Interpretation of time-to-event outcomes in randomized trials: an online randomized experiment

Background

Multiple features in the presentation of randomized controlled trial (RCT) results are known to influence comprehension and interpretation. We aimed to compare interpretation of cancer RCTs with time-to-event outcomes when the reported treatment effect measure is the hazard ratio (HR), difference in restricted mean survival times (RMSTD), or both (HR+RMSTD). We also assessed the prevalence of misinterpretation of the HR.

Methods

We carried out a randomized experiment. We selected 15 cancer RCTs with statistically significant treatment effects for the primary outcome. We masked each abstract and created three versions reporting either the HR, RMSTD, or HR+RMSTD. We randomized corresponding authors of RCTs and medical residents and fellows to one of 15 abstracts and one of 3 versions. We asked how beneficial the experimental treatment was (0–10 Likert scale). All participants answered a multiple-choice question about interpretation of the HR. Participants were unaware of the study purpose.

Results

We randomly allocated 160 participants to evaluate an abstract reporting the HR, 154 to the RMSTD, and 155 to both HR+RMSTD. The mean Likert score was statistically significantly lower in the RMSTD group when compared with the HR group (mean difference −0.8, 95% confidence interval, −1.3 to −0.4, P < 0.01) and when compared with the HR+RMSTD group (difference −0.6, −1.1 to −0.1, P = 0.05). In all, 47.2% (42.7%−51.8%) of participants misinterpreted the HR, with 40% equating it with a reduction in absolute risk.

Conclusion

Misinterpretation of the HR is common. Participants judged experimental treatments to be less beneficial when presented with RMSTD when compared with HR. We recommend that authors present RMST-based measures alongside the HR in reports of RCT results.

Whole mount immunofluorescence analysis of placentas from normotensive versus preeclamptic pregnancies

INTRODUCTION

Defects in placental angiogenesis and spiral artery remodeling have been proposed to play essential roles in the development of preeclampsia. However, the specific molecular mechanism(s) responsible for aberrant placental angiogenesis in preeclampsia are incompletely understood. The vascular endothelial growth factor receptors (VEGFR1, R2, R3) and STAT3 have critical functions in normal blood vessel development, but their potential roles in preeclampsia are currently unclear. In this study, we utilized a novel whole mount immunofluorescence (WMIF) method to compare expression of VEGFR1, R2, R3 and activated, phosphorylated STAT3 (pSTAT3) in placentas of preeclamptic (PE) versus normotensive (NT) pregnancies.

METHODS

Placental biopsies collected from NT and PE pregnant women were fixed and stained with fluorochrome-conjugated antibodies to identify specific cell populations as follows: CD31 for blood vessel endothelial cells, cytokeratin-7 for trophoblast cells, and CD45 for immune cells. Expression of the VEGFRs and pSTAT3 were subsequently characterized by WMIF in conjunction with confocal microscopy.

RESULTS

A total of 18 PE and 18 NT placentas were evaluated. No significant differences in the cell type-specific expression patterns or expression levels of VEGFR1, VEGFR2 or VEGFR3 were detected between NT and PE placentas. In contrast, statistically significant increases in pSTAT3 staining were detected in endothelial cells of PE placentas versus NT controls.

DISCUSSION

Our study demonstrates that increased pSTAT3 expression in placental endothelial cells is associated with PE. We speculate that elevated pSTAT3 expression in the blood vessels of PE placentas may be due to aberrant angiogenesis, increased pro-inflammatory cytokine expression, and/or placental stress.

Mechanism of IL-12 mediated alterations in tumour blood vessel morphology: analysis using whole-tissue mounts

New blood vessel formation within tumours is a critical feature for tumour growth. A major limitation in understanding this complex process has been the inability to visualise and analyse vessel formation. Here, we report on the development of a whole-tissue mount technique that allows visualisation of vessel structure. Mice expressing green fluorescent protein (GFP) made it possible to easily see GFP(+) vessels within non-GFP-expressing B16 melanoma tumours. The small fragments of tumour used in this technique were also effectively stained with fluorescent probe-conjugated antibodies, allowing characterisation of the vessels based on surface marker phenotype. The vessels within tumour tissue were much more irregular and tortuous compared to those within surrounding normal muscle. B16 tumours stably transfected with the genes for IL-12 were used to assess the effects of this cytokine on tumour growth and vessel formation. The IL-12-expressing tumours grew more slowly and had much smaller blood vessels than the large, webbed vessels characteristic of the parental tumours, effects that were dependent on interferon gamma (IFN-gamma). Vessels in the parental tumours were found to express VEGFR-3, the receptor for VEGF-C and VEGF-D. Expression of this receptor by the endothelial cells of the blood vessels was lost in the cytokine expressing tumours, thus suggesting a mechanism for the antiangiogenic effects of IL-12. The combination of the whole mount technique and the GFP transgenic mice provides a powerful method for visualising tumour vasculature and characterising the effects of agents such as cytokines.

Adhesion and guidance in compatible pollination

The mechanisms of compatible pollination are less studied than those of incompatible pollination and yet most of the angiosperms show self-compatibility. From the release of pollen from anthers to the penetration of the micropyle by the pollen tube tip, there are numerous steps where the interaction between pollen and the pistil can be regulated. Recent studies have documented some diverse ways in which pollen tubes carrying sperm cells are guided to the ovules through the pistil extracellular matrices of the transmitting tract. What is still missing is an understanding of pollen tube cell biology in vivo. A recent finding supports the role of the synergids in the crucial guidance cue for the pollen tube tip at the micropyle, but experimental evidence for other 'guidepost' cells in the pistil is still lacking. The fact that the pollen tube must first travel through the matrices of the stigma and style before it can respond to the cue from the ovule makes it likely that there is a hierarchy of signalling events in pollen-pistil interactions starting at the stigma and ending at the micropyle. On the pistil side, several model systems have been used in the discovery of molecules implicated in either physical or chemical guidance. In lily, which has a hollow style, adhesion molecules (pectin and SCA) are implicated in guidance. SCA alone is also capable of inducing pollen chemotropism in an in vitro assay, suggesting that this peptide plays a dual role in lily pollination: chemotactic in the stigma and haptotactic (adhesion mediated) in the style.

Adhesion and guidance in compatible pollination

The mechanisms of compatible pollination are less studied than those of incompatible pollination and yet most of the angiosperms show self-compatibility. From the release of pollen from anthers to the penetration of the micropyle by the pollen tube tip, there are numerous steps where the interaction between pollen and the pistil can be regulated. Recent studies have documented some diverse ways in which pollen tubes carrying sperm cells are guided to the ovules through the pistil extracellular matrices of the transmitting tract. What is still missing is an understanding of pollen tube cell biology in vivo. A recent finding supports the role of the synergids in the crucial guidance cue for the pollen tube tip at the micropyle, but experimental evidence for other 'guidepost' cells in the pistil is still lacking. The fact that the pollen tube must first travel through the matrices of the stigma and style before it can respond to the cue from the ovule makes it likely that there is a hierarchy of signalling events in pollen-pistil interactions starting at the stigma and ending at the micropyle. On the pistil side, several model systems have been used in the discovery of molecules implicated in either physical or chemical guidance. In lily, which has a hollow style, adhesion molecules (pectin and SCA) are implicated in guidance. SCA alone is also capable of inducing pollen chemotropism in an in vitro assay, suggesting that this peptide plays a dual role in lily pollination: chemotactic in the stigma and haptotactic (adhesion mediated) in the style.

