Transport of macromolecules in tumor microcirculation

Non-invasive imaging of interstitial fluid transport parameters in solid tumors in vivo

In this paper, new and non-invasive imaging methods to assess interstitial fluid transport parameters in tumors in vivo are developed, analyzed and experimentally validated. These parameters include extracellular volume fraction (EVF), interstitial fluid volume fraction (IFVF) and interstitial hydraulic conductivity (IHC), and they are known to have a critical role in cancer progression and drug delivery effectiveness. EVF is defined as the volume of extracellular matrix per unit volume of the tumor, while IFVF refers to the volume of interstitial fluid per unit bulk volume of the tumor. There are currently no established imaging methods to assess interstitial fluid transport parameters in cancers in vivo. We develop and test new theoretical models and imaging techniques to assess fluid transport parameters in cancers using non-invasive ultrasound methods. EVF is estimated via the composite/mixture theory with the tumor being modeled as a biphasic (cellular phase and extracellular phase) composite material. IFVF is estimated by modeling the tumor as a biphasic poroelastic material with fully saturated solid phase. Finally, IHC is estimated from IFVF using the well-known Kozeny-Carman method inspired by soil mechanics theory. The proposed methods are tested using both controlled experiments and in vivo experiments on cancers. The controlled experiments were performed on tissue mimic polyacrylamide samples and validated using scanning electron microscopy (SEM). In vivo applicability of the proposed methods was demonstrated using a breast cancer model implanted in mice. Based on the controlled experimental validation, the proposed methods can estimate interstitial fluid transport parameters with an error below 10% with respect to benchmark SEM data. In vivo results demonstrate that EVF, IFVF and IHC increase in untreated tumors whereas these parameters are observed to decrease over time in treated tumors. The proposed non-invasive imaging methods may provide new and cost-effective diagnostic and prognostic tools to assess clinically relevant fluid transport parameters in cancers in vivo.

Redox-Responsive Hydrogels with Decoupled Initial Stiffness and Degradation

Disulfide-cross-linked hydrogels have been widely used for biological applications because of their degradability in response to redox stimuli. However, degradability often depends on polymer concentration, which also influences the hydrogel mechanical properties such as the initial stiffness. Here, we describe a one-pot cross-linking approach utilizing both a thiol-ene reaction through a Michael pathway with divinyl sulfone (DVS) to form non-reducible thioether bonds and thiol oxidation promoted by ferric ethylenediaminetetraacetic acid (Fe-EDTA) to form reducible disulfide bonds. The ratio between these two bonds was modulated by varying the DVS concentration used, and the initial shear or elastic modulus and degradation rate of the hydrogels were decoupled. These gels had tunable release rates of encapsulated dextran when exposed to 10 μM glutathione. Fibroblast encapsulation results suggested good cytocompatibility of the cross-linking reactions. This work shows the potential of combining DVS and Fe-EDTA to create thiol-cross-linked hydrogels as redox-responsive drug delivery vehicles and tissue engineering scaffolds with variable degradability.

Textures of the tumour microenvironment

In this review, we present recent findings on the dynamic nature of the tumour microenvironment (TME) and how intravital microscopy studies have defined TME components in a spatiotemporal manner. Intravital microscopy has shed light into the nature of the TME, revealing structural details of both tumour cells and other TME co-habitants in vivo, how these cells communicate with each other, and how they are organized in three-dimensional space to orchestrate tumour growth, invasion, dissemination and metastasis. We will review different imaging tools, imaging reporters and fate-mapping strategies that have begun to uncover the complexity of the TME in vivo.

Structural Reconstruction of the Perivascular Space in the Adult Mouse Neurohypophysis During an Osmotic Stimulation

Oxytocin (OXT) and arginine vasopressin (AVP) neuropeptides in the neurohypophysis (NH) control lactation and body fluid homeostasis, respectively. Hypothalamic neurosecretory neurones project their axons from the supraoptic and paraventricular nuclei to the NH to make contact with the vascular surface and release OXT and AVP. The neurohypophysial vascular structure is unique because it has a wide perivascular space between the inner and outer basement membranes. However, the significance of this unique vascular structure remains unclear; therefore, we aimed to determine the functional significance of the perivascular space and its activity-dependent changes during salt loading in adult mice. The results obtained revealed that pericytes were the main resident cells and defined the profile of the perivascular space. Moreover, pericytes sometimes extended their cellular processes or 'perivascular protrusions' into neurohypophysial parenchyma between axonal terminals. The vascular permeability of low-molecular-weight (LMW) molecules was higher at perivascular protrusions than at the smooth vascular surface. Axonal terminals containing OXT and AVP were more likely to localise at perivascular protrusions than at the smooth vascular surface. Chronic salt loading with 2% NaCl significantly induced prominent changes in the shape of pericytes and also increased the number of perivascular protrusions and the surface area of the perivascular space together with elevations in the vascular permeability of LMW molecules. Collectively, these results indicate that the perivascular space of the NH acts as the main diffusion route for OXT and AVP and, in addition, changes in the shape of pericytes and perivascular reconstruction occur in response to an increased demand for neuropeptide release.

