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.

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.

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.

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: EPAS1^HIF2α 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.

In vivo remote delivery of DNA encoding for hypoxia-inducible factor 1 alpha reduces myocardial infarct size

We tested if remote gene delivery of hypoxia-inducible factor 1 alpha (HIF-1 alpha) protected hearts against induced ischemia, hypothesizing that gene delivery into skeletal muscle may lead to secretion of proteins with actions elsewhere. Murine quadriceps muscles were transfected with DNA encoding for human HIF-1 alpha, which resulted in a local, but lasting expression (mRNA and protein, where the latter had nuclear localization). Subjection of isolated hearts to global ischemia and reperfusion 1, 4, and 8 weeks after gene delivery resulted in infarct size reduction (p < 0.05). Supporting that this was due to paracrine effects, HL-1 cells treated with conditioned media from cells transfected with HIF-1 alpha or serum from HIF-1 alpha-treated mice were protected against H(2)O(2)-induced cell death (p < 0.05, respectively). The latter protection was reduced when a heme oxygenase activity blocker was used. Taqman low-density array of 47 HIF-1 alpha-regulated genes at the treatment site showed nine specific upregulations (p < 0.05). Of the corresponding proteins, PDGF-B and adrenomedullin were upregulated in the heart. HIF-1 alpha treatment induced an increased vascularization of the heart and skeletal muscle. In conclusion, remote delivery of DNA for HIF-1 alpha was cardioprotective, represented by consistent infarct size reduction, which may be due to release of paracrine factors from the transfected muscle.

Double oxygen-sensing vector system for robust hypoxia/ischemia-regulated gene induction in cardiac muscle in vitro and in vivo

High-fidelity genetically encoded bio-sensors that respond to changes in cellular environmental milieu in disease offer great potential in a range of patho-physiological settings. Here a unique hypoxia-regulated vector-based system with double oxygen-sensing transcriptional elements was developed for rapid and robust hypoxia-regulated gene expression in the heart. Hypoxia-responsive cis elements were used in tandem with a single proline-modified oxygen-dependent degradation (ODD) domain of hypoxia-inducible factor-1alpha to form a double oxygen-sensing vector system (DOSVS). In adult cardiac myocytes in vitro, the DOSVS demonstrated a low background expression not different from baseline control in normoxia, and with 100% efficiency, robust, 1,000-fold induction upon hypoxia. In the heart in vivo, hypoxic and ischemic challenges elicited rapid 700-fold induction in living animals, exceeding that obtained by a high-fidelity constitutive cytomegalovirus (CMV) viral promoter. DOSVS also showed high temporal resolution in the heart in response to cyclical bouts of hypoxia in vivo. We propose that DOSVS will be valuable for a range of applications, including bio-sensing and therapeutic gene expression in the heart and other organ systems that are confronted by chronic or episodic hypoxic/ischemic stresses in vivo.

Constitutively active HIF-1alpha improves perfusion and arterial remodeling in an endovascular model of limb ischemia

OBJECTIVE

Hypoxia-inducible factor 1 (HIF-1) regulates the expression of angiogenic growth factors. We analyzed the effect of intramuscular (i.m.) delivery of AdCA5, an adenovirus encoding a constitutively active form of the HIF-1alpha subunit, in a novel model of limb ischemia.

METHODS

AdCa5 or AdLacZ (6 x 10(8) pfu) was injected into male New Zealand White rabbits that were untreated or subjected to occlusion of the left superficial femoral artery by endovascular coils. Expression of mRNAs was quantified 1, 3, and 7 days after adenovirus injection into rabbits without occlusion. Calf blood pressure (BP), angiography, and immunohistochemical analyses were performed 14 days after arterial occlusion and adenovirus injection.

RESULTS

AdCA5 increased the expression of HIF-1alpha, monocyte chemotactic protein-1, placental growth factor, platelet-derived growth factor B, stromal-derived factor 1alpha, and vascular endothelial growth factor (VEGF) mRNA as well as HIF-1alpha and VEGF protein. On day 14, AdCA5-injected limbs showed improved calf BP ratios (0.89+/-0.13 vs. 0.51+/-0.05, p=0.02), angiographic perfusion scores (3.50+/-0.56 vs. 8.33+/-1.31, p=0.007), and distal deep femoral artery diameter ratio (1.84+/-0.25 vs. 0.93+/-0.22, p=0.02) relative to those receiving AdLacZ. The capillary/myocyte ratio (0.93+/-0.03 vs. 0.78+/-0.06, p=0.04) and arterial luminal area (0.32+/-0.05 mm2 vs. 0.21+/-0.03 mm2, p=0.04) were significantly increased in the AdCA5 group.

CONCLUSION

In a model that resembles atherosclerotic obstruction of peripheral arteries in patients, the i.m. administration of AdCA5 promoted arteriogenic and angiogenic responses.

[Antisense hypoxia inducible factor-1alpha and B7-1 combination gene therapy for mouse lymphoma]

OBJECTIVE

To investigate the synergistic effects of antisense HIF-1alpha gene therapy combined with B7-1-mediated immunotherapy on cancer treatment.

METHODS

Antisense HIF-1alpha and B7-1 expression vector were constructed. Lymphoma cells EL-4 were injected subcutaneously into C57BL/6 mice and transplanted lymphomas were established. The mice received either antisense HIF-1alpha, B7-1, or a combinational agent, complexed with DOTAP cationic liposomes. The tumor growth in the mice was monitored. Expression of HIF-1alpha, B7-1 and VEGF were detected by immunohistochemistry and Western blotting. The tumor blood vessels were immunostained with CD31- antibodies and the tumor vascular density was assessed by light microscopy.

RESULTS

Gene transfer of plasmid expressing the encoded antisense HIF-1alpha inhibited VEGF expression and reduced vascular density in the tumors, eradicated tumors in diameter smaller than 0.1 cm and only retarded the growth of larger tumors. Whereas combination of antisense HIF-1alpha gene therapy and B7-1 immunotherapy eradicated all tumors in diameter of 0.4 cm.

CONCLUSION

Antisense HIF-1alpha blocks tumor hypoxia pathway by downregulating VEGF expression, reduction of vascular density and enhances B7-1-mediated immunotherapy. Strategies that target HIF-1 may have therapeutic potential in cancer treatment and are worthy of further studying.