Dual-Knockout of Mutant Isocitrate Dehydrogenase 1 and 2 Subtypes Towards Glioma Therapy: Structural Mechanistic Insights on the Role of Vorasidenib

Recently, Vorasidenib (AG-881) has been reported as a therapeutic alternative that exerts potent dual inhibitory activity against mIDH1/2 towards the treatment of low-grade glioma. However, structural and dynamic events associated with its dual inhibition mechanism remain unclear. As such, we employ integrative computer-assisted atomistic techniques to provide thorough structural and dynamic insights. Our analysis proved that the dual-targeting ability of AG-881 is mediated by Val255/Val294 within the binding pockets of both mIDH1 and mIDH2 which are shown to elicit a strong intermolecular interaction, thus favoring binding affinity. The structural orientations of AG-881 within the respective hydrophobic pockets allowed favorable interactions with binding site residues which accounted for its high binding free energy of -28.69 kcal/mol and -19.89 kcal/mol towards mIDH1 and mIDH2, respectively. Interestingly, upon binding, AG-881 was found to trigger systemic alterations of mIDH1 and mIDH2 characterized by restricted residue flexibility and a reduction in exposure of residues to the solvent surface area. As a result of these structural alterations, crucial interactions of the mutant enzymes were inhibited, a phenomenon that results in a suppression of the production of oncogenic stimulator 2-HG. Findings therefore provide thorough structural and dynamic insights associated with the dual inhibitory activity of AG-881 towards glioma therapy.

Phase I Assessment of Safety and Therapeutic Activity of BAY1436032 in Patients with IDH1-Mutant Solid Tumors

PURPOSE

BAY1436032, an inhibitor of mutant isocitrate dehydrogenase 1 (mIDH1), was active against multiple IDH1-R132X solid tumors in preclinical models. This first-in-human study was designed to determine the safety and pharmacokinetics of BAY1436032, and to evaluate its potential pharmacodynamics and antitumor effects.

PATIENTS AND METHODS

The study comprised of dose escalation and dose expansion cohorts. BAY1436032 tablets were orally administered twice daily on a continuous basis in subjects with mIDH1 solid tumors.

RESULTS

In dose escalation, 29 subjects with various tumor types were administered BAY1436032 across five doses (150-1,500 mg twice daily). BAY1432032 exhibited a relatively short half-life. Most evaluable subjects experienced target inhibition as indicated by a median maximal reduction of plasma R-2-hydroxyglutarate levels of 76%. BAY1436032 was well tolerated and an MTD was not identified. A dose of 1,500 mg twice daily was selected for dose expansion, where 52 subjects were treated in cohorts representing four different tumor types [lower grade glioma (LGG), glioblastoma, intrahepatic cholangiocarcinoma, and a basket cohort of other tumor types]. The best clinical outcomes were in subjects with LGG (n = 35), with an objective response rate of 11% (one complete response and three partial responses) and stable disease in 43%. As of August 2020, four of these subjects were in treatment for >2 years and still ongoing. Objective responses were observed only in LGG.

CONCLUSIONS

BAY1436032 was well tolerated and showed evidence of target inhibition and durable objective responses in a small subset of subjects with LGG.

Evaluation of Glycolytic Response to Multiple Classes of Anti-glioblastoma Drugs by Noninvasive Measurement of Pyruvate Kinase M2 Using [18F]DASA-23

PURPOSE

Pyruvate kinase M2 (PKM2) catalyzes the final step in glycolysis, the key process of tumor metabolism. PKM2 is found in high levels in glioblastoma (GBM) cells with marginal expression within healthy brain tissue, rendering it a key biomarker of GBM metabolic re-programming. Our group has reported the development of a novel radiotracer, 1-((2-fluoro- 6-[¹⁸F]fluorophenyl)sulfonyl)-4-((4-methoxyphenyl)sulfonyl)piperazine ([¹⁸F]DASA- 23), to non-invasively detect PKM2 levels with positron emission tomography (PET).

