Tumor hypoxia: definitions and current clinical, biologic, and molecular aspects

Hypoxia inhibits expression of prolactin and secretion of cathepsin-D by the GH4C1 pituitary adenoma cell line

Diminished oxygen concentration within growing tumors may stimulate neovascularization by inducing both up-regulation of angiogenic factors and down-regulation of antiangiogenic agents. A potentially important molecule in the growth of pituitary adenomas is prolactin (PRL), which can be cleaved by cathepsin-D to yield a 16-kDa form (16K-PRL) with potent antiangiogenic effects. We examined the expression of PRL in cultured GH4C1 pituitary adenoma cells after exposure to hypoxia (0.1% oxygen) for periods of 12 to 36 hours. In contrast to increased expression of the angiogenic factor vascular endothelial growth factor in hypoxic cells, PRL mRNA and levels of intracellular and secreted PRL were significantly reduced under hypoxia. The reduction was not attributable to a general suppression of either transcription or protein synthesis. Although 16K-PRL was not evident in conditioned medium at physiologic pH, lowering the pH to mimic the acidic tumor microenvironment resulted in generation of 16K-PRL, which was sharply reduced in medium drawn from hypoxic cells. Production of 16K-PRL was blocked by the cathepsin-D inhibitor pepstatin-A, and the reduced 16K-PRL formation in hypoxic-conditioned medium correlated with a decrease in secretion of cathepsin-D and its precursor, procathepsin-D. Thus, hypoxia acts upon GH4C1 cells to increase vascular endothelial growth factor expression, decrease PRL synthesis, and suppress conversion of PRL to 16K-PRL via inhibition of cathepsin-D proteolysis. These mechanisms may act in concert to stimulate angiogenesis in prolactinomas.

Glycolysis and glucose transporter 1 as markers of response to hormonal therapy in breast cancer

Estrogen plays a key role in the development and progression of breast cancer; hence, antiestrogens, such as tamoxifen, have a marked impact on the treatment and outcome of breast cancer patients. Estrogen-induced growth requires continuous replenishment of energy, predominantly generated by glycolysis. Previous work from this laboratory demonstrated estrogen induction and tamoxifen inhibition of glycolysis in MCF7 human breast cancer cells in vitro (Furman et al., J Steroid Biochem Mol Biol 1992;43:189-95). We present here studies of estrogen vs. tamoxifen regulation of glycolysis in orthotopic MCF7 human breast cancer xenografts in vivo. In addition we investigated mediation of this metabolic regulation through glucose transporter 1, in the same cells, in vitro, as well as in 2 other hormone-responsive human breast cancer cells. Tumor response and glycolysis were monitored noninvasively by means of magnetic resonance imaging and 13C spectroscopy, respectively. During estrogen-stimulated tumor growth (from approximately 0.5 to approximately 1.3 cm3 in 10 days), the rate of glucose metabolism through glycolysis in vivo was high at 40 +/- 4 micromole/g/min. However, treatment for 10 days with tamoxifen induced growth arrest and a concomitant decrease of 2-fold in the rate of glycolysis. In congruence, glucose transporter 1 expression was stimulated by estrogen, reaching after 72 hr a 2- to 3-fold higher level of expression relative to that in tamoxifen-treated cells. Thus, estrogen-induced changes in glycolysis appeared to be mediated via its regulation of glucose transporter 1 expression. The in vivo monitoring of glycolysis may serve as a tool to expose hormonal regulation of glucose transporter 1 expression in breast cancer tumors, as well as to assess response to hormonal therapy.

Quantitative assessment of tumor oxygen dynamics: molecular imaging for prognostic radiology

One of the fundamental molecules governing the survival of mammalian cells is oxygen. Oxygen has gained particular significance in tumor developmental biology and oncology. An increasingly diverse array of methods is now available to characterize tumor oxygenation. This Prospect will consider a new method, Fluorocarbon Relaxometry using Echo planar imaging for Dynamic Oxygen Mapping (FREDOM), which we have recently developed for oximetry, examine application to a specific therapeutic example and place this technique in the context of other approaches.

Targeting HIF-1 for cancer therapy

Hypoxia-inducible factor 1 (HIF-1) activates the transcription of genes that are involved in crucial aspects of cancer biology, including angiogenesis, cell survival, glucose metabolism and invasion. Intratumoral hypoxia and genetic alterations can lead to HIF-1alpha overexpression, which has been associated with increased patient mortality in several cancer types. In preclinical studies, inhibition of HIF-1 activity has marked effects on tumour growth. Efforts are underway to identify inhibitors of HIF-1 and to test their efficacy as anticancer therapeutics.

Pretreatment haemoglobin levels significantly predict the tumour response to primary chemotherapy in human breast cancer

The purpose of this study was to evaluate whether tumour response to primary chemotherapy in human breast cancer is influenced by baseline haemoglobin (Hb) status. A total of 157 patients with T2-4, N0-1 M0 breast cancer were treated with chemotherapy consisting of either the CMF regimen + tamoxifen (the first 76 cases) or the single-agent epirubicin (the subsequent 81) before definitive surgery. In total, 144 patients were fully assessable. Ki67, p53, bcl-2, c-erbB2, steroid hormone receptor, and microvessel density were evaluated immunohistochemically in tumour specimens obtained before chemotherapy and at surgery. Tumour shrinkage >50% occurred in 72.1% of patients. Responding patients had higher baseline Hb levels and red blood cell counts than nonresponders (P<0.01 and <0.003, respectively). The distribution of disease response according to increasing cutoffs of baseline Hb status showed that from 12.5 mg l(-1) onwards, patients with Hb levels above the cutoff obtained a greater response rate than those with lower Hb values. The difference attained the statistical significance at 12.5 (76.1 vs 59.5%, P<0.05) and 13.0 g/dl(-1) (81.0 vs 57.6%, P<0.002) cutoffs, respectively. The predictive role of Hb levels was maintained in multivariate analysis after adjustment for clinical and biological characteristics and treatment regimen. Patients with baseline Hb levels </=13 g dl(-1) showed a lower treatment-induced reduction in Ki67 expression (P<0.04) and a higher Ki67 expression at postoperative evaluation (P<0.02) than their counterparts. In conclusion, low Hb levels may negatively influence the response rate of chemotherapy in breast cancer patients. Inhibition of antiproliferative activity could be a possible mechanism.

Increased growth factor production in a human prostatic stromal cell culture model caused by hypoxia

BACKGROUND

Local hypoxia may be one of the triggers of embryonic reawakening of the stroma and subsequent hyperplastic growth in the prostate. Using a cell culture model of human prostatic stromal cells, we investigated the effects of hypoxia on activation of hypoxia-inducible factor 1 (HIF 1) and on the production of growth factors.

METHODS

Primary prostatic stromal cells were grown in normal and hypoxic (1% O(2)) atmosphere. Activation of HIF 1 was evaluated after different time intervals by Western blot. Induced secretion of growth factors VEGF, FGF-7, TGF-beta, IL 8, and FGF-2 were analyzed by ELISA. To confirm the in vitro findings we also performed immunohistochemistry of HIF 1alpha as well as pro-collagen I, collagens I, III, and IV in the benign tissue of radical prostatectomy specimens.

RESULTS

HIF 1 is activated in a time-dependent manner, already starting 1 hr after exposure of stromal cells to hypoxic conditions. Secretion of VEGF, FGF-7, TGF-beta, FGF-2, and IL 8 is increased under hypoxic in vitro conditions in comparison to normoxia. Levels of TGF-beta, VEGF, and IL 8 were rapidly and statistically significantly increased in the supernatant of hypoxic cells. Consistent with the in vitro findings, immunohistochemistry of HIF 1alpha in (benign prostatic hyperplasia) BPH tissue revealed strong HIF 1alpha nuclear staining in hyperplastic areas. No difference was observed in the collagen pattern between hyperplastic and normal prostate tissue.

