An enzyme-linked immunosorbent assay for hypoxia marker binding in tumours

Oxygen levels epigenetically regulate fate switching of neural precursor cells via hypoxia-inducible factor 1α-notch signal interaction in the developing brain

Oxygen levels in tissues including the embryonic brain are lower than those in the atmosphere. We reported previously that Notch signal activation induces demethylation of astrocytic genes, conferring astrocyte differentiation ability on midgestational neural precursor cells (mgNPCs). Here, we show that the oxygen sensor hypoxia-inducible factor 1α (HIF1α) plays a critical role in astrocytic gene demethylation in mgNPCs by cooperating with the Notch signaling pathway. Expression of constitutively active HIF1α and a hyperoxic environment, respectively, promoted and impeded astrocyte differentiation in the developing brain. Our findings suggest that hypoxia contributes to the appropriate scheduling of mgNPC fate determination.

Prospects for bioreductive drug development

Bioreductive drugs are inactive prodrugs that are converted into potent cytotoxins under conditions of either low oxygen tension or in the presence of high levels of specific reductases. The biochemical basis for selectivity relies on the ability of oxygen to reverse the activation process and the presence of elevated reductase levels in some tumour types. Key criteria for an ideal bioreductive drug should include poor activity against aerobic cells, activation over a broad range of oxygen tensions and, penetration through the aerobic fraction of cells. In addition, the active drug should be capable of killing non-proliferating cells. Numerous compounds are currently at various stages of drug development but Mitomycin C, which is generally considered to be the prototype bioreductive drug, is the only one in clinical use today. Of the drugs currently being evaluated clinically, tirapazamine has definite clinical activity against a variety of solid tumours when used in combination with cisplatin. Other drugs, such as EO9 and various nitroimidazoles, have not been impressive in the clinic and further development is required to improve properties such as drug delivery in the case of indoloquinones. A novel approach to exploiting tumour hypoxia is the development of a gene-directed enzyme prodrug therapy (GDEPT) strategy, where a gene encoding for a prodrug activating enzyme has been placed under the control of a hypoxia responsive promoter sequence. It is generally recognised that bioreductive drugs must be directed towards patients whose tumours have hypoxic regions or have appropriate enzymological characteristics. In terms of identifying tumour hypoxia, there has been considerable progress in the development of nitroimidazole based hypoxia markers that can be detected either via non-invasive or invasive procedures. Another strategy currently undergoing preclinical evaluation is the use of agents that modulate tumour blood flow and synergistic effects have been reported between bioreductive drugs and photodynamic therapy or inhibitors of nitric oxide synthase for example. The development of clinically useful bioreductive drugs depends therefore on the expertise of scientists and clinicians with varying backgrounds. The purpose of this review is to describe and critically assess recent developments in this field, with particular emphasis being placed on drug development and strategies aimed at optimising bioreductive drug activity.

Inhibition of tumor necrosis factor-alpha improves physiological angiogenesis and reduces pathological neovascularization in ischemic retinopathy

The present study was undertaken to test whether inhibition of the proangiogenic inflammatory cytokine tumor necrosis factor (TNF)-alpha can modulate retinal hypoxia and preretinal neovascularization in a murine model of oxygen-induced retinopathy (OIR). OIR was produced in TNF-alpha-/- and wild-type (WT) control C57B6 neonatal mice by exposure to 75% oxygen between postnatal days 7 and 12 (P7 to P12). Half of each WT litter was treated with the cytokine inhibitor semapimod (formerly known as CNI-1493) (5 mg/kg) by daily intraperitoneal injection from the time of reintroduction to room air at P12 until P17. The extent of preretinal neovascularization and intraretinal revascularization was quantified by image analysis of retinal flat-mounts and retinal hypoxia correlated with vascularization by immunofluorescent localization of the hypoxia-sensitive drug pimonidazole (hypoxyprobe, HP). HP adducts were also characterized by Western analysis and quantified by competitive enzyme-linked immunosorbent assay. TNF-alpha-/- and WT mice showed a similar sensitivity to hyperoxia-induced retinal ischemia at P12. At P13 some delay in early reperfusion was evident in TNF-alpha-/- and WT mice treated with semapimod. However, at P17 both these groups had significantly better vascular recovery with less ischemic/hypoxic retina and preretinal neovascularization compared to untreated retinopathy in WT mice. Immunohistochemistry showed deposition of HP in the avascular inner retina but not in areas underlying preretinal neovascularization, indicating that such aberrant vasculature can reduce retinal hypoxia. Inhibition of TNF-alpha significantly improves vascular recovery within ischemic tissue and reduces pathological neovascularization in OIR. HP provides a useful tool for mapping and quantifying tissue hypoxia in experimental ischemic retinopathy.

