Distribution of hypoxia and proliferation associated markers in spontaneous canine tumors

Canine Cancer: Strategies in Experimental Therapeutics

Cancer is the most common cause of death in adult dogs. Many features of spontaneously developing tumors in pet dogs contribute to their potential utility as a human disease model. These include similar environmental exposures, similar clonal evolution as it applies to important factors such as immune avoidance, a favorable body size for imaging and serial biopsy, and a relatively contracted time course of disease progression, which makes evaluation of temporal endpoints such as progression free or overall survival feasible in a comparatively short time frame. These criteria have been leveraged to evaluate novel local therapies, demonstrate proof of tumor target inhibition or tumor localization, evaluate potential antimetastatic approaches, and assess the efficacy, safety and immune effects of a variety of immune-based therapeutics. Some of these canine proof of concept studies have been instrumental in informing subsequent human clinical trials. This review will cover key aspects of clinical trials in dogs with spontaneous neoplasia, with examples of how these studies have contributed to human cancer therapeutic development.

High-uptake areas on positron emission tomography with the hypoxic radiotracer (18)F-FRP170 in glioblastomas include regions retaining proliferative activity under hypoxia

Objective

The aim was to evaluate the proliferative activity of high-uptake areas on positron emission tomography (PET) with the hypoxic cell radiotracer, 1-(2-[¹⁸F]fluoro-1-[hydroxymethyl]ethoxy)methyl-2-nitroimidazole (FRP170).

Methods

Thirteen patients with glioblastoma underwent FRP170 PET before tumor resection. During surgery, tumor specimens were stereotaxically obtained from regions corresponding to high (high-uptake areas, HUAs) and relatively low (low-uptake areas, LUAs) accumulation of FRP170. We compared immunohistochemical staining for Ki-67 and hypoxia-inducible factor (HIF)-1α between HUA and LUA.

Results

HIF-1α index was significantly higher in HUAs than in LUAs. In contrast, mean Ki-67 indices did not differ significantly between HUAs and LUAs.

Conclusions

Findings for HIF-1α index clearly indicated that HUAs on FRP170 PET represented hypoxic regions in glioblastoma. However, findings of Ki-67 index suggest that HUAs on FRP170 PET include regions retaining proliferative activity regardless of tissue hypoxia.

No detectable hypoxia in malignant salivary gland tumors: preliminary results

PURPOSE

Hypoxia is detected in most solid tumors and is associated with malignant progression and adverse treatment outcomes. However, the oxygenation status of malignant salivary gland tumors has not been previously studied. The aim of this study was to investigate the potential clinical relevance of hypoxia in this tumor type.

METHODS AND MATERIALS

Twelve patients scheduled for surgical resection of a salivary gland tumor were preoperatively injected with the hypoxia marker pimonidazole and the proliferation marker iododeoxyuridine. Tissue samples of the dissected tumor were immunohistochemically stained for blood vessels, pimonidazole, carbonic anhydrase-IX, glucose transporters-1 and -3 (Glut-1, Glut-3), hypoxia-inducible factor-1alpha, iododeoxyuridine, and epidermal growth factor receptor. The tissue sections were quantitatively assessed by computerized image analysis.

RESULTS

The tissue material from 8 patients was of sufficient quality for quantitative analysis. All tumors were negative for pimonidazole binding, as well as for carbonic anhydrase-IX, Glut-1, Glut-3, and hypoxia-inducible factor-1alpha. The vascular density was high, with a median value of 285 mm(-2) (range, 209-546). The iododeoxyuridine-labeling index varied from <0.1% to 12.2% (median, 2.2%). Epidermal growth factor receptor expression levels were mostly moderate to high. In one-half of the cases, nuclear expression of epidermal growth factor receptor was observed.

CONCLUSION

The absence of detectable pimonidazole binding, as well as the lack of expression of hypoxia-associated proteins in all tumors, indicates that malignant salivary gland tumors are generally well oxygenated. It is unlikely that hypoxia is a relevant factor for their clinical behavior and treatment responsiveness.

