AG-221, a First-in-Class Therapy Targeting Acute Myeloid Leukemia Harboring Oncogenic IDH2 Mutations

Management of toxicities associated with targeted therapies for acute myeloid leukemia: when to push through and when to stop

The recent advent of myriad targeted therapies for acute myeloid leukemia (AML) has led to new hope for our patients but has also introduced new challenges in managing the disease. For clinicians, the ability to treat AML in the outpatient setting with novel agents of equal or greater efficacy than 7+3 has been transformative. Despite the enthusiasm, however, the reality is that many patients are still frail and remain at risk for treatment-related complications. Translating the results of clinical trials into improved outcomes for these individuals requires an understanding of how best to manage the adverse effects of these agents. Which patients benefit most and what to watch for? When to stop therapy? Using illustrative case presentations, this review details the unique toxicities associated with each of the approved mutation-specific and nonspecific targeted drugs for AML. The goal of this review is to help clinicians determine the risk:benefit ratio in decision making for individual patients with AML.

2-Oxoglutarate-dependent dioxygenases in cancer

2-Oxoglutarate-dependent dioxygenases (2OGDDs) are a superfamily of enzymes that play diverse roles in many biological processes, including regulation of hypoxia-inducible factor-mediated adaptation to hypoxia, extracellular matrix formation, epigenetic regulation of gene transcription and the reprogramming of cellular metabolism. 2OGDDs all require oxygen, reduced iron and 2-oxoglutarate (also known as α-ketoglutarate) to function, although their affinities for each of these co-substrates, and hence their sensitivity to depletion of specific co-substrates, varies widely. Numerous 2OGDDs are recurrently dysregulated in cancer. Moreover, cancer-specific metabolic changes, such as those that occur subsequent to mutations in the genes encoding succinate dehydrogenase, fumarate hydratase or isocitrate dehydrogenase, can dysregulate specific 2OGDDs. This latter observation suggests that the role of 2OGDDs in cancer extends beyond cancers that harbour mutations in the genes encoding members of the 2OGDD superfamily. Herein, we review the regulation of 2OGDDs in normal cells and how that regulation is corrupted in cancer.

Advances in Epigenetic Cancer Therapeutics

Cancer has traditionally been hailed a genetic disease, dictated by successive genetic aberrations which alter gene expression. Yet, recent advances in molecular sequencing technologies, enabling the characterisation of cancer patient phenotypes on a large scale, have highlighted epigenetic changes as a hallmark of cancer. Epigenetic modifications, including DNA methylation and demethylation and histone modifications, have been found to play a key role in the pathogenesis of a wide variety of cancers through the regulation of chromatin state, gene expression and other nuclear events. Targeting epigenetic aberrations offers remarkable promise as a potential anti-cancer therapy given the reversible nature of epigenetic changes. Hence, epigenetic therapy has emerged as a rapidly advancing field of cancer research. A plethora of epigenetic therapies which inhibit enzymes of post-translational histone modifications, so-called 'writers', 'erasers' and 'readers', have been developed, with several epigenetic inhibitor agents approved for use in routine clinical practice. Epigenetic therapeutics inhibit the methylation or demethylation and acetylation or deacetylation of DNA and histone proteins. Their targets include writers (DNA methyltransferases [DNMT], histone acetyltransferases [HAT] and histone deacetylases [HDAC]) and erasers (histone demethylases [HDM] and histone methylases [HMT]). With new epigenetic mechanisms increasingly being elucidated, a vast array of targets and therapeutics have been brought to the fore. This review discusses recent advances in cancer epigenetics with a focus on molecular targets and mechanisms of action of epigenetic cancer therapeutics.

Identification of new IDH2R140Q inhibitors by discriminatory analysis-based molecular docking and biological evaluation

Isocitrate dehydrogenase 2 (IDH2) is a key enzyme in the regulation of cell metabolism. Its mutated type can lead to the accumulation of 2-hydroxyglutarate, which is often related to malignancies such as acute myeloid leukemia. Therefore, it is necessary to find new inhibitors targeting mutant IDH2. Discriminatory analysis-based molecular docking was employed to screen the ChemDiv compound library, which resulted in the identification of three new IDH2^R140Q inhibitors with moderate-to-good IC₅₀ values. Among them, compounds 1 and 3 displayed good selectivity against other mutant or wild-type IDH proteins. The most potent compound 1, bearing the [1,2,4]triazolo[1,5-a]pyrimidin scaffold, was subjected to dynamic simulations to provide more information on the binding mode with IDH2^R140Q , providing structural clues to further optimize compound 1 as a new mutant IDH2 inhibitor.

IDH Signalling Pathway in Cholangiocarcinoma: From Biological Rationale to Therapeutic Targeting

Biliary tract cancers are anatomically distinct and genetically diverse tumors, evenly characterized by poor response to standard treatments and a bleak outlook. The advent of comprehensive genomic profiling using next-generation sequencing has unveiled a plethora of potentially actionable aberrations, changing the view of biliary tract cancers from an "orphan" to a "target-rich" disease. Recently, mutations in isocitrate dehydrogenase genes (IDH1/2) and fusions of the fibroblast growth factor receptor have emerged as the most amenable to molecularly targeted inhibition, with several compounds actively investigated in advanced-phase clinical trials. Specifically, the IDH1 inhibitor ivosidenib has been the first targeted agent to show a survival benefit in a randomized phase III trial of cholangiocarcinoma patients harboring IDH1 mutations. In this review article, we will focus on the IDH1/IDH2 pathway, discussing the preclinical rationale of its targeting as well as the promises and challenges of the clinical development of IDH inhibitors in biliary tract cancers.

Can a metabolism-targeted therapeutic intervention successfully subjugate SARS-COV-2? A scientific rational

As a process entailing a high turnover of the host cell molecules, viral replication is required for a successful viral infection and requests virus capacity to acquire the macromolecules required for its propagation. To this end, viruses have adopted several strategies to harness cellular metabolism in accordance with their specific demands. Most viruses upregulate specific cellular anabolic pathways and are largely dependent on such alterations. RNA viruses, for example, upregulate both glycolysisand glycogenolysis providing TCA cycle intermediates essential for anabolic lipogenesis. Also, these infections usually induce the PPP, leading to increased nucleotide levels supporting viral replication. SARS-CoV-2 (the cause of COVID-19)that has so far spread from China throughout the world is also an RNA virus. Owing to the more metabolic plasticity of uninfected cells, a promising approach for specific antiviral therapy, which has drawn a lot of attention in the recent years, would be the targeting of metabolic changes induced by viruses. In the current review, we first summarize some of virus-induced metabolic adaptations and then based on these information as well as SARS-CoV-2 pathogenesis, propose a potential therapeutic modality for this calamitous world-spreading virus with the hope of employing this strategy for near-future clinical application.

