Fumarate Hydratase Loss Research Articles

Response to systemic therapy in patients with metastatic fumarate hydratase (FH) deficient renal cell carcinoma (RCC).

686 Background: FH-deficient RCC (FHRCC) is characterized by unique pathologic features and lack of FH staining on immunohistochemistry (IHC). Most cases are associated with germline FH mutations and poor prognosis, but there is limited data on the efficacy of systemic therapy. Methods: Patients with metastatic FHRCC, defined by presence of FH germline or somatic mutation with loss of FH by IHC [FH and 2-succino-cysteine (2SC)], were identified from an institutional database. Clinical and treatment data was obtained from electronic records. The primary outcome was best objective response rate to first, second or third-line systemic therapy by blinded investigator RECIST v1.1 assessment. Results: 32 patients (median age 46; range 20-74; M:F, 20:12) were identified. All patients had evidence of FH-deficiency by IHC, 23 (72%) had germline FH mutations, 9 (28%) had somatic only FH mutations. 20 patients (62.5%) presented with de novo metastatic disease. Most common sites of metastasis were retroperitoneal lymph nodes (82%), lung (78%) and peritoneal spread (70%); no patients developed brain metastases. Median overall survival (OS) from diagnosis of metastatic disease is 28.1 months (95% CI: 14.9, 33.8). Median follow-up is 14.8 months. 25 patients were evaluable for response to first-line therapy, 5 to second-line and 4 to third-line therapy (Table). Most common first-line therapies were combination mTOR/VEGFR (50%) and VEGFR monotherapy (20%). ORR to first, second and third-line therapy was 40%, 20% and 25%, with no complete responses. 8 patients who received IO monotherapy were evaluable; 3 had stable disease, no responses were seen. Conclusions: Patients with FHRCC show distinct patterns of disease progression with primary peritoneal spread. Although there was high ORR to VEGFR/mTOR inhibitor combinations, there were limited responses to IO monotherapy.[Table: see text]

Prevalence of somatic and germline mutations of Fumarate hydratase in uterine leiomyomas from young patients.

Hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome is caused by germline mutations in the Fumarate hydratase (FH) gene. In young women, the syndrome often presents with symptomatic uterine leiomyomas, leading to myomectomy or hysterectomy. In this study, we aimed to investigate the incidence and mutational profiles of FH-negative leiomyomas from young patients, thus allowing for early identification and triage of syndromic patients for surveillance. We evaluated 153 cases of uterine leiomyomas from women aged up to 30years for loss of FH expression by tissue microarray (TMA)-based immunohistochemical staining. Mutational analysis of tumours with loss of FH was carried out by polymerase chain reaction (PCR) amplification of 10 exons within the FH gene and subsequent Sanger sequencing. The status of promoter methylation was assessed by bisulphite sequencing. Loss of FH protein expression was detected in seven (4.6%) of 153 tested uterine leiomyomas from young patients. All FH-negative leiomyomas displayed staghorn vasculature and fibrillary/neurophil-like cytoplasm. We found that six (86%) of seven FH-negative tumours detected by immunohistochemistry harboured FH mutations, 50% of which contained germline mutations. In particular, the germline mutational rate in FH gene was 2.0% (three of 153 cases). Bisulphite sequencing analysis failed to detect promoter methylation in any of the seven tumours. Our study showed a relatively high rate of FH germline mutation in FH-negative uterine leiomyomas from patients aged up to 30years. While genetic mutations confer protein expression loss, epigenetic regulation of the FH gene appears to be unrelated to this phenotype.

Detailed Morphologic and Immunohistochemical Characterization of Myomectomy and Hysterectomy Specimens From Women With Hereditary Leiomyomatosis and Renal Cell Carcinoma Syndrome (HLRCC).

