Von Hippel-Lindau Research Articles

In Silico Exploration of AHR-HIF Pathway Interplay: Implications for Therapeutic Targeting in ccRCC.

The oxygen-sensing pathway is a crucial regulatory circuit that defines cellular conditions and is extensively exploited in cancer development. Pathogenic mutations in the von Hippel-Lindau (VHL) tumour suppressor impair its role as a master regulator of hypoxia-inducible factors (HIFs), leading to constitutive HIF activation and uncontrolled angiogenesis, increasing the risk of developing clear cell renal cell carcinoma (ccRCC). HIF hyperactivation can sequester HIF-1β, preventing the aryl hydrocarbon receptor (AHR) from correctly activating gene expression in response to endogenous and exogenous ligands such as TCDD (dioxins). In this study, we used protein-protein interaction networks and gene expression profiling to characterize the impact of VHL loss on AHR activity. Our findings reveal specific expression patterns of AHR interactors following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and in ccRCC. We identified several AHR interactors significantly associated with poor survival rates in ccRCC patients. Notably, the upregulation of the androgen receptor (AR) and retinoblastoma-associated protein (RB1) by TCDD, coupled with their respective downregulation in ccRCC and association with poor survival rates, suggests novel therapeutic targets. The strategic activation of the AHR via selective AHR modulators (SAhRMs) could stimulate its anticancer activity, specifically targeting RB1 and AR to reduce cell cycle progression and metastasis formation in ccRCC. Our study provides comprehensive insights into the complex interplay between the AHR and HIF pathways in ccRCC pathogenesis, offering novel strategies for targeted therapeutic interventions.

Citrullination modulation stabilizes HIF-1α to promote tumour progression

Citrullination plays an essential role in various physiological or pathological processes, however, whether citrullination is involved in regulating tumour progression and the potential therapeutic significance have not been well explored. Here, we find that peptidyl arginine deiminase 4 (PADI4) directly interacts with and citrullinates hypoxia-inducible factor 1α (HIF-1α) at R698, promoting HIF-1α stabilization. Mechanistically, PADI4-mediated HIF-1αR698 citrullination blocks von Hippel-Lindau (VHL) binding, thereby antagonizing HIF-1α ubiquitination and subsequent proteasome degradation. We also show that citrullinated HIF-1αR698, HIF-1α and PADI4 are highly expressed in hepatocellular carcinoma (HCC) tumour tissues, suggesting a potential correlation between PADI4-mediated HIF-1αR698 citrullination and cancer development. Furthermore, we identify that dihydroergotamine mesylate (DHE) acts as an antagonist of PADI4, which ultimately suppresses tumour progression. Collectively, our results reveal citrullination as a posttranslational modification related to HIF-1α stability, and suggest that targeting PADI4-mediated HIF-1α citrullination is a promising therapeutic strategy for cancers with aberrant HIF-1α expression.

SUCCESSFUL TREATMENT OF VON HIPPEL-LINDAU DISEASE-ASSOCIATED RETINAL CAPILLARY HEMANGIOBLASTOMA WITH BELZUTIFAN IN A PEDIATRIC PATIENT.

The authors describe a case of a retinal capillary hemangioblastoma (RCH) in a pediatric patient with von Hippel-Lindau (VHL) syndrome that was successfully treated with systemic belzutifan. The clinical course was documented with serial fundus examinations and multimodal imaging, including Optos widefield fundus photography and optical coherence tomography. A literature review was conducted to look for similar cases and/or discussion. A left RCH was noted on a standard VHL surveillance retinal examination of a then 15-year-old male patient with VHL syndrome. Over the course of 17 months, this RCH was treated with focal laser therapy, photodynamic therapy, cryotherapy, bevacizumab injection, and endolaser ablation. Complications of these treatments included subretinal fluid and vitreomacular traction necessitating laser retinopexy, scleral buckle, and pars plana vitrectomy with membrane stripping. After a 6-month interval from the last local therapy (endolaser treatment), there was minimal regression of the lesion, and many concerning features persisted. At 22 months from presentation, the patient started belzutifan 120 mg PO daily with subsequent regression in size and less perfusion to the hemangioblastoma within 4 months. The patient is tolerating the systemic belzutifan with only the expected normocytic anemia and has not required transfusion therapy after 12 months of treatment. von Hippel-Lindau disease is a rare and serious condition associated with multiple types of benign and malignant tumors. Belzutifan is tolerated in the adolescent population and can provide a systemic treatment alternative for VHL-associated RCH.

