Current Landscape and the Potential Role of Hypoxia-Inducible Factors and Selenium in Clear Cell Renal Cell Carcinoma Treatment.
ABSTRACT: In the last two decades, the discovery of various pathways involved in renal cell carcinoma (RCC) has led to the development of biologically-driven targeted therapies. Hypoxia-inducible factors (HIFs), angiogenic growth factors, von Hippel?Lindau (VHL) gene mutations, and oncogenic microRNAs (miRNAs) play essential roles in the pathogenesis and drug resistance of clear cell renal cell carcinoma. These insights have led to the development of vascular endothelial growth factor (VEGF) inhibitors, Mechanistic target of rapamycin (mTOR) inhibitors, and immunotherapeutic agents, which have significantly improved the outcomes of patients with advanced RCC. HIF inhibitors will be a valuable asset in the growing therapeutic armamentarium of RCC. Various histone deacetylase (HDAC) inhibitors, selenium, and agents like PT2385 and PT2977 are being explored in various clinical trials as potential HIF inhibitors, to ameliorate the outcomes of RCC patients. In this article, we will review the current treatment options and highlight the potential role of selenium in the modulation of drug resistance biomarkers expressed in clear cell RCC (ccRCC) tumors.
Project description:PURPOSE:The heterodimeric transcription factor HIF-2 is arguably the most important driver of clear cell renal cell carcinoma (ccRCC). Although considered undruggable, structural analyses at the University of Texas Southwestern Medical Center (UTSW, Dallas, TX) identified a vulnerability in the ? subunit, which heterodimerizes with HIF1?, ultimately leading to the development of PT2385, a first-in-class inhibitor. PT2385 was safe and active in a first-in-human phase I clinical trial of patients with extensively pretreated ccRCC at UTSW and elsewhere. There were no dose-limiting toxicities, and disease control ?4 months was achieved in 42% of patients. PATIENTS AND METHODS:We conducted a prospective companion substudy involving a subset of patients enrolled in the phase I clinical trial at UTSW (n = 10), who were treated at the phase II dose or above, involving multiparametric MRI, blood draws, and serial biopsies for biochemical, whole exome, and RNA-sequencing studies. RESULTS:PT2385 inhibited HIF-2 in nontumor tissues, as determined by a reduction in erythropoietin levels (a pharmacodynamic marker), in all but one patient, who had the lowest drug concentrations. PT2385 dissociated HIF-2 complexes in ccRCC metastases, and inhibited HIF-2 target gene expression. In contrast, HIF-1 complexes were unaffected. Prolonged PT2385 treatment resulted in the acquisition of resistance, and we identified a gatekeeper mutation (G323E) in HIF2?, which interferes with drug binding and precluded HIF-2 complex dissociation. In addition, we identified an acquired TP53 mutation elsewhere, suggesting a possible alternate mechanism of resistance. CONCLUSIONS:These findings demonstrate a core dependency on HIF-2 in metastatic ccRCC and establish PT2385 as a highly specific HIF-2 inhibitor in humans. New approaches will be required to target mutant HIF-2 beyond PT2385 or the closely related PT2977 (MK-6482).
Project description:Clear cell renal cell carcinoma (ccRCC) is the most common subtype of renal cell carcinoma (RCC), and is frequently accompanied by the genetic features of von Hippel-Lindau (VHL) loss. VHL loss increases the expression of hypoxia-inducible factors (HIFs) and their targets, including epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF). The primary treatment for metastatic RCC (mRCC) is molecular-targeted therapy, especially anti-angiogenic therapy. VEGF monoclonal antibodies and VEGF receptor (VEGFR) tyrosine kinase inhibitors (TKIs) are the main drugs used in anti-angiogenic therapy. However, crosstalk between VEGFR and other tyrosine kinase or downstream pathways produce resistance to TKI treatment, and the multi-target inhibitors, HIF inhibitors or combination strategies are promising strategies for mRCC. HIFs are upstream of the crosstalk between the growth factors, and these factors may regulate the expression of VEGR, EGF, PDGF and other growth factors. The frequent VHL loss in ccRCC increases HIF expression, and HIFs may be an ideal candidate to overcome the TKI resistance. The combination of HIF inhibitors and immune checkpoint inhibitors is also anticipated. Various clinical trials of programmed cell death protein 1 inhibitors are planned. The present study reviews the effects of current and potential TKIs on mRCC, with a focus on VEGF/VEGFR and other targets for mRCC therapy.