Targeting tumor microenvironment: crossing tumor interstitial fluid by multifunctional nanomedicines

Introduction: The genesis of cancer appears to be a complex matter, which is not simply based upon few genetic abnormalities/alteration. In fact, irregular microvasculature and aberrant interstitium of solid tumors impose significant pathophysiologic barrier functions against cancer treatment modalities, hence novel strategies should holistically target bioelements of tumor microenvironment (TME). In this study, we provide some overview and insights on TME and important strategies used to control the impacts of such pathophysiologic barriers.

Methods: We reviewed all relevant literature for the impacts of tumor interstitium and microvasculature within the TME as well as the significance of the implemented strategies.

Results: While tumorigenesis initiation seems to be in close relation with an emergence of hypoxia and alterations in epigenetic/genetic materials, large panoplies of molecular events emerge as intricate networks during oncogenesis to form unique lenient TME in favor of tumor progression. Within such irregular interstitium, immune system displays defective surveillance functionalities against malignant cells. Solid tumors show multifacial traits with coadaptation and self-regulation potentials, which bestow profound resistance against the currently used conventional chemotherapy and immunotherapy agents that target solely one face of the disease.

Conclusion: The cancerous cells attain unique abilities to form its permissive microenvironment, wherein (a) extracellular pH is dysregulated towards acidification, (b) extracellular matrix (ECM) is deformed, (c) stromal cells are cooperative with cancer cells, (d) immune system mechanisms are defective, (e) non-integrated irregular microvasculature with pores (120-1200 nm) are formed, and (h) interstitial fluid pressure is high. All these phenomena are against cancer treatment modalities. As a result, to control such abnormal pathophysiologic traits, novel cancer therapy strategies need to be devised using multifunctional nanomedicines and theranostics.

Plasmonic photothermal heating of intraperitoneal tumors through the use of an implanted near-infrared source

Plasmonic nanomaterials including gold nanorods are effective agents for inducing heating in tumors. Because near-infrared (NIR) light has traditionally been delivered using extracorporeal sources, most applications of plasmonic photothermal therapy have focused on isolated subcutaneous tumors. For more complex models of disease such as advanced ovarian cancer, one of the primary barriers to gold nanorod-based strategies is the adequate delivery of NIR light to tumors located at varying depths within the body. To address this limitation, a series of implanted NIR illumination sources are described for the specific heating of gold nanorod-containing tissues. Through computational modeling and ex vivo studies, a candidate device is identified and validated in a model of orthotopic ovarian cancer. As the therapeutic, imaging, and diagnostic applications of plasmonic nanomaterials progress, effective methods for NIR light delivery to challenging anatomical regions will complement ongoing efforts to advance plasmonic photothermal therapy toward clinical use.

Diffusion of macromolecules through sclera

PURPOSE

To quantify the in vitro permeability coefficient over different topographical locations of porcine sclera to macromolecules with different molecular weight.

METHODS

Fresh equatorial and posterior superotemporal porcine sclera was mounted in a two-chamber diffusion apparatus, and its permeability to fluorescein isothiocyanate (FITC)-conjugated dextrans ranging in molecular weight from 40 kDa to 150 kDa was determined by fluorescence spectrophotometry. The sclera was processed as frozen sections and viewed with a fluorescence microscope. The thickness of the area and the thickness that macromolecules enriched in the surface of sclera were measured.

RESULTS

The permeability coefficient (Pc) of porcine sclera to macromolecules was significantly higher (40 kDa, p = 0.028; 70 kDa, p = 0.033; 150 kDa, p = 0.007) in equatorial region than posterior, which could be attributed to the significant difference of thickness (p < 0.001, Kruskal-Wallis) between them. Moreover, linear regression indicated a significant negative relationship (40 kDa, p < 0.001; 70 kDa, p = 0.015; 150 kDa, p < 0.001) between scleral permeability coefficient and thickness. Also, Pc declined significantly with increasing molecular weight (MW, p < 0.001, Kruskal-Wallis). The area that the macromolecules enriched in the scleral surface was thicker for those with larger MW (p < 0.001, Kruskal-Wallis). The maximum MW and size for equatorial and posterior superotemporal scleral tissue were 185.01 KDa and 180.42 KDa, 9.92 nm and 9.67 nm, respectively.