Tumor microenvironment in head and neck squamous cell carcinomas: Predictive value and clinical relevance of hypoxic markers. A review

BACKGROUND

Hypoxia and tumor cell proliferation are important factors determining the treatment response of squamous cell carcinomas of the head and neck. Successful approaches have been developed to counteract these resistance mechanisms although usually at the cost of increased short- and long-term side effects. To provide the best attainable quality of life for individual patients and the head and neck cancer patient population as a whole, it is of increasing importance that tools be developed that allow a better selection of patients for these intensified treatments.

METHODS

A literature review was performed with special focus on the predictive value and clinical relevance of endogenous hypoxia-related markers.

RESULTS

New methods for qualitative and quantitative assessment of functional microenvironmental parameters such as hypoxia, proliferation, and vasculature have identified several candidate markers for future use in predictive assays. Hypoxia-related markers include hypoxia inducible factor (HIF)-1alpha, carbonic anhydrase IX, glucose transporters, erythropoietin receptor, osteopontin, and others. Although several of these markers and combinations of markers are associated with treatment outcome, their clinical value as predictive factors remains to be established.

CONCLUSIONS

A number of markers and marker profiles have emerged that may have potential as a predictive assay. Validation of these candidate assays requires testing in prospective trials comparing standard treatment against experimental treatments targeting the related microregional constituent.

Colocalization of Carbonic Anhydrase 9 Expression and Cell Proliferation in Human Head and Neck Squamous Cell Carcinoma

Purpose: Tumor cells undergo a variety of biological changes under sustained hypoxic conditions, allowing cells to survive and retain their clonogenic potential. The purpose of this study is to relate the expression of the hypoxia marker carbonic anhydrase 9 (CA9) to the uptake of iododeoxyuridine (IdUrd), a marker of proliferation, in head and neck squamous cell carcinomas. Colocalization of IdUrd and CA9 may identify an important subpopulation of tumor cells that might be responsible for repopulation and disease progression.

Experimental Design: Expression of CA9, IdUrd labeling, and colocalization between IdUrd and CA9 was examined by immunohistochemistry in biopsies of head and neck squamous cell carcinomas. Biopsies were taken from 51 patients recruited between 1998 and 2001 after administration of the proliferation marker IdUrd.

Results: A large variation was observed between the tumors in CA9 expression (range 0-39%), IdUrd labeling (range 0-81%), and colocalization between IdUrd and CA9 [FId(CA9); range 0-53%]. FId(CA9), the fraction of IdUrd-labeled cells positive for CA9, was highest at an intermediate distance from the blood vessels (100-150 μm). IdUrd labeling was higher in T4 carcinomas relative to lower stage tumors (P = 0.04). High FId(CA9) correlated with the worst disease-free survival rates (P = 0.04).

Conclusions: Colocalization between IdUrd labeling and CA9 expression was observed in head and neck squamous cell carcinomas, suggesting the presence of a population of tumor cells under intermediate hypoxic conditions which still has proliferative capacity. The size of this subpopulation may be indicative of tumor aggressiveness and is associated with the worst disease-free survival rates.

The role of hypoxia inducible factor 1 (HIF-1) in hypoxia induced apoptosis

Apoptosis can be induced in response to hypoxia. The severity of hypoxia determines whether cells become apoptotic or adapt to hypoxia and survive. A hypoxic environment devoid of nutrients prevents the cell undergoing energy dependent apoptosis and cells become necrotic. Apoptosis regulatory proteins are delicately balanced. In solid tumours, hypoxia is a common phenomenon. Cells adapt to this environmental stress, so that after repeated periods of hypoxia, selection for resistance to hypoxia induced apoptosis occurs. These resistant tumours probably have a more aggressive phenotype and may have decreased responsiveness to treatment. The key regulator of this process, hypoxia inducible factor 1 (HIF-1), can initiate apoptosis by inducing high concentrations of proapoptotic proteins, such as BNIP3, and can cause stabilisation of p53. However, during hypoxia, antiapoptotic proteins, such as IAP-2, can be induced, whereas the proapoptotic protein Bax can be downregulated. During hypoxia, an intricate balance exists between factors that induce or counteract apoptosis, or even stimulate proliferation. Understanding the regulation of apoptosis during hypoxia and the mechanisms of resistance to apoptosis might lead to more specific treatments for solid tumours.

