Effect of host microenvironment on the microcirculation of human colon adenocarcinoma

It is generally accepted that the host microenvironment influences tumor biology. There are discrepancies in growth rate, metastatic potential, and efficacy of systemic treatment between ectopic and orthotopic tumors. Liver is the most common and critical site of distant metastasis of colorectal carcinoma. Tumorigenicity and efficacy of chemotherapeutic agents in colorectal tumors are different in liver and subcutaneous sites. Thus, we hypothesize that the liver (orthotopic) versus subcutaneous (ectopic) microenvironment would have different effects on the angiogenesis and maintenance of the microcirculation of colorectal tumor. To this end, we developed a new method to monitor and to quantify microcirculatory parameters in the tumor grown in the liver. Using this approach, we compared the microcirculation of LS174T, a human colon adenocarcinoma, metastasized to the liver with that of the host liver vessels and that of the same tumor grown in the subcutaneous space. In the liver metastasis model, 5 x 10(6) LS174T cells were injected into the spleen of nude mice. Four to eight weeks later, the liver with metastatic tumors was exteriorized and placed on a special stage and observed under an intravital fluorescence microscope. The dorsal skinfold chamber model was used to study the subcutaneous tumors. Red blood cell velocity, vessel diameter, density, permeability, and leukocyte-endothelial interactions were measured using fluorescence microscopy and image analysis. Vascular endothelial growth factor/ vascular permeability factor (VEGF/VPF) mRNA expression was determined by the Northern blot analysis. LS174T tumor foci in the liver had tortuous vascular architecture, heterogeneous blood flow, significantly lower vascular density, and significantly higher vascular permeability than normal liver tissue. Tumors grown in the liver had significantly lower vessel density, especially in the center coincident with central necrosis, than the subcutaneous tumors. The frequency distribution of vessel diameters of liver tumor was slightly shifted to smaller size compared with that of subcutaneous tumor. Leukocyte rolling in liver tumor was twofold lower than that in subcutaneous tumor. These physiological findings were consistent with the measurement of VEGF/VPF in that the VEGF/VPF mRNA level was lower in the liver tumor than that in the subcutaneous tumor. However, macromolecular vascular permeability in the liver tumor was significantly higher than in the subcutaneous tumor. Liver sinusoidal endothelial cells, the origin of liver tumor vessel endothelium, are known to be fenestrated and not to have a basement membrane, suggesting that the difference in endothelial cell origin may explain the difference in tumor vascular permeability in two sites. These findings demonstrate that liver microenvironment has different effects on some aspects of the tumor angiogenesis and microcirculation compared with the subcutaneous tissues. The new model/method described in this paper has significant implications in two research areas: 1) the liver microenvironment and its effect on tumor pathophysiology in conjunction with cytokine/ growth factor regulation and 2) the delivery of drugs, cells, and genes to liver tumors.

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.

The enzymatic sulfation of glycoprotein carbohydrate units: blood group T-hapten specific and two other distinct Gal:3-O-sulfotransferases as evident from specificities and kinetics and the influence of sulfate and fucose residues occurring in the carbohydrate chain on C-3 sulfation of terminal Gal

