Development of an ELISA for the detection of 2-nitroimidazole hypoxia markers bound to tumor tissue

A Microfluidic Chip-Based MRS Immunosensor for Biomarker Detection via Enzyme-Mediated Nanoparticle Assembly

Conventional immunoassay methods have their common defects, such as tedious processing steps and inadequate sensitivity, in detecting whole blood. To overcome the above problems, we report a microfluidic chip-based magnetic relaxation switching (MRS) immunosensor via enzyme-mediated nanoparticles to simplify operation and amplify the signal in detecting whole blood samples. In the silver mirror reaction with catalase (CAT) as the catalyst, H2O2 can effectively control the production of Ag NPs. The amount of Ag NPs formed further affects the degree of aggregation of magnetic nanoparticles (MNPS), which gives rise to the changes of transverse relaxation time (T2). Both sample addition and reagent reaction are carried out in the microfluidic chip, thereby saving time and reagent consumption. We also successfully apply the sensor to detect alpha-fetoprotein (AFP) in real samples with a satisfied limit of detection (LOD = 0.56 ng/ml), which is superior to the conventional ELISA.

Importance of antibody concentration in the assessment of cellular hypoxia by flow cytometry: EF5 and pimonidazole

The binding kinetics of the hypoxia marker EF5 can be quantified by uptake of (14)C-labeled drug or calibrated flow cytometry using antibodies specific for drug adducts. Maximum EF5 binding is cell-line dependent and varies directly with drug exposure (area under the curve; concentration integrated over time) but inversely with pO(2) from 0 to >100 mmHg. For pimonidazole, binding is reported to be independent of the cell line and drug AUC, being zero above 10 mmHg, with an easily discriminated increase at lower pO(2). The basis for these kinetic differences is unknown, but the main experimental variable distinguishing the two marker techniques is antibody concentration ([Ab] - pimonidazole << EF5). In this study, EF5 and pimonidazole binding kinetics were compared as a function of pO(2) and antibody concentration in cells of two rat (9L and R3230) and two human (HT1080 and SiHa) cancer cell lines. For both markers, binding varied directly with AUC at all pO(2). The dynamic range of observed binding (maximum change from 0 to 76 mmHg oxygen) decreased with antibody concentration. The pO(2) dependence of binding for pimonidazole, but not EF5, varied dramatically with antibody concentration. Thus the data presented herein do not support the reported binding kinetics of pimonidazole. In particular, it is shown that the common use of antibody concentrations much lower than antigen concentrations can lead to unreliable estimations of adduct level and hence pO(2).

Dynamics of tumor hypoxia measured with bioreductive hypoxic cell markers

Hypoxic cells are common in tumors and contribute to malignant progression, distant metastasis and resistance to radiotherapy. It is well known that tumors are heterogeneous with respect to the levels and duration of hypoxia. Several strategies, including high-oxygen-content gas breathing, radiosensitizers and hypoxic cytotoxins, have been developed to overcome hypoxia-mediated radioresistance. However, with these strategies, an increased tumor control rate is often accompanied by more severe side effects. Consequently, development of assays for prediction of tumor response and early monitoring of treatment responses could reduce both over- and undertreatment, thereby avoiding unnecessary side effects. The purpose of this review is to discuss different assays for measurement of hypoxia that can be used to detect changes in oxygen tension. The main focus is on exogenous bioreductive hypoxia markers (2-nitroimidazoles) such as pimonidazole, CCI-103F, EF5 and F-misonidazole. These are specifically reduced and bind to macromolecules in viable hypoxic cells. A number of these bioreductive drugs are approved for clinical use and can be detected with methods ranging from noninvasive PET imaging (low resolution) to microscopic imaging of tumor sections (high resolution). If the latter are stained for multiple markers, hypoxia can be analyzed in relation to different microenvironmental parameters such as vasculature, proliferation and endogenous hypoxia-related markers, for instance HIF1alpha and CA-IX. In addition, temporal and spatial changes in hypoxia can be analyzed by consecutive injection of two different hypoxia markers. Therefore, bioreductive exogenous hypoxia markers are promising as tools for development of predictive assays or as tools for early treatment monitoring and validation of potential endogenous hypoxia markers.

