Therapeutic Effects of Inhibition of Sphingosine-1-Phosphate Signaling in HIF-2α Inhibitor-Resistant Clear Cell Renal Cell Carcinoma

Simple Summary

Clear cell renal cell carcinoma is a common malignancy that represents 80% of all kidney tumors. Most tumors harbor an inactivation of the VHL gene, leading to the accumulation of HIF-1α and HIF-2α. Promising clinical results of specific HIF-2α inhibitors will soon lead to new treatment options for advanced cancer patients, although primary and acquired resistance to these agents are common. We here show that Acriflavine, which inhibits both HIF-1α and HIF-2α, and Fingolimod (FTY720), which inhibits sphingosine-1-phosphate signaling, show therapeutic activities in several experimental ccRCC models that are resistant to HIF-2α-inhibitor treatment. Additionally, we show that specific HIF-2α-inhibition suppresses the tumor immune microenvironment, which will be important to consider for future combination studies with immune checkpoint inhibitors.

Abstract

Specific inhibitors of HIF-2α have recently been approved for the treatment of ccRCC in VHL disease patients and have shown encouraging results in clinical trials for metastatic sporadic ccRCC. However, not all patients respond to therapy and pre-clinical and clinical studies indicate that intrinsic as well as acquired resistance mechanisms to HIF-2α inhibitors are likely to represent upcoming clinical challenges. It would be desirable to have additional therapeutic options for the treatment of HIF-2α inhibitor resistant ccRCCs. Here we investigated the effects on tumor growth and on the tumor microenvironment of three different direct and indirect HIF-α inhibitors, namely the HIF-2α-specific inhibitor PT2399, the dual HIF-1α/HIF-2α inhibitor Acriflavine, and the S1P signaling pathway inhibitor FTY720, in the autochthonous Vhl/Trp53/Rb1 mutant ccRCC mouse model and validated these findings in human ccRCC cell culture models. We show that FTY720 and Acriflavine exhibit therapeutic activity in several different settings of HIF-2α inhibitor resistance. We also identify that HIF-2α inhibition strongly suppresses T cell activation in ccRCC. These findings suggest prioritization of sphingosine pathway inhibitors for clinical testing in ccRCC patients and also suggest that HIF-2α inhibitors may inhibit anti-tumor immunity and might therefore be contraindicated for combination therapies with immune checkpoint inhibitors.

Vhl deletion in renal epithelia causes HIF-1α-dependent, HIF-2α-independent angiogenesis and constitutive diuresis

One of the earliest requirements for the formation of a solid tumor is the establishment of an adequate blood supply. Clear cell renal cell carcinomas (ccRCC) are highly vascularized tumors in which the earliest genetic event is most commonly the biallelic inactivation of the VHL tumor suppressor gene, leading to constitutive activation of the HIF-1α and HIF-2α transcription factors, which are known angiogenic factors. However it remains unclear whether either or both HIF-1α or HIF-2α stabilization in normal renal epithelial cells are necessary or sufficient for alterations in blood vessel formation. We show that renal epithelium-specific deletion of Vhl in mice causes increased medullary vascularization and that this phenotype is completely rescued by Hif1a co-deletion, but not by co-deletion of Hif2a. A physiological consequence of changes in the blood vessels of the vasa recta in Vhl-deficient mice is a diabetes insipidus phenotype of excretion of large amounts of highly diluted urine. This constitutive diuresis is fully compensated by increased water consumption and mice do not show any signs of dehydration, renal failure or salt wasting and blood electrolyte levels remain unchanged. Co-deletion of Hif1a, but not Hif2a, with Vhl, fully restored kidney morphology and function, correlating with the rescue of the vasculature. We hypothesize that the increased medullary vasculature alters salt uptake from the renal interstitium, resulting in a disruption of the osmotic gradient and impaired urinary concentration. Taken together, our study characterizes a new mouse model for a form of diabetes insipidus and non-obstructive hydronephrosis and provides new insights into the physiological and pathophysiological effects of HIF-1α stabilization on the vasculature in the kidney.