Enzymatic 3-O-sulfation of terminal beta-Gal residues was investigated by screening sulfotransferase activity present in 37 human tissue specimens toward the following synthesized acceptor moieties: Galbeta1,3GalNAc alpha-O-Al, Galbeta1,4GlcNAcbeta-O-Al, Galbeta1,3GlcNAcbeta-O-Al, and mucin-type Galbeta1,4GlcNAcbeta1,6(Galbeta1,3)GalNAc alpha-O-Bn structures containing a C-3 methyl substituent on either Gal. Two distinct types of Gal: 3-O-sulfotransferases were revealed. One (Group A) was specific for the Galbeta1, 3GalNAc alpha- linkage and the other (Group B) was directed toward the Galbeta1,4GlcNAc branch beta1,6 linked to the blood group T hapten. Enzyme activities found in breast tissues were unique in showing a strict specificity for the T-hapten. Galbeta-O-allyl or benzyl did not serve as acceptors for Group A but were very active with Group B. An examination of activity present in six human sera revealed a specificity of the serum enzyme toward beta1,3 linked Gal, particularly, the T-hapten without beta1,6 branching. Group A was highly active toward T-hapten/acrylamide copolymer, anti-freeze glycoprotein, and fetuin O-glycosidic asialo glycopeptide; less active toward fetuin triantennary asialo glycopeptide; and least active toward bovine IgG diantennary glycopeptide. Group B was moderately and highly active, respectively, with the latter two glycopeptides noted and least active with the first two. Competition experiments performed with Galbeta1,3GalNAc alpha-O-Al and Galbeta1,4GlcNAcbeta1,6(Galbeta1,3)GalNAc alpha-O-Bn having a C-3 substituent (methyl or sulfate) on either Gal reinforced earlier findings on the specificity characteristics of Group A and Group B. Group A displayed a wider range of optimal activity (pH 6.0-7.4), whereas Group B possessed a peak of activity at pH 7.2. Mg2+ stimulated Group A 55% and Group B 150%, whereas Mn+2 stimulated Group B 130% but inhibited Group A 75%. Ca2+ stimulated Group B 100% but inhibited Group A 35%. Group A and Group B enzymes appeared to be of the same molecular size (<100,000 Da) as observed by Sephacryl S-100 HR column chromatography. The following effects upon Gal: 3-O-sulfotransferase activities by fucose, sulfate, and other substituents on the carbohydrate chains were noted. (1) A methyl or GlcNAc substituent on C-6 of GalNAc diminished the ability of Galbeta1,3GalNAc alpha-O-Al to act as an acceptor for Group A. (2) An alpha1,3-fucosyl residue on the beta1,6 branch in the mucin core structure did not affect the activity of Group A toward Gal linked beta1,3 to GalNAc alpha-. (3) Lewis x and Lewis a terminals did not serve as acceptors for either Group A or B enzymes. (4) Elimination of Group B activity on Gal in the beta1,6 branch owing to the presence of a 3-fucosyl or 6-sulfo group on GlcNAc did not hinder any action toward Gal linked beta1,3 to GalNAc alpha. (5) Group A activity on Gal linked beta1,3 to GalNAc remained unaffected by 3'-sulfation of the beta1,6 branch. The reverse was true for Group B. (6) The acceptor activity of the T-hapten was increased somewhat upon C-6 sulfation of GalNAc, whereas, C-6 sialylation resulted in an 85% loss of activity. (7) A novel finding was that Galbeta1,4GlcNAcbeta-O-Al and Galbeta1,3GlcNAcbeta-O-Al, upon C-6 sulfation of the GlcNAc moiety, became 100% inactive and 5- to 7-fold active, respectively, in their ability to serve as acceptors for Group B.

Solid stress inhibits the growth of multicellular tumor spheroids

In normal tissues, the processes of growth, remodeling, and morphogenesis are tightly regulated by the stress field; conversely, stress may be generated by these processes. We demonstrate that solid stress inhibits tumor growth in vitro, regardless of host species, tissue of origin, or differentiation state. The inhibiting stress for multicellular tumor spheroid growth in agarose matrices was 45 to 120 mm Hg. This stress, which greatly exceeds blood pressure in tumor vessels, is sufficient to induce the collapse of vascular or lymphatic vessels in tumors in vivo and can explain impaired blood flow, poor lymphatic drainage, and suboptimal drug delivery previously reported in solid tumors. The stress-induced growth inhibition of plateau-phase spheroids was accompanied, at the cellular level, by decreased apoptosis with no significant changes in proliferation. A concomitant increase in the cellular packing density was observed, which may prevent cells from undergoing apoptosis via a cell-volume or cell-shape transduction mechanism. These results suggest that solid stress controls tumor growth at both the macroscopic and cellular levels, and thus influences tumor progression and delivery of therapeutic agents.

Early events of metastasis in the microcirculation involve changes in gene expression of cancer cells. Tracking mRNA levels of metastasizing cancer cells in the chick embryo chorioallantoic membrane

The early events of metastasis involve multiple interactions between cancer cells and the host microcirculation during cancer cell arrest, adhesion, and extravasation. These interactions may lead to changes in gene expression of the metastasizing cancer cells, although such changes have never been demonstrated directly. To test this hypothesis, B16-F10 murine melanoma cells were injected intravenously into the chick embryo chorioallantoic membrane (CAM), and mRNA levels in the metastasizing cancer cells were evaluated by species-specific reverse transcription polymerase chain reaction. Unlike standard mouse models of experimental metastasis, the CAM model showed successful extravasation of a large number of the arrested cancer cells in the CAM microcirculation without significant cancer cell death, providing a unique opportunity to keep track of mRNA levels in cancer cells during the early phases of metastasis. Using this model, we were able to demonstrate directly the temporal induction of cancer cell genes that potentially affect metastatic efficiency, namely, Fos (5 to 60 minutes after injection), vascular permeability factor (4 to 7 hours), and urokinase plasminogen activator (> 9 hours). In conclusion, using the CAM system, we have observed an alteration of gene expression in cancer cells in the early phases of metastasis, most likely as a consequence of host-cancer cell interactions. These changes may influence the metastatic behavior of cancer cells.