CONCLUSIONS

Prostatic stromal cells respond to hypoxia by upregulation of secretion of several growth factors suggesting that hypoxia can trigger prostatic growth. Therefore, hypoxia might be a key factor contributing to the pathogenesis of BPH.

Investigating hypoxic tumor physiology through gene expression patterns

Clinical evidence shows that tumor hypoxia is an independent prognostic indicator of poor patient outcome. Hypoxic tumors have altered physiologic processes, including increased regions of angiogenesis, increased local invasion, increased distant metastasis and altered apoptotic programs. Since hypoxia is a potent controller of gene expression, identifying hypoxia-regulated genes is a means to investigate the molecular response to hypoxic stress. Traditional experimental approaches have identified physiologic changes in hypoxic cells. Recent studies have identified hypoxia-responsive genes that may define the mechanism(s) underlying these physiologic changes. For example, the regulation of glycolytic genes by hypoxia can explain some characteristics of the Warburg effect. The converse of this logic is also true. By identifying new classes of hypoxia-regulated gene(s), we can infer the physiologic pressures that require the induction of these genes and their protein products. Furthermore, these physiologically driven hypoxic gene expression changes give us insight as to the poor outcome of patients with hypoxic tumors. Approximately 1-1.5% of the genome is transcriptionally responsive to hypoxia. However, there is significant heterogeneity in the transcriptional response to hypoxia between different cell types. Moreover, the coordinated change in the expression of families of genes supports the model of physiologic pressure leading to expression changes. Understanding the evolutionary pressure to develop a 'hypoxic response' provides a framework to investigate the biology of the hypoxic tumor microenvironment.

The Presence of a Fibrotic Focus in Invasive Breast Carcinoma Correlates with the Expression of Carbonic Anhydrase IX and is a Marker of Hypoxia and Poor Prognosis

The value of the fibrotic focus (FF) as a marker of intra-tumoral hypoxia in invasive breast carcinoma was assessed by studying its relationship with the expression of the hypoxia-induced carbonic anhydrase IX (CA IX), angiogenesis indices and prognosis. CA IX expression was immunohistochemically detected in 2 independent study groups, totaling 184 patients, and correlated with tumor characteristics, angiogenesis related parameters and patient outcome by univariate analysis. CA IX immunostaining scores in carcinoma cells and in tumoral fibroblasts were significantly higher in expansively growing tumors (p = 0.0001 and p < 10(-4), respectively), containing an FF (p = 0.0004 and p < 10(-4)) and showing high histological grade (p = 0.016 and p = 0.0006). Microvessel density, quantified by Chalkley counting, was correlated with CA IX expression both in the carcinoma cells and in the fibroblasts (p = 0.0076 and p = 0.0025) and with the presence and relative size of an FF (p = 0.006). The fraction of proliferating endothelial cells was positively correlated with CA IX scores in the fibroblasts (r = 0.4, p = 0.02) and with the presence of an FF (p = 0.02). CA IX scores in the fibroblasts--and to a lesser extent in the carcinoma cells--were associated with a higher relapse rate (p = 0.006) and a worse overall survival (p = 0.003). The highest CA IX immunostaining scores were found in the fibroblasts of large FF occupying more than one-third of the tumor. A large FF was associated with worse overall survival in a consecutive patient group (p = 0.01) and with shorter disease-free (p = 0.02) and overall survival (p = 0.0005) in T1-2N0 breast cancer patients. The strong association of CA IX expression with the presence of an FF shows that the latter is a marker of intra-tumoral hypoxia. FF is useful as a surrogate marker of hypoxia-driven ongoing angiogenesis and is associated with a higher relapse rate and a worse overall survival.

Targeted molecular mechanisms of epoetin alfa

Despite therapeutic improvements and ongoing efforts to develop more efficacious therapies, the majority of lung cancer patients face a poor prognosis. Therefore, the primary goal of current treatment is palliation, improvement and maintenance of quality of life (QOL), and (modest) prolongation of survival. Anemia frequently occurs in lung cancer patients and has been associated with decreased QOL, impaired treatment outcomes, and shortened survival time. Furthermore, anemia is a causative factor of tumor hypoxia, which compromises the efficacy of chemotherapy and radiotherapy. Thus, correction of even mild anemia seems to have a beneficial effect on QOL and cancer treatment outcomes. The current article describes the basis and mechanism for the use of recombinant human erythropoietin (rHuEPO, epoetin alfa), a molecular targeted therapy, for the treatment of cancer-related anemia, with a focus on lung cancer. Epoetin alfa has proven efficacy and safety in correcting anemia and improving QOL based on numerous clinical studies and over a decade of clinical practice. In addition, emerging data show that epoetin alfa may offer potential benefits beyond treating anemia, specifically in terms of treatment outcomes and cognitive function. Future research needs to be conducted to explore the potential for epoetin alfa to improve survival time in lung cancer patients.

Tumour hypoxia, chemotherapeutic resistance and hypoxia-related therapies

Tissue hypoxia occurs where there is an imbalance between oxygen supply and consumption. Hypoxia occurs in solid tumours as a result of an inadequate supply of oxygen, due to exponential cellular proliferation and an inefficient vascular supply. It is an adverse prognostic indicator in cancer as it is associated with tumour progression and resistance to therapy. The expression of several genes controlling tumour cell survival are regulated by hypoxia, e.g., growth factors governing the formation of new blood vessels, and hypoxia-responsive transcription factors modulating the expression of genes, which promote tumour cell survival. This review outlines some of the pathways by which tumour hypoxia leads to chemotherapeutic resistance, directly due to lack of oxygen availability, and indirectly due to alterations in the proteome/genome, angiogenesis and pH changes. Some innovative therapies are also detailed which may potentially minimise or eliminate these problems associated with targeting solid tumours.

Temporal heterogeneity in oxygen tension in human melanoma xenografts

The spatial heterogeneity of the oxygen tension (pO(2)) in human and experimental tumours has been studied extensively, whereas studies of the temporal heterogeneity in pO(2) are sparse. In the work reported here, pO(2) was measured continuously over periods of at least 60 min in A-07 human melanoma xenografts by using the OxyLite fibre-optic oxygen-sensing device. The main purpose of the work was to establish the usefulness of the OxyLite system in measuring the temporal heterogeneity in pO(2) in tissues and to characterise the fluctuations in tissue pO(2) in A-07 tumours. The OxyLite device was found to be suitable for studies of the temporal heterogeneity in pO(2) in tumours. However, potential pitfalls were identified, and reliable pO(2) measurements require that precautions are taken to avoid these pitfalls, that is, erroneous pO(2) readings caused by tissue trauma induced by the probe, probe movements induced by reflex actions of the host mouse and occasional probe drift. Significant fluctuations in pO(2) were detected in the majority of the 70 tumour regions subjected to measurement. The fluctuations in different regions of the same tumour were in general temporally independent, implying that they were caused primarily by redistribution of the tumour perfusion rather than fluctuations in global perfusion. Fourier analysis of the pO(2) traces showed that the pO(2) usually fluctuated at frequencies lower than 1.5-2.0 mHz, corresponding to less than 0.1 cycle min(-1). Haemodynamic effects may cause pO(2) fluctuations in this frequency range, and hence, the redistribution of the perfusion could have been caused by morphological abnormalities of the tumour microvasculature. Moreover, acute hypoxia, that is, pO(2) fluctuations around 10 or 5 mmHg, was detected in 20 of 70 regions, that is, 29% (10 mmHg), or 27 of 70 regions, that is, 39% (5 mmHg). The median fraction of the time these regions were acutely hypoxic was 73% (10 mmHg) or 53% (5 mmHg). Consequently, if A-07 tumours are adequate models of tumours in man, acute hypoxia may be a commonly occurring phenomenon in neoplastic tissues, and hence, acute hypoxia is likely to cause resistance to radiation therapy and promote tumour aggressiveness.