The immunohistochemical assessment of hypoxia, vascularity and proliferation in bladder carcinoma

BACKGROUND AND PURPOSE

Hypoxia and proliferation are important determinants of radiation responsiveness; prospective measures of these before radiotherapy may enable individualisation of treatment schedules. Immunohistochemical techniques offer a potential means of achieving this in routine biopsy material.

MATERIAL AND METHODS

Cellular hypoxia as measured by pimonidazole fixation and immunohistochemistry has been evaluated in a series of human bladder cancers with dual staining of sections for pimonidazole and either the vascular markers, CD31/34, or proliferation markers, Ki-67 or cyclin A. Twenty one tumour specimens were examined suitable for the double staining technique.

RESULTS

The median hypoxic fraction was 9% (range 0-38). Seven tumours did not stain for pimonidazole and 11 exhibited necrosis. The mean vascular density ranged from 16.7 to 160.6 vessels per mm2. The median hot spot count was 30 (range 16-43). There was a statistically significant increase in vessel density in hypoxic compared to oxic regions measured by both vessel density (P = 0.02) and hot spot count (P = 0.004). Proliferation indices decreased from oxic to hypoxic areas close to blood vessels.

CONCLUSIONS

We have demonstrated that bladder cancer exhibits a range of hypoxia, proliferation and vascular density which may be used to form the basis for patient selection for hypoxia modification, accelerated radiotherapy and vascular targeting agents.

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.

Hypoxia imaging in brain tumors

Assessment of the oxygenation status of brain tumors has been studied increasingly with imaging techniques in light of recent advances in oncology. Tumor oxygen tension is a critical factor influencing the effectiveness of radiation and chemotherapy and malignant progression. Hypoxic tumors are resistant to treatment, and prognostic value of tumor oxygen status is shown in head and neck tumors. Strategies increasing the tumor oxygenation are being investigated to overcome the compromising [figure: see text] effect of hypoxia on tumor treatment. Administration of nicotinamide and inhalation of various high oxygen concentrations have been implemented. Existing methods for assessment of tissue oxygen level are either invasive or insufficient. Accurate and noninvasive means to measure tumor oxygenation are needed for treatment planning, identification of patients who might benefit from oxygenation strategies, and assessing the efficacy of interventions aimed to increase the radiosensitivity of tumors. Of the various imaging techniques used to assess tissue oxygenation, MR spectroscopy and MR imaging are widely available, noninvasive, and clinically applicable techniques. Tumor hypoxia is related closely to insufficient blood flow through chaotic and partially nonfunctional tumor vasculature and the distance between the capillaries and the tumor cells. Information on characteristics of tumor vasculature such as blood volume, perfusion, and increased capillary permeability can be provided with MR imaging. MR imaging techniques can provide a measure of capillary permeability based on contrast enhancement and relative cerebral blood volume estimates using dynamic susceptibility MR imaging. Blood oxygen level dependent contrast MR imaging using gradient echo sequence is intrinsically sensitive to changes in blood oxygen level. Animal models using blood oxygen level-dependent contrast imaging reveal the different responses of normal and tumor vasculature under hyperoxia. Normobaric hyperoxia is used in MR studies as a method to produce MR contrast in tissues. Increased T2* signal intensity of brain tissue has been observed using blood oxygen level-dependent contrast MR imaging. Dynamic blood oxygen level-dependent contrast MR imaging during hyperoxia is suggested to image tumor oxygenation. Quantification of cerebral oxygen saturation using blood oxygen level-dependent MR imaging also has been reported. Quantification of cerebral blood oxygen saturation using MR imaging has promising clinical applications; however, technical difficulties have to be resolved. Blood oxygen level dependent MR imaging is an emerging technique to evaluate the cerebral blood oxygen saturation, and it has the potential and versatility to assess oxygenation status of brain tumors. Upon improvement and validation of current MR techniques, better diagnostic, prognostic, and treatment monitoring capabilities can be provided for patients with brain tumors.