CONCLUSIONS

The permeability coefficient of porcine sclera has a significant negative relationship with scleral thickness and MW of macromolecules. Larger macromolecules are more likely to accumulate in scleral surface. The difference between topographical locations may have pharmacokinetic implications when considering transscleral diffusion of macromolecules.

Quantitative full-colour transmitted light microscopy and dyes for concentration mapping and measurement of diffusion coefficients in microfluidic architectures

A simple and versatile methodology has been developed for the simultaneous measurement of multiple concentration profiles of colourants in transparent microfluidic systems, using a conventional transmitted light microscope, a digital colour (RGB) camera and numerical image processing combined with multicomponent analysis. Rigorous application of the Beer-Lambert law would require monochromatic probe conditions, but in spite of the broad spectral bandwidths of the three colour channels of the camera, a linear relation between the measured optical density and dye concentration is established under certain conditions. An optimised collection of dye solutions for the quantitative optical microscopic characterisation of microfluidic devices is proposed. Using the methodology for optical concentration measurement we then implement and validate a simplified and robust method for the microfluidic measurement of diffusion coefficients using an H-filter architecture. It consists of measuring the ratio of the concentrations of the two output channels of the H-filter. It enables facile determination of the diffusion coefficient, even for non-fluorescent molecules and nanoparticles, and is compatible with non-optical detection of the analyte.

Tumour angiogenesis: vascular growth and survival

Angiogenesis starts at the edge of a malignant epithelial tumour concurrently with tumour cell invasion and stromatogenesis, i.e. the formation of specific connective tissue stroma amenable to easy penetration by endothelial and tumour cells. However, as the tumour continues its growth, the edge becomes the inner tumour area, and a new invading tumour front is formed by the multiplying malignant cells which outflank the initial edge. This process, which repeats itself again and again, forms the "relay race" model of tumour vascular growth and regression. At the heart of the tumour unfavourable environmental conditions prevail -- hypoxia, acidity, lack of nutrients, failure of waste removal, and apoptosis rather than proliferation. Blood vessels and tumour cells are greatly decreased, but do not vanish, as tumour cells are shifting to anaerobic glycolysis, and blood vessels are turning into anti-apoptotic pathways -- vascular survival ability (VSA). Thus, assessing vascular density (VD) by simply counting "hot spots" at the edge of a tumour, where conditions are most favourable, is futile; it may reflect tumour angiogenic activity (TAA), but is not representative of genuine tumour vasculature. By combining vessel counts at the invading tumour front with those of the inner tumour areas a complete picture of tumour VD can be achieved. The thus formed four patterns of vascularization, designated as "edvin" (edge vsinner tumour area), are: edvin 1: low TAA/low VSA; edvin 4: high TAA/high VSA; edvin 2: low TAA/high VSA; and edvin 3: high TAA/low VSA. It is expected that this scheme will prove useful in the field of chemoradiotherapy and anti-angiogenic treatment.

The vascular network of tumours--what is it not for?

It is becoming almost a dogma that tumours cannot grow beyond 1-2 mm(3) unless they are supported by a rich vascular supply 1. It is true that tumours promote angiogenesis and that highly vascularized carcinomas have, in general, a more aggressive clinical course than carcinomas of low vascularization 23. However, a study of intratumoral angiogenesis reveals that the newly formed vessels are commonly deprived of those structural qualities that would allow them to perform an optimal oxygenation function 3. Thus, most tumours, irrespective of their angiogenic status, behave as if they were 'hypoxic', urging (via angiogenic mediators) for, what would look paradoxical at first sight, more defective angiogenesis. It is hypothesized that tumour cells can grow into solid neoplasms by exploiting the host's pre-existing vessels, without the need for new blood vessel formation. Neovascularization, however, may be important for tumours with an exophytic pattern of growth as these, by their very nature, lose the host's sheltering stroma. Shifting to anaerobic glycolysis and activation of anti-apoptotic pathways are complementary mechanisms for tumour cell survival and growth. Besides, continuous and indiscriminate production of a defective vascular network ensures an increased metastatic potential since the newly formed intratumoral vessels, simulating venular-like spaces, are easily permeable to tumour cells, facilitating metastases.