Hypoxia-induced dedifferentiation in neuroblastoma cells

Hypoxia in solid tumors is associated with aggressive behavior and poor outcome. We recently discovered that hypoxia alters the expression of differentiation marker genes in neuroblastoma cells, in that the tumor cells adjust to the hypoxic environment by down-regulating genes associated with a neuronal and upregulating genes associated with a neural crest-like phenotype. As there is a correlation in neuroblastoma between low stage of differentiation and high (aggressive) clinical stage, we propose that dedifferentiation of neuroblastoma cells in hypoxic tumor regions contribute to the malignancy of the tumor.

Impact of oxygenation status and patient age on DNA content in cancers of the uterine cervix

PURPOSE

In carcinomas of the uterine cervix, the tumor oxygenation status has been shown to be a prognostic indicator that is independent of treatment modality. In vitro studies suggest gene amplification and polyploidization to be among the major consequences of hypoxia (with or without consecutive reoxygenation) and to be associated with treatment resistance and tumor progression. This study analyzed whether hypoxia alters net DNA content in uterine cervix cancer cells to the extent that it is identifiable by DNA image cytometry.

MATERIALS AND METHODS

In 64 patients with primary cervical cancer, tumor oxygenation was assessed polarographically and correlated with cell DNA content (DNA image cytometry) in areas adjacent to the oxygen microsensor tracks in which oxygenation measurements were made.

RESULTS

No correlation between DNA content (stemline position, Auer classification, and 2c deviation index) and oxygenation status was observed. However, an association between DNA content and patient age and menopausal status was found.

CONCLUSION

Using DNA cytometry, hypoxia-associated genomic changes in uterine cervix cancer cells could not be detected. The impact of tumor hypoxia on the genome may be masked by the effects of alternative mechanisms of genomic instability that can also influence DNA content.

Linking radiation oncology and imaging through molecular biology (or now that therapy and diagnosis have separated, it's time to get together again!)

Among the areas defined by the National Cancer Institute as "Extraordinary Opportunities for Research Investment" that are highly relevant to the technology-oriented disciplines within the broad field of radiology are cancer imaging, defining the signatures (ie, underlying molecular features) of cancer cells, and molecular targets of prevention and treatment. In molecular target credentialing, a specific molecular target is imaged, the molecular signature is defined, a treatment is given, and the effect of the intervention on the image findings and the signature is then evaluated. Such an approach is used to validate the proposed target as a legitimate one for cancer therapy or prevention and to provide the opportunity to ultimately individualize therapy on the basis of both the initial characteristics of the tumor and the tumor's response to an intervention. Therapeutic radiation is focused biology (ie, radiation produces molecular events in the irradiated tissue). Radiation can (a) kill cancer cells by itself, (b) be combined with cytotoxic or cytostatic drugs, and (c) serve to initiate radiation-inducible molecular targets that are amenable to treatment with drugs and/or biologic therapies. Focused biology can be anatomically confined with various types of external beams and with brachytherapy, and it can be used systemically with targeted radioisotopes. These new paradigms link diagnostic imaging, radiation therapy, and nuclear medicine in unique ways by way of basic biology. It is timely to develop new collaborative research, training, and education agendas by building on one another's expertise and adopting new fields of microtechnology, nanotechnology, and mathematical analysis and optimization.

Anemia in cervical cancers: impact on survival, patterns of relapse, and association with hypoxia and angiogenesis

PURPOSE

The prognostic impact of anemia in cervical cancers is well established. We have investigated the impact of anemia on prognosis and patterns of relapse in cervical cancers. Furthermore, we analyzed the relationship between anemia, tumor hypoxia, and angiogenesis.

METHODS AND MATERIALS

Eighty-seven patients (mean age 58 years) with squamous cell cancer of the cervix (Stage IIB: n = 19; Stage IIIB: n = 59; Stage IVA: n = 9) were prospectively enrolled in the study from 1995 through 1999. Patients underwent definitive radiotherapy with a combination of external beam radiotherapy (45-50.4 Gy) and high-dose-rate brachytherapy (5 x 7 Gy). Tumor oxygenation was measured with the Eppendorf pO(2)-histograph before radiotherapy and after 19.8 Gy. Angiogenesis was determined by measuring the microvessel density in pretreatment biopsies in 46 patients. The impact of tumor oxygenation (at 0 Gy and 19.8 Gy), hemoglobin (hb) level (at 0 Gy and 19.8 Gy), angiogenesis and clinical parameters on survival and relapse was investigated.

RESULTS

The 3-year overall survival rate (after a median follow-up of 42 months) was 57% for the whole group of patients, 72% for Stage IIB, 60% for Stage IIIB, and 22% for Stage IVA. The presence of pretreatment anemia had a significant impact on the relapse rate. However, the midtherapy hb level (at 19.8 Gy) had the strongest impact on local failure rate and survival: 3-year local failure rate was 6% in 20 patients with a hb > 13 g/dL at 19.8 Gy, 15% in 47 patients with an hb between 11 and 13 g/dL, and 67% in 20 patients with an hb < 11 g/dL, p = 0.0001. This was associated with a significant impact on the 3-year overall survival, 79% vs. 64% vs. 32%. Twenty-three tumors were poorly oxygenated at both measurements (oxygen pressure [median pO(2)] < 15 mm Hg before therapy and at 19.8 Gy). This group had a significantly lower 3-year overall survival as compared with patients with high pO(2) before and/or at 19.8 Gy (38% vs. 68%, p = 0.02), and these poorly oxygenated tumors had also a significantly increased microvessel density. In a multivariate model, the midtherapy hb level maintained an overwhelming impact on local failure rate and survival.

CONCLUSION

Hemoglobin level during radiotherapy was the strongest prognostic factor for local control and survival. We could further identify a poor prognostic subgroup with persisting hypoxia during radiotherapy, low hb levels, and increased angiogenesis. According to these findings, an association between anemia, poor tumor oxygenation, and angiogenesis is likely.

Angiogenesis in ischemic and neoplastic disorders

Vascular development involves vasculogenesis, in which endothelial cells form a primary tubular network, as well as angiogenesis, in which vessel size and structure are modified based upon flow and branching occurs to insure that all cells receive adequate O2 delivery. In adults, angiogenesis occurs in response to tissue hypoxia/ischemia and plays an important role in determining the progression of ischemic heart disease and cancer. A critical molecular pathway induced by hypoxia/ischemia is the activation of hypoxia-inducible factor 1, a transcriptional activator of genes encoding vascular endothelial growth factor and other important mediators of angiogenesis. Novel therapeutic approaches that involve stimulating angiogenesis in ischemic tissue and inhibiting angiogenesis in neoplastic tissue are currently being evaluated in clinical trials.

Hypoxia-inducible erythropoietin signaling in squamous dysplasia and squamous cell carcinoma of the uterine cervix and its potential role in cervical carcinogenesis and tumor progression

Tissue hypoxia is a characteristic property of cervical cancers that makes tumors resistant to chemo- and radiation therapy. Erythropoietin (Epo) is a hypoxia-inducible stimulator of erythropoiesis. Acting via its receptor (EpoR), Epo up-regulates bcl-2 and inhibits apoptosis of erythroid cells and rescues neurons from hypoxic damage. In addition to human papillomavirus infection, increased bcl-2 expression and decreased apoptosis are thought to play a role in the progression of cervical neoplasia. Using reverse transcriptase-polymerase chain reaction and Western blotting we showed that HeLa and SiHa cervical carcinoma cells and human cervical carcinomas express EpoR, and that hypoxia enhances EpoR expression. Exogenous Epo stimulated tyrosine phosphorylation and inhibited the cytotoxic effect of cisplatin in HeLa cervical carcinoma cells. Using immunohistochemistry, we examined the expression of Epo, EpoR, p16, hypoxia-inducible factor (HIF)-1alpha, and bcl-2 in benign and dysplastic cervical squamous epithelia and invasive squamous cell carcinomas (ISCCs). EpoR expression in benign epithelia was confined to the basal cell layers, whereas in dysplasias it increasingly appeared in more superficial cell layers and showed a significant correlation with severity of dysplasia. Diffuse EpoR expression was found in all ISCCs. Expression of Epo and HIF-1alpha was increased in dysplasias compared to benign epithelia. Focal Epo and HIF-1alpha expression was seen near necrotic areas in ISCCs, and showed correlation in their spatial distribution. Significant correlation was found between expression of EpoR, and p16 and bcl-2 in benign and dysplastic squamous epithelia. Our results suggest that increased expression of Epo and EpoR may play a significant role in cervical carcinogenesis and tumor progression. Hypoxia-inducible Epo signaling may play a significant role in the aggressive behavior and treatment resistance of hypoxic cervical cancers.