Hyperplasia of lymphatic vessels in VEGF-C transgenic mice

No growth factors specific for the lymphatic vascular system have yet been described. Vascular endothelial growth factor (VEGF) regulates vascular permeability and angiogenesis, but does not promote lymphangiogenesis. Overexpression of VEGF-C, a ligand of the VEGF receptors VEGFR-3 and VEGFR-2, in the skin of transgenic mice resulted in lymphatic, but not vascular, endothelial proliferation and vessel enlargement. Thus, VEGF-C induces selective hyperplasia of the lymphatic vasculature, which is involved in the draining of interstitial fluid and in immune function, inflammation, and tumor metastasis. VEGF-C may play a role in disorders involving the lymphatic system and may be of potential use in therapeutic lymphangiogenesis.

Potential and limitations of radioimmunodetection and radioimmunotherapy with monoclonal antibodies

Recently, we developed a physiologically based pharmacokinetic model capable of predicting antibody biodistribution in humans by scaling up from mice. By applying this model to anticarcinoembryonic antigen murine antibody ZCE025, we address several critical issues in radioimmunodetection and radioimmunotherapy, including the optimal antibody doses, the desirable antibody form for cancer detection, the optimal combinations of antibody forms and radionuclides for cancer treatment and the effectiveness of the modality.

METHODS

Under the baseline conditions of a standard 70-kg man with a 20-g tumor embedded in the liver, the model was used to: (a) estimate absorbed doses in tumor and normal tissues, (b) determine dose-dependent antibody uptake in the tumor, (c) simulate tumor-to-background antibody concentration ratio and (d) calculate therapeutic ratios for different antibody forms and radionuclides. Sensitivity analysis further enabled us to determine antibody delivery barriers and to assess the modality under average and favorable tumor physiological conditions.

RESULTS

By using ZCE025 under the baseline conditions, the model found that Fab was the most suitable form for cancer diagnosis, while 131l combined with F(ab')2 provided the highest tumor-to-bone marrow therapeutic ratio for cancer treatment. Sensitivity analysis showed that antibody permeability was the major barrier for antibody accretion in tumors. It also demonstrated that normal tissue antigen expression at a level lower than in the tumor had little effect on the therapeutic ratio.

CONCLUSION

The model demonstrates that: (a) for radioimmunodetection, the most effective antibody form (Fab for ZCE025) was the lower mol weight form, yet not sensitive enough for hepatic metastasis detection; and (b) for radioimmunotherapy, a relatively fast-clearing antibody form (F(ab')2 for ZCE025) in combination with long half-life beta(-)-emitters was optimal, yet inadequate as the sole therapeutic modality for solid tumors.

Measuring intracavity phase changes by use of double pulses in a linear cavity

We report the use of a mode-locked linear-cavity Ti:sapphire laser as a sensitive phasemeter. We were able to generate two pulses in the cavity by placing an absorbing-dye jet in the middle of the cavity. A voltage applied to an intracavity LiNbO(3) crystal modified the phase velocity for one of the two pulses at each of its passes. We could then measure accurately the change in optical cavity length by observing a beat frequency between the two pulses. We measured the ratio of the r(33) to r(13) electro-optic coefficients in LiNbO(3) to be 3.57+/-0.1 , in close agreement with the accepted value of 3.62.

Direct in vivo measurement of targeted binding in a human tumor xenograft

Binding is crucial to the function of most biologically active molecules, but difficult to quantify directly in living tissue. To this end, fluorescence recovery after photobleaching was used to detect the immobilization of fluorescently labeled ligand caused by binding to receptors in vivo. Measurements of mAb affinity to target antigen within human tumor xenografts revealed a saturable binding isotherm, from which an in vivo carcinoembryonic antigen density of 0.56 nmol/g (5.0 x 10(5)/cell) and an association constant of Ka < or = 4 x 10(7) M(-1) were estimated. The present method can be adapted for in vivo studies of cell signaling, targeted drugs, gene therapy, and other processes involving receptor-ligand binding.