Hypoxia in the Androgen-Dependent Shionogi Model for Prostate Cancer at Three Stages1

The objective of this study was to investigate a possible relationship between androgen status and hypoxia in the Shionogi murine prostate tumor model, which is widely used to study the effects of androgen withdrawal on hormone resistance and radiation response. Binding of the nitroimidazole hypoxia marker EF5 was assessed using the Cy3-tagged monoclonal antibody ELK3-51. Three hours after injection of EF5 (30 mg/kg), tumors from the following three stages were excised: androgen-dependent, regressed tumors 7 days after castration, and androgen-independent. Half of each tumor was disaggregated for analysis by flow cytometry and the remainder was flash frozen. Statistically significant differences (P < 0.01) were found between androgen-dependent, regressed and androgen-dependent tumors: approximately 30, approximately 2 and approximately 50% hypoxic cells, respectively. Frozen sections from androgen-dependent tumors exhibited highly variable EF5 binding; regressed tumors showed very little or no binding; each section from androgen-dependent tumors showed high levels and uniformly distributed binding of EF5. There was no correlation between the degree of hypoxia and tumor weight (P > 0.1). The results from this preliminary study indicate that hypoxia may play an important role with respect to the timing of irradiation in prostate cancer treatments and possibly may be a useful prognostic tool. In addition, hypoxia may also be relevant to progression in this disease after androgen ablation.

Evidence that involucrin, a marker for differentiation, is oxygen regulated in human squamous cell carcinomas

The majority of hypoxic cells in squamous cell carcinomas of the head and neck and cervix express involucrin, a molecular marker for differentiation. This raises the question of whether involucrin is an oxygen-regulated protein and, if so, whether it could serve as an endogenous marker for tumour hypoxia. Consistent with oxygen regulation, involucrin protein was found to increase with increasing hypoxia in confluent cultures of moderately differentiated human SCC9 cells. Cells harvested at the point of confluence and exposed to graded concentrations of oxygen revealed a K_m of approximately 15 mmHg for involucrin induction. This is similar to K_ms for HIF-1α, CAIX and VEGF. Involucrin induction showed a steep dependence on pO₂ with a transition from minimum to maximum expression occurring over less than an order of magnitude change in pO₂. In contrast to SCC9 cells, involucrin was not induced by hypoxia in poorly differentiated SCC4 cells. It is concluded that involucrin is an oxygen-regulated protein, but that differentiation modulates its transcription status with respect to hypoxia induction.

Activated Kupffer cells cause a hypermetabolic state after gentle in situ manipulation of liver in rats

Harvesting trauma to the graft dramatically decreases survival after liver transplantation. Since activated Kupffer cells play a role in primary nonfunction, the purpose of this study was to test the hypothesis that organ manipulation activates Kupffer cells. To mimic what occurs with donor hepatectomy, livers from Sprague-Dawley rats underwent dissection with or without gentle organ manipulation in a standardized manner in situ. Perfused livers exhibited normal values for O(2) uptake (105 +/- 5 micromol. g(-1). h(-1)) measured polarigraphically; however, 2 h after organ manipulation, values increased significantly to 160 +/- 8 micromol. g(-1). h(-1) and binding of pimonidazole, a hypoxia marker, increased about threefold (P < 0.05). Moreover, Kupffer cells from manipulated livers produced three- to fourfold more tumor necrosis factor-alpha and PGE(2), whereas intracellular calcium concentration increased twofold after lipopolysaccharide compared with unmanipulated controls (P < 0.05). Gadolinium chloride and glycine prevented both activation of Kupffer cells and effects of organ manipulation. Furthermore, indomethacin given 1 h before manipulation prevented the hypermetabolic state, hypoxia, depletion of glycogen, and release of PGE(2) from Kupffer cells. These data indicate that gentle organ manipulation during surgery activates Kupffer cells, leading to metabolic changes dependent on PGE(2) from Kupffer cells, which most likely impairs liver function. Thus modulation of Kupffer cell function before organ harvest could be beneficial in human liver transplantation and surgery.