Metabolic classification of human rectal adenocarcinomas: a novel guideline for clinical oncologists?

PURPOSE

Based on previous findings in SCC of the human uterine cervix and of the head and neck, metastasis- and survival-related metabolic classification was performed in human rectal adenocarcinomas. Such a characterization is suggested as basis of a novel clinical guideline for an appropriate therapy of epithelium-derived malignancies.

METHODS

Tissue concentrations of ATP, glucose, and lactate in viable tumor regions of 33 pretherapeutically taken cryobiopsies from 24 patients were measured at a microscopic level using the technique of imaging bioluminescence.

RESULTS

In metastatic carcinomas, lactate levels were significantly higher (mean+/-SD: 13.4+/-3.8 vs 6.9+/-2.5 micro mol/g, P = 0.0046) and glucose levels significantly lower (0.3+/-0.2 vs 1.0+/-0.4 micro mol/g, P = 0.0020) than in non-metastatic carcinomas. No patients had distant metastasis with tumor lactate levels below the population median of 8.0 micro mol/g or glucose levels above 0.9 micro mol/g.

CONCLUSIONS

These results support the hypothesis that lactate and glucose levels measured in human primary carcinomas may serve as an early prognostic tool in the clinic with regard to formation of metastasis and patient survival. The present data encourage further studies on possible strategies for a metabolic classification of tumors as a prognostic tool.

Single-dose pharmacokinetics of the DNA-binding bioreductive agent NLCQ-1 (NSC 709257) in CD2F1 mice

NLCQ-1 (NSC 709257) is a weak DNA-binding bioreductive antiproliferative agent, with potent in vitro antiproliferative activity against rodent and human tumor cell lines under aerobic and anaerobic conditions. Interest in this quinoline analog is based in part on its in vivo synergistic antitumor effect with radiotherapy or chemotherapy against mouse tumors and human xenografts. A sensitive, specific HPLC method was developed to measure NLCQ-1 in biological fluids. Calibration curves were linear in the range 10.4-667 ng/ml and the lower limit of quantitation was 10.4 ng/ml in plasma. NLCQ-1 was stable in organic solvents, buffered solutions and human plasma for 24 h at 37 degrees C. NLCQ-1 was unstable in rodent and dog plasma when incubated for longer than 10 h. NLCQ-1 human plasma protein binding was high (about 99%), and included binding to both alpha(1)-acid glycoprotein and serum albumin. The plasma elimination of NLCQ-1 in mice after a 10-mg/kg intravenous bolus dose was described by a two-compartment open model with t(1/2beta), V(ss), and Cl(TB) values of 41.3 min, 2.04 l/kg and 69.9 ml/min per kg, respectively. NLCQ-1 had high (85%) intraperitoneal and modest (28%) oral relative bioavailability. Little of the administered NLCQ-1 dose (6.4%) was excreted in 24-h urine. The mouse pharmacokinetic data suggested that oral administration may achieve plasma concentration and systemic exposure similar to those observed after intravenous administration of NLCQ-1.

Dynamic response of breast tumor oxygenation to hyperoxic respiratory challenge monitored with three oxygen-sensitive parameters

The simultaneous measurement of three oxygen-sensitive parameters [arterial hemoglobin oxygen saturation (SaO2), tumor vascular-oxygenated hemoglobin concentration ([HbO2]), and tumor oxygen tension (pO2)] in response to hyperoxic respiratory challenge is demonstrated in rat breast tumors. The effects of two hyperoxic gases [oxygen and carbogen (5% CO2 and 95% O2)] were compared, by use of two groups of Fisher rats with subcutaneous 13762NF breast tumors implanted in pedicles on the foreback. Two different gas-inhalation sequences were compared, i.e., air-carbogen-air-oxygen-air and air-oxygen-air-carbogen-air. The results demonstrate that both of the inhaled, hyperoxic gases significantly improved the tumor oxygen status. All three parameters displayed similar dynamic response to hyperoxic gas interventions, but with different response times: the fastest for arterial SaO2, followed by biphasic changes in tumor vascular [HbO2], and then delayed responses for pO2. Both of the gases induced similar changes in vascular oxygenation and regional tissue pO2 in the rat tumors, and changes in [HbO2] and mean pO2 showed a linear correlation with large standard deviations, which presumably results from global versus local measurements. Indeed, the pO2 data revealed hetergeneous regional response to hyperoxic interventions. Although preliminary near-infrared measurements had been demonstrated previously in this model, the addition of the pO2 optical fiber probes provides a link between the noninvasive relative measurements of vascular phenomena based on endogenous reporter molecules, with the quantitative, albeit, invasive pO2 determinations.

Carbonic anhydrase inhibitors. Inhibition of tumor-associated isozyme IX by halogenosulfanilamide and halogenophenylaminobenzolamide derivatives

Two series of halogenated sulfonamides have been prepared. The first consists of mono/dihalogenated sulfanilamides, whereas the second one consists of the mono/dihalogenated aminobenzolamides, incorporating equal or different halogens (F, Cl, Br, and I). These sulfonamides have been synthesized from the corresponding anilines by acetylation (protection of the amino group), chlorosulfonylation, followed either by amidation, or reaction with 5-amino-1,3,4-thiadiazole-2-sulfonamide (and eventually deacetylation). All these compounds, together with the six clinically used sulfonamide inhibitors (acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, and brinzolamide) were investigated as inhibitors of the transmembrane, tumor-associated isozyme carbonic anhydrase (CA) IX. Inhibition data against the classical, physiologically relevant isozymes I, II, and IV were also obtained. CA IX shows an inhibition profile which is generally completely different from those of isozymes I, II, and IV, with potent inhibitors (inhibition constants in the range of 12-40 nM) among both simple aromatic (such as 3-fluoro-5-chloro-4-aminobenzenesulfonamide) as well as heterocyclic compounds (such as acetazolamide, methazolamide, 5-amino-1,3,4-thiadiazole-2-sulfonamide, aminobenzolamide, and dihalogenated aminobenzolamides). This first detailed CA IX inhibition study revealed many interesting leads, suggesting the possibility to design even more potent and eventually CA IX-selective inhibitors, with putative applications as antitumor agents.

Carbonic anhydrase inhibitors. Inhibition of cytosolic isozymes I and II and transmembrane, tumor-associated isozyme IX with sulfamates including EMATE also acting as steroid sulfatase inhibitors

A series of sulfamates or bis-sulfamates incorporating aliphatic, aromatic, polycyclic (steroidal), and sugar moieties in their molecules has been synthesized and assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of the cytosolic isozymes CA I andII, and the transmembrane, tumor-associated isozymes CA IX. Some of these compounds were previously reported to act as inhibitors of steroid sulfatases, among which estrone sulfatase (ES) and dehydroepiandrosterone sulfatase (DHEAS) are the key therapeutic targets for estrogen-dependent tumors. Very potent (nanomolar) inhibitors were detected against the three investigated CA isozymes. Best CA I inhibitors were phenylsulfamate and some of its 4-halogeno derivatives, as well as the aliphatic compound n-octyl sulfamate. Against CA II, low nanomolar inhibitors (1.1-5 nM) were phenylsulfamate and some of its 4-halogeno/nitro derivatives, n-octyl sulfamate, and estradiol 3,17beta-disulfamate among others. All the investigated sulfamates showed efficient CA IX inhibitory properties, with inhibition constants in the range of 18-63 nM. The best CA IX inhibitor detected so far was 4-chlorophenylsulfamate. These data are critical for the design of novel antitumor properties, mainly for hypoxic tumors that overexpress CA IX, which are nonresponsive to radiation or chemotherapy. The antitumor properties of the ES/DHEAS inhibitors in clinical trials may on the other hand also be due to their potent inhibitory properties of CA isozymes involved in tumorigenicity, such as CA II and CA IX.