Dendritic cells transduced with HSV-1 amplicons expressing prostate-specific antigen generate antitumor immunity in mice

There is currently much interest in generating cytotoxic T lymphocyte (CTL) responses against tumor antigens as a therapy for cancer. This work describes a novel gene transfer technique utilizing dendritic cells (DCs), an extremely potent form of antigen-presenting cell (APC), and herpes simplex virus-1 (HSV-1) amplicons. HSV-1 amplicons are plasmid-based viral vectors that are packaged into HSV-1 capsids, but lack viral coding sequences. Amplicon vectors have been constructed that encode the model tumor antigen ovalbumin (HSV-OVA) and human prostate-specific antigen (HSV-PSA), a protein that is expressed specifically in prostate epithelium and prostate carcinoma cells. These amplicons were packaged using a helper virus-free system that produces vector stocks that are devoid of contaminating cytotoxic helper virus. Transduction of DCs with HSV-OVA or HSV-PSA and co-culture with CTL hybridomas results in specific activation, indicating that transduced DCs express these transgenes and process the tumor antigens for class I MHC presentation to CTL. Mice immunized with HSV-PSA-transduced DCs generate a specific CTL response that can be detected in vitro by a (51)Cr-release assay and are protected from challenge with tumors that express PSA. These results indicate that DCs transduced with HSV-1 amplicon vectors may provide a tool for investigation of the biology of CTL activation by DCs and a new modality for immunotherapy of cancer.

T-cell antigen discovery (T-CAD) assay: a novel technique for identifying T cell epitopes

The identification of T cell epitopes is a critical step in evaluating and monitoring T cell mediated immune responses. Here, we describe a novel technique for simultaneously identifying class I and class II MHC restricted epitopes using a one-step protein purification system. This method uses Ni/chelate coated magnetic beads and magnetic separation to isolate poly-histidine tagged recombinant antigen from bacterial lysates. These beads, once coated with antigen, are also used to deliver antigen to APC where it is processed and presented to T cells. A colorimetric assay and ovalbumin specific, lacZ inducible, T cell hybridomas were used to validate the system. Further, using PSA specific hybrids, generated from T cells isolated from PSA secreting tumors, both class I and class II MHC restricted epitopes of PSA were identified. Additional characterization has shown that these peptides contribute significantly to the overall PSA specific response in vivo, and may represent the dominant epitopes of PSA.

Intravascular HBO(2) saturations, perfusion and hypoxia in spontaneous and transplanted tumor models

Clinical trials utilizing strategies to manipulate tumor oxygenation, blood flow and angiogenesis are under way, although limited quantitative information exists regarding basic tumor pathophysiology. The current study utilized murine KHT fibrosarcomas, spontaneous mammary carcinomas and first-generation spontaneous transplants to examine heterogeneity in vascular structure and function, to relate these changes to the distribution of tumor hypoxia and to determine whether fundamental relationships among the different pathophysiological parameters exist. Three methods were included: (i) immunohistochemical staining of anatomical and perfused blood vessels, (ii) cryospectrophotometric measurement of intravascular oxyhemoglobin saturations and (iii) fluorescent detection of the EF5 hypoxic marker. While a distinct pattern of decreasing oxygenation with increasing distance from the tumor surface was observed for KHT tumors, striking intertumor variability was found in both spontaneous and first-generation transplants, with a reduced dependence on tumor volume. EF5 hypoxic marker uptake was also much more heterogeneous among individual spontaneous and first-generation tumors compared to KHT. Although mammary carcinomas demonstrated fewer anatomical blood vessels than fibrosarcomas, the proportion of perfused vessels was substantially reduced in KHT tumors, especially at larger tumor volumes. Vascular morphology, tissue histological appearance and pathophysiological parameters differed substantially between KHT tumors and both spontaneous and first-generation tumors. Such differences in vascular structure and function are also likely to correlate with altered response to therapies targeted to the vascular system. Finally, spontaneous differentiation status, tumor morphology, vascular configuration and function were well preserved in first-generation transplanted tumors, suggesting a close relationship between vascular development and function in early-generation transplants and spontaneous tumor models.

Tumours can act as adjuvants for humoral immunity

Tumour cells transfected with cDNAs encoding non-self proteins were used to investigate the ability of the immune system to respond to immunogenic antigens expressed by tumours. Secreted, intracellular and surface proteins were used as model antigens, as these reflect the potential forms of tumour antigens. Syngeneic BALB/c mice injected with viable line 1 lung carcinoma or EMT6 mammary tumour cells secreting ovalbumin (OVA) or prostate-specific antigen (PSA) produced very high immunoglobulin G (IgG) antibody titres, equivalent to those of mice injected with protein in Freund's complete adjuvant (FCA). Secretion of the antigens was not necessary as tumour cells expressing a cell-surface antigen (HER-2/Neu) or an intracellular antigen - green fluorescence protein (GFP) - also generated high-titre antigen-specific IgG antibodies. In interleukin-4 (IL-4)-deficient mice, both IgG1 and IgG2a were produced in response to OVA administered in FCA, whereas in response to tumour-produced antigen, the antibodies switched from predominantly IgG1 to IgG2a, indicating that the mechanisms responsible for antibody induction differed between these forms of immunization. In contrast to the line 1 and EMT6 tumours, which are of BALB/c origin, OVA- or PSA-producing B16 melanoma cells, which are of C57BL/6 origin, failed to elicit antibody production. This was not the result of strain differences, as a similar finding was observed when the tumours were grown in (BALB/c x C57BL/6)F1 mice, but appeared to be caused by intrinsic differences in the tumours. Furthermore, co-injection of both B16/OVA and line 1 tumours resulted in production of anti-OVA antibody, indicating that B16 tumours were not immunosuppressive, but instead line 1 tumours appear to exert an adjuvant effect.

Effects of radiation on tumor intravascular oxygenation, vascular configuration, development of hypoxia, and clonogenic survival

The underlying physiological mechanisms leading to tumor reoxygenation after irradiation have elicited considerable interest, but they remain somewhat unclear. The current study was undertaken to determine the effects of a single dose of 10 Gy gamma radiation on both tumor pathophysiology and radiobiologically hypoxic fraction. Immunohistochemical staining and perfusion markers were used to quantify tumor vasculature, uptake of the hypoxia marker EF5 to assess the distribution of hypoxia, and intravascular HbO(2) measurements to determine oxygen availability. Tumor radiosensitivity was measured by a clonogenic assay. At 24 h postirradiation, oxygen availability increased, perfused vessel numbers decreased, EF5 uptake decreased, and the radiobiologically hypoxic fraction was unchanged. Together, these results demonstrate that tumor hypoxia develops at an increased distance from perfused blood vessels after irradiation, suggesting a decrease in oxygen consumption at 24 h. By 72 h postirradiation, all physiological parameters had returned to the levels in volume-matched, nonirradiated controls. These studies clearly show that single measures of either tumor oxygenation or vascular structure are inadequate for assessing the effects of radiation on tumor clonogenicity. Although such direct measurements have previously proven valuable in predicting tumor response to therapy or oxygen manipulation, a combination of parameters is required to adequately describe the mechanisms underlying these changes after irradiation.

A lily stylar pectin is necessary for pollen tube adhesion to an in vitro stylar matrix

Pollen tube cells adhere to the wall surface of the stylar transmitting tract epidermis in lily. This adhesion has been proposed as essential for the proper delivery of the sperm cells to the ovule. An in vitro adhesion bioassay has been used to isolate two stylar molecules required for lily pollen tube adhesion. The first molecule was determined to be a small, cysteine-rich protein with some sequence similarity to lipid transfer proteins and now called stigma/stylar cysteine-rich adhesin (SCA). The second, larger, molecule has now been purified from style fragments and characterized. Chemical composition, specific enzyme degradations, and immunolabeling data support the idea that this molecule required for pollen tube adhesion is a pectic polysaccharide. In vitro binding assays revealed that this lily stylar adhesive pectin and SCA are able to bind to each other in a pH-dependent manner.

