Treatment with a Small Molecule Mutant IDH1 Inhibitor Suppresses Tumorigenic Activity and Decreases Production of the Oncometabolite 2-Hydroxyglutarate in Human Chondrosarcoma Cells

Isocitrate Dehydrogenase Mutations in Cancer: Mechanisms of Transformation and Metabolic Liability

Isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are metabolic enzymes that interconvert isocitrate and 2-oxoglutarate (2OG). Gain-of-function mutations in IDH1 and IDH2 occur in a number of cancers, including acute myeloid leukemia, glioma, cholangiocarcinoma, and chondrosarcoma. These mutations cripple the wild-type activity of IDH and cause the enzymes to catalyze a partial reverse reaction in which 2OG is reduced but not carboxylated, resulting in production of the (R)-enantiomer of 2-hydroxyglutarate ((R)-2HG). (R)-2HG accumulation in IDH-mutant tumors results in profound dysregulation of cellular metabolism. The most well-characterized oncogenic effects of (R)-2HG involve the dysregulation of 2OG-dependent epigenetic tumor-suppressor enzymes. However, (R)-2HG has many other effects in IDH-mutant cells, some that promote transformation and others that induce metabolic dependencies. Herein, we review how cancer-associated IDH mutations impact epigenetic regulation and cellular metabolism and discuss how these effects can potentially be leveraged to therapeutically target IDH-mutant tumors.

A personalized medicine approach identifies enasidenib as an efficient treatment for IDH2 mutant chondrosarcoma

BACKGROUND

Sarcomas represent an extensive group of malignant diseases affecting mesodermal tissues. Among sarcomas, the clinical management of chondrosarcomas remains a complex challenge, as high-grade tumours do not respond to current therapies. Mutations in the isocitrate dehydrogenase (IDH) 1 and 2 genes are among the most common mutations detected in chondrosarcomas and may represent a therapeutic opportunity. The presence of mutated IDH (mIDH) enzymes results in the accumulation of the oncometabolite 2-HG leading to molecular alterations that contribute to drive tumour growth.

METHODS

We developed a personalized medicine strategy based on the targeted NGS/Sanger sequencing of sarcoma samples (n = 6) and the use of matched patient-derived cell lines as a drug-testing platform. The anti-tumour potential of IDH mutations found in two chondrosarcoma cases was analysed in vitro, in vivo and molecularly (transcriptomic and DNA methylation analyses).

FINDINGS

We treated several chondrosarcoma models with specific mIDH1/2 inhibitors. Among these treatments, only the mIDH2 inhibitor enasidenib was able to decrease 2-HG levels and efficiently reduce the viability of mIDH2 chondrosarcoma cells. Importantly, oral administration of enasidenib in xenografted mice resulted in a complete abrogation of tumour growth. Enasidenib induced a profound remodelling of the transcriptomic landscape not associated to changes in the 5 mC methylation levels and its anti-tumour effects were associated with the repression of proliferative pathways such as those controlled by E2F factors.

INTERPRETATION

Overall, this work provides preclinical evidence for the use of enasidenib to treat mIDH2 chondrosarcomas.

FUNDING

Supported by the Spanish Research Agency/FEDER (grants PID2022-142020OB-I00; PID2019-106666RB-I00), the ISC III/FEDER (PI20CIII/00020; DTS18CIII/00005; CB16/12/00390; CB06/07/1009; CB19/07/00057); the GEIS group (GEIS-62); and the PCTI (Asturias)/FEDER (IDI/2021/000027).

IDH mutations in G2-3 conventional central bone chondrosarcoma: a mono institutional experience

BACKGROUND

Heterozygous isocitrate dehydrogenase (IDH) mutations occur in about half of conventional central bone chondrosarcomas (CCBC). Aim of this study was to assess the frequency and prognostic impact of IDH mutations in high grade CCBC patients.

METHODS

64 patients with G2 and G3 CCBC were included. DNA extraction, PCR amplification of IDH1/2 exon 4s, and sequencing analysis with Sanger were performed.

RESULTS

IDH mutations were detected in 24/54 patients (44%): IDH1 in 18, IDH2 in 4, and both IDH1/2 in 2 patients. The frequency of mutations was 37% in G2 vs. 69% in G3 (p = 0.039), and 100% in three Ollier disease associated chondrosarcoma. 5-year overall survival (OS) at 124 months (range 1-166) was 51%, with no significant difference based on the IDH mutational status: 61% in IDHmut vs. 44% in IDH wild type (IDHwt). The 5-year relapse free survival (RFS) was 33% (95% CI:10-57) for IDHmut vs. 57% (95%CI: 30-77) for IDHwt. Progression free survival (PFS) was 25% (95%CI:1-65) IDHmut vs. 16% (95%CI: 0.7-52) IDHwt. 55% (5/9) of IDHmut G2 became higher grade at the recurrence, as compared with 25% (3/12) of G2 IDHwt.

CONCLUSIONS

This study shows a higher frequency of IDH mutations in G3 CCBC as compared with G2. No significant differences in OS, RFS, and PFS by mutational status were detected. After relapse, a higher rate of G3 for IDH mutated CCBC was observed.

IDH Mutations in Chondrosarcoma: Case Closed or Not?

Chondrosarcomas are malignant cartilage-producing tumours that frequently harbour isocitrate dehydrogenase 1 and -2 (IDH) gene mutations. Several studies have confirmed that these mutations are key players in the early stages of cartilage tumour development, but their role in later stages remains ambiguous. The prognostic value of IDH mutations remains unclear and preclinical studies have not identified effective treatment modalities (in)directly targeting these mutations. In contrast, the IDH mutation status is a prognostic factor in other cancers, and IDH mutant inhibitors as well as therapeutic strategies targeting the underlying vulnerabilities induced by IDH mutations seem effective in these tumour types. This discrepancy in findings might be ascribed to a difference in tumour type, elevated D-2-hydroxyglutarate levels, and the type of in vitro model (endogenous vs. genetically modified) used in preclinical studies. Moreover, recent studies suggest that the (epi)genetic landscape in which the IDH mutation functions is an important factor to consider when investigating potential therapeutic strategies or patient outcomes. These findings imply that the dichotomy between IDH wildtype and mutant is too simplistic and additional subgroups indeed exist within chondrosarcoma. Future studies should focus on the identification, characterisation, and tailoring of treatments towards these biological subgroups within IDH wildtype and mutant chondrosarcoma.

Mutant IDH regulates glycogen metabolism from early cartilage development to malignant chondrosarcoma formation

Chondrosarcomas are the most common malignancy of cartilage and are associated with somatic mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 genes. Somatic IDH mutations are also found in its benign precursor lesion, enchondromas, suggesting that IDH mutations are early events in malignant transformation. Human mutant IDH chondrosarcomas and mutant Idh mice that develop enchondromas investigated in our studies display glycogen deposition exclusively in mutant cells from IDH mutant chondrosarcomas and Idh1 mutant murine growth plates. Pharmacologic blockade of glycogen utilization induces changes in tumor cell behavior, downstream energetic pathways, and tumor burden in vitro and in vivo. Mutant IDH1 interacts with hypoxia-inducible factor 1α (HIF1α) to regulate expression of key enzymes in glycogen metabolism. Here, we show a critical role for glycogen in enchondromas and chondrosarcomas, which is likely mediated through an interaction with mutant IDH1 and HIF1α.