Combined mutation in Vhl, Trp53 and Rb1 causes clear cell renal cell carcinoma in mice

Clear cell renal cell carcinomas (ccRCC) frequently exhibit inactivation of the VHL tumour suppressor gene and often harbour multiple copy number alterations in genes that regulate cell cycle progression. We show here that modelling these genetic alterations by combined renal epithelium-specific deletion of Vhl, Trp53 and Rb1 in mice caused ccRCC. These tumours arose from proximal tubule epithelial cells and shared molecular markers and mRNA expression profiles with human ccRCC. Exome sequencing revealed that mouse and human ccRCCs exhibit recurrent mutations in genes associated with the primary cilium, uncovering a mutational convergence on this organelle and implicating a subset of ccRCCs as genetic ciliopathies. Different mouse tumours responded differently to standard therapies for advanced human ccRCC, mimicking the range of clinical behaviours in the human disease. Inhibition of HIF-α transcription factors with Acriflavine as third line therapy had therapeutic effects in some tumours, providing pre-clinical evidence for further investigation of HIF-α inhibition as a ccRCC treatment. This autochthonous mouse ccRCC model represents a tool to investigate the biology of ccRCC and to identify new treatment strategies.

Formation of Renal Cysts and Tumors in Vhl/Trp53-Deficient Mice Requires HIF1α and HIF2α

The von Hippel-Lindau (VHL) tumor suppressor gene is inactivated in the majority of clear cell renal cell carcinomas (ccRCC), but genetic ablation of Vhl alone in mouse models is insufficient to recapitulate human tumorigenesis. One function of pVHL is to regulate the stability of the hypoxia-inducible factors (HIF), which become constitutively activated in the absence of pVHL. In established ccRCC, HIF1α has been implicated as a renal tumor suppressor, whereas HIF2α is considered an oncoprotein. In this study, we investigated the contributions of HIF1α and HIF2α to ccRCC initiation in the context of Vhl deficiency. We found that deleting Vhl plus Hif1a or Hif2a specifically in the renal epithelium did not induce tumor formation. However, HIF1α and HIF2α differentially regulated cell proliferation, mitochondrial abundance and oxidative capacity, glycogen accumulation, and acquisition of a clear cell phenotype in Vhl-deficient renal epithelial cells. HIF1α, but not HIF2α, induced Warburg-like metabolism characterized by increased glycolysis, decreased oxygen consumption, and decreased ATP production in mouse embryonic fibroblasts, providing insights into the cellular changes potentially occurring in Vhl mutant renal cells before ccRCC formation. Importantly, deletion of either Hif1a or Hif2a completely prevented the formation of renal cysts and tumors in Vhl/Trp53 mutant mice. These findings argue that both HIF1α and HIF2α exert protumorigenic functions during the earliest stages of cyst and tumor formation in the kidney. Cancer Res; 76(7); 2025-36. ©2016 AACR.

Combined mutation of Vhl and Trp53 causes renal cysts and tumours in mice

The combinations of genetic alterations that cooperate with von Hippel–Lindau (VHL) mutation to cause clear cell renal cell carcinoma (ccRCC) remain poorly understood. We show that the TP53 tumour suppressor gene is mutated in approximately 9% of human ccRCCs. Combined deletion of Vhl and Trp53 in primary mouse embryo fibroblasts causes proliferative dysregulation and high rates of aneuploidy. Deletion of these genes in the epithelium of the kidney induces the formation of simple cysts, atypical cysts and neoplasms, and deletion in the epithelia of the genital urinary tract leads to dysplasia and tumour formation. Kidney cysts display a reduced frequency of primary cilia and atypical cysts and neoplasms exhibit a pro-proliferative signature including activation of mTORC1 and high expression of Myc, mimicking several cellular and molecular alterations seen in human ccRCC and its precursor lesions. As the majority of ccRCC is associated with functional inactivation of VHL, our findings suggest that for a subset of ccRCC, loss of p53 function represents a critical event in tumour development.