Randomized phase II dose comparison LITESPARK-013 study of belzutifan in patients with advanced clear cell renal cell carcinoma

Belzutifan is a first-in-class hypoxia-inducible factor subunit 2α (HIF-2α) inhibitor approved at a dose of 120 mg once daily for certain adults with VHL disease and adults with advanced renal cell carcinoma (RCC) following therapy with a programmed cell death protein 1 (PD-1) [or programmed death ligand 1 (PD-L1)] inhibitor and a vascular endothelial growth factor tyrosine kinase inhibitor. However, whether the belzutifan dose could be optimized is unclear. The phase II LITESPARK-013 study (NCT04489771) enrolled patients with advanced clear cell RCC whose disease progressed after one to three prior systemic therapies, including an anti-PD-(L)1 regimen. Patients were randomly assigned 1 : 1 to receive belzutifan 120 or 200 mg once daily. The primary endpoint was the objective response rate (ORR) per RECIST version 1.1. The secondary endpoints were duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Overall, 154 patients were enrolled (120 mg: n= 76; 200 mg: n= 78). The median follow-up was 20.1 months (range 14.8-28.4). The ORR was 23.7% versus 23.1% for the 120 mg and 200 mg groups, respectively [P= 0.5312;-0.5%, 95% confidence interval (CI)-14.0% to 12.9%]. The median DOR was not reached for the 120 mg arm and was 16.1 months (2.1+ to 23.5+) for the 200 mg arm. No between-group differences were observed for PFS [hazard ratio (HR) 0.94, 95% CI 0.63-1.40] or OS (medians not reached; HR 1.11, 95% CI 0.65-1.90). Grade 3 or 4 treatment-related adverse events were observed in 35 patients (46.1%) in the 120 mg group and 36 patients (46.2%) in the 200 mg group. The efficacy of belzutifan was similar between the 120 mg dose and the 200 mg dose for previously treated clear cell RCC. Safety at both doses was consistent with the known safety profile of belzutifan. These results further support 120 mg once daily as the preferred dose for belzutifan.

Immunotherapeutic Innovations in Clear Cell Renal Cell Carcinoma: Current Strategies and Future Directions.

Approximatively 80% of kidney cancers globally are clear cell kidney cancers (ccRCCs), with 80% of these malignancies featuring an inactivating mutation of the Von Hippel-Lindau gene. This genetic alteration leads to the stabilization of hypoxia inducible factors 1 and 2 alpha (HIF 1 and 2α), resulting in the over-expression of target genes such as vascular endothelial growth factor (VEGF), which is crucial for angiogenesis. As a result, ccRCCs are highly vascularized and serve as models for anti-angiogenic treatments (AAT). Current AAT therapies comprise antibodies targeting VEGFs, tyrosine kinase inhibitors (TKi) (Sunitinib) that target neo-angiogenesis receptors, and competitive inhibitor receptors (Aflibercept) that trap VEGFA and PlGF. The over-expression of VEGF and related members such as VEGFC significantly influences angiogenesis, lymph-angiogenesis, and immune tolerance. This has resulted in the approval of various immune checkpoint inhibitors (known as anti-PD-1, anti-PD-L1, and anti-CTLA-4) as viable treatment options for kidney cancer. Despite these advances, ccRCC remains challenging to treat adequately. Thus, future research is imperative to better understand the biology and pathophysiology of RCC, the tumor microenvironment, and mechanisms of resistance, with the aim of developing new therapies.

Genetics, Pathophysiology, and Current Challenges in Von Hippel-Lindau Disease Therapeutics.

VHL disease is caused by mutations in the VHL tumor suppressor gene located on chromosome 3. These mutations can be inherited or occur spontaneously. This article details the different types of mutations and their associated clinical features. The underlying cause of VHL disease is the loss of function of the VHL protein (pVHL). This protein normally regulates hypoxia-inducible factors (HIFs), which are involved in cell growth and survival. When pVHL is dysfunctional, HIF levels become elevated, leading to uncontrolled cell growth and tumor formation. VHL disease can affect various organs, including the brain, spinal cord, retina, kidneys, pancreas, and adrenal glands. Symptoms depend on the location and size of the tumors. Diagnosis of VHL disease involves a combination of clinical criteria, imaging studies, and genetic testing. Treatment options for VHL disease depend on the type and location of the tumors. Surgery is the mainstay of treatment, but other options like radiation therapy may also be used. This article highlights the challenges in VHL disease management, including the lack of effective therapies for some tumor types and the need for better methods to monitor disease progression. In conclusion, we emphasize the importance of ongoing research to develop new and improved treatments for VHL disease.

Clear Cell Renal Cell Carcinoma: Characterizing the Phenotype of Von Hippel-Lindau Mutation Using MRI.