Effect of tumor necrosis factor alpha on vascular resistance, nitric oxide production, and glucose and oxygen consumption in perfused tissue-isolated human melanoma xenografts

The effect of tumor necrosis factor alpha (TNF-alpha) on vascular resistance, nitric oxide production, and consumption of oxygen and glucose was examined in a perfused tissue-isolated tumor model in nude mice. One experimental group was perfused with heparinized Krebs-Henseleit buffer, a second one was perfused with TNF-alpha (500 microgram/kg) 5 h before perfusion. The vascular resistance increased significantly 5 h after TNF-alpha injection. The increase in vascular resistance did not seem to be mediated by a decrease in tumor nitric oxide production, as determined by perfusate nitrate/nitrite concentrations, but may be due to aggregation of leukocytes, platelets, and erythrocytes and/or endothelial consumption among the three experimental groups. The oxygen consumption was linearly dependent on the amount of available oxygen in the perfusate, whereas the glucose consumption was constant and independent of the glucose delivery rate. The present experiments provide new insights into physiological and metabolic mechanisms of action of TNF- alpha for optimization of future treatment schedules involving TNF-alpha.

Geometric resistance and microvascular network architecture of human colorectal carcinoma

OBJECTIVE

To measure the geometric resistance to blood flow in human colorectal carcinoma. Although tumor blood flow is of central importance in both the detection and the treatment of cancer, the determinants of blood flow through the neoplastic circulation are poorly understood.

METHODS

Human colorectal carcinomas (tissue weight = 272 g +/- 43 g (SD), n = 6) were perfused ex vivo with a buffered physiological salt solution of known viscosity at flow rates ranging from 2.5 to 40 ml/min and perfusion pressures from 8 to 100 mm Hg. The geometric resistance was determined from the slope of the pressure-flow curve. For examination of the principal determinant of geometric resistance, the vascular architecture, one of the tumors was perfused with Batson's No. 17 polymer and macerated in KOH to produce a positive vascular east that was used for measurement of vascular branching patterns and dimensions.

RESULTS

The pressure-flow relationship was linear at perfusion pressures above 40 mm Hg, and the geometric resistance, zzero, was constant at approximately 6.5 x 10(9) g/cm3. Below 40 mm Hg, zzero increased rapidly. The architecture of the arteriolar and capillary networks of human colorectal carcinoma is similar to those of experimental rodent tumors. Capillaries in planar and nonplanar meshworks had mean segment diameters of 11 +/- 2 and 9.6 +/- 2 microns, lengths of 46 +/- 24 and 107 +/- 40 microns, and intercapillary distances of 46 +/- 13 and 74 +/- 24 microns, respectively.

CONCLUSIONS

The geometric flow resistance in neoplastic tissue is 1-2 orders of magnitude higher than that observed in normal tissues. A decrease in functional vascular cross-sectional area may explain the additional increase in resistance at small perfusion pressures. The observed flow resistance may be due to the specialized arteriolar and capillary network architecture, pressure exerted by proliferating cancer cells, and/or coupling between vascular and extravascular flow. These observations demonstrate that tumor vascularity alone may not be indicative of flow resistance or tumor susceptibility to blood-borne therapeutic agents.

Transmural coupling of fluid flow in microcirculatory network and interstitium in tumors

The growth of tumors and their response to treatment are determined by delivery of diffusible substances to cancer cells and hence by their blood supply. Relative to most normal tissues, tumor blood flow is highly heterogeneous. Several hypotheses have been postulated to explain this anomalous behavior of tumor microcirculation, but the underlying mechanisms for these heterogeneities are not fully understood. In this study we consider a potential source of nonuniformity in the blood flow: the enhanced fluid exchange between the vascular and interstitial space mediated by the high leakiness of tumor vessels which could lead to a coupling between vascular, transvascular, and interstitial fluid flow. A simple network model is presented to describe the basic features of flow through a network of permeable and compliant vessels embedded in an isotropic porous medium. Two vascular geometries are considered: a regular mesh of identical vessels and a pair of countercurrent vessels of equal diameter. In each case, the flow through each vessel of the network is described by Poiseuille's law; the transmural flow between the vessels and the external porous medium is governed by Starling's law; the fluid movement through the porous medium is described by Darcy's law; and the vessel wall is assumed to be elastic. Our results show that the behavior of microcirculation may be strongly modified as a result of vascular compliance and enhanced vascular leakiness of tumor vessels. We found not only that the vascular pressure generates the well-known, high central interstitial fluid pressure, but also that the elevated interstitial pressure in turn alters the vascular pressure distribution. These changes in vascular pressure distribution result in a modification of the blood flow pattern. As the leakiness and compliance of the vessels increase, the blood is diverted away from the center of the tumor to a more peripheral path. The clinical significance of these results is that drug delivery for chemotherapy and oxygenation needed for radiotherapy may well be hampered in the central region of the tumor, despite the presence of highly permeable vessels in these regions.

