Targeting the SphK1/S1P/PFKFB3 axis suppresses hepatocellular carcinoma progression by disrupting glycolytic energy supply that drives tumor angiogenesis

BACKGROUND

Hepatocellular carcinoma (HCC) remains a leading life-threatening health challenge worldwide, with pressing needs for novel therapeutic strategies. Sphingosine kinase 1 (SphK1), a well-established pro-cancer enzyme, is aberrantly overexpressed in a multitude of malignancies, including HCC. Our previous research has shown that genetic ablation of Sphk1 mitigates HCC progression in mice. Therefore, the development of PF-543, a highly selective SphK1 inhibitor, opens a new avenue for HCC treatment. However, the anti-cancer efficacy of PF-543 has not yet been investigated in primary cancer models in vivo, thereby limiting its further translation.

METHODS

Building upon the identification of the active form of SphK1 as a viable therapeutic target in human HCC specimens, we assessed the capacity of PF-543 in suppressing tumor progression using a diethylnitrosamine-induced mouse model of primary HCC. We further delineated its underlying mechanisms in both HCC and endothelial cells. Key findings were validated in Sphk1 knockout mice and lentiviral-mediated SphK1 knockdown cells.

RESULTS

SphK1 activity was found to be elevated in human HCC tissues. Administration of PF-543 effectively abrogated hepatic SphK1 activity and significantly suppressed HCC progression in diethylnitrosamine-treated mice. The primary mechanism of action was through the inhibition of tumor neovascularization, as PF-543 disrupted endothelial cell angiogenesis even in a pro-angiogenic milieu. Mechanistically, PF-543 induced proteasomal degradation of the critical glycolytic enzyme 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3, thus restricting the energy supply essential for tumor angiogenesis. These effects of PF-543 could be reversed upon S1P supplementation in an S1P receptor-dependent manner.

CONCLUSIONS

This study provides the first in vivo evidence supporting the potential of PF-543 as an effective anti-HCC agent. It also uncovers previously undescribed links between the pro-cancer, pro-angiogenic and pro-glycolytic roles of the SphK1/S1P/S1P receptor axis. Importantly, unlike conventional anti-HCC drugs that target individual pro-angiogenic drivers, PF-543 impairs the PFKFB3-dictated glycolytic energy engine that fuels tumor angiogenesis, representing a novel and potentially safer therapeutic strategy for HCC.

Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) Promotes Angiogenesis and Ischemia-Induced Neovascularization Via NADPH Oxidase 4 (NOX4) and Nitric Oxide-Dependent Mechanisms

Background

Tumor necrosis factor–related apoptosis‐inducing ligand (TRAIL) has the ability to inhibit angiogenesis by inducing endothelial cell death, as well as being able to promote pro‐angiogenic activity in vitro. These seemingly opposite effects make its role in ischemic disease unclear. Using Trail^−/− and wildtype mice, we sought to determine the role of TRAIL in angiogenesis and neovascularization following hindlimb ischemia.

Methods and Results

Reduced vascularization assessed by real‐time 3‐dimensional Vevo ultrasound imaging and CD31 staining was evident in Trail^−/− mice after ischemia, and associated with reduced capillary formation and increased apoptosis. Notably, adenoviral TRAIL administration significantly improved limb perfusion, capillary density, and vascular smooth‐muscle cell content in both Trail^−/− and wildtype mice. Fibroblast growth factor‐2, a potent angiogenic factor, increased TRAIL expression in human microvascular endothelial cell‐1, with fibroblast growth factor‐2‐mediated proliferation, migration, and tubule formation inhibited with TRAIL siRNA. Both fibroblast growth factor‐2 and TRAIL significantly increased NADPH oxidase 4 (NOX4) expression. TRAIL‐inducible angiogenic activity in vitro was inhibited with siRNAs targeting NOX4, and consistent with this, NOX4 mRNA was reduced in 3‐day ischemic hindlimbs of Trail^−/− mice. Furthermore, TRAIL‐induced proliferation, migration, and tubule formation was blocked by scavenging H₂O₂, or by inhibiting nitric oxide synthase activity. Importantly, TRAIL‐inducible endothelial nitric oxide synthase phosphorylation at Ser‐1177 and intracellular human microvascular endothelial cell‐1 cell nitric oxide levels were NOX4 dependent.