Carrier proteins determine local pharmacokinetics and arterial distribution of paclitaxel

The growing use of local drug delivery to vascular tissues has increased interest in hydrophobic compounds. The binding of these drugs to serum proteins raises their levels in solution, but hinders their distribution through tissues. Inside the arterial interstitium, viscous and steric forces and binding interactions impede drug motion. As such, this might be the ideal scenario for increasing the amount of drug delivered to, and residence time within, arterial tissues. We quantified carrier-mediated transport for paclitaxel, a model hydrophobic agent with potential use in proliferative vascular diseases, by determining, in the presence or absence of carrier proteins, the maximum concentration of drug in aqueous solution, the diffusivity in free solution, and the diffusivity in arterial tissues. Whereas solubility of paclitaxel was raised 8.1-, 21-, and 57-fold by physiologic levels of alpha(1)-acid glycoproteins, bovine serum albumin, and calf serum over that in protein-free solution, diffusivity of paclitaxel in free solution was reduced by 41, 49, and 74%, respectively. When paclitaxel mixed in these solutions was applied to arteries both in vitro and in vivo, drug was more abundant at the tissue interface, but protein carriers tended to retain drug in the lumen. Once within the tissue, these proteins did not affect the rate at which drug traverses the tissue because this hydrophobic drug interacted with the abundant fixed proteins and binding sites. The protein binding properties of hydrophobic compounds allow for beneficial effects on transvascular transport, deposition, and distribution, and may enable prolonged effect and rationally guide local and systemic strategies for their administration.

Biocompatibility of electroactive polymers in tissues

The biocompatibility of ethylene-vinyl acetate copolymer (EVAc), polyethylene (PE), and polyaniline (PANi) films in the emeraldine (EM), nigraniline (NA) and leucoemeraldine (LM) intrinsic oxidation states were assessed through subcutaneous implantation into male Sprague-Dawley rats beneath the dorsal skin, for a period ranging from 19 to 90 weeks. Histological examination, interstitial pressure measurement, and X-ray photoelectron spectroscopy (XPS) were employed to determine the biocompatibility of the polymers. The polymers did not provoke inflammatory responses in the subcutaneous tissues over the entire implantation period. Characteristics features associated with tissue-implant incompatibility were not evident near the implantation. Interstitial pressure was measured to evaluate the development of tissue. Low interstitial pressure readings on the region of implantation confirmed the biocompatibility of these polymer types. The surface composition of the electroactive aniline polymers before and after the implantation was characterized by XPS.

Correlation of transarterial transport of various dextrans with their physicochemical properties

Local vascular drug delivery provides elevated concentrations of drug in the target tissue while minimizing systemic side effects. To better characterize local pharmacokinetics we examined the arterial transport of locally applied dextran and dextran derivatives in vivo. Using a two-compartment pharmacokinetic model to correct the measured transmural flux of these compounds for systemic redistribution and elimination as delivered from a photopolymerizable hydrogel surrounding rat carotid arteries, we found that the diffusivities and the transendothelial permeabilities were strongly dependent on molecular weight and charge. For neutral dextrans, the effective diffusive resistance in the media increased with molecular weight approximately 4.1-fold between the molecular weights of 10 and 282 kDa. Similarly, endothelial resistance increased 28-fold over the same molecular weight range. The effective medial diffusive resistance was unaffected by cationic charge as such molecules moved identically to neutral compounds, but increased approximately 40% when dextrans were negatively charged. Transendothelial resistance was 20-fold lower for the cationic dextrans, and 11-fold higher for the anionic dextrans, when both were compared to neutral counterparts. These results suggest that, while low molecular weight drugs will rapidly traverse the arterial wall with the endothelium posing a minimal barrier, the reverse is true for high molecular weight agents. With these data, the deposition and distribution of locally released vasotherapeutic compounds might be predicted based upon chemical properties, such as molecular weight and charge.

Effects of VEGF on Ca(2+)-transient in cultured lymphatic endothelial cells and mechanical activity of isolated lymph vessels