Metabolism in tumour-associated macrophages: a quid pro quo with the tumour microenvironment

Lung cancer is the leading cause of death from cancer worldwide. Recent studies demonstrated that the tumour microenvironment (TME) is pivotal for tumour progression, providing multiple targeting opportunities for therapeutic strategies. As one of the most abundant stromal cell types in the TME, tumour-associated macrophages (TAMs) exhibit high plasticity. Malignant cells alter their metabolic profiles to adapt to the limited availability of oxygen and nutrients in the TME, resulting in functional alteration of TAMs. The metabolic features of TAMs are strongly associated with their functional plasticity, which further impacts metabolic profiling in the TME and contributes to tumourigenesis and progression. Here, we review the functional determination of the TME by TAM metabolic alterations, including glycolysis as well as fatty acid and amino acid metabolism, which in turn are influenced by environmental changes. Additionally, we discuss metabolic reprogramming of TAMs to a tumouricidal phenotype as a potential antitumoural therapeutic strategy.

Tumour-associated macrophages (TAMs) display a high level of functional plasticity and altered metabolism symbolised by high sensitivity to the surrounding tumour microenvironment. The metabolism of TAMs provides novel therapeutic opportunities to treat cancer.https://bit.ly/31OqHhe

The epigenomics of sarcoma

Epigenetic regulation is critical to physiological control of development, cell fate, cell proliferation, genomic integrity and, fundamentally, transcriptional regulation. This epigenetic control occurs at multiple levels including through DNA methylation, histone modification, nucleosome remodelling and modulation of the 3D chromatin structure. Alterations in genes that encode chromatin regulators are common among mesenchymal neoplasms, a collection of more than 160 tumour types including over 60 malignant variants (sarcomas) that have unique and varied genetic, biological and clinical characteristics. Herein, we review those sarcomas in which chromatin pathway alterations drive disease biology. Specifically, we emphasize examples of dysregulation of each level of epigenetic control though mechanisms that include alterations in metabolic enzymes that regulate DNA methylation and histone post-translational modifications, mutations in histone genes, subunit loss or fusions in chromatin remodelling and modifying complexes, and disruption of higher-order chromatin structure. Epigenetic mechanisms of tumorigenesis have been implicated in mesenchymal tumours ranging from chondroblastoma and giant cell tumour of bone to chondrosarcoma, malignant peripheral nerve sheath tumour, synovial sarcoma, epithelioid sarcoma and Ewing sarcoma - all diseases that present in a younger patient population than most cancers. Finally, we review current and potential future approaches for the development of sarcoma therapies based on this emerging understanding of chromatin dysregulation.

Enasidenib and ivosidenib in AML

The isocitrate dehydrogenases enzymes, IDH1 and IDH2, catalyze the conversion of isocitrate to α-ketoglutarate (αKG) in the cell cytoplasm and mitochondria, respectively, and contribute to generating the dihydronicotinamide-adenine dinucleotide phosphate (NADPH) as reductive potential in different cellular processes. Mutations in IDH1 and IDH2 genes are found collectively in about 20-25% of acute myeloid leukemia (AML) patients. Mutant IDH enzymes have neomorphic activity and convert αKG to the oncometabolite R-2-hydroxyglutarate (R-2-HG) which accumulates at high levels in the cell and hampers the function of αKG-dependent enzymes, including epigenetic regulators, thus leading to altered gene expression and block of differentiation and contributing to leukemia development. Inhibition of the neomorphic mutants induces marked decrease in R-2-HG levels and restores myeloid differentiation. Enasidenib and ivosidenib are potent and selective inhibitors of mutant IDH2 and IDH1, respectively, act as differentiating agents and showed clinical activity in relapsed/refractory (R/R) AML harboring the specific mutation. As single agents, both drugs have been approved by the Food and Drug Administration (FDA) for the treatment of R/R AML. The relevance of IDH targeting within either single agent approach or, most importantly, combinatorial treatments in AML will be discussed.

Systemic Immunometabolism: Challenges and Opportunities

Over the past 10 years, the field of immunometabolism made great strides to unveil the crucial role of intracellular metabolism in regulating immune cell function. Emerging insights into how systemic inflammation and metabolism influence each other provide a critical additional dimension on the organismal level. Here, we discuss the concept of systemic immunometabolism and review the current understanding of the communication circuits that underlie the reciprocal impact of systemic inflammation and metabolism across organs in inflammatory and infectious diseases, as well as how these mechanisms apply to homeostasis. We present current challenges of systemic immunometabolic research, and in this context, highlight opportunities and put forward ideas to effectively explore organismal physiological complexity in both health and disease.

All-Trans Retinoic Acid Synergizes with Enasidenib to Induce Differentiation of IDH2-Mutant Acute Myeloid Leukemia Cells

PURPOSE

Pharmacological inhibition of mutant isocitrate dehydrogenase (IDH) reduces R-2-hydroxyglutarate (2-HG) levels and restores cellular differentiation in vivo and in vitro. The IDH2 inhibitor enasidenib (AG-221) has been approved by the FDA as a first-in-class inhibitor for the treatment of relapsed or refractory (R/R) IDH2-mutant acute myeloid leukemia (AML). In this study, the effects of a combination of all-trans retinoic acid (ATRA) and AG-221 on AML cell differentiation was explored, along with the mechanisms employed by IDH2-mutant cells in AML.

MATERIALS AND METHODS

We treated the human AML cell line, IDH2-mutant-TF-1, and primary human AML cells carrying IDH2 mutation with 30 μM AG-221 and 100 nM ATRA, alone or in combination.

RESULTS

Combined treatment with AG-221 and ATRA inhibited 2-HG production and resulted in synergistic effects on differentiation among IDH2-mutant AML cells and primary AML cells expressing IDH2 mutation. Combined treatment with AG-221 and ATRA altered autophagic activity. AG-221 and ATRA treatment-induced differentiation of IDH2-mutant AML cells was associated with autophagy induction, without suppressing autophagy flux at maturation and degradation stages. A RAF-1/MEK/ERK pathway was founded to be associated with AG-221 and ATRA-induced differentiation in IDH2-mutant AML cells. IDH-associated changes in histone methylation markers decreased after AG-221 and ATRA combination treatment.

CONCLUSION

Our preliminary evidence indicates that the addition of ATRA to treatments with IDH2 inhibitor may lead to further improvements or increases in response rates in IDH2-mutant AML patients who do not appear to benefit from treatments with IDH2 inhibitor alone.

Isocitrate Dehydrogenase Mutations in Myelodysplastic Syndromes and in Acute Myeloid Leukemias

Acute myeloid leukemia (AML) is a heterogeneous disease generated by the acquisition of multiple genetic and epigenetic aberrations which impair the proliferation and differentiation of hematopoietic progenitors and precursors. In the last years, there has been a dramatic improvement in the understanding of the molecular alterations driving cellular signaling and biochemical changes determining the survival advantage, stimulation of proliferation, and impairment of cellular differentiation of leukemic cells. These molecular alterations influence clinical outcomes and provide potential targets for drug development. Among these alterations, an important role is played by two mutant enzymes of the citric acid cycle, isocitrate dehydrogenase (IDH), IDH1 and IDH2, occurring in about 20% of AMLs, which leads to the production of an oncogenic metabolite R-2-hydroxy-glutarate (R-2-HG); this causes a DNA hypermethylation and an inhibition of hematopoietic stem cell differentiation. IDH mutations differentially affect prognosis of AML patients following the location of the mutation and other co-occurring genomic abnormalities. Recently, the development of novel therapies based on the specific targeting of mutant IDH may contribute to new effective treatments of these patients. In this review, we will provide a detailed analysis of the biological, clinical, and therapeutic implications of IDH mutations.