The hypoxia-inducible factor-1 alpha is a negative factor for tumor therapy

Tumor hypoxia negatively regulates cell growth and causes a more malignant phenotype by increasing the expression of genes encoding angiogenic, metabolic and metastatic factors. Of clinical importance, insufficient tumor oxygenation affects the efficiency of chemotherapy and radiotherapy by poorly understood mechanisms. The hypoxia-inducible factor (HIF)-1 is a master transcriptional activator of oxygen-regulated genes and HIF-1 is constitutively upregulated in several tumor types. HIF-1 might thus be implicated in tumor therapy resistance. We found that transformed mouse embryonic fibroblasts deficient for HIF-1alpha are more susceptible to the treatment with carboplatin, etoposide and ionizing radiation than wild-type cells. Increased cell death in HIF-1alpha-deficient cells was because of apoptosis and did not involve p53 induction. Tumor chemotherapy of experimental fibrosarcoma in immunocompromised mice with carboplatin and etoposide confirmed the enhanced susceptibility of HIF-1alpha-deficient cells. Agents that did not cause DNA double-strand breaks, such as DNA-synthesis inhibitors or a DNA single-strand break-causing agent equally impaired cell growth, independent of the HIF-1alpha genotype. Functional repair of a fragmented reporter gene was decreased in HIF-1alpha-deficient cells. Thus, hypoxia-independent basal HIF-1alpha expression in tumor cells, as known from untransformed embryonic stem cells, is sufficient to induce target gene expression, probably including DNA double-strand break repair enzymes.

SKIP3, a novel Drosophila tribbles ortholog, is overexpressed in human tumors and is regulated by hypoxia

Regions of hypoxia are a hallmark of solid tumors. Tumor cells modulate the regulation of specific genes allowing adaptation and survival in the harsh hypoxic environment. We have identified SKIP3, a novel human kinase-like gene, which is overexpressed in multiple human tumors and is regulated by hypoxia. SKIP3 is an ortholog of the Drosophila tribbles, rat NIPK, dog C5FW, and human C8FW genes. Drosophila tribbles is involved in slowing cell-cycle progression during Drosophila development, but little is known regarding the function or tissue distribution of the vertebrate orthologs. We show that the normal tissue expression of SKIP3 is confined to human liver, while multiple primary human lung, colon, and breast tumors express high levels of SKIP3 transcript. Endogenous SKIP3 protein accumulates within 48 h under hypoxic growth conditions in HT-29 and PC-3 cells, with upregulation of the SKIP3 mRNA transcript by 72 h. We identified activating transcription factor 4 (ATF4) as a SKIP3-binding partner using the yeast-two-hybrid assay. Coexpression of SKIP3 and ATF4 showed that SKIP3 is associated with the proteolysis of ATF4, which can be blocked using a proteosome inhibitor. These results indicate that SKIP3 may be an important participant in tumor cell growth.

Angiopoietin-like 4 is a proangiogenic factor produced during ischemia and in conventional renal cell carcinoma

Ischemic and solid tumor tissues are less well perfused than normal tissue, leading to metabolic changes and chronic hypoxia, which in turn promotes angiogenesis. We identified human angiopoietin-like 4 (angptl4) as a gene with hypoxia-induced expression in endothelial cells. We showed that the levels of both mRNA and protein for ANGPTL4 increased in response to hypoxia. When tested in the chicken chorioallantoic membrane assay, ANGPTL4 induced a strong proangiogenic response, independently of vascular endothelial growth factor. In human pathology, ANGPTL4 mRNA is produced in ischemic tissues, in conditions such as critical leg ischemia. In tumors, ANGPTL4 is produced in the hypoxic areas surrounding necrotic regions. We observed particularly high levels of ANGPTL4 mRNA in tumor cells of conventional renal cell carcinoma. Other benign and malignant renal tumor cells do not produce ANGPTL4 mRNA. This molecule therefore seems to be a marker of conventional renal cell carcinoma. ANGPTL4, originally identified as a peroxisome proliferator-activated receptor alpha and gamma target gene, has potential for use as a new diagnostic tool and a potential therapeutic target, modulating angiogenesis both in tumors and in ischemic tissues. This study also suggests that ANGPTL4 may provide a link between metabolic disorders and hypoxia-induced angiogenesis.

Correlation of tumor oxygen dynamics with radiation response of the dunning prostate R3327-HI tumor

Our previous studies have shown that oxygen inhalation significantly reduces tumor hypoxia in the moderately well-differentiated HI subline of the Dunning prostate R3327 rat carcinoma. To test our hypothesis that modifying hypoxia could improve the radiosensitivity of these tumors, we performed experimental radiotherapy to compare the tumor response to ionizing radiation alone or in combination with oxygen inhalation. Tumor pO(2) measurements were performed on size-selected tumors several hours before radiotherapy using (19)F nuclear magnetic resonance echo planar imaging relaxometry (FREDOM) of the reporter molecule hexafluorobenzene. In common with our previous findings, the larger tumors (>3.5 cm(3)) exhibited greater hypoxia than the smaller tumors (<2 cm(3); P < 0.001), and oxygen inhalation reduced the hypoxic fraction (<10 Torr): In the larger tumors, hypoxic fraction dropped significantly from a mean baseline value of 80% to 17% (P < 0.001). The effect of oxygen administered 30 min before and during irradiation on tumor response to a single 30-Gy dose of photons was evaluated by growth delay. For the smaller tumors, no difference in growth delay was found when treatment was given with or without oxygen breathing. By contrast, breathing oxygen before and during irradiation significantly enhanced the growth delay in the larger tumors (additional 51 days). The differential behavior may be attributed to the low baseline hypoxic fraction (<10 Torr) in small tumors (20%) as a target for oxygen inhalation. There was a strong correlation between the estimated initial pO(2) value and the radiation-induced tumor growth delay (R > 0.8). Our histological studies showed a good match between the perfused vessels marked by Hoechst 33342 dye and the total vessels immunostained by anti-CD31 and indicated extensive perfusion in this tumor line. In summary, the present results suggest that the ability to detect modulation of tumor pO(2), in particular, the residual hypoxic fraction, with respect to an intervention, could have prognostic value for predicting the efficacy of radiotherapy.

Genetic analysis of hypoxia signaling and response in C elegans

During normal development and homeostasis, animals use cellular and systemic strategies to adapt to changing oxygen levels. In mammals, hypoxic tissues secrete growth factors to induce angiogenesis, and individual cells increase anaerobic metabolism in order to sustain basic cellular functions. Many of these critical responses to decreased oxygen availability are regulated by the hypoxia-inducible factors, dimeric transcriptional complexes consisting of alpha and beta subunits. HIFalpha proteins are specialized for hypoxia response, and oxygen levels regulate their stability and activity. The C. elegans hif-1 gene is orthologous to mammalian HIFalpha genes, and C. elegans has proven to be a powerful system for the study of hypoxia-inducible factor regulation and function. Mutants lacking hif-1 function are viable in normoxic or anoxic conditions, but they cannot adapt to hypoxia. Recent genetic analyses in C. elegans led to the identification of the evolutionarily conserved enzyme that hydroxylates HIFa in an oxygen-dependent manner. Once modified, HIFalpha binds the von Hippel-Lindau tumor suppressor protein and is targeted for proteasomal degradation. Here, we briefly review the characterization of C. elegans hif-1 and interacting genes, and discuss genetic strategies for studying hypoxia signaling and response.

