Hypoxia-inducible factors--regulation, role and comparative aspects in tumourigenesis

Prognostic Factors for the Efficiency of Radiation Therapy in Dogs with Oral Melanoma: A Pilot Study of Hypoxia in Intraosseous Lesions

Unresectable oral melanoma is often treated with radiation therapy (RT) and may show a temporary response to therapy. The clinical stage is one of the well-known prognostic factors for canine oral melanoma. However, the factors that directly affect the response to RT have remained unclear. This study aimed to validate the risk factors for recurrence after RT. Sixty-eight dogs with oral melanomas were included in this study. All dogs were treated with palliative RT using a linear accelerator without adjuvant therapies. After RT, the time to local recurrence (TTR) and overall survival (OS) were evaluated using the log-rank test. As a result, clinical stage and response to therapy were the significant independent prognostic factors in the multivariate analysis. The presence of local bone lysis and non-combination with cytoreductive surgery were associated with a worse response to RT. Immunohistochemical analysis for hypoxia-inducible factor-1α indicated that tumor cells invading the bone are under hypoxic conditions, which may explain a poorer efficiency of RT in dogs with bone lysis. In conclusion, clinical stage and combination with debulking surgery were needed to improve the efficiency of RT.

The effect of HIF-1α inhibition in breast cancer cells prior to doxorubicin treatment under conditions of normoxia and hypoxia

BACKGROUND

Oxygen deprivation is a key hallmark within solid tumours that contributes to breast-tumour pathophysiology. Under these conditions, neoplastic cells activate several genes, regulated by the HIF-1 transcription factor, which alters the tumour microenvironment to promote survival - including resistance to cell death in therapeutic attempts such as doxorubicin (Dox) treatment.

METHODS

We investigated HIF-1ɑ as a therapeutic target to sensitize breast cancer cells to Dox treatment. Under both normoxic (21% O₂) and hypoxic (∼0.1% O₂) conditions, the HIF-1 inhibitor, 2-methoxyestradiol (2-ME), was investigated as an adjuvant for its ability to alter MCF-7 cell viability, apoptosis, autophagy and molecular pathways which are often associated with increased cell survival.

RESULTS

Here we observed that an inverse relationship between HIF-1ɑ and apoptosis exists and that Dox promotes autophagy under hypoxic conditions. Although adjuvant therapy with 2-ME induced an antagonistic effect in breast cancer cells, upregulated HIF-1ɑ expression in a hypoxic environment promotes treatment resistance and this was attenuated once HIF-1ɑ gene expression was silenced.

CONCLUSION

Therefore, highlighting the identification of possible hypoxia-targeting therapies for breast cancer patients can be beneficial by promoting more favourable treatment responses.

A positive feedback regulatory loop involving the lncRNA PVT1 and HIF-1α in pancreatic cancer

Extreme hypoxia is among the most prominent pathogenic features of pancreatic cancer (PC). Both the long non-coding RNA (lncRNA) plasmacytoma variant translocation 1 (PVT1) and hypoxic inducible factor-1α (HIF-1α) are highly expressed in PC patients and play a crucial role in disease progression. Reciprocal regulation involving PVT1 and HIF-1α in PC, however, is poorly understood. Here, we report that PVT1 binds to the HIF-1α promoter and activates its transcription. In addition, we found that PVT1 could bind to HIF-1α and increases HIF-1α post-translationally. Our findings suggest that the PVT1‒HIF-1α positive feedback loop is a potential therapeutic target in the treatment of PC.

Clinical significance and in vitro cellular regulation of hypoxia mimicry on HIF-1α and downstream genes in canine appendicular osteosarcoma

Cellular adaptation to a hypoxic microenvironment is essential for tumour progression and is largely mediated by HIF-1α and hypoxia-regulated factors, including CXCR4, VEGF-A and GLUT-1. In human osteosarcoma, hypoxia is associated with resistance to chemotherapy as well as with metastasis and poor survival, whereas little is known about its role in canine osteosarcoma (cOSA). This study aimed primarily to evaluate the prognostic value of several known hypoxic markers in cOSA. Immunohistochemical analysis for HIF-1α, CXCR4, VEGF-A and GLUT-1 was performed on 56 appendicular OSA samples; correlations with clinicopathological features and outcome was investigated. The second aim was to investigate the in vitro regulation of markers under chemically induced hypoxia (CoCl₂). Two primary canine osteosarcoma cell lines were selected, and Western blotting, immunofluorescence and qRT-PCR were used to study protein and gene expression. Dogs with high-grade OSA (35.7%) were more susceptible to the development of metastases (P = 0.047) and showed high HIF-1α protein expression (P = 0.007). Moreover, HIF-1α overexpression (56%) was correlated with a shorter disease-free interval (DFI; P = 0.01), indicating that it is a reliable negative prognostic marker. The in vitro experiments identified an accumulation of HIF-1α in cOSA cells after chemically induced hypoxia, leading to a significant increase in GLUT-1 transcript (P = 0.02). HIF-1α might be a promising prognostic marker, highlighting opportunities for the use of therapeutic strategies targeting the hypoxic microenvironment in cOSA. These results reinforce the role of the dog as a comparative animal model since similar hypoxic mechanisms are reported in human osteosarcoma.