A comparison of oral and intravenous pimonidazole in canine tumors using intravenous CCI-103F as a control hypoxia marker

PURPOSE

Pimonidazole HCl is widely used in immunohistochemical analyses of hypoxia in normal and malignant tissues. The present study investigates oral administration as a means of minimizing invasiveness.

METHODS AND MATERIALS

Twelve dogs with confirmed malignancy received 0.5 g/m2 of pimonidazole HCl: 6 by mouth and 6 by i.v. infusion. All dogs received i.v. CCI-103F as a control. Plasma levels of pimonidazole, pimonidazole N-oxide, and CCI-103F were measured. Tumor biopsies were formalin fixed, paraffin embedded, sectioned, immunostained, and analyzed for pimonidazole and CCI-103F binding. pH dependence for pimonidazole and CCI-103F binding was studied in vitro.

RESULTS

Pimonidazole and CCI-103F binding in carcinomas and sarcomas was strongly correlated for both oral and i.v. pimonidazole HCl (r2=0.97). On average, the extent of pimonidazole binding exceeded that for CCI-103F by a factor of approximately 1.2, with the factor ranging from 1.0 to 1.65. Binding of both markers was pH dependent, but pimonidazole binding was greater at all values of pH.

CONCLUSIONS

Oral pimonidazole HCl is effective as a hypoxia marker in spontaneously arising canine tumors. Selective cellular uptake and concomitant higher levels of binding in regions of hypoxia at the high end of pH gradients might account for the greater extent of pimonidazole binding.

Mechanism of hypertensive nephropathy in the Dahl/Rapp rat: a primary disorder of vascular smooth muscle

The Dahl/Rapp salt-sensitive (S) rat is a model of salt-sensitive hypertension and hypertensive renal disease. This study explored the role of vascular remodeling in the development of renal failure in S rats. Groups of S and Sprague-Dawley rats were given 0.3 and 8.0% NaCl diets for up to 21 days and evidence of smooth muscle proliferation identified using immunohistochemistry that showed nuclear accumulation of proliferating cell nuclear antigen and 5-bromo-2′-deoxy-uridine. Compared with the other three groups, S rats on 8.0% NaCl diet showed increased nuclear labeling of cells of the aorta and arteries and arterioles of the kidney by the end of the first week of study. Progressive luminal narrowing of the interlobular arteries and preglomerular arterioles occurred in S rats over the 3 wk on the 8.0% NaCl diet. Accumulation of pimonidazole adducts and nuclear accumulation of hypoxia-inducible factor-1α (HIF-1α) were used as markers of tissue hypoxia. By the end of the second week of study, pimonidazole levels increased in S rats on 8.0% NaCl diet and deposition was apparent in tubular cells in the cortex and medulla. At the completion of the experiment, HIF-1α levels were increased in nuclear extracts from the cortex and medulla of S rats on this diet, compared with the other three groups of rats. The data demonstrated a disorder of the vascular remodeling process with proliferation of vascular smooth muscle cells temporally followed by development of tissue hypoxia in the hypertensive nephropathy of S rats on 8.0% NaCl diet.

Metabolic mapping with bioluminescence: basic and clinical relevance

This review is focused on metabolic mapping in biological tissue with quantitative bioluminescence and single photon imaging. Metabolites, such as ATP, glucose and lactate, can be imaged quantitatively and within microscopic dimensions in cryosections from shock frozen biological specimens using enzyme reactions and light emission by luciferases. The technique has been applied in numerous targets and models of experimental biomedical research, such as multicellular spheroids, various organs of laboratory animals in a physiological or pathophysiological state, and even in plant seeds. Among numerous other aspects, data obtained with this method have contributed to the elucidation of mechanisms that are involved in the development of necrosis in multicellular spheroids. The combination of the bioluminescence technique with immunohistochemistry, autoradiography or in situ hybridization can considerably reduce ambiguities in the interpretation of the experimental results. Although, an invasive technique, bioluminescence imaging has been used most intensively in clinical oncology using tumor biopsies taken at the first diagnosis of the disease. It has been shown for squamous cell carcinomas of the head and neck and of the uterine cervix that accumulation of high levels of lactate in the primary lesions is associated with a high risk of metastasis formation and a reduced overall and disease-free patient survival. Thus, metabolic imaging can provide additional information on the degree of malignancy and the prognosis of tumors which may help the oncologist in improving specific treatment approaches for each individual malignant disease. Last but not least, metabolic mapping in clinical oncology has stimulated a number of investigations in basic cancer research on mechanisms that underlie the correlation between tumor metabolism and malignancy.