Isocitrate dehydrogenase variants in cancer - Cellular consequences and therapeutic opportunities

Abnormal metabolism is common in cancer cells and often correlates with mutations in genes encoding for enzymes involved in small-molecule metabolism. Isocitrate dehydrogenase 1 (IDH1) is the most frequently mutated metabolic gene in cancer. Cancer-associated substitutions in IDH1 and IDH2 impair wild-type production of 2-oxoglutarate and reduced nicotinamide adenine dinucleotide phosphate (NADPH) from isocitrate and oxidised nicotinamide adenine dinucleotide phosphate (NADP⁺ ), and substantially promote the IDH variant catalysed conversion of 2-oxoglutarate to d-2-hydroxyglutarate (d-2HG). Elevated d-2HG is a biomarker for some cancers, and inhibition of IDH1 and IDH2 variants is being pursued as a medicinal chemistry target. We provide an overview of the types of cancer-associated IDH variants, discuss some of the proposed consequences of altered metabolism as a result of elevated d-2HG, summarise therapeutic efforts targeting IDH variants and identify areas for future research.

Metabolomics in acute myeloid leukemia

Acute myeloid leukemia (AML) is a complex, heterogenous hematological malignancy caused by mutations in myeloid differentiation and proliferation. Response to therapy and long-term outcomes vary widely based on chromosomal and molecular aberrations. Many platforms have been used to characterize and stratify AML. Metabolomics, the global profiling of small molecules in a biological sample, has emerged in the last decade as an important tool for studying the metabolic dependency of cancer cells. Metabolic reprogramming is not only an important manifestation of AML but clinically relevant for diagnosis, risk stratification and targeted drug development. In this review, we discuss notable metabolic studies of the last decade and their application to novel therapies.

Interplay between Cellular Metabolism and the DNA Damage Response in Cancer

Metabolism is a fundamental cellular process that can become harmful for cells by leading to DNA damage, for instance by an increase in oxidative stress or through the generation of toxic byproducts. To deal with such insults, cells have evolved sophisticated DNA damage response (DDR) pathways that allow for the maintenance of genome integrity. Recent years have seen remarkable progress in our understanding of the diverse DDR mechanisms, and, through such work, it has emerged that cellular metabolic regulation not only generates DNA damage but also impacts on DNA repair. Cancer cells show an alteration of the DDR coupled with modifications in cellular metabolism, further emphasizing links between these two fundamental processes. Taken together, these compelling findings indicate that metabolic enzymes and metabolites represent a key group of factors within the DDR. Here, we will compile the current knowledge on the dynamic interplay between metabolic factors and the DDR, with a specific focus on cancer. We will also discuss how recently developed high-throughput technologies allow for the identification of novel crosstalk between the DDR and metabolism, which is of crucial importance to better design efficient cancer treatments.

Challenges and Opportunities in Cancer Drug Resistance

There has been huge progress in the discovery of targeted cancer therapies in recent years. However, even for the most successful and impactful cancer drugs which have been approved, both innate and acquired mechanisms of resistance are commonplace. These emerging mechanisms of resistance have been studied intensively, which has enabled drug discovery scientists to learn how it may be possible to overcome such resistance in subsequent generations of treatments. In some cases, novel drug candidates have been able to supersede previously approved agents; in other cases they have been used sequentially or in combinations with existing treatments. This review summarizes the current field in terms of the challenges and opportunities that cancer resistance presents to drug discovery scientists, with a focus on small molecule therapeutics. As part of this review, common themes and approaches have been identified which have been utilized to successfully target emerging mechanisms of resistance. This includes the increase in target potency and selectivity, alternative chemical scaffolds, change of mechanism of action (covalents, PROTACs), increases in blood-brain barrier permeability (BBBP), and the targeting of allosteric pockets. Finally, wider approaches are covered such as monoclonal antibodies (mAbs), bispecific antibodies, antibody drug conjugates (ADCs), and combination therapies.

Genomic landscape in acute myeloid leukemia and its implications in risk classification and targeted therapies

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy in terms of clinical features, underlying pathogenesis and treatment outcomes. Recent advances in genomic techniques have unraveled the molecular complexity of AML leukemogenesis, which in turn have led to refinement of risk stratification and personalized therapeutic strategies for patients with AML. Incorporation of prognostic and druggable genetic biomarkers into clinical practice to guide patient-specific treatment is going to be the mainstay in AML therapeutics. Since 2017 there has been an explosion of novel treatment options to tailor personalized therapy for AML patients. In the past 3 years, the U.S. Food and Drug Administration approved a total of eight drugs for the treatment of AML; most specifically target certain gene mutations, biological pathways, or surface antigen. These novel agents are especially beneficial for older patients or those with comorbidities, in whom the treatment choice is limited and the clinical outcome is very poor. How to balance efficacy and toxicity to further improve patient outcome is clinically relevant. In this review article, we give an overview of the most relevant genetic markers in AML with special focus on the therapeutic implications of these aberrations.

Cutting Edge Molecular Therapy for Acute Myeloid Leukemia

Recently, whole exome sequencing for acute myeloid leukemia (AML) has been performed by a next-generation sequencer in several studies. It has been revealed that a few gene mutations are identified per AML patient. Some of these mutations are actionable mutations that affect the response to an approved targeted treatment that is available for off-label treatment or that is available in clinical trials. The era of precision medicine for AML has arrived, and it is extremely important to detect actionable mutations relevant to treatment decision-making. However, the percentage of actionable mutations found in AML is about 50% at present, and therapeutic development is also needed for AML patients without actionable mutations. In contrast, the newly approved drugs are less toxic than conventional intensive chemotherapy and can be combined with low-intensity treatments. These combination therapies can contribute to the improvement of prognosis, especially in elderly AML patients who account for more than half of all AML patients. Thus, the treatment strategy for leukemia is changing drastically and showing rapid progress. In this review, we present the latest information regarding the recent development of treatment for AML.

Structure-based design, synthesis and bioactivity evaluation of macrocyclic inhibitors of mutant isocitrate dehydrogenase 2 (IDH2) displaying activity in acute myeloid leukemia cells

The enzymes involved in the metabolic pathways in cancer cells have been demonstrated as important therapeutic targets such as the isocitrate dehydrogenase 2 (IDH2). A series of macrocyclic derivatives was designed based on the marketed IDH2 inhibitor AG-221 by using the conformational restriction strategy. The resulted compounds showed moderate to good inhibitory potential against different IDH2-mutant enzymes. Amongst, compound C6 exhibited better IDH2^R140Q inhibitory potency than AG-221, and showed excellent activity of 2-hydroxyglutarate (2-HG) suppression in vitro and its mesylate displayed good pharmacokinetic profiles. Moreover, C6 performed strong binding mode to IDH2^R140Q after computational docking and dynamic simulation, which may serve as a good starting point for further development.