Chicken ovalbumin upstream promoter transcription factor II regulates renin gene expression

This study aimed to investigate the possible involvement of the orphan nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) in the regulation of renin gene expression. COUP-TFII colocalized with renin in the juxtaglomerular cells of the kidney, which are the main source of renin in vivo. Protein-DNA binding studies demonstrated that COUP-TFII binds to an imperfect direct repeat COUP-TFII recognition sequence (termed hereafter proxDR) in the proximal renin promoter. Because cAMP signaling plays a central role in the control of the renin gene expression, we suggested that COUP-TFII may modulate this cAMP effect. Accordingly, knockdown of COUP-TFII in the clonal renin-producing cell lines As4.1 and Calu-6 diminished the stimulation of the renin mRNA expression by cAMP agonists. In addition, the mutation of the proxDR element in renin promoter reporter gene constructs abrogated the inducibility by cAMP. The proxDR sequence was found to be necessary for the function of a proximal renin promoter cAMP-response element (CRE). Knockdown of COUP-TFII or cAMP-binding protein (CREB), which is the archetypal transcription factor binding to CRE, decreased the basal renin gene expression. However, the deficiency of COUP-TFII did not further diminish the renin expression when CREB was knocked down. In agreement with the cell culture studies, mutant mice deficient in COUP-TFII have lower renin expression than their control strain. Altogether our data show that COUP-TFII is involved in the control of renin gene expression.

cAMP target sequences enhCRE and CNRE sense low-salt intake to increase human renin gene expression in vivo

This study aimed to assess the role of cAMP target sequences enhancer cAMP response element (enhCRE) and cAMP and overlapping negative response element (CNRE) in the control of human renin gene (REN) in vivo. enhCRE and CNRE were silenced by mutations in a 12.2-kb human renin promoter fused to LacZ reporter gene. This construct was used to generate transgenic mice (RENMut-LacZ). The expression of the transgene was correctly targeted to the juxtaglomerular portions of renal afferent arterioles which express endogenous mouse renin. Therefore, enhCRE and CNRE do not seem to be relevant for the control of the cell-specific expression of the human renin gene. The β-adrenoreceptor agonist isoproterenol (10 mg/kg/day, for 2 days) stimulated the endogenous renin, but not the LacZ mRNA expression. Treatment of RENMut-LacZ mice with the angiotensin converting enzyme inhibitor (enalapril 10 mg/kg/day, for 7 days) or their crossing to angiotensin receptor type 1a knockout mice led to increased renin and LacZ mRNA levels. Renin expression was upregulated by low-salt diet (0.03% NaCl, for 10 days) and downregulated by high-salt diet (4% NaCl, for 10 days). In contrast, low-salt diet did not influence, while high-salt diet inhibited the expression of LacZ. In summary, enhCRE and CNRE appear to be necessary for the transactivation of the human renin gene through β-adrenoreceptors and by low-salt diet. Our data also suggest that different intracellular mechanisms mediate the effect of low- and high-salt intake on renin expression in vivo.

WHO-sponsored international collaborative study to evaluate methods for subtyping Listeria monocytogenes: restriction fragment length polymorphism (RFLP) analysis using ribotyping and Southern hybridization with two probes derived from L. monocytogenes chromosome