Vascular architecture, hypoxia, and proliferation in first-generation xenografts of human head-and-neck squamous cell carcinomas

PURPOSE

To quantify the physiologic status of human tumor cells in relation to the tumor vasculature.

METHODS AND MATERIALS

Fourteen tumors of 11 first-generation xenograft lines of human head-and-neck squamous cell carcinoma were injected with the hypoxic cell marker pimonidazole, the proliferation marker BrdUrd, and the perfusion marker Hoechst 33342. Consecutive tissue sections were processed with immunohistochemical methods and analyzed with image-analysis techniques.

RESULTS

Three different hypoxic patterns were found: patchy, ribbon-like, and mixed. An image-analysis method was developed to quantify these, and an elongation index (length/width) was calculated for hypoxia. The mean elongation indices ranged from 2.0 to 28.3 and showed a good correlation with the visual scoring of hypoxic patterns. Comparative analysis of hypoxic and proliferating cells in zones around the tumor vasculature showed the presence of both hypoxic and proliferating cells in all zones up to 250 microm from the vessels. The largest coexistence of hypoxic and proliferating cells seemed to occur at 50-100 microm from the vessels.

CONCLUSIONS

The three hypoxic patterns could be quantified by an elongation index, which is an additional parameter that allows distinction of tumors with similar fractions of hypoxic cells. The analysis of hypoxic and proliferating cells as a function of distance from the tumor vasculature indicates that proliferation does occur also at low oxygen tensions.

Differential oxygen dynamics in two diverse Dunning prostate R3327 rat tumor sublines (MAT-Lu and HI) with respect to growth and respiratory challenge

PURPOSE

Since hypoxia may influence tumor response to therapy and prognosis, we have compared oxygenation of tumors known to exhibit differential growth rate and tissue differentiation.

METHODS AND MATERIALS

Regional tumor oxygen tension was measured using 19F nuclear magnetic resonance echo planar imaging relaxometry of hexafluorobenzene, which provided dynamic maps with respect to respiratory intervention. Investigations used two Dunning prostate R3327 rat tumor sublines: the fast growing, highly metastatic MAT-Lu and the moderately well-differentiated, slower growing HI.

RESULTS

Both sublines showed significantly higher oxygen tension in smaller tumors (<2 cm(3)) than in larger tumors (>3.5 cm(3)). Pooled data showed that MAT-Lu tumors exhibited greater hypoxia compared with the size-matched HI tumors (p < 0.0001). Respiratory challenge (oxygen or carbogen) produced significant increases in mean pO(2) for tumors of both sublines (p < 0.0001). However, initially hypoxic regions displayed very different behavior in each subline: those in the HI tumors responded rapidly with significant elevation in pO(2), while those in the MAT-Lu tumors showed little response to respiratory intervention.

CONCLUSIONS

These results concur with hypotheses that hypoxia is related to tumor growth rate and degree of differentiation. Under baseline conditions, the differences were subtle. However, response to respiratory intervention revealed highly significant differences, which, if held valid in the clinic, could have prognostic value.

Hypoxia in the thymus: role of oxygen tension in thymocyte survival

Our previous studies using oxygen microelectrodes showed that the thymus is grossly hypoxic under normal physiological conditions. We now have investigated how oxygen tension affects the thymus at the cellular and molecular level. Adducts of the hypoxia marker drug pimonidazole accumulated in foci within the cortex and medulla and at the corticomedullary junction, consistent with the presence of widespread cellular hypoxia in the normal thymus. Hypoxia-associated pimonidazole accumulation was decreased but not abrogated by oxygen administration. Genes previously reported to be induced by hypoxia were expressed at baseline levels in the normal thymus, indicating that physiological adaptation to hypoxia occurred. Despite changes in thymus size and cellularity, thymic PO(2) did not change with age. Combined assays for hypoxia and cell death showed that hypoxia achieved using either hypoxic gas mixtures or high-density culture in normoxia decreased spontaneous thymocyte apoptosis in vitro. Taken together, these data suggest that regulatory mechanisms exist to maintain thymic cellular hypoxia in vivo and that oxygen tension may regulate thymocyte survival both in vitro and in vivo.