(R)-2-Hydroxyglutarate Inhibits KDM5 Histone Lysine Demethylases to Drive Transformation in IDH-Mutant Cancers

Oncogenic mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 occur in a wide range of cancers, including acute myeloid leukemia (AML) and glioma. Mutant IDH enzymes convert 2-oxoglutarate (2OG) to (R)-2-hydroxyglutarate [(R)-2HG], an oncometabolite that is hypothesized to promote cellular transformation by dysregulating 2OG-dependent enzymes. The only (R)-2HG target that has been convincingly shown to contribute to transformation by mutant IDH is the myeloid tumor suppressor TET2. However, there is ample evidence to suggest that (R)-2HG has other functionally relevant targets in IDH-mutant cancers. Here, we show that (R)-2HG inhibits KDM5 histone lysine demethylases and that this inhibition contributes to cellular transformation in IDH-mutant AML and IDH-mutant glioma. These studies provide the first evidence of a functional link between dysregulation of histone lysine methylation and transformation in IDH-mutant cancers.

SIGNIFICANCE

Mutant IDH is known to induce histone hypermethylation. However, it is not known if this hypermethylation is functionally significant or is a bystander effect of (R)-2HG accumulation in IDH-mutant cells. Here, we provide evidence that KDM5 inhibition by (R)-2HG contributes to mutant IDH-mediated transformation in AML and glioma. This article is highlighted in the In This Issue feature, p. 1275.

Bad to the Bone: Emerging Approaches to Aggressive Bone Sarcomas

Bone sarcomas are rare heterogeneous tumors that affect patients of all ages including children, adolescent young adults, and older adults. They include many aggressive subtypes and patient groups with poor outcomes, poor access to clinical trials, and lack of defined standard therapeutic strategies. Conventional chondrosarcoma remains a surgical disease, with no defined role for cytotoxic therapy and no approved targeted systemic therapies. Here, we discuss promising novel targets and strategies undergoing evaluation in clinical trials. Multiagent chemotherapy has greatly improved outcomes for patients with Ewing sarcoma (ES) and osteosarcoma, but management of those with high-risk or recurrent disease remains challenging and controversial. We describe the impact of international collaborative trials, such as the rEECur study, that aim to define optimal treatment strategies for those with recurrent, refractory ES, and evidence for high-dose chemotherapy with stem-cell support. We also discuss current and emerging strategies for other small round cell sarcomas, such as CIC-rearranged, BCOR-rearranged tumors, and the evaluation of emerging novel therapeutics and trial designs that may offer a new paradigm to improve survival in these aggressive tumors with notoriously bad (to the bone) outcomes.

Molecular In-Depth Characterization of Chondrosarcoma for Current and Future Targeted Therapies

Chondrosarcoma (CHS) are heterogenous, but as a whole, represent the second most common primary malignant bone tumor entity. Although knowledge on tumor biology has grown exponentially during the past few decades, surgical resection remains the gold standard for the treatment of these tumors, while radiation and differentiated chemotherapy do not result in sufficient cancer control. An in-depth molecular characterization of CHS reveals significant differences compared to tumors of epithelial origin. Genetically, CHS are heterogenous, but there is no characteristic mutation defining CHS, and yet, IDH1 and IDH2 mutations are frequent. Hypovascularization, extracellular matrix composition of collagen, proteoglycans, and hyaluronan create a mechanical barrier for tumor suppressive immune cells. Comparatively low proliferation rates, MDR-1 expression and an acidic tumor microenvironment further limit therapeutic options in CHS. Future advances in CHS therapy depend on the further characterization of CHS, especially the tumor immune microenvironment, for improved and better targeted therapies.

Chondrosarcoma Resistance to Radiation Therapy: Origins and Potential Therapeutic Solutions

Chondrosarcoma is a malignant cartilaginous tumor that is particularly chemoresistant and radioresistant to X-rays. The first line of treatment is surgery, though this is almost impossible in some specific locations. Such resistances can be explained by the particular composition of the tumor, which develops within a dense cartilaginous matrix, producing a resistant area where the oxygen tension is very low. This microenvironment forces the cells to adapt and dedifferentiate into cancer stem cells, which are described to be more resistant to conventional treatments. One of the main avenues considered to treat this type of tumor is hadrontherapy, in particular for its ballistic properties but also its greater biological effectiveness against tumor cells. In this review, we describe the different forms of chondrosarcoma resistance and how hadrontherapy, combined with other treatments involving targeted inhibitors, could help to better treat high-grade chondrosarcoma.

Epigenetic Abnormalities in Chondrosarcoma

In recent years, our understanding of the epigenetic mechanisms involved in tumor pathology has improved greatly. DNA and histone modifications, such as methylation, demethylation, acetylation, and deacetylation, can lead to the up-regulation of oncogenic genes, as well as the suppression of tumor suppressor genes. Gene expression can also be modified on a post-transcriptional level by microRNAs that contribute to carcinogenesis. The role of these modifications has been already described in many tumors, e.g., colorectal, breast, and prostate cancers. These mechanisms have also begun to be investigated in less common tumors, such as sarcomas. Chondrosarcoma (CS) is a rare type of tumor that belongs to sarcomas and is the second most common malignant bone tumor after osteosarcoma. Due to unknown pathogenesis and resistance to chemo- and radiotherapies of these tumors, there is a need to develop new potential therapies against CS. In this review, we summarize current knowledge on the influence of epigenetic alterations in the pathogenesis of CS by discussing potential candidates for future therapies. We also emphasize ongoing clinical trials that use drugs targeting epigenetic modifications in CS treatment.

Dysregulated Lipid Synthesis by Oncogenic IDH1 Mutation Is a Targetable Synthetic Lethal Vulnerability

Isocitrate dehydrogenase 1 and 2 (IDH) are mutated in multiple cancers and drive production of (R)-2-hydroxyglutarate (2HG). We identified a lipid synthesis enzyme [acetyl CoA carboxylase 1 (ACC1)] as a synthetic lethal target in mutant IDH1 (mIDH1), but not mIDH2, cancers. Here, we analyzed the metabolome of primary acute myeloid leukemia (AML) blasts and identified an mIDH1-specific reduction in fatty acids. mIDH1 also induced a switch to b-oxidation indicating reprogramming of metabolism toward a reliance on fatty acids. Compared with mIDH2, mIDH1 AML displayed depletion of NADPH with defective reductive carboxylation that was not rescued by the mIDH1-specific inhibitor ivosidenib. In xenograft models, a lipid-free diet markedly slowed the growth of mIDH1 AML, but not healthy CD34+ hematopoietic stem/progenitor cells or mIDH2 AML. Genetic and pharmacologic targeting of ACC1 resulted in the growth inhibition of mIDH1 cancers not reversible by ivosidenib. Critically, the pharmacologic targeting of ACC1 improved the sensitivity of mIDH1 AML to venetoclax.

SIGNIFICANCE

Oncogenic mutations in both IDH1 and IDH2 produce 2-hydroxyglutarate and are generally considered equivalent in terms of pathogenesis and targeting. Using comprehensive metabolomic analysis, we demonstrate unexpected metabolic differences in fatty acid metabolism between mutant IDH1 and IDH2 in patient samples with targetable metabolic interventions. See related commentary by Robinson and Levine, p. 266. This article is highlighted in the In This Issue feature, p. 247.