The Eugene M. Landis Award Lecture 1996. Delivery of molecular and cellular medicine to solid tumors

To reach cancer cells in a tumor, a blood-borne therapeutic molecule or cell must make its way into the blood vessels of the tumor and across the vessel wall into the interstitium and finally migrate through the interstitium. Unfortunately, tumors often develop in ways that hinder each of these steps. Our research goals are to analyze each of these steps experimentally and theoretically and then integrate the resulting information in a unified theoretical framework. This paradigm of analysis and synthesis has allowed us to obtain a better understanding of physiologic barriers in solid tumors and to develop novel strategies to exploit and/or to overcome these barriers for improved cancer detection and treatment.

Role of nitric oxide in tumor microcirculation. Blood flow, vascular permeability, and leukocyte-endothelial interactions

The present study was designed to define the role of nitric oxide (NO) in tumor microcirculation, through the direct intravital microcirculatory observations after administration of NO synthase (NOS) inhibitor and NO donor both regionally and systemically. More specifically, we tested the following hypotheses: 1) endogenous NO derived from tumor vascular endothelium and/or tumor cells increases and/or maintains tumor blood flow, decreases leukocyte-endothelial interactions, and increases vascular permeability, 2) exogenous NO can increase tumor blood flow via vessel dilatation and decrease leukocyte-endothelial interactions, and 3) NO production and tissue responses to NO are tumor dependent. To this end, a murine mammary adenocarcinoma (MCaIV) and a human colon adenocarcinoma (LS174T) were implanted in the dorsal skinfold chamber in C3H and severe combined immunodeficient mice, respectively, and observed by means of intravital fluorescence microscopy. Both regional and systemic inhibition of endogenous NO by N omega-nitro-L-arginine methyl ester (L-NAME; 100 mumol/L superfusion or 10 mg/kg intravenously) significantly decreased vessel diameter and local blood flow rate. The diameter change was dominant on the arteriolar side. Superfusion of NO donor (spermine NO, 100 mumol/L) increased tumor vessel diameter and flow rate, whereas systemic injection of spermine NO (2.62 mg/kg) had no significant effect on these parameters. Rolling and stable adhesion of leukocytes were significantly increased by intravenous injection of L-NAME. In untreated animals, both MCaIV and LS174T tumor vessels were leaky to albumin. Systemic NO inhibition significantly attenuated tumor vascular permeability of MCaIV but not of LS174T tumor. Immunohistochemical studies, using polyclonal antibodies to endothelial NOS and inducible NOS, revealed a diffuse pattern of positive labeling in both MCaIV and LS174T tumors. Nitrite and nitrate levels in tumor interstitial fluid of MCaIV but not of LS174T were significantly higher than that in normal subcutaneous interstitial fluid. These results support our hypotheses regarding the microcirculatory response to NO in tumors. Modulation of NO level in tumors is a potential strategy for altering tumor hemodynamics and thus improving oxygen, drug, gene vector, and effector cell delivery to solid tumors.

Interstitial pH and pO2 gradients in solid tumors in vivo: high-resolution measurements reveal a lack of correlation

The partial pressure of oxygen (pO2) and pH play critical roles in tumor biology and therapy. We report here the first combined, high-resolution (< or = 10 microns) measurements of interstitial pH and pO2 profiles between adjacent vessels in a human tumor xenograft, using fluorescence ratio imaging and phosphorescence quenching microscopy. We found (1) heterogeneity in shapes of pH and pO2 profiles; (2) a discordant relation between local pH profiles and corresponding pO2 profiles, yet a strong correlation between mean pH and pO2 profiles; (3) no correlation between perivascular pH/pO2 and nearest vessel blood flow; and (4) well-perfused tumor vessels that were hypoxic and, consequently, large hypoxic areas in the surrounding interstitium. Such multiparameter measurements of the in vivo microenvironment provide unique insights into biological processes in tumors and their response to treatment.

Spectrometrically monitored selection experiments: quantitative laser desorption mass spectrometry of small chemical libraries

BACKGROUND

Selection experiments involving chemical libraries are routinely used in the pharmaceutical industry for finding and optimizing lead compounds. In principle, almost any process involving a binding event or a reaction could be probed systematically with chemical libraries prepared by combinatorial synthesis. Traditionally, however, the vast majority of library members cannot be monitored during the selection, making a systematic correlation of structure and activity difficult. To interpret selection experiments on the level of all library components, monitoring technologies are required that give a unique and quantitative spectroscopic signal for every compound in a mixture.

