The Interplay Between HIF-1α and EZH2 in Lung Cancer and Dual-Targeted Drug Therapy.

Interactions between oncogenic proteins contribute to the phenotype and drug resistance. Here, EZH2 (enhancer of zest homolog 2) is identified as a crucial factor that mediates HIF-1 (hypoxia-inducible factor) inhibitor resistance. Mechanistically, targeting HIF-1 enhanced the activity of EZH2 through transcription activation of SUZ12 (suppressor of zest 12 protein homolog). Conversely, inhibiting EZH2 increased HIF-1α transcription, but not the transcription of other HIF family members. Additionally, the negative feedback regulation between EZH2 and HIF-1α is confirmed in lung cancer patient tissues and a database of cell lines. Moreover, molecular prediction showed that a newly screened dual-target compound, DYB-03, forms multiple hydrogen bonds with HIF-1α and EZH2 to effectively inhibit the activity of both targets. Subsequent studies revealed that DYB-03 could better inhibit migration, invasion, and angiogenesis of lung cancer cells and HUVECs in vitro and in vivo compared to single agent. DYB-03 showed promising antitumor activity in a xenograft tumor model by promoting apoptosis and inhibiting angiogenesis, which could be almost abolished by the deletion of HIF-1α and EZH2. Notably, DYB-03 could reverse 2-ME2 and GSK126-resistance in lung cancer. These findings clarified the molecular mechanism of cross-regulation of HIF-1α and EZH2, and the potential of DYB-03 for clinical combination target therapy.

Sononeoperfusion effect by ultrasound and microbubble promotes nitric oxide release to alleviate hypoxia in a mouse MC38 tumor model.

Tumor hypoperfusion not only impedes therapeutic drug delivery and accumulation, but also leads to a hypoxic and acidic tumor microenvironment, resulting in tumor proliferation, invasion, and therapeutic resistance. Sononeoperfusion effect refers to tumor perfusion enhancement using ultrasound and microbubbles. This study aimed to further investigate hypoxia alleviation by sononeoperfusion effect and explore the characteristics and mechanism of sononeoperfusion effect. To stimulate the sononeoperfusion effect, mice bearing MC38 colon cancers were included in this study and diagnostic ultrasound for therapy was set at a mechanical index (MI) of 0.1, 0.3, and 0.5, frequency of 3 MHz, pulse length of 5 cycles, and pulse repetition frequency of 2000 Hz. The results demonstrated that a single ultrasound and microbubble (USMB) treatment resulted in tumor perfusion enhancement at MI = 0.3, and nitric oxide (NO) concentration increased at MI = 0.3/0.5 (P < 0.05). However, there were no significant difference in the hypoxia-inducible factor-1α (HIF-1α) or D-lactate (D-LA) (P > 0.05) levels. Multiple sononeoperfusion effects were observed at MI = 0.3/0.5 (P < 0.05). For each treatment, USMB slightly but steadily improved the tumor tissue oxygen partial pressure (pO2) during and post treatment. It alleviated tumor hypoxia by decreasing HIF-1α, D-LA level and the hypoxic immunofluorescence intensity at MI = 0.3/0.5 (P < 0.05). The sononeoperfusion effect was not stimulated after eNOS inhibition. In conclusion, USMB with appropriate MI could lead to a sononeoperfusion effect via NO release, resulting in hypoxia amelioration. The tumors were not resistant to multiple sononeoperfusion effects. Repeated sononeoperfusion is a promising approach for relieving tumor hypoxia and resistance to therapy.

SENP3 facilitates M1 macrophage polarization via the HIF-1α/PKM2 axis in lipopolysaccharide-induced acute lung injury.