EZH2/hSULF1 axis mediates receptor tyrosine kinase signaling to shape cartilage tumor progression

Chondrosarcomas are primary cancers of cartilaginous tissue and capable of alteration to highly aggressive, metastatic, and treatment-refractory states, leading to a poor prognosis with a five-year survival rate at 11 months for dedifferentiated subtype. At present, the surgical resection of chondrosarcoma is the only effective treatment, and no other treatment options including targeted therapies, conventional chemotherapies, or immunotherapies are available for these patients. Here, we identify a signal pathway way involving EZH2/SULF1/cMET axis that contributes to malignancy of chondrosarcoma and provides a potential therapeutic option for the disease. A non-biased chromatin immunoprecipitation sequence, cDNA microarray analysis, and validation of chondrosarcoma cell lines identified sulfatase 1 (SULF1) as the top EZH2-targeted gene to regulate chondrosarcoma progression. Overexpressed EZH2 resulted in downregulation of SULF1 in chondrosarcoma cell lines, which in turn activated cMET pathway. Pharmaceutical inhibition of cMET or genetically silenced cMET pathway significantly retards the chondrosarcoma growth and extends mice survival. The regulation of EZH2/SULF1/cMET axis were further validated in patient samples with chondrosarcoma. The results not only established a signal pathway promoting malignancy of chondrosarcoma but also provided a therapeutic potential for further development of effective target therapy to treat chondrosarcoma.

Atypical cartilage in type II germ cell tumors of the mediastinum show significantly different patterns of IDH1/2 mutations from conventional chondrosarcoma

Neoplastic cartilage is a common component of teratomas in type II germ cell tumors. Although IDH1/2 mutations have been well-described in somatic cartilaginous tumors, ranging from benign enchondromas to highly aggressive dedifferentiated chondrosarcomas, the presence of IDH1/2 mutations in cartilaginous neoplasms arising from germ cell tumors has not been previously investigated. To better understand the relationship between these tumors and their bone/soft tissue counterpart, we studied the IDH1/2 mutational status of 20 cases of primary mediastinal mixed germ cell tumors with areas of readily identifiable cartilaginous differentiation. Our study found that cartilaginous lesions arising in germ cell tumors have a different frequency and distribution of IDH1/2 mutations compared to those at somatic sites. We identified IDH1/2 mutations in only 15% (3/20) of cases, compared to a frequency in the literature among differentiated chondroid tumors of bone and soft tissue of 54%, a highly significant decreased frequency (p = 0.0011; chi-square test). Furthermore, they were exclusively IDH2 R172 mutations that occurred at a non-significant, increased frequency in the germ cell tumor group compared to conventional chondrosarcoma (15% vs. 5%, respectively, p > 0.05, chi-square test). The unexpected finding, therefore, was entirely attributable to the absence of IDH1 R132 mutation in chondroid neoplasia of germ cell origin (p < 0.00001, Fisher exact test). Our results suggest that a subset of cartilaginous lesions arising within type II germ cell tumors have a similar oncogenic mechanism to their bone/soft tissue counterpart but that the majority form using different oncogenic mechanisms compared to their somatic counterparts.

Connections between metabolism and epigenetics: mechanisms and novel anti-cancer strategy

Cancer cells undergo metabolic adaptations to sustain their growth and proliferation under several stress conditions thereby displaying metabolic plasticity. Epigenetic modification is known to occur at the DNA, histone, and RNA level, which can alter chromatin state. For almost a century, our focus in cancer biology is dominated by oncogenic mutations. Until recently, the connection between metabolism and epigenetics in a reciprocal manner was spotlighted. Explicitly, several metabolites serve as substrates and co-factors of epigenetic enzymes to carry out post-translational modifications of DNA and histone. Genetic mutations in metabolic enzymes facilitate the production of oncometabolites that ultimately impact epigenetics. Numerous evidences also indicate epigenome is sensitive to cancer metabolism. Conversely, epigenetic dysfunction is certified to alter metabolic enzymes leading to tumorigenesis. Further, the bidirectional relationship between epigenetics and metabolism can impact directly and indirectly on immune microenvironment, which might create a new avenue for drug discovery. Here we summarize the effects of metabolism reprogramming on epigenetic modification, and vice versa; and the latest advances in targeting metabolism-epigenetic crosstalk. We also discuss the principles linking cancer metabolism, epigenetics and immunity, and seek optimal immunotherapy-based combinations.

Methylation-mediated silencing of protein kinase C zeta induces apoptosis avoidance through ATM/CHK2 inactivation in dedifferentiated chondrosarcoma

BACKGROUND

Dedifferentiated chondrosarcoma (DDCS) is an aggressive bone tumour with a poor prognosis and no effective treatment. Because changes in DNA methylation play critical roles in DDCS, we explored the roles that DNA methylation plays in oncogenesis to potentially identify an effective epigenetic treatment.

METHODS

We identified genes downregulated in DDCS vs. conventional chondrosarcoma (CCS) due to DNA methylation using in silico analysis. The results were validated in DDCS clinical samples, and the molecular functions of the genes of interest were investigated in multiple chondrosarcoma cell lines (NDCS-1, SW1353, and OUMS-27). The therapeutic effect of decitabine, a DNA methyltransferase inhibitor, was evaluated in vitro and in vivo.

RESULTS

PRKCZ was specifically downregulated by DNA methylation in DDCS. Overexpression of PRKCZ decreased the proliferation of NDCS-1 and SW1353 cells. PRKCZ directly bound to and activated ATM, which was followed by phosphorylation of CHK2 and subsequent apoptosis. Decitabine increased PRKCZ expression through de-methylating the promoter region of PRKCZ, which activated the ATM/CHK2 pathway and inhibited cell proliferation by inducing apoptosis.

CONCLUSIONS

Increased DNA methylation and reduced expression of PRKCZ prevents apoptosis via inactivation of the ATM/CHK2 pathway in DDCS. Decitabine-induced expression of PRKCZ represents a promising therapy for DDCS.

IDH1 Mutation Induces HIF-1α and Confers Angiogenic Properties in Chondrosarcoma JJ012 Cells

Chondrosarcoma is a group of primary bone cancers that arise from transformed cells of chondrocytic lineage. Tumor recurrence and metastasis are devastating for patients with chondrosarcoma since there are no effective treatment options. IDH mutations occur in over 50% of tumors from patients with conventional or dedifferentiated chondrosarcomas and represent an attractive target for therapy. However, their role in the pathogenesis of chondrosarcoma remains largely unknown. In this study, we sought to determine the association of IDH mutation and HIF-1α in chondrosarcoma. We used the chondrosarcoma JJ012 cell line and its derived CRISPR/Cas9 mutant IDH1 (IDH1^mut) knockout (KO) cells. RNA-Seq data analysis revealed downregulation of several HIF-1α target genes upon loss of IDH1^mut. This was associated with reduced HIF-1α levels in the IDH1^mut KO cells and tumors. Loss of IDH1^mut also attenuated the expression of angiogenic markers in tumor tissues and abrogated the angiogenic capacity of JJ012 cells. Moreover, we observed that exogenous expression of HIF-1α significantly promoted anchorage-independent colony-formation by IDH1^mut KO cells. These results suggest IDH1 mutation confers angiogenic and tumorigenic properties of JJ012 cells by inducing HIF-1α. Thus, the HIF pathway represents a promising candidate for combinatorial regimens to target IDH1 mutated chondrosarcomas.

Therapeutic Targets and Emerging Treatments in Advanced Chondrosarcoma

Due to resistance to standard anticancer agents, it is difficult to control the disease progression in patients with metastatic or unresectable chondrosarcoma. Novel therapeutic approaches, such as molecule-targeting drugs and immunotherapy, are required to improve clinical outcomes in patients with advanced chondrosarcoma. Recent studies have suggested several promising biomarkers and therapeutic targets for chondrosarcoma, including IDH1/2 and COL2A1. Several molecule-targeting agents and immunotherapies have shown favorable antitumor activity in clinical studies in patients with advanced chondrosarcomas. This review summarizes recent basic studies on biomarkers and molecular targets and recent clinical studies on the treatment of chondrosarcomas.

