert a critical impact on the immunity of the human body. Vitamin deficiency causes increased levels of inflammation and decreased immunity, which usually starts in the oral tissues. Appropriate vitamin supplementation can help the body optimize immune function, enhance oral immunity, and reduce the negative impact of pathogen infection on the human body, which makes it a feasible, effective, and universally applicable anti-infection solution. This review focuses on the immunomodulatory effects of vitamin A, B, C, D, and E and proposes that an omics-based new systemic approach will lead to a breakthrough of the limitations in traditional single-factor single-pathway research and provide the direction for the basic and applied research of vitamin immune regulation and anti-infection in all aspects.

Noncanonical EZH2 drives retinoic acid resistance of variant acute promyelocytic leukemias

Cancer cell heterogeneity is a major driver of therapy resistance. To characterize resistant cells and their vulnerabilities, we studied the PLZF-RARA variant of acute promyelocytic leukemia, resistant to retinoic acid (RA), using single-cell multiomics. We uncovered transcriptional and chromatin heterogeneity in leukemia cells. We identified a subset of cells resistant to RA with proliferation, DNA replication, and repair signatures that depend on a fine-tuned E2F transcriptional network targeting the epigenetic regulator enhancer of zeste homolog 2 (EZH2). Epigenomic and functional analyses validated the driver role of EZH2 in RA resistance. Targeting pan-EZH2 activities (canonical/noncanonical) was necessary to eliminate leukemia relapse-initiating cells, which underlies a dependency of resistant cells on an EZH2 noncanonical activity and the necessity to degrade EZH2 to overcome resistance. Our study provides critical insights into the mechanisms of RA resistance that allow us to eliminate treatment-resistant leukemia cells by targeting EZH2, thus highlighting a potential targeted therapy approach. Beyond RA resistance and acute promyelocytic leukemia context, our study also demonstrates the power of single-cell multiomics to identify, characterize, and clear therapy-resistant cells.

Recurrent noncoding somatic and germline WT1 variants converge to disrupt MYB binding in acute promyelocytic leukemia

Genetic alternations can occur at noncoding regions, but how they contribute to cancer pathogenesis is poorly understood. Here, we established a mutational landscape of cis-regulatory regions (CREs) in acute promyelocytic leukemia (APL) based on whole-genome sequencing analysis of paired tumor and germline samples from 24 patients and epigenetic profiling of 16 patients. Mutations occurring in CREs occur preferentially in active enhancers bound by the complex of master transcription factors in APL. Among significantly enriched mutated CREs, we found a recurrently mutated region located within the third intron of WT1, an essential regulator of normal and malignant hematopoiesis. Focusing on noncoding mutations within this WT1 intron, an analysis on 169 APL patients revealed that somatic mutations were clustered into a focal hotspot region, including one site identified as a germline polymorphism contributing to APL risk. Significantly decreased WT1 expression was observed in APL patients bearing somatic and/or germline noncoding WT1 variants. Furthermore, biallelic WT1 inactivation was recurrently found in APL patients with noncoding WT1 variants, which resulted in the complete loss of WT1. The high incidence of biallelic inactivation suggested the tumor suppressor activity of WT1 in APL. Mechanistically, noncoding WT1 variants disrupted MYB binding on chromatin and suppressed the enhancer activity and WT1 expression through destroying the chromatin looping formation. Our study highlights the important role of noncoding variants in the leukemogenesis of APL.

Co-targeting leukemia-initiating cells and leukemia bulk leads to disease eradication

According to a hierarchical model, targeting leukemia-initiating cells (LICs) was speculated to achieve complete remission (CR) or cure. Nonetheless, increasing evidence emphasized the plasticity of differentiated blasts undergoing interconversion into LICs. We exploited murine models of acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia driven by the promyelocytic leukemia/retinoic acid receptor (PML-RARα) oncofusion protein, which recruits histone deacetylase (HDAC)-containing complexes. We studied APLs with different LIC frequencies and investigated the effect of two HDAC inhibitors: valproic acid (VPA), with relative selectivity towards class I HDAC enzymes and vorinostat/suberoylanilide hydroxamic acid (SAHA) (pan-HDAC inhibitor) in combination with all-trans retinoic acid (ATRA), on the bulk APL cells and APL LICs. Indeed, we found that while VPA differentiates the bulk APL cells, SAHA selectively targets LICs. ATRA + VPA + SAHA combination efficiently induced CR in an APL model with lower LIC frequency. Substituting ATRA with synthetic retinoids as etretinate which promotes APL differentiation without downregulating PML/RARα compromised the therapeutic benefit of ATRA + VPA + SAHA regimen. Altogether, our study emphasizes the therapeutic power of co-targeting the plasticity and heterogeneity of cancer -herein demonstrated by tackling LICs and bulk leukemic blasts - to achieve and maintain CR.