In vivo behavior of peptide-specific T cells during mucosal tolerance induction: antigen introduced through the mucosa of the conjunctiva elicits prolonged antigen-specific T cell priming followed by anergy

The mucosa of the conjunctiva is an important site of entry for environmental Ags as well as Ags emanating from the eye itself. However, very little is known about T cell recognition of Ag introduced through this important mucosal site. We have characterized the in vivo process of CD4 T cell recognition of Ag delivered via the conjunctival mucosa. Application of soluble OVA to the conjunctiva of BALB/c mice induced potent T cell tolerance. APC-presenting OVA peptide in vivo was only found in the submandibular lymph node and not in other lymph nodes, spleen, or nasal-associated lymphoid tissue. Similarly, in TCR transgenic DO11. 10 adoptive transfer mice, OVA-specific CD4+ T cell clonal expansion was only observed in the submandibular lymph node following conjunctival application of peptide. These experiments thus define a highly specific lymphatic drainage pathway from the conjunctiva. OVA-specific T cell clonal expansion peaked at day 3 following initiation of daily OVA administration and gradually declined during the 10-day treatment period, but remained elevated compared with nontreated adoptive transfer mice. During this period, the T cells expressed activation markers, and proliferated and secreted IL-2 in vitro in response to OVA stimulation. In contrast, these cells were unable to clonally expand in vivo, or proliferate in vitro following a subsequent OVA/CFA immunization. These results suggest that Ag applied to a mucosal site can be efficiently presented in a local draining lymph node, resulting in initial T cell priming and clonal expansion, followed by T cell anergy.

Detection of hypoxia in human squamous cell carcinoma by EF5 binding

Localization and quantitation of 2-nitroimidazole drug binding in low pO2 tumors is a technique that can allow the assessment of hypoxia as a predictive assay. EF5 [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide] is such a drug, and it has been shown to be predictive of radiation response in rodent tumors. Using fluorescence immunohistochemical techniques, we provide data on the presence, distribution, and levels of EF5 binding as a surrogate for hypoxia in human head and neck and uterine cervix squamous cell cancers (SCCs). Six patients with SCC were studied. Four patients had head and neck tumors, and two had uterine cervix cancers. The incubation of fresh tissue cubes in EF3 under hypoxic conditions ("reference binding") demonstrated that all tumors were capable of binding drug, and that this binding varied by a factor of 2.9-fold (174.5-516.1) on an absolute fluorescence scale. In the five patients treated at the lowest drug doses (9 mg/kg), in situ binding was quantitatable. For all six patients, the maximum rate of in situ binding varied by a factor of 6.7 between the lowest and highest binding tumor (24.8-160.3) on an absolute fluorescence scale. In tumors with high binding regions, intratumoral heterogeneity was large, extending from minimal fluorescence (<1%) up to 88.6% of reference binding. In tumors with minimal binding, there was little intratumoral heterogeneity. These studies demonstrate substantial heterogeneity of in situ binding between and within individual squamous cell tumors.

Noninvasive detection of tumor hypoxia using the 2-nitroimidazole [18F]EF1

The noninvasive assessment of tumor hypoxia in vivo is under active investigation because hypoxia has been shown to be an important prognostic factor for therapy resistance. Various nuclear medicine imaging modalities are being used, including PET imaging of 18F-containing compounds. In this study, we report the development of 18F-labeled EF1 for noninvasive imaging of hypoxia. EF1 is a 3-monofluoro analog of the well-characterized hypoxia marker EF5, 2(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetami de, which has been used to detect hypoxia in tumor and nontumor systems using immunohistochemical methods.

METHODS

We have studied 2 rat tumor types: the hypoxic Morris 7777 (Q7) hepatoma and the oxic 9LF glioma tumor, each grown in subcutaneous sites. PET studies were performed using a pharmacological dose of nonradioactive carrier in addition to [18F]EF1 to optimize and assess drug biodistribution. After PET imaging of the tumor-bearing rats, tissues were obtained for gamma-counting of the 18F in various tissues and immunohistochemical detection of intracellular drug adducts in tumors. In one pair of tumors, Eppendorf needle electrode studies were performed.

RESULTS

[18F]EF1 was excreted dominantly through the urinary tract. The tumor-to-muscle (T/M) ratio of [18F]EF1 in the Q7 tumors was 2.7 and 2.4 based on PET studies and 2.1, 2.5, and 3.0 based on gamma-counting of the tissues (n = 3). In contrast, the T/M ratio of [18F]EF1 in the 9LF glioma tumor was 0.8 and 0.5 based on PET studies and 1.0, 1.2, and 1.4 based on gamma-counting of the tissues (n = 3). Immunohistochemical analysis of drug adducts for the two tumor types agreed with the radioactivity analysis. In the Q7 tumor, substantial heterogeneous binding was observed throughout the tumor, whereas in the 9LF tumor minimal binding was found.

CONCLUSION

[18F]EF1 is an excellent radiotracer for noninvasive imaging of tumor hypoxia.

Alteration of tumour response to radiation by interleukin-2 gene transfer

We have previously shown that BALB/c-derived EMT6 mammary tumours transfected with interleukin (IL)-2 have decreased hypoxia compared to parental tumours, due to increased vascularization. Since hypoxia is a critical factor in the response of tumours to radiation treatment, we compared the radiation response of IL-2-transfected tumours to that of parental EMT6 tumours. Because the IL-2 tumours have an altered host cell composition, which could affect the interpretation of radiation sensitivity as measured by clonogenic cells, we employed flow cytometric analysis to determine the proportion of tumour cells vs host cells in each tumour type. Using this approach, we were able to correct the plating efficiency based on the number of actual tumour cells derived from tumours, making the comparison of the two types of tumours possible. We also excluded the possibility that cytotoxic T-cells present in EMT6/IL-2 tumours could influence the outcome of the clonogenic cell survival assay, by demonstrating that the plating efficiency of cells derived from EMT6/IL-2 tumours remained unchanged after depletion of Thy-1+ cells. The in vivo radiation response results demonstrated that IL-2-transfected tumours were more sensitive to radiation than parental EMT6 tumours. The hypoxic fraction of the EMT6/IL-2 tumours growing in vivo was markedly decreased relative to parental EMT6 tumours thus the increased sensitivity results from the increased vascularity we have previously observed in these tumours. These results indicate the potential therapeutic benefit of combining radiation and immunotherapy in the treatment of tumours.

A lipid transfer-like protein is necessary for lily pollen tube adhesion to an in vitro stylar matrix

Flowering plants possess specialized extracellular matrices in the female organs of the flower that support pollen tube growth and sperm cell transfer along the transmitting tract of the gynoecium. Transport of the pollen tube cell and the sperm cells involves a cell adhesion and migration event in species such as lily that possess a transmitting tract epidermis in the stigma, style, and ovary. A bioassay for adhesion was used to isolate from the lily stigma/stylar exudate the components that are responsible for in vivo pollen tube adhesion. At least two stylar components are necessary for adhesion: a large molecule and a small (9 kD) protein. In combination, the two molecules induced adhesion of pollen tubes to an artificial stylar matrix in vitro. The 9-kD protein was purified, and its corresponding cDNA was cloned. This molecule shares some similarity with plant lipid transfer proteins. Immunolocalization data support its role in facilitating adhesion of pollen tubes to the stylar transmitting tract epidermis.