Hypoxia inhibits G1/S transition through regulation of p27 expression

Mammalian cellular responses to hypoxia include adaptive metabolic changes and a G1 cell cycle arrest. Although transcriptional regulation of metabolic genes by the hypoxia-induced transcription factor (HIF-1) has been established, the mechanism for the hypoxia-induced G1 arrest is not known. By using genetically defined primary wild-type murine embryo fibroblasts and those nullizygous for regulators of the G1/S checkpoint, we observed that the retinoblastoma protein is essential for the G1/S hypoxia-induced checkpoint, whereas p53 and p21 are not required. In addition, we found that the cyclin-dependent kinase inhibitor p27 is induced by hypoxia, thereby inhibiting CDK2 activity and forestalling S phase entry through retinoblastoma protein hypophosphorylation. Reduction or absence of p27 abrogated the hypoxia-induced G1 checkpoint, suggesting that it is a key regulator of G1/S transition in hypoxic cells. Intriguingly, hypoxic induction of p27 appears to be transcriptional and through an HIF-1-independent region of its proximal promoter. This demonstration of the molecular mechanism of hypoxia-induced G1/S regulation provides insight into a fundamental response of mammalian cells to low oxygen tension.

Semiquantitative immunohistochemical analysis for hypoxia in human tumors

OBJECTIVE

The goal of this study was to develop a semiquantitative scoring system for measuring hypoxia in human tumors by an immunohistochemical marker approach.

METHODS AND MATERIALS

Eighteen patients diagnosed with squamous cell carcinoma of the uterine cervix or head and neck were infused intravenously with a solution of pimonidazole hydrochloride at a dose of 0.5 gm/m2. Twenty-four hours later, four biopsies on average from each tumor were fixed in formalin, processed into paraffin blocks, and sectioned. Tissue sections were immunostained for the presence of pimonidazole adducts. Microscopic images (x200) of immunostaining were captured and quantitated by standard image analysis. Images with known amounts of hypoxia spanning ranges of > 0% to 5%, > 5% to 15%, > 15% to 30%, and >30% were assigned scores of +1, +2, +3, and +4, respectively. Three observers then used this calibrated scoring system to analyze hypoxia in tumor sections in a blinded fashion.

RESULTS

Excellent interobserver reproducibility was obtained with the calibrated, semiquantitative, immunohistochemical assay for hypoxia in squamous cell carcinomas.

CONCLUSION

The calibrated, semiquantitative assay shows promise as an approach to simplifying the quantitation of human tumor hypoxia by immunohistochemical techniques.

Impact of neoadjuvant chemotherapy on Ki-67 and PCNA labeling indices for esophageal squamous cell carcinomas

PURPOSE

The effects of neoadjuvant chemotherapy (CT) on Ki-67 and proliferating cell nuclear antigen (PCNA) labeling index (LI) were analyzed, using biopsy and surgical specimens of esophageal cancer.

METHOD AND MATERIALS

Immunohistochemical staining for Ki-67 and PCNA was performed for biopsy and surgical specimens of 35 patients with esophageal squamous cell carcinoma. Seventeen patients were treated with neoadjuvant CT (CT group), while no preoperative treatment was performed for the remaining 18 patients (control group). As neoadjuvant CT, cisplatin of 50 mg/body/week was administered 2-5 times (100-250 mg in total) until 7-10 days before subtotal esophagectomy.

RESULT

Significant correlation between the LIs of biopsy and surgical specimens was observed for the control group (p = 0.006 for Ki-67 and p = 0.005 for PCNA), although both LIs of surgical specimens were significantly higher than those of biopsy specimens (p < 0.05). However, no significant correlation between LIs of biopsy specimens and those of surgical specimens was observed for the CT group. In addition, the LIs of the surgical specimens of the CT group were significantly lower than the LIs of the control group (p < 0.005 for Ki-67 and p < 0.05 for PCNA). Significant decrease in Ki-67 LI after neoadjuvant CT was noted especially for well or moderately differentiated squamous cell carcinomas and/or tumors treated with high-dose cisplatin (150-250 mg).