RESULTS

Quantitative matrix-assisted laser desorption mass spectrometry of libraries of porphyrins and peptide-DNA hybrids consisting of 2-35 compounds is described. Porphyrin libraries were subjected to in vitro selections for liposome incorporation and binding to a protein pocket. It was shown that mesohydroxyphenyl substituted porphyrins, known high activity photosensitizers of tumors, are preferentially incorporated in liposome membranes. A mixture of peptide-DNA hybrids was assayed for the nuclease stability of its components.

CONCLUSIONS

Small libraries of non-isobaric compounds can be exhaustively or near-exhaustively monitored by mass spectrometry. Monitored selection experiments can yield detailed structure-activity maps in a single experiment, speeding up drug discovery and the probing of biochemically relevant recognition events. It is proposed that monitored assays for target binding, membrane partitioning, and biostability could be run in parallel, to select drug candidates combining several favorable properties in 'multidimensional' selection experiments.

Interstitial fluid pressure in intracranial tumours in patients and in rodents

Fluid transport parameters in intracranial tumours influence the delivery of therapeutic agents and the resolution of peritumoral oedema. The tumour and cortex interstitial fluid pressure (IFP) and the cerebrospinal fluid pressure (CSFP) were measured during the growth of brain and pial surface tumours [R3230AC mammary adenocarcinoma (R3230AC) and F98 glioma (F98)] in rats. Intratumoral and intracranial pressures were also measured in rodents and patients treated with dexamethasone, mannitol and furosemide (DMF), and hypocapnia. The results show that (1) for the R3230AC on the pial surface, IFP increased with tumour volume and CSFP increased exponentially for tumours occupying a brain volume of 5% or greater; (2) in F98 with volumes of approximately 10 mm3, IFP decreased from the tumour to the cortex, whereas for tumour volumes > 16 mm3 IFP equilibrates between F98 and the cortex; (3) DMF treatment reduced the IFP of intraparenchymal tumours significantly and induced a pressure gradient from the tumour to the cortex; and (4) in 11 patients with intracranial tumours, the mean IFP was 2.0 +/- 2.5 mmHg. In conclusion, the IFP gradient between intraparenchymal tumours and the cortex decreases with tumour growth, and treatment with DMF can increase the pressure difference between the tumour and surrounding brain. The results also suggest that antioedema therapy in patients with brain tumours is responsible in part for the low tumour IFP.

Effect of basic fibroblast growth factor on angiogenesis and growth of isografted bone: quantitative in vitro-in vivo analysis in mice

Basic fibroblast growth factor (bFGF), a constituent of bone and cartilage matrix, has been shown to be a potent mitogen for osteoblasts and chondrocytes and yet an inhibitor of chondrocyte terminal differentiation in cell culture. To characterize the effect of bFGF on bone formation, whole neonatal murine femora were cultured in the presence or absence of bFGF and a neutralizing antibody against bFGF. In vitro, femoral elongation was provided by cartilage growth only; the calcified diaphyseal zone stained by oxytetracycline did not increase. When bFGF was added to the culture medium, longitudinal growth of the proximal and distal cartilage was inhibited in a dose-dependent manner (p < 0.05), and the number of hypertrophic chondrocytes in the growth plate was reduced. This phenomenon was absent in the presence of a neutralizing antibody, which when given alone significantly promoted femoral elongation. In contrast, in vivo after transplantation into adult mice bearing dorsal skin fold chambers, femora rapidly calcified after revascularization. This observation supports the notion that bone formation largely depends on angiogenesis-mediated events. To verify this hypothesis, angiogenesis and bone formation were quantified using bFGF known to be a stimulator of angiogenesis. Calcification of grafted femora was accelerated by bFGF given intraperitoneally. The neutralizing antibody slightly suppressed angiogenesis and femoral elongation (not statistically significant), whereas intravenous injections of both substances did not reveal a significant modulatory effect. In vivo the effect of systemically administered bFGF was inhomogeneous, but there was a strong correlation between angiogenesis and endochondral calcification (p < 0.001). These results suggest that exogenous bFGF modulates bone formation in vitro by inhibition of terminal differentiation of chondrocytes in the growth plate, and angiogenesis and concomitant in vivo events are pivotal in the promotion of rapid bone formation.