Project description:<h4>Background</h4>In clear cell renal cell carcinoma, 80% of cases have biallelic inactivation of the VHL gene, leading to constitutive activation of both HIF1α and HIF2α. As HIF2α is the driver of the disease promoting tumour growth and metastasis, drugs targeting HIF2α have been developed. However, resistance is common, therefore new therapies are needed.<h4>Methods</h4>We assessed the effect of the HIF2α antagonist PT2385 in several steps of tumour development and performed RNAseq to identify genes differentially expressed upon treatment. A drug screening was used to identify drugs with antiproliferative effects on VHL-mutated HIF2α-expressing cells and could increase effectiveness of PT2385.<h4>Results</h4>PT2385 did not reduce cell proliferation or clonogenicity but, in contrast to the genetic silencing of HIF2α, it reduced in vitro cell invasion. Many HIF-inducible genes were down-regulated upon PT2385 treatment, whereas some genes involved in cell migration or extracellular matrix were up-regulated. HIF2α was associated with resistance to statins, addition to PT2385 did not increase the sensitivity.<h4>Conclusions</h4>this study shows key differences between inhibiting a target versus knockdown, which are potentially targetable.
Project description:Hypoxia-inducible factor (HIF) is strikingly upregulated in many types of cancer, and there is great interest in applying inhibitors of HIF as anticancer therapeutics. The most advanced of these are small molecules that target the HIF-2 isoform through binding the PAS-B domain of HIF-2?. These molecules are undergoing clinical trials with promising results in renal and other cancers where HIF-2 is considered to be driving growth. Nevertheless, a central question remains as to whether such inhibitors affect physiological responses to hypoxia at relevant doses. Here, we show that pharmacological HIF-2? inhibition with PT2385, at doses similar to those reported to inhibit tumor growth, rapidly impaired ventilatory responses to hypoxia, abrogating both ventilatory acclimatization and carotid body cell proliferative responses to sustained hypoxia. Mice carrying a HIF-2? PAS-B S305M mutation that disrupts PT2385 binding, but not dimerization with HIF-1?, did not respond to PT2385, indicating that these effects are on-target. Furthermore, the finding of a hypomorphic ventilatory phenotype in untreated HIF-2? S305M mutant mice suggests a function for the HIF-2? PAS-B domain beyond heterodimerization with HIF-1?. Although PT2385 was well tolerated, the findings indicate the need for caution in patients who are dependent on hypoxic ventilatory drive.
Project description:Chromophobe kidney cancer accounts for approximately 5% of cases of renal cell carcinoma (RCC). While the genetics of clear cell RCC has been a major focus of research, little is known about the biology of chromophobe tumors. There is ample preclinical rationale for the use of targeted therapy in clear cell tumors, and agents targeting the VHL/HIF pathway are now widely used in clinical practice. However, there is limited experience with targeted agents in non-clear cell tumors. Recently, a few case reports have emerged which report the use of mTOR inhibitors in chromophobe tumors. Here, we report our experience with targeted therapy in a patient with advanced chromophobe RCC who had a durable partial response to temsirolimus. We also include a literature review summarizing the published experience with targeted therapeutic approaches in chromophobe RCC. Additionally, the preclinical rationale for the use of mTOR inhibitors in this population based on our characterization of the hereditary form of chromophobe kidney cancer, Birt-Hogg-Dube syndrome, is discussed.