Metabolic adaptations in cancers expressing isocitrate dehydrogenase mutations

The most frequently mutated metabolic genes in human cancer are those encoding the enzymes isocitrate dehydrogenase 1 (IDH1) and IDH2; these mutations have so far been identified in more than 20 tumor types. Since IDH mutations were first reported in glioma over a decade ago, extensive research has revealed their association with altered cellular processes. Mutations in IDH lead to a change in enzyme function, enabling efficient conversion of 2-oxoglutarate to R-2-hydroxyglutarate (R-2-HG). It is proposed that elevated cellular R-2-HG inhibits enzymes that regulate transcription and metabolism, subsequently affecting nuclear, cytoplasmic, and mitochondrial biochemistry. The significance of these biochemical changes for tumorigenesis and potential for therapeutic exploitation remains unclear. Here we comprehensively review reported direct and indirect metabolic changes linked to IDH mutations and discuss their clinical significance. We also review the metabolic effects of first-generation mutant IDH inhibitors and highlight the potential for combination treatment strategies and new metabolic targets.

The Extracellular Matrix in Soft Tissue Sarcomas: Pathobiology and Cellular Signalling

Soft tissue sarcomas are rare cancers of mesenchymal origin or differentiation comprising over 70 different histological subtypes. Due to their mesenchymal differentiation, sarcomas are thought to produce and deposit large quantities of extracellular matrix (ECM) components. Interactions between ECM ligands and their corresponding adhesion receptors such as the integrins and the discoidin domain receptors play key roles in driving many fundamental oncogenic processes including uncontrolled proliferation, cellular invasion and altered metabolism. In this review, we focus on emerging studies that describe the key ECM components commonly found in soft tissue sarcomas and discuss preclinical and clinical evidence outlining the important role that these proteins and their cognate adhesion receptors play in sarcomagenesis. We conclude by providing a perspective on the need for more comprehensive in-depth analyses of both the ECM and adhesion receptor biology in multiple histological subtypes in order to identify new drug targets and prognostic biomarkers for this group of rare diseases of unmet need.

Metabolic Pathways and Targets in Chondrosarcoma

Chondrosarcomas are the second most common primary bone malignancy. Chondrosarcomas are characterized by the production of cartilaginous matrix and are generally resistant to radiation and chemotherapy and the outcomes are overall poor. Hence, there is strong interest in determining mechanisms of cancer aggressiveness and therapeutic resistance in chondrosarcomas. There are metabolic alterations in chondrosarcoma that are linked to the epigenetic state and tumor microenvironment that drive treatment resistance. This review focuses on metabolic changes in chondrosarcoma, and the relationship between signaling via isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2), hedgehog, PI3K-mTOR-AKT, and SRC, as well as histone acetylation and angiogenesis. Also, potential treatment strategies targeting metabolism will be discussed including potential synergy with immunotherapies.

Vulnerability of IDH1-Mutant Cancers to Histone Deacetylase Inhibition via Orthogonal Suppression of DNA Repair

Exploitation of DNA repair defects has enabled major advances in treating specific cancers. Recent work discovered that the oncometabolite 2-hydroxyglutarate (2-HG), produced by neomorphic isocitrate dehydrogenase 1/2 (IDH1/2) mutations, confers a homology-directed repair (HDR) defect through 2-HG-induced histone hypermethylation masking HDR signaling. Here, we report that IDH1-mutant cancer cells are profoundly sensitive to the histone deacetylase inhibitor (HDACi) vorinostat, by further suppressing the residual HDR in 2-HG-producing cells. Vorinostat downregulates repair factors BRCA1 and RAD51 via disrupted E2F-factor regulation, causing increased DNA double-strand breaks, reduced DNA repair factor foci, and functional HDR deficiency even beyond 2-HG's effects. This results in greater cell death of IDH1-mutant cells and confers synergy with radiation and PARPi, both against cells in culture and patient-derived tumor xenografts. Our work identifies HDACi's utility against IDH1-mutant cancers, and presents IDH1/2 mutations as potential biomarkers to guide trials testing HDACi in gliomas and other malignancies. IMPLICATIONS: IDH1-mutant cells show profound vulnerability to HDACi treatment, alone and with PARPi and radiation, via HDR suppression, presenting IDH1/2 mutations as biomarkers for HDACi use in gliomas and other malignancies.

The implications of IDH mutations for cancer development and therapy

Mutations in the genes encoding the cytoplasmic and mitochondrial forms of isocitrate dehydrogenase (IDH1 and IDH2, respectively; collectively referred to as IDH) are frequently detected in cancers of various origins, including but not limited to acute myeloid leukaemia (20%), cholangiocarcinoma (20%), chondrosarcoma (80%) and glioma (80%). In all cases, neomorphic activity of the mutated enzyme leads to production of the oncometabolite D-2-hydroxyglutarate, which has profound cell-autonomous and non-cell-autonomous effects. The broad effects of IDH mutations on epigenetic, differentiation and metabolic programmes, together with their high prevalence across a variety of cancer types, early presence in tumorigenesis and uniform expression in tumour cells, make mutant IDH an ideal therapeutic target. Herein, we describe the current biological understanding of IDH mutations and the roles of mutant IDH in the various associated cancers. We also present the available preclinical and clinical data on various methods of targeting IDH-mutant cancers and discuss, based on the underlying pathogenesis of different IDH-mutated cancer types, whether the treatment approaches will converge or be context dependent.

Sarcoma Metabolomics: Current Horizons and Future Perspectives

The vast array of metabolic adaptations that cancer cells are capable of assuming, not only support their biosynthetic activity, but also fulfill their bioenergetic demands and keep their intracellular reduction-oxidation (redox) balance. Spotlight has recently been placed on the energy metabolism reprogramming strategies employed by cancer cells to proliferate. Knowledge regarding soft tissue and bone sarcomas metabolome is relatively sparse. Further characterization of sarcoma metabolic landscape may pave the way for diagnostic refinement and new therapeutic target identification, with benefit to sarcoma patients. This review covers the state-of-the-art knowledge on cancer metabolomics and explores in detail the most recent evidence on soft tissue and bone sarcoma metabolomics.

Effect of Cryoablation Treatment on the Protein Expression Profile of Low-Grade Central Chondrosarcoma Identified by LC-ESI-MS/MS

The use of cryoablation/cryosurgery in treating solid tumors has been proven as a unique technique that uses lethal temperatures to destroy the tumors and impart better functions for the affected organs. This novel technique recently demonstrated the best clinical results in chondrosarcoma (CSA) with faster recovery, less recurrence, and metastasis. Due to the resistant nature of CSA to chemo and radiation therapy, cryoablation comes to light as the best alternative approach. Therefore, for the first time, we aimed to compare CSA-untreated with cryoablation treated samples to discover some potential markers that may provide various clues in terms of diagnosis and pathophysiology and may facilitate the development of novel methods to treat sarcoma efficiently. To find the altered proteins among both groups, a mass-based label-free approach was employed and identified a total of 160 significantly altered proteins. Among these, 138 proteins were dysregulated with <1- to -0.1-fold, 18 proteins were up-regulated with >3 folds, and four proteins were similarly expressed in the untreated group compared to the treated. Interestingly, the differential expressions of proteins from the untreated group showed contrast expressions in the treated group. Furthermore, the functional enrichment analysis revealed that most of the identified proteins from this study were associated with various significant pathways such as glycolysis, MAPK activation, PI3K-Akt signaling, extracellular matrix degradation, etc. In addition, two protein expressions, such as fibronectin and annexin-1, were validated by immunoblot analysis. Therefore, this study signifies the most comprehensive discovery of altered protein expressions to date and the first large-scale detection of protein profiles from CSA-cryoablation treated compared to untreated. This work may serve as the basis for future research to open novel treatment options for chondrosarcoma.