We investigated the effects of vascular endothelial growth factor (VEGF(165)) on [Ca(2+)](i)-transient in cultured lymphatic endothelial cells (LEC) and mechanical activity of isolated dog thoracic ducts. VEGF (0.1-10 ng/ml) caused a dose-dependent increase of the [Ca(2+)](i) in LEC. Pretreatment with 10(-5) M genistein or 5x10(-6) M herbimycin A produced a significant reduction of the VEGF-induced [Ca(2+)](i)-transient. In the presence of 10(-6) M thapsigargin, VEGF caused no significant effect on the [Ca(2+)](i)-transient. Pretreatment with Ca(2+)-free solution containing 0.1 mM EGTA produced no significant effect on the peak increase of [Ca(2+)](i) induced by 0.1 or 10 ng/ml VEGF, but significantly depressed the sustained part of [Ca(2+)](i) observed at the higher concentration of VEGF. The VEGF (0.1-10 ng/ml) caused a significant dilation of the isolated lymph vessels with intact endothelium, which were precontracted with U46,619. The 10 ng/ml VEGF-induced dilation was significantly reduced by 3 x 10(-5) M N(omega)-nitro-L-arginine methyl ester (L-NAME). The action of L-NAME was inhibited by the simultaneous application of 10(-3) M L-arginine. Mechanical rubbing of the endothelium also caused significant inhibition of the VEGF-induced dilation. The findings suggest that VEGF(165) may activate the receptor-related tyrosine kinase and cause the release of Ca(2+) from the inositol 1,4, 5-triphosphate-sensitive intracellular Ca(2+) stores in LEC. VEGF(165) also produces endothelium-dependent nitric oxide-mediated dilation of the precontracted isolated lymph vessels.

Arterial paclitaxel distribution and deposition

Successful implementation of local arterial drug delivery requires transmural distribution of drug. The physicochemical properties of the applied compound, which govern its transport and tissue binding, become as important as the mode of delivery. Hydrophilic compounds distribute freely but are cleared rapidly. Hydrophobic drugs, insoluble in aqueous solutions, bind to fixed tissue elements, potentially prolonging tissue residence and biological effect. Paclitaxel is such a hydrophobic compound, with tremendous therapeutic potential against proliferative vascular disease. We hypothesized that the recent favorable preclinical data with this compound may derive in part from preferential tissue binding as a result of unique physicochemical properties. The arterial transport of paclitaxel was quantified through application ex vivo and measurement of the subsequent transmural distribution. Arterial paclitaxel deposition at equilibrium varied across the arterial wall and was everywhere greater in concentration than in the applied drug source. Permeation into the wall increased with time, from 15 minutes to 4 hours, and varied with the origin of delivery. In contrast to hydrophilic compounds, the concentration in tissue exceeds the applied concentration and the rate of transport was markedly slower. Furthermore, endovascular and perivascular paclitaxel application led to markedly differential deposition across the blood vessel wall. These data suggest that paclitaxel interacts with arterial tissue elements as it moves under the forces of diffusion and convection and can establish substantial partitioning and spatial gradients across the tissue. The complexity of paclitaxel pharmacokinetics requires in-depth investigation if this drug is to reach its full clinical potential in proliferative vascular diseases.

Activity of doxorubicin covalently bound to a novel human serum albumin microcapsule

Doxorubicin is widely used in the treatment of human malignancies, however is associated with significant cardiac, bone marrow and gastro-intestinal toxicity. Delivery systems may ameliorate this toxicity and increase treatment specificity by increasing the proportion of drug delivered to sites of disease. We have developed a novel preparation of doxorubicin (Dox) covalently linked to a heat stabilised human serum albumin microparticle (HSAM) carrier (median particle diameter of 4 microm) and assessed its activity in 4 malignant cell lines.

MATERIALS AND METHODS

Doxorubicin microcapsules were compared with free doxorubicin in the rat carcinoma cell line, WRC256, and the human lines, OVCAR3, MCF7 and the Dox resistant MCF7/Dox, using a cell counting technique. IC50 were calculated from regression analysis of the resulting survival curves. Endocytosis of the microcapsules by cells in culture was observed. The rate of microcapsule uptake was assessed using dual wavelength filtered fluorescence microscopy and flow cytometry.

RESULTS

The mean IC50 following incubation with the Dox microcapsules was around 5 times greater than Dox for WRC256 (p < 0.001), MCF7 (p < 0.01) and for OVCAR3 (p < 0.01). MCF7/Dox was significantly more sensitive to Dox microcapsules than free Dox (p = 0.034). A negative correlation between the rate of microcapsule uptake and the IC50 values for each cell line in culture exists (r = -0.96, p = 0.04).

CONCLUSIONS

We conclude that: 1) Doxorubicin microcapsules retain activity in vitro and appear to overcome p-glycoprotein mediated Dox resistance. 2) The observed activity of Dox microcapsules correlates with the rate of particle uptake. Further studies in animal tumour models are in progress.