CONCLUSION

Significant correlation of Ki-67 and PCNA LIs between biopsy and surgical specimens was demonstrated for the control group. Neoadjuvant CT decreased the percentage of cycling and proliferative tumor cells of esophageal cancer.

Spatial relationship between hypoxia and the (perfused) vascular network in a human glioma xenograft: a quantitative multi-parameter analysis

PURPOSE

To quantitatively study the spatial distribution of tumor hypoxia in relation to the perfused vasculature.

METHODS AND MATERIALS

Using a human glioma xenograft model, nude mice were administered two different hypoxia markers (NITP or pimonidazole) and the perfusion marker Hoechst 33342. Frozen tumor sections were sequentially scanned for perfusion, hypoxia, and vasculature, respectively, to quantitate perfusion, vasculature, and hypoxia parameters in the same section.

RESULTS

All tumors showed incomplete perfusion. Both NITP and pimonidazole stained the same hypoxic tumor areas. No statistically significant differences between the two markers were observed. The density of the perfused vessels was inversely related to the hypoxic fraction. At critical distances from perfused vessels, hypoxia occurred. These data suggest that predominantly diffusion-limited hypoxia was detected, based on the spatial distribution of nearby vessels. Also, the proportion of hypoxia distributed over arbitrary zones of 50 microm around perfused vessels was calculated. The largest proportion of hypoxia was found at distances beyond 100 microm from perfused vessels.

CONCLUSION

With the multiple staining and functional microscopic imaging technique described here, the spatial relationship between perfused vessels and hypoxia was quantified in whole tumor cross-sections. The usefulness of this histologically-based method to quantitate morphological and physiological aspects of the tumor microenvironment was evaluated.

Apoptosis, PCNA, and p53 in Fundulus grandis fish liver after in vivo exposure to N-methyl-N'-nitro-N-nitrosoguanidine and 2-aminofluorene

Dysfunction in homeostatic mechanisms of cell death and proliferation are considered to be important in the pathogenesis of chemically induced neoplasia. p53 has been implicated in the regulation of cell death and proliferation. To determine whether expression of apoptosis, proliferating cell nuclear antigen (PCNA), and p53 differ between an alkylating agent and a polycyclic aromatic hydrocarbon, host response was measured through sequential immunohistochemical detection of apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling method), PCNA PC-10, and p53 (PAb 240) in livers of the fish Fundulus grandis. Nine hundred fish were randomly assigned to 3 groups of 300 fish each and kept in separate aquarium tanks. One group of fish was exposed to 6.7 microM N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 1 group was exposed to 6.9 mM 2-aminofluorene (2-AF), and the remaining group served as a control. A significant decrease (p = 0.005) in the level of apoptosis and a significant increase (p < 0.0001) in the level of p53 were found on experimental day 180 in the livers of MNNG-exposed fish. PCNA was significantly increased (p < 0.005) by day 9 of the experiment in both MNNG and 2-AF fish when compared with controls, but no significant differences existed between the 2 groups of treated fish. Response of fish liver cells to MNNG-mediated and 2-AF-mediated injury differs, at least initially, in the expression of p53, inhibition of apoptosis, and increased net cell proliferation. Concurrent use of a marker for cell death with a marker of proliferation greatly enhances the assessment of the effect of these compounds on liver cells.

Interrelationship of proliferation and hypoxia in carcinoma of the cervix

PURPOSE

In human cervix cancer treated with radiotherapy, we have previously shown from separate groups of patients that tumor hypoxia and proliferation rate as measured by bromodeoxyuridine (BrdU) labeling index (LI) are important determinants of clinical outcome. We now examine the relationship of these two pre-treatment predictive assays in 43 patients studied prospectively from 1994-98 where both tests were performed for each patient.

MATERIAL AND METHODS

Newly diagnosed patients with carcinoma of the cervix were examined under anesthesia for staging purposes. Patients were given BrdU (200 mg) by intravenous route prior to the procedure. Tumor oxygenation was measured with the Eppendorf pO2 histograph. Biopsy of tumor was then performed and the BrdU LI was obtained by flow cytometry. The degree of tumor hypoxia for each tumor was expressed as median pO2 values, and as the percentage of pO2 readings <5 mm Hg (HP5).