Spontaneously occurring tumors of companion animals as models for human cancer

Spontaneous tumors in companion animals (dog and cat) offer a unique opportunity as models for human cancer biology and translational cancer therapeutics. The relatively high incidence of some cancers, similar biologic behavior, large body size, comparable responses to cytotoxic agents, and shorter overall lifespan are the factors that contribute to the advantages of the companion animal model. The tumor types that offer the best comparative interest include lymphoma/leukemia, osteosarcoma, STS, melanoma, and mammary tumors. With the increase in new therapeutic agents (traditional chemotherapy, gene therapy, biologic agents, etc.), the companion animal model can provide useful populations to test new agents where efficacy and toxicity can be examined.

Early wound healing exhibits cytokine surge without evidence of hypoxia

OBJECTIVE

To ascertain the spatial and temporal relation of wound hypoxia to the cell types involved, expression of selected angiogenic cytokines, the proliferative status of cells in the wound site, and angiogenesis.

SUMMARY BACKGROUND DATA

Hypoxia is considered to drive the angiogenic response by upregulating angiogenic cytokines observed during wound healing. But this correlation has not been shown on a cell-to-cell basis in vivo because of limitations in measuring tissue PO2 at the cellular level.

METHODS

Using punch biopsy wounds in rats as a wound healing model, the distributions of vascular endothelial growth factor, transforming growth factor-beta, tumor necrosis factor-alpha, and pimonidazole adducts (as a hypoxia marker) were followed immunohistochemically during the healing process.

RESULTS

Hypoxia was absent on day 1 after wounding, even though angiogenesis and maximal expression of cytokines were observed in the wounds. Hypoxia peaked in the granulation tissue stage at day 4 and correlated with increased cellularity and cellular proliferation. Hypoxia started to decrease after day 4 and was limited to the remnant blood vessels and epithelial layer in the scar tissue.

CONCLUSIONS

Induction of angiogenic cytokines early during wound healing may be due to triggering mechanisms other than hypoxia. Alternatively, the unique pattern of development and decline of cellular hypoxia as wound cellularity and proliferation regress suggest its involvement in initiating vascular regression during the later stages of healing.

Feasibility study of lactate imaging of head and neck tumors

A proton spectroscopic imaging sequence was used to investigate the feasibility of lactate imaging in head and neck tumors. The sequence employs a two-shot lactate editing method with inversion recovery for additional lipid suppression, and a restricted field of view to suppress motion artifacts. Variations in acquisition parameters and two different receive coils were investigated on twelve patients. Elevated lactate was detected in three patients, no lactate was observed in seven patients, and two studies were inconclusive because of severe motion or inhomogeneity artifacts. Best results were obtained with an anterior/posterior neck coil at a 288 ms echo time (TE).

ELISA quantification of CCI-103F binding in canine tumors prior to and during irradiation

PURPOSE

The purpose of this work was to evaluate multiple injections of CCI-103F, a marker of hypoxia, as a method to quantify alterations in tumor hypoxia during irradiation.

METHODS AND MATERIALS

Twelve dogs with spontaneous solid tumors were given intravenous CCI-103F, and tumor biopsies were taken at various times after injection. Two tumor samples were taken at each biopsy procedure. CCI-103F antigen concentration was quantified by ELISA. Four of the dogs were given one injection of CCI-103F, and the other eight received two injections. In dogs receiving two injections, CCI-103F was administered before irradiation and 7 days later, following a total dose of 15.0 Gy. Plasma CCI-103F pharmacokinetics were assessed in dogs receiving two injections.