Relapsed/refractory acute promyelocytic leukemia with RARA-LBD region mutation was salvaged by venetoclax: A case report

RATIONALE

Acute promyelocytic leukemia (APL) is one of the most curable cancers. However, relapse of the disease is a difficult issue in clinical practice and it remains a great challenge that patients have a poor effect of conventional treatment in the clinic. Therefore, new and more effective therapeutic measures are urgently needed. Herein, we report a case of relapsed and refractory APL harboring a RARA-LBD region mutation successfully treated with venetoclax (VEN).

PATIENT CONCERNS

A 37-years-old woman was admitted to our hospital with worsening spontaneous gingival bleeding and skin ecchymosis. Physical examination revealed multiple petechiae and ecchymosis in the extremities.

DIAGNOSES

The patient was diagnosed with L-type PML-RARα-positive APL, harboring a RARA-LBD region mutation, low-risk, based on bone marrow cytology, immunophenotypic analysis by flow cytometry, karyotype analysis, and molecular analysis.

INTERVENTIONS

Complete remission was achieved after the first induction therapy of all-trans retinoic acid (ATRA) combined with arsenic trioxide, but relapse was observed only after 11 months. Reinduction with ATRA and arsenic trioxide combined with anthracycline failed. Therefore, we tried to provide a new treatment with the Bcl-2 inhibitor VEN orally (100 mg d1, 200 mg d2 to d18, followed by 300 mg daily continuously).

OUTCOMES

Clinical symptoms and laboratory indicators improved rapidly with VEN treatment. A complete hematologic response was achieved with VEN-based therapy.

LESSONS

Related drug resistance gene monitoring should be performed canonically in relapsed and refractory APL. Some relapsed and refractory APL that failed to respond to conventional treatment were at risk of death. Bcl-2 inhibitors are expected to be an effective salvage therapy for patients with resistance to ATRA, which is worthy of further discussion.

A Pin1/PML/P53 axis activated by retinoic acid in NPM-1c acute myeloid leukemia

Retinoic acid (RA) was proposed to increase survival of chemotherapy- treated patients with nucleophosmin-1 (NPM-1c)-mutated acute myeloid leukemia. We reported that, ex vivo, RA triggers NPM-1c degradation, P53 activation and growth arrest. PML organizes domains that control senescence or proteolysis. Here, we demonstrate that PML is required to initiate RA-driven NPM-1c degradation, P53 activation and cell death. Mechanistically, RA enhances PML basal expression through inhibition of activated Pin1, prior to NPM-1c degradation. Such PML induction drives P53 activation, favoring blast response to chemotherapy or arsenic in vivo. This RA/PML/P53 cascade could mechanistically explain RA-facilitated chemotherapy response in patients with NPM-1c mutated acute myeloid leukemia.

Acute myeloid leukemia maturation lineage influences residual disease and relapse following differentiation therapy

Acute myeloid leukemia (AML) is a malignancy of immature progenitor cells. AML differentiation therapies trigger leukemia maturation and can induce remission, but relapse is prevalent and its cellular origin is unclear. Here we describe high resolution analysis of differentiation therapy response and relapse in a mouse AML model. Triggering leukemia differentiation in this model invariably produces two phenotypically distinct mature myeloid lineages in vivo. Leukemia-derived neutrophils dominate the initial wave of leukemia differentiation but clear rapidly and do not contribute to residual disease. In contrast, a therapy-induced population of mature AML-derived eosinophil-like cells persists during remission, often in extramedullary organs. Using genetic approaches we show that restricting therapy-induced leukemia maturation to the short-lived neutrophil lineage markedly reduces relapse rates and can yield cure. These results indicate that relapse can originate from therapy-resistant mature AML cells, and suggest differentiation therapy combined with targeted eradication of mature leukemia-derived lineages may improve disease outcome.