Time-dependent vascular regression and permeability changes in established human tumor xenografts induced by an anti-vascular endothelial growth factor/vascular permeability factor antibody

The hyperpermeability of tumor vessels to macromolecules, compared with normal vessels, is presumably due to vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) released by neoplastic and/or host cells. In addition, VEGF/VPF is a potent angiogenic factor. Removal of this growth factor may reduce the permeability and inhibit tumor angiogenesis. To test these hypotheses, we transplanted a human glioblastoma (U87), a human colon adenocarcinoma (LS174T), and a human melanoma (P-MEL) into two locations in immunodeficient mice: the cranial window and the dorsal skinfold chamber. The mice bearing vascularized tumors were treated with a bolus (0.2 ml) of either a neutralizing antibody (A4.6.1) (492 micrograms/ml) against VEGF/VPF or PBS (control). We found that tumor vascular permeability to albumin in antibody-treated groups was lower than in the matched controls and that the effect of the antibody was time-dependent and influenced by the mode of injection. Tumor vascular permeability did not respond to i.p. injection of the antibody until 4 days posttreatment. However, the permeability was reduced within 6 h after i.v. injection of the same amount of antibody. In addition to the reduction in vascular permeability, the tumor vessels became smaller in diameter and less tortuous after antibody injections and eventually disappeared from the surface after four consecutive treatments in U87 tumors. These results demonstrate that tumor vascular permeability can be reduced by neutralization of endogenous VEGF/ VPF and suggest that angiogenesis and the maintenance of integrity of tumor vessels require the presence of VEGF/VPF in the tissue microenvironment. The latter finding reveals a new mechanism of tumor vessel regression-i.e., blocking the interactions between VEFG/VPF and endothelial cells or inhibiting VEGF/VPF synthesis in solid tumors causes dramatic reduction in vessel diameter, which may block the passage of blood elements and thus lead to vascular regression.

Perfusion of single tumor microvessels: application to vascular permeability measurement

OBJECTIVE

To develop a new method for determining the relative importance of convection versus diffusion in macromolecular transport across tumor microvessel walls.

METHODS

The human colon adenocarcinoma LS174T was transplanted in the dorsal skinfold chamber in a severe combined immunodeficient (SCID) mouse. The vasculature at the tumor surface was exposed by carefully removing the glass window of the chamber. A tumor microvessel was randomly selected, which was approximately 20-40 microns in diameter, embedded in the connective tissue 10-12 microns below the surface of the tumor. The vessel was cannulated with a micropipette and perfused with fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA) at different perfusion pressures. The fluorescence intensity was recorded on videotapes via a video system attached to the fluorescence microscope for offline analysis. The apparent vascular permeability was determined based on the time-dependence of fluorescence intensity and the vessel diameter.

RESULTS

The apparent vascular permeability of single vessels to FITC-labeled BSA was quantified at perfusion pressures of 20-45 cmH2O. The pressure dependence of vascular permeability in LS174T tumors was heterogeneous. On average, there was no correlation between the apparent vascular permeability and the perfusion pressure in the range of 20-35 cmH2O (p = 0.73), even though the apparent permeability increased significantly when the pressure was increased from 20 to 45 cmH2O (p = 0.008).

CONCLUSIONS

These results indicate that convection in the transvascular transport of albumin is not significant in non-peripheral regions of solid tumors in which the pressure difference across the vessel wall is small or even negligible. In addition to the permeability studies, this preparation can be used to study cell-cell interactions in single tumor vessels under defined flow conditions.

Lateral diffusion of small compounds in human stratum corneum and model lipid bilayer systems

An image-based technique of fluorescence recovery after photobleaching (video-FRAP) was used to measure the lateral diffusion coefficients of a series of nine fluorescent probes in two model lipid bilayer systems, dimyristoylphosphatidylcholine (DMPC) and DMPC/cholesterol (40 mol%), as well as in human stratum corneum-extracted lipids. The probes were all lipophilic, varied in molecular weight from 223 to 854 Da, and were chosen to characterize the lateral diffusion of small compounds in these bilayer systems. A clear molecular weight dependence of the lateral diffusion coefficients in DMPC bilayers was observed. Values ranged from 6.72 x 10(-8) to 16.2 x 10(-8) cm2/s, with the smaller probes diffusing faster than the larger ones. Measurements in DMPC/cholesterol bilayers, which represent the most thorough characterization of small-solute diffusion in this system, exhibited a similar molecular weight dependence, although the diffusion coefficients were lower, ranging from 1.62 x 10(-8) to 5.60 x 10(-8) cm2/s. Lateral diffusion measurements in stratum corneum-extracted lipids, which represent a novel examination of diffusion in this unique lipid system, also exhibited a molecular weight dependence, with values ranging from 0.306 x 10(-8) to 2.34 x 10(-8) cm2/s. Literature data showed that these strong molecular weight dependencies extend to even smaller compounds than those examined in this study. A two-parameter empirical expression is presented that describes the lateral diffusion coefficient in terms of the solute's molecular weight and captures the size dependence over the range examined. This study illustrates the degree to which small-molecule lateral diffusion in stratum corneum-extracted lipids can be represented by diffusion in DMPC and DMPC/cholesterol bilayer systems, and may lead to a better understanding of small-solute transport across human stratum corneum.