The von Hippel-Lindau (VHL) mutation is an important alteration in clear cell renal cell carcinoma (ccRCC); however, its imaging phenotype remains unclear. To investigate whether MRI features can reflect the VHL mutation status. Retrospective. 3 T/fast spin echo T2-weighted, spin-echo echo planar diffusion-weighted, gradient recalled echo T1-weighted, gradient recalled echo chemical-shift T1-weighted, and contrast-enhanced gradient recalled echo T1-weighted sequences. One hundred five patients with ccRCC who underwent preoperative contrast-enhanced MRI and subsequent genomic sequencing: 59 consecutive patients from our institution (38 [64.41%] with VHL mutations) formed a training cohort, and 46 from The Cancer Genome Atlas (TCGA) database (24 [52.17%] with VHL mutations) formed an independent test cohort. Two radiologists, with 23 and 33 years of experience respectively, jointly evaluated the semantic MRI features of the primary lesion in ccRCCs to propose potential features related to VHL mutations in both cohorts. Three additional readers, with 5, 7, and 10 years of experience respectively, independently reviewed all lesions to assess the interobserver agreement of MRI features. A VHL mutational likelihood score (VHL-MULIS) system was constructed using the training cohort and validated using the independent test cohort. Fisher's test or chi-square test, t-test or Mann-Whitney U test, logistic regression, Cohen's kappa (κ), area under the receiver operating characteristic curve (AUC). A two-sided P value <0.05 was considered statistically significant. In both the local and public cohorts, T2-weighted signal intensity and presence of microscopic fat from primary lesions were significantly associated with VHL mutation status. The VHL-MULIS incorporated maximum diameter, T2-weighted signal intensity, and presence of microscopic fat in the training cohort and demonstrated promising diagnostic ability (AUC, 0.82; sensitivity, 0.79; specificity, 0.82) and substantial interobserver agreement (κ, 0.787) in the test cohort. The VHL mutation exhibited a distinct MRI phenotype. Integrating multiple semantic MRI features has potential to reflect the mutation status in patients with ccRCC. 3 TECHNICAL EFFICACY: Stage 2.

Molecular Dynamics Reveals Altered Interactions between Belzutifan and HIF-2 with Natural Variant G323E or Proximal Phosphorylation at T324.

In patients with von-Hippel Lindau (VHL) disease, hypoxia-independent accumulation of HIF-2α leads to increased transcriptional activity of HIF-2α:ARNT that drives cancers such as renal cell carcinoma. Belzutifan, a recently FDA-approved drug, is designed to prevent the transcriptional activity of HIF-2α:ARNT, thereby overcoming the consequences of its unnatural accumulation in VHL-dependent cancers. Emerging evidence suggests that the naturally occurring variant G323E located in the HIF-2α drug binding pocket prevents inhibitory activity of belzutifan analogs, though the mechanism of inhibition remains unclear. Interestingly, proximal phosphorylation at neighboring T324, previously shown to regulate HIF-2 protein interactions, has also been proposed to affect HIF-2 drug binding. Here, we used molecular dynamics (MD) simulations to understand and compare the molecular-level effects of G323E and phospho-T324 (pT324) on the belzutifan bound-HIF-2α:ARNT complex. We find that both G323E and pT324 increase structural flexibility within the drug binding site and reduce the apparent binding affinity for belzutifan. Whereas the effects of G323E are concentrated in the binding pocket Fα helix within the HIF-2α PAS-B domain, pT324 decreased the belzutifan binding affinity and stabilized the HIF-2 heterodimer through an alternate mechanism involving polar interactions between the HIF-2α PAS-B and PAS-A domains. Further analysis via ensemble machine learning uncovered important and distinct interchain residue interactions modified by G323E and pT324. These findings reveal a molecular mechanism of G323E-induced drug resistance and suggest that pT324 may also affect the efficacy of HIF-2 drug binding interactions via allosteric effects.

LAT1 expression in colorectal cancer cells is unresponsive to HIF-1/2α accumulation under experimental hypoxia

L-type amino acid transporter 1 (LAT1) is upregulated in various cancer types and contributes to disease progression. Previous studies have demonstrated or suggested that hypoxia-inducible factors (HIFs), the key transcription factors in hypoxic responses, control the expression of LAT1 gene in several types of cancer cells. However, this regulatory relationship has not been investigated yet in colorectal cancer (CRC), one of the cancer types in which the increased LAT1 expression holds prognostic significance. In this study, we found that neither LAT1 mRNA nor protein is induced under hypoxic condition (1% O2) in CRC HT-29 cells in vitro, regardless of the prominent HIF-1/2α accumulation and HIFs-dependent upregulation of glucose transporter 1. The hypoxic treatment generally did not increase either the mRNA or protein expression of LAT1 in eight CRC cell lines tested, in contrast to the pronounced upregulation by amino acid restriction. Interestingly, knockdown of von Hippel-Lindau ubiquitin ligase to inhibit the proteasomal degradation of HIFs caused an accumulation of HIF-2α and increased the LAT1 expression in certain CRC cell lines. This study contributes to delineating the molecular mechanisms responsible for the pathological expression of LAT1 in CRC cells, emphasizing the ambiguity of HIFs-dependent transcriptional upregulation of LAT1 across cancer cells.