Genomic Abnormalities as Biomarkers and Therapeutic Targets in Acute Myeloid Leukemia

Simple Summary

AML is a heterogenous malignancy with a variety of underlying genomic abnormalities. Some of the genetic aberrations in AML have led to the development of specific inhibitors which were approved by the Food and Drug Administration (FDA) and are currently used to treat eligible patients. In this review, we describe five gene mutations for which approved inhibitors have been developed, the response of AML patients to these inhibitors, and the known mechanism(s) of resistance. This review also highlights the significance of developing function-based screens for target discovery in the era of personalized medicine.

Abstract

Acute myeloid leukemia (AML) is a highly heterogeneous malignancy characterized by the clonal expansion of myeloid stem and progenitor cells in the bone marrow, peripheral blood, and other tissues. AML results from the acquisition of gene mutations or chromosomal abnormalities that induce proliferation or block differentiation of hematopoietic progenitors. A combination of cytogenetic profiling and gene mutation analyses are essential for the proper diagnosis, classification, prognosis, and treatment of AML. In the present review, we provide a summary of genomic abnormalities in AML that have emerged as both markers of disease and therapeutic targets. We discuss the abnormalities of RARA, FLT3, BCL2, IDH1, and IDH2, their significance as therapeutic targets in AML, and how various mechanisms cause resistance to the currently FDA-approved inhibitors. We also discuss the limitations of current genomic approaches for producing a comprehensive picture of the activated signaling pathways at diagnosis or at relapse in AML patients, and how innovative technologies combining genomic and functional methods will improve the discovery of novel therapeutic targets in AML. The ultimate goal is to optimize a personalized medicine approach for AML patients and possibly those with other types of cancers.

Ultrasound-assisted one-pot three-component synthesis of new isoxazolines bearing sulfonamides and their evaluation against hematological malignancies

In the present study, following a one-pot two-step protocol, we have synthesized novel sulfonamides-isoxazolines hybrids (3a-r) via a highly regioselective 1,3-dipolar cycloaddition. The present methodology capitalized on trichloroisocyanuric acid (TCCA) as a safe and ecological oxidant and chlorinating agent for the in-situ conversion of aldehydes to nitrile oxides in the presence of hydroxylamine hydrochloride, under ultrasound activation. These nitrile oxides could be engaged in 1,3-dipolar cycloaddition reactions with various alkene to afford the targeted sulfonamides-isoxazolines hybrids (3a-r). The latter were assessed for their antineoplastic activity against model leukemia cell lines (Chronic Myeloid Leukemia, K562 and Promyelocytic Leukemia, HL-60).

Surface antigen-guided CRISPR screens identify regulators of myeloid leukemia differentiation

Lack of cellular differentiation is a hallmark of many human cancers, including acute myeloid leukemia (AML). Strategies to overcome such a differentiation blockade are an approach for treating AML. To identify targets for differentiation-based therapies, we applied an integrated cell surface-based CRISPR platform to assess genes involved in maintaining the undifferentiated state of leukemia cells. Here we identify the RNA-binding protein ZFP36L2 as a critical regulator of AML maintenance and differentiation. Mechanistically, ZFP36L2 interacts with the 3' untranslated region of key myeloid maturation genes, including the ZFP36 paralogs, to promote their mRNA degradation and suppress terminal myeloid cell differentiation. Genetic inhibition of ZFP36L2 restores the mRNA stability of these targeted transcripts and ultimately triggers myeloid differentiation in leukemia cells. Epigenome profiling of several individuals with primary AML revealed enhancer modules near ZFP36L2 that associated with distinct AML cell states, establishing a coordinated epigenetic and post-transcriptional mechanism that shapes leukemic differentiation.

Acute Promyelocytic Leukemia in Children: A Model of Precision Medicine and Chemotherapy-Free Therapy

Acute promyelocytic leukemia (APL) represents a paradigm of precision medicine. Indeed, in the last decades, the introduction of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) completely revolutionized the therapeutic approach to this previously highly fatal disorder. This entirely chemotherapy-free treatment, which provided excellent survival rates, has been initially validated in adults and, recently, translated in the pediatric setting. This review summarizes currently available data on the use of ATRA and ATO combination in pediatric APL, providing a particular focus on peculiar issues and challenges, such as the occurrence of pseudotumor cerebri and death during induction (early death), as well as the advantage offered by the ATO/ATRA combination in sparing long-term sequelae.

