How to overcome (and exploit) tumor hypoxia for targeted gene therapy

Leveraging hypoxia in triple-negative breast cancer as a promising treatment strategy

Current treatment strategies for triple-negative breast cancer (TNBC) are based upon conventional chemotherapy, immunotherapy, or a combination of both. The treatment regimen for chemotherapy is often a combination of two or more drugs, either dose dense or low dose for synergy. Anthracyclines, alkylating agents, antimicrotubule agents, and antimetabolites for early-stage TNBC; and antimetabolites, non-taxane microtubule inhibitors, and cross-linker platinums for late-stage TNBC are usually administered in the clinical setting. Newer options for patients with advanced TNBC, such as poly (ADP-ribose) polymerase (PARP) inhibitors and immune checkpoint inhibitors, have recently emerged for cases where surgery is not a viable option and the disease has metastasized. This review outlines the current trends in hypoxia-inspired treatment strategies for TNBC with a focus on clinical trials.

Clinical Efficacy of ONC201 in H3K27M-Mutant Diffuse Midline Gliomas Is Driven by Disruption of Integrated Metabolic and Epigenetic Pathways

Patients with H3K27M-mutant diffuse midline glioma (DMG) have no proven effective therapies. ONC201 has recently demonstrated efficacy in these patients, but the mechanism behind this finding remains unknown. We assessed clinical outcomes, tumor sequencing, and tissue/cerebrospinal fluid (CSF) correlate samples from patients treated in two completed multisite clinical studies. Patients treated with ONC201 following initial radiation but prior to recurrence demonstrated a median overall survival of 21.7 months, whereas those treated after recurrence had a median overall survival of 9.3 months. Radiographic response was associated with increased expression of key tricarboxylic acid cycle-related genes in baseline tumor sequencing. ONC201 treatment increased 2-hydroxyglutarate levels in cultured H3K27M-DMG cells and patient CSF samples. This corresponded with increases in repressive H3K27me3 in vitro and in human tumors accompanied by epigenetic downregulation of cell cycle regulation and neuroglial differentiation genes. Overall, ONC201 demonstrates efficacy in H3K27M-DMG by disrupting integrated metabolic and epigenetic pathways and reversing pathognomonic H3K27me3 reduction.

SIGNIFICANCE

The clinical, radiographic, and molecular analyses included in this study demonstrate the efficacy of ONC201 in H3K27M-mutant DMG and support ONC201 as the first monotherapy to improve outcomes in H3K27M-mutant DMG beyond radiation. Mechanistically, ONC201 disrupts integrated metabolic and epigenetic pathways and reverses pathognomonic H3K27me3 reduction. This article is featured in Selected Articles from This Issue, p. 2293.

Applications of tissue-specific and cancer-selective gene promoters for cancer diagnosis and therapy

Current treatment of solid tumors with standard of care chemotherapies, radiation therapy and/or immunotherapies are often limited by severe adverse toxic effects, resulting in a narrow therapeutic index. Cancer gene therapy represents a targeted approach that in principle could significantly reduce undesirable side effects in normal tissues while significantly inhibiting tumor growth and progression. To be effective, this strategy requires a clear understanding of the molecular biology of cancer development and evolution and developing biological vectors that can serve as vehicles to target cancer cells. The advent and fine tuning of omics technologies that permit the collective and spatial recognition of genes (genomics), mRNAs (transcriptomics), proteins (proteomics), metabolites (metabolomics), epiomics (epigenomics, epitranscriptomics, and epiproteomics), and their interactomics in defined complex biological samples provide a roadmap for identifying crucial targets of relevance to the cancer paradigm. Combining these strategies with identified genetic elements that control target gene expression uncovers significant opportunities for developing guided gene-based therapeutics for cancer. The purpose of this review is to overview the current state and potential limitations in developing gene promoter-directed targeted expression of key genes and highlights their potential applications in cancer gene therapy.

AKT, a Key Transmitter of HIF-1α and AR Signaling Pathways, Has a Critical Role in the Apigetrin-Mediated Anti-Cancer Effects in Prostate Cancer Cells

Apigetrin is a flavonoid glycoside phytochemical that is derived from various herbs and exhibits several beneficial biological activities, including anti-oxidant, anti-inflammatory, anti-obesity, and anti-cancer effects. In the present study, we elucidated the anti-cancer effect and targeting mechanism of apigetrin in LNCaP and PC-3 cells through various experiments, including cell viability by CELLOMAX^TM Viability Assay kit, cell migration by scratch wound assays, and 2D-and 3D- cell growth assay. Apigetrin inhibited the viability, migration, proliferation, and growth of cells in long-term 2D- and 3D- cultures cell growth. A high dose of apigetrin induced apoptosis, as evidenced by increased cleavage of poly ADP-ribose polymerase (PARP) and caspase-3 (c-cas3) in both LNCaP and PC-3 cells. Furthermore, apigetrin inhibited AR, PSA, HIF-1α, and VEGF expression in LNCaP and PC-3 cells. Apigetrin also suppressed the hypoxia-induced HIF-1α expression in these cells. Furthermore, apigetrin reduced hypoxia-induced VEGF secretion in the culture medium and inhibited hypoxia-induced tube formation of HUVECs. Silencing of AKT revealed that the anti-cancer activity of apigetrin is mediated via AKT. Thus, our data suggest that apigetrin exerts anti-cancer effects by inhibiting AKT, a central key of HIF-1α and AR signaling, in early-and late-stage prostate cancer cells.

Tumor Microenvironment Features and Chemoresistance in Pancreatic Ductal Adenocarcinoma: Insights into Targeting Physicochemical Barriers and Metabolism as Therapeutic Approaches

Currently, the median overall survival of PDAC patients rarely exceeds 1 year and has an overall 5-year survival rate of about 9%. These numbers are anticipated to worsen in the future due to the lack of understanding of the factors involved in its strong chemoresistance. Chemotherapy remains the only treatment option for most PDAC patients; however, the available therapeutic strategies are insufficient. The factors involved in chemoresistance include the development of a desmoplastic stroma which reprograms cellular metabolism, and both contribute to an impaired response to therapy. PDAC stroma is composed of immune cells, endothelial cells, and cancer-associated fibroblasts embedded in a prominent, dense extracellular matrix associated with areas of hypoxia and acidic extracellular pH. While multiple gene mutations are involved in PDAC initiation, this desmoplastic stroma plays an important role in driving progression, metastasis, and chemoresistance. Elucidating the mechanisms underlying PDAC resistance are a prerequisite for designing novel approaches to increase patient survival. In this review, we provide an overview of the stromal features and how they contribute to the chemoresistance in PDAC treatment. By highlighting new paradigms in the role of the stromal compartment in PDAC therapy, we hope to stimulate new concepts aimed at improving patient outcomes.

Targeting Drug Chemo-Resistance in Cancer Using Natural Products

Cancer is one of the leading causes of death globally. The development of drug resistance is the main contributor to cancer-related mortality. Cancer cells exploit multiple mechanisms to reduce the therapeutic effects of anticancer drugs, thereby causing chemotherapy failure. Natural products are accessible, inexpensive, and less toxic sources of chemotherapeutic agents. Additionally, they have multiple mechanisms of action to inhibit various targets involved in the development of drug resistance. In this review, we have summarized the basic research and clinical applications of natural products as possible inhibitors for drug resistance in cancer. The molecular targets and the mechanisms of action of each natural product are also explained. Diverse drug resistance biomarkers were sensitive to natural products. P-glycoprotein and breast cancer resistance protein can be targeted by a large number of natural products. On the other hand, protein kinase C and topoisomerases were less sensitive to most of the studied natural products. The studies discussed in this review will provide a solid ground for scientists to explore the possible use of natural products in combination anticancer therapies to overcome drug resistance by targeting multiple drug resistance mechanisms.