Hypoxia-mediated mitochondria apoptosis inhibition induces temozolomide treatment resistance through miR-26a/Bad/Bax axis

Glioblastoma multiforme (GBM) is one of the most hypoxic tumors of the central nervous system. Although temozolomide (TMZ) is an effective clinical agent in the GBM therapy, the hypoxic microenvironment remains a major barrier in glioma chemotherapy resistance, and the underlying mechanisms are poorly understood. Here, we find hypoxia can induce the protective response to mitochondrion via HIF-1α-mediated miR-26a upregulation which is associated with TMZ resistance in vitro and in vivo. Further, we demonstrated that HIF-1α/miR-26a axis strengthened the acquisition of TMZ resistance through prevention of Bax and Bad in mitochondria dysfunction in GBM. In addition, miR-26a expression levels negatively correlate with Bax, Bad levels, and GBM progression; but highly correlate with HIF-1α levels in clinical cancer tissues. These findings provide a new link in the mechanistic understanding of TMZ resistance under glioma hypoxia microenvironment, and consequently HIF-1α/miR-26a/Bax/Bad signaling pathway as a promising adjuvant therapy for GBM with TMZ.

Long non-coding RNA and tumor hypoxia: new players ushered toward an old arena

Hypoxia is a classic feature of the tumor microenvironment with a profound impact on cancer progression and therapeutic response. Activation of complex hypoxia pathways orchestrated by the transcription factor HIF (hypoxia-inducible factor) contributes to aggressive phenotypes and metastasis in numerous cancers. Over the past few decades, exponentially growing research indicated the importance of the non-coding genome in hypoxic tumor regions. Recently, key roles of long non coding RNAs (lncRNAs) in hypoxia-driven cancer progression have begun to emerge. These hypoxia-responsive lncRNAs (HRLs) play pivotal roles in regulating hypoxic gene expression at chromatic, transcriptional, and post-transcriptional levels by acting as effectors of the indirect response to HIF or direct modulators of the HIF-transcriptional cascade. Notably, the aberrant expression of HRLs significantly correlates with poor outcomes in cancer patients, showing promise for future utility as a tumor marker or therapeutic target. Here we address the latest advances made toward understanding the functional relevance of HRLs, the involvement of these transcripts in hypoxia response and the underlying action mechanisms, highlighting their specific roles in HIF-1 signaling regulation and hypoxia-associated malignant transformation.

Micro Regional Heterogeneity of 64Cu-ATSM and 18F-FDG Uptake in Canine Soft Tissue Sarcomas: Relation to Cell Proliferation, Hypoxia and Glycolysis

OBJECTIVES

Tumour microenvironment heterogeneity is believed to play a key role in cancer progression and therapy resistance. However, little is known about micro regional distribution of hypoxia, glycolysis and proliferation in spontaneous solid tumours. The overall aim was simultaneous investigation of micro regional heterogeneity of 64Cu-ATSM (hypoxia) and 18F-FDG (glycolysis) uptake and correlation to endogenous markers of hypoxia, glycolysis, proliferation and angiogenesis to better therapeutically target aggressive tumour regions and prognosticate outcome.

METHODS

Exploiting the different half-lives of 64Cu-ATSM (13 h) and 18F-FDG (2 h) enabled simultaneous investigation of micro regional distribution of hypoxia and glycolysis in 145 tumour pieces from four spontaneous canine soft tissue sarcomas. Pairwise measurements of radioactivity and gene expression of endogenous markers of hypoxia (HIF-1α, CAIX), glycolysis (HK2, GLUT1 and GLUT3), proliferation (Ki-67) and angiogenesis (VEGFA and TF) were performed. Dual tracer autoradiography was compared with Ki-67 immunohistochemistry.

RESULTS

Micro regional heterogeneity in hypoxia and glycolysis within and between tumour sections of each tumour piece was observed. The spatial distribution of 64Cu-ATSM and 18F-FDG was rather similar within each tumour section as reflected in moderate positive significant correlations between the two tracers (ρ = 0.3920-0.7807; p = 0.0180 -<0.0001) based on pixel-to-pixel comparisons of autoradiographies and gamma counting of tumour pieces. 64Cu-ATSM and 18F-FDG correlated positively with gene expression of GLUT1 and GLUT3, but negatively with HIF-1α and CAIX. Significant positive correlations were seen between Ki-67 gene expression and 64Cu-ATSM (ρ = 0.5578, p = 0.0004) and 18F-FDG (ρ = 0.4629-0.7001, p = 0.0001-0.0151). Ki-67 gene expression more consistently correlated with 18F-FDG than with 64Cu-ATSM.