Diffusion coefficients in the lateral intercellular spaces of Madin-Darby canine kidney cell epithelium determined with caged compounds

The diffusion coefficients of two caged fluorescent dyes were measured in free solution and in the lateral intercellular spaces (LIS) of cultured Madin-Darby canine kidney (MDCK) cells after photoactivation by illumination with a continuous or pulsed UV laser. Both quantitative video imaging and a new photometric method were utilized to determine the rates of diffusion of the caged fluorescent dyes: 8-((4,5-dimethoxy-2-nitrobenzyl)oxy)pyrene-1,3,6-trisulfonic acid (DMNB-HPTS) and (4,5-dimethoxy-2-nitrobenzyl) fluorescein dextran (10,000 MW) (DMNB-caged fluorescein dextran). The diffusion coefficients at 37 degrees C in free solution were 3.3 x 10(-6) cm2/s (HPTS) and 0.98 x 10(-6) cm2/s (10,000 MW dextran). Diffusion of HPTS within nominally linear stretches of the LIS of MDCK cells grown on glass coverslips was indistinguishable from that in free solution, whereas dextran showed a 1.6 +/- 0.5-fold reduction in diffusivity. Measurements of HPTS diffusion within the LIS of multicellular regions also exhibited a diffusivity comparable to the free solution value. The restriction to diffusion of the dextran within the LIS may be due to molecular hindrance.

Basic fibroblast growth factor-mediated lymphangiogenesis of lymphatic endothelial cells isolated from dog thoracic ducts: effects of heparin

We have attempted to evaluate whether, similar to the angiogenesis of blood vessels, cultures of lymphatic endothelial cells (LEC) isolated from dog thoracic ducts have an ability to induce lymphangiogenesis in response to basic fibroblast growth factor (bFGF), then to examine the effects of heparin on the bFGF-mediated morphogenesis. The effects of bFGF and/or heparin on the proliferation and migration of the LEC were evaluated by changing the number of the subconfluent cells and by wound migration assay, respectively. The effects of the agents on invasion and tube formation of the LEC into a three-dimensional collagen gel and on collagen gel induced tube formation of the LEC were also investigated by a phase-contrast microscope and an electron microscope. The bFGF (10 ng/ml) caused a significant induction of proliferation and migration of the LEC, the induction of which was augmented dose-dependently by an additional treatment with heparin ranging from 1 to 100 microg/ml. The bFGF produced invasion and tube formation of the LEC into a three-dimensional collagen gel. The bFGF also facilitated to form capillary-like tubes of the LEC between two layers of collagen gels. Heparin (10 microg/ml) accelerated both processes of bFGF-mediated lymphangiogenesis of the LEC. These findings suggest that the cultured LEC isolated from dog thoracic ducts have an ability to form lymphatic capillary-like tubes in response to bFGF and that heparin accelerates dose-dependently the process of the bFGF-mediated neovascularization of lymph vessels.

Selective accumulation and tumoricidal effect of cisplatin suspended in viscous ethyl oleate on hepatic cancers in animals after intraarterial infusion

The selective accumulation and tumoricidal effects of cisplatin after intra-arterial infusion suspended in viscous ethyl oleate (VEO) on hepatic cancers of AH 272 tumor-bearing rats and VX-2 tumor-bearing rabbits were compared with those of cisplatin suspensions in ethyl oleate (EO) and Lipiodol Ultra Fluide (LP). The viscosities of VEO, EO and LP were 120, 4, and 21 centipoise (cp) respectively. Complete in vitro release of cisplatin from EO and LP occurred within 24 h, whereas only about 25% of cisplatin was released from VEO over the same period. When EO or VEO containing 3H-oleic acid were infused into the hepatic artery of rat liver inoculated with AH 272 tumor cells, radioactivity in the tumor site was higher than that in normal liver. In the case of cisplatin, concentration ratios after the infusion of EO and VEO were almost the same as those of oily carriers. Similar results were obtained in rabbit liver inoculated with VX-2 tumor cells. Cisplatin concentration in the tumor site seven days after intra-arterial infusion of VEO suspension was 5- and 1.7-fold higher, respectively, than that after EO and LP suspensions. The tumoricidal effect of cisplatin in VEO suspension on AH 272 tumor-bearing rats was higher than that after cisplatin solution and EO and LP suspensions, while VX-2 tumor growth was inhibited by the infusion of all cisplatin-containing oily carriers. VEO suspension thus appears very promising in intra-arterial infusion therapy.