Conclusions

This is the first report demonstrating that TRAIL can promote angiogenesis following hindlimb ischemia in vivo. The angiogenic effect of TRAIL on human microvascular endothelial cell‐1 cells is downstream of fibroblast growth factor‐2, involving NOX4 and nitric oxide signaling. These data have significant therapeutic implications, such that TRAIL may improve the angiogenic response to ischemia and increase perfusion recovery in patients with cardiovascular disease and diabetes.

TNF-related apoptosis-inducing ligand (TRAIL) protects against diabetes and atherosclerosis in Apoe ⁻/⁻ mice

AIMS/HYPOTHESIS

TNF-related apoptosis-inducing ligand (TRAIL) is implicated in the regulation of diabetes and is reduced in patients with cardiovascular disease. Although TRAIL receptors are widespread, and TRAIL can promote cell proliferation and apoptosis, it is not known how TRAIL might protect against diabetes and atherosclerosis.

METHODS

We examined the development of atherosclerosis and diabetes in Apoe (-/-), Trail (also known as Tnfsf10)( -/- ) Apoe ( -/- ) and Trail ( -/- ) mice that were fed a high-fat diet. Plasma cholesterol, triacylglycerol, glucose and insulin, as well as changes in various metabolic enzymes and regulators were assessed. Glucose and insulin tolerance tests were performed. Pancreatic islets were examined for insulin and beta cell dysfunction (apoptosis and macrophage infiltration).

RESULTS

Compared with Apoe ( -/- ) mice, Trail ( -/- ) Apoe ( -/- ) and Trail ( -/- ) mice exhibited several features of diabetes, including increased weight, hyperglycaemia, reduced plasma insulin, impaired glucose tolerance, beta cell dysfunction, reduced islet insulin, macrophage infiltration and increased apoptosis. Trail ( -/- ) Apoe ( -/- ) mice had increased plasma cholesterol, triacylglycerol, and VLDL- and LDL-cholesterol, and increased expression of genes involved in cholesterol synthesis and lipogenesis. Trail ( -/- ) Apoe ( -/- ) mice also had increased atherosclerosis, with several features of plaque instability.

CONCLUSIONS/INTERPRETATION

We show for the first time that TRAIL deficiency promotes numerous features of diabetes that are typical of human disease, and are associated with reduced insulin and pancreatic inflammation/apoptosis. TRAIL also regulates cholesterol and triacylglycerol homeostasis in Apoe ( -/- ) mice by increasing the expression of genes involved in (1) cholesterol synthesis and absorption, and (2) triacylglycerol production.

Vessel wall apoptosis and atherosclerotic plaque instability

Atherosclerotic cardiovascular disease remains the leading cause of death in the industrialized world. Most cardiovascular deaths result from acute coronary syndromes, including unstable angina pectoris and acute myocardial infarction. Coronary syndromes often arise from acute coronary thrombosis, itself commonly a result of disruption or rupture of the fibrous cap of a lipid-laden atherosclerotic plaque. Despite this huge clinical burden of atherosclerotic plaque instability, our understanding of the molecular mechanisms mediating atherosclerotic plaque disruption and rupture, at a cellular level, remains limited. Placed in a clinical context, this review discusses our current understanding of the molecular basis for atherosclerotic plaque instability, with particular emphasis on the process of apoptosis-or programmed cell death-seen increasingly as playing a key role in a number of cell types within the vessel wall.