RESULTS

The median age was 53 years (range 23-79 years). There were 32 squamous, and 11 non-squamous carcinomas. FIGO stages were: IB and IIA, 8; IIB, 17; IIIB, 18; with a median tumor size of 6 cm (range 2-10 cm). The patients received uniform treatment with radical radiation therapy. There were 22 diploid and 21 aneuploid tumors. The median LI, pO2, and HP5 were 8.0%, 5.4 mm Hg, and 46.8%, respectively. Tests for linear associations showed no significant correlation between median pO2 vs. LI (r = 0.078, p = 0.62), and HP5 vs. LI (r = -0.14, p = 0.38).

CONCLUSIONS

The clinical outcome in this group of patients is immature, but these results suggest that tumor hypoxia and proliferation measurements are independent and potentially complementary predictive assays in cervix carcinoma. Further investigations are required to examine the distribution of proliferating tumor cells and its relationship with hypoxic tumor cells in tissue sections with the use of immunohistological techniques and image analysis systems.

The cell cycle: a review

The cell cycle is a complex process that involves numerous regulatory proteins that direct the cell through a specific sequence of events culminating in mitosis and the production of two daughter cells. Central to this process are the cyclin-dependent kinases (cdks), which complex with the cyclin proteins. These proteins regulate the cell's progression through the stages of the cell cycle and are in turn regulated by numerous proteins, including p53, p21, p16, and cdc25. Downstream targets of cyclin-cdk complexes include pRb and E2F. The cell cycle can be altered to the advantage of many viral agents, most notably polyomaviruses, papillomaviruses, and adenoviruses. The cell cycle often is dysregulated in neoplasia due to alterations either in oncogenes that indirectly affect the cell cycle or in tumor suppressor genes or oncogenes that directly impact cell cycle regulation, such as pRb, p53, p16, cyclin D1, or mdm-2. The cell cycle has become an intense subject of research in recent years. This research has led to the development of techniques useful for the determination of the effects of drugs and toxins on the cell cycle. Any drug or toxin with DNA damaging ability would be expected to alter cell cycle progression, and therefore, the cell cycle should be considered in the design of studies using such chemicals. With the appropriate techniques, cell cycle alterations may also be detected in tissue sections. Because of the ubiquitous nature of the cell cycle, it deserves consideration in the design and interpretation of studies in a wide variety of disciplines.

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.

Hypoxia marker labeling in tumor biopsies: quantification of labeling variation and criteria for biopsy sectioning

BACKGROUND AND PURPOSE

The error associated with using biopsy-based methods for assessing parameters reflective of the tumor microenvironment depends on the variability in distribution of the parameter throughout the tumor and the biopsy sample. Some attention has been given to intratumoral distribution of parameters, but little attention has been given to their intrabiopsy distribution. We evaluated the intrabiopsy distribution of CCI-103F, a 2-nitroimidazole hypoxia marker.

MATERIALS AND METHODS

The hypoxia marker CCI-103F was studied in dogs bearing spontaneous solid tumors. Two biopsies were taken from each of seven tumors, for a total of 14 biopsies. Biopsies were serially sectioned and four to six contiguous slides from each 100-150 microm of the biopsy were used to formulate the best estimate of CCI-103F labeled area throughout the biopsy sample. One, two or four slides were then randomly selected from each biopsy and the labeled area, based on this limited sample, was compared to the estimate obtained from counting all available slides. Random sampling of slides was repeated 1000 times for each biopsy sample.

RESULTS

CCI-103F labeling variance throughout the biopsy decreased as the estimated overall labeled area in the biopsy decreased. The error associated with estimating the overall labeled area in a biopsy from a randomly selected subset of slides decreased as the number of slides increased, and as the overall labeled area in the biopsy decreased. No minimally labeled biopsy was classified as unlabeled based on limited sampling.

CONCLUSION

With regard to CCI-103F labeling, quantification of the labeled area in four randomly selected slides from a biopsy can provide, in most biopsies, an estimate of the labeled area in the biopsy within an absolute range of +/-0.05.

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.