Glutathione-Activated NO-/ROS-Generation Nanoparticles to Modulate the Tumor Hypoxic Microenvironment for Enhancing the Effect of HIFU-Combined Chemotherapy

The combination of high-intensity focused ultrasound (HIFU) and chemotherapy has promising potential in the synergistic treatment of various types of solid tumors. However, the clinical efficacy of HIFU in combination chemotherapy is often impeded by the pre-existing hypoxia tumor microenvironment-induced multidrug resistance (MDR). Therefore, it is imperative for HIFU combined with chemotherapy to overcome MDR by improving the tumor hypoxic microenvironment. Hence, we developed highly stable nanoparticles (P@BDOX/β-lapachone-NO-NPs) with intracellular nitric oxide (NO)- and reactive oxygen species (ROS)-generating capabilities at the tumor site to relieve the hypoxic tumor microenvironment in solid tumors. Doxorubicin prodrug (boronate-DOX, BDOX) and β-lapachone were concurrently loaded onto actively targeted pH (low) insertion peptides (pHLIPs)-poly(ethylene glycol) and nitrated gluconic acid copolymers. Our results showed that the ability of P@BDOX/β-lapachone-NO-NPs to generate NO and ROS simultaneously is vital for the sensitization of hypoxic solid tumors for chemotherapy, as evidenced by the suppression of tumor cells and tissues (in vitro and in the nude mice model). Thus, this combined therapy holds considerable potential in the management of hypoxic solid tumors.

Correlation between tumor glucose metabolism and multiparametric functional MRI (IVIM and R2*) metrics in cervical carcinoma: Evidence from integrated 18 F-FDG PET/MR

BACKGROUND

Multiparameter, multimodality ¹⁸ F-FDG PET/MRI holds great potential for the diagnosis of cervical cancer based on the correlation between tumor glucose metabolism and imaging parameters.

PURPOSE

To characterize the heterogeneity of tumor glucose metabolism by evaluating the correlation between ¹⁸ F-FDG uptake parameters and multiparametric functional MRI metrics in cervical carcinoma.

STUDY TYPE

Retrospective.

POPULATION

Fifty-four patients with cervical carcinoma.

FIELD STRENGTH/SEQUENCE

Hybrid PET/MR (3T), multi-b DWI, and R2* mapping.

ASSESSMENT

The maximum and mean standardized uptake values (SUV_max and SUV_mean , respectively) from PET and functional MRI metrics (D, D*, f, and R2*) were obtained. Cervical carcinoma tissues also underwent HIF-1α, VEGF, and GLUT-1 immunohistochemical staining.

STATISTICAL TESTS

Single-factor Spearman rank and Pearson correlation analysis and multiple linear regression (MLR) analysis were applied.

RESULTS

R2*, D, and f have different degrees of correlation (moderate, weak, moderately strong correlation, respectively) with SUV_max and SUV_mean (r = 0.530 and 0.527, and P < 0.001 for R2*; r = -0.292 and -0.291, and P < 0.05 for D; r = 0.539 and 0.520, and P < 0.001 for f, respectively). Immunohistochemical staining showed that HIF-1α expression has a moderate degree of correlation with R2* (r = 0.491; P < 0.001); GLUT-1 expression was significantly correlated with SUV_max and SUV_mean (r = 0.633 and 0.622; P < 0.001), and VEGF expression had a moderately strong correlation with f (r = 0.457; P = 0.001). If SUV_max is the dependent variable, MLR yields an R-squared value after adjustment (adjusted R-squared) = 0.358, and F = 10.833 (P < 0.001), and the fitting linear equation is Y (SUV_max ) = 9.184 + 0.161X1 (R2*)+50.343X2 (f)-4.780 (D). Otherwise, MLR yields the adjusted R-squared = 0.342, and F = 10.187 (P < 0.001), and the linear regression equation is Y (SUV_mean ) = 5.925 + 0.102X1 (R2*)+28.029X2 (f)-2.907X3 (D).

DATA CONCLUSION

The functional MRI sequence parameters R2*, f, and D can provide information on the hypoxic condition, blood perfusion, and molecular diffusion of the tumor. ¹⁸ F-FDG PET/MR multi-imaging technique can be adopted to evaluate the heterogeneity of glucose metabolism in cervical carcinoma.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;49:1704-1712.

Effect of propofol on androgen receptor activity in prostate cancer cells

Androgen receptor is a nuclear receptor and transcription factor activated by androgenic hormones. Androgen receptor activity plays a pivotal role in the development and progression of prostate cancer. Although accumulating evidence suggests that general anesthetics, including opioids, affect cancer cell growth and impact patient prognosis, the effect of those drugs on androgen receptor in prostate cancer is not clear. The purpose of this study was to investigate the effect of the general anesthetic propofol on androgen receptor activity in prostate cancer cells. An androgen-dependent human prostate cancer cell line (LNCaP) was stimulated with dihydrotestosterone (DHT) and exposed to propofol. The induction of androgen receptor target genes was investigated using real-time reverse transcription polymerase chain reaction, and androgen receptor protein levels and localization patterns were analyzed using immunoblotting and immunofluorescence assays. The effect of propofol on the proliferation of LNCaP cells was analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Propofol significantly inhibited DHT-induced expression of androgen receptor target genes in a dose- and time-dependent manner, and immunoblotting and immunofluorescence assays indicated that propofol suppressed nuclear levels of androgen receptor proteins. Exposure to propofol for 24h suppressed the proliferation of LNCaP cells, whereas 4h of exposure did not exert significant effects. Together, our results indicate that propofol suppresses nuclear androgen receptor protein levels, and inhibits androgen receptor transcriptional activity and proliferation in LNCaP cells.

Anti-cancer effect of pristimerin by inhibition of HIF-1α involves the SPHK-1 pathway in hypoxic prostate cancer cells

BACKGROUND

Hypoxia is a typical character of locally advanced solid tumours. The transcription factor hypoxia-inducible factor 1α (HIF-1α) is the main regulator under the hypoxic environment. HIF-1α regulates various genes to enhance tumour progression, angiogenesis, and metastasis. Sphingosine kinase 1 (SPHK-1) is a modulator of HIF-1α.

METHODS

To investigate the molecular mechanisms of pristimerin in association with SPHK-1 pathways in hypoxic PC-3 cancer cells. Vascular endothelial growth factor (VEGF) production, cell cycles, and SPHK-1 activity were measured, and western blotting, an MTT assay, and an RNA interference assay were performed.

RESULTS

Pristimerin inhibited HIF-1α accumulation in a concentration- and-time-dependent manner in hypoxic PC-3 cells. Pristimerin suppressed the expression of HIF-1α by inhibiting SPHK-1. Moreover, inhibiting SPHK-1 with a sphingosine kinase inhibitor enhanced the suppression of HIF-1α, phosphorylation AKT, and glycogen synthase kinase-3β (GSK-3β) by pristimerin under hypoxia. Furthermore, a reactive oxygen species (ROS) scavenger enhanced the inhibition of HIF-1α and SPHK-1 by pristimerin.

CONCLUSION

Taken together, these findings suggest that pristimerin can exert an anti-cancer activity by inhibiting HIF-1α through the SPHK-1 pathway.