Transcriptional Targeting in Cancer Gene Therapy

Cancer gene therapy has been one of the most exciting areas of therapeutic research in the past decade. In this review, we discuss strategies to restrict transcription of transgenes to tumour cells. A range of promoters which are tissue-specific, tumour-specific, or inducible by exogenous agents are presented. Transcriptional targeting should prevent normal tissue toxicities associated with other cancer treatments, such as radiation and chemotherapy. In addition, the specificity of these strategies should provide improved targeting of metastatic tumours following systemic gene delivery. Rapid progress in the ability to specifically control transgenes will allow systemic gene delivery for cancer therapy to become a real possibility in the near future.

YC-1: a potential anticancer drug targeting hypoxia-inducible factor 1

BACKGROUND

Hypoxia-inducible factor 1 alpha (HIF-1alpha), a component of HIF-1, is expressed in human tumors and renders cells able to survive and grow under hypoxic (low-oxygen) conditions. YC-1, 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole, an agent developed for circulatory disorders that inhibits platelet aggregation and vascular contraction, inhibits HIF-1 activity in vitro. We tested whether YC-1 inhibits HIF-1 and tumor growth in vivo.

METHODS

Hep3B hepatoma, NCI-H87 stomach carcinoma, Caki-1 renal carcinoma, SiHa cervical carcinoma, and SK-N-MC neuroblastoma cells were grown as xenografts in immunodeficient mice (69 mice total). After the tumors were 100-150 mm(3), mice received daily intraperitoneal injections of vehicle or YC-1 (30 microg/g) for 2 weeks. HIF-1 alpha protein levels and vascularity in tumors were assessed by immunohistochemistry, and the expression of HIF-1-inducible genes (vascular endothelial growth factor, aldolase, and enolase) was assessed by reverse transcription-polymerase chain reaction. All statistical tests were two-sided.

RESULTS

Compared with tumors from vehicle-treated mice, tumors from YC-1-treated mice were statistically significantly smaller (P<.01 for all comparisons), expressed lower levels of HIF-1 alpha (P<.01 for all comparisons), were less vascularized (P<.01 for all comparisons), and expressed lower levels of HIF-1-inducible genes, regardless of tumor type.

CONCLUSIONS

The inhibition of HIF-1 alpha activity in tumors from YC-1-treated mice is associated with blocked angiogenesis and an inhibition of tumor growth. YC-1 has the potential to become the first antiangiogenic anticancer agent to target HIF-1 alpha.

Regulation of cancer metastasis by stress pathways

The presence of activated oncogenes and/or inactivated tumor suppressor genes may result in constitutive activation of multiple transcription factors. This may be especially true in the early stages of tumor development. At advanced stages, however, uncontrolled tumor growth and the consequent development of a stress microenvironment, such as hypoxia, acidosis, and free radical overproduction, may further alter the activity of these transcription factors. Abnormal activation of and interplay between these factors lead to aberrant expression of multiple metastasis-related proteins and confer a tremendous survival and growth advantage to emerging metastatic variants. Understanding the expression and regulation of these molecules may shed more light on the biology of cancer metastasis as well as suggest new preventive and therapeutic approaches.

Dominant-negative hypoxia-inducible factor-1 alpha reduces tumorigenicity of pancreatic cancer cells through the suppression of glucose metabolism

In the tumor cells exposed to hypoxia, hypoxia-inducible factor-1 (HIF-1)-mediated adaptation responses such as angiogenesis and anaerobic metabolism are induced for their survival. We have recently reported that the constitutive expression of HIF-1 alpha renders pancreatic cancer cells resistant to apoptosis induced by hypoxia and glucose deprivation. We then established dominant-negative HIF-1 alpha (dnHIF-1 alpha) transfectants and examined their susceptibility to apoptosis and growth inhibition induced by hypoxia and glucose deprivation in vitro and their tumorigenicity in SCID mice. We further examined the expressions of aldolase A and Glut-1 in vitro and Glut-1 expression and glucose uptake in the tumor tissues and microvessel counts in the tumor tissues. As a result, dnHIF-1 alpha rendered the pancreatic cancer cells sensitive to apoptosis and growth inhibition induced by hypoxia and glucose deprivation. Also it abrogated the enhanced expression of Glut-1 and aldolase A mRNAs under hypoxia and reduced the expression of Glut-1 and the glucose uptake in the tumor tissues and consequently in vivo tumorigenicity. We found no significant difference in the microvessel counts among the tumor tissues. From these results, we suggest that the disruption of the HIF-1 pathway might be effective in the treatment of pancreatic cancers.

In vivo colocalization of 2-nitroimidazole EF5 fluorescence intensity and electron paramagnetic resonance oximetry in mouse tumors

BACKGROUND AND PURPOSE

The primary objective of this study was to establish in vivo the relationship between 2-2-nitro-1H-imidazol-1yl-N-(2,2,3,3,3-pentafluoropropyl)-acetamide (EF5) adduct formation and intratumoral oxygen concentrations measured by electron paramagnetic resonance (EPR) in a tumor model mimicking a clinical situation. The secondary objective was an attempt to calibrate in situ the immunofluorescence (IF) signal with EPR oximetry.

MATERIALS AND METHODS

IM syngeneic fibrosarcoma (NFSA) bearing C3H mice were used. Three days after injection of a paramagnetic charcoal into the tumor, the mice were anesthetized, injected with the hypoxic marker EF5, and monitored every 20 min for 3 h with a low-frequency EPR spectrometer. Animals were allowed to breath either under 21 or 100% O(2). Tumors were then harvested, frozen, cut into sections including the charcoal and processed for EF5 adducts detection using monoclonal antibodies. Slices were viewed with a fluorescence microscope and 190x140 micrometer areas surrounding the charcoal were digitized and analyzed with the NIH-Image and Adobe Photoshop software. The fluorescence intensity (FI) was measured in the whole pictures and in strips of 10 micrometer around the charcoal.

RESULTS

EF5 binding increased with decreasing pO(2), most substantially at pO(2) below 5 mm Hg. Baseline (ambient air) pO(2) reached 3.2+/-2.1 mm Hg in NFSA tumors. It increased to 9.8+/-3.2 mm Hg under 100% O(2). A statistically significant correlation was observed on an individual tumor basis between the FI in the first 10 micrometer strip around the charcoal and the pO(2) determined by EPR oximetry (Wilcoxon signed rank test: P<0.001).

CONCLUSIONS

The present study confirms the intrinsic relationship between EF5 adduct binding and intratumoral pO(2) in an in vivo environment under biologically-relevant pO(2) values of less than 10 mm Hg.

Hypoxia promotes invasive growth by transcriptional activation of the met protooncogene

Hypoxia unleashes the invasive and metastatic potential of tumor cells by largely unknown mechanisms. The Met tyrosine kinase, a high affinity receptor for hepatocyte growth factor (HGF), plays a crucial role in controlling invasive growth and is often overexpressed in cancer. Here we show that: (1) hypoxia activates transcription of the met protooncogene, resulting in higher levels of Met; (2) hypoxic areas of tumors overexpress Met; (3) hypoxia amplifies HGF signaling; (4) hypoxia synergizes with HGF in inducing invasion; (5) the proinvasive effects of hypoxia are mimicked by Met overexpression; and (6) inhibition of Met expression prevents hypoxia-induced invasive growth. These data show that hypoxia promotes tumor invasion by sensitizing cells to HGF stimulation, providing a molecular basis to explain Met overexpression in cancer.

Tumor hypoxia at the micro-regional level: clinical relevance and predictive value of exogenous and endogenous hypoxic cell markers

BACKGROUND AND PURPOSE

Tumor oxygenation is recognized as an important determinant of the outcome of radiotherapy and possibly also of other treatment modalities in a number of tumor types and in particular in squamous cell carcinomas. The hypoxic status of various solid tumors has been related to a poor prognosis due to tumor progression towards a more malignant phenotype, with increased metastatic potential, and an increased resistance to treatment. It has been demonstrated in head and neck cancer that hypoxic radioresistance can be successfully counteracted by hypoxia modifying approaches. The microregional distribution and the level of tumor hypoxia depend on oxygen consumption and temporal and spatial variations in blood supply. It is unclear if severely hypoxic cells can resume clonogenicity when O(2) and nutrients become available again as a result of (treatment related) changes in the tumor microenvironment. Non-terminally differentiated hypoxic cells that are capable of proliferation are important for outcome because of their resistance to radiotherapy and possibly other cytotoxic treatments. Various exogenous and endogenous markers for hypoxia are currently available and can be studied in relation to each other, the tumor architecture and the tumor microenvironment. Use of nitroimidazole markers with immunohistochemical detection allows studying tumor cell hypoxia at the microscopic level. Co-registration with other microenvironmental parameters, such as vascular architecture (vascular density), blood perfusion, tumor cell proliferation and apoptosis, offers the possibility to obtain a comprehensive functional image of tumor patho-physiology and to study the effects of different modalities of cancer treatment.