Determining hypoxic fraction in a rat glioma by uptake of radiolabeled fluoromisonidazole

The usefulness of radiolabeled nitroimidazoles for measuring hypoxia will be clarified by defining the relationship between tracer uptake and radiobiologically hypoxic fraction. We determined the radiobiologically hypoxic fraction from radiation response data in 36B10 rat gliomas using the paired cell survival curve technique and compared the values to the radiobiologically hypoxic fraction inferred from mathematical modeling of time-activity data acquired by PET imaging of [(18)F]FMISO uptake. Rats breathed either air or 10% oxygen during imaging, and timed blood samples were taken. The uptake of [(3)H]FMISO by 36B10 cells in vitro provided cellular binding characteristics of this radiopharmaceutical as a function of oxygen concentration. The radiobiologically hypoxic fraction determined for tumors in air-breathing rats using the paired survival curve technique was 6.1% (95% CL = 4.3- 8.6%), which agreed well with that determined by modeling FMISO time-activity data (7. 4%; 95% CL = 2.5-17.3%). These results are consistent with the agreement between the two techniques for measuring radiobiologically hypoxic fraction in Chinese hamster V79 cell spheroids. In contrast, the FMISO-derived radiobiologically hypoxic fraction in rats breathing 10% oxygen was 13.1% (95% CL 7.9-8.3%), much lower than the radiobiologically hypoxic fraction of 43% determined from the radiation response data. This discrepancy may be due to the failure of FMISO to identify hypoxic cells residing at or above an oxygen level of 2-3 mmHg that will still confer substantial protection against radiation. The presence of transiently hypoxic cells in rats breathing reduced oxygen may also be under-reported by nitroimidazole binding, which is strongly dependent on time and concentration.

Graft survival is improved by hepatic denervation before organ harvesting

BACKGROUND

In a recent study, disturbances of hepatic microcirculation at harvesting caused by in situ organ manipulation dramatically reduced survival after a liver transplant. Because hepatic innervation is involved in the regulation of liver hemodynamics, the effect of denervation before harvesting was assessed here.

METHODS

The livers were harvested from female Lewis rats (200-230 g) within 25 min. Briefly, after minimal dissection during the first 12 min, the livers were either manipulated gently or left alone for 13 min. Subsequently, an orthotopic liver transplant was performed after 1 hr of storage in cold UW solution. Some donors livers underwent microsurgical denervation before harvesting or rats were given hexamethonium (10 mg/kg, i.v.), a ganglionic blocking agent.

RESULTS

In the nonmanipulated group, survival was 100% after the transplant; however, gentle manipulation decreased survival by about 50%. Furthermore, manipulation elevated serum transaminases and bilirubin 6- to 8-fold 8 hr after the transplant and caused necrosis of about 25% of hepatocytes. After organ harvesting, the rate of entry and exit of fluorescein dextran, a dye confined to the vascular space, was decreased 2- to 4-fold, and the maximal increase of surface fluorescence was blunted about 2-fold. Pimonidazole binding, which reflects tissue hypoxia, was increased 2-fold by manipulation. Denervation of the liver before organ harvesting or treatment with hexamethonium prevented the effects of organ manipulation on all parameters studied.

CONCLUSION

These data indicate for the first time that hepatic denervation before organ harvesting prevents detrimental effects of brief, gentle manipulation of the liver during harvesting on survival after the transplant. This is consistent with the hypothesis that organ manipulation disturbs the hepatic microcirculation and causes hypoxia at harvesting using mechanisms dependent on innervation.