A comprehensive review of genetic alterations and molecular targeted therapies for the implementation of personalized medicine in acute myeloid leukemia

Acute myeloid leukemia (AML) is an extremely heterogeneous disease defined by the clonal growth of myeloblasts/promyelocytes not only in the bone marrow but also in peripheral blood and/or tissues. Gene mutations and chromosomal abnormalities are usually associated with aberrant proliferation and/or block in the normal differentiation of hematopoietic cells. So far, the combination of cytogenetic profiling and molecular and gene mutation analyses remains an essential tool for the classification, diagnosis, prognosis, and treatment for AML. This review gives an overview on how the development of novel innovative technologies has allowed us not only to detect the genetic alterations as early as possible but also to understand the molecular pathogenesis of AML to develop novel targeted therapies. We also discuss the remarkable advances made during the last decade to understand the AML genome both at primary and relapse diseases and how genetic alterations might influence the distinct biological groups as well as the clonal evolution of disease during the diagnosis and relapse. Also, the review focuses on how the persistence of epigenetic gene mutations during morphological remission is associated with relapse. It is suggested that along with the prognostic and therapeutic mutations, the novel molecular targeted therapies either approved by FDA or those under clinical trials including CART-cell therapy would be of immense importance in the effective management of AML.

The progress and development of GLUT1 inhibitors targeting cancer energy metabolism

A major difference between glucose metabolism in cancer cells and normal cells is that glucose in cancer cells is preferably converted to lactate in aerobic conditions rather than oxidized in mitochondria. This process is called aerobic glycolysis, known as the 'Warburg effect'. In this review, we focus on the energy-metabolism characteristics between tumor and normal cells, analyzing the regulation mechanism of energy metabolism based on glycolysis, and summarizing two targets on the upstream proteins of glycolysis, including glucose transporter (GLUT) and hexokinase. In addition, we proposed the risks and limitations of GLUT1-based drug research and summarized the current research progress of representative drugs, including natural and synthetic GLUT1 inhibitors. This will provide guidance for designing and synthesizing small molecule drugs targeting GLUT1 in glycolysis.

Is Mitochondrial Dysfunction a Common Root of Noncommunicable Chronic Diseases?

Mitochondrial damage is implicated as a major contributing factor for a number of noncommunicable chronic diseases such as cardiovascular diseases, cancer, obesity, and insulin resistance/type 2 diabetes. Here, we discuss the role of mitochondria in maintaining cellular and whole-organism homeostasis, the mechanisms that promote mitochondrial dysfunction, and the role of this phenomenon in noncommunicable chronic diseases. We also review the state of the art regarding the preclinical evidence associated with the regulation of mitochondrial function and the development of current mitochondria-targeted therapeutics to treat noncommunicable chronic diseases. Finally, we give an integrated vision of how mitochondrial damage is implicated in these metabolic diseases.

Mitochondria Targeting as an Effective Strategy for Cancer Therapy

Mitochondria are well known for their role in ATP production and biosynthesis of macromolecules. Importantly, increasing experimental evidence points to the roles of mitochondrial bioenergetics, dynamics, and signaling in tumorigenesis. Recent studies have shown that many types of cancer cells, including metastatic tumor cells, therapy-resistant tumor cells, and cancer stem cells, are reliant on mitochondrial respiration, and upregulate oxidative phosphorylation (OXPHOS) activity to fuel tumorigenesis. Mitochondrial metabolism is crucial for tumor proliferation, tumor survival, and metastasis. Mitochondrial OXPHOS dependency of cancer has been shown to underlie the development of resistance to chemotherapy and radiotherapy. Furthermore, recent studies have demonstrated that elevated heme synthesis and uptake leads to intensified mitochondrial respiration and ATP generation, thereby promoting tumorigenic functions in non-small cell lung cancer (NSCLC) cells. Also, lowering heme uptake/synthesis inhibits mitochondrial OXPHOS and effectively reduces oxygen consumption, thereby inhibiting cancer cell proliferation, migration, and tumor growth in NSCLC. Besides metabolic changes, mitochondrial dynamics such as fission and fusion are also altered in cancer cells. These alterations render mitochondria a vulnerable target for cancer therapy. This review summarizes recent advances in the understanding of mitochondrial alterations in cancer cells that contribute to tumorigenesis and the development of drug resistance. It highlights novel approaches involving mitochondria targeting in cancer therapy.

Molecular modeling studies to discover novel mIDH2 inhibitors with high selectivity for the primary and secondary mutants

Mutant isocitrate dehydrogenase 2 (mIDH2) is an emerging target for the treatment of cancer. AG-221 is the first mIDH2 inhibitor approved by the FDA for acute myeloid leukemia treatment, but its acquired resistance has recently been observed, necessitating the development of new inhibitor. In this study, a multi-step virtual screening protocol was employed for the analysis of a large database of compounds to identify potential mIDH2 inhibitors. To this end, we firstly utilized molecular dynamics (MD) simulations and binding free energy calculations to elucidate the key factors affecting ligand binding and drug resistance. Based on these findings, the receptor-ligand interaction-based pharmacophore (IBP) model and hierarchical docking-based virtual screening were sequentially carried out to assess 212,736 compounds from the Specs database. The resulting hits were finally ranked by PAINS filter and ADME prediction and the top compounds were obtained. Among them, six molecules were identified as mIDH2 putative inhibitors with high selectivity by interacting with the capping residue Asp312. Furthermore, subsequent docking and MD experiments demonstrated that compound V2 might have potential inhibitory activity against the AG-221-resistant mutants, thereby making it a promising lead for the development of novel mIDH2 inhibitors.

Impact of the Protein Data Bank on antineoplastic approvals

Open access to 3D structure information from the Protein Data Bank (PDB) facilitated discovery and development of >90% of the 79 new antineoplastic agents (54 small molecules, 25 biologics) with known molecular targets approved by the FDA 2010-2018. Analyses of PDB holdings, the scientific literature and related documents for each drug-target combination revealed that the impact of public-domain 3D structure data was broad and substantial, ranging from understanding target biology (∼95% of all targets) to identifying a given target as probably druggable (∼95% of all targets) to structure-guided lead optimization (>70% of all small-molecule drugs). In addition to aggregate impact assessments, illustrative case studies are presented for three protein kinase inhibitors, an allosteric enzyme inhibitor and seven advanced-stage melanoma therapeutics.

Identification of a selective inhibitor of IDH2/R140Q enzyme that induces cellular differentiation in leukemia cells

Background

IDH2/R140Q mutation is frequently detected in acute myeloid leukemia (AML). It contributes to leukemia via accumulation of oncometabolite D-2-HG. Therefore, mutant IDH2 is a promising target for AML. Discovery of IDH2 mutant inhibitors is in urgent need for AML therapy.

Methods

Structure-based in silico screening and enzymatic assays were used to identify IDH2/R140Q inhibitors. Molecular docking, mutant structure building and molecular dynamics simulations were applied to investigate the inhibitory mechanism and selectivity of CP-17 on IDH2/R140Q. TF-1 cells overexpressed IDH2/R140Q mutant were used to study the effects of CP-17 on cellular proliferation and differentiation, the wild-type TF-1 cells were used as control. The intracellular D-2-HG production was measured by LC-MS. The histone methylation was evaluated with specific antibodies by western blot.