A phase I clinical study to evaluate safety of orally administered, genetically engineered Salmonella enterica serovar Typhimurium for canine osteosarcoma

We conducted a prospective phase I study to evaluate safety of an orally administered Salmonella encoding IL‐2 (SalpIL2) in combination with amputation and adjuvant doxorubicin for canine appendicular osteosarcoma. Efficacy was assessed as a secondary measure. The first dose of SalpIL2 was administered to 19 dogs on Day 0; amputation was done after 10 days with chemotherapy following 2 weeks later. SalpIL2 was administered concurrent with chemotherapy, for a total of five doses of doxorubicin and six doses of SalpIL2. There were six reportable events prior to chemotherapy, but none appeared due to SalpIL2. Dogs receiving SalpIL2 had significantly longer disease‐free interval (DFI) than a comparison group of dogs treated with doxorubicin alone. Dogs treated using lower doses of SalpIL2 also had longer DFI than dogs treated using the highest SalpIL2 dose. The data indicate that SalpIL2 is safe and well tolerated, which supports additional testing to establish the potential for SalpIL2 as a novel form of adjuvant therapy for dogs with osteosarcoma.

Progress and problems with the use of suicide genes for targeted cancer therapy

Among various gene therapy methods for cancer, suicide gene therapy attracts a special attention because it allows selective conversion of non-toxic compounds into cytotoxic drugs inside cancer cells. As a result, therapeutic index can be increased significantly by introducing high concentrations of cytotoxic molecules to the tumor environment while minimizing impact on normal tissues. Despite significant success at the preclinical level, no cancer suicide gene therapy protocol has delivered the desirable clinical significance yet. This review gives a critical look at the six main enzyme/prodrug systems that are used in suicide gene therapy of cancer and familiarizes readers with the state-of-the-art research and practices in this field. For each enzyme/prodrug system, the mechanisms of action, protein engineering strategies to enhance enzyme stability/affinity and chemical modification techniques to increase prodrug kinetics and potency are discussed. In each category, major clinical trials that have been performed in the past decade with each enzyme/prodrug system are discussed to highlight the progress to date. Finally, shortcomings are underlined and areas that need improvement in order to produce clinical significance are delineated.

Inhibitory action of pristimerin on hypoxia‑mediated metastasis involves stem cell characteristics and EMT in PC-3 prostate cancer cells

The aim of the present study was to investigate whether pristimerin affects the bone metastasis, stem cell characteristics and epithelial-mesenchymal transition (EMT) of prostate cancer (PCa) PC-3 cells subjected to hypoxia. The PC-3 cells were cultured under hypoxia or normoxia for 48 h and were then treated with increasing concentrations of pristimerin from 0 to 0.8 µmol/l, under normoxia. Hypoxia‑inducible factor-1α (HIF-1α) was detected by western blotting. Proliferation was assessed with the CCK-8 assay. Transwell invasion assay was used to analyze the potency of invasion. Stem cell characteristics were detected by sphere formation, colony formation assay and western blotting, including CD44, KLF4, OCT4 and AGO2, which are stem cell characteristic-related markers. EMT was confirmed by the expression changes of EMT-related markers, including N-cadherin, fibronectin, vimentin and ZEB1, which were evaluated by western blotting. The addition of pristimerin to the medium reduced the hypoxia-induced PC-3 cell proliferation in a dose-dependent manner. Pristimerin effectively inhibited hypoxia‑induced invasion of the PCa cells in vitro. Moreover, the treatment of cells with pristimerin induced the reversal of hypoxia-induced stem cell characteristics and EMT, which was confirmed by sphere formation, colony formation assay and the expression changes of CSC- and EMT-related markers. The reversal of hypoxia‑induced stem cell characteristics and EMT in the PCa cells by low-dose pristimerin was dose‑dependent. These results showed that treatment with pristimerin may be a potential strategy for the suppression of hypoxia-induced metastasis through the reversal of hypoxia-induced stem cell characteristics and EMT in cancer cells, which justifies the potential use of pristimerin as a practical chemopreventive approach for patients with PCa.

Progress in aptamer-mediated drug delivery vehicles for cancer targeting and its implications in addressing chemotherapeutic challenges

Aptamers are novel oligonucleotides with flexible three-dimensional configurations that recognize and bind to their cognate targets, including tumor surface receptors, in a high-affinity and highly specific manner. Because of their unique intrinsic properties, a variety of aptamer-mediated nanovehicles have been developed to directionally transport anti-cancer drugs to tumor sites to minimize systemic cytotoxicity and to enhance permeation by these tumoricidal agents. Despite advances in the selection and synthesis of aptamers and in the conjugation and self-assembly of nanotechnologies, current chemotherapy and drug delivery systems face great challenges. These challenges are due to the limitations of aptamers and vehicles and because of complicated tumor mechanisms, including heterogeneity, anti-cancer drug resistance, and hypoxia-induced aberrances. In this review, we will summarize current approaches utilizing tumor surface hallmarks and aptamers and their roles and mechanisms in therapeutic nanovehicles targeting tumors. Delivery forms include nanoparticles, nanotubes, nanogels, aptamer-drug conjugates, and novel molecular trains. Moreover, the obstacles posed by the aforementioned issues will be highlighted, and possible solutions will be acknowledged. Furthermore, future perspectives will be presented, including cutting-edge integration with RNA interference nanotechnology and personalized chemotherapy, which will facilitate innovative approaches to aptamer-based therapeutics.

Hypoxia-targeted triple suicide gene therapy radiosensitizes human colorectal cancer cells

The hypoxic microenvironment, an important feature of human solid tumors but absent in normal tissue, may provide an opportunity for cancer-specific gene therapy. The purpose of the present study was to investigate whether hypoxia-driven triple suicide gene TK/CD/UPRT expression enhances cytotoxicity to ganciclovir (GCV) and 5-fluorocytosine (5-FC), and sensitizes human colorectal cancer to radiation in vitro and in vivo. Stable transfectant of human colorectal HCT8 cells was established which expressed hypoxia-inducible vectors (HRE-TK/eGFP and HRE-CD/UPRT/mDsRed). Hypoxia-induced expression/function of TK, CD and UPRT was verified by western blot analysis, flow cytometry, fluorescent microscopy and cytotoxicity assay of GCV and 5-FC. Significant radiosensitization effects were detected after 5-FC and GCV treatments under hypoxic conditions. In the tumor xenografts, the distribution of TK/eGFP and CD/UPRT/mDsRed expression visualized with fluorescence microscopy was co-localized with the hypoxia marker pimonidazole positive staining cells. Furthermore, administration of 5-FC and GCV in mice in combination with local irradiation resulted in tumor regression, as compared with prodrug or radiation treatments alone. Our data suggest that the hypoxia-inducible TK/GCV+CDUPRT/5-FC triple suicide gene therapy may have the ability to specifically target hypoxic cancer cells and significantly improve the tumor control in combination with radiotherapy.

Metabolomic Dynamic Analysis of Hypoxia in MDA-MB-231 and the Comparison with Inferred Metabolites from Transcriptomics Data

Hypoxia affects the tumor microenvironment and is considered important to metastasis progression and therapy resistance. Thus far, the majority of global analyses of tumor hypoxia responses have been limited to just a single omics level. Combining multiple omics data can broaden our understanding of tumor hypoxia. Here, we investigate the temporal change of the metabolite composition with gene expression data from literature to provide a more comprehensive insight into the system level in response to hypoxia. Nuclear magnetic resonance spectroscopy was used to perform metabolomic profiling on the MDA-MB-231 breast cancer cell line under hypoxic conditions. Multivariate statistical analysis revealed that the metabolic difference between hypoxia and normoxia was similar over 24 h, but became distinct over 48 h. Time dependent microarray data from the same cell line in the literature displayed different gene expressions under hypoxic and normoxic conditions mostly at 12 h or earlier. The direct metabolomic profiles show a large overlap with theoretical metabolic profiles deduced from previous transcriptomic studies. Consistent pathways are glycolysis/gluconeogenesis, pyruvate, purine and arginine and proline metabolism. Ten metabolic pathways revealed by metabolomics were not covered by the downstream of the known transcriptomic profiles, suggesting new metabolic phenotypes. These results confirm previous transcriptomics understanding and expand the knowledge from existing models on correlation and co-regulation between transcriptomic and metabolomics profiles, which demonstrates the power of integrated omics analysis.

