The two major theories of cancer metastasis, the seed and soil hypothesis and the mechanical trapping theory, view tumor cell adhesion to blood vessel endothelia and cancer cell aggregation as corresponding key components of the metastatic process. Here, we demonstrate in vitro, ex vivo, and in vivo that metastatic breast and prostate carcinoma cells form multicellular homotypic aggregates at the sites of their primary attachment to the endothelium. Our results suggest that metastatic cell heterotypic adhesion to the microvascular endothelium and homotypic aggregation represent two coordinated subsequent steps of the metastatic cascade mediated largely by similar molecular mechanisms, specifically by interactions of tumor-associated Thomsen-Friedenreich glycoantigen with the ␤-galactoside-binding protein, galectin-3. In addition to inhibiting neoplastic cell adhesion to the endothelium and homotypic aggregation, disrupting this line of intercellular communication using synthetic ThomsenFriedenreich antigen masking and Thomsen-Friedenreich antigen mimicking compounds greatly affects cancer cell clonogenic survival and growth as well. Thus, ␤-galactoside-mediated intravascular heterotypic and homotypic tumor cell adhesive interactions at the sites of a primary attachment to the microvascular endothelium could play an important role during early stages of hematogenous cancer metastasis.

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We have extended the use of a microscope densitometric technique [Am. J. Physiol. 245 (Heart Circ. Physiol. 14): H495-H505, 1983] to measure the solute permeability coefficients (Pa) of fluorescently labeled solutes in single perfused capillaries of frog mesentery. The method enables the transcapillary flux of solutes larger than 10,000 mol wt to be measured under conditions where the forces that determine both solute and water flows across the capillary wall are known. The Pa for alpha-lactalbumin (mol wt 14,176, Stokes radius 2.02 nm) increased from a mean value of 2.1 X 10(-6) cm/s when capillary pressure was 3.0 cmH2O (no net filtration) to greater than 4.0 X 10(-6) cm/s when capillary pressure was 15 cmH2O. Taking a value of 0.35 for the solvent drag reflection coefficient for alpha-lactalbumin, we conclude that the increased solute flux represents solvent drag through a water pathway with a hydraulic conductivity of 3.6 X 10(-7) cm X s-1 X cmH2O-1. Our data conforms to the hypothesis that alpha-lactalbumin is transported across the capillary wall by restricted diffusion and solvent drag in a pathway that carries 90% of the transcapillary water flow (the principle water pathway). In vitro and in vivo calibration experiments have been carried out to test the assumption that the measured fluorescent light intensity is proportional to the number of fluorescent molecules in the measuring window of the photometer.

In this report, we challenge a common perception that tumor embolism is a size-limited event of mechanical arrest, occurring in the first capillary bed encountered by blood-borne metastatic cells. We tested the hypothesis that mechanical entrapment alone, in the absence of tumor cell adhesion to blood vessel walls, is not sufficient for metastatic cell arrest in target organ microvasculature. The in vivo metastatic deposit formation assay was used to assess the number and location of fluorescently labeled tumor cells lodged in selected organs and tissues following intravenous inoculation. We report that