Results

CP-17, a heterocyclic urea amide compound, was identified as a potent inhibitor of IDH2/R140Q mutant by in silico screening and enzymatic assay. It exhibits excellent inhibitory activity with IC₅₀ of 40.75 nM against IDH2/R140Q. More importantly, it shows poor activity against the wild-type IDH1/2, resulting in a high selectivity of over 55 folds, a dramatic improvement over previously developed inhibitors such as AGI-6780 and Enasidenib. Molecular simulations suggested that CP-17 binds to IDH2/R140Q at the allosteric site within the dimer interface through extensive polar and hydrophobic interactions, locking the enzyme active sites in open conformations with abolished activity to produce D-2-HG. Cellular assay results demonstrated that CP-17 inhibits intracellular D-2-HG production and suppresses the proliferation of TF-1 erythroleukemia cells carrying IDH2/R140Q mutant. Further, CP-17 also restores the EPO-induced differentiation that is blocked by the mutation and decreases hypermethylation of histone in the TF-1(IDH2/R140Q) cells.

Conclusions

These results indicate that CP-17 can serve as a lead compound for the development of inhibitory drugs against AML with IDH2/R140Q mutant.

Dysregulation of metabolic enzymes in tumor and stromal cells: Role in oncogenesis and therapeutic opportunities

Altered cellular metabolism is a hallmark of cancer. Metabolic rewiring in cancer cells occurs due to the activation of oncogenes, inactivation of tumor suppressor genes, and/or other adaptive changes in cell signaling pathways. Furthermore, altered metabolism is also reported in tumor-corrupted stromal cells as a result of their interaction with cancer cells or due to their adaptation in the dynamic tumor microenvironment. Metabolic alterations are associated with dysregulation of metabolic enzymes and tumor-stromal metabolic crosstalk is vital for the progressive malignant journey of the tumor cells. Therefore, several therapies targeting metabolic enzymes have been evaluated and/or are being investigated in preclinical and clinical studies. In this review, we discuss some important metabolic enzymes that are altered in tumor and/or stromal cells, and focus on their role in supporting tumor growth. Moreover, we also discuss studies carried out in various cancers to target these metabolic abnormalities for therapeutic exploitation.

Development and Validation of UPLC-MS/MS Method for Determination of Enasidenib in Rat Plasma and Its Pharmacokinetic Application

In our research, a straightforward UPLC-MS/MS method, with diazepam as the internal standard (IS), was proposed and acknowledged to determine the concentrations of enasidenib in rat plasma. When preparing the sample, we used acetonitrile for protein precipitation. The gradient elution method was used, and the mobile phase was acetonitrile and 0.1% formic acid. Diazepam was used as the IS. We used the Acquity UPLC BEH C18 column to separate enasidenib and IS. Under the positive ion electrospray ionization (ESI) source conditions, the mass transfer pairs of enasidenib were monitored by multiple reaction monitoring (MRM) to be m/z 474.2 ⟶ 456.1 and m/z 474.2 ⟶ 267.0, and the IS mass transfer pairs were m/z 285.0 ⟶ 154.0. Enasidenib had good linearity (r ² = 0.9985) in the concentration range of 1.0-1000 ng/mL. Besides, the values of intraday and interday precision were 2.25-8.40% and 3.94-5.46%, respectively, and the range of the accuracy values varied from -1.44 to 2.34%. Matrix effect, extraction recovery, and stability were compliant with FDA approval guidelines in terms of bioanalytical method validation. We had established a new method that had been applied to the pharmacokinetic study of enasidenib in rats.

Enasidenib in patients with mutant IDH2 myelodysplastic syndromes: a phase 1 subgroup analysis of the multicentre, AG221-C-001 trial

BACKGROUND

Mutations in isocitrate dehydrogenase-2 (IDH2) occur in around 5% of patients with myelodysplastic syndromes. Neomorphic activity of mutant IDH2 proteins results in hypermethylation of DNA and histones, leading to blocked haemopoietic differentiation. Enasidenib, an inhibitor of mutated IDH2 proteins, induces responses in patients with IDH2-mutated, relapsed or refractory acute myeloid leukaemia. We aimed to establish the clinical outcomes of enasidenib monotherapy in a subgroup of patients with myelodysplastic syndromes harbouring mutations in IDH2 from the AG221-C-001 trial.

METHODS

The multicentre, open-label, phase 1-2 AG221-C-001 trial enrolled patients with advanced haematological malignancies (2008 WHO criteria) harbouring an IDH2 mutation. The present study is a subgroup analysis of patients with IDH2-mutated myelodysplastic syndromes in the phase 1 dose-escalation and expansion portions of the trial. Patients with myelodysplastic syndromes were aged 18 years or older with an ECOG performance status score of 2 or lower, and were relapsed or refractory to, or ineligible for, standard treatments. Patients received oral doses of enasidenib at 60-300 mg per day in repeated 28-day treatment cycles. In this subgroup analysis, we focused on the safety and activity of enasidenib as main outcomes. Overall response rate, duration of response, and overall and event-free survival analyses were by intention-to-treat. Safety was assessed in all participants who received at least one dose of study drug in terms of treatment-emergent adverse events. The AG221-C-001 trial is registered on ClinicalTrials.gov, NCT01915498, status ongoing but closed to recruitment.

FINDINGS

17 patients with myelodysplastic syndromes harbouring an IDH2 mutation (median age, 67·0 years [IQR 60·5-73·0]) were enrolled between Feb 18, 2014, and Sept 1, 2015. At data cutoff (Oct 1, 2018), after a median follow-up of 11·0 months (IQR 6·8-23·0), all patients had discontinued enasidenib, with a median of 3 treatment cycles (2-15) for all patients (five [29%] received ≥12 cycles). At entry, three (18%) patients had relapsed after allogeneic stem-cell transplants, 13 (76%) had previously received therapy with hypomethylating agents, and ten (59%) had received at least two previous therapies. No dose-limiting toxicities were reported. The most common treatment-emergent adverse events were diarrhoea and nausea (in nine [53%] patients each). Most common grade 3-4 treatment-emergent adverse events were indirect hyperbilirubinaemia (in six [35%] patients), pneumonia (in five [29%] patients), and thrombocytopaenia (in four [24%] patients). Serious treatment-emergent adverse events in more than one patient were pneumonia (in five [29% patients); tumor lysis syndrome (in three [18%] patients); and sepsis, atrial flutter, indirect hyperbilirubinaemia, cerebral hemorrhage, and mental status change (in two [12%] patients each). No treatment-related deaths occurred. An overall response was achieved in 9 patients (53% [95% CI 28-77]), with a median duration of response of 9·2 months (95% CI 1·0-not reached). Six (46%) of 13 patients previously treated with hypomethylating agents responded. Median overall survival was 16·9 months (95% CI 1·5-32·3), and median event-free survival was 11·0 months (1·5-16·7).