All-trans retinoic acid in non-promyelocytic acute myeloid leukemia: driver lesion dependent effects on leukemic stem cells

Acute myeloid leukemia (AML) is an aggressive, often fatal hematopoietic malignancy. All-trans retinoic acid (atRA), one of the first molecularly targeted drugs in oncology, has greatly improved the outcome of a subtype of AML, acute promyelocytic leukemia (APL). In contrast, atRA has so far provided little therapeutic benefit in the much larger group of patients with non-APL AML. Attempts to identify genetically or molecularly defined subgroups of patients that may respond to atRA have not yielded consistent results. Since AML is a stem cell-driven disease, understanding the effectiveness of atRA may require an appreciation of its impact on AML stem cells. Recent studies reported that atRA decreased stemness of AML with an FLT3-ITD mutation, yet increased it in AML1-ETO driven or EVI1-overexpressing AML. This review summarizes the role of atRA in normal hematopoiesis and in AML, focusing on its impact on AML stem cells.

Interconversion between Tumorigenic and Differentiated States in Acute Myeloid Leukemia

Tumors are composed of phenotypically heterogeneous cancer cells that often resemble various differentiation states of their lineage of origin. Within this hierarchy, it is thought that an immature subpopulation of tumor-propagating cancer stem cells (CSCs) differentiates into non-tumorigenic progeny, providing a rationale for therapeutic strategies that specifically eradicate CSCs or induce their differentiation. The clinical success of these approaches depends on CSC differentiation being unidirectional rather than reversible, yet this question remains unresolved even in prototypically hierarchical malignancies, such as acute myeloid leukemia (AML). Here, we show in murine and human models of AML that, upon perturbation of endogenous expression of the lineage-determining transcription factor PU.1 or withdrawal of established differentiation therapies, some mature leukemia cells can de-differentiate and reacquire clonogenic and leukemogenic properties. Our results reveal plasticity of CSC maturation in AML, highlighting the need to therapeutically eradicate cancer cells across a range of differentiation states.

Classic and Variants APLs, as Viewed from a Therapy Response

Most acute promyelocytic leukemia (APL) are caused by PML-RARA, a translocation-driven fusion oncoprotein discovered three decades ago. Over the years, several other types of rare X-RARA fusions have been described, while recently, oncogenic fusion proteins involving other retinoic acid receptors (RARB or RARG) have been associated to very rare cases of acute promyelocytic leukemia. PML-RARA driven pathogenesis and the molecular basis for therapy response have been the focus of many studies, which have now converged into an integrated physio-pathological model. The latter is well supported by clinical and molecular studies on patients, making APL one of the rare hematological disorder cured by targeted therapies. Here we review recent data on APL-like diseases not driven by the PML-RARA fusion and discuss these in view of current understanding of "classic" APL pathogenesis and therapy response.

Acute Promyelocytic Leukemia: A Constellation of Molecular Events around a Single PML-RARA Fusion Gene

Although acute promyelocytic leukemia (APL) is one of the most characterized forms of acute myeloid leukemia (AML), the molecular mechanisms involved in the development and progression of this disease are still a matter of study. APL is defined by the PML-RARA rearrangement as a consequence of the translocation t(15;17)(q24;q21). However, this abnormality alone is not able to trigger the whole leukemic phenotype and secondary cooperating events might contribute to APL pathogenesis. Additional somatic mutations are known to occur recurrently in several genes, such as FLT3, WT1, NRAS and KRAS, whereas mutations in other common AML genes are rarely detected, resulting in a different molecular profile compared to other AML subtypes. How this mutational spectrum, including point mutations in the PML-RARA fusion gene, could contribute to the 10%–15% of relapsed or resistant APL patients is still unknown. Moreover, due to the uncertain impact of additional mutations on prognosis, the identification of the APL-specific genetic lesion is still the only method recommended in the routine evaluation/screening at diagnosis and for minimal residual disease (MRD) assessment. However, the gene expression profile of genes, such as ID1, BAALC, ERG, and KMT2E, once combined with the molecular events, might improve future prognostic models, allowing us to predict clinical outcomes and to categorize APL patients in different risk subsets, as recently reported. In this review, we will focus on the molecular characterization of APL patients at diagnosis, relapse and resistance, in both children and adults. We will also describe different standardized molecular approaches to study MRD, including those recently developed. Finally, we will discuss how novel molecular findings can improve the management of this disease.