Renal protective and immunoregulatory effects of Lactobacillus casei strain Shirota in nephropathy-prone mice.

The incidence of severe acute kidney injury (AKI) is considerably high worldwide. A previous study showed that gut microbial dysbiosis was a hallmark of AKI in mice. Whether the probiotic Lactobacillus casei strain Shirota (LcS) plays a role in kidney disease, particularly AKI, remains unclear. To investigate the effects of LcS on kidney injury, tubule-specific conditional von Hippel-Lindau gene-knockout C57BL/6 mice (Vhlhdel/del mice) were supplemented without (Ctrl) or with probiotics (LcS) in Experiment 1, and their lifespan was monitored. Additionally, the Vhlhdel/+ mice were supplemented without (Ctrl and AA) or with probiotics (LcS and LcS + AA) in Experiment 2. Probiotic LcS (1 × 109 colony-forming units) was supplemented once daily. After 4 weeks of LcS supplementation, AA and LcS + AA mice were administered aristolochic acid (AA; 4 mg/kg body weight/day)-containing purified diet for 2 weeks to induce AA nephropathy before sacrifice. Supplementation of LcS significantly prolonged the lifespan of Vhlhdel/del mice, suggesting a potential renal protective effect. AA induced-nephropathy increased not only the indicators of renal dysfunction and injury, including urinary protein and kidney injury molecule (KIM)-1, serum blood urea nitrogen (BUN) and creatinine, but also serum interleukin (IL)-6 levels, renal macrophage infiltrations, and pathological lesions in Vhlhdel/+ mice. LcS supplementation significantly reduced urinary protein and KIM-1 levels, serum BUN and IL-6 levels, and renal M1 macrophages, tissue lesions, and injury scores. We also found that LcS maintained gut integrity under AA induction and increased intestinal lamina propria dendritic cells. Furthermore, LcS significantly reduced pro-inflammatory IL-17A and upregulated anti-inflammatory IL-10 production by immune cells from intestinal Peyer's patches (PP) or mesenteric lymph nodes (MLN), and significantly increased IL-10 and reduced IL-6 production by splenocytes. Prior supplementation with probiotic LcS significantly alleviated the severity of renal injury. This renal protective effect was partially associated with the enhancements of intestinal and systemic anti-inflammatory immune responses, suggesting that LcS-induced immunoregulation might contribute to its renal protective effects.

Advances in Molecular Mechanisms of Kidney Disease: Integrating Renal Tumorigenesis of Hereditary Cancer Syndrome.

Renal cell carcinoma (RCC) comprises various histologically distinct subtypes, each characterized by specific genetic alterations, necessitating individualized management and treatment strategies for each subtype. An exhaustive search of the PubMed database was conducted without any filters or restrictions. Inclusion criteria encompassed original English articles focusing on molecular mechanisms of kidney cancer. On the other hand, all non-original articles and articles published in any language other than English were excluded. Hereditary kidney cancer represents 5-8% of all kidney cancer cases and is associated with syndromes such as von Hippel-Lindau syndrome, Birt-Hogg-Dubè syndrome, succinate dehydrogenase-deficient renal cell cancer syndrome, tuberous sclerosis complex, hereditary papillary renal cell carcinoma, fumarate hydratase deficiency syndrome, BAP1 tumor predisposition syndrome, and other uncommon hereditary cancer syndromes. These conditions are characterized by distinct genetic mutations and related extra-renal symptoms. The majority of renal cell carcinoma predispositions stem from loss-of-function mutations in tumor suppressor genes. These mutations promote malignant advancement through the somatic inactivation of the remaining allele. This review aims to elucidate the main molecular mechanisms underlying the pathophysiology of major syndromes associated with renal cell carcinoma. By providing a comprehensive overview, it aims to facilitate early diagnosis and to highlight the principal therapeutic options available.