PROCEDURE

U87 human GBM cells were treated with the IC50 concentration of various agents used in the treatment of GBM, including alkylating agents (temozolomide, carmustine, lomustine, procarbazine), inhibitor of topoisomerase I (irinotecan), vascular endothelial and epidermal growth factor receptor inhibitors (cediranib and erlotinib, respectively) anti-metabolite (5-fluorouracil), microtubule inhibitor (vincristine), and metabolic agents (dichloroacetate and IDH1 inhibitor ivosidenib). Following drug exposure for three or 6 days (n = 6 replicates per condition), the radiotracer uptake of [¹⁸F]DASA-23 and 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) was assessed. Changes in PKM2 protein levels were determined via Western blot and correlated to radiotracer uptake.

RESULTS

Significant interactions were found between the treatment agent (n = 12 conditions total comprised 11 drugs and vehicle) and the duration of treatment (3- or 6-day exposure to each drug) on the cellular uptake of [¹⁸F]DASA-23 (p = 0.0001). The greatest change in the cellular uptake of [¹⁸F]DASA-23 was found after exposure to alkylating agents (p < 0. 0001) followed by irinotecan (p = 0. 0012), erlotinib (p = 0. 02), and 5-fluorouracil (p = 0. 005). Correlation of PKM2 protein levels and [¹⁸F]DASA-23 cellular uptake revealed a moderate correlation (r = 0.44, p = 0.15).

CONCLUSIONS

These proof of principle studies emphasize the superiority of [¹⁸F]DASA-23 to [¹⁸F]FDG in detecting the glycolytic response of GBM to multiple classes of anti-neoplastic drugs in cell culture. A clinical trial evaluating the diagnostic utility of [¹⁸F]DASA-23 PET in GBM patients (NCT03539731) is ongoing.

Targeting Cancer Metabolism and Current Anti-Cancer Drugs

Several studies have exploited the metabolic hallmarks that distinguish between normal and cancer cells, aiming at identifying specific targets of anti-cancer drugs. It has become apparent that metabolic flexibility allows cancer cells to survive during high anabolic demand or the depletion of nutrients and oxygen. Cancers can reprogram their metabolism to the microenvironments by increasing aerobic glycolysis to maximize ATP production, increasing glutaminolysis and anabolic pathways to support bioenergetic and biosynthetic demand during rapid proliferation. The increased key regulatory enzymes that support the relevant pathways allow us to design small molecules which can specifically block activities of these enzymes, preventing growth and metastasis of tumors. In this review, we discuss metabolic adaptation in cancers and highlight the crucial metabolic enzymes involved, specifically those involved in aerobic glycolysis, glutaminolysis, de novo fatty acid synthesis, and bioenergetic pathways. Furthermore, we also review the success and the pitfalls of the current anti-cancer drugs which have been applied in pre-clinical and clinical studies.

Recent developments and future directions in adult lower-grade gliomas: Society for Neuro-Oncology (SNO) and European Association of Neuro-Oncology (EANO) consensus

The finding that most grades II and III gliomas harbor isocitrate dehydrogenase (IDH) mutations conveying a relatively favorable and fairly similar prognosis in both tumor grades highlights that these tumors represent a fundamentally different entity from IDH wild-type gliomas exemplified in most glioblastoma. Herein we review the most recent developments in molecular neuropathology leading to reclassification of these tumors based upon IDH and 1p/19q status, as well as the potential roles of methylation profiling and deletional analysis of cyclin-dependent kinase inhibitor 2A and 2B. We discuss the epidemiology, clinical manifestations, benefit of surgical resection, and neuroimaging features of lower-grade gliomas as they relate to molecular subtype, including advanced imaging techniques such as 2-hydroxyglutarate magnetic resonance spectroscopy and amino acid PET scanning. Recent, ongoing, and planned studies of radiation therapy and both cytotoxic and targeted chemotherapies are summarized, including both small molecule and immunotherapy approaches specifically targeting the mutant IDH protein.

Molecular characteristics of diffuse lower grade gliomas: what neurosurgeons need to know

The importance of genomic information in intrinsic brain tumors is highlighted in the World Health Organization (WHO) 2016 classification of gliomas, which now incorporates both phenotype and genotype data to assign a diagnosis. By using genetic markers to both categorize tumors and advise patients on prognosis, this classification system has minimized the risk of tissue sampling error, improved diagnostic accuracy, and reduced inter-rater variability. In the neurosurgical community, it is critical to understand the role genetics plays in tumor biology, what certain mutations mean for the patient's prognosis and adjuvant treatment, and how to interpret the results of sequencing data that are generated following tumor resection. In this review, we examine the critical role of genetics for diagnosis and prognosis and highlight the importance of tumor genetics for neurosurgeons caring for patients with diffuse lower grade gliomas.