Melatonin suppresses tumor progression by reducing angiogenesis stimulated by HIF-1 in a mouse tumor model

The sustained expansion of a tumor mass requires new blood vessel formation to provide rapidly proliferating tumor cells with an adequate supply of oxygen and nutrients. Hypoxia-inducible factor-1 (HIF-1) plays an essential role in tumor angiogenesis and growth by regulating the transcription of genes in response to hypoxic stress. This study was designed to investigate the effects of melatonin on tumor growth and angiogenesis, as well as the mechanism underlying the antitumor activities of melatonin. In this study, we show that the administration of melatonin inhibits tumor growth and blocks tumor angiogenesis in mice. Moreover, melatonin diminished the expression of the HIF-1α protein within the tumor mass during tumorigenesis. Our findings suggest that melatonin is a promising anti-angiogenic therapeutic agent targeting HIF-1α in cancer. Considering that HIF-1α is overexpressed in a majority of human cancers, melatonin could offer a potent therapeutic agent for cancer.

Adenovirus-mediated transcriptional targeting of colorectal cancer and effects on treatment-resistant hypoxic cells

BACKGROUND

Colorectal cancer is the second leading cause of cancer-related mortality and frequently presents with locally advanced or metastatic disease. Adenovirus (Ad) vectors are important gene delivery agents because they offer efficient and broad tissue transduceability. However, their ability to penetrate through multicell layers in colorectal cancers and maintain expression in colon tumor-related hypoxic conditions has yet to be analyzed. Furthermore, their broad tissue tropism presents safety concerns.

MATERIALS AND METHODS

An ex vivo cultured patient tumor sample model was employed to examine Ad transduction of colorectal tumors.

RESULTS

Results obtained from Ad delivery of the firefly luciferase (FLuc) reporter gene indicated that colon tumor tissue was more amenable to Ad transduction than other tumor histologic types examined (breast and ovary). Ad transduction levels were significantly higher than a range of viral and nonviral methods examined in patient colon tissue. Control of transgene expression using the CXC chemokine receptor 4 (CXCR4) promoter was examined as a strategy to confine expression to tumor cells. An Ad construct carrying FLuc under the control of the human CXCR4 promoter demonstrated low reporter gene expression compared with the ubiquitously expressing cytomegalovirus promoter in normal colon and liver tissue while providing high expression in tumors, demonstrating a 'tumour-on' and 'normal-off' phenotype in patient tissue. The effects of changing hypoxia on Ad-related transgene expression were examined in an in vitro model of hypoxic conditions relevant to clinical colorectal tumors. Reporter gene expression varied depending on the level of hypoxia, with significantly reduced levels observed with prolonged hypoxia. However, transgene expression was robust in the cycling hypoxic conditions relevant to colorectal tumors.

CONCLUSION

This study provides novel, clinically relevant data demonstrating the potential for efficient gene delivery to colorectal tumors using Ad.

The synergistic therapeutic effect of temozolomide and hyperbaric oxygen on glioma U251 cell lines is accompanied by alterations in vascular endothelial growth factor and multidrug resistance-associated protein-1 levels

OBJECTIVE

Temozolomide (TMZ) is an oral alkylating agent widely used in the treatment of refractory glioma. Its efficacy is limited, however, by poor cancer cell penetration and drug resistance. The present study, therefore, aimed to investigate whether hyperbaric oxygen (HBO) may facilitate drug delivery and enhance the anticancer effect of TMZ.

METHODS

Cultured glioma U251 cells were treated with HBO, TMZ, or TMZ + HBO, or were untreated (controls). Rates of growth inhibition, cell death and apoptosis were investigated using the 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, propidium iodide staining and flow cytometry, respectively. Protein levels of vascular endothelial growth factor (VEGF) and multidrug resistance-associated protein-1 (MRP-1) were evaluated by enzyme-linked immunosorbent assay.

RESULTS

Compared with TMZ or HBO alone, combined treatment with both therapies synergistically inhibited growth and induced apoptosis and death of cultured glioma U251 cells, which was accompanied by a significant decrease in levels of VEGF and MRP-1.

CONCLUSIONS

TMZ and HBO synergistically induced the apoptosis of glioma cells, possibly through reduced vascularization and inhibition of drug resistance. The combination of TMZ and HBO may be a powerful treatment for malignant glioma.

Anti-proliferation and anti-invasion effects of diosgenin on gastric cancer BGC-823 cells with HIF-1α shRNAs

Drug resistance is a major factor for the limited efficacy of chemotherapy in gastric cancer treatment. Hypoxia-inducible factor-1α (HIF-1α), a central transcriptional factor in hypoxia, is suggested to participate in the resistance. Here, we identified a hypoxia-mimic (cobalt chloride) sensitive gastric cell line BGC-823 to explore whether diosgenin, an aglycone of steroidal saponins, can inhibit cancer cell invasion and survival of solid tumor in a hypoxic mimic microenvironment. We have shown that diosgenin is a potent candidate for decreasing the ability of invasion and survival in cobalt chloride treated BGC-823 cells. In addition, when combined with HIF-1α specific short hairpin RNA (shRNA), diosgenin can inhibit BGC-823 cells more effectively. The anti-invasion role of diosgenin may be related to E-cadherin, integrinα5 and integrin β6. These results suggest that diosgenin may be a useful compound in controlling gastric cancer cells in hypoxia condition, especially when combined with down-regulated HIF-1α.

Radiolabeled Cu-ATSM as a novel indicator of overreduced intracellular state due to mitochondrial dysfunction: studies with mitochondrial DNA-less ρ0 cells and cybrids carrying MELAS mitochondrial DNA mutation

OBJECTIVES

Radiolabeled Cu-diacetyl-bis (N(4)-methylthiosemicarbazone) (*Cu-ATSM), including (60/62/64)Cu-ATSM, is a potential imaging agent of hypoxic tumors for positron emission tomography (PET). We have reported that *Cu-ATSM is trapped in tumor cells under intracellular overreduced states, e.g., hypoxia. Here we evaluated *Cu-ATSM as an indicator of intracellular overreduced states in mitochondrial disorders using cell lines with mitochondrial dysfunction.

METHODS

Mitochondrial DNA-less ρ(0)206 cells; the parental 143B human osteosarcoma cells; the cybrids carrying mutated mitochondria from a patient of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) (2SD); and that carrying wild-type one (2SA) were used. Cells were treated under normoxia or hypoxia, and (64)Cu-ATSM uptake was examined to compare it with levels of biological reductant NADH and NADPH.

RESULTS

ρ(0)206 cells showed higher (64)Cu-ATSM uptake than control 143B cells under normoxia, whereas (64)Cu-ATSM uptake was not significantly increased under hypoxia in ρ(0)206 cells. Additionally, (64)Cu-ATSM uptake showed correlate change to the NADH and NADPH levels, but not oxygenic conditions. 2SD cells showed increased (64)Cu-ATSM uptake under normoxia as compared with the control 2SA, and (64)Cu-ATSM uptake followed NADH and NADPH levels, but not oxygenic conditions.

CONCLUSIONS

(64)Cu-ATSM accumulated in cells with overreduced states due to mitochondrial dysfunction, even under normoxia. We recently reported that (62)Cu-ATSM-PET can visualize stroke-like episodes maintaining oxygen supply in MELAS patients. Taken together, our data indicate that *Cu-ATSM uptake reflects overreduced intracellular states, despite oxygenic conditions; thus, *Cu-ATSM would be a promising marker of intracellular overreduced states for disorders with mitochondrial dysfunction, such as MELAS, Parkinson's disease and Alzheimer's disease.