RESULTS

CCI-103F antigen was detectable in the initial biopsy in each of the four dogs receiving one injection, and the amount of detectable antigen decreased in subsequent biopsies with an initial half life of approximately 19 h. This suggests that multiple injections of CCI-103F could be used in the same subject to monitor tumor hypoxia as a function of time or during a course of treatment. In the eight dogs receiving two injections of CCI-103F, the CCI-103F antigen concentration in the 24 h samples ranged from 4.66-151.9 mumol CCI-103F antigen/kg tumor, a difference of a factor of approximately 33. The ratio of maximum to minimum concentration of CCI-103F antigen in 51 paired biopsy samples ranged from 1.01-4.07, with a mean (+/- s.d.) of 1.67 +/- 0.67. Seventy-five percent of the ratios were < or = 2.02. There was no apparent relationship between the magnitude of the ratio, i.e., intratumoral variation, and tumor volume or the absolute tumor concentration of CCI-103F antigen. Absolute radiobiologic hypoxic fraction was not known but the pattern of change in amount of intratumoral CCI-103F antigen in dogs given two injections of CCI-103F was consistent with little change in pretreatment oxygen status in six dogs, and an increase in tumor oxygenation in two dogs.

CONCLUSION

It appears possible to obtain an estimate of the change in tumor hypoxia in an individual tumor over time by assaying biopsy samples for CCI-103F antigen concentration.

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

An enzyme-linked immunosorbent assay (ELISA) has been developed for measuring the in vivo binding of a hexafluorinated 2-nitroimidazole (CCI-103F) in tumour tissue biopsies. The binding of CCI-103F is believed to reflect the presence of hypoxia in tumours. The ELISA provides a sensitive and convenient method of measuring CCI-103F binding which does not require the injection of radioactive reagents. The ELISA is based on reagents prepared from synthetic antigens formed by the reductive activation and binding of CCI-103F to proteins in novel test tube experiments. Calibration of the ELISA involved comparing the ELISA with the radioactivity contained either in protein-CCI-103F adducts formed in vitro with tritiated CCI-103F or in tissues isolated from a tumour-bearing dog which had been injected with tritium-labelled CCI-103F. The two approaches to calibration are compared. The scope and limitation of the ELISA for measuring the binding of CCI-103F is discussed and an example of the application of the ELISA to measuring changes in tumour hypoxia in canine patients undergoing fractionated radiation therapy is presented.

The relationship between proliferative and oxygenation status in spontaneous canine tumors

PURPOSE

Immunocytochemical markers have been applied to biopsy specimens from spontaneous canine tumors to assess the prevalence and spatial distribution of proliferating and hypoxic cells, and their "geographic" relationship to each other. Both types of cells have been implicated in the failure to locally control human tumors treated with radiation and chemotherapy.

METHODS AND MATERIALS

For the detection of hypoxic cells, a rabbit polyclonal antibody raised against a protein-bound, hexafluorinated, 2-nitroimidazole, designated CCI-103F, was used. The unmetabolized drug must first be injected into the dog to allow time for hypoxic metabolism and cellular binding to occur. For the detection of proliferating cells, a mouse monoclonal antibody raised against an endogenous nuclear protein, the "proliferating cell nuclear antigen," or PCNA, was used. This protein is expressed in most actively proliferating cells, but not in quiescent ones. An indirect immunostaining technique was used to visualize these markers in the tissue sections, and image analysis was used to estimate the area fraction of positive staining in representative, low magnification microscope fields.

RESULTS

Tumors with both high and low hypoxic and proliferative area fractions have been identified. No systematic relationship between the prevalence of the two markers, nor of the relationship between tumor grade and proliferative fraction, could be established. Staining with the proliferation marker was more commonly found near blood vessels, but some "nests" of tumor cells apparently distant from vasculature contained many proliferating cells. Staining with the hypoxia marker tended to be distant from the vasculature and/or bordering regions of tumor necrosis, but some labeled cells appeared near blood vessels, and in the absence of necrosis. Staining of sequential sections, one with the proliferation marker and one with the hypoxia marker, indicated that the two cell populations overlapped to varying extents. Some incidental staining of canine normal tissues with both the proliferative and hypoxia markers was observed as well.

CONCLUSION

The immunochemical marker approach promises to be a useful tool to increase both our basic understanding of tumor physiology and the complex nature of tumor heterogeneity.