Further understanding of glioma mechanisms of pathogenesis: implications for therapeutic development

Introduction: Recent discoveries in the molecular makeup of gliomas, the relationship of certain molecular drivers, and the patient's response to therapy and overall prognosis have resulted in a paradigm shift and redefined our understanding of glioma and revealed potential vulnerabilities within this recalcitrant and lethal disease.Areas covered: We summarize the current classification of malignant glioma in the context of the historical background, current data-driven treatment strategies, and recent discoveries of the mechanisms of pathogenesis of this disease which recapitulates the developing brain. We describe the relationship to common genetic alterations found in glioma, and possible avenues to exploit these newly revealed mechanisms.Expert opinion: Improved understanding of the molecular underpinnings of this disease has been directly translated into treatment decisions and an improved ability to counsel patients regarding their prognosis. We are beginning to see the first glimmer of a return on the investment in regard to immunotherapy in malignant glioma, with further anticipated successful exploitations of the unique pathophysiology of glioma.

IDH mutation in glioma: molecular mechanisms and potential therapeutic targets

Isocitrate dehydrogenase (IDH) enzymes catalyse the oxidative decarboxylation of isocitrate and therefore play key roles in the Krebs cycle and cellular homoeostasis. Major advances in cancer genetics over the past decade have revealed that the genes encoding IDHs are frequently mutated in a variety of human malignancies, including gliomas, acute myeloid leukaemia, cholangiocarcinoma, chondrosarcoma and thyroid carcinoma. A series of seminal studies further elucidated the biological impact of the IDH mutation and uncovered the potential role of IDH mutants in oncogenesis. Notably, the neomorphic activity of the IDH mutants establishes distinctive patterns in cancer metabolism, epigenetic shift and therapy resistance. Novel molecular targeting approaches have been developed to improve the efficacy of therapeutics against IDH-mutated cancers. Here we provide an overview of the latest findings in IDH-mutated human malignancies, with a focus on glioma, discussing unique biological signatures and proceedings in translational research.

Current Landscape and Emerging Fields of PET Imaging in Patients with Brain Tumors

The number of positron-emission tomography (PET) tracers used to evaluate patients with brain tumors has increased substantially over the last years. For the management of patients with brain tumors, the most important indications are the delineation of tumor extent (e.g., for planning of resection or radiotherapy), the assessment of treatment response to systemic treatment options such as alkylating chemotherapy, and the differentiation of treatment-related changes (e.g., pseudoprogression or radiation necrosis) from tumor progression. Furthermore, newer PET imaging approaches aim to address the need for noninvasive assessment of tumoral immune cell infiltration and response to immunotherapies (e.g., T-cell imaging). This review summarizes the clinical value of the landscape of tracers that have been used in recent years for the above-mentioned indications and also provides an overview of promising newer tracers for this group of patients.

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.

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.

New metabolic imaging tools in neuro-oncology

PURPOSE OF REVIEW

The current treatment of gliomas dovetails results of decades-old clinical trials with modern trends in chemotherapy. Molecular characterization now plays a pivotal role, and IDH mutations are key characteristics and the subject of active debate. IDH-mutant tumors produce the 'onco-metabolite', 2-hydroxyglutarate. Metabolic changes have become central to the understanding of tumor biology, and tumors display a fundamental metabolic change called the Warburg Effect. The Warburg Effect represents a preference for glycolysis, as opposed to oxidative phosphorylation. The present review details the clinical context and discusses clinical and preclinical metabolic imaging tools to characterize the Warburg Effect.

RECENT FINDINGS

A clinical Warburg Index is proposed, defined as the lactate concentration measured by H-MRSI over the SUV measured by FDG-PET, to measure the Warburg Effect. A preclinical technique called deuterium metabolic imaging has successfully imaged the Warburg Effect in vivo in glioblastoma.

SUMMARY

Metabolic imaging provides an opportunity to measure the Warburg Effect and other metabolic changes in brain tumors. An increased understanding of metabolic shifts integral to brain cancer has the potential to address multiple contemporary debates on glioma pathophysiology and treatment. Metabolic imaging tools thus have the potential to advance research findings, clinical trial development, and clinical care.