ZIP11 and ZnT1 are Differentially Expressed in Human Renal Cell Carcinoma

Renal cell carcinoma (RCC) is a solid, malignant, and heterogeneous tumor originating in the renal tubular epithelium. There are several histopathological classifications, with clear-cell carcinoma (ccRCC) being the most common. Its occurrence is associated with mutations in the von Hippel-Lindau gene, which regulates cellular responses to stress, division, death, and differentiation. The loss of functionality affects the degradation of hypoxia-inducible factor (HIF). In turn, the HIF1α subunit becomes highly expressed. Zinc (Zn) is the second most abundant trace element in the human body, and small variations in its concentration can lead to disturbances in the cellular environment. Zn transporters play a fundamental role in Zn homeostasis. In this study, the expression and localization of the Zn channels ZIP11 and ZnT1 were verified in normal tubular renal cells (HK-2) and a clear cell renal adenocarcinoma line (786-0). RT-PCR and western blotting data showed that the ZIP-11 channel was highly expressed in tumor cells. In contrast, the ZnT1 channel was expressed at lower levels in tumor cells. Immunofluorescence data revealed different localization patterns between the two lines. The expression of ZIP-11 in HK-2 cells was predominantly cytoplasmic, while in 786-0 tumor cells, in addition to strong cytoplasmic staining, nuclear staining was also observed. ZnT1 expression in HK-2 cells was cytoplasmic and accentuated on the cell membrane, while that in 786-0 tumor cells was nuclear. These results demonstrated different expression patterns of the key Zn transporters, ZIP11 and ZnT1, in RCC cells compared to those in the normal kidney epithelium. Further elucidation of the molecular mechanisms underlying Zn dysregulation in RCC may reveal potential therapeutic targets.

Clinicopathological features of BAP1 mutated clear cell renal cell carcinoma

Objective: To investigate the clinicopathological characteristics, immunophenotypes, molecular features, and differential diagnosis of BAP1 mutated clear cell renal cell carcinoma (CCRCC) for better understanding this entity. Methods: Clinical data, histological morphology, immunophenotypes and molecular characteristics of 18 BAP1 mutated CCRCC cases diagnosed at the Department of Pathology, the First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China from January 2020 to December 2022 were analyzed. The patients were followed up. Results: There were 17 males and 1 female patients, aged from 39 to 72 years, with an average age of 56.3 years. Sixteen patients with primary CCRCC were followed up for an average of 24 months, 7 patients had metastases occurred from 4 to 22 months postoperatively. Thirteen of the 16 patients were alive at the time of the last follow-up while 3 patients died 12, 15, and 20 months after the surgery, respectively. One patient underwent retroperitoneal mass resection, but had lung metastasis 32 months after surgery. One case received cervical tumor resection and died at 22 months after the surgery. Characteristic CCRCC regions were identified in 11 of the 18 cases. The tumor cells were arranged in papillary, alveolar, and large nest patterns. Abundant lymphoid tissue, necrosis, and psammoma bodies were seen. Tumor cells showed abundant eosinophilic cytoplasm, and sometimes exhibited rhabdoid differentiation. Round eosinophilic globules were located in the cytoplasm and extracellular matrix. There were 9 cases with WHO/International Society of Urological Pathology grade 3, and 9 cases with grade 4. PAX8 (18/18), carbonic anhydrase 9 (CA9, 16/18), CD10 (18/18), and vimentin (18/18) were positive in the vast majority of tumors.TFE3 was expressed in 5 cases, with strong expression in only 1 case. Eighteen cases were all positive for P504s. Twelve cases harbored a BAP1 mutation combined with von Hippel-Lindau (VHL) mutation, and 2 cases had mutations in BAP1, VHL and PBRM1 simultaneously. SETD2 mutation was not found in any of the cases. Conclusions: BAP1 mutated CCRCC contained papillary, alveolar, and large nest patterns, eosinophilic cytoplasm, high-grade nucleoli, and collagen globules, with P504s positivity. In practical work, when encountering CCRCC containing these features, pathologists should consider the possibility of BAP1 mutations and conduct related molecular tests.

Genotype-phenotype associations in Von-Hippel Lindau Syndrome: implications for screening