Vascular and interstitial barriers to delivery of therapeutic agents in tumors

The efficacy in cancer treatment of novel therapeutic agents such as monoclonal antibodies, cytokines and effector cells has been limited by their inability to reach their target in vivo in adequate quantities. Molecular and cellular biology of neoplastic cells alone has failed to explain the nonuniform uptake of these agents. This is not surprising since a solid tumor in vivo is not just a collection of cancer cells. In fact, it consists of two extracellular compartments: vascular and interstitial. Since no blood-borne molecule or cell can reach cancer cells without passing through these compartments, the vascular and interstitial physiology of tumors has received considerable attention in recent years. Three physiological factors responsible for the poor localization of macromolecules in tumors have been identified: (i) heterogeneous blood supply, (ii) elevated interstitial pressure, and (iii) large transport distances in the interstitium. The first factor limits the delivery of blood-borne agents to well-perfused regions of a tumor; the second factor reduces extravasation of fluid and macromolecules in the high interstitial pressure regions and also leads to an experimentally verifiable, radially outward convection in the tumor periphery which opposes the inward diffusion; and the third factor increases the time required for slowly moving macromolecules to reach distal regions of a tumor. Binding of the molecule to an antigen further lowers the effective diffusion rate by reducing the amount of mobile molecule. Although the effector cells are capable of active migration, peculiarities of the tumor vasculature and interstitium may be also responsible for poor delivery of lymphokine activated killer cells and tumor infiltrating lymphocytes in solid tumors. Due to micro- and macroscopic heterogeneities in tumors, the relative magnitude of each of these physiological barriers would vary from one location to another and from one day to the next in the same tumor, and from one tumor to another. If the genetically engineered macromolecules and effector cells, as well as low molecular weight cytotoxic agents, are to fulfill their clinical promise, strategies must be developed to overcome or exploit these barriers. Some of these strategies are discussed, and situations wherein these barriers may not be a problem are outlined. Finally, some therapies where the tumor vasculature or the interstitium may be a target are pointed out.

Physiology of monoclonal antibody accretion by tumors

During the past 8 years numerous patients have been injected with radiolabeled monoclonal antibodies for both the diagnosis and treatment of cancer. In general the results, while somewhat promising, have failed to fulfill initial expectations. It is now clear that there are many physiologic barriers that antibodies face in their trek toward their tumor-binding site. Use of terms such as antibody-guided delivery or antibody-guided targeting do not take into account the fact that the antibodies are subject to the same physiologic rules as drugs and hormones. Antibodies are no more 'guided' than any drug or hormone. They reach their binding site via the same delivery mechanisms and accumulate in proportion to their 'receptor's' (antigen's) density. Our knowledge and understanding of the physiologic barriers to the uptake of tumor-associated monoclonal antibodies is limited. To date very few studies have been reported that shed light on this problem. For radiolabeled monoclonal antibodies to fulfill their promise, a greater understanding of these physiologic barriers is needed in order to devise ways in which they may be overcome.

Vascular markers for murine tumours

Damage to the vasculature may represent an important component of several forms of cancer therapy. Methods for studying the structure and function of the vasculature of experimental mouse tumours are required. In this paper several relatively simple methods are described for the histological examination of the vascular structure of murine tumours. The methods have been applied to cryostat sections of two sarcomas and two carcinomas. Immunoperoxidase staining with polyclonal antibodies to laminin highlights the vascular basement membrane of sarcomas, but has limited use with carcinomas, while the monoclonal antibody MECA-20 is a good marker for the endothelial cells of all vessels in all four tumours tested. The presence of endothelial cells in normal tissues can also be demonstrated by the use of enzyme-histochemical techniques for alkaline phosphatase, 5'-nucleotidase and nucleotide diphosphatase (ADPase), but only one of these methods (ADPase) works consistently in tumours. The relative merits of these methods are discussed and in all cases related to the staining pattern obtained with normal mouse tissues. The significance of these methods for vascular targeting is also discussed.

Response of tumours to hyperglycaemia: characterization, significance and role in hyperthermia

The response of both neoplastic and surrounding normal tissue to hyperthermia is influenced by a number of physical, physiological, biological and immunological factors. Two physiological factors that play an important role are blood flow and pH. Temperature distributions within neoplastic and surrounding normal tissue during hyperthermia are influenced by convective heat transfer between the blood and tissue bed. A number of in vitro studies have illustrated that lowering media pH sensitizes cells to hyperthermia. It has been suggested that pharmacological agents could be used in conjunction with hyperthermia treatment to improve cancer treatment if these agents decrease tumour blood flow and/or decrease tumour pH. One agent that has been studied extensively for this purpose is glucose. The objective of this paper is to review the results on the effect of hyperglycaemia on normal and tumour tissue blood flow and pH and its role in hyperthermia. After a brief discussion of the role of tumour pH and blood flow in hyperthermia treatment, data available in the literature on the effect of hyperglycaemia on normal and tumour tissue blood flow and pH are reviewed. Finally, the role of hyperglycaemia in hyperthermia treatment is discussed, and various studies involving the combined treatment are summarized. Key unanswered questions and directions for future research are pointed out.