INTERPRETATION

Enasidenib is generally well tolerated and can induce responses in patients with mutant IDH2 myelodysplastic syndromes, including in those who have had previous therapy with hypomethylating agents. Testing for IDH2 mutations in myelodysplastic syndromes is essential for identifying patients who might benefit from enasidenib therapy, including those patients in whom conventional treatments have been unsuccessful.

FUNDING

Celgene and Agios Pharmaceuticals.

The leukaemia stem cell: similarities, differences and clinical prospects in CML and AML

For two decades, leukaemia stem cells (LSCs) in chronic myeloid leukaemia (CML) and acute myeloid leukaemia (AML) have been advanced paradigms for the cancer stem cell field. In CML, the acquisition of the fusion tyrosine kinase BCR-ABL1 in a haematopoietic stem cell drives its transformation to become a LSC. In AML, LSCs can arise from multiple cell types through the activity of a number of oncogenic drivers and pre-leukaemic events, adding further layers of context and genetic and cellular heterogeneity to AML LSCs not observed in most cases of CML. Furthermore, LSCs from both AML and CML can be refractory to standard-of-care therapies and persist in patients, diversify clonally and serve as reservoirs to drive relapse, recurrence or progression to more aggressive forms. Despite these complexities, LSCs in both diseases share biological features, making them distinct from other CML or AML progenitor cells and from normal haematopoietic stem cells. These features may represent Achilles' heels against which novel therapies can be developed. Here, we review many of the similarities and differences that exist between LSCs in CML and AML and examine the therapeutic strategies that could be used to eradicate them.

Gray Areas in the Gray Matter: IDH1/2 Mutations in Glioma

Since the first discovery of isocitrate dehydrogenase (IDH) mutations in cancer, considerable progress has been made in our understanding of their contribution to cancer development. For glioma, this has helped to identify two diagnostic groups of tumors (oligodendroglioma and astrocytoma IDHmt) with distinct clinical characteristics and that are now diagnosed by the presence of the IDH mutations. The metabolic changes occurring as the consequence of the altered substrate affinity of the mutant IDH protein results in a cascade of intracellular changes, also inducing a relative sensitivity to chemotherapy and radiotherapy compared with IDHwt tumors. Pharmacologic blockade of the mutant enzyme with first-in-class inhibitors has been efficacious for the treatment of IDH-mutant acute myeloid leukemia (AML) and is currently being evaluated in phase III trials for IDH-mutant glioma (INDIGO) and cholangiocarcinoma (ClarIDHy). It seems likely that acquired resistance to mutant IDH inhibitors will eventually emerge, and combination therapies to augment the antitumor activity of mutant IDH inhibitors have already been initiated. Approaches to exploit, rather than inhibit, the unique metabolism of IDH-mutant cancer cells have emerged from laboratory studies and are now also being tested in the clinic. Results of these clinical trials are eagerly awaited and will likely provide new key insights and direction of the treatment of IDH-mutant human cancer.

The paradox of cancer genes in non-malignant conditions: implications for precision medicine

Next-generation sequencing has enabled patient selection for targeted drugs, some of which have shown remarkable efficacy in cancers that have the cognate molecular signatures. Intriguingly, rapidly emerging data indicate that altered genes representing oncogenic drivers can also be found in sporadic non-malignant conditions, some of which have negligible and/or low potential for transformation to cancer. For instance, activating KRAS mutations are discerned in endometriosis and in brain arteriovenous malformations, inactivating TP53 tumor suppressor mutations in rheumatoid arthritis synovium, and AKT, MAPK, and AMPK pathway gene alterations in the brains of Alzheimer's disease patients. Furthermore, these types of alterations may also characterize hereditary conditions that result in diverse disabilities and that are associated with a range of lifetime susceptibility to the development of cancer, varying from near universal to no elevated risk. Very recently, the repurposing of targeted cancer drugs for non-malignant conditions that are associated with these genomic alterations has yielded therapeutic successes. For instance, the phenotypic manifestations of CLOVES syndrome, which is characterized by tissue overgrowth and complex vascular anomalies that result from the activation of PIK3CA mutations, can be ameliorated by the PIK3CA inhibitor alpelisib, which was developed and approved for breast cancer. In this review, we discuss the profound implications of finding molecular alterations in non-malignant conditions that are indistinguishable from those driving cancers, with respect to our understanding of the genomic basis of medicine, the potential confounding effects in early cancer detection that relies on sensitive blood tests for oncogenic mutations, and the possibility of reverse repurposing drugs that are used in oncology in order to ameliorate non-malignant illnesses and/or to prevent the emergence of cancer.

Vorasidenib (AG-881): A First-in-Class, Brain-Penetrant Dual Inhibitor of Mutant IDH1 and 2 for Treatment of Glioma

Inhibitors of mutant isocitrate dehydrogenase (mIDH) 1 and 2 cancer-associated enzymes prevent the accumulation of the oncometabolite d-2-hydroxyglutarate (2-HG) and are under clinical investigation for the treatment of several cancers harboring an IDH mutation. Herein, we describe the discovery of vorasidenib (AG-881), a potent, oral, brain-penetrant dual inhibitor of both mIDH1 and mIDH2. X-ray cocrystal structures allowed us to characterize the compound binding site, leading to an understanding of the dual mutant inhibition. Furthermore, vorasidenib penetrates the brain of several preclinical species and inhibits 2-HG production in glioma tissue by >97% in an orthotopic glioma mouse model. Vorasidenib represents a novel dual mIDH1/2 inhibitor and is currently in clinical development for the treatment of low-grade mIDH glioma.

Water Networks and Correlated Motions in Mutant Isocitrate Dehydrogenase 1 (IDH1) Are Critical for Allosteric Inhibitor Binding and Activity

Point mutations in human isocitrate dehydrogenase 1 (IDH1) can drive malignancies, including lower-grade gliomas and secondary glioblastomas, chondrosarcomas, and acute myeloid leukemias. These mutations, which usually affect residue R132, ablate the normal activity of catalyzing the NADP⁺-dependent oxidation of isocitrate to α-ketoglutarate (αKG) while also acquiring a neomorphic activity of reducing αKG to d-2-hydroxyglutarate (D2HG). Mutant IDH1 can be selectively therapeutically targeted due to structural differences that occur in the wild type (WT) versus mutant form of the enzyme, though the full mechanisms of this selectivity are still under investigation. Here we probe the mechanistic features of the neomorphic activity and selective small molecule inhibition through a new lens, employing WaterMap and molecular dynamics simulations. These tools identified a high-energy path of water molecules connecting the inhibitor binding site with the αKG and NADP⁺ binding sites in mutant IDH1. This water path aligns spatially with the α10 helix from WT IDH1 crystal structures. Mutating residues at the termini of this water path specifically disrupted inhibitor binding and/or D2HG production, revealing additional key residues to consider in optimizing druglike molecules against mutant IDH1. Taken together, our findings from molecular simulations and mutant enzyme kinetic assays provide insight into how disrupting water paths through enzyme active sites can impact not only inhibitor potency but also substrate recognition and activity.

Is the IDH Mutation a Good Target for Chondrosarcoma Treatment?