Adenovirus-mediated hypoxia-targeted gene therapy using HSV thymidine kinase and bacterial nitroreductase prodrug-activating genes in vitro and in vivo

Hypoxia is an important factor in tumor growth. It is associated with resistance to conventional anticancer treatments. Gene therapy targeting hypoxic tumor cells therefore has the potential to enhance the efficacy of treatment of solid tumors. Transfection of a panel of tumor cell lines with plasmid constructs containing hypoxia-responsive promoter elements from the genes, vascular endothelial growth factor (VEGF) and erythropoietin, linked to the minimal cytomegalovirus (mCMV) or minimal interleukin-2 (mIL-2) promoters showed optimum hypoxia-inducible luciferase reporter gene expression with five repeats of VEGF hypoxic-response element linked to the mCMV promoter. Adenoviral vectors using this hypoxia-inducible promoter to drive therapeutic transgenes produced hypoxia-specific cell kill of HT1080 and HCT116 cells in the presence of prodrug with both herpes simplex virus thymidine kinase/ganciclovir and nitroreductase (NTR)/CB1954 prodrug-activating systems. Significant cytotoxic effects were also observed in patient-derived human ovarian cancer cells. The NTR/CB1954 system provided more readily controllable transgene expression and so was used for in vivo experiments of human HCT116 xenografts in nude mice. Subjects treated intratumorally with Ad-VEGFmCMV-NTR and intraperitoneal injection of CB1954 demonstrated a statistically significant reduction in tumor growth. Immunohistochemistry of treated xenografts showed a good correlation between transgene expression and hypoxic areas. Further investigation of these hypoxia-inducible adenoviral vectors, alone or in combination with existing modalities of cancer therapy, may aid in the future development of successful Gene-Directed Enzyme Prodrug Therapy systems, which are much needed for targeting solid tumors.

How can we overcome tumor hypoxia in radiation therapy?

Local recurrence and distant metastasis frequently occur after radiation therapy for cancer and can be fatal. Evidence obtained from radiochemical and radiobiological studies has revealed these problems to be caused, at least in part, by a tumor-specific microenvironment, hypoxia. Moreover, a transcription factor, hypoxia-inducible factor 1 (HIF-1), was identified as pivotal to hypoxia-mediated radioresistance. To overcome the problems, radiation oncologists have recently obtained powerful tools, such as "simultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT), which enables a booster dose of radiation to be delivered to small target fractions in a malignant tumor", "hypoxia-selective cytotoxins/drugs", and "HIF-1 inhibitors" etc. In order to fully exploit these innovative and interdisciplinary strategies in cancer therapy, it is critical to unveil the characteristics, intratumoral localization, and dynamics of hypoxia/HIF-1-active tumor cells during tumor growth and after radiation therapy. We have performed optical imaging experiments using tumor-bearing mice and revealed that the locations of HIF-1-active tumor cells changes dramatically as tumors grow. Moreover, HIF-1 activity changes markedly after radiation therapy. This review overviews 1) fundamental problems surrounding tumor hypoxia in current radiation therapy, 2) the function of HIF-1 in tumor radioresistance, 3) the dynamics of hypoxic tumor cells during tumor growth and after radiation therapy, and 4) how we should overcome the difficulties with radiation therapy using innovative interdisciplinary technologies.

Melatonin suppresses tumor angiogenesis by inhibiting HIF-1alpha stabilization under hypoxia

Angiogenesis is an important mediator of tumor progression. As tumors expand, diffusion distances from the existing vascular supply increases, resulting in hypoxia in the cancer cells. Sustained expansion of a tumor mass requires new blood vessel formation to provide rapidly proliferating tumor cells with an adequate supply of oxygen and nutrients. The key regulator of hypoxia-induced angiogenesis is the transcription factor known as hypoxia-inducible factor (HIF)-1. HIF-1alpha is stabilized by hypoxia-induced reactive oxygen species (ROS) and enhances the expression of several types of hypoxic genes, including that of the angiogenic activator known as vascular endothelial cell growth factor (VEGF). In this study, we found that melatonin, a small lipophilic molecule secreted primarily by the pineal gland, destabilizes hypoxia-induced HIF-1alpha protein levels in the HCT116 human colon cancer cell line. This destabilization of HIF-1alpha resulted from the antioxidant activity of melatonin against ROS induced by hypoxia. Moreover, under hypoxia, melatonin suppressed HIF-1 transcriptional activity, leading to a decrease in VEGF expression. Melatonin also blocked in vitro tube formation and invasion and migration of human umbilical vein endothelial cells induced by hypoxia-stimulated conditioned media of HCT116 cells. These findings suggest that melatonin could play a pivotal role in tumor suppression via inhibition of HIF-1-mediated angiogenesis.

Molecular imaging in clinical trials

Imaging of biological processes using specific molecular probes allows exploration of the mechanism of action and efficacy for new therapies. This molecular imaging has made use of modalities including single photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance imaging (MRI), and optical techniques. Molecular imaging can be used to explore many of the hallmarks of cancer biology, including angiogenesis, proliferation, tissue invasion, evasion of apoptosis, and self-sufficiency in growth signals. Since many of these aspects of cancer biology are in turn the targets of novel therapies in development, molecular imaging techniques have great potential to inform trials of these new agents. The high cost of clinical drug development mandates the optimisation of early phase trial design to maximise the collection of evidence for efficacy and proof of mechanism, endpoints which have, in a number of examples, already been provided by molecular imaging. The variety provided by novel chemistry, and the availability of isotopes with varying physical properties, particularly suits PET imaging as a functional modality for application in clinical trials.

The HIF-1-active microenvironment: an environmental target for cancer therapy

Solid tumors possess unique microenvironments that are exposed to chronic hypoxic conditions, so-called tumor hypoxia. Although more than half a century has passed since it was suggested that tumor hypoxia correlated with bad treatment outcomes and contributed to the recurrence of cancer, no fundamental solution to this problem has yet been found. Hypoxia-inducible factor HIF-1 is the main transcription factor that regulates the cellular response to hypoxia. It induces various genes, whose function is strongly associated with the malignant alteration of the entire tumor. The cellular changes induced by HIF-1 are extremely important therapeutic targets of cancer therapy, particularly in the therapy against refractory cancers. Therefore targeting strategies to overcome the HIF-1-active microenvironment are important for cancer therapy.

Hypoxia-mediated up-regulation of MGr1-Ag/37LRP in gastric cancers occurs via hypoxia-inducible-factor 1-dependent mechanism and contributes to drug resistance

Our previous study demonstrated hypoxia-inducible factor-1(HIF-1) could prompt multidrug resistance (MDR) phenotype and MGr1-Ag/37LRP, a novel drug-resistance protein was reported by our labortary, associated with multidrug resistance in gastric cancer. Given this association, we hypothesized that MGr1-Ag/37LRP contributed to HIF-1-dependent hypoxia-induced MDR phenotype. Initial experiments revealed that blocking MGr1-Ag/37LRP expression by siRNA in gastric cancer cells effectively reversed multidrug resistance phenotype induced by hypoxia. Subsequent analysis of MGr1-Ag/37LRP mRNA and protein in gastric cancer cells revealed a time-dependent manner increase with hypoxia. While the up-regulation of MGr1-Ag/37LRP was abolished by HIF-1 inhibition with siRNA. Studies using luciferase promoter constructs revealed a significant increase in activity in cells subject to hypoxia and such hypoxia inducibility was lost in cells co-transfected siRNA targeting HIF-1. Analysis of the MGr1-Ag/37LRP promoter revealed several potential binding sites for HIF-1. Electrophoretic mobility shift assay and chromatin immunoprecipitation demonstrated a functional HIF-1 binding site within MGr1-Ag/37LRP gene regulatory sequence located at -16 to -11 relative to the transcriptional initiation point. These observations demonstrate that MGr1-Ag/37LRP is actively engaged by hypoxia and represent a novel HIF-1 target. Such results suggest hypoxia-elicited MGr1-Ag/37LRP expression as a pathway for resistance of gastric cancer to chemotherapeutics.