From Metabolism to Genetics and Vice Versa: The Rising Role of Oncometabolites in Cancer Development and Therapy

Over the last decades, the study of cancer metabolism has returned to the forefront of cancer research and challenged the role of genetics in the understanding of cancer development. One of the major impulses of this new trend came from the discovery of oncometabolites, metabolic intermediates whose abnormal cellular accumulation triggers oncogenic signalling and tumorigenesis. These findings have led to reconsideration and support for the long-forgotten hypothesis of Warburg of altered metabolism as oncogenic driver of cancer and started a novel paradigm whereby mitochondrial metabolites play a pivotal role in malignant transformation. In this review, we describe the evolution of the cancer metabolism research from a historical perspective up to the oncometabolites discovery that spawned the new vision of cancer as a metabolic disease. The oncometabolites’ mechanisms of cellular transformation and their contribution to the development of new targeted cancer therapies together with their drawbacks are further reviewed and discussed.

Immunotherapy for Chordoma and Chondrosarcoma: Current Evidence

Chordomas and chondrosarcomas are rare but devastating neoplasms that are characterized by chemoradiation resistance. For both tumors, surgical resection is the cornerstone of management. Immunotherapy agents are increasingly improving outcomes in multiple cancer subtypes and are being explored in chordoma and chondrosarcoma alike. In chordoma, brachyury has been identified as a prominent biomarker and potential molecular immunotherapy target as well as PD-1 inhibition. While studies on immunotherapy in chondrosarcoma are sparse, there is emerging evidence and ongoing clinical trials for PD-1 as well as IDH inhibitors. This review highlights potential biomarkers and targets for immunotherapy in chordoma and chondrosarcoma, as well as current clinical evidence and ongoing trials.

Enchondromatosis and Growth Plate Development

PURPOSE OF REVIEW

Enchondroma is a common cartilage benign tumor that develops from dysregulation of chondrocyte terminal differentiation during growth plate development. Here we provide an overview of recent progress in understanding causative mutations for enchondroma, dysregulated signaling and metabolic pathways in enchondroma, and the progression from enchondroma to malignant chondrosarcoma.

RECENT FINDINGS

Several signaling pathways that regulate chondrocyte differentiation are dysregulated in enchondromas. Somatic mutations in the metabolic enzymes isocitrate dehydrogenase 1 and 2 (IDH1/2) are the most common findings in enchondromas. Mechanisms including metabolic regulation, epigenetic regulation, and altered signaling pathways play a role in enchondroma formation and progression. Multiple pathways regulate growth plate development in a coordinated manner. Deregulation of the process can result in chondrocytes failing to undergo differentiation and the development of enchondroma.

Quantitative Analysis of Oncometabolite 2-Hydroxyglutarate

Gain-of-function mutations of isocitrate dehydrogenase 1 and 2 (IDH1/2) were demonstrated to induce the production and accumulation of oncometabolite 2-hydroxyglutarate (2HG). 2HG is a potent competitor of α-ketoglutarate (α-KG) and can inhibit multiple α-KG-dependent dioxygenases that are critical for regulating the metabolic and epigenetic state of cells. The accumulation of 2HG contributes to elevated risk of malignant tumors. 2HG carries an asymmetric carbon atom in its carbon backbone and therefore occurs in two enantiomers, D-2-hydroxyglutarate (D-2HG) and L-2-hydroxyglutarate (L-2HG). Each enantiomer is produced and metabolized in independent biochemical pathway and catalyzed by different enzymes. The accurate diagnosis of 2HG-related diseases relies on determining the configuration of the two enantiomers. Quantitative methods for analysis of D-2HG and L-2HG have been well developed. These analytical strategies mainly include the use of chiral chromatography medium to facilitate chromatographic separation of enantiomers prior to spectroscopy or mass spectrometry analysis and the use of chiral derivatization reagents to convert the enantiomers to diastereomers with differential physical and chemical properties that can improve their chromatographic separation. Here, we summarize and discuss these established methods for analysis of total 2HG as well as the determination of the enantiomers of D-2HG and L-2HG.

Selection of Effective Therapies Using Three-Dimensional in vitro Modeling of Chondrosarcoma

Purpose: Chondrosarcomas are a group of cartilaginous malignant neoplasms characterized by the deposition of chondrogenic extracellular matrix. Surgical resection is currently the only curative treatment option, due to their high resistance to conventional chemotherapy and radiotherapy. Novel therapeutic treatment options may improve outcome. Predominantly used cell line monolayer in vitro models lack in vivo complexity, such as the presence of extracellular matrix, and differing oxygen access. Hence, we aimed to improve pre-clinical chondrosarcoma research by developing an alginate-based 3D cell culture model.

Method: An alginate scaffold was applied to generate spheroids of three chondrosarcoma cell lines (CH2879, JJ012, SW1353). Morphological, histological and immunohistochemical assessment of the spheroids were used to characterize the chondrosarcoma model. Presto blue assay, morphological and immunohistochemical assessment were applied to assess spheroid response to a panel of chemotherapeutics and targeted therapies, which was compared to conventional 2D monolayer models. Synergistic effect of doxorubicin and ABT-737 (Bcl-2 inhibitor) was compared between monolayer and spheroid models using excess over Bliss. A 3D colony formation assay was developed for assessment of radiotherapy response.

Results: Chondrosarcoma spheroids produced chondrogenic matrix and remained proliferative after 2 weeks of culture. When treated with chemotherapeutics, the spheroids were more resistant than their monolayer counterparts, in line with animal models and clinical data. Moreover, for sapanisertib (mTOR inhibitor) treatment, a recovery in chondrosarcoma growth, previously observed in mice models, was also observed using long-term treatment. Morphological assessment was useful in the case of YM-155 (survivin inhibitor) treatment where a fraction of the spheroids underwent cell death, however a large fraction remained proliferative and unaffected. Synergy was less pronounced in 3D compared to 2D. A 3D clonogenic assay confirmed increased resistance to radiotherapy in 3D chondrosarcoma spheroids.

Conclusion: We demonstrate that the chondrosarcoma alginate spheroid model is more representative of chondrosarcoma in vivo and should be used instead of the monolayer model for therapy testing. Improved selection at in vitro stage of therapeutic testing will increase the amount of information available for experimental design of in vivo animal testing and later, clinical stages. This can potentially lead to increased likelihood of approval and success at clinical trials.

New insights into molecules and pathways of cancer metabolism and therapeutic implications

Cancer cells are abnormal cells that can reproduce and regenerate rapidly. They are characterized by unlimited proliferation, transformation and migration, and can destroy normal cells. To meet the needs for cell proliferation and migration, tumor cells acquire molecular materials and energy through unusual metabolic pathways as their metabolism is more vigorous than that of normal cells. Multiple carcinogenic signaling pathways eventually converge to regulate three major metabolic pathways in tumor cells, including glucose, lipid, and amino acid metabolism. The distinct metabolic signatures of cancer cells reflect that metabolic changes are indispensable for the genesis and development of tumor cells. In this review, we report the unique metabolic alterations in tumor cells which occur through various signaling axes, and present various modalities available for cancer diagnosis and clinical therapy. We further provide suggestions for the development of anti‐tumor therapeutic drugs.