The Mitochondrion as an Emerging Therapeutic Target in Cancer

Mitochondria have emerged as important pharmacological targets because of their key role in cellular proliferation and death. In tumor tissues, mitochondria can switch metabolic phenotypes to meet the challenges of high energy demand and macromolecular synthesis. Furthermore, mitochondria can engage in crosstalk with the tumor microenvironment, and signals from cancer-associated fibroblasts can impinge on mitochondria. Cancer cells can also acquire a hybrid phenotype in which both glycolysis and oxidative phosphorylation (OXPHOS) can be utilized. This hybrid phenotype can facilitate metabolic plasticity of cancer cells more specifically in metastasis and therapy-resistance. In light of the metabolic heterogeneity and plasticity of cancer cells that had until recently remained unappreciated, strategies targeting cancer metabolic dependency appear to be promising in the development of novel and effective cancer therapeutics.

Mutant Isocitrate Dehydrogenase Inhibitors as Targeted Cancer Therapeutics

The identification of heterozygous neomorphic isocitrate dehydrogenase (IDH) mutations across multiple cancer types including both solid and hematologic malignancies has revolutionized our understanding of oncogenesis in these malignancies and the potential for targeted therapeutics using small molecule inhibitors. The neomorphic mutation in IDH generates an oncometabolite product, 2-hydroxyglutarate (2HG), which has been linked to the disruption of metabolic and epigenetic mechanisms responsible for cellular differentiation and is likely an early and critical contributor to oncogenesis. In the past 2 years, two mutant IDH (mutIDH) inhibitors, Enasidenib (AG-221), and Ivosidenib (AG-120), have been FDA-approved for IDH-mutant relapsed or refractory acute myeloid leukemia (AML) based on phase 1 safety and efficacy data and continue to be studied in trials in hematologic malignancies, as well as in glioma, cholangiocarcinoma, and chondrosarcoma. In this review, we will summarize the molecular pathways and oncogenic consequences associated with mutIDH with a particular emphasis on glioma and AML, and systematically review the development and preclinical testing of mutIDH inhibitors. Existing clinical data in both hematologic and solid tumors will likewise be reviewed followed by a discussion on the potential limitations of mutIDH inhibitor monotherapy and potential routes for treatment optimization using combination therapy.

Cancer-associated mutation and beyond: The emerging biology of isocitrate dehydrogenases in human disease

Isocitrate dehydrogenases (IDHs) are critical metabolic enzymes that catalyze the oxidative decarboxylation of isocitrate to α-ketoglutarate (αKG), NAD(P)H, and CO₂. IDHs epigenetically control gene expression through effects on αKG-dependent dioxygenases, maintain redox balance and promote anaplerosis by providing cells with NADPH and precursor substrates for macromolecular synthesis, and regulate respiration and energy production through generation of NADH. Cancer-associated mutations in IDH1 and IDH2 represent one of the most comprehensively studied mechanisms of IDH pathogenic effect. Mutant enzymes produce (R)-2-hydroxyglutarate, which in turn inhibits αKG-dependent dioxygenase function, resulting in a global hypermethylation phenotype, increased tumor cell multipotency, and malignancy. Recent studies identified wild-type IDHs as critical regulators of normal organ physiology and, when transcriptionally induced or down-regulated, as contributing to cancer and neurodegeneration, respectively. We describe how mutant and wild-type enzymes contribute on molecular levels to disease pathogenesis, and discuss efforts to pharmacologically target IDH-controlled metabolic rewiring.

Emerging drug profile: Krebs cycle and cancer: IDH mutations and therapeutic implications

Mutations in IDH1 and IDH2 genes occur frequently in myeloid malignancies and certain solid tumors. IDH1 and IDH2 are enzymes that are involved in the tricarboxylic acid (TCA) cycle. Activating mutations in IDH1 and IDH2 leads to increased production of 2-hydroxygluterate and epigenetic modification, affecting cell differentiation. Small molecule inhibitors of mutated IDH1 and IDH2 have shown promising anti-cancer activity in both preclinical models and early clinical trials. Recently, enasidenib and ivosidenib, oral inhibitors of mutated IDH2 and IDH1 genes, respectively, were approved for use in relapsed or refractory acute myeloid leukemia. This review will focus on the underlying biological mechanism and clinical relevance of IDH mutations in cancer.