Enhancement of tumor perfusion and oxygenation by carbogen and nicotinamide during single- and multifraction irradiation

Numerous experimental and clinical studies have been completed regarding the effects of carbogen and nicotinamide on tumor oxygenation and radiosensitivity. The current study incorporates three physiological measurement techniques to further define spatial variations in oxygen availability and development of hypoxia after single- and multifraction irradiation in KHT murine fibrosarcomas. Distances to anatomical and perfused blood vessels were measured using immunohistochemical and fluorescent staining, intravascular oxygen levels were determined cryospectrophotometrically, and tumor hypoxia was quantified using uptake of EF5, a marker of hypoxia. Carbogen, nicotinamide, and the combination of both all increased intravascular oxygen availability compared to controls. While nicotinamide had no effect on the number of perfused blood vessels in nonirradiated tumors, carbogen produced a substantial closing of vessels. After a single dose of 4 Gy, only the combination of nicotinamide and carbogen produced significant improvements in oxygen availability, while numbers of perfused vessels were significantly increased for nicotinamide, unchanged for the combination of nicotinamide and carbogen, and significantly decreased for carbogen. After 4 x 4-Gy fractions, oxygen availability was increased substantially with the combination of nicotinamide and carbogen, somewhat with carbogen, and not at all with nicotinamide. Tumor oxygenation changes were estimated by EF5/Cy3 intensity distributions, which demonstrated that manipulative agents could produce disparate effects on tumor hypoxia when combined with either single- or multifraction irradiation.

A lipid transfer-like protein is necessary for lily pollen tube adhesion to an in vitro stylar matrix

Flowering plants possess specialized extracellular matrices in the female organs of the flower that support pollen tube growth and sperm cell transfer along the transmitting tract of the gynoecium. Transport of the pollen tube cell and the sperm cells involves a cell adhesion and migration event in species such as lily that possess a transmitting tract epidermis in the stigma, style, and ovary. A bioassay for adhesion was used to isolate from the lily stigma/stylar exudate the components that are responsible for in vivo pollen tube adhesion. At least two stylar components are necessary for adhesion: a large molecule and a small (9 kD) protein. In combination, the two molecules induced adhesion of pollen tubes to an artificial stylar matrix in vitro. The 9-kD protein was purified, and its corresponding cDNA was cloned. This molecule shares some similarity with plant lipid transfer proteins. Immunolocalization data support its role in facilitating adhesion of pollen tubes to the stylar transmitting tract epidermis.

A lipid transfer-like protein is necessary for lily pollen tube adhesion to an in vitro stylar matrix

Flowering plants possess specialized extracellular matrices in the female organs of the flower that support pollen tube growth and sperm cell transfer along the transmitting tract of the gynoecium. Transport of the pollen tube cell and the sperm cells involves a cell adhesion and migration event in species such as lily that possess a transmitting tract epidermis in the stigma, style, and ovary. A bioassay for adhesion was used to isolate from the lily stigma/stylar exudate the components that are responsible for in vivo pollen tube adhesion. At least two stylar components are necessary for adhesion: a large molecule and a small (9 kD) protein. In combination, the two molecules induced adhesion of pollen tubes to an artificial stylar matrix in vitro. The 9-kD protein was purified, and its corresponding cDNA was cloned. This molecule shares some similarity with plant lipid transfer proteins. Immunolocalization data support its role in facilitating adhesion of pollen tubes to the stylar transmitting tract epidermis.

Hypoxia-mediated apoptosis from angiogenesis inhibition underlies tumor control by recombinant interleukin 12

The role of angiogenesis inhibition in the antitumor activity of recombinant murine interleukin 12 (rmIL-12) was studied in K1735 murine melanomas, the growth of which is rapidly and markedly suppressed by rmIL-12 treatment. On the basis of the prediction that tumor ischemia should result from therapeutic angiogenesis inhibition, tumor cell hypoxia was evaluated as a marker of ischemia using the EF5 [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)aceta mide] approach. This method measures intracellular binding of the nitroimidazole EF5, which covalently binds to cellular macromolecules selectively under hypoxic conditions. Whereas 1 week of rmIL-12 treatment effectively inhibited K1735 cell-induced angiogenesis in Matrigel neovascularization assays, 2 weeks of treatment were needed before severe tumor cell hypoxia was detected in K1735 tumors. The hypoxia that developed was regional and localized to tumor areas distant from blood vessels. The great majority of severely hypoxic tumor cells were apoptotic, and in vitro studies indicated that the degree of hypoxia present within treated tumors was sufficient to trigger K1735 apoptosis. Tumor cell apoptosis was also prevalent in the first week of rmIL-12 treatment when few cells were hypoxic. In vitro studies indicated that this non-hypoxia-related apoptosis was induced directly by IFN-gamma produced in response to rmIL-12 administration. These studies reveal that rmIL-12 controls K1735 tumors initially by IFN-gamma-induced apoptosis and later by hypoxia-induced apoptosis. They also establish hypoxia as an expected result of tumor angiogenesis inhibition and a mediator of its therapeutic effect.

Uncoupling secretion and tip growth in lily pollen tubes: evidence for the role of calcium in exocytosis

Cytoplasmic calcium concentration ([Ca2+]i) and extracellular calcium (Ca2+o) influx has been studied in pollen tubes of Lilium longliflorum in which the processes of cell elongation and exocytosis have been uncoupled by use of Yariv phenylglycoside ((beta-D-Glc)3). Growing pollen tubes were pressure injected with the ratio dye fura-2 dextran and imaged after application of (beta-D-Glc)3, which binds arabinogalactan proteins (AGPs). Application of (beta-D-Glc)3 inhibited growth but not secretion. Ratiometric imaging of [Ca2+]i revealed an initial spread in the locus of the apical [Ca2+]i gradient and substantial elevations in basal [Ca2+]i followed by the establishment of new regions of elevated [Ca2+]i on the flanks of the tip region. Areas of elevated [Ca2+]i corresponded to sites of pronounced exocytosis, as evidenced by the formation of wall ingrowths adjacent to the plasma membrane. Ca2+o influx at the tip of (beta-D-Glc)3-treated pollen tubes was not significantly different to that of control tubes. Taken together these data indicate that regions of elevated [Ca2+]i, probably resulting from Ca2+o influx across the plasma membrane, stimulate exocytosis in pollen tubes independent of cell elongation.

Detection of hypoxic cells with the 2-nitroimidazole, EF5, correlates with early redox changes in rat brain after perinatal hypoxia-ischemia

The hypoxia-dependent activation of nitroheterocyclic drugs by cellular nitroreductases leads to the formation of intracellular adducts between the drugs and cellular macromolecules. Because this covalent binding is maximal in the absence of oxygen, detection of bound adducts provides an assay for estimating the degree of cellular hypoxia in vivo. Using a pentafluorintated derivative of etanidazole called EF5, we studied the distribution of EF5 adducts in seven-day-old rats subjected to different treatments which decrease the level of oxygen in the brain. EF5 solution was administered intraperitoneally 30 min prior to each treatment. The effect of acute and chronic hypoxia on EF5 adduct formation (binding) was studied in the brain of newborn rats exposed to global hypoxia (8% O2 for 30, 90 or 150 min) and in the brain of chronically hypoxic rat pups with congenital cardiac defects (Wistar Kyoto). The effect of combined hypoxia-ischemia was investigated in rat pups subjected to right carotid coagulation and concurrent exposure to 8% O2 for 30, 90 or 150 min. Brains were frozen immediately at the end of each treatment. Using a Cy3-conjugated monoclonal mouse antibody (ELK3-51) raised against EF5 adducts, hypoxic cells within brain regions were visualized by fluorescence immunocytochemistry. Brains from controls or vehicle-injected animals showed no EF5 binding. Notably, brains from animals which were chronically hypoxemic as a result of congenital cardiac defects also showed no EF5 binding. A short exposure (30 min) to hypoxia or to combined hypoxia-ischemia resulted in increased background stain and few scattered cells with low-intensity immunostaining. Acute hypoxia exposure of at least 90-150 min, which in this age animal does not result in frank cellular damage, produced patchy areas of low- to moderate-intensity fluorescence scattered throughout the brain. In contrast, 90-150 min of hypoxia-ischemia was associated with intense immunofluorescence in the hemisphere ipsilateral to the carotid occlusion, with a pattern similar to that reported previously for the histological damage seen in this model. This study provides a sensitive method for the evaluation of the level of oxygen depletion in brain tissue after neonatal hypoxia-ischemia at times much earlier than any method demonstrates apoptotic or necrotic cell death Since the level of in vivo formation of macromolecular adducts of EF5 depends on the degree of oxygen depletion in a tissue, intracellular EF5 binding may serve as a useful marker of regional cellular vulnerability and redox state after brain injury resulting from hypoxia-ischemia.