M1/M2 macrophage polarization plays a pivotal role in the development of acute lung injury (ALI). The hypoxia-inducible factor-1α/pyruvate kinase M2 (HIF-1α/PKM2) axis, which functions upstream of macrophage polarization, has been implicated in this process. The function of HIF-1α is known to be tightly regulated by SUMOylation. Upregulation of SUMO-specific peptidase 3 (SENP3), a deSUMOylation enzyme, is induced by reactive oxygen species (ROS), which are abundantly produced during ALI. To explore the links between SENP3, macrophage polarization, and lung injury, we used mice with Senp3 conditional knockout in myeloid cells. In the lipopolysaccharide (LPS)-induced ALI model, we found that in vitro and in vivo SENP3 deficiency markedly inhibited M1 polarization and production of pro-inflammatory cytokines and alleviated lung injury. Further, we demonstrated that SENP3 deficiency suppressed the LPS-induced inflammatory response through PKM2 in a HIF-1α-dependent manner. Moreover, mice injected with LPS after PKM2 inhibitor (shikonin) treatment displayed inhibition of M1 macrophage polarization and reduced lung injury. In summary, this work revealed that SENP3 promotes M1 macrophage polarization and production of proinflammatory cytokines via the HIF-1α/PKM2 axis, contributing to lung injury; thus, SENP3 may represent a potential therapeutic target for ALI treatment.

Hypoxia signaling in hepatocellular carcinoma: Challenges and therapeutic opportunities.

Hepatocellular carcinoma (HCC) is one of the most common cancers with a relatively high cancer-related mortality. The uncontrolled proliferation of HCC consumes a significant amount of oxygen, causing the development of a hypoxic tumor microenvironment (TME). Hypoxia-inducible factors (HIFs), crucial regulators in the TME, activate several cancer hallmarks leading to the hepatocarcinogenesis of HCC and resistance to current therapeutics. As such, HIFs and their signaling pathways have been explored as potential therapeutic targets for the future management of HCC. This review discusses the current understanding of the structure and function of HIFs and their complex relationship with the various cancer hallmarks. To address tumor hypoxia, this review provides an insight into the various potential novel therapeutic agents for managing HCC, such as hypoxia-activated prodrugs, HIF inhibitors, nanomaterials, antisense oligonucleotides, and natural compounds, that target HIFs/hypoxic signaling pathways in HCC. Because of HCC's relatively high incidence and mortality rates in the past decades, greater efforts should be put in place to explore novel therapeutic approaches to improve the outcome for HCC patients.

Casein kinase 1α 1 is involved in the progression of glioblastoma through HIF-1α-mediated autophagy.

Glioblastoma (GBM) is a malignant tumor prone to recurrence and resistant to conventional therapies. GBM cells show high autophagy activity, contributing to its rapid progression. Casein kinase 1 family, such as casein kinase 1α (CK1α), has shown its effect on autophagy by binding to the hypoxia-inducible factor-1α (HIF-1α). This study investigates the expression of CK1α and HIF-1α in healthy and GBM tissues and its relations with autophagy-related genes and GBM cell viability. The expressions of CK1α, HIF-1α, and autophagy-related proteins in normal tissues, GBM tissues, and GBM cell lines (U87MG, U251, U118-MG, LN229, and SHG44) were analyzed by qRT-PCR and Western blotting. In vitro, the U87MG cell line was transfected with pcDNA3.1-CK1α to enhance the expression of CK1α or both pcDNA3.1-CK1α and siRNA-HIF-1α. The expression of CK1α, HIF-1α, and autophagy-related proteins in GBM brain tissues and cell lines was higher than in normal brain tissues. In U87MG cells, enhanced CK1α expression upregulated the expression of HIF-1α and autophagy-related proteins and promoted cell proliferation. Inhibiting the expression of HIF-1α reduced the expression of autophagy-related proteins and decreased U87MG cell viability. Overexpressed CK1α positively regulates autophagy activity through the HIF-1α pathway. Inhibition of CK1α might be a potential therapeutic approach for glioblastoma therapy.NEW & NOTEWORTHY The study demonstrated that overexpressed CK1α positively regulated autophagy activity through the HIF-1α pathway to promote the progression. Thus, CK1α might be a potential treatment target for glioblastoma.