Absence of GAPDH regulation in tumor-cells of different origin under hypoxic conditions in - vitro

Background

Gene expression studies related to cancer diagnosis and treatment are important. In order to conduct such experiment accurately, absolutely reliable housekeeping genes are essential to normalize cancer related gene expression. The most important characteristics of such genes are their presence in all cells and their expression levels remain relatively constant under different experimental conditions. However, no single gene of this group of genes manifests always stable expression levels under all experimental conditions. Incorrect choice of housekeeping genes leads to interpretation errors of experimental results including evaluation and quantification of pathological gene expression. Here, we examined (a) the degree of GAPDH expression regulation in Hep-1-6 mouse hepatoma and Hep-3-B and HepG2 human hepatocellular carcinoma cell lines as well as in human lung adenocarcinoma epithelial cell line (A-549) in addition to both HT-29, and HCT-116 colon cancer cell lines, under hypoxic conditions in vitro in comparison to other housekeeping genes like β-actin, serving as experimental loading controls, (b) the potential use of GAPDH as a target for tumor therapeutic approaches was comparatively examined in vitro on both protein and mRNA level, by western blot and semi quantitative RT-PCR, respectively.

Findings

No hypoxia-induced regulatory effect on GAPDH expression was observed in the cell lines studied in vitro that were; Hep-1-6 mouse hepatoma and Hep-3-B and HepG2 human hepatocellular carcinoma cell lines, Human lung adenocarcinoma epithelial cell line (A-549), both colon cancer cell lines HT-29, and HCT-116.

Conclusion

As it is the case for human hepatocellular carcinoma, mouse hepatoma, human colon cancer, and human lung adenocarcinoma, GAPDH represents an optimal choice of a housekeeping gene and/(or) loading control to determine the expression of hypoxia induced genes in tumors of different origin. The results confirm our previous findings in human glioblastoma that this gene is not an attractive target for tumor therapeutic approaches because of the lack of GAPDH regulation under hypoxia.

Efficacy of suicide gene therapy in hypoxic rat 9L glioma cells

Viral vector mediated suicide gene therapy (SGT) involving thymidine kinase (TK) or cytosine deaminase (CD) have considerable promise in the treatment of malignant brain tumors. An unresolved issue is to what extent tumor hypoxia influences the outcome of SGT since brain tumors characterized by regions of hypoxia have potentially reduced cellular metabolism and SGT's cytotoxicity is manifest through cellular metabolism. We studied in vitro and in vivo, the effect of hypoxia on the cytotoxicity of SGT in rat 9L glioma cells. Neither acute nor chronic hypoxia affected the cell killing of SGT by TK or CD. In vivo confirmation that SGT efficacy was not adversely affected by tumor hypoxia using the hypoxic cell marker pimonidazole was shown by the absence of a change in tumor hypoxia by SGT. These studies support the use of SGT utilizing either TK or CD gene strategies even when tumors are characterized by a hypoxic microenvironment.

Hypoxia-inducible factor-1 alpha contributes to hypoxia-induced chemoresistance in gastric cancer

Hypoxia induced drug resistance is a major obstacle in the development of effective cancer therapy. Our previous study revealed that hypoxia-inducible factor-1 (HIF-1), the major transcriptional factor significantly activated by hypoxia, was overexpressed in gastric vincristine-resistant cells SGC7901/vincristine (VCR) under normoxic conditions, which suggested that it was associated with drug resistance in gastric cancer cells. In the present study, a colony-forming assay revealed that hypoxia and forced HIF-1 alpha expression increased maximal -8.9-fold or -14.8-fold of IC(50) toward vincristine in gastric cancer cell lines SGC7901 and SGC7901/VCR, respectively (P < 0.01). Annexin-V/propidium iodide staining analysis revealed hypoxia or forced HIF-1 alpha expression reduced apoptosis by 24% or 18% in SGC7901 cells (P < 0.05). Flow cytometry analysis of intracellular adriamycin revealed that hypoxia and forced expression of HIF-1 alpha increased -1.79-fold or -2.36-fold of the adriamycin releasing index, respectively (P < 0.05). However, resistance acquisition subject to hypoxia in vitro and in vivo was suppressed by blocking HIF-1 alpha expression with siRNA. We further demonstrated that HIF-1 alpha overexpression showed a 1.85-fold increased expression of Bcl-2 and a 2.16-fold decreased expression of Bax, and also showed significantly induced expression of p-gp and MRP1, which indicated that HIF-1 alpha may confer hypoxia-induced drug resistance via inhibition of drug-induced apoptosis and decreases in intracellular drug accumulation.

GAPDH is not regulated in human glioblastoma under hypoxic conditions

Background

Gene expression studies related to cancer diagnosis and treatment are becoming more important. Housekeeping genes that are absolutely reliable are essential for these studies to normalize gene expression. An incorrect choice of housekeeping genes leads to interpretation errors of experimental results including evaluation and quantification of pathological gene expression. Here, we examined (a) the degree of regulation of GAPDH expression in human glioblastoma cells under hypoxic conditions in vitro in comparison to other housekeeping genes like β-actin, serving as experimental loading controls, (b) the potential use of GAPDH as a target for tumor therapeutic approaches and (c) differences in GAPDH expression between low-grade astrocytomas and glioblastomas, for which modest and severe hypoxia, respectively, have been previously demonstrated. GAPDH and β-actin expression was comparatively examined in vivo in human low-grade astrocytoma and glioblastoma on both protein and mRNA level, by Western blot and semiquantitative RT-PCR, respectively. Furthermore, the same proteins were determined in vitro in U373, U251 and GaMG human glioblastoma cells using the same methods. HIF-1α protein regulation under hypoxia was also determined on mRNA level in vitro in GaMG and on protein level in U251, U373 and GaMG cells.

Results

We observed no hypoxia-induced regulatory effect on GAPDH expression in the three glioblastoma cell lines studied in vitro. In addition, GAPDH expression was similar in patient tumor samples of low-grade astrocytoma and glioblastoma, suggesting a lack of hypoxic regulation in vivo.

Conclusion

GAPDH represents an optimal choice of a housekeeping gene and/or loading control to determine the expression of hypoxia induced genes at least in glioblastoma. Because of the lack of GAPDH regulation under hypoxia, this gene is not an attractive target for tumor therapeutic approaches in human glioblastoma.