Interleukin-3 and granulocyte-macrophage colony-stimulating factor enhance the generation and function of dendritic cells

Dendritic cells, well-known for their potent antigen-presenting activity, are generally present at very low frequency in the spleens of naive mice. We examined the ability of mice to generate functional dendritic cells (DC) following exposure to the cytokines interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Tumours secreting these cytokines provided a continuous stimulus resulting in a greatly increased number and frequency of DC in the spleen. These cells were purified by conventional DC isolation techniques and were found to exhibit many of the characteristics of DC from unmanipulated mice, including high allo-stimulatory activity in mixed lymphocyte reactions and expression of many similar cell surface markers. Using ovalbumin-peptide specific class I- and class II-restricted hybridomas containing the lacZ reporter gene, we found that these cytokine-generated DC had a greatly increased efficacy in the uptake and processing of particulate antigen. These cells appear to have retained the ability to ingest antigen that is generally associated with immature DC, but also exhibit the peptide/major histocompatibility complex (MHC)-presenting capabilities of mature DC. Development of an assay to measure the activity of a single DC revealed that these dual activities were the properties of the majority of the cytokine-generated DC. These findings indicate that exposure in vivo to the cytokines IL-3 and GM-CSF can result in the generation of large numbers of DC with increased capability of stimulating T cells. Thus, these cells may be important in vivo in the process of cross-priming and the subsequent generation of tumour-reactive cytotoxic T lymphocytes (CTL).

Quantification of tumour vasculature and hypoxia by immunohistochemical staining and HbO2 saturation measurements

Despite the possibility that tumour hypoxia may limit radiotherapeutic response, the underlying mechanisms remain poorly understood. A new methodology has been developed in which information from several sophisticated techniques is combined and analysed at a microregional level. First, tumour oxygen availability is spatially defined by measuring intravascular blood oxygen saturations (HbO2) cryospectrophotometrically in frozen tumour blocks. Second, hypoxic development is quantified in adjacent sections using immunohistochemical detection of a fluorescently conjugated monoclonal antibody (ELK3-51) to a nitroheterocyclic hypoxia marker (EF5), thereby providing information relating to both the oxygen consumption rates and the effective oxygen diffusion distances. Third, a combination of fluorescent (Hoechst 33342 or DiOC7(3)) and immunohistological (PECAM-1/CD31) stains is used to define the anatomical vascular densities and the fraction of blood vessels containing flow. Using a computer-interfaced microscope stage, image analysis software and a 3-CCD colour video camera, multiple images are digitized, combined to form a photo-montage and revisited after each of the three staining protocols. By applying image registration techniques, the spatial distribution of HbO2 saturations is matched to corresponding hypoxic marker intensities in adjacent sections. This permits vascular configuration to be related to oxygen availability and allows the hypoxic marker intensities to be quantitated in situ.

Permanent anatomic closure of the ductus arteriosus in newborn baboons: the roles of postnatal constriction, hypoxia, and gestation

Permanent closure of the ductus arteriosus requires loss of cells from the muscle media and development of neointimal mounds, composed in part of proliferating endothelial cells. We hypothesized that postnatal ductus constriction produces hypoxia of the inner vessel wall; we also hypothesized that hypoxia might lead to cell death and the production of vascular endothelial cell growth factor (VEGF), a hypoxia-inducible growth factor that stimulates endothelial proliferation. We mapped the distribution of hypoxia in newborn baboons and correlated it with the appearance of cell death (TUNEL technique), VEGF expression, and endothelial proliferation (proliferating cell nuclear antigen expression). In the full-term baboon (n=10), the ductus was functionally closed on Doppler examination by 24 h after delivery. Regions of the ductus where the lumen was most constricted were associated with moderate/intense hypoxia; VEGF expression was increased in the hypoxic muscle media, and luminal endothelial cells, adjacent to the hypoxic media, were proliferating. Cells in the most hypoxic regions of the ductus wall were undergoing DNA fragmentation. In contrast, regions of the ductus with mild degrees of hypoxia had no evidence of cell death, VEGF expression, or endothelial proliferation. Cell death and endothelial proliferation seemed to be limited to regions of the full-term ductus experiencing moderate/intense hypoxia. In the premature baboon (67% gestation) (n=24), only 29% closed their ductus by Doppler examination before d 6. None of the premature baboons, including those with a closed ductus by Doppler, had evidence of moderate/intense hypoxia; also, there was no evidence of cell death, VEGF expression, endothelial proliferation, or neointima formation by d 6. Therefore, the premature ductus is resistant to developing hypoxia, even when its lumen is constricted; this may make it susceptible to later reopening.

Regulation of human prostate-specific antigen gene expression in transgenic mice: evidence for an enhancer between the PSA and human glandular kallikrein-1 genes

The human prostate-specific antigen (PSA) and glandular kallikrein-1 (hGK-1, also known as hK2) genes are tandemly located on chromosome 19, separated by a 12-kb intergenic region. The coordinate regulation of these two genes suggests the presence of common regulatory elements responsible for tissue specificity and/or levels of expression within this region. To identify such regulatory elements, we generated two sets of transgenic mice, which had incorporated either the PSA gene alone or together with the intergenic region. Both sets of transgenics exhibit remarkably prostate-specific expression of the transgene. However, the presence of the intergenic region abrogates the dependence on high PSA gene copy-number for high levels of PSA expression. This suggests the existence of a positive regulatory element in the intergenic region. By using a previously identified distal enhancer element of PSA (termed DEE 1) as a probe, we identified a cross-hybridizing fragment, which we termed DEE 2, in the intergenic region. Sequence analysis shows that DEE 2 is 76% identical to DEE 1, and it includes a putative androgen-responsive element. Here, we propose a model to illustrate how the two enhancers may work to regulate the transcription of PSA and hK2.

IL-3 enhances both presentation of exogenous particulate antigen in association with class I major histocompatibility antigen and generation of primary tumor-specific cytolytic T lymphocytes

Recent studies have reported that APC can present particulate exogenous Ag in the context of class I MHC to CD8+ CTL, and our laboratory demonstrated that IL-3 could enhance CTL generation to exogenous Ag. In this paper, we wished to determine whether presentation of particulate Ag could be enhanced by IL-3. A T cell hybridoma, B3Z86/90.14 (B3Z) restricted to Ova/Kb, was used as an indicator for presentation of particulate Ag with class I MHC. When activated, this hybridoma expresses lacZ, allowing a simple colorimetric measurement of Ag-specific T cell stimulation. We demonstrated that bone marrow cells stimulated by IL-3 in vivo and in vitro exhibited significantly increased presentation of exogenous OVA linked to beads. Lysate from OVA-transfected line 1 murine lung adenocarcinoma cells (line 1/OVA) was also presented by IL-3-stimulated bone marrow cells, suggesting that these APC can process tumor fragments or debris. Studies using TAP1/2-deficient mice and Ag presentation inhibitors indicate that this exogenous Ag presentation is mediated via the conventional class I MHC pathway. Adoptive transfer of IL-3-stimulated bone marrow cells pulsed with lysate from line 1/OVA tumor cells into naive recipient mice led to the generation of a potent CTL response. These observations indicate that use of such cells may provide a new avenue for development of tumor vaccines.