Signaling and transcriptional control of Fas ligand gene expression

Fas ligand (FasL), a member of the tumor necrosis factor family, initiates apoptosis by binding to its surface receptor Fas. As a consequence, there is sequential activation of caspases and the release of cytochrome c from the mitochondria, with additional caspase activation followed by cellular degradation and death. Recent studies have shed important insight into the molecular mechanisms controlling FasL gene expression at the level of transcription. Nuclear factors such as nuclear factor in activated T cells, nuclear factor-kappa B, specificity protein-1, early growth response factor, interferon regulatory factor, c-Myc and the forkhead transcriptional regulator, alone or cooperatively, activate FasL expression. These factors are often coexpressed with FasL in pathophysiologic settings including human atherosclerotic lesions. Here, we review these important advances in our understanding of the signaling and transcriptional mechanisms controlling FasL gene expression.

Catalytic oligodeoxynucleotides define a key regulatory role for early growth response factor-1 in the porcine model of coronary in-stent restenosis

Early growth response factor-1 (Egr-1) controls the expression of a growing number of genes involved in the pathogenesis of atherosclerosis and postangioplasty restenosis. Egr-1 is activated by diverse proatherogenic stimuli. As such, this transcription factor represents a key molecular target in efforts to control vascular lesion formation in humans. In this study, we have generated DNAzymes targeting specific sequences in human EGR-1 mRNA. These molecules cleave in vitro transcribed EGR-1 mRNA efficiently at preselected sites, inhibit EGR-1 protein expression in human aortic smooth muscle cells, block serum-inducible cell proliferation, and abrogate cellular regrowth after mechanical injury in vitro. These DNAzymes also selectively inhibit EGR-1 expression and proliferation of porcine arterial smooth muscle cells and reduce intimal thickening after stenting pig coronary arteries in vivo. These findings demonstrate that endoluminally delivered DNAzymes targeting EGR-1 may serve as inhibitors of in-stent restenosis.

Sp1 phosphorylation regulates apoptosis via extracellular FasL-Fas engagement

Apoptosis of smooth muscle cells (SMC) in atherosclerotic vessels can destabilize the atheromatus plaque and result in rupture, thrombosis, and sudden death. In efforts to understand the molecular processes regulating apoptosis in this cell type, we have defined a novel mechanism involving the ubiquitously expressed transcription factor Sp1. Subtypes of SMC expressing abundant levels of Sp1 produce the death agonist, Fas ligand (FasL) and undergo greater spontaneous apoptosis. Sp1 activates the FasL promoter via a distinct nucleotide recognition element whose integrity is crucial for inducible expression. Inducible FasL promoter activation is also inhibited by a dominant-negative form of Sp1. Increased SMC apoptosis is preceded by Sp1 phosphorylation, increased FasL transcription, and the autocrine/paracrine engagement of FasL with its cell-surface receptor, Fas. Inducible FasL transcription and apoptosis are blocked by dominant-negative protein kinase C-zeta, whose wild-type counterpart phosphorylates Sp1. Thus, Sp1 phosphorylation is a proapoptotic transcriptional event in vascular SMC and, given the wide distribution of this housekeeping transcription factor, may be a common regulatory theme in apoptotic signal transduction.

New DNA enzyme targeting Egr-1 mRNA inhibits vascular smooth muscle proliferation and regrowth after injury

Early growth response factor-1 (Egr-1) binds to the promoters of many genes whose products influence cell movement and replication in the artery wall. Here we targeted Egr-1 using a new class of DNA-based enzyme that specifically cleaved Egr-1 mRNA, blocked induction of Egr-1 protein, and inhibited cell proliferation and wound repair in culture. The DNA enzyme also inhibited Egr-1 induction and neointima formation after balloon injury to the rat carotid artery wall. These findings demonstrate the utility of DNA enzymes as biological tools to delineate the specific functions of a given gene, and implicate catalytic nucleic acid molecules composed entirely of DNA as potential therapeutic agents.