Intravenous glycine improves survival in rat liver transplantation

In situ manipulation by touching, retracting, and moving liver lobes gently during harvest dramatically reduces survival after transplantation (P. Schemmer, R. Schoonhoven, J. A. Swenberg, H. Bunzendahl, and R. G. Thurman. Transplantation 65: 1015-1020, 1998). The development of harvest-dependent graft injury upon reperfusion can be prevented with GdCl3, a rare earth metal and Kupffer cell toxicant, but it cannot be used in clinical liver transplantation because of its potential toxicity. Thus the effect of glycine, which prevents activation of Kupffer cells, was assessed here. Minimal dissection of the liver for 12 min plus 13 min without manipulation had no effect on survival (100%). However, gentle manipulation decreased survival to 46% in the control group. Furthermore, serum transaminases and liver necrosis were elevated 4- to 12-fold 8 h after transplantation. After organ harvest, the rate of entry and exit of fluorescein dextran, a dye confined to the vascular space, was decreased about twofold, indicating disturbances in the hepatic microcirculation. Pimonidazole binding, which detects hypoxia, increased about twofold after organ manipulation, and Kupffer cells isolated from manipulated livers produced threefold more tumor necrosis factor-alpha after lipopolysaccharide than controls. Glycine given intravenously to the donor increased the serum glycine concentration about sevenfold and largely prevented the effect of gentle organ manipulation on all parameters studied. These data indicate for the first time that pretreatment of donors with intravenous glycine minimizes reperfusion injury due to organ manipulation during harvest and after liver transplantation.

Pimonidazole: a novel hypoxia marker for complementary study of tumor hypoxia and cell proliferation in cervical carcinoma

BACKGROUND

Tumor hypoxia may be associated with treatment resistance, cell proliferation, and metastatic potential, which contribute to poor prognosis. Complementary techniques for detecting hypoxia, cell growth, and metastases are required to study these relationships.

OBJECTIVES

The purpose of this study was to demonstrate the clinical feasibility of quantitative hypoxia detection with pimonidazole, a novel hypoxia marker, and to correlate hypoxia with S-phase markers of tumor proliferation.

METHODS

Pimonidazole binds to thiol-containing proteins specifically in hypoxic cells. Ten patients with cervical carcinoma received 0.5 g/m2 pimonidazole intravenously followed by biopsy of the cervical carcinoma the next day. Hypoxic cells were recognized by immunohistochemical detection of pimonidazole using a mouse monoclonal antibody. Cell proliferation was detected with a commercially available monoclonal antibody for proliferating cell nuclear antigen (PCNA). Assessment of hypoxia and cell proliferation was made qualitatively with light microscopy and quantitatively using point counting and image analysis software methods.

RESULTS

No clinical toxic effects were associated with pimonidazole administration. Immunostaining with pimonidazole antibody was observed in 9 of 10 tumors, suggesting that hypoxia is a common occurrence in cervical carcinoma. Quantitatively, tumors that had large numbers of hypoxic cells had the greatest percentage of S-phase cells, but some tumors with smaller amounts of hypoxia also had substantial numbers of S-phase cells.

CONCLUSION

Pimonidazole can be used for qualitative and quantitative assessment of tumor hypoxia.

Cyclosporin A increases hypoxia and free radical production in rat kidneys: prevention by dietary glycine

The major side effect of cyclosporin A is severe nephrotoxicity. It is likely that cyclosporin A causes vasoconstriction leading to hypoxia-reperfusion injury; therefore, these experiments were designed to attempt to obtain physical evidence for hypoxia and free radical production in kidney following cyclosporin A. Rats were treated daily with cyclosporin A (25 mg/kg ig) for 5 days, and pimonidazole, a hypoxia marker, was injected 2 h after the last dose of cyclosporin A. A dose of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) was injected 3 h after cyclosporin A to trap free radicals. Cyclosporin A doubled serum creatinine and decreased glomerular filtration rates by 65% as expected. Pimonidazole adduct binding in the kidney was increased nearly threefold by cyclosporin A, providing physical evidence for tissue hypoxia. Moreover, cyclosporin A increased 4-POBN/radical adducts nearly sixfold in the urine but did not alter levels in the serum. Glycine, which causes vasodilatation and prevents cyclosporin A toxicity, minimized hypoxia and blocked free radical production; however, it did not alter cyclosporin A blood levels. These results demonstrate for the first time that cyclosporin A causes hypoxia and increases production of a new free radical species exclusively in the kidney. Therefore, it is concluded that cyclosporin A causes renal injury by mechanisms involving hypoxia-reoxygenation, effects which can be prevented effectively by dietary glycine.