The Role of Adjuvant Treatment in Craniofacial Malignancy: A Critical Review

Background: Tumors originating from the craniofacial region usually present in a locally advanced stage with frequent involvement of adjacent sites and have a strong tendency for local recurrence in the absence of adjuvant therapy, even when the original surgical resection was presumed to be radical. In the past decades, several advances in the radiological diagnosis and treatment of craniofacial malignancies have been introduced. There are, however, no randomized trials that define the optimal multimodal treatment of these tumors because of their rarity as well as heterogeneity in both histology and site of origin. The aim of this study was to conduct a critical review of the role of adjuvant therapy in the treatment of craniofacial malignancy. Method: We conducted a critical review of the past and contemporary literature available, focusing on adjuvant oncological treatments of the most common craniofacial malignancies. Results: Preoperative radiotherapy can have a documented role in the treatment of olfactory neuroblastoma and soft tissue sarcoma, while preoperative chemotherapy can be advocated in the treatment of sinonasal undifferentiated carcinoma, neuroendocrine carcinoma, olfactory neuroblastoma, and craniofacial sarcoma (both soft-tissue and high-grade osteosarcoma). Postoperative radiotherapy has a well-established role in the treatment of most craniofacial malignancies. The role of postoperative chemotherapy is unclear in most histologies, but is commonly used during the treatment of well-selected cases of paranasal sinus carcinoma, olfactory neuroblastoma, mucosal melanoma, soft tissue sarcoma and high-grade craniofacial osteosarcoma. Discussion: Alongside developments in surgery, there have also been improvements in diagnostics, radiotherapy, and chemotherapy. Implementation of novel radiation techniques allows delivery of higher radiation doses while minimizing irradiation-related morbidity. Better understanding of tumor biology allows the construction of more complex treatment strategies, incorporating adjuvant chemotherapy either pre- or postoperatively. In the era of personalized targeted therapy, rapid strides are being made to identify specific tumor-targets for use of novel biologic agents, with the potential to change current management paradigms.

Phase I Study of the Mutant IDH1 Inhibitor Ivosidenib: Safety and Clinical Activity in Patients With Advanced Chondrosarcoma

PURPOSE

Surgery is the primary therapy for localized chondrosarcoma; for locally advanced and/or metastatic disease, no known effective systemic therapy exists. Mutations in the isocitrate dehydrogenase 1/2 (IDH1/2) enzymes occur in up to 65% of chondrosarcomas, resulting in accumulation of the oncometabolite D-2-hydroxyglutarate (2-HG). Ivosidenib (AG-120) is a selective inhibitor of mutant IDH1 approved in the United States for specific cases of acute myeloid leukemia. We report outcomes of patients with advanced chondrosarcoma in an ongoing study exploring ivosidenib treatment.

PATIENTS AND METHODS

This phase I multicenter open-label dose-escalation and expansion study of ivosidenib monotherapy enrolled patients with mutant IDH1 advanced solid tumors, including chondrosarcoma. Ivosidenib was administered orally (100 mg twice daily to 1,200 mg once daily) in continuous 28-day cycles. Responses were assessed every other cycle using RECIST (version 1.1).

RESULTS

Twenty-one patients (escalation, n = 12; expansion, n = 9) with advanced chondrosarcoma received ivosidenib (women, n = 8; median age, 55 years; range, 30-88 years; 11 had received prior systemic therapy). Treatment-emergent adverse events (AEs) were mostly grade 1 or 2. Twelve patients experienced grade ≥ 3 AEs; only one event was judged treatment related (hypophosphatemia, n = 1). Plasma 2-HG levels decreased substantially in all patients (range, 14%-94.2%), to levels seen in healthy individuals. Median progression-free survival (PFS) was 5.6 months (95% CI, 1.9 to 7.4 months); the PFS rate at 6 months was 39.5%. Eleven (52%) of 21 patients experienced stable disease.

CONCLUSION

In patients with chondrosarcoma, ivosidenib showed minimal toxicity, substantial 2-HG reduction, and durable disease control. Future studies of ivosidenib monotherapy or rational combination approaches should be considered in patients with advanced mutant IDH1 chondrosarcoma.

[Cartilage tumors: morphology, genetics, and current aspects of target therapy]

Cartilage tumors are a heterogeneous group of mesenchymal tumors whose common characteristic is the formation of a chondroblastic differentiated groundsubstance by the tumor cells. The basic features of their histological classification were already developed in the 1940s and supplemented by further entities in the following decades. Only in the past 10-15 years have fundamental new insights been gained through molecular genetic analysis. So, osteochondromas are characterized by alterations in the EXT1 and EXT2 genes. The description of mutations of isocitrate dehydrogenase 1 and 2 (IDH 1 and 2) in chondromas and chondrosarcomas is particularly important. The mesenchymal chondrosarcoma is characterized by a fusion of the HEY1-NCOA2 genes. The molecular genetic alterations characteristic for the individual tumor entities are first of all an essential supplement for the differential diagnosis of radiologically and histologically difficult cases. They also provide the basis for the establishment of molecular target therapies for malignant chondrogenic tumors. This applies in particular to conventional chondrosarcoma, for which all approaches to chemo- and radiotherapy have proven to be ineffective. However, the use of target therapies is still in its beginnings.

Total mRNA Quantification in Single Cells: Sarcoma Cell Heterogeneity

Single-cell analysis enables detailed molecular characterization of cells in relation to cell type, genotype, cell state, temporal variations, and microenvironment. These studies often include the analysis of individual genes and networks of genes. The total amount of RNA also varies between cells due to important factors, such as cell type, cell size, and cell cycle state. However, there is a lack of simple and sensitive methods to quantify the total amount of RNA, especially mRNA. Here, we developed a method to quantify total mRNA levels in single cells based on global reverse transcription followed by quantitative PCR. Standard curve analyses of diluted RNA and sorted cells showed a wide dynamic range, high reproducibility, and excellent sensitivity. Single-cell analysis of three sarcoma cell lines and human fibroblasts revealed cell type variations, a lognormal distribution of total mRNA levels, and up to an eight-fold difference in total mRNA levels among the cells. The approach can easily be combined with targeted or global gene expression profiling, providing new means to study cell heterogeneity at an individual gene level and at a global level. This method can be used to investigate the biological importance of variations in the total amount of mRNA in healthy as well as pathological conditions.

Characterisation of isocitrate dehydrogenase 1/isocitrate dehydrogenase 2 gene mutation and the d-2-hydroxyglutarate oncometabolite level in dedifferentiated chondrosarcoma

AIMS

Dedifferentiated chondrosarcoma (DDCHS) is an aggressive type of chondrosarcoma that results from high-grade transformation of a low-grade chondrosarcoma. Mutations in the isocitrate dehydrogenase (IDH) 1 gene and the IDH2 gene that lead to increased d-2-hydroxyglutarate (2HG) oncometabolite production, promoting tumorigenesis, have been recently described in low-grade cartilaginous neoplasms. The aims of this study were to examine the prevalence of IDH mutations in a single-institution cohort of DDCHS cases and correlate 2HG levels with mutation status.