CONCLUSION

A number of functional microregional parameters have emerged that are good candidates for future use as indicators of tumor aggressiveness and treatment response. The key question is whether these parameters can be used as tools for selection of treatment strategies for individual patients. This requires testing of these markers in prospective randomized clinical trials comparing standard treatment against experimental treatments targeting the relevant microregional constituent.

Carbonic anhydrase inhibitors: inhibition of the tumor-associated isozyme IX with aromatic and heterocyclic sulfonamides

The inhibition of the tumor-associated transmembrane carbonic anhydrase IX (CA IX) isozyme has been investigated with a series of aromatic and heterocyclic sulfonamides, including the six clinically used derivatives acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide and brinzolamide. Inhibition data for the physiologically relevant isozymes I and II (cytosolic forms) and IV (membrane-bound) were also provided for comparison. A very interesting and unusual inhibition profile against CA IX with these sulfonamides has been observed. Several nanomolar (K(I)-s in the range of 14-50 nM) CA IX inhibitors have been detected, both among the aromatic (such as orthanilamide, homosulfonilamide, 4-carboxy-benzenesulfonamide, 1-naphthalenesulfonamide and 1,3-benzenedisulfonamide derivatives) as well as the heterocylic (such as 1,3,4-thiadizole-2-sulfonamide, etc.) sulfonamides examined. Because CA IX is a highly active isozyme predominantly expressed in tumor tissues with poor prognosis of disease progression, this finding is very promising for the potential design of CA IX-specific inhibitors with applications as anti-tumor agents.

Autophagy: a barrier or an adaptive response to cancer

Macroautophagy or autophagy is a degradative pathway terminating in the lysosomal compartment after the formation of a cytoplasmic vacuole that engulfs macromolecules and organelles. The recent discovery of the molecular controls of autophagy that are common to eukaryotic cells from yeast to human suggests that the role of autophagy in cell functioning is far beyond its nonselective degradative capacity. The involvement of proteins with properties of tumor suppressor and oncogenic properties at different steps of the pathway implies that autophagy must be considered in tumor progression. Autophagy as a stress response mechanism protects cancer cells from low nutrient supply or therapeutic insults. Autophagy is also involved in the elimination of cancer cells by triggering a non-apoptotic cell death program, suggesting a negative role in tumor development. These two aspects of autophagy will be discussed in this review.

Levels of hypoxia-inducible factor-1alpha independently predict prognosis in patients with lymph node negative breast carcinoma

BACKGROUND

Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that plays an important role in tumor growth and metastasis by regulating energy metabolism and inducing angiogenesis to survive cellular hypoxia. Increased levels of HIF-1alpha, the O(2)-regulated subunit of HIF-1, were noted during breast carcinogenesis. In this study, the prognostic value of HIF-1alpha expression and its correlation with various clinicopathologic variables in patients with invasive breast carcinoma were investigated.

METHODS

Expression levels of HIF-1alpha, HER-2/neu, estrogen receptor, and progesterone receptor were analyzed in 150 patients with early-stage breast carcinoma by immunohistochemistry. HER-2/neu gene amplification was investigated with automated fluorescent in situ hybridization. The mitotic activity index, histologic grade, and tumor type were assessed in hematoxylin and eosinstained specimens. Clinical data included disease-free survival, overall survival, lymph node status, and tumor size. The data were analyzed with two-sided univariate and multivariate tests, with P values < 0.05 considered significant.

RESULTS

High levels of HIF-1alpha had an association of borderline significance with decreased overall survival (P = 0.059) and disease-free survival (P = 0.110) that was ascribed completely to the subgroup of women with lymph node negative tumors (n = 81 patients; P = 0.008 and P = 0.004, respectively). HER-2/neu immunoreactivity (P < 0.001) and gene amplification (P < 0.001), vascular endothelial growth factor expression (P = 0.016), and Ki-67 expression (P < 0.001) were correlated strongly with HIF-1alpha positivity, although none of those factors had an independent effect on survival.

CONCLUSIONS

Increased levels of HIF-1alpha were associated independently with shortened survival in patients with lymph node negative breast carcinoma. Therefore, the use of immunohistochemical assessment of HIF-1alpha as a new predictor of poor outcome may improve clinical decision-making regarding adjuvant treatment of patients with lymph node negative breast carcinoma.

GLUT-1 and CAIX as intrinsic markers of hypoxia in carcinoma of the cervix: relationship to pimonidazole binding

The presence of hypoxia in tumours results in the overexpression of certain genes, which are controlled via the transcription factor HIF-1. Hypoxic cells are known to be radioresistant and chemoresistant, thus, a reliable surrogate marker of hypoxia is desirable to ensure that treatment may be rationally applied. Recently, the HIF-1-regulated proteins Glut-1 and CAIX were validated as intrinsic markers of hypoxia by comparison with pO(2) measured using oxygen electrodes. We compare the expression of Glut-1 and CAIX with the binding of the bioreductive drug hypoxia marker pimonidazole. Pimonidazole was administered to 42 patients with advanced carcinoma of the cervix, 16 hr before biopsy. Sections of single or multiple biopsies were then immunostained for Glut-1 and CAIX, and the area of staining scored by eye, using a "field-by-field" semi-quantitative averaging system. Using 1 biopsy only, Glut-1 (r = 0.54, p = <0.001) correlated with the level of pimonidazole binding, and Glut-1 and CAIX expression also correlated significantly (r = 0.40, p = <0.009). Thus, our study has shown that HIF-1 regulated genes have potential for future use as predictors of the malignant changes mediated by hypoxia, and warrant further investigation as indicators of response to cancer therapy.

A mathematical model of tumor oxygen and glucose mass transport and metabolism with complex reaction kinetics

Hypoxia imparts radioresistance to tumors, and various approaches have been developed to enhance oxygenation, thereby improving radiosensitivity. This study explores the influence of kinetic and physical factors on substrate metabolism in a tumor model, based on a Krogh cylinder. In tissue, aerobic metabolism is assumed to depend on glucose and oxygen, represented by the product of Michaelis-Menten expressions. For the base case, an inlet pO(2) of 40 mmHg, a hypoxic limit of 5 mmHg, and a tissue/capillary radius ratio of 10 are used. For purely aerobic metabolism, a hypoxic fraction of 0.16 and volume-average pO(2) of 8 mmHg are calculated. Reducing the maximum oxygen rate constant by 9%, decreasing the tissue cylinder radius by 5%, or increasing the capillary radius by 8% abolishes the hypoxic fraction. When a glycolytic term is added, concentration profiles are similar to the base case. Using a distribution of tissue/capillary radius ratios increases the hypoxic fraction and reduces sensitivity to the oxygen consumption rate, compared to the case with a single tissue/capillary radius ratio. This model demonstrates that hypoxia is quite sensitive to metabolic rate and geometric factors. It also predicts quantitatively the effects of inhibited oxygen metabolism and enhanced mass transfer on tumor oxygenation.