Seven laboratories participated in a WHO-sponsored international collaborative study, to evaluate methods for subtyping Listeria monocytogenes, by performing restriction fragment length polymorph sm (RFLP) analysis-based subtyping of an international study set of 80 strains of L. monocytogenes that included 22 epidemiologically related groups. The RFLP analysis was done by Southern hybridization with one of two types of probes found in multiple copies on the chromosome of L. monocytogenes. Six laboratories performed ribotyping. These laboratories used EcoRI enzyme to restrict the L. monocytogenes DNA and ribosomal RNA or DNA as the probe for Southern hybridizations. The seventh laboratory used Ncil to restrict the DNA, and two probes, one randomly cloned and the other containing repeat sequences cloned from L. monocytogenes DNA. The overall discriminating power of ribotyping, as estimated by calculation of Simpson's index of diversity, ranged from 0.83 to 0.88 for the six laboratories. The discriminating power of the combination of two probes used by Laboratory 7 was 0.91. Ribotyping and the cloned probes used by Laboratory 7 discriminated poorly between serotype 4b strains. Neither method identified three atypical strains (identified by other subtyping methods) included in three apparently epidemiologically related groups. Ribotyping did not discriminate between strains of serotypes 4b and 4b(X) in one epidemiologically related group of strains; one cloned probe used by Laboratory 7 discriminated between these strains. Intra-laboratory reproducibilities for the seven laboratories ranged from 80.0 to 100%. as determined by their abilities to correctly identify 11 pairs of duplicate strains included in the study set. Inter-laboratory reproducibilities were generally very good considering that no attempt was made to standardize protocols used by the participants.

Construction of an integrative food-grade cloning vector for Lactobacillus acidophilus

An integrative cloning vector was constructed using a randomly cloned HindIII-digested chromosomal fragment from Lactobacillus acidophilus ADH inserted into an Escherichia coli vector, pBluescript II SK+. Southern hybridization studies demonstrated homology of the inserted fragment with one other L. acidophilus strain and one Bifidobacterium strain. Identification of a SauI site located near the middle of the 1.9-kb ADH chromosomal fragment made it possible to clone the Lactobacillus bulgaricus beta-galactosidase (EC 3.2.1.23) gene into this vector. The vector was unable to replicate in the homologous host, L. acidophilus ADH, following electroporation. The chromosomal fragment allowed the integration of the beta-galactosidase gene (beta gal) into the host chromosome via homologous recombination. The size of the two flanking L. acidophilus ADH chromosomal fragments, approximately 0.95 kb each, was sufficient to allow the double cross-over to take place. Southern hybridization demonstrated that only L. acidophilus and L. bulgaricus DNA had been integrated into the chromosome of the host strain. The beta-galactosidase activity of the transformant was increased approximately 200-fold when compared to the enzyme activity of the wild-type strain. The beta gal gene remained stable in the transformant strain after 30 transfers in growth media without selection pressure. This first-generation integrative cloning vector is constructed solely of DNA from organisms consumed by humans and could be considered a food-grade vector system.

Influence of nonfermented dairy products containing bacterial starter cultures on lactose maldigestion in humans

The effect of nonfermented dairy products containing yogurt or acidophilus cultures on lactose utilization by lactose-maldigesting humans was investigated. Yogurt and acidophilus milk containing 10(7) or 10(8) of Streptococcus thermophilus and Lactobacillus bulgaricus, or Lactobacillus acidophilus, respectively, were prepared using commercially processed 2% low fat milk. Immediately following inoculation, products were refrigerated. Lactose maldigestion was monitored by measuring breath hydrogen excretion at hourly intervals for 8 h following consumption of 400 ml of each test meal containing approximately 20 g of lactose. The yogurt milk containing 10(8) cfu/ml was shown to contain significant concentrations of microbial beta-galactosidase (EC 3.2.1.23; approximately 3 U/ml), which remained stable for at least 14 d at refrigerator temperatures. Breath hydrogen peaks were delayed and significantly lower (approximately 20 ppm at 5 to 7 h) than control values (approximately 70 ppm at 4 h), and intolerance symptoms were eliminated in all subjects. Yogurt milk containing 10(7) cfu/ml demonstrated intermediate breath hydrogen values and was marginally significantly different from control values. Lactobacillus acidophilus strains with varying resistance to bile and total beta-galactosidase-producing potential were also tested. Only one strain, LA-1, which demonstrated low bile resistance and intermediate beta-galactosidase activity, was capable of significantly decreasing breath hydrogen values when 10(8) cfu/ml of milk was consumed.