METHODS AND RESULTS

We examined a series of 21 primary DDCHS cases by using Sanger sequencing and quantitative polymerase chain reaction genotyping to look for IDH1/IDH2 mutations, and evaluated the 2HG levels in formalin-fixed paraffin-embedded tumour and matched normal tissue samples by using a fluorometric assay. Seventy-six per cent of DDCHS cases (16/21) harboured a heterozygous IDH1 or IDH2 mutation. Six of 14 IDH-mutated DDCHS cases showed elevated 2HG levels in tumour tissue relative to matched normal tissue. There were no consistent histological or disease-specific survival differences between IDH-mutated tumours and wild-type tumours.

CONCLUSIONS

Our study confirms the frequent presence of a variety of IDH1 and IDH2 mutation variants, indicating that a sequencing-based approach is required for DDCHS if IDH is to be used as a diagnostic marker. Similarly to other IDH-mutated tumour types, IDH-mutated DDCHS cases show elevated 2HG levels, indicating that the oncometabolite activity of 2HG may contribute to DDCHS oncogenesis and progression.

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.

Mutant IDH1 Depletion Downregulates Integrins and Impairs Chondrosarcoma Growth

Chondrosarcomas are a heterogeneous group of malignant bone tumors that produce hyaline cartilaginous matrix. Mutations in isocitrate dehydrogenase enzymes (IDH1/2) were recently described in several cancers, including conventional and dedifferentiated chondrosarcomas. These mutations lead to the inability of IDH to convert isocitrate into α-ketoglutarate (α-KG). Instead, α-KG is reduced into D-2-hydroxyglutarate (D-2HG), an oncometabolite. IDH mutations and D-2HG are thought to contribute to tumorigenesis due to the role of D-2HG as a competitive inhibitor of α-KG-dependent dioxygenases. However, the function of IDH mutations in chondrosarcomas has not been clearly defined. In this study, we knocked out mutant IDH1 (IDH1^mut) in two chondrosarcoma cell lines using the CRISPR/Cas9 system. We observed that D-2HG production, anchorage-independent growth, and cell migration were significantly suppressed in the IDH1^mut knockout cells. Loss of IDH1^mut also led to a marked attenuation of chondrosarcoma formation and D-2HG production in a xenograft model. In addition, RNA-Seq analysis of IDH1^mut knockout cells revealed downregulation of several integrin genes, including those of integrin alpha 5 (ITGA5) and integrin beta 5 (ITGB5). We further demonstrated that deregulation of integrin-mediated processes contributed to the tumorigenicity of IDH1-mutant chondrosarcoma cells. Our findings showed that IDH1^mut knockout abrogates chondrosarcoma genesis through modulation of integrins. This suggests that integrin molecules are appealing candidates for combinatorial regimens with IDH1^mut inhibitors for chondrosarcomas that harbor this mutation.

Mutation-driven epigenetic alterations as a defining hallmark of central cartilaginous tumours, giant cell tumour of bone and chondroblastoma

Recently, specific driver mutations were identified in chondroblastoma, giant cell tumour of bone and central cartilaginous tumours (specifically enchondroma and central chondrosarcoma), sharing the ability to induce genome-wide epigenetic alterations. In chondroblastoma and giant cell tumour of bone, the neoplastic mononuclear stromal-like cells frequently harbour specific point mutations in the genes encoding for histone H3.3 (H3F3A and H3F3B). The identification of these driver mutations has led to development of novel diagnostic tools to distinguish between chondroblastoma, giant cell tumour of bone and other giant cell containing tumours. From a biological perspective, these mutations induce several global and local alterations of the histone modification marks. Similar observations are made for central cartilaginous tumours, which frequently harbour specific point mutations in the metabolic enzymes IDH1 or IDH2. Besides an altered methylation pattern on histones, IDH mutations also induce a global DNA hypermethylation phenotype. In all of these tumour types, the mutation-driven epigenetic alterations lead to a highly altered transcriptome, resulting for instance in alterations in differentiation. These genomic alterations have diagnostic impact. Further research is needed to identify the genes and signalling pathways that are affected by the epigenetic alterations, which will hopefully lead to a better understanding of the biological mechanism underlying tumourigenesis.

An update on current and future treatment options for chondrosarcoma

Introduction: Human chondrosarcomas (CS; a malignant cartilage-forming bone tumor) respond poorly to chemotherapy and radiation treatment, resulting in high morbidity and mortality rates. Expanded treatment options are urgently needed. Areas covered: This article updates our 2014 review, in which we evaluated the CS treatments available at that time and potential treatment options under investigation. Since then, advances in research findings, particularly from Chinese herbal medicines, may be bringing us closer to more effective therapies for CS. In particular, promising findings have been reported from research targeting platelet-derived growth factor receptor. Expert opinion: Few treatment options exist for CS; chemotherapy is not even an option for unresectable disease, in which 5-year survival rates are just 2%. New information about the multitude of genes and signaling pathways that encourage CS growth, invasion and metastasis are clarifying how certain signaling pathways and plant-derived active compounds, especially molecularly-targeted therapies that inhibit the PDGF receptor, interfering with these biological processes. This review summarizes discoveries from the last 5 years and discusses how these findings are fueling ongoing work into effectively dealing with the disease process and improving the treatment of CS.

Metabolic Dysregulations and Epigenetics: A Bidirectional Interplay that Drives Tumor Progression

Cancer has been considered, for a long time, a genetic disease where mutations in keyregulatory genes drive tumor initiation, growth, metastasis, and drug resistance. Instead, theadvent of high-throughput technologies has revolutionized cancer research, allowing to investigatemolecular alterations at multiple levels, including genome, epigenome, transcriptome, proteome,and metabolome and showing the multifaceted aspects of this disease. The multi-omics approachesrevealed an intricate molecular landscape where different cellular functions are interconnected andcooperatively contribute to shaping the malignant phenotype. Recent evidence has brought to lighthow metabolism and epigenetics are highly intertwined, and their aberrant crosstalk can contributeto tumorigenesis. The oncogene-driven metabolic plasticity of tumor cells supports the energeticand anabolic demands of proliferative tumor programs and secondary can alter the epigeneticlandscape via modulating the production and/or the activity of epigenetic metabolites. Conversely,epigenetic mechanisms can regulate the expression of metabolic genes, thereby altering themetabolome, eliciting adaptive responses to rapidly changing environmental conditions, andsustaining malignant cell survival and progression in hostile niches. Thus, cancer cells takeadvantage of the epigenetics-metabolism crosstalk to acquire aggressive traits, promote cellproliferation, metastasis, and pluripotency, and shape tumor microenvironment. Understandingthis bidirectional relationship is crucial to identify potential novel molecular targets for theimplementation of robust anti-cancer therapeutic strategies.

HSP90 Molecular Chaperones, Metabolic Rewiring, and Epigenetics: Impact on Tumor Progression and Perspective for Anticancer Therapy

Heat shock protein 90 (HSP90) molecular chaperones are a family of ubiquitous proteins participating in several cellular functions through the regulation of folding and/or assembly of large multiprotein complexes and client proteins. Thus, HSP90s chaperones are, directly or indirectly, master regulators of a variety of cellular processes, such as adaptation to stress, cell proliferation, motility, angiogenesis, and signal transduction. In recent years, it has been proposed that HSP90s play a crucial role in carcinogenesis as regulators of genotype-to-phenotype interplay. Indeed, HSP90 chaperones control metabolic rewiring, a hallmark of cancer cells, and influence the transcription of several of the key-genes responsible for tumorigenesis and cancer progression, through either direct binding to chromatin or through the quality control of transcription factors and epigenetic effectors. In this review, we will revise evidence suggesting how this interplay between epigenetics and metabolism may affect oncogenesis. We will examine the effect of metabolic rewiring on the accumulation of specific metabolites, and the changes in the availability of epigenetic co-factors and how this process can be controlled by HSP90 molecular chaperones. Understanding deeply the relationship between epigenetic and metabolism could disclose novel therapeutic scenarios that may lead to improvements in cancer treatment.