Hereditary leiomyomatosis and renal cell carcinoma syndrome (HLRCC), caused by a germline mutation in the fumarate hydratase (FH) gene, predisposes patients to uterine and cutaneous smooth muscle tumors and an aggressive type of renal cell carcinoma. Almost all women with HLRCC develop symptomatic uterine leiomyomas resulting in surgery at young ages, presenting an ideal opportunity for early detection of these patients and the implementation of surveillance measures for renal cell carcinoma. FH-deficient uterine leiomyomas can show characteristic morphologic features (FH-d morphology) that have been previously described. Immunohistochemistry (IHC) for FH can also be helpful in detecting FH deficiency in leiomyomas, which manifests as complete loss of staining for FH. However, the distribution and topography of FH-d morphology and FH loss by IHC in the context of multiple leiomyomas in patients with HLRCC has not been evaluated. The aim of this study is to describe in detail the clinical and pathologic characteristics of uterine leiomyomas from women with HLRCC. Six patients with proven FH germline mutations were included. All available slides were reviewed and FH IHC staining was performed on multiple blocks when possible. Clinical data were extracted from online medical records. All 6 patients presented with symptomatic uterine fibroids and underwent myomectomy (age 24 to 36 y), followed by hysterectomy in 2 patients (age 31 and 40 y). Specimens showed conventional leiomyomas, cellular leiomyomas and leiomyomas with bizarre nuclei. FH-d morphology was present in leiomyomas from all patients and was typically observed as a diffuse finding in the majority of slides across different leiomyoma types. FH-d morphology was absent in some leiomyoma sections from one patient and the morphologic features were focal and subtle in leiomyomas from 2 patients. Both hysterectomy specimens were also notable for showing scattered irregular tongues and nodules of smooth muscle proliferation (leiomyomatosis-like) in the background myometrium. Immunohistochemical staining of multiple slides per patient for FH showed either retained staining in all sections (2/6 cases), loss of staining in all sections (1 case) or variable staining across different leiomyomas (3 cases). In conclusion, patients with HLRCC undergo surgery at young ages for highly symptomatic uterine leiomyomas. FH-d morphology is usually a diffuse and well developed finding across different leiomyomas but may be absent or focal and subtle. FH IHC can show variable results and presence of retained FH staining should not be used to exclude the possibility of HLRCC. Referral for genetic counselling and testing should be considered in a young patient with uterine leiomyomas showing FH-d morphology even if immunohistochemical staining for FH is retained.

Incidence of succinate dehydrogenase and fumarate hydratase–deficient renal cell carcinoma based on immunohistochemical screening with SDHA/SDHB and FH/2SC

Mutations of the succinate dehydrogenase (SDHX) enzyme subunits commonly lead to a loss of function of the holoenzyme complex, and germline SDHX mutations lead to a genetic predisposition to SDH-deficient neoplasms, including renal cell carcinomas (RCC). Similarly, loss-of-function alterations of fumarate hydratase (FH) leads to a genetic predisposition to hereditary leiomyomatosis and renal cell cancer (HLRCC)-associated RCC. Loss of FH leads to an accumulation of fumarate and aberrantly high levels of S-(2-succino)-cysteine (2SC). Subtype-specific consecutively diagnosed renal cell neoplasms were selected for the study and cases were not otherwise selected based on clinicopathologic features. Tissue microarrays were constructed from 1009 renal cell neoplasms (papillary: 400, clear cell: 203, chromophobe: 87, oncocytomas [original diagnosis]: 273, unclassified: 46) and these cases were immunostained for SDHA/SDHB to screen for SDH loss. A smaller subset (n = 730; oncocytomas, papillary and unclassified RCCs) were screened for FH-deficiency using immunohistochemistry for FH/2SC. Loss of SDHA/SDHB was seen in three of 273 tumors originally diagnosed as oncocytomas (1.1%). Diffuse nuclear and cytoplasmic 2SC staining, with retained FH expression was seen in one case (suggestive of dysfunctional FH protein), while absent FH was seen in 3 cases (2/400 papillary RCCs, 0.5% and 2/46 unclassified RCCs, 4.35%). No aberrant FH/2SC expression was noted in 273 cases originally diagnosed as oncocytomas. SDH-deficient RCCs were identified only in the cases originally diagnosed as oncocytomas (1.1%), while FH-deficient RCCs were identified in the papillary (0.5%) and unclassified RCC cohorts (4.35%). These results can help guide immunohistochemistry-based screening strategies for these tumors.