Neuro-oncology: Implications of the molecular era

The field of neuro-oncology has recently experienced a renaissance in the understanding of the molecular underpinnings and pathophysiology of glioma. Genetic markers have significant implications regarding treatment responsiveness and prognosis and are now the primary basis for classification. This article gives an updated understanding of the pathogenesis and mechanisms of resistance of glioma via discussion of 4 molecular and genetic markers: MGMT, IDH, 1p/19q, and TERT.

The clinical use of IDH1 and IDH2 mutations in gliomas

Introduction: Mutations in the genes isocitrate dehydrogenase (IDH) 1 and 2 have been reported in a limited number of tumors. In gliomas, IDH mutations are primarily detected in WHO grade II-III tumors and represent a major biomarker with diagnostic, prognostic, and predictive implications. The recent development of IDH inhibitors and vaccines suggests that the IDH mutation is also an appealing target for therapy. Areas covered: This review focuses on the role of IDH mutations in diffuse gliomas. Besides discussing their role in gliomagenesis, we will emphasize the role of IDH mutations in clinical practice as a diagnostic, prognostic and predictive biomarker, and as a potential therapeutic target. Noninvasive detection of the IDH mutation by means of liquid biopsy and MR spectroscopy will also be discussed. Expert commentary: While IDH mutation is a consolidated diagnostic and prognostic biomarker in clinical practice, its role in oncogenesis is far from being elucidated, and there are several pending issues. The routine use of noninvasive techniques for detection and monitoring of the IDH status remains challenging. Although the IDH mutation is a very early alteration in gliomagenesis, it may then be omitted during tumor progression. This observation has important implications when designing targeted clinical trials.

Anaplastic Glioma: Treatment Approaches in the Era of Molecular Diagnostics

OPINION STATEMENT

The treatment paradigm for anaplastic glioma has shifted, owing to new diagnostic criteria and new phase III clinical trial evidence. In 2016, the WHO classification of brain tumors including diffuse gliomas was redefined to include molecular criteria, often supplanting the morphological appearance of the tumor cells. This was necessary as prognosis is more closely associated with molecular diagnosis than with morphology and grade. Recently, the benefit of adjuvant chemotherapy in addition to radiotherapy has been demonstrated in both anaplastic oligodendroglioma and anaplastic astrocytoma, as well as lower grade gliomas with the most marked benefit evident in IDH-mutated (astrocytoma) and 1p/19q co-deleted (oligodendroglial) tumors. The defining principle of recent breakthroughs has been the benefit of combinatorial therapy (chemo-radiation) as opposed to treatment in series or treatment of either modality after a period of observation upon evidence of progression.

[Hot topics about early clinical trials at ASCO congress 2018: News pathways, new targets, new associations]

Looking at the results of the early trials presented at the 2018 American Society of Clinical Oncology (ASCO) conference can help identify the molecules and strategies that will potentially enter the practices of tomorrow. It is in this spirit that this subject has justified the attention of residents in oncology and the writing of this synthesis. Molecules that can represent breakthrough innovations are presented as well as new therapeutics under development acting on targets already validated in clinical practice and early data of checkpoint inhibitors in combination with different immunomodulators, as well as new strategies for immunotherapies (vaccines and cell therapy).

Genetic Abnormalities, Clonal Evolution, and Cancer Stem Cells of Brain Tumors

Brain tumors are highly heterogeneous and have been classified by the World Health Organization in various histological and molecular subtypes. Gliomas have been classified as ranging from low-grade astrocytomas and oligodendrogliomas to high-grade astrocytomas or glioblastomas. These tumors are characterized by a peculiar pattern of genetic alterations. Pediatric high-grade gliomas are histologically indistinguishable from adult glioblastomas, but they are considered distinct from adult glioblastomas because they possess a different spectrum of driver mutations (genes encoding histones H3.3 and H3.1). Medulloblastomas, the most frequent pediatric brain tumors, are considered to be of embryonic derivation and are currently subdivided into distinct subgroups depending on histological features and genetic profiling. There is emerging evidence that brain tumors are maintained by a special neural or glial stem cell-like population that self-renews and gives rise to differentiated progeny. In many instances, the prognosis of the majority of brain tumors remains negative and there is hope that the new acquisition of information on the molecular and cellular bases of these tumors will be translated in the development of new, more active treatments.