E2F7 promotes mammalian target of rapamycin inhibitor resistance in hepatocellular carcinoma after liver transplantation.

The mammalian target of rapamycin (mTOR) pathway is frequently deregulated and has critical roles in cancer progression. mTOR inhibitor has been widely used in several kinds of cancers and is strongly recommended in patients with hepatocellular carcinoma (HCC) after liver transplantation (LT). However, the poor response to mTOR inhibitors due to resistance remains a challenge. Hypoxia-associated resistance limits the therapeutic efficacy of targeted drugs. The present study established models of HCC clinical samples and cell lines resistance to mTOR inhibitor sirolimus and screened out E2F7 as a candidate gene induced by hypoxia and promoting sirolimus resistance. E2F7 suppressed mTOR complex 1 via directly binding to the promoter of the TSC1 gene and stabilizes hypoxia-inducible factor-1α activating its downstream genes, which are responsible for E2F7-dependent mTOR inhibitor resistance. Clinically, low E2F7 expression could be an effective biomarker for recommending patients with HCC for anti-mTOR-based therapies after LT. Targeting E2F7 synergistically inhibited HCC growth with sirolimus in vivo. E2F7 is a promising target to reverse mTOR inhibition resistance. Collectively, our study points to a role for E2F7 in promoting mTOR inhibitor resistance in HCC and emphasizes its potential clinical significance in patients with HCC after LT.

Randomised clinical trial: a phase 1b study of GB004, an oral HIF-1α stabiliser, for treatment of ulcerative colitis.

BACKGROUND: Epithelial barrier dysfunction contributes to a dysregulated intestinal immune response in ulcerative colitis (UC). GB004 is an orally administered, small molecule, gut-targeted stabiliser of hypoxia-inducible factor-1α, a transcription factor with protective roles at the epithelial layer of the inflamed gut. AIMS: To evaluate safety, pharmacokinetics, pharmacodynamics and efficacy of GB004 in patients with active UC. METHODS: This double-blind, placebo-controlled study randomised patients 2:1 to receive an oral solution of GB004 120 mg or placebo once daily for 28 days. Eligible patients had a Robarts Histopathology Index score ≥4 with neutrophils in the epithelium, total Mayo Clinic score 3-12, Mayo Clinic endoscopic subscore ≥1, and blood in the stool, despite treatment with 5-aminosalicylates, corticosteroids or immunosuppressants. RESULTS: Thirty-four patients were randomised. GB004 120 mg for 28 days was generally well-tolerated. Adverse events occurred in 27.3% (3/11) and 39.1% (9/23) of patients in the placebo and GB004 groups respectively. Nausea and dysgeusia were most commonly reported in the GB004 group (0% for placebo and 21.7% [5/23] and 13.0% [3/23] respectively for GB004). There were no treatment-related serious adverse events or deaths. GB004 exhibited minimal accumulation, with higher colonic concentrations relative to plasma. Exploratory pharmacodynamic and efficacy analyses demonstrated GB004 target engagement and numerically higher proportions of patients achieving improvement in multiple measures of disease activity, respectively, at day 28 for GB004 compared to placebo. CONCLUSION: Results from this phase 1b trial support evaluation of the full therapeutic potential of GB004 for the treatment of UC. A phase 2 study (NCT04556383) is ongoing. Clinicaltrials.gov NCT03860896.

Correlation analysis of HIF-1α and Ca15-3 in response to neoadjuvant chemotherapy in locally advanced breast cancer: A cohort study in Indonesia.