Abstract 3992: Comparison of AKR1B10, 2SC, and FH as biomarkers for HLRCC detection

Abstract HLRCC is an autosomal dominant tumor predisposition syndrome characterized by cutaneous and uterine leiomyomas (ULs), and increased risk for aggressive type 2 papillary renal cell carcinoma (RCC). The syndrome is caused by germline mutations in fumarate hydratase (FH). Loss of FH causes dysfunction of the Crebs cycle and an increase of succinated proteins, which can be detected using anti-2-succinocysteine (2SC) antibody. Recently, we have observed that aldo-keto reductase family 1, member B10 (AKR1B10) is overexpressed in RNA-level in ULs with biallelic loss of FH. Here, we compared anti-AKR1B10, anti-2SC, and anti-FH antibodies in detection of FH loss in protein-level in HLRCC-associated ULs. The study material consisted of 142 formalin-fixed paraffin-embedded (FFPE) UL samples collected at the University hospitals in Finland. The sample series include 77 FH-deficient UL samples from 25 HLRCC patients and 65 sporadic conventional ULs. HLRCC background was verified by detected germline mutation of FH. Four 0.8 mm cores of representative FFPE tumor tissue were used to construct tissue microarrays. Immunohistochemistry (IHC) was executed using an anti-AKR1B10 (1:300, H00057016-M01, Abnova), anti-2SC (1:2000, provided by Dr. Norma Frizzell), and anti-FH (1:1000, sc-100743, Santa Cruz Biotechnology, Inc) antibodies. Expression was detected by BrightVision (Immunologic) and DAB Quanto (Thermo Fisher Scientific) systems. Pathologist specialized in gynecological pathology evaluated the IHC staining from the smooth muscle tumor cells. AKR1B10 and 2SC detected all 77 HLRCC samples. AKR1B10 displayed either mild (12/77, 16%) or strong (65/77, 84%) expression and succination level was strong in all cases. Loss of FH expression was displayed in 68/77 (88%) of the FH-deficient ULs. All conventional ULs displayed negative AKR1B10 and 2SC staining and expressed FH. FH was expressed either mildly (15/65, 23%) or strongly (50/65, 77%) in the samples. Reliable methods for FH-deficient UL detection in the clinics are currently lacking. Here, comparison of AKR1B10, 2SC, and FH showed that all three biomarkers identified HLRCC-ULs with 100% specificity. The sensitivity was 100% with AKR1B10 and 2SC, and 88% with FH. It seems that even with known mutation in FH, in some cases the likely inactive protein is retained in tumor cells and is thus detectable by anti-FH. To conclude, we show that anti-AKR1B10 and anti-2SC detect FH-deficient ULs with 100% specificity and sensitivity. Anti-FH is lacking sensitivity in 12% of HLRCC cases. Reliable detection of FH-deficient ULs enables the patients and their families to be directed to genetic counseling, family planning, and regular renal monitoring. Citation Format: Terhi Ahvenainen, Outi Uimari, Anne Ahtikoski, Kati Kämpjärvi, Ralf Bützow, Pia Vahteristo. Comparison of AKR1B10, 2SC, and FH as biomarkers for HLRCC detection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3992.

Abstract SY19-01: Metabolic consequences and liabilities of TCA cycle truncation in cancer