Abstract Background Von Hippel-Lindau (VHL) is an autosomal dominant genetic disease with an estimated incidence of 1:36,000. The type of germline VHLI alteration has been shown to impact downstream VHL expression and clinical phenotype. However, current screening practices do not differ based on VHL genomic subtype. We aim to assess genotype-phenotype association among an institutional cohort of VHL patients. Methods We conducted a retrospective cohort study of 69 patients (27 families) at the University of Utah and Huntsman Cancer Institute from 1998- December 2023. 41 patients had documented germline testing in our system to define VHL type. VHL Type 1 was defined as those with nonsense mutations, deletions, and duplications and Type 2 as those with missense and splice mutations. Mean follow-up was 86- and 59-months for VHL type 1 and 2 respectively. We then evaluated the association of VHL type with risk of pheochromocytoma (Pheo), renal cancer (RCC), and hemangioblastoma (HB). Results We identified 24 unique VHL alterations among 41 patients. 83% (29/41) patients had missense mutations, 7.5% (3/41) had nonsense mutations, 17% (6/41) had splice mutations, and 3% (3/41) had a deletion. The median age at VHL diagnosis was 43 years old for type 1 (range 19-76) and 38 for VHL type 2 (range 4-67). VHL Type 2 was more common, 85% (35/41). All VHL Type 1 patients (6/6) developed RCC and HB. No patients with VHL Type 1 developed PheoPara. Of the 35 patients diagnosed with VHL Type 2, 20% (7/35) were diagnosed with PheoPara, 9% (3/35) with RCC, 31% (n = 11) with HB, and 37% (n = 13) were asymptomatic. No VHL Type 1 patients were asymptomatic. Conclusions VHL type 2 comprised the majority of VHL diagnoses in our cohort. Individuals diagnosed with VHL type 2 have the highest penetrance for: hemangioblastoma (hb), Pheo-Para, and renal cell carcinoma (RCC). In our study, 37% of VHL type 2 participants did not demonstrate any VHL manifestation. VHL type 1 had a high prevalence for RCC and HB, with a notable absence of PheoPara manifestation. However, majority of these patients (75%) were below the age of 20, and thus likely did not develop a manifestation yet. This cohort add to evidence supporting utilizing genetic VHL Types to personalize surveillance guidelines. Validation in larger cohorts with longer follow-up suggest that VHL type 1 patients could forgo pheo/para screening.

39 Safety profile of belzutifan monotherapy in patients with renal cell carcinoma: A pooled analysis of 4 clinical trials

Abstract Background The first-in-class hypoxia-inducible factor-2α inhibitor, belzutifan, is indicated in the United States for the treatment of certain patients with von Hippel-Lindau (VHL) disease–associated renal cell carcinoma (RCC), central nervous system hemangioblastomas, or pancreatic neuroendocrine tumors not requiring immediate surgery and for patients with advanced RCC previously treated with a PD-(L)1 inhibitor and a vascular endothelial growth factor tyrosine kinase inhibitor. Due to its unique mechanism of action, belzutifan has a distinct safety profile. We characterized the safety profile of belzutifan monotherapy in a post hoc pooled analysis of patients with previously treated advanced clear cell RCC in the phase 1 LITESPARK-001 (NCT02974738), phase 3 LITESPARK-005 (NCT04195750), and phase 2 LITESPARK-013 (NCT04489771) studies and patients with RCC associated with VHL disease in the phase 2 LITESPARK-004 study (NCT03401788). Methods All patients who received ≥1 dose of belzutifan 120 mg orally once daily across the 4 studies were included. Severity of adverse events (AEs) were graded per the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.03 or 5.0, and were descriptively summarized. Results A total of 576 patients were included (n = 58 [including 3 patients with advanced solid tumors other than RCC], LITESPARK-001; n = 381, LITESPARK-005; n = 76, LITESPARK-013; and n = 61, LITESPARK-004). Overall, 572 patients (99.3%) had ≥1 all-cause AE and 355 patients (61.6%) had ≥1 grade 3-5 AE. AEs led to dose modification (reduction, interruption, or discontinuation) in 288 patients (50.0%), although treatment discontinuation for AEs occurred in 37 patients (6.4%). The most common all-grade AEs were anemia (including patients with decreased hemoglobin; n = 485 [84.2%]; grade 3 or 4, n = 166 [28.8%]), fatigue (n = 246 [42.7%]; grade 3, n = 16 [2.8%]), nausea (n = 139 [24.1%]; grade 3, n = 5 [0.9%]), and dyspnea (n = 123 [21.4%]; grade 3 or 4, n = 10 [1.7%]). Hypoxia was reported in 94 patients (16.3%); grade 3 or 4 hypoxia occurred in 57 patients (9.9%). Summary and time to first onset of adverse drug reactions (AEs considered associated with belzutifan), including anemia and hypoxia, are reported in the table. Among 485 patients with anemia or decreased hemoglobin, 111 (22.9%) were treated with erythropoiesis-stimulating agent (ESA) only, 85 (17.5%) were treated with blood transfusions only, and 62 (12.8%) were treated with ESA and blood transfusions. Among 94 patients with hypoxia, 66 (70.2%) were treated with oxygen therapy. Treatment-related AEs occurred in 526 patients (91.3%) and 217 (37.7%) experienced a grade 3-5 treatment-related AE. One grade 5 adverse event (multiple organ dysfunction syndrome) was considered related to treatment. Conclusions To date, this is the largest pooled safety dataset for belzutifan monotherapy in patients with RCC. The results provide an in-depth characterization of the safety profile for belzutifan and the associated AE management strategies.