BACKGROUND: Breast cancer (BC) is the most common cancer among women worldwide and a leading cause of death in Indonesia. The primary treatment of locally advanced BC is neoadjuvant chemotherapy (NAC). The rapid proliferation of tumor cells in a neoplastic microenvironment is largely due to hypoxia, which also encourages the development of chemoresistant BC. The master regulator of the hypoxia response is hypoxia-inducible factor-1α (HIF-1α). The response evaluation criteria in solid tumors (RECIST) is an objective response metric that demonstrates the efficacy of a NAC based mostly on the size of the tumor. Ca15-3 is the protein product of the MUC1 gene and is the most widely used serum marker in BC. The purpose of this study is to investigate the relationship between HIF-1α and RECIST and between Ca15-3 and RECIST and to assess the relationship among all of them in BC. METHODS: This observational study used the prospective cohort method included 11 patients with histopathologically confirmed BC, specifically invasive ductal carcinoma. We evaluated the changes in HIF-1α and Ca15-3 serum levels using ELISA and measured tumor lesions with RECIST. The procedure was carried out twice. Serum levels were measured at baseline, and after receiving two cycles of NAC (5 weeks). RESULTS: Among the 11 patients included in this study, HIF-1α, Ca15-3, and RECIST decreased significantly after NAC. The changes in RECIST correlated with Ca15-3: each unit decrease in RECIST score was associated with a 0.3-unit decrease in Ca15-3 levels (p = 0.019). CONCLUSIONS: There was a decrease in HIF-1α, followed by a decrease in Ca15-3 and RECIST in response to chemotherapy. There was a statistically significant correlation between Ca15-3 and response to chemotherapy. This study evidences the relationship between factors that shape the local tumor microenvironment.

Baicalein resensitizes tamoxifen-resistant breast cancer cells by reducing aerobic glycolysis and reversing mitochondrial dysfunction via inhibition of hypoxia-inducible factor-1α.

Drug resistance is a major hurdle for the effectiveness of tamoxifen (TAM) to provide clinical benefit. Therefore, it is essential to identify a sensitizer that could be used to improve TAM efficacy in treating TAM-resistant breast cancer. Here, we investigated the ability of baicalein to reverse TAM resistance. We found that baicalein increased the efficacy of TAM in inhibiting proliferation and inducing apoptosis of TAM-resistant cells. It also enhanced the TAM-induced growth reduction of resistant cells from NOD/SCID mouse mammary fat pads, without causing obvious systemic toxicity. Analyses using the CellMiner tool and the Kaplan-Meier plotter database showed that HIF-1α expression was inversely correlated with TAM therapeutic response in NCI-60 cancer cells and breast cancer patients. HIF-1α expression was increased in TAM-resistant cells due to an increase in mRNA levels and reduced ubiquitin-mediated degradation. Baicalein reduced HIF-1α expression by promoting its interaction with PHD2 and pVHL, thus facilitating ubiquitin ligase-mediated proteasomal degradation and thereby suppressing the nuclear translocation, binding to the hypoxia-response element, and transcriptional activity of HIF-1α. As a result, baicalein downregulated aerobic glycolysis by restricting glucose uptake, lactate production, ATP generation, lactate/pyruvate ratio and expression of HIF-1α-targeted glycolytic genes, thereby enhancing the antiproliferative efficacy of TAM. Furthermore, baicalein interfered with HIF-1α inhibition of mitochondrial biosynthesis, which increased mitochondrial DNA content and mitochondrial numbers, restored the generation of reactive oxygen species in mitochondria, and thus enhanced the TAM-induced mitochondrial apoptotic pathway. The HIF-1α stabilizer dimethyloxallyl glycine prevented the baicalein-induced downregulation of glycolysis and mitochondrial biosynthesis and reduced the effects of baicalein on reversing TAM resistance. Our results indicate that baicalein is a promising candidate to help overcome TAM resistance by sensitizing resistant cells to TAM-induced growth inhibition and apoptosis. The mechanism underlying the effects of baicalein consists of inhibition of HIF-1α-mediated aerobic glycolysis and mitochondrial dysfunction.

Hypoxia-Inducible Factors as an Alternative Source of Treatment Strategy for Cancer.