Abstract Succinate dehydrogenase (SDH) and fumarate hydratase (FH) are tricarboxylic acid (TCA) cycle enzymes while SDH is also part of the respiratory chain. Despite their key housekeeping activities, the genetic loss of FH or of any of the SDH subunits is associated with susceptibility to cancers. SDH or FH inactivation leads to the accumulation of metabolites which cause the activation of hypoxia-inducible factors and the inhibition of histone and DNA demethylases, establishing pseudohypoxic and hypermethylator phenotype. However, surviving the loss of these essential metabolic enzymes requires a significant metabolic adaptation as backup mechanisms for the dysfunctional TCA cycle and oxidative phosphorylation in these tumors. Identifying these adaptations would reveal effective and specific metabolic vulnerabilities which can serve as potential molecular targets for therapeutic intervention. We have identified in the past a few metabolic essentialities in cells deficient in FH and SDH and now performed a pharmacologic phenotypic synthetic lethal screen to identified effective drugs that specifically kill SDH- and FH-deficient cells. Utilizing metabolomics, we have delineated the molecular target of the effective compounds. Citation Format: Eyal Gottlieb. Metabolic consequences and liabilities of TCA cycle truncation in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr SY19-01.

Fumarate hydratase loss promotes mitotic entry in the presence of DNA damage after ionising radiation

An altered response to DNA damage is commonly associated with genomic instability, a hallmark of cancer. Fumarate hydratase (FH) was recently characterised as a DNA repair factor required in non-homologous end-joining (NHEJ) through the local production of fumarate. Inactivating germline mutations in FH cause hereditary leiomyomatosis and renal cell cancer (HLRCC), a cancer syndrome characterised by accumulation of fumarate. Recent data indicate that, in FH-deficient cells, fumarate suppresses homologous recombination DNA repair upon DNA double-strand breaks, compromising genome integrity. Here, we show that FH loss confers resistance to DNA damage caused by ionising radiation (IR), and promotes early mitotic entry after IR in a fumarate-specific manner, even in the presence of unrepaired damage, by suppressing checkpoint maintenance. We also showed that higher levels of DNA damage foci are detectable in untreated FH-deficient cells. Overall, these data indicate that FH loss and fumarate accumulation lead to a weakened G2 checkpoint that predisposes to endogenous DNA damage and confers resistance to IR.

Fumarate hydratase (FH) deficiency in uterine leiomyomas: recognition by histological features versus blind immunoscreening.

Hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome is a rare autosomal dominant disease caused by germline mutations in the fumarate hydratase (FH) gene. Affected individuals develop cutaneous and uterine leiomyomas and aggressive RCC. To date, only few publications described the frequency and morphology of FH-deficient uterine leiomyomas. We reviewed 22 cases collected over 8years from routine and consultation files based on distinctive histological features. In addition, we screened 580 consecutive uterine leiomyomas from 484 patients, 23 extra-uterine and 8 uterine leiomyosarcomas, and 6 leiomyomas with bizarre nuclei for FH loss using immunohistochemistry (IHC) on tissue microarrays (TMAs). All 22 FH-deficient cases were suspected on H&E sections and confirmed by FH IHC. Patients' ages ranged from 25 to 70years (median 36). Seventeen patients had multiple nodules (2-14) measuring up to 11.8cm. None of the patients had stigmata or family history of the HLRCC syndrome. Histologically, all FH-deficient tumors showed consistent and reproducible features as reported previously. FH loss was detected in 2/534 evaluable leiomyomas (0.4%), but in none of leiomyosarcomas. Two of six leiomyomas with bizarre nuclei were FH-deficient. FH-deficient uterine leiomyomas are rare in routine material (= 0.4%). They can be reliably identified or suspected by consistent morphological features. Our data showed predictive morphology to be superior to blind IHC screening for detecting them. The relationship of FH-deficient uterine smooth muscle tumors to the HLRCC syndrome needs further clarification.

Fumarate Hydratase Loss Causes Combined Respiratory Chain Defects

SummaryFumarate hydratase (FH) is an enzyme of the tricarboxylic acid (TCA) cycle mutated in hereditary and sporadic cancers. Despite recent advances in understanding its role in tumorigenesis, the effects of FH loss on mitochondrial metabolism are still unclear. Here, we used mouse and human cell lines to assess mitochondrial function of FH-deficient cells. We found that human and mouse FH-deficient cells exhibit decreased respiration, accompanied by a varying degree of dysfunction of respiratory chain (RC) complex I and II. Moreover, we show that fumarate induces succination of key components of the iron-sulfur cluster biogenesis family of proteins, leading to defects in the biogenesis of iron-sulfur clusters that affect complex I function. We also demonstrate that suppression of complex II activity is caused by product inhibition due to fumarate accumulation. Overall, our work provides evidence that the loss of a single TCA cycle enzyme is sufficient to cause combined RC activity dysfunction.