Proliferation and hypoxia in human squamous cell carcinoma of the cervix: first report of combined immunohistochemical assays

PURPOSE

To characterize the distribution of hypoxia and proliferation in human squamous cell carcinoma of the cervix via an immunohistochemical approach prior to initiation of therapy.

METHODS AND MATERIALS

Patients with primary squamous cell carcinoma of the cervix uteri received a single infusion of the 2-nitroimidazole, pimonidazole (0.5 g/m2 i.v.), and 24 h later punch biopsies of the primary tumor were taken. Tissue was formalin fixed, paraffin embedded, and sectioned for immunohistochemistry. Hypoxia was detected by monoclonal antibody binding to adducts of reductively activated pimonidazole in malignant cells. Staining for endogenous MIB-1 and PCNA was detected in tumor cells via commercially available monoclonal antibodies. Point counting was used to quantitate the fraction of tumor cells immunostained for MIB-1, PCNA, and hypoxia marker binding.

RESULTS

Immunostaining for pimonidazole binding was distant from blood vessels. There was no staining in necrotic regions, and only minimal nonspecific staining, mostly in keratin. In general, cells immunostaining for MIB-1 and PCNA did not immunostain for pimonidazole binding. Cells immunostaining for MIB-1 and PCNA showed no obvious geographic predilection such as proximity to vasculature. Quantitative comparison showed an inverse relationship between hypoxia marker binding and proliferation.

CONCLUSIONS

Immunohistochemical staining for pimonidazole binding is consistent with the presence of hypoxic cells in human tumors and may be useful for estimating tumor hypoxia prior to radiation therapy. Immunostaining for pimonidazole binding is an ideal complement to immunohistochemical assays for endogenous proliferation markers allowing for comparisons of tumor hypoxia with other physiological parameters. These parameters might be used to select patients for radiation protocols specifically designed to offset the negative impact of hypoxia and/or proliferation on therapy. The inverse relationship between pimonidazole binding and proliferation markers is a preliminary result requiring verification.

Marking hypoxic cells for complement and cytotoxic T lymphocyte-mediated lysis: using pimonidazole

Artificial antigens are created when 2-nitroimidazoles bind to hypoxic cells. These antigens have been used in the immunodetection of tumour hypoxia but they might also serve to stimulate immune lysis of hypoxic tumour cells by complement- and cell-mediated processes. In order to test this hypothesis, lymphocytes isolated from the spleens of C3H/HeN mice that had been immunised with pimonidazole-labelled 3152-PRO cells were subcultured and tested for their ability to lyse chromium-51 loaded, pimonidazole-labelled 3152-PRO cells in an in vitro assay. In a parallel study, commercially available, rabbit complement was tested for its ability to lyse pimonidazole-labelled V79-4 cells in the presence of monoclonal antibodies which recognise protein adducts of reductively activated pimonidazole. Complement-mediated cell lysis was measured by means of an MTT assay. Complement-mediated and cell-mediated lysis was observed at pimonidazole concentrations which, in themselves, do not produce cell killing.

Detection of individual hypoxic cells in multicellular spheroids by flow cytometry using the 2-nitroimidazole, EF5, and monoclonal antibodies

PURPOSE

The purpose of this work was to evaluate EF5, a 2-nitroimidazole compound, and anti-EF5 antibodies as a method to quantify radiobiologically hypoxic cells.

METHODS AND MATERIALS

Multicellular spheroids of EMT6 mammary sarcoma cells were used as a model to identify hypoxic cells that were resistant to radiation damage. This was accomplished by incubating the spheroids with the 2-nitroimidazole (EF5), which forms hypoxia-dependent adducts with cellular macromolecules that are detected by fluorescent monoclonal antibodies.