Regulation of the multidrug resistance transporter P-glycoprotein in multicellular tumor spheroids by hypoxia-inducible factor (HIF-1) and reactive oxygen species

Hypoxia in tumors is generally associated with chemoresistance and radioresistance. However, the correlation between the heterodimeric hypoxia-inducible factor-1 (HIF-1) and the multidrug resistance transporter P-glycoprotein (P-gp) has not been investigated. Herein, we demonstrate that with increasing size of DU-145 prostate multicellular tumor spheroids the pericellular oxygen pressure and the generation of reactive oxygen species decreased, whereas the alpha-subunit of HIF-1 (HIF-1alpha) and P-gp were up-regulated. Furthermore, P-gp was up-regulated under experimental physiological hypoxia and chemical hypoxia induced by either cobalt chloride or desferrioxamine. The pro-oxidants H2O2 and buthionine sulfoximine down-regulated HIF-1alpha and P-gp, whereas up-regulation was achieved with the radical scavengers dehydroascorbate, N-acetylcysteine, and vitamin E. The correlation of HIF-1alpha and P-gp expression was validated by the use of hepatoma tumor spheroids that were either wild type (Hepa1) or mutant (Hepa1C4) for aryl hydrocarbon receptor nuclear translocator (ARNT), i.e., HIF-1beta. Chemical hypoxia robustly increased HIF-1alpha as well as P-gp expression in Hepa1 tumor spheroids, whereas no changes were observed in Hepa1C4 spheroids. Hence, our data demonstrate that expression of P-gp in multicellular tumor spheroids is under the control of HIF-1.

NO and TNF-alpha released from activated macrophages stabilize HIF-1alpha in resting tubular LLC-PK1 cells

Hypoxic/ischemic conditions provoke activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). HIF-1 is composed of HIF-1alpha (subjected to protein stability regulation) and constitutively expressed HIF-1beta. Besides hypoxia, diverse agonists are identified that stabilize HIF-1alpha during normoxia. Here we used a coculture system of RAW 264.7 macrophage cells and tubular LLC-PK(1) cells to establish that lipopolysaccharide- and interferon-gamma-stimulated but not resting macrophages elicited HIF-1alpha accumulation in LLC-PK(1) cells. Via pharmacological interventions such as blockade of nitric oxide (NO) production in macrophages, scavenging of NO with the use of 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, or application of tumor necrosis factor-alpha (TNF-alpha)-neutralizing antibodies, we identified NO and TNF-alpha as signaling molecules. Working in concert, NO and TNF-alpha have a stronger response when allowed direct cell-to-cell contact instead of contact with only the cell supernatant of activated macrophages. We show that signal transmission by NO with TNF-alpha in LLC-PK(1) cells is mediated via the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway, because it is blocked by wortmannin or dominant-negative forms of PI3-K as well as protein kinase B. We conclude that NO and TNF-alpha, derived from activated macrophages, provoke HIF-1alpha stabilization in LLC-PK(1) cells under normoxic conditions, which underscores HIF-1alpha stabilization due to intercellular regulation.

Radiation response non-invasively imaged by [18F]FDG-PET predicts local tumor control and survival in advanced oral squamous cell carcinoma

It is a major challenge to preoperatively identify patients who will profit from surgery of advanced oral cancer. In multimodality therapy, response to neoadjuvant radiation correlates to treatment success. Hence, for preoperative decisions, assessment of treatment response is required. Therefore, we analysed the prognostic significance of glucose metabolism after preoperative radiotherapy. [(18)F]FDG-PET investigations were performed for re-staging 35 patients after neoadjuvant radiotherapy (36Gy) immediately prior to tumor resection. Emission and transmission measurements were obtained and SUV's were calculated for the sites of maximum [(18)F]FDG-uptake. Subpopulations of "low" (SUV < 4) and "high" (SUV > or = 4) glucose metabolism were compared by univariate and multivariate survival analysis. 3-years survival was 80% in the "low" SUV group and 43% in the "high" SUV group. Post-irradiation [(18)F]FDG-uptake significantly predicts survival (P = 0.046) and local tumor control (P = 0.0017). High [(18)F]FDG-uptake was associated with an increased hazard of death (P = 0.037) and especially of local progress (P = 0.011) even when radical resection was performed. Thus, [(18)F]FDG-PET non invasively identified patients with poor prognosis whose indication for radical surgery has to be considered with caution.

The von Hippel-Lindau tumor suppressor, hypoxia-inducible factor-1 (HIF-1) degradation, and cancer pathogenesis

Recently, work on the mechanism of action of the von Hippel-Lindau tumour suppressor protein (pVHL) and studies on hypoxic gene regulation have converged, providing insights into both cellular oxygen sensing and cancer pathogenesis. pVHL is the recognition component of the E3-ubiquitin ligase complex involved in the degradation of hypoxia-inducible factor-1 (HIF) alpha-subunits, a process regulated by oxygen availability and blocked by disease causing pVHL mutations. In normoxic cells, pVHL targeting of HIF-alpha subunits follows hydroxylation of critical HIF prolyl residues by a group of oxygen, 2-oxoglutarate- and iron-dependent enzymes. In this review, we outline current understanding of HIF/pVHL/prolyl hydroxylase pathway and consider the implications for VHL-associated cancer.

Hypoxia regulates expression and activity of Kv1.3 channels in T lymphocytes: a possible role in T cell proliferation

T lymphocytes are exposed to hypoxia during their development and also when they migrate to hypoxic pathological sites such as tumors and wounds. Although hypoxia can affect T cell development and function, the mechanisms by which immune cells sense and respond to changes in O(2)-availability are poorly understood. K(+) channels encoded by the Kv1.3 subtype of the voltage-dependent Kv1 gene family are highly expressed in lymphocytes and are involved in the control of membrane potential and cell function. In this study, we investigate the sensitivity of Kv1.3 channels to hypoxia in freshly isolated human T lymphocytes and leukemic Jurkat T cells. Acute exposure to hypoxia (20 mmHg, 2 min) inhibits Kv1.3 currents in both cell types by 20%. Prolonged exposure to hypoxia (1% O(2) for 24 h) selectively decreases Kv1.3 protein levels in Jurkat T cells by 47%, but not Kvbeta2 and SK2 Ca-activated K(+) channel subunit levels. The decrease in Kv1.3 protein levels occurs with no change in Kv1.3 mRNA expression and is associated with a significant decrease in K(+) current density. A decrease in Kv1.3 polypeptide levels similar to that obtained during hypoxia is produced by Kv1.3 channel blockage. Our results indicate that hypoxia produces acute and long-term inhibition of Kv1.3 channels in T lymphocytes. This effect could account for the inhibition of lymphocyte proliferation during hypoxia. Indeed, we herein present evidence showing that hypoxia selectively inhibits TCR-mediated proliferation and that this inhibition is associated with a decrease in Kv1.3 proteins.

Mechanisms underlying PTEN regulation of vascular endothelial growth factor and angiogenesis

Inactivation of the tumor suppressor gene PTEN and overexpression of VEGF are two of the most common events observed in high-grade malignant gliomas. The purpose of this study was to determine whether PTEN controls VEGF expression in gliomas under normoxic conditions. Transfer of PTEN to human glioma cells resulted in the transduction of a functional PTEN protein as evidenced by the upregulation of p27 and modification of the phosphorylation status of Akt. Under normoxic conditions, enzyme-linked immunosorbent assay and Northern blot analyses showed downregulation of VEGF in PTEN-treated cells. Moreover, conditioned media from PTEN-treated glioma cells significantly diminished the ability of endothelial cells to grow and migrate. Western blot assays demonstrated that, in a normoxic environment, PTEN downregulates HIF-1 alpha. Finally, promoter activity assays showed that the VEGF promoter region containing the HIF-1alpha binding site is necessary and sufficient for PTEN-mediated downregulation of VEGF. Experiments with PI3-K inhibitors and kinase assays suggested that PI3-K is mediating the effect of PTEN on VEGF, and not the p42/p48 or p38 MAP kinases. These results indicate that restoration of PTEN function in gliomas may induce therapeutic effect by downregulating VEGF. Furthermore, this close functional relationship between PTEN and VEGF suggests that a better understanding of the transduction signal regulated by PTEN might enhance the knowledge of the cause and physiology of vascular and inflammatory diseases.