Loss of Fumarate Hydratase and Aberrant Protein Succination Detected With S-(2-Succino)-Cysteine Staining to Identify Patients With Multiple Cutaneous and Uterine Leiomyomatosis and Hereditary Leiomyomatosis and Renal Cell Cancer Syndrome.

Hereditary leiomyomatosis and renal cell cancer (HLRCC) syndrome is an autosomal dominant disorder caused by heterozygotic germline mutations in fumarate hydratase (FH) with incomplete penetrance, and clinically challenging to diagnose. Immunohistochemical stainings may favor an earlier diagnosis. The authors have tested 31 smooth muscle neoplasms. Ten of the 13 lesions from patients with HLRCC syndrome showed negative FH staining. Most sporadic piloleiomyomas presented strongly positive FH staining although 5 cases were negative. Sensitivity of FH staining in our series is 83.3% but specificity is 75%. Anti-S-(2-succino)-cysteine (2SC) showed the opposite intensity staining pattern and showed great correlation with anti-FH (rho spearman = -0.797). Anti-2SC staining increased the diagnostic accuracy in 19% of the cases. The main limitation of this study is the lack additional clinical data to further classify the cases as the case inclusion was histopathological. Negative FH staining could indicate a high risk of HLRCC but it could also suggest the presence of a syndrome in up to 25% of sporadic cases. Thus, when there is a doubtful case, anti-2SC may be added to exclude the syndrome if a negative staining is found.

Tubulocystic Carcinoma of the Kidney With Poorly Differentiated Foci: A Frequent Morphologic Pattern of Fumarate Hydratase-deficient Renal Cell Carcinoma.

An emerging group of high-grade renal cell carcinomas (RCCs), particularly carcinomas arising in the hereditary leiomyomatosis renal cell carcinoma syndrome (HLRCC), show fumarate hydratase (FH) gene mutation and loss of function. On the basis of similar cytomorphology and clinicopathologic features between these tumors and cases described as tubulocystic carcinomas with poorly differentiated foci (TC-PD) of infiltrative adenocarcinoma, we hypothesized a relationship between these entities. First, 29 RCCs with morphology of TC-PD were identified retrospectively and assessed for FH expression and aberrant succination (2SC) by immunohistochemistry (IHC), with targeted next-generation sequencing of 409 genes-including FH-performed on a subset. The 29 TC-PD RCCs included 21 males and 8 females, aged 16 to 86 years (median, 46), with tumors measuring 3 to 21 cm (median, 9) arising in the right (n=16) and left (n=13) kidneys. Family history or stigmata of HLRCC were identifiable only retrospectively in 3 (12%). These tumors were aggressive, with 79% showing perinephric extension, nodal involvement in 41%, and metastasis in 86%. Of these, 16 (55%) demonstrated loss of FH by IHC (14/14 with positive 2SC). In contrast, 5 (17%) showed a wild-type immunoprofile of FH+/2SC-. An intriguing group of 8 (28%) showed variable FH± positivity, but with strong/diffuse 2SC+. Next-generation sequencing revealed 8 cases with FH mutations, including 5 FH-/2SC+ and 3 FH±/2SC+ cases, but none in FH+/2SC- cases. Secondly, we retrospectively reviewed the morphology of 2 well-characterized cohorts of RCCs with FH-deficiency determined by IHC or sequencing (n=23 and n=9), unselected for TC-PD pattern, identifying the TC-PD morphology in 10 (31%). We conclude that RCCs with TC-PD morphology are enriched for FH deficiency, and we recommend additional workup, including referral to genetic counseling, for prospective cases. In addition, based on these and other observations, we propose the term "FH-deficient RCC" as a provisional term for tumors with a combination of suggestive morphology and immunophenotype but where genetic confirmation is unavailable upon diagnosis. This term will serve as a provisional nomenclature that will enable triage of individual cases for genetic counseling and testing, while designating these cases for prospective studies of their relationship to HLRCC.