Project description:Clear-cell renal cell carcinoma (RCC) is, in most cases, caused by loss of function of the tumor suppressor gene von Hippel-Lindau, resulting in constitutive activation of hypoxia-inducible factor (HIF)-1? and expression of hypoxia-induced genes in normoxic conditions. Clear-cell RCC cells are characterized histologically by accumulation of cholesterol, mainly in its ester form. The origin of the increased cholesterol remains unclear, but it is likely explained by an HIF-1?-driven imbalance between cholesterol uptake and excretion. Here, we showed that expression of the very low-density lipoprotein receptor (VLDL-R) was significantly increased in clear-cell RCC human biopsies compared with normal kidney tissue. Partial knockdown of HIF-1? in clear-cell RCC cells significantly reduced the VLDL-R expression, and knockdown of either HIF-1? or VLDL-R reduced the increased lipid accumulation observed in these cells. We also showed increased uptake of fluorescently labeled lipoproteins in clear-cell RCC cells, which was significantly reduced by knockdown of HIF-1? or VLDL-R. Taken together, our results support the concept that the pathological increase of HIF-1? in clear-cell RCC cells upregulates VLDL-R, which mediates increased uptake and accumulation of lipids. These results explain the morphological characteristics of clear-cell RCC, and open up novel possibilities for detection and treatment of clear-cell RCC.
Project description:The loss of the von Hippel-Lindau (<i>VHL</i>) tumor-suppressor is a major driver of Clear Cell Renal Cell Carcinoma (CC-RCC) resulting in the stabilization and overactivation of hypoxia inducible factors (HIFs). ROCK1 is a well-known protein serine/threonine kinase which is recognized as having a role in cancer including alterations in cell motility, metastasis and angiogenesis. We recently investigated and identified a synthetic lethal interaction between VHL loss and ROCK1 inhibition in CC-RCC that is dependent on HIF overactivation. Increased expression and activity of both HIFs and ROCK1 occurs in many types of cancer supporting the potential therapeutic role of ROCK inhibitors beyond CC-RCC. We also discuss future research required to establish prognostic markers to predict tumor response to ROCK inhibitors.
Project description:Inactivation of von Hippel-Lindau (VHL) gene in clear-cell renal cell carcinoma (RCC) leads to increased levels of hypoxia-inducible factors (HIF) and overexpression of HIF target genes, such as VEGF and others. VEGF-targeted agents are standard in advanced clear-cell RCC but biomarkers of activity are lacking.We analyzed tumor tissue samples from metastatic clear-cell RCC patients who received pazopanib as part of clinical trial VEG102616. We evaluated several components of the VHL/HIF pathway: VHL gene inactivation (mutation and/or methylation), HIF-1? and HIF-2? immunohistochemistry staining, and HIF-1? transcriptional signature. We evaluated the association of these biomarkers with best overall response rate (ORR) and progression-free survival (PFS) to pazopanib, a standard first-line VEGF-targeted agent.The VEG102616 trial enrolled 225 patients, from whom 78 samples were available for tumor DNA extraction. Of these, 70 patients had VHL mutation or methylation. VHL gene status did not correlate with ORR or PFS. Similarly, HIF-1? (65 samples) and HIF-2? (66 samples) protein levels (high vs. low) did not correlate with ORR or PFS to pazopanib. The HIF-1? transcriptional signature (46 samples) was enriched in tumors expressing high HIF-1? levels. However, the HIF-1? gene expression signature was not associated with clinical outcome to pazopanib.In patients with advanced clear-cell RCC, several potential biomarkers along the VHL/HIF-1?/HIF-2? axis were not found to be predictive for pazopanib activity. Additional efforts must continue to identify biomarkers associated with clinical outcome to VEGF-targeted agents in metastatic RCC.
Project description:HIF-2alpha promotes von Hippel-Lindau (VHL)-deficient renal clear cell carcinoma (RCC) tumorigenesis, while HIF-1alpha inhibits RCC growth. As HIF-1alpha antagonizes c-Myc function, we hypothesized that HIF-2alpha might enhance c-Myc activity. We demonstrate here that HIF-2alpha promotes cell-cycle progression in hypoxic RCCs and multiple other cell lines. This correlates with enhanced c-Myc promoter binding, transcriptional effects on both activated and repressed target genes, and interactions with Sp1, Miz1, and Max. Finally, HIF-2alpha augments c-Myc transformation of primary mouse embryo fibroblasts (MEFs). Enhanced c-Myc activity likely contributes to HIF-2alpha-mediated neoplastic progression following loss of the VHL tumor suppressor and influences the behavior of hypoxic tumor cells.