IL-3-mediated enhancement of particulate antigen presentation by macrophages

Mice were exposed to interleukin- (IL-) 3 in vivo by injection of tumor cells transfected with the IL-3 gene. At 10 days post tumor injection, bone marrow cells were recovered, pulsed with particulate antigen in the form of ovalbumin (Ova)-coated magnetic beads, and tested for their ability to present antigen via class I to an Ova/class I-restricted T cell hybridoma. Cells from IL-3-stimulated mice exhibited a marked increase in antigen presentation compared with cells from mice injected with control non-cytokine-secreting tumor cells. These cells were markedly more efficient at presenting particulate Ova antigen than in presenting soluble Ova. Based on adherence, radiation resistance, and surface markers, the cells presenting antigen appear to be in the macrophage cell lineage. These cells are susceptible to lysis by antigen-specific cytotoxic T lymphocytes, which may contribute to limiting the effectiveness of antitumor responses.

Tumor immunotherapy: cytokines and antigen presentation

Increasing the ability of tumor-reactive T cells to mediate tumor regression in vivo has been a major goal of tumor immunologists. Progress toward this goal has been aided by the identification of tumor-associated antigens on both experimental mouse tumors and human tumors. However, the self-like nature and low immunogenicity of these antigens has made it clear that other measures to enhance the effectiveness of the T cells reactive to these antigens are essential if immunotherapy is to be clinically effective. An increased understanding of antigen processing and presentation is an important step in this process, as is the use of cytokines to increase immune responsiveness. Despite recent advances, there is still much to be learned before the specificity of the immune system is safely harnessed to halt malignant cell growth effectively.

Interleukin 2 expression by tumor cells alters both the immune response and the tumor microenvironment

Microenvironmental conditions within solid tumors can have marked effects on the growth of the tumors and their response to therapies. The disorganized growth of tumors and their attendant vascular systems tends to result in areas of the tumors that are deficient in oxygen (hypoxic). Cells within these hypoxic areas are more resistant to conventional therapies such as radiation and chemotherapy. Here, we examine the hypoxic state of EMT6 mouse mammary tumors and the location of host cells within the different areas of the tumors to determine whether such microenvironmental conditions might also affect their ability to be recognized by the immune system. Hypoxia within tumors was quantified by flow cytometry and visualized by immunohistochemistry using a monoclonal antibody (ELK3-51) against cellular adducts of 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetam ide (EF5), a nitroimidazole compound that binds selectively to hypoxic cells. Thy-1+ cells, quantified using a monoclonal antibody, were found only in the well-oxygenated areas. The location of these Thy-1+ cells was also examined in EMT6 tumors that had been transfected with the gene for interleukin-2 (IL-2) because these tumors contain greatly increased numbers of host cells. Surprisingly, we found that IL-2-transfected tumors had significantly decreased hypoxia compared to parental tumors. Furthermore, using the fluorescent dye Hoechst 33342, an in vivo marker of perfused vessels, combined with immunochemical staining of PECAM-1 (CD31) as a marker of tumor vasculature, we found increased vascularization in the IL-2-transfected tumors. Thus, expression of IL-2 at the site of tumor growth may enhance tumor immunity not only by inducing the generation of tumor-reactive CTLs but also by allowing increased infiltration of activated T cells into the tumors.

Effects of Yariv phenylglycoside on cell wall assembly in the lily pollen tube

Arabinogalactan-proteins (AGPs) are proteoglycans with a high level of galactose and arabinose. Their current functions in plant development remain speculative. In this study, (beta-D-glucosyl)3 Yariv phenyl-glycoside [(beta-D-Glc)3] was used to perturb AGPs at the plasmalemma-cell wall interface in order to understand their functional significance in cell wall assembly during pollen tube growth. Lily (Lilium longiflorum Thunb.) pollen tubes, in which AGPs are deposited at the tip, were used as a model. Yariv phenylglycoside destabilizes the normal intercalation of new cell wall subunits, while exocytosis of the secretory vesicles still occurs. The accumulated components at the tip are segregated between fibrillar areas of homogalacturonans and translucent domains containing callose and AGPs. We propose that the formation of AGP/(beta-D-Glc)3 complexes is responsible for the lack of proper cell wall assembly. Pectin accumulation and callose synthesis at the tip may also change the molecular architecture of the cell wall and explain the lack of proper cell wall assembly. The data confirm the importance of AGPs in pollen tube growth and emphasize their role in the deposition of cell wall subunits within the previously synthesized cell wall.

A transgenic strategy for analyzing the regulatory regions of the human prostate-specific antigen gene: potential applications for the treatment of prostate cancer (Review)

Prostate-specific antigen (PSA) has been used clinically as a marker for the diagnosis and staging of prostate cancer due to its specific expression in prostate epithelial cells. In addition to its medical importance, its complex hormonal and tissue-specific regulation makes it an attractive model to study gene regulation. Two approaches have been applied to the identification of regulatory regions which confer this specific expression pattern. In vitro analysis of the regulatory regions of the human PSA gene using promoter reporter constructs and tumor cell lines has revealed a number of the DNA sequences involved in the hormone-dependent expression of PSA. We have pursued an alternative in vivo approach using transgenic animal technology, which is the focus of this review. Using this second approach, a transgenic mouse was generated using a 14 kilobase (kb) region of the human PSA gene encompassing the coding region and intervening sequences as well as 6 kb of upstream sequence and 2 kb of downstream sequence. This genomic DNA clone confers a PSA expression pattern in mice which appears to be very similar if not identical to that of humans, allowing us to investigate tissue-specificity and developmental regulation of PSA expression. In addition, these mice, for which PSA is a self-antigen, provide a model to test the feasibility and efficacy of PSA-directed immunotherapy for prostate cancer. The further identification of the PSA regulatory regions important for tissue-specificity may ultimately allow the design of new therapeutics for the treatment of prostate cancer.

Expression of B7-1 by Pam 212 squamous cell carcinoma enhances tumor cell interactions with dendritic epidermal cells but does not affect in vivo tumor growth

Direct antigen presentation of tumor-associated antigens by tumor cells to T lymphocytes may induce clonal anergy as a mechanism of escape from immune surveillance. B7-1 is a costimulatory molecule for the activation of both CD4+ and CD8+ T lymphocytes that prevents the induction of clonal anergy. Thus, the transfer of B7-1 genes into tumor cells can induce protective immunity and lead to tumor rejection of some tumors in model systems of in vivo tumor growth; however, there is no information on whether stable expression of B7-1 can affect the in vivo growth of squamous cell carcinoma, a common skin cancer. Here, we study how the stable cell surface expression of high levels of B7-1 by Pam 212, a murine squamous cell carcinoma, affects tumor cell-lymphocyte interactions (lymphocyte proliferation and cytotoxicity). Consistent with its costimulatory role, we demonstrate that B7-1 can efficiently induce dendritic epidermal T-cell proliferation in three different dendritic epidermal T-cell cell lines. In addition, B7-1 enhances dendritic epidermal T-cell cytolytic activity against Pam 212 cells in an in vitro 51Cr-release assay, which was blocked by CTLA-4/Ig fusion protein. In contrast to dendritic epidermal T cells, the expression of B7-1 does not alter Pam 212 interactions with either cytotoxic T-lymphocytes, natural killer, or lymphokine-activated killer cells. B7-1 expression by Pam 212 cells did not alter its ability to grow tumors in vivo, as their rate of tumor growth was the same as vector-transfected Pam 212 cells, which were B7-1 negative. Our studies indicate that B7-1 gene transfer into Pam 212 does not alter its tumorigenicity, because it does not alter tumor cell-lymphocyte interactions with cytotoxic T lymphocytes, natural killer cells, and lymphokine-activated killer cells. Further studies of B7-1 modified Pam 212 and dendritic epidermal T cells will clarify whether T-cell receptor-gamma/delta-bearing T lymphocytes can play a role in immunotherapy of Pam 212 squamous cell carcinoma.