16 Linking VHL and SETD2 in a common oncogenic pathway that converges on the mitoticspindle

Abstract Background Loss of chromosome 3p is a landmark event in clear cell renal cell carcinoma (ccRCC) that results in mono-allelic loss of VHL (von Hippel Lindau) and SETD2 (Set-domain containing 2) (and other tumor suppressors co-located on 3p). Second hits in VHL inactivate this key tumor suppressor initiating tumor progression. SETD2, a histone methyltransferase, was previously shown to have a dual function in methylating both histones and microtubules, thereby contributing to both the histone and tubulin codes. Methylation by SETD2 on microtubules occurs at the mitotic spindle and is essential for normal mitosis and cytokinesis, with loss of SETD2 acting as a strong driver of apoptosis. This raises a conundrum of how cancer cells survive early mono-allelic loss of SETD2, escaping cell death. Methods Using biochemical kinase assays and mass spectrometry we have identified SETD2 as a substrate for AURKA. In addition, we have used immunoblotting and immunofluorescence assays to probe phosphorylation on SETD2 and the impact of phosphorylation of SETD2 both on its chromatin and cytoskeleton targets. Results We have identified the mitotic kinase, Aurora kinase A (AURKA), as a regulator of SETD2. Our data uncover SETD2 as a unique substrate for phosphorylation by AURKA, with mass spectrometry identifying serine 2080 (S2080) as the site of phosphorylation on SETD2. We found phosphorylation of SETD2 by AURKA at S2080 contributes to its methyltransferase (i.e. enzymatic) activity on microtubules but does not impact chromatin methylation on H3K36 which remains unaltered. We show that VHL regulates SETD2 via AURKA, and loss of phosphorylation on SETD2 results in mitotic defects and genomic instability. Importantly, we demonstrate that inhibition of AURKA is synthetic lethal in the setting of VHL and SETD2 deficiency. Conclusions AURKA expression levels are high in VHL-null cells resulting from an inability of VHL to target AURKA for degradation and our data now highlight a direct link between VHL and SETD2, two tumor suppressors believed to independently drive RCC pathogenesis. In summary, our data reveal a tumor-specific vulnerability linked to mitotic fragility that can be precisely targeted to ultimately drive mitotic catastrophe. DOD CDMRP Funding: yes

Concurrent multiple cerebral cavernous malformations and cauda equina paraganglioma: illustrative case.

Cauda equina neuroendocrine tumors (CENETs), previously known as cauda equina paragangliomas, and multiple cerebral cavernous malformations (CCMs) are uncommon conditions affecting the central nervous system. To the authors' knowledge, they have not been reported in the same patient. The authors present the case of a 45-year-old male with CENET and concurrent incidental MRI findings of multiple CCMs. Familial CCMs are associated with mutations in the KRIT1 (CCM1), MGC4607 (CCM2), and PDCD10 (CCM3) genes. Peripheral paragangliomas have been associated with mutations in succinate dehydrogenase (SDHx), RET (multiple endocrine neoplasia 2), VHL (von Hippel-Lindau syndrome), and NF1 (neurofibromatosis type 1) genes. Except for a single case, cauda equina paragangliomas have not been associated with any underlying genetic mutations. It is unclear whether the co-occurrence of these two rare conditions in the same patient is coincidental or suggests a possible shared pathogenesis. https://thejns.org/doi/10.3171/CASE24102.

21 Unconventional mechanisms of action and resistance to rapalogs in renal cancer

Abstract Background Clear cell renal cell carcinoma (ccRCC) is a prevalent cancer type in the United States driven by inactivation of the von Hippel-Lindau (VHL) gene and with frequent hyperactivation of mammalian target of rapamycin complex 1 (mTORC1). Multiple drugs have been developed to target VEGF/VEGFR2 and mTORC1 for advanced RCC treatment. Two specific mTORC1 inhibitors, temsirolimus and everolimus (known as rapalogs), are FDA-approved for the treatment of RCC but their clinical efficacy is hindered by the emergence of resistance. Methods To study the development of rapalog resistance in RCC, we utilized patient-derived tumorgrafts (TGs) implanted in immunocompromised mice and treated the mice with rapamycin for prolonged periods to generate resistance. Resistance was studied by transplanting resistant tumors into additional cohorts of mice and establishing primary cultures. The impact of rapamycin on tumor growth and mTORC1 activity in both tumor and stromal cells was assessed using molecular techniques. To dissect the role of the tumor microenvironment (TME), we generated genetically engineered immunocompromised recipient mice with an mTOR inhibitor resistance mutation (S2035T). Coculture experiments were performed to further explore the interplay. Results Prolonged rapamycin treatment resulted in the development of resistance in TGs. Notably, this occurred despite persistent inhibition of mTORC1 in tumor cells. Resistance was transient and lost with subsequent transplantation and in cell culture. Surprisingly, resistance was accompanied by mTORC1 reactivation in the TME, specifically in cancer associated fibroblasts. Introducing an mTOR resistance mutation (S2035T) into recipient mice was sufficient to cause resistance. Co-culture experiments with fibroblasts further demonstrated that rapamycin-resistant mutant fibroblasts conferred resistance in tumor cells even in the absence of mTORC1 activity. Conclusions This study uncovers a critical role of the TME, in mediating the response and resistance to rapalogs in RCC. Our data show that inhibition of mTORC1 in non-tumor cells is essential for the anti-tumor activity of rapalogs. These findings shed light on why mTOR mutations are rarely observed in resistant RCC patients and highlight the significance of the TME in modulating drug response and resistance. Moreover, our study emphasizes the potential of targeting TME cells as a therapeutic strategy in RCC and possibly other cancers. DOD CDMRP Funding: yes