CONCLUSIONS

Micro regional heterogeneity of hypoxia and glycolysis was documented in spontaneous canine soft tissue sarcomas. 64Cu-ATSM and 18F-FDG uptakes and distributions showed significant moderate correlations at the micro regional level indicating overlapping, yet different information from the tracers.18F-FDG better reflected cell proliferation as measured by Ki-67 gene expression than 64Cu-ATSM.

The A Allele at rs13419896 of EPAS1 Is Associated with Enhanced Expression and Poor Prognosis for Non-Small Cell Lung Cancer

Hypoxia-inducible factor-2α (HIF-2α, or EPAS1) is important for cancer progression, and is a putative biomarker for poor prognosis for non-small cell lung cancer (NSCLC). However, molecular mechanisms underlying the EPAS1 overexpression are not still fully understood. We explored a role of a single nucleotide polymorphism (SNP), rs13419896 located within intron 1 of the EPAS1 gene in regulation of its expression. Bioinformatic analyses suggested that a region including the rs13419896 SNP plays a role in regulation of the EPAS1 gene expression and the SNP alters the binding activity of transcription factors. In vitro analyses demonstrated that a fragment containing the SNP locus function as a regulatory region and that a fragment with A allele showed higher transactivation activity than one with G, especially in the presence of overexpressed c-Fos or c-Jun. Moreover, NSCLC patients with the A allele showed poorer prognosis than those with G at the SNP even after adjustment with various variables. In conclusion, the genetic polymorphism of the EPAS1 gene may lead to variation of its gene expression levels to drive progression of the cancer and serve as a prognostic marker for NSCLC.

An immunohistochemical study of the expression of the hypoxia markers Glut-1 and Ca-IX in canine sarcomas

Tumor hypoxia has been associated with increased malignancy, likelihood of metastasis, and increased resistance to radiotherapy and chemotherapy in human medicine. Hypoxia-inducible factor-1 (HIF-1) is a key transcription factor that is induced by tumor hypoxia and regulates the pathways involved in cellular response and adaptation to the hostile tumor microenvironment. HIF-1 induces transcription of different proteins, including Ca-IX and Glut-1, which are considered endogenous markers of chronic hypoxia in solid tumors in humans. In this study, sections from 40 canine sarcomas (20 histiocytic sarcomas and 20 low-grade soft-tissue sarcomas) were immunostained for these markers. Expression of Glut-1 was scored based on percentage of positive staining cells (0 = <1%; 1 = 1%-50%; 2 = >50%) and intensity of cellular staining (1 = weak; 2 = strong); Ca-IX was scored based on percentage of positive cells (0 = <1%; 1 = 1%-30%; 2 = >30%). Intratumoral microvessel density was measured using CD31 to assess intratumoral neoangiogenesis. Histiocytic sarcomas showed statistically significant higher Glut-1 immunoreactivity and angiogenesis than did low-grade soft-tissue sarcomas. Intratumoral microvessel density in histiocytic sarcomas was positively associated with Glut-1 immunoreactivity score. These findings suggest a potential role of hypoxia in the biology of these tumors and may provide a base for investigation of the potential prognostic use of these markers in naturally occurring canine tumors.

Hypoxia stimulates the production of the angiogenesis inhibitor 2-methoxyestradiol by swine granulosa cells

We previously demonstrated the presence of 2-methoxyestradiol (2-ME) in swine follicular fluid. Present study was aimed first of all to investigate if swine granulosa cell produce 2-ME; in addition, we tried to assess a potential effect of hypoxia in modulating 2-ME output. Finally, we explored the effect of 2-ME in an angiogenesis bioassay set up in our lab. Our data show that cultured granulosa cells are able to produce 2-ME; interestingly, the secretion of the hormone appeared to be stimulated by hypoxia. Angiogenesis bioassay points out that 2-ME displays an inhibitory effect on neovascularisation. Therefore our data suggest that 2-ME could be a local effector in determining the fine tuning responsible for follicle angiogenesis. These data deserve special attention since the ovary is a valuable experimental model in angiogenesis research.

Hypoxia, stem cells and bone tumor

Normal oxygen level is critical for niches that together with other components of the niche play vital role in regulating stem or tumor cells behavior. Hypoxia plays an important role in normal development and disease progression, including the growth of solid tumors. The hypoxia inducible factors (HIFs) are the key mediators of the cellular response to hypoxia. In this review, we focused on the role of HIFs on bone tumor formation. Further, we also emphasized how hypoxia, stem cells, and its niches regulate the bone tumorigenesis.