Hypoxia-inducible factors (HIFs) are transcription factors that activate the transcription of genes necessary to circumvent to hypoxic (low oxygen level) environments. In carcinogenesis, HIFs play a critical role. Indeed, HIF-1α has been validated as a promising target for novel cancer therapeutics, even as clinical investigations have linked increased levels of HIF-1α with aggressive cancer progression as well as poor patient prognosis. More so, inhibiting HIF-1 activity restricted cancer progression. Therefore, HIF-1 is a viable target for cancer therapy. This may be expected considering the fact that cancer cells are known to be hypoxic. In order to survive the hypoxic microenvironment, cancer cells activate several biochemical pathways via the HIF-1α. Additionally, cellular and molecular insights have proved prospects of the HIF-1α pathway for the development of novel anticancer treatment strategies. The biochemical importance of hypoxia-inducible factors (HIFs) cannot be overemphasized as carcinogenesis, cancer progression, and HIFs are intricately linked. Therefore, this review highlights the significance of these linkages and also the prospects of HIFs as an alternative source of cancer therapies.

ß Cell Hypoxia-Inducible Factor-1α Is Required for the Prevention of Type 1 Diabetes.

The development of autoimmune disease type 1 diabetes (T1D) is determined by both genetic background and environmental factors. Environmental triggers include RNA viruses, particularly coxsackievirus (CV), but how they induce T1D is not understood. Here, we demonstrate that deletion of the transcription factor hypoxia-inducible factor-1α (HIF-1α) from ß cells increases the susceptibility of non-obese diabetic (NOD) mice to environmentally triggered T1D from coxsackieviruses and the ß cell toxin streptozotocin. Similarly, knockdown of HIF-1α in human islets leads to a poorer response to coxsackievirus infection. Studies in coxsackievirus-infected islets demonstrate that lack of HIF-1α leads to impaired viral clearance, increased viral load, inflammation, pancreatitis, and loss of ß cell mass. These findings show an important role for ß cells and, specifically, lack of ß cell HIF-1α in the development of T1D. These data suggest new strategies for the prevention of T1D.

Role of HIF-1α in response of tumors to a combination of hyperthermia and radiation in vivo.

PURPOSE: Mild temperature hyperthermia (MTH) increases blood flow and oxygenation in tumours. On the other hand, high-dose-per-fraction irradiation damages blood vessels, decreases blood flow and increases hypoxia in tumours. The radiation-induced hypoxia in tumours activates hypoxia-inducible factor-1α (HIF-1α) and its target genes, such as vascular endothelial growth factor (VEGF), promoting revascularization and recurrence. In the present study, we examined the hypothesis that MTH inhibits radiation-induced upregulation of HIF-1α and its target genes by increasing tumour oxygenation. MATERIALS AND METHODS: FSaII fibrosarcoma tumours grown subcutaneously in the legs of C3H mice were used. Tumours were irradiated with 15 Gy using a 60Co irradiator or heated at 41 °C for 30 min using an Oncothermia heating unit. Blood perfusion and hypoxia in tumours were assessed with Hoechst 33342 and pimonidazole staining, respectively. Expression levels of HIF-1α and VEGF were determined using immunohistochemical techniques. Apoptosis of tumour cells was quantitated via TUNEL staining and the effects of treatments on tumour growth rate were assessed by measuring tumour diameters. RESULTS: Irradiation of FSaII tumours with a single dose of 15 Gy led to significantly decreased blood perfusion, increased hypoxia and upregulation of HIF-1α and VEGF. On the other hand, MTH at 41 °C for 30 min increased blood perfusion and tumour oxygenation, thereby suppressing radiation-induced HIF-1α and VEGF in tumours, leading to enhanced apoptosis of tumour cells and tumour growth delay. CONCLUSION: MTH enhances the anti-tumour effect of high-dose irradiation, at least partly by inhibiting radiation-induced upregulation of HIF-1α.