Chondrosarcomas are rare cancers of bone that arise from the malignant transformation of cells of chondrocytic lineage. They are known to be resistant to systemic cytotoxic chemotherapy and radiotherapy. The mainstay of management of localised disease is en bloc surgical resection with curative intent. Metastatic chondrosarcoma has a dismal prognosis, and to date, there are no proven effective systemic therapies in the advanced setting. Genomic studies have demonstrated that 50 to 80% of chondrosarcomas harbour a mutation in either the IDH1 or IDH2 gene. IDH inhibitors are currently under investigation in clinical trials, after showing promising results in phase 1 studies in IDH mutated cancers. In chondrosarcoma, IDH mutations represent an attractive target, however, early results with IDH inhibitors in IDH mutated chondrosarcoma are modest and the final results of ongoing trials are eagerly awaited.

Optimal Bayesian Filtering for Biomarker Discovery: Performance and Robustness

Optimal Bayesian feature filtering (OBF) is a fast and memory-efficient algorithm that optimally identifies markers with distributional differences between treatment groups under Gaussian models. Here, we study the performance and robustness of OBF for biomarker discovery. Our contributions are twofold: (1) we examine how OBF performs on data that violates modeling assumptions, and (2) we provide guidelines on how to set input parameters for robust performance. Contribution (1) addresses an important, relevant, and commonplace problem in computational biology, where it is often impossible to validate an algorithm's core assumptions. To accomplish both tasks, we present a battery of simulations that implement OBF with different inputs and challenge each assumption made by OBF. In particular, we examine the robustness of OBF with respect to incorrect input parameters, false independence, imbalanced sample size, and we address the Gaussianity assumption by considering performance on an extensive family of non-Gaussian distributions. We address advantages and disadvantages between different priors and optimization criteria throughout. Finally, we evaluate the utility of OBF in biomarker discovery using acute myeloid leukemia (AML) and colon cancer microarray datasets, and show that OBF is successful at identifying well-known biomarkers for these diseases that rank low under moderated t-test.

Targeting DNA repair in gliomas

PURPOSE OF REVIEW

Gliomas represent a disparate group of malignancies with varying clinical outcomes despite a tremendous amount of time, effort, and resources dedicated to their management and understanding. The most aggressive entity, glioblastoma, has a dismal prognosis with poor local control despite intense local and systemic treatment, including radiation therapy.

RECENT FINDINGS

Given the heterogeneity in genotype, phenotype, and patient outcomes, researchers and clinicians have turned their attention toward attacking DNA damage response and repair mechanisms in gliomas in an effort to develop novel chemo and radiosensitizers. However, despite extensive work in both the laboratory and the clinic, no sensitizers have yet to emerge as clear options in the treatment of glioma, often because of meager preclinical data or an inability to penetrate the blood-brain barrier.

SUMMARY

This review will examine current understanding of molecular DNA repair targets in glioma and their potential exploitation to improve local control and, ultimately, overall survival of patients afflicted with these diseases.

A Potent Blood-Brain Barrier-Permeable Mutant IDH1 Inhibitor Suppresses the Growth of Glioblastoma with IDH1 Mutation in a Patient-Derived Orthotopic Xenograft Model

Gliomas are the second most common primary brain tumors in adults. They are treated with combination therapies, including surgery, radiotherapy, and chemotherapy. There are currently limited treatment options for recurrent gliomas, and new targeted therapies need to be identified, especially in glioblastomas, which have poor prognosis. Isocitrate dehydrogenase (IDH) mutations are detected in various tumors, including gliomas. Most patients with IDH mutant glioma harbor the IDH1R132H subtype. Mutant IDH catalyzes the conversion of α-ketoglutarate to the oncometabolite 2-hydroxyglutarate (2-HG), which induces aberrant epigenetic status and contributes to malignant progression, and is therefore a potential therapeutic target for IDH mutant tumors. The present study describes a novel, orally bioavailable selective mutant IDH1 inhibitor, DS-1001b. The drug has high blood-brain barrier (BBB) permeability and inhibits IDH1R132H. Continuous administration of DS-1001b impaired tumor growth and decreased 2-HG levels in subcutaneous and intracranial xenograft models derived from a patient with glioblastoma with IDH1 mutation. Moreover, the expression of glial fibrillary acidic protein was strongly induced by DS-1001b, suggesting that inhibition of mutant IDH1 promotes glial differentiation. These results reveal the efficacy of BBB-permeable DS-1001b in orthotopic patient-derived xenograft models and provide a preclinical rationale for the clinical testing of DS-1001b in recurrent gliomas.

Isocitrate dehydrogenase inhibitors in acute myeloid leukemia

Isocitrate dehydrogenase (IDH) is a key enzyme involved in the conversion of isocitrate to α-ketoglutarate (α-KG) in the tricarboxylic acid (TCA) cycle. IDH mutation produces a neomorphic enzyme, which can lead to the abnormal accumulation of R-2-HG and promotes leukemogenesis. IDH mutation occurs in 20% of acute myeloid leukemia (AML) patients, mainly including IDH1 R132, IDH2 R140, and IDH2 R172. Different mutant isoforms have different prognostic values. In recent years, IDH inhibitors have shown good clinical response in AML patients. Hence, enasidenib and ivosidenib, the IDH2 and IDH1 inhibitors developed by Agios Pharmaceuticals, have been approved by the Food and Drug Administration on 1 August 2017 and 20 July 2018 for the treatment of adult relapsed or refractory (R/R) AML with IDH2 and IDH1 mutations, respectively. IDH inhibitor monotherapy for R/R AML is efficacious and safe; however, there are problems, such as primary or acquired resistance. Clinical trials of IDH inhibitors combined with hypomethylating agents or standard chemotherapy for the treatment of R/R AML or newly diagnosed AML, as well as in post hematopoietic stem cell transplantation as maintenance therapy, are ongoing. This article summarizes the use of IDH inhibitors in AML with IDH mutations.

Epigenetic Therapies for Acute Myeloid Leukemia and Their Immune-Related Effects

Over the past decades, our molecular understanding of acute myeloid leukemia (AML) pathogenesis dramatically increased, thanks also to the advent of next-generation sequencing (NGS) technologies. Many of these findings, however, have not yet translated into new prognostic markers or rationales for treatments. We now know that AML is a highly heterogeneous disease characterized by a very low mutational burden. Interestingly, the few mutations identified mainly reside in epigenetic regulators, which shape and define leukemic cell identity. In the light of these discoveries and given the increasing number of drugs targeting epigenetic regulators in clinical development and testing, great interest is emerging for the use of small molecules targeting leukemia epigenome. Together with their effects on leukemia cell-intrinsic properties, such as proliferation and survival, epigenetic drugs may affect the way leukemic cells communicate with the surrounding components of the tumor and immune microenvironment. Here, we review current knowledge on alterations in the AML epigenetic landscape and discuss the promises of epigenetic therapies for AML treatment. Finally, we summarize emerging molecular studies elucidating how epigenetic rewiring in cancer cells may as well exert immune-modulatory functions, boost the immune system, and potentially contribute to better patient outcomes.