Fumarate is an epigenetic modifier that elicits epithelial-to-mesenchymal transition.

Mutations of the tricarboxylic acid cycle (TCA cycle) enzyme fumarate hydratase (FH) cause Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC)1. FH-deficient renal cancers are highly aggressive and metastasise even when small, leading to an abysmal clinical outcome2. Fumarate, a small molecule metabolite that accumulates in FH-deficient cells, plays a key role in cell transformation, making it a bona fide oncometabolite3. Fumarate was shown to inhibit α-ketoglutarate (aKG)-dependent dioxygenases involved in DNA and histone demethylation4,5. However, the link between fumarate accumulation, epigenetic changes, and tumorigenesis is unclear. Here we show that loss of FH and the subsequent accumulation of fumarate elicits an epithelial-to-mesenchymal-transition (EMT), a phenotypic switch associated with cancer initiation, invasion, and metastasis6. We demonstrate that fumarate inhibits Tet-mediated demethylation of a regulatory region of the antimetastatic miRNA cluster6 miR-200ba429, leading to the expression of EMT-related transcription factors and enhanced migratory properties. These epigenetic and phenotypic changes are recapitulated by the incubation of FH-proficient cells with cell-permeable fumarate. Loss of FH is associated with suppression of miR-200 and EMT signature in renal cancer patients, and is associated with poor clinical outcome. These results imply that loss of FH and fumarate accumulation contribute to the aggressive features of FH-deficient tumours.

Immunohistochemistry for 2-Succinocysteine (2SC) and Fumarate Hydratase (FH) in Cutaneous Leiomyomas May Aid in Identification of Patients With HLRCC (Hereditary Leiomyomatosis and Renal Cell Carcinoma Syndrome).

Hereditary leiomyomatosis and renal cell carcinoma syndrome (HLRCC) is caused by germline mutations in the fumarate hydratase (FH) gene and predisposes to cutaneous and uterine leiomyomas and renal cell carcinoma (RCC). HLRCC-associated renal tumors are clinically aggressive, and patients would benefit from surveillance and early detection. Cutaneous leiomyomas that occur in association with HLRCC typically present early and are multiple. Thus far, the presence of certain morphologic features (large eosinophilic macronucleoli surrounded by halos and eosinophilic cytoplasmic inclusions) in RCC and uterine leiomyomas has been shown to correlate with FH mutations. Immunohistochemistry (IHC) for 2-succinocysteine (2SC) and FH has also been shown to correlate well with FH gene mutation status in RCC and uterine leiomyomas. The aim of this study was to assess the effectiveness of morphologic features and IHC at predicting FH gene mutations in cutaneous leiomyomas. We identified 22 patients with multiple cutaneous leiomyomas (40 total MCLs) and 25 patients with single leiomyomas (25 SCLs). Mutations in the FH gene were detected in 11 of 13 (85%) sequenced MCLs and 1 of 11 (9%) SCLs. A strong association was observed between 2SC positivity by IHC and presence of FH gene mutation (P=0.0028 for 2SC) but not with FH loss by IHC (P=0.4 for FH). All 11 MCLs with an FH mutation showed positive staining for 2SC, whereas 6 of 11 showed complete loss of FH staining. Our study suggests that the presence of MCLs should raise the possibility of HLRCC. IHC for FH and 2SC is helpful in detection of FH gene mutations and should be considered in all newly diagnosed cutaneous leiomyomas.

Fumarate induces redox-dependent senescence by modifying glutathione metabolism.