RESULTS

Cells from spheroids grown for 2 days in sealed flasks had an increased surviving fraction following radiation as compared to fully reoxygenated spheroids, indicating the presence of radiobiological hypoxia. Treatment of the spheroids with EF5 and subsequent immunohistochemical staining of cryosections with an anti-EF5 fluorochrome conjugated monoclonal antibody allowed for the identification of EF5-adduct containing cells. Spheroids grown under hypoxic conditions in the presence of EF5 showed limited staining of the peripheral cell layers, intense staining of the interior, and an absence of staining within the necrotic center. In contrast, there was minimal staining in reoxygenated spheroids and no staining in control spheroids incubated in the absence of EF5. Flow cytometric analysis of single cells dissociated from spheroids allowed for the calculation of the percentage of stained cells, as well as the intensity of staining. A comparison of the intensity of staining of EF5 treated hypoxic spheroids with the intensity of staining of single cells incubated with EF5 under controlled oxygen concentrations was used to estimate the oxygen concentration range within spheroids. Selective dissociation of spheroids provided a direct demonstration that the cells containing the highest level of EF5 binding were also the cells with increased radiation resistance.

CONCLUSION

This technique provides an excellent means of detecting and quantifying hypoxia, which should be directly applicable in tumors.

Evidence that hypoxia markers detect oxygen gradients in liver: pimonidazole and retrograde perfusion of rat liver

Nitroimidazole markers of tumour hypoxia bind to normoxic liver and the question has been raised whether this is due to low oxygen concentration or microregional activity of specialised nitroreductases. To answer this question, the binding patterns of the 2-nitroimidazole, pimonidazole, were compared following perfusion of surgically isolated rat livers in anterograde and retrograde directions. Perfusion at low flow rates in anterograde or retrograde directions can be used intentionally to alter oxygen gradients without altering enzyme distributions. Perfusion by means of the portal vein (anterograde direction) produced pimonidazole binding in the pericentral region of liver similar to that observed for pimonidazole binding in vivo. A complete reversal of this binding pattern occurred when the isolated liver was perfused by way of the central vein (retrograde direction). In this case, pimonidazole binding occurred in the periportal region. The extent and intensity of binding in the periportal region during perfusion in the retrograde direction was similar to that in the pericentral region during perfusion in the anterograde direction. It is concluded that low oxygen concentration rather than the non-homogeneous distribution of nitroreductase activity is the primary determinant of 2-nitroimidazole binding in liver.

The novel fluorinated 2-nitroimidazole hypoxia probe SR-4554: reductive metabolism and semiquantitative localisation in human ovarian cancer multicellular spheroids as measured by electron energy loss spectroscopic analysis

The novel fluorinated 2-nitroimidazole SR-4554 is undergoing preclinical development as a magnetic resonance spectroscopy and imaging probe for hypoxic tumour cells. We have used electron energy loss spectroscopic analysis (EELS) to show selective reduction and differential subcellular localisation of SR-4554 in human ovarian multicellular spheroids. SR-4554 was demonstrated to be metabolised by these A2780 cells under hypoxic but not under normal aerobic cell culture conditions. The EELS technique illustrated that the relative amount of drug within the cytoplasm of cells from both the inner region (150-160 microns from edge) and outer edge of the spheroid did not differ significantly after an initial 3 h incubation with drug. In contrast, an 8-fold differential between the amount of drug retained in the cytoplasm (primarily ribosomes and endoplasmic reticulum) of cells from the inner vs outer regions of the spheroids was observed following a subsequent 2 h 'chase' culture in drug-free medium. Within cells from the hypoxic region of the spheroid, SR-4554 was mainly associated with the endoplasmic reticulum, nucleus and the cytoplasmic side of intracellular vesicles and also to a lesser extent with the nuclear periphery. Interestingly, the drug was only weakly associated with the mitochondria and plasma membrane of the cells. The characteristics of cellular and subcellular distribution of SR-4554 are consistent with the hypothesis that 2-nitroimidazole compounds undergo hypoxia-mediated enzymatic reduction to reactive species. These reactive species are selectively retained in the cells in which they are metabolised through covalent association with subcellular components. These findings provide additional support for the clinical development of the drug as a non-invasive probe for tumour hypoxia and at the same time illustrate the utility of the EELS technique for examining the heterogeneity of drug distribution both between and within cells.