Pharmacological characterization of TQ05310, a potent inhibitor of isocitrate dehydrogenase 2 R140Q and R172K mutants

Isocitrate dehydrogenase 2 (IDH2), an important mitochondrial metabolic enzyme involved in the tricarboxylic acid cycle, is mutated in a variety of cancers. AG-221, an inhibitor primarily targeting the IDH2-R140Q mutant, has shown remarkable clinical benefits in the treatment of relapsed or refractory acute myeloid leukemia patients. However, AG-221 has weak inhibitory activity toward IDH2-R172K, a mutant form of IDH2 with more severe clinical manifestations. Herein, we report TQ05310 as the first mutant IDH2 inhibitor that potently targets both IDH2-R140Q and IDH2-R172K mutants. TQ05310 inhibited mutant IDH2 enzymatic activity, suppressed (R)-2-hydroxyglutarate (2-HG) production and induced differentiation in cells expressing IDH2-R140Q and IDH2-R172K, but not in cells expressing wild-type IDH1/2 or mutant IDH1. TQ05310 bound to both IDH2-R140Q and IDH2-R172K, with Q316 being the critical residue mediating the binding of TQ05310 with IDH2-R140Q, but not with IDH2-R172K. TQ05310 also had favorable pharmacokinetic characteristics and profoundly inhibited 2-HG production in a tumor xenografts model. The results of the current study establish a solid foundation for further clinical investigation of TQ05310, and provide new insight into the development of novel mutant IDH2 inhibitors.

Differentiation Syndrome Associated With Enasidenib, a Selective Inhibitor of Mutant Isocitrate Dehydrogenase 2: Analysis of a Phase 1/2 Study

Importance

Enasidenib mesylate, a mutant isocitrate dehydrogenase 2 (IDH2) protein inhibitor that promotes differentiation of leukemic myeloblasts, was recently approved by the US Food and Drug Administration for use in relapsed/refractory (R/R) mutant IDH2 acute myeloid leukemia (AML). During the first study of enasidenib in humans, a minority of patients with advanced myeloid neoplasms experienced unexpected signs/symptoms of a differentiation syndrome (DS), a potentially lethal entity.

Objective

To characterize IDH-inhibitor-associated DS (IDH-DS) and its effective management.

Design, Setting, and Participants

Using data obtained from a multicenter, open-label, pivotal phase 1/2 study of enasidenib, a differentiation syndrome review committee retrospectively evaluated potential cases of IDH-DS in enasidenib-treated patients with R/R AML. Data were collected between August 27, 2013, and October 14, 2016. The committee identified and agreed on signs and symptoms characteristic of IDH-DS and developed an algorithm for identification and treatment. Among 281 patients with R/R AML enrolled in the trial, the committee identified 72 patients for review based on investigator-reported cases of DS (n = 33) or reported adverse events or signs and symptoms characteristic of IDH-DS.

Interventions

Treatment with enasidenib at a dosage of 50 to 650 mg/d was evaluated during the dose-escalation phase, and a dosage of 100 mg/d was used in the phase 1 expansion and phase 2, all in continual 28-day cycles.

Main Outcomes and Measures

Unexpected adverse events of IDH-DS during the phase 1/2 study.

Results

Thirty-three of the 281 patients (11.7%) were identified as having possible or probable IDH-DS. Median age of those 33 patients was 70 years (range, 38-80 years); 20 (60.6%) were male. The most frequent manifestations were dyspnea, fever, pulmonary infiltrates, and hypoxia. Median time to onset was 30 days (range, 7-129 days). Patients who experienced IDH-DS were less likely to have less than 20% bone marrow blasts (6% vs 22%, P = .04) and more likely to have undergone fewer previous anticancer regimens (median, 1.0 [range, 1-4] vs 2.0 [range, 1-14], P = .05) at study entry than those who did not. Thirteen patients (39.4%) had concomitant leukocytosis. Isocitrate dehydrogenase differentiation syndrome was effectively managed with systemic corticosteroids. The enasidenib regimen was interrupted for 15 patients (45.5%), but permanent discontinuation of treatment was not required.

Conclusions and Relevance

Isocitrate dehydrogenase differentiation syndrome is a recognizable and potentially lethal clinical entity, occurring in approximately 12% of enasidenib-treated patients with mutant-IDH2 R/R AML. It requires prompt recognition and management. As use of mutant IDH inhibitors increases, these findings and recommendations are increasingly germane to care of patients with mutant-IDH neoplasms.

Trial Registration

clinicaltrials.gov Identifier: NCT01915498.

Transient-State Analysis of Human Isocitrate Dehydrogenase I: Accounting for the Interconversion of Active and Non-Active Conformational States

Human isocitrate dehydrogenase 1 (HsICDH1) is a cytoplasmic homodimeric Mg(II)-dependent enzyme that converts d-isocitrate (D-ICT) and NADP⁺ to α-ketoglutarate (AKG), CO₂, and NADPH. The active sites are formed at the subunit interface and incorporate residues from both protomers. The turnover number titrates hyperbolically from 17.5 s^-1 to a minimum of 7 s^-1 with an increasing enzyme concentration. As isolated, the enzyme adopts an inactive open conformation and binds NADPH tightly. The open conformation displaces three of the eight residues that bind D-ICT and Mg(II). Enzyme activation occurs with the addition of Mg(II) or D-ICT with a rate constant of 0.12 s^-1. The addition of both Mg(II) and D-ICT activates the enzyme with a rate constant of 0.6 s^-1 and displaces half of the bound NADPH. This indicates that HsICDH1 may have a half-site mechanism in which the active sites alternate in catalysis. The X-ray crystal structure of the half-site activated complex reveals asymmetry in the homodimer with a single NADPH bound. The structure also indicates a pseudotetramer interface that impedes the egress of NADPH consistent with the suppression of the turnover number at high enzyme concentrations. When the half-site activated form of the enzyme is reacted with NADP⁺, NADPH forms with a rate constant of 204 s^-1 followed by a shift in the NADPH absorption spectrum with a rate constant of 28 s^-1. These data indicate the accumulation of two intermediate states. Once D-ICT is exhausted, HsICDH1 relaxes to the inactive open state with a rate constant of ∼3 s^-1.

Enasidenib in acute myeloid leukemia: clinical development and perspectives on treatment

Recently there has been a significant progression in the understanding of molecular mutations driving biochemical and cellular signaling changes leading to survival and proliferation of leukemia cells in patients with acute myeloid leukemia (AML). Preclinical studies have demonstrated a mutated enzyme in the citric acid cycle, isocitrate dehydrogenase (IDH), leads to the production of an oncogenic metabolite R-2-hydroxy-glutarate (R-2-HG). This causes the arrest in the differentiation of hematopoietic stem cells leading to the promotion of leukemia. Inhibitors of the IDH enzyme have been shown in preclinical studies to reduce the production of R-2-HG, resulting in terminal differentiation of leukemia blast cells. In recent phase I and II trials, the IDH2 inhibitor enasidenib has shown clinical activity in patients with relapsed and refractory (R/R) AML. This review will describe the preclinical and clinical developments of enasidenib and its Food and Drug Administration approval in R/R AML, treatment recommendations and management will be outlined.