New HIF2α inhibitors: potential implications as therapeutics for advanced pheochromocytomas and paragangliomas.

Two recent independent studies published in Nature show robust responses of clear cell renal cell carcinoma (ccRCC) cell lines, preclinical ccRCC xenograft models and, remarkably, a patient with progressive ccRCC despite receiving multiple lines of treatment, to the long-awaited, recently developed inhibitors of hypoxia-inducible factor 2-alpha (HIF2α). This commentary published in Endocrine-Related Cancer is based on the recognition of similar molecular drivers in ccRCC and the endocrine neoplasias pheochromocytomas and paragangliomas (PPGLs), ultimately leading to stabilization of HIFs. HIF-stabilizing mutations have been detected in the von Hippel-Lindau (VHL) gene, as well as in other genes, such as succinate dehydrogenase (SDHx), fumarate hydratase (FH) and transcription elongation factor B subunit 1 (TCEB1), as well as the gene that encodes HIF2α itself: EPAS1HIF2α Importantly, the recent discovery of EPAS1 mutations in PPGLs and the results of comprehensive in vitro and in vivo studies revealing their oncogenic roles characterized a hitherto unknown direct mechanism of HIF2α activation in human cancer. The now available therapeutic opportunity to successfully inhibit HIF2α pharmacologically with PT2385 and PT2399 will certainly spearhead a series of investigations in several types of cancers, including patients with SDHB-related metastatic PPGL for whom limited therapeutic options are currently available. Future studies will determine the efficacy of these promising drugs against the hotspot EPAS1 mutations affecting HIF2α amino acids 529-532 (in PPGLs) and amino acids 533-540 (in erythrocytosis type 4), as well as against HIF2α protein activated by VHL, SDHx and FH mutations in PPGL-derived chromatin cells.

New strategy for renal fibrosis: Targeting Smad3 proteins for ubiquitination and degradation.

PURPOSE: Smad3 is a critical signaling protein in renal fibrosis. Proteolysis targeting chimeric molecules (PROTACs) are small molecules designed to degrade target proteins via ubiquitination. They have three components: (1) a recognition motif for E3 ligase; (2) a linker; and (3) a ligand for the target protein. We aimed to design a new PROTAC to prevent renal fibrosis by targeting Smad3 proteins and using hydroxylated pentapeptide of hypoxia-inducible factor-1α as the recognition motif for von Hippel-Lindau (VHL) ubiquitin ligase (E3). METHODS: Computer-aided drug design was used to find a specific ligand targeting Smad3. Surface plasmon resonance (SPR) was used to verify and optimize screening results. Synthesized PROTAC was validated by two-stage mass spectrometry. The PROTAC's specificity for VHL (E3 ligase) was proved with two human renal carcinoma cell lines, 786-0 (VHL(-)) and ACHN (VHL(+)), and its anti-fibrosis effect was tested in renal fibrosis cell models. RESULTS: Thirteen small molecular compounds (SMCs) were obtained from the Enamine library using GLIDE molecular docking program. SPR results showed that #8 SMC (EN300-72284) combined best with Smad3 (KD=4.547×10(-5)M). Mass spectrometry showed that synthesized PROTAC had the correct peptide molecular weights. Western blot showed Smad3 was degraded by PROTAC with whole-cell lysate of ACHN but not 786-0. Degradation, but not ubiquitination, of Smad3 was inhibited by proteasome inhibitor MG132. The upregulation of fibronectin and Collagen I induced by TGF-ß1 in both renal fibroblast and mesangial cells were inhibited by PROTAC. CONCLUSION: The new PROTAC might prevent renal fibrosis by targeting Smad3 for ubiquitination and degradation.

Novel Masters of Erythropoiesis: Hypoxia Inducible Factors and Recent Advances in Anemia of Renal Disease.