Fluorescence ratio imaging of interstitial pH in solid tumours: effect of glucose on spatial and temporal gradients

Tumour pH plays a significant role in cancer treatment. However, because of the limitations of the current measurement techniques, spatially and temporally resolved pH data, obtained non-invasively in solid tumours, are not available. Fluorescence ratio imaging microscopy (FRIM) has been used previously for noninvasive, dynamic evaluation of pH in neoplastic tissue in vivo (Martin GR, Jain RK 1994, Cancer Res., 54, 5670-5674). However, owing to problems associated with quantitative fluorescence in thick biological tissues, these studies were limited to thin (50 microns) tumours. We, therefore, adapted the FRIM technique for pH determination in thick (approximately 2 mm) solid tumours in vivo using a pinhole illumination-optical sectioning (PIOS) method. Results show that (1) steep interstitial pH gradients (5 microns resolution), with different spatial patterns, exist between tumour blood vessels; (2) pH decreased by an average of 0.10 pH units over a distance of 40 microns away from the blood vessel wall, and by 0.33 pH units over a 70 microns distance; (3) the maximum pH drop, defined as the pH difference between the intervessel midpoint and the vessel wall, was positively correlated with the intervessel distance; (4) 45 min following a systemic glucose injection (6 g kg-1 i.v), interstitial pH gradients were shifted to lower pH values by an average of 0.15 pH units, while the spatial gradient (slope) was maintained, when compared with preglucose values. This pH decrease was not accompanied by significant changes in local blood flow. pH gradients returned to near-baseline values 90 min after glucose injection; (5) interstitial tumour pH before hyperglycaemia and the glucose-induced pH drop strongly depended on the local vessel density; and (6) sodium bicarbonate treatment, either acute (1 M, 0.119 ml h-1 for 3 h i.v.) or chronic (1% in drinking water for 8 days), did not significantly change interstitial tumour pH. Modified FRIM may be combined with other optical methods (e.g. phosphorescence quenching) to evaluate non-invasively the spatial and temporal characteristics of extracellular pH, intracellular pH and pO2 in solid tumours. This will offer unique information about tumour metabolism and its modification by treatment modalities used in different cancer therapies.

Tumor angiogenesis and interstitial hypertension

Due to the high permeability of tumor vessels to fluids and plasma proteins, the microvascular pressure (MVP) is the principal driving force for interstitial hypertension in solid tumors; as a result, hydrostatic pressures between the microvascular and interstitial space are close to equilibrium. Based on these observations, we hypothesized that the tumor interstitial fluid pressure (IFP) should increase following the onset of angiogenesis. To this end, the relationship between IFP and tumor neovascularization was determined in the human colon adenocarcinoma (LS174T) and the murine carcinoma (MCaIV) implanted in a transparent dorsal skin fold chamber in severe combined immunodeficient mice. Three stages in the development of the tumor neovasculature were characterized by intravital microscopy. Stage I tumors were avascular, stage II was characterized by vascular sprouts and loops, and in stage III, the tumor vasculature was completely developed and blood flow was obvious. The IFP was measured with micropipettes and a servo-null system. For both tumor types, the IFP in stage I tumors was close to 0 mm Hg, and IFP increased significantly from one stage to the next. To further confirm that interstitial hypertension was associated with the development of the tumor vasculature, IFP was measured in LS174T spheroids. The mean pressure in spheroids was 0.2 +/- 0.3 mm Hg. In stage III tumors, the IFP was compared to the MVP. In MCaIV, the MVP was comparable to the IFP; however, in LS174T the MVP was significantly higher than the IFP. In conclusion, the results demonstrate that avascular tumors have atmospheric pressures and that tumor interstitial hypertension is associated with the development of the neovasculature.