Myocyte apoptosis during acute myocardial infarction in the mouse localizes to hypoxic regions but occurs independently of p53

Significant numbers of myocytes die by apoptosis during myocardial infarction. The molecular mechanism of this process, however, remains largely unexplored. To facilitate a molecular genetic analysis, we have developed a model of ischemia-induced cardiac myocyte apoptosis in the mouse. Surgical occlusion of the left coronary artery results in apoptosis, as indicated by the presence of nucleosome ladders and in situ DNA strand breaks. Apoptosis occurs mainly in cardiac myocytes, and is shown for the first time to be limited to hypoxic regions during acute infarction. Since hypoxia-induced apoptosis in other cell types is dependent on p53, and p53 is induced by hypoxia in cardiac myocytes, we investigated the necessity of p53 for myocyte apoptosis during myocardial infarction. Myocyte apoptosis occurs as readily, however, in the hearts of mice nullizygous for p53 as in wild-type littermates. These data demonstrate the existence of a p53-independent pathway that mediates myocyte apoptosis during myocardial infarction.

Interlaboratory variation in oxygen tension measurement by Eppendorf "Histograph" and comparison with hypoxic marker

BACKGROUND AND OBJECTIVES

The median of pO2 values in tumor measured by Eppendorf "Histograph" with a needle-type electrode has been used as a prognostic indicator in cancer patients. However, it is not established that a pretreatment measured pO2 value can be used as a universal predictor of local control probability, because the variation in pO2 values, especially in hypoxic tissue, among institutes may not allow comparison of measured "absolute pO2 values." The purpose of this study was to examine the variation in oxygen tension measurement by Eppendorf "Histograph" among six laboratories using a single batch of mice and tumors and the same detailed protocol. These results were also compared to the immunohistochemical staining of 2-nitromidazole adducts.

METHODS

C3H mice bearing FSaII murine fibrosarcoma subcutaneously were shipped to all laboratories, and the oxygen status in tumors and in normal subcutis was examined using Eppendorf "Histograph" and immunohistochemical hypoxic marker.

RESULTS

All laboratories showed that the FSaII tumor was hypoxic with at least 77% of measured points under 10 mmHg in pO2 and with a median pO2 value less than that of normal subcutis. These results were further confirmed immunohistochemically. These findings are interpreted as evidence that the pO2 values measured by Eppendorf "Histograph" can be useful. However, the median values of tumor pO2 varied from 1.5 mmHg to 5.6 mmHg among the laboratories, and pO2 of normal subcutis also varied from 28 mmHg to 38 mmHg. There were also significant differences in hypoxic fraction, defined as the fraction under a given oxygen partial pressure (i.e., under 2.5, 5, or 10 mmHg), among institutes.

CONCLUSIONS

Caution needs to be exercised in using the absolute, median, or distribution of pO2 values measured by the Eppendorf "Histograph" to compare the data between laboratories or to predict the radiation response in an individual subject.

Tissue-specific expression of the human prostate-specific antigen gene in transgenic mice: implications for tolerance and immunotherapy

Human prostate-specific antigen (PSA) has been widely used as a serum marker for cancer of the prostate. The cell type-specific expression of PSA also makes it a potential tumor antigen for prostate cancer immunotherapy. Study of the immunological aspects of PSA within either normal or malignant prostate tissue has been hampered by the lack of a mouse model, because no PSA counterpart has been identified in mice. Using a 14-kb genomic DNA region that encompasses the entire human PSA gene and adjacent flanking sequences, we generated a series of human PSA transgenic mice. In the six independent lines of transgenic mice generated, the expression of the human PSA transgene, driven by its own cis-acting regulatory elements, is specifically targeted to the prostate. Tissue distribution analysis demonstrated that PSA transgene expression closely follows the human expression pattern. Immunohistochemical analysis of the prostate tissue also showed that the expression of the PSA transgene is confined to the ductal epithelial cells. Despite expressing PSA as a self-antigen in the prostate, these transgenic mice were able to mount a cytotoxic immune response against PSA expressed by tumor cells, indicating that expression of the transgene has not resulted in complete nonresponsiveness. This transgenic mouse model will provide a well defined system to gain an insight into the mechanisms of nonresponsiveness to PSA, ultimately leading to strategies for immunotherapy of human prostate cancer using PSA as the target antigen.

Chondrocytes in the endochondral growth cartilage are not hypoxic

From an anatomic viewpoint, the blood supply to chondrocytes in the growth cartilage is limited. As a result, it has been suggested that these cells are hypoxic and that this condition regulates chondrocyte maturation and cartilage mineralization. We examined the state of chondrocyte oxygenation in the chick growth plate using a hypoxia-sensing drug, EF5. EF5 is a pentafluorinated derivative of the 2-nitroimidazole, etanidazole, that is metabolically reduced by oxygen-inhibitable nitroreductase(s). Reduced EF5 covalently forms adducts with cellular macromolecules that can be visualized with a highly specific fluorochrome-conjugated monoclonal antibody. When EF5 was injected into chicks and tissues were subsequently examined by immunohistochemical techniques, chondrocytes in articular, proliferating, and hypertrophic cartilage exhibited a low level of fluorescence-detectable binding, suggesting the absence of significant hypoxia. We confirmed that the results were not confounded by tissue-specific factors related to low-chondrocyte nitroreductase activity or problems from drug diffusion into cartilage. Using in vitro systems, we showed that, under conditions of imposed hypoxia, EF5 diffused into the tissue and was bound to chondrocytes. With the use of an in vivo model in which hypoxia was artificially induced by death, chick chondrocytes were found to bind the drug. Although the EF5-binding method is not optimally suited for determining the precise oxygen partial pressure in heterogeneous tissues, such as the growth plate, we concluded that chick chondrocytes are not oxygen deficient in vivo.

Direct relationship between radiobiological hypoxia in tumors and monoclonal antibody detection of EF5 cellular adducts

While the potential importance of hypoxia in limiting the sensitivity of tumor cells to ionizing radiation has long been appreciated, methods for accurately quantifying the number of radiation-resistant hypoxic cells within tumors have been lacking. We have used the pentafluorinated derivative [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acet amide] of etanidazole (EF5), which binds selectively to hypoxic cells. The adducts formed between EF5 and cellular proteins in the hypoxic cells were detected using the specific monoclonal antibody (MAb), ELK3-51 conjugated to the flurochrome Cy3, and the number of hypoxic cells was quantified by flow cytometry. To verify the validity of this technique for the detection of hypoxic cells, mice bearing KHT sarcomas were treated with various agents to alter tumor oxygenation and hence vary the fraction of radiobiologically hypoxic tumor cells. The percentage of EF5 binding cells was then compared directly with the clonogenic survival of the tumor cells following radiation treatment under the various pretreatment conditions. The results showed that allowing the mice to breathe carbogen (5% CO2/95% O2) prior to irradiation reduced clonogenic cell survival approx. 6-fold and led to an absence of cells binding high levels of EF5. In contrast, pretreating the tumor-bearing animals with either hydralazine, which decreased tumor blood flow, or phenylhydrazine hydrochloride, which made the mice anemic, increased tumor cell survival following irradiation 2- to 4-fold, indicative of an increase in the fraction of hypoxic tumor cells. EF5 measurements made under identical conditions illustrated a shift in the cells in the tumor to high EF5 binding. Our results demonstrate that flow cytometric measurement by fluorescent MAb binding to EF5 adducts may relate directly to radiobiological hypoxia in KHT tumors measured by conventional methods.