Anemia seen in patients with chronic kidney disease is a particular form of 'anemia of chronic disease'. Although multifactorial in origin, erythropoiesis-stimulating agents (ESAs) and adjuvant iron therapy represent the primary treatment for anemia in chronic kidney disease. Subsequent clinical observations revealed that these ESA hyporesponsive patients often had increased systemic inflammation as a consequence of their comorbidities. Use of high ESA doses to overcome this ESA hyporesponsiveness posed some concerns regarding associated adverse events of therapy and increased mortality in this special patient population. Recognizing the pivotal roles of hypoxia inducible factors (HIFs) in orchestrating elements of erythropoiesis opened new avenues in the management of renal anemia. Several phase 1 and 2 studies confirmed the results of early experimental studies supporting the beneficial role of augmenting HIFs for erythropoiesis. In this review, we describe the physiologic functions of HIF in erythropoiesis with special emphasis on interactions with iron and hepcidin metabolism and inflammation.

Expression of hypoxia-inducible factor 1 alpha ameliorate myocardial ischemia in rat.

Hypoxia-inducible factor 1 alpha (HIF-1a), the upstream regulator of Vascular endothelial growth factor (VEGF), is the vital hypoxia related gene expression control factor. To evaluate HIF-1a therapeutic efficacy to acute myocardial infarction, the HIF-1a expressing recombinant Adeno-associated virus (rAAV) was constructed. The Wistar rat ischemic heart animal model was established with left anterior descending coronary artery ligation. The ischemic rats were treated with HIF-1a expressing and GFP expressing rAAVs respectively. Four weeks post the injection, the cardiac function of treated rat was compared by TM_WAVE system; size of infracted area was calculated by Evan's blue stain and capillary density was determined by CD31 immunohistochemical staining. Compare to the control group, the rats received HIF-1a expressing rAAV have smaller infracted heart size, the better heart function and higher capillary density than vehicle control group. The results show that the injection of HIF1a expressing rAAV can improve cardiac function and ameliorate acute myocardial ischemia (AMI) in rats.

Xenon Treatment Protects against Remote Lung Injury after Kidney Transplantation in Rats.

BACKGROUND: Ischemia-reperfusion injury (IRI) of renal grafts may cause remote organ injury including lungs. The authors aimed to evaluate the protective effect of xenon exposure against remote lung injury due to renal graft IRI in a rat renal transplantation model. METHODS: For in vitro studies, human lung epithelial cell A549 was challenged with H2O2, tumor necrosis factor-α, or conditioned medium from human kidney proximal tubular cells (HK-2) after hypothermia-hypoxia insults. For in vivo studies, the Lewis renal graft was stored in 4°C Soltran preserving solution for 24 h and transplanted into the Lewis recipient, and the lungs were harvested 24 h after grafting. Cultured lung cells or the recipient after engraftment was exposed to 70% Xe or N2. Phospho (p)-mammalian target of rapamycin (mTOR), hypoxia-inducible factor-1α (HIF-1α), Bcl-2, high-mobility group protein-1 (HMGB-1), TLR-4, and nuclear factor κB (NF-κB) expression, lung inflammation, and cell injuries were assessed. RESULTS: Recipients receiving ischemic renal grafts developed pulmonary injury. Xenon treatment enhanced HIF-1α, which attenuated HMGB-1 translocation and NF-κB activation in A549 cells with oxidative and inflammatory stress. Xenon treatment enhanced p-mTOR, HIF-1α, and Bcl-2 expression and, in turn, promoted cell proliferation in the lung. Upon grafting, HMGB-1 translocation from lung epithelial nuclei was reduced; the TLR-4/NF-κB pathway was suppressed by xenon treatment; and subsequent tissue injury score (nitrogen vs. xenon: 26 ± 1.8 vs. 10.7 ± 2.6; n = 6) was significantly reduced. CONCLUSION: Xenon treatment confers protection against distant lung injury triggered by renal graft IRI, which is likely through the activation of mTOR-HIF-1α pathway and suppression of the HMGB-1 translocation from nuclei to cytoplasm.