Reduced survivin expression and tumor cell survival during chronic hypoxia and further cytotoxic enhancement by the cyclooxygenase-2 inhibitor celecoxib

Hypoxia is a characteristic feature of advanced solid tumors and may worsen prognosis. The development of tumor-targeted and hypoxia-inducible gene therapy vectors holds promise to selectively deliver and express suicidal or cytotoxic genes in hypoxic regions of tumors. In this regard, the promoter of the survivin gene, which encodes an anti-apoptotic protein that is strongly expressed in tumor tissue, has received attention because of its supposed inducibility by hypoxia. However, in our present study we demonstrate that treatment of various tumor cell lines with chronic hypoxia or with the hypoxia-mimetic CoCl(2) does not result in increased expression of survivin, but rather strongly suppresses this gene's activity. In contrast, expression of glucose-regulated protein 78 (GRP78/Bip) is substantially elevated under chronic hypoxia in vitro and in hypoxic areas of tumor tissue in vivo. Although tumor cells in general exhibit increased chemoresistance under hypoxic conditions, we found that hypoxic glioblastoma cells are more sensitive to killing by the selective cyclooxygenase-2 (COX-2) inhibitor celecoxib, and this effect is reflected by further decreased expression of survivin. Intriguingly, 2,5-dimethyl-celecoxib (DMC), a close structural analog of celecoxib that lacks the ability to inhibit COX-2, is able to potently mimic the anti-tumor effects of its parent compound, indicating that inhibition of COX-2 is not involved in these processes. Taken together, our results caution against the use of survivin-based promoters to target hypoxic areas of tumors, but favor constructs that include the strongly hypoxia-inducible GRP78 promoter. In addition, our data introduce celecoxib as a drug with increased cytotoxicity against hypoxic tumor cells.

Human prx1 gene is a target of Nrf2 and is up-regulated by hypoxia/reoxygenation: implication to tumor biology

Peroxiredoxin 1 (Prx1) has been found to be elevated in several human cancers. The cell survival-enhancing function of Prx1 is traditionally attributed to its reactive oxygen species-removing capacity, although the growth-promoting role of Prx1 independent of this antioxidant activity is increasingly gaining attention. Although much progress has been made in understanding the behavior of Prx1, little information is available on the mechanism responsible for the abnormal elevation of Prx1 level in cancer. We hypothesized that the hypoxic and unstable oxygenation microenvironment of a tumor might be crucial for prx1 up-regulation. In this study, we cloned the human prx1 promoter and identified nuclear factor (erythroid-derived 2)-related factor 2 (Nrf2) as a key transcription factor. Hypoxia/reoxygenation, an in vitro condition suited to mimic changes of oxygenation, increased Nrf2 nuclear localization and its binding to the electrophile-responsive elements located at the proximal (-536 to -528) and distal (-1429 to -1421) regions of the prx1 promoter. A significant reduction of both steady-state and hypoxia/reoxygenation-mediated prx1 gene expression was shown in Nrf2 knock-out cells. Our results indicated that decreased Kelch-like ECH-associated protein, Keap1, might be an important mechanism for the increased nuclear translocation and activation of Nrf2 in response to hypoxia/reoxygenation. A constitutive elevation of prx1 mRNA and protein was observed in Keap1 knock-out cells. The above information suggests that the Nrf2-Prx1 axis may be a fruitful target for intervention with respect to inhibiting the malignant progression and/or reducing the treatment resistance of cancer cells.

Tumor hypoxia and targeted gene therapy

Hypoxia is an integral characteristic of the tumor microenvironment, primarily due to the microvascular defects that accompany the accelerated neoplastic growth. The presence of tumor hypoxic areas correlates with negative outcome after radiotherapy, chemotherapy, and surgery, as hypoxia not only provides an environment directly facilitating chemo- and radio-resistance, but also encourages the evolution of phenotypic changes inducing permanent resistance to treatment and metastatic spread. Therefore, successful treatment of hypoxic cells has the potential to not only improve local control but also impact overall patient survival. Specific and selective targeting of hypoxic tumor areas can be achieved at all three steps of a gene therapy treatment: delivery of the therapeutic gene to the tumor, regulation of gene expression, and therapeutic efficacy. In this review the latest developments and innovations in hypoxia-targeted gene therapy are discussed. In particular, approaches such as hypoxia-conditionally replicating viruses, cellular vehicles, and gene therapy means to disrupt the hypoxia-inducible factor (HIF) signaling are outlined.

Selective gene delivery for cancer therapy using cationic liposomes: in vivo proof of applicability

Targeted gene therapy is essential if cancer treatment is to become a reality with this form of therapy. In the past few years, cationic liposomes, discovered 2 decades ago, and at present, the most commonly used class of transfection reagents, have been tested in various clinical trials for diseases not restricted to cancer. They have been shown to be selective for tumour vascular endothelial cells raising hopes for antiangiogenic and antivascular therapies. They are also capable of being selectively delivered to the lungs and liver when administered intravenously. These vesicles are also being targeted to the tumour in various parts of the body by using advanced liposomal systems such as antibody-antigen and ligand-receptor combinations. This review looks at the state of play in this rapidly growing field.

A novel chimeric promoter that is highly responsive to hypoxia and metals

To develop a potent hypoxia-inducible promoter, we evaluated the usefulness of chimeric combinations of the (Egr-1)-binding site (EBS) from the Egr-1 gene, the metal-response element (MRE) from the metallothionein gene, and the hypoxia-response element (HRE) from the phosphoglycerate kinase 1 gene. In transient transfection assays, combining three copies of HRE (3 x HRE) with either EBS or MRE significantly increased hypoxia responsiveness. When a three-enhancer combination was tested, the EBS-MRE-3 x HRE (E-M-H) gave a hypoxia induction ratio of 69. The expression induced from E-M-H-pGL3 was 2.4-fold higher than that induced from H-pGL3 and even surpassed the expression from a human cytomegalovirus promoter-driven vector. The high inducibility of E-M-H was confirmed by validation studies in different cells and by expressing other cDNAs. Gel shift assays together with functional overexpression studies suggested that increased levels of hypoxia-inducible factor 1alpha, metal transcription factor-1 and Egr-1 may be associated with the high inducibility of the E-M-H chimeric promoter. E-M-H was also induced by hypoxia mimetics such as Co2+ and deferoxamine (DFX) and by hydrogen peroxide. Gene expression from the E-M-H was reversible as shown by the reduced expression of the transgene upon removal of inducers such as hypoxia and DFX. In vivo evaluation of the E-M-H in ischemic muscle revealed that erythropoietin secretion and luciferase and LacZ expression were significantly higher in the E-M-H group than in a control or H group. With its high induction capacity and versatile means of modulation, this novel chimeric promoter should find wide application in the treatment of ischemic diseases and cancer.

Hypoxia- and radiation-inducible, breast cell-specific targeting of retroviral vectors

To facilitate a more efficient radiation and chemotherapy of mammary tumours, synthetic enhancer elements responsive to hypoxia and ionizing radiation were coupled to the mammary-specific minimal promoter of the murine whey acidic protein (WAP) encoding gene. The modified WAP promoter was introduced into a retroviral promoter conversion (ProCon) vector. Expression of a transduced reporter gene in response to hypoxia and radiation was analysed in stably infected mammary cancer cell lines and an up to 9-fold increase in gene expression demonstrated in comparison to the respective basic vector. Expression analyses in vitro, moreover, demonstrated a widely preserved mammary cell-specific promoter activity. For in vivo analyses, xenograft tumours consisting of infected human mammary adenocarcinoma cells were established in SCID/beige mice. Immunohistochemical analyses demonstrated a hypoxia-specific, markedly increased WAP promoter-driven expression in these tumours. Thus, this retroviral vector will facilitate a targeted gene therapeutic approach exploiting the unique environmental condition in solid tumours.

Delivery of viral vectors to tumor cells: extracellular transport, systemic distribution, and strategies for improvement

It is a challenge to deliver therapeutic genes to tumor cells using viral vectors because (i) the size of these vectors are close to or larger than the space between fibers in extracellular matrix and (ii) viral proteins are potentially toxic in normal tissues. In general, gene delivery is hindered by various physiological barriers to virus transport from the site of injection to the nucleus of tumor cells and is limited by normal tissue tolerance of toxicity determined by local concentrations of transgene products and viral proteins. To illustrate the obstacles encountered in the delivery and yet limit the scope of discussion, this review focuses only on extracellular transport in solid tumors and distribution of viral vectors in normal organs after they are injected intravenously or intratumorally. This review also discusses current strategies for improving intratumoral transport and specificity of viral vectors.