Mutations in the tricarboxylic acid (TCA) cycle enzyme fumarate hydratase (FH) are associated with a highly malignant form of renal cancer. We combined analytical chemistry and metabolic computational modelling to investigate the metabolic implications of FH loss in immortalized and primary mouse kidney cells. Here, we show that the accumulation of fumarate caused by the inactivation of FH leads to oxidative stress that is mediated by the formation of succinicGSH, a covalent adduct between fumarate and glutathione. Chronic succination of GSH, caused by the loss of FH, or by exogenous fumarate, leads to persistent oxidative stress and cellular senescence in vitro and in vivo. Importantly, the ablation of p21, a key mediator of senescence, in Fh1-deficient mice resulted in the transformation of benign renal cysts into a hyperplastic lesion, suggesting that fumarate-induced senescence needs to be bypassed for the initiation of renal cancers.

The Oncometabolite Fumarate Promotes Pseudohypoxia Through Noncanonical Activation of NF-κB Signaling

Inactivating mutations of the gene encoding the tricarboxylic acid cycle enzyme fumarate hydratase (FH) have been linked to an aggressive variant of hereditary kidney cancer (hereditary leiomyomatosis and renal cell cancer). These tumors accumulate markedly elevated levels of fumarate. Fumarate is among a growing list of oncometabolites identified in cancers with mutations of genes involved in intermediary metabolism. FH-deficient tumors are notable for their pronounced accumulation of the transcription factor hypoxia inducible factor-1α (HIF-1α) and aggressive behavior. To date, HIF-1α accumulation in hereditary leiomyomatosis and renal cell cancer tumors is thought to result from fumarate-dependent inhibition of prolyl hydroxylases and subsequent evasion from von Hippel-Lindau-dependent degradation. Here, we demonstrate a novel mechanism by which fumarate promotes HIF-1α mRNA and protein accumulation independent of the von Hippel-Lindau pathway. Here we demonstrate that fumarate promotes p65 phosphorylation and p65 accumulation at the HIF-1α promoter through non-canonical signaling via the upstream Tank binding kinase 1 (TBK1). Consistent with these data, inhibition of the TBK1/p65 axis blocks HIF-1α accumulation in cellular models of FH loss and markedly reduces cell invasion of FH-deficient RCC cancer cells. Collectively, our data demonstrate a novel mechanism by which pseudohypoxia is promoted in FH-deficient tumors and identifies TBK1 as a novel putative therapeutic target for the treatment of aggressive fumarate-driven tumors.

The Proto-oncometabolite Fumarate Binds Glutathione to Amplify ROS-Dependent Signaling

The tricarboxylic acid cycle enzyme fumarate hydratase (FH) has been identified as a tumor suppressor in a subset of human renal cell carcinomas. Human FH-deficient cancer cells display high fumarate concentration and ROS levels along with activation of HIF-1. The underlying mechanisms by which FH loss increases ROS and HIF-1 are not fully understood. Here, we report that glutamine-dependent oxidative citric acid cycle metabolism is required to generate fumarate and increase ROS and HIF-1 levels. Accumulated fumarate directly bonds the antioxidant glutathione in vitro and in vivo to produce the metabolite succinated glutathione (GSF). GSF acts as an alternative substrate to glutathione reductase to decrease NADPH levels and enhance mitochondrial ROS and HIF-1 activation. Increased ROS also correlates with hypermethylation of histones in these cells. Thus, fumarate serves as a proto-oncometabolite by binding to glutathione which results in the accumulation of ROS.

Reversed argininosuccinate lyase activity in fumarate hydratase-deficient cancer cells

BackgroundLoss of function of fumarate hydratase (FH), the mitochondrial tumor suppressor and tricarboxylic acid (TCA) cycle enzyme, is associated with a highly malignant form of papillary and collecting duct renal cell cancer. The accumulation of fumarate in these cells has been linked to the tumorigenic process. However, little is known about the overall effects of the loss of FH on cellular metabolism.MethodsWe performed comprehensive metabolomic analyses of urine from Fh1-deficient mice and stable isotopologue tracing from human and mouse FH-deficient cell lines to investigate the biochemical signature of the loss of FH.ResultsThe metabolomics analysis revealed that the urea cycle metabolite argininosuccinate is a common metabolic biomarker of FH deficiency. Argininosuccinate was found to be produced from arginine and fumarate by the reverse activity of the urea cycle enzyme argininosuccinate lyase (ASL), making these cells auxotrophic for arginine. Depleting arginine from the growth media by the addition of pegylated arginine deiminase (ADI-PEG 20) decreased the production of argininosuccinate in FH-deficient cells and reduced cell survival and proliferation.ConclusionsThese results unravel a previously unidentified correlation between fumarate accumulation and the urea cycle enzyme ASL in FH-deficient cells. The finding that FH-deficient cells become auxotrophic for arginine opens a new therapeutic perspective for the cure of hereditary leiomyomatosis and renal cell cancer (HLRCC).