Transport of molecules across tumor vasculature

The vascular-extravascular exchange of fluid and solute molecules in a tissue is determined by three transport parameters (vascular permeability, P, hydraulic conductivity, Lp, and reflection coefficient, sigma); the surface area for exchange, A; and the transluminal concentration and pressure gradients. The transport parameters and the exchange area for a given molecule are governed by the structure of the vessel wall. In general, tumor vessels have wide interendothelial junctions; large number of fenestrae and transendothelial channels formed by vesicles; and discontinuous or absent basement membrane. While these factors favor movement of molecules across tumor vessels, high interstitial pressure and low microvascular pressure may retard extravasation of molecules and cells, especially in large tumors. These characteristics of the transvascular transport have significant implications in tumor growth, metastasis, detection and treatment.

Vascular permeability and interstitial diffusion of macromolecules in the hamster cheek pouch: effects of vasoactive drugs

A simple one-dimensional mathematical model which relates the number of "leaky" sites in postcapillary venules to the extravasation of macromolecules in terms of an effective microvascular permeability, P, and an effective interstitial diffusion coefficient, D, is developed. The model is used to analyze the data of E. Svensjö and K. Roempke [in "Progress in Microvascular Research II" (F. C. Courtice, D. C. Garlick, and M. A. Perry, Eds.), pp. 449-463, 1984] and C. G. A. Persson and E. Svensjö [in "Handbook of Inflammation" (J. L. Bonta, M. A. Bray, and M. J. Parnham, Eds.), pp. 61-82, 1985] for the transport of 70,000 molecular weight dextran in a hamster cheek pouch prior to and following topical application of two vasoactive agents: histamine and bradykinin. D ranged from 2.2 to 4.0 X 10(-9) cm2/sec, and P was found to be 4.1 X 10(-8) cm/sec. The increased number of leaky sites resulted in a sixfold increase in P due to histamine, at a dose of 2.5 X 10(-6) M, and a fourfold increase in P due to bradykinin, at a dose of 4.0 X 10(-7) M.

Tumour microcirculation as a target for hyperthermia

A great number of investigators have, independently, shown that tumour blood flow is affected by a hyperthermic treatment to a larger extent than normal tissue blood flow. While the majority of the studies on experimental tumours show a decrease and even a lapse in blood flow within the microcirculation during or after hyperthermia, the data on human tumours are less conclusive. Some of the investigators do not find a decrease in circulation, while others do. Obviously, this is an important field of investigation in the clinical application of hyperthermia because a shut down of the circulation would not only facilitate tumour heating (by reducing venous outflow, this reducing the 'heat clearance' from the tumour), but would also facilitate tumour cell destruction. The same holds for alterations that occur subsequently to the circulatory changes, like a heat-induced decrease of tissue pO2 and pH. If the frequently reported circulatory collapse of the tumour circulation could selectively be stimulated by, e.g. acidification or by vasoactive agents, hyperthermic treatment of patients would possibly be greatly facilitated and intensified. In hyperthermic tumour therapy a number of complex processes and interactions takes place, especially when the treatment is performed in combination with radiation therapy. One of them represents the group of processes related to the random probability of cell sterilization of individual tumour cells resulting in exponential survival curves which are typically evaluated with e.g. cell survival assays. This aspect has not been the issue of this paper. The other group of processes deals with the heat-induced changes in the micro-physiology of tumours and normal tissues which, as discussed before, may not only enhance the exponential cell kill, but which may also culminate in vascular collapse with the ensuing necrosis of the tumour tissue in the areas affected. If this takes place, a process of bulk killing of tumour cells results, rather than the random type of cell sterilization. At present it is not clear to what extent the various separate mechanisms contribute to the total effect of tumour control. With all these considerations in mind, one should be aware of the fact that effects, secondary to heat-induced vascular stasis alone will never be efficient enough to eliminate all tumour cells, even though a heat reservoir is created. This is so because some malignant cells will inevitably have already infiltrated normal, surrounding structures and will therefore not be affected by changes in the tumour vascular bed.(ABSTRACT TRUNCATED AT 400 WORDS)