Expression of human prostate-specific antigen (PSA) in a mouse tumor cell line reduces tumorigenicity and elicits PSA-specific cytotoxic T lymphocytes

Human prostate-specific antigen (PSA) has a highly restricted tissue distribution. Its expression is essentially limited to the epithelial cells of the prostate gland. Moreover, it continues to be synthesized by prostate carcinoma cells. This makes PSA an attractive candidate for use as a target antigen in the immunotherapy of prostate cancer. As a first step in characterizing the specific immune response to PSA and its potential use as a tumor-rejection antigen, we have incorporated PSA into a well-established mouse tumor model. Line 1, a mouse lung carcinoma, and P815, a mouse mastocytoma, have been transfected with the cDNA for human PSA. Immunization with a PSA-expressing tumor cell line demonstrated a memory response to PSA which protected against subsequent challenge with PSA-expressing, but not wild-type, tumors. Tumor-infiltrating lymphocytes could be isolated from PSA-expressing tumors grown in naive hosts and were specifically cytotoxic against a syngeneic cell line that expressed PSA. Immunization with tumor cells resulted in the generation of primary and memory cytotoxic T lymphocytes (CTL) specific for PSA. The isolation of PSA-specific CTL clones from immunized animals further demonstrated that PSA can serve as a target antigen for antitumor CTL. The immunogenicity studies carried out in this mouse tumor model provide a rationale for the design of methods to elicit PSA-specific cell-mediated immunity in humans.

Biodistribution of the nitroimidazole EF5 (2-[2-nitro-1H-imidazol-1-yl]-N-(2,2,3,3,3-pentafluoropropyl) acetamide) in mice bearing subcutaneous EMT6 tumors

The characteristic reduction and binding of nitroimidazoles to cellular macromolecules in the absence of oxygen allows their use for detection and characterization of hypoxia. The biodistribution of a new nitroimidazole, EF5 (2-[2-nitro-1H-imidazol-1-yl]-N-(2,2,3,3,3-pentafluoropropyl) acetamide), in mice bearing EMT6 tumors is described. Detection methods based on radioactivity and monoclonal antibody techniques are compared for liver and tumor. All nonexcretory tissues demonstrated similar levels of radioactivity at 0.5 hr postinjection of drug, demonstrating equivalent access of EF5 to all tissues. At 24 hr, when unbound drug has been cleared, the tissues with the highest binding are the liver, esophagus, bladder and tumor. Typically, liver tissue contains the highest level of radioactivity at this time. Examination of tumor and liver tissue by use of fluorescence microscopy and Cy3-bound monoclonal antibodies specific for EF5 adducts showed that the patterns of binding in tumor are considerably more heterogeneous than those of liver. Histograms of fluorescence intensity, with use of these antibodies, demonstrate average and maximal binding higher in tumors than in the liver. This divergence from the radioactivity data was determined to be unrelated to sampling error, differential antibody access or staining efficiency of liver vs. tumor tissue. A possible cause is the scavenging of radioactive drug metabolites by liver. The data presented herein suggest that EF5 is useful as a hypoxia detector and that monoclonal antibody detection methods can give detailed information on the distribution of EF5 binding. This technology may allow an accurate estimation of the oxygenation and/or nitroreductase levels in both tumor and normal tissues.

Interleukin 3 enhances cytotoxic T lymphocyte development and class I major histocompatibility complex "re-presentation" of exogenous antigen by tumor-infiltrating antigen-presenting cells

We show that interleukin 3 (IL-3) enhances the generation of tumor-specific cytotoxic T lymphocytes (CTLs) through the stimulation of host antigen-presenting cells (APCs). The BALB/c (H-2d) spontaneous lung carcinoma line 1 was modified by gene transfection to express ovalbumin as a nominal "tumor antigen" and to secrete IL-3, a cytokine enhancing myeloid development. IL-3-transfected tumor cells are less tumorigenic than the parental cell line, and tumor-infiltrating lymphocytes isolated from these tumors contain increased numbers of tumor-specific CTLs. By using B3Z86/90.14 (B3Z), a unique T-cell hybridoma system restricted to ovalbumin/H-2b and implanting the tumors in (BALB/c x C57BL/6)F1 (H-2d/b) mice, we demonstrate that the IL-3-transfected tumors contain an increased number of a rare population of host cells that can process and "re-present" tumor antigen to CTLs. Electron microscopy allowed direct visualization of these host APCs, and these studies, along with surface marker phenotyping, indicate that these APCs are macrophage-like. The identification of these cells and their enhancement by IL-3 offers a new opportunity for tumor immunotherapy.

2-Nitroimidazole (EF5) binding predicts radiation resistance in individual 9L s.c. tumors

The presence of hypoxic tumor cells is known to be an important cause of radiation treatment resistance in vivo. The ability to predict the presence and extent of hypoxic cells in individual tumors would allow the addition of specific "antihypoxia"-based treatment regimes. Hypoxia can be monitored by measuring the binding of 2-nitroimidazoles. We have tested the hypothesis that binding of EF5, a fluorinated derivative of the 2-nitroimidazole, Etanidazole, can predict radioresistance in individual tumors. Fischer rats bearing 9L s.c. tumors were given injections i.v. with EF5 3 h before irradiation and tumor harvest. Tumor cells were dissociated for flow cytometric analysis and plating efficiency studies. EF5 binding was detected via monoclonal antibodies conjugated to the orange emitting dye, Cy3. In air breathing rats, for a given radiation dose, a large amount of variation in plating efficiency was seen. However, there was minimal variability of the plating efficiency for tumors irradiated in euthanized animals (hypoxic tumors; correlation coefficient for the fitted curve = 0.93) and in cells dissociated from tumors and irradiated in suspension (correlation coefficient for the fitted curve = 0.99), suggesting that varying sensitivity to the cell disaggregation technique was not responsible. In contrast, a good correlation between the relative radiation resistance or hypoxic survival and EF5 binding of "moderately" hypoxic cells in air breathing rats was identified using these techniques. In these 9L s.c. tumors, intertumor variation in oxygenation accounted for most of the range in individual tumor radiation response, and this was found to be independent of tumor size. This study provides evidence for the application of EF5 binding with monoclonal antibody detection as an in vivo predictive assay of individual tumor hypoxia and resultant therapy resistance.

Lily cofactor-independent phosphoglycerate mutase: purification, partial sequencing, and immunolocalization

A cofactor-independent phosphoglycerate mutase (PGAM-i) was isolated to homogeneity from monocotyledonous Lilium longiflorum Thunb. Two-dimensional (2D) polyacrylamide gel electrophoresis resolved three PGAM-i forms. This enzyme was originally identified by cross-reactivity to antibodies affinity-purified from 2D gels using human vitronectin (VN). Antibody produced against a denatured protein spot from a 2D gel did not recognize VN protein, but partial protein and DNA sequencing showed similarity of the former protein to maize PGAM-i. Immunoblots from roots, styles, leaves, and anthers showed the presence of PGAM-i in all tissues examined; it was isolated predominantly from the soluble cell fraction, with some present in the insoluble cell fraction. Immunoelectron microscopy demonstrated its localization in the cytoplasm and plastids in root cells near the apical meristem. In addition, immunogold labeling detected signals from the nucleus. The immunohistochemical localization of the enzyme in the nucleus, as well as in the cytosol and plastids, indicates that lily PGAM-i might have multiple functions in the cell.

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.

Mapping of the vascular endothelial growth factor-producing hypoxic cells in multicellular tumor spheroids using a hypoxia-specific marker

We have investigated the hypoxia inducibility of vascular endothelial growth factor (VEGF) in multicellular tumor spheroids of HT29 cells using a monoclonal antibody to a fluorinated bioreductive drug, EF5 [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)aceta mide], a chemical probe for hypoxia. We have shown that VEGF expression is predominantly localized in interior spheroid cells that are sufficiently hypoxic to bioreductively activate the 2-nitroimidazole and produce immunologically detectable adducts of the EF5 compound. Northern blotting analyses demonstrated that VEGF165 is the predominant form of VEGF produced by HT29 cells and that the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate did not induce VEGF expression. This study demonstrates that VEGF expression is up-regulated in response to hypoxia and in the microenvironments found in human multicellular tumor spheroids. This investigation also illustrates the utility of the EF5 binding in multi-cellular tumor spheroids as a means of studying the expression and regulation of hypoxia-inducible genes.