Clinical implications of activation of the LIMD1-VHL-HIF1α pathway during head-&-neck squamous cell carcinoma development.

Background & objectives Given the importance of the role of hypoxia induced pathway in different cancers including head-and-neck squamous cell carcinoma (HNSCC), this study delved into elucidating the molecular mechanism of hypoxia-inducible factor-1α (HIF1α) activation in HNSCC. Additionally, it analyzes the alterations of its regulatory genes [von Hippel-Lindau (VHL) and LIM domain containing 1 (LIMD1)] and target gene vascular endothelial growth factor (VEGF) in head-and-neck lesions at different clinical stages in relation with human papillomavirus (HPV) infection. Methods Global mRNA expression profiles of HIF1α, VHL, LIMD1 and VEGF were evaluated from public datasets of HNSCC, followed by validation of their expression (mRNA/protein) in an independent set of HPV+ve/-ve HNSCC samples of different clinical stages. Results A diverse expression pattern of the HIF1α pathway genes was observed, irrespective of HPV infection, in the datasets. In validation in an independent set of HNSCC samples, high mRNA expressions of HIF1α/VEGF were observed particularly in HPV positive samples. However, VHL/LIMD1 mRNA expression was low in tumours regardless of HPV infection status. In immunohistochemical analysis, high/medium (H/M) expression of HIF1α/VEGF was observed in basal/parabasal layers of normal epithelium, with significantly higher expression in tumours, especially in HPV-positive samples. Conversely, high cytoplasmic VHL expression in these layers gradually decreased with the progression of HNSCC, regardless of HPV infection. A similar trend was noted in LIMD1 expression (nuclear/cytoplasmic) during the disease development. The methylation pattern of VHL and LIMD1 promoters in the basal/parabasal layers of normal epithelium correlated with their expression, exhibiting a gradual increase with the progression of HNSCC. The H/M expression of HIF1α/VEGF proteins and reduced VHL expression was associated with poor clinical outcomes. Interpretation & conclusions The results of this study showed differential regulation of the LIMD1-VHL-HIF1α pathway in HPV positive and negative HNSCC samples, illustrating the molecular distinctiveness of these two groups.

Renal cancer: signaling pathways and advances in targeted therapies.

Renal cancer is a highlyheterogeneous malignancy characterized by rising global incidence and mortalityrates. The complex interplay and dysregulation of multiple signaling pathways,including von Hippel-Lindau (VHL)/hypoxia-inducible factor (HIF), phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR), Hippo-yes-associated protein (YAP), Wnt/ß-catenin, cyclic adenosine monophosphate (cAMP), and hepatocyte growth factor (HGF)/c-Met, contribute to theinitiation and progression of renal cancer. Although surgical resection is thestandard treatment for localized renal cancer, recurrence and metastasiscontinue to pose significant challenges. Advanced renal cancer is associatedwith a poor prognosis, and current therapies, such as targeted agents andimmunotherapies, have limitations. This review presents a comprehensiveoverview of the molecular mechanisms underlying aberrant signaling pathways inrenal cancer, emphasizing their intricate crosstalk and synergisticinteractions. We discuss recent advancements in targeted therapies, includingtyrosine kinase inhibitors, and immunotherapies, such as checkpoint inhibitors.Moreover, we underscore the importance of multiomics approaches and networkanalysis in elucidating the complex regulatory networks governing renal cancerpathogenesis. By integrating cutting-edge research and clinical insights, this review contributesto the development of innovative diagnostic and therapeutic strategies, whichhave the potential to improve risk stratification, precision medicine, andultimately, patient outcomes in renal cancer.