Metabolic dependencies and vulnerabilities in leukemia

In this Review, Rashkovan et al. discuss the role of cancer metabolic circuitries feeding anabolism and redox potential in leukemia development and recent progress in translating these important findings to the clinic.

Leukemia cell proliferation requires up-regulation and rewiring of metabolic pathways to feed anabolic cell growth. Oncogenic drivers directly and indirectly regulate metabolic pathways, and aberrant metabolism is central not only for leukemia proliferation and survival, but also mediates oncogene addiction with significant implications for the development of targeted therapies. This review explores leukemia metabolic circuitries feeding anabolism, redox potential, and energy required for tumor propagation with an emphasis on emerging therapeutic opportunities.

Acute Promyelocytic Leukemia: Update on the Mechanisms of Leukemogenesis, Resistance and on Innovative Treatment Strategies

This review highlights new findings that have deepened our understanding of the mechanisms of leukemogenesis, therapy and resistance in acute promyelocytic leukemia (APL). Promyelocytic leukemia-retinoic acid receptor α (PML-RARa) sets the cellular landscape of acute promyelocytic leukemia (APL) by repressing the transcription of RARa target genes and disrupting PML-NBs. The RAR receptors control the homeostasis of tissue growth, modeling and regeneration, and PML-NBs are involved in self-renewal of normal and cancer stem cells, DNA damage response, senescence and stress response. The additional somatic mutations in APL mainly involve FLT3, WT1, NRAS, KRAS, ARID1B and ARID1A genes. The treatment outcomes in patients with newly diagnosed APL improved dramatically since the advent of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). ATRA activates the transcription of blocked genes and degrades PML-RARα, while ATO degrades PML-RARa by promoting apoptosis and has a pro-oxidant effect. The resistance to ATRA and ATO may derive from the mutations in the RARa ligand binding domain (LBD) and in the PML-B2 domain of PML-RARa, but such mutations cannot explain the majority of resistances experienced in the clinic, globally accounting for 5-10% of cases. Several studies are ongoing to unravel clonal evolution and resistance, suggesting the therapeutic potential of new retinoid molecules and combinatorial treatments of ATRA or ATO with different drugs acting through alternative mechanisms of action, which may lead to synergistic effects on growth control or the induction of apoptosis in APL cells.

The cell nucleus. A study in Burgundy

Wilhelm Bernhard’s revolutionary microscopy techniques helped him put forward the hypothesis of specialized compartmentalization of the nucleus. He also described for the first time the nuclear bodies and peri-chromatin fibrils, and demonstrated that these granules contain an RNA component. The tradition of biennial workshops, named after this great scientist, continues, and this year it took place in the heart of Burgundy, in Dijon, France (May 20–24, 2019, organized by INSERM UMR1231, UBFC), where well-fed participants emphasized the importance of viewing the cell nucleus as a hub of specialized colloidal compartments that orchestrate replication, transcription and nuclear transport.

Extracellular-signal-regulated kinase/mitogen-activated protein kinase signaling as a target for cancer therapy: an updated review

Mitogen-activated protein kinase (MAPK) signaling pathway is activated in a wide spectrum of human tumors, exhibiting cardinal oncogenic roles and sustained inhibition of this pathway is considered as a primary goal in clinic. Within this pathway, receptor tyrosine kinases such as epithelial growth factor receptor, mesenchymal-epithelial transition, and AXL act as upstream regulators of RAS/RAF/MEK/extracellular-signal-regulated kinase. MAPK signaling is active in both early and advanced stages of tumorigenesis, and it promotes tumor proliferation, survival, and metastasis. MAPK regulatory effects on cellular constituent of the tumor microenvironment is for immunosuppressive purposes. Cross-talking between MAPK with oncogenic signaling pathways including WNT, cyclooxygenase-2, transforming growth factor-β, NOTCH and (in particular) with phosphatidylinositol 3-kinase is contributed to the multiplication of tumor progression and drug resistance. Developing resistance (intrinsic or acquired) to MAPK-targeted therapy also occurs due to heterogeneity of tumors along with mutations and negative feedback loop of interactions exist between various kinases causing rebound activation of this signaling. Multidrug regimen is a preferred therapeutic avenue for targeting MAPK signaling. To enhance patient tolerance and to mitigate potential adversarial effects related to the combination therapy, determination of a desired dose and drug along with pre-evaluation of cancer-type-specific kinase mutation and sensitivity, especially for patients receiving triplet therapy is an urgent need.