Update on clinical radiobiology

Radiation therapy is an important local cytotoxic modality for cancer treatment whose aim is to control the disease while minimising damage to normal tissue. The combination of different treatment modalities offers a more effective cure and reduction in normal tissue toxicity. However, the differences in genetic profiles can cause diverse treatment outcomes. Multidisciplinary research, where technologies and knowledge from different areas are integrated, is necessary to design the optimal regimen for individualised cancer treatment. This paper offers an overview of some new cancer treatment strategies; the impact of molecular imaging on radiation oncology; and a computer simulation model to optimise treatment planning based on patient information. It briefly discusses molecular targeted therapy, tumour microenvironment and bioreductive agents, and evidence for making individualised medicine a reality. Using DNA microarrays and proteomic technologies, information on defined molecular targets and genetic profiling for individual patients can be obtained and new algorithms for radiation oncology-related diagnosis, treatment response and prognosis can be developed.

Hypoxia- and radiation-activated Cre/loxP ‘molecular switch’ vectors for gene therapy of cancer

Although a significant negative prognostic factor, tumor hypoxia can be exploited for gene therapy. To maximize targeting within the tumor mass, we have developed synthetic gene promoters containing hypoxia-responsive elements (HREs) from the erythropoietin (Epo) gene as well as radiation-responsive CArG elements from the early growth response (Egr) 1 gene. Furthermore, to achieve high and sustained expression of the suicide gene herpes simplex virus thymidine kinase (HSVtk), our gene therapy vectors contain an expression amplification system, or 'molecular switch', based on Cre/loxP recombination. In human glioma and breast adenocarcinoma cells exposed to hypoxia and/or radiation, the HRE/CArG promoter rapidly activated Cre recombinase expression leading to selective and sustained HSVtk synthesis. Killing of transfected tumor cells was measured after incubation with the prodrug ganciclovir (GCV; converted by HSVtk into a cytotoxin). In vitro, higher and more selective GCV-mediated toxicity was achieved with the switch vectors, when compared with the same inducible promoters driving HSVtk expression directly. In tumor xenografts implanted in nude mice, the HRE/CArG-switch induced significant growth delay and tumor eradication. In conclusion, hypoxia- and radiation-activated 'molecular switch' vectors represent a promising strategy for both targeted and effective gene therapy of solid tumors.

Evaluation of a synthetic CArG promoter for nitric oxide synthase gene therapy of cancer

Nitric oxide synthase gene therapy has been shown to be effective at inducing apoptosis in experimental tumours and sensitizing them to radiotherapy. We have also shown that expression of inducible nitric oxide synthase (iNOS) can be effectively restricted to the tumour volume by the use of the radiation inducible promoter (WAF1) to drive the transgene in clinically relevant protocols. A synthetic construct (pE9), incorporating nine radiosensitive CArG elements from the Egr1 promoter, has recently been developed for cancer gene therapy. We have now investigated basal gene expression of transgenes driven by this promoter to assess its suitability for use in iNOS gene therapy protocols in vivo. Transfection of human microvascular endothelial cells (HMEC-1) with pE9iNOS, using a cationic lipid vector, resulted in progressively increasing (<5-fold) levels of iNOS protein expression up to 8 h after transfection. Transfection of an ex vivo rat artery preparation with pE9iNOS caused 83% inhibition of response to the vasoconstrictor phenylephrine (PE). CMViNOS transfection also reduced response to PE, but by only 52%. A single injection of 25 microg of pE9iNOS DNA in a lipid vector into the centre of a murine sarcoma (RIF1) induced iNOS protein expression by four-fold and increased nitrite concentration eight-fold. This caused a 7-day delay in tumour growth and was more effective than the constitutive CMV-driven construct. Our data suggest that generation of NO*, as a result of iNOS overexpression, is capable of further activating the E9 promoter, through a positive feedback loop, yielding stronger and sustained levels of NO*. This pE9iNOS combination may, therefore, be particularly useful in an anticancer gene therapy strategy as its antitumour effect in vivo was clearly superior to that of the strong constitutive promoter, CMV.

Hypoxia inducible factor pathways as targets for functional foods

The etiology of most chronic angiogenic diseases such as rheumatoid arthritis, atherosclerosis, diabetes complications, and cancer includes the presence of pockets of hypoxic cells growing behind aerobic cells and away from blood vessels. Hypoxic cells are the result of uncontrolled growth and insufficient vascularization and have undergone a shift from aerobic to anaerobic metabolism. Cells respond to hypoxia by stimulating the expression of hypoxia inducible factor (HIF), which is critical for survival under hypoxic conditions and in embryogenesis. HIF is a heterodimer consisting of the O2-regulated subunit, HIF-1alpha, and the constitutively expressed aryl hydrocarbon receptor nuclear translocator, HIF-1beta. Under hypoxic conditions, HIF-1alpha is stable, accumulates, and migrates to the nucleus where it binds to HIF-1beta to form the complex (HIF-1alpha + HIF-1beta). Transcription is initiated by the binding of the complex (HIF-1alpha + HIF-1beta) to hypoxia responsive elements (HREs). The complex [(HIF-1alpha + HIF-1beta) + HREs] stimulates the expression of genes involved in angiogenesis, anaerobic metabolism, vascular permeability, and inflammation. Experimental and clinical evidence show that these hypoxic cells are the most aggressive and difficult angiogenic disease cells to treat and are a major reason for antiangiogenic and conventional treatment failure. Hypoxia occurs in early stages of disease development (before metastasis), activates angiogenesis, and stimulates vascular remodeling. HIF-1alpha has also been identified under aerobic conditions in certain types of cancer. This review summarizes the role of hypoxia in some chronic degenerative angiogenic diseases and discusses potential functional foods to target the HIF-1alpha pathways under hypoxic and normoxic conditions. It is reported that dietary quinones, semiquinones, phenolics, vitamins, amino acids, isoprenoids, and vasoactive compounds can down-regulate the HIF-1 pathways and therefore the expression of several proangiogenic factors. Considering the lack of efficiency or the side effects of synthetic antiangiogenic drugs at clinical trials, down-regulation of hypoxia-induced angiogenesis by use of naturally occurring functional foods may provide an effective means of prevention.

VP22-mediated intercellular transport for suicide gene therapy under oxic and hypoxic conditions

During herpes simplex virus type 1 (HSV 1) infection, the tegument protein VP22 is exported from infected cells to the nuclei of surrounding uninfected cells. These intercellular transport characteristics have prompted the exploitation of VP22 fusion proteins for cancer gene therapy, with the goal of maximizing the bystander effect. Since solid tumors contain hypoxic cell populations that are often refractive to therapy, for efficient targeting, it would be optimal if VP22 functioned even at reduced oxygen concentrations. In the present work, VP22 activity under hypoxic conditions was examined for the first time. Plasmid-transfected human glioma U87-MG and U373-MG cells expressing VP22 fused to the green fluorescent protein (GFP) showed protein export to untransfected cells under tumor oxygenation conditions (0-5% O(2)). For suicide gene therapy, VP22 activity was demonstrated under hypoxia by coupling VP22 to the HSV thymidine kinase (HSVtk). In the presence of the prodrug ganciclovir, cell cultures expressing VP22-HSVtk showed a significant increase in toxicity compared with cells transfected with a construct containing HSVtk only, under all tested conditions. To allow effective suicide gene therapy and simultaneous visualization of therapeutic enzyme localization, a triple fusion protein GFP-HSVtk-VP22 was engineered. Functionality of all components was demonstrated under oxia and hypoxia.