Abstract 3820: Deregulation of KEAP1-NRF axis in phenotypically type 2 papillary renal cell carcinoma

Abstract Type 2 papillary renal cell carcinoma (PRCC2) is an aggressive subtype of kidney cancer that has no known effective treatment modality. The hereditary form of the tumor is known to associate with the loss of fumarate hydratase (FH) gene function. However, FH gene mutation has yet to be found in sporadic PRCC2. Herein, we report the overexpression of antioxidant response element (ARE) controlled genes as a common feature that is shared between the hereditary and sporadic form of PRCC2. We demonstrate that fumarate stabilizes NRF1 and NRF2, which drive the upregulation of ARE controlled genes. We propose that fumarate stabilizes NRF1 and NRF2 through direct suppression of KEAP1. This finding better explains the phenotypical differences that are apparent between PRCC2 and CCRCC and may lead to the development of an effective therapeutic against PRCC2. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3820. doi:10.1158/1538-7445.AM2011-3820

Pseudohypoxic Pathways in Renal Cell Carcinoma

Mutations of the von Hippel-Lindau (VHL) or fumarate hydratase (FH) genes lead to morphologically different renal cell carcinomas with distinct clinical courses and outcomes. The VHL protein is a part of an ubiquitin ligase complex that targets proteins for proteosomal degradation. FH is one of the mitochondrial enzymes of the Kreb's cycle. Despite two different functionalities and cellular locations, loss of either VHL or FH products has been shown to alter expression levels of hypoxia-inducible factors (HIF-1alpha and HIF-2alpha) and their downstream targets. HIF proteins are key regulators of oxygen homeostasis. Tight regulation of HIF allows for cell survival and growth at the time of hypoxic stress. HIF acts via transcriptional regulation of vascular endothelial growth factor, platelet derived growth factor, endothelial growth factor receptor, glucose transporter protein 1, erythropoietin, and transforming growth factor-alpha. Loss of VHL or FH is thought to result in a pseudohypoxic state so that cellular response pathways mediated by HIF are activated despite normal oxygen conditions. Understanding of these pseudohypoxic pathways has provided a better appreciation of the molecular mechanisms of carcinogenesis in addition to providing a rationale for targeted therapeutic approaches.

Cell-Permeating α-Ketoglutarate Derivatives Alleviate Pseudohypoxia in Succinate Dehydrogenase-Deficient Cells

Succinate dehydrogenase (SDH) and fumarate hydratase (FH) are components of the tricarboxylic acid (TCA) cycle and tumor suppressors. Loss of SDH or FH induces pseudohypoxia, a major tumor-supporting event, which is the activation of hypoxia-inducible factor (HIF) under normoxia. In SDH- or FH-deficient cells, HIF activation is due to HIF1alpha stabilization by succinate or fumarate, respectively, either of which, when in excess, inhibits HIFalpha prolyl hydroxylase (PHD). To reactivate PHD, we focused on its substrate, alpha-ketoglutarate. We designed and synthesized cell-permeating alpha-ketoglutarate derivatives, which build up rapidly and preferentially in cells with a dysfunctional TCA cycle. This study shows that succinate- or fumarate-mediated inhibition of PHD is competitive and is reversed by pharmacologically elevating intracellular alpha-ketoglutarate. Introduction of alpha-ketoglutarate derivatives restores normal PHD activity and HIF1alpha levels to SDH-suppressed cells, indicating new therapy possibilities for the cancers associated with TCA cycle dysfunction.