Genetics and mechanisms of NT5C2-driven chemotherapy resistance in relapsed ALL

Mutations in the cytosolic 5' nucleotidase II (NT5C2) gene drive resistance to thiopurine chemotherapy in relapsed acute lymphoblastic leukemia (ALL). Mechanistically, NT5C2 mutant proteins have increased nucleotidase activity as a result of altered activating and autoregulatory switch-off mechanisms. Leukemias with NT5C2 mutations are chemoresistant to 6-mercaptopurine yet show impaired proliferation and self-renewal. Direct targeting of NT5C2 or inhibition of compensatory pathways active in NT5C2 mutant cells may antagonize the emergence of NT5C2 mutant clones driving resistance and relapse in ALL.

FLT3-ITD impedes retinoic acid, but not arsenic, responses in murine acute promyelocytic leukemias

Acute promyelocytic leukemia (APL) is often associated with activating FLT3 signaling mutations. These are highly related to hyperleukocytosis, a major adverse risk factor with chemotherapy-based regimens. APL is a model for oncogene-targeted therapies: all-trans retinoic acid (ATRA) and arsenic both target and degrade its ProMyelocytic Leukemia/Retinoic Acid Receptor α (PML/RARA) driver. The combined ATRA/arsenic regimen now cures virtually all patients with standard-risk APL. Although FLT3-internal tandem duplication (ITD) was an adverse risk factor for historical ATRA/chemotherapy regimens, the molecular bases for this effect remain unknown. Using mouse APL models, we unexpectedly demonstrate that FLT3-ITD severely blunts ATRA response. Remarkably, although the transcriptional output of initial ATRA response is unaffected, ATRA-induced PML/RARA degradation is blunted, as is PML nuclear body reformation and activation of P53 signaling. Critically, the combination of ATRA and arsenic fully rescues therapeutic response in FLT3-ITD APLs, restoring PML/RARA degradation, PML nuclear body reformation, P53 activation, and APL eradication. Moreover, arsenic targeting of normal PML also contributes to APL response in vivo. These unexpected results explain the less favorable outcome of FLT3-ITD APLs with ATRA-based regimens, and stress the key role of PML nuclear bodies in APL eradication by the ATRA/arsenic combination.

Recognition of the toxicity of aristolochic acid

WHAT IS KNOWN AND OBJECTIVE

Aristolochic acid (AA) is an abundant compound in Aristolochia plants and various natural herbs. In the 1990s, a slimming formula used in Belgium that contains Aristolochia fangchi was reported to cause kidney damage and bladder cancer, and aristolochic acid nephropathy (AAN) is now well recognized worldwide. In October 2017, researchers reported an AA signature that is closely associated with hepatocellular carcinoma (HCC) worldwide.

COMMENT

There are differing opinions on the toxicity of AA, and different countries have taken different measures to address the issue. There is a lack of clarity on the causal role of AA in hepatocarcinogenesis and on the potential underlying mechanisms for the reported nephrotoxicity and carcinogenicity. The toxicity of AA differs depending on gender and age, and other risk factors that could explain the variability in the toxicity of AA remain to be identified.

WHAT IS NEW AND CONCLUSION

Whether preparations containing AA, such as many Chinese medicines, should be used remains controversial, and this issue warrants further investigation before definite conclusions can be drawn.

Expanding the clinical relevance of the 5'-nucleotidase cN-II/NT5C2

Purine metabolism is depending on a large amount of enzymes to ensure cellular homeostasis. Among these enzymes, we have been interested in the 5'-nucleotidase cN-II and its role in cancer biology and in response of cancer cells to treatments. This protein has been cited and studied in a large number of papers published during the last decade for its involvement in non-cancerous pathologies such as hereditary spastic paraplegia, schizophrenia, and blood pressure regulation. Here, we review these articles in order to give an overview of the recently discovered clinical relevance of cN-II.