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.

Consequences of IDH1/2 Mutations in Gliomas and an Assessment of Inhibitors Targeting Mutated IDH Proteins

Isocitrate dehydrogenases (IDH) 1 and 2 are key metabolic enzymes that generate reduced nicotinamide adenine dinucleotide phosphate (NADPH) to maintain a pool of reduced glutathione and peroxiredoxin, and produce α-ketoglutarate, a co-factor of numerous enzymes. IDH1/2 is mutated in ~70–80% of lower-grade gliomas and the majority of secondary glioblastomas. The mutant IDH1 (R132H), in addition to losing its normal catalytic activity, gains the function of producing the d-(R)-2-hydroxyglutarate (2-HG). Overproduction of 2-HG in cancer cells interferes with cellular metabolism and inhibits histone and DNA demethylases, which results in histone and DNA hypermethylation and the blockade of cellular differentiation. We summarize recent findings characterizing molecular mechanisms underlying oncogenic alterations associated with mutated IDH1/2, and their impact on tumor microenvironment and antitumor immunity. Isoform-selective IDH inhibitors which suppress 2-HG production and induce antitumor responses in cells with IDH1 and IDH2 mutations were developed and validated in preclinical settings. Inhibitors of mutated IDH1/2 enzymes entered clinical trials and represent a novel drug class for targeted therapy of gliomas. We describe the development of small-molecule compounds and peptide vaccines targeting IDH-mutant gliomas and the results of their testing in preclinical and clinical studies. All those results support the translational potential of strategies targeting gliomas carrying IDH1 mutations.

Epigenetic Modifications in Acute Myeloid Leukemia: Prognosis, Treatment, and Heterogeneity

Leukemia, specifically acute myeloid leukemia (AML), is a common malignancy that can be differentiated into multiple subtypes based on leukemogenic history and etiology. Although genetic aberrations, particularly cytogenetic abnormalities and mutations in known oncogenes, play an integral role in AML development, epigenetic processes have been shown as a significant and sometimes independent dynamic in AML pathophysiology. Here, we summarize how tumors evolve and describe AML through an epigenetic lens, including discussions on recent discoveries that include prognostics from epialleles, changes in RNA function for hematopoietic stem cells and the epitranscriptome, and novel epigenetic treatment options. We further describe the limitations of treatment in the context of the high degree of heterogeneity that characterizes acute myeloid leukemia.

Bridging Cancer Biology with the Clinic: Comprehending and Exploiting IDH Gene Mutations in Gliomas

Isocitrate dehydrogenases 1 and 2 (IDH1/2) are enzymes that play a major role in the Krebs cycle. Mutations in these enzymes are found in the majority of lower gliomas and secondary glioblastomas, but also in myeloid malignancies and other cancers. IDH1 and IDH2 mutations are restricted to specific arginine residues in the active site of the enzymes and are gain-of-function, i.e. they confer a neomorphic enzyme activity resulting in the accumulation of D-2-hydroxyglutarate (2-HG). 2-HG is an oncometabolite causing profound metabolic dysregulation which, among others, results in methylator phenotypes and in defects in homologous recombination repair. In this review, we summarize current knowledge regarding the function of normal and mutated IDH, explain the possible mechanisms through which these mutations might drive malignant transformation of progenitor cells in the central nervous system, and provide a comprehensive review of potential treatment strategies for IDH-mutated malignancies, focusing on gliomas.

Metabolism and Epigenetic Interplay in Cancer: Regulation and Putative Therapeutic Targets

Alterations in the epigenome and metabolism affect molecular rewiring of cancer cells facilitating cancer development and progression. Modulation of histone and DNA modification enzymes occurs owing to metabolic reprogramming driven by oncogenes and expression of metabolism-associated genes is, in turn, epigenetically regulated, promoting the well-known metabolic reprogramming of cancer cells and, consequently, altering the metabolome. Thus, several malignant traits are supported by the interplay between metabolomics and epigenetics, promoting neoplastic transformation. In this review we emphasize the importance of tumour metabolites in the activity of most chromatin-modifying enzymes and implication in neoplastic transformation. Furthermore, candidate targets deriving from metabolism of cancer cells and altered epigenetic factors is emphasized, focusing on compounds that counteract the epigenomic-metabolic interplay in cancer.

RNA-Binding Protein HuR Regulates Both Mutant and Wild-Type IDH1 in IDH1-Mutated Cancer

Isocitrate dehydrogenase 1 (IDH1) is the most commonly mutated metabolic enzyme in human malignancy. A heterozygous genetic alteration, arginine 132, promotes the conversion of α-ketoglutarate to D-2-hydroxyglutarate (2-HG). Although pharmacologic inhibitors of mutant IDH1 are promising, resistance mechanisms to targeted therapy are not understood. Additionally, the role of wild-type IDH1 (WT.IDH1) in cancer requires further study. Recently, it was observed that the regulatory RNA-binding protein, HuR (ELAVL1), protects nutrient-deprived cancer cells without IDH1 mutations, by stabilizing WT.IDH1 transcripts. In the present study, a similar regulatory effect on both mutant (Mut.IDH1) and WT.IDH1 transcripts in heterozygous IDH1-mutant tumors is observed. In ribonucleoprotein immunoprecipitation assays of IDH1-mutant cell lines, wild-type and mutant IDH1 mRNAs each bound to HuR. Both isoforms were profoundly downregulated at the mRNA and protein levels after genetic suppression of HuR (siRNAs or CRISPR deletion) in HT1080 (R132C IDH1 mutation) and BT054 cells (R132H). Proliferation and invasion were adversely affected after HuR suppression and metabolomic studies revealed a reduction in Pentose Phosphate Pathway metabolites, nucleotide precursors, and 2-HG levels. HuR-deficient cells were especially sensitive to stress, including low glucose conditions or a mutant IDH1 inhibitor (AGI-5198). IDH1-mutant cancer cells were rescued by WT.IDH1 overexpression to a greater extent than Mut.IDH1 overexpression under these conditions. This study reveals the importance of HuR's regulation of both mutant and wild-type IDH1 in tumors harboring a heterozygous IDH1 mutation with implications for therapy. IMPLICATIONS: This study highlights the HuR-IDH1 (mutant and wild-type IDH1) regulatory axis as a critical, actionable therapeutic target in IDH1-mutated cancer, and incomplete blockade of the entire HuR-IDH1 survival axis would likely diminish the efficacy of drugs that selectively target only the mutant isoenzyme.

Response to PD1 inhibition in conventional chondrosarcoma

Background

Chondrosarcoma is one of the most common malignant bone tumors in adults. Conventional chondrosarcoma represents around 85% of all chondrosarcomas and is notoriously difficult to treat with chemotherapy.

Case presentation

We describe a 67-year-old man with metastatic conventional chondrosarcoma who was treated with nivolumab. Treatment was discontinued after restaging showed increased tumor burden, which later proved to be pseudoprogression. The patient restarted nivolumab and continues to have a near complete response.

Conclusion

Conventional chondrosarcoma may be sensitive to checkpoint inhibitors. Further, this case demonstrates clearly the phenomenon of pseudo-progression in this disease, a factor that must be considered in the design of clinical trials and clinical care. This case supports additional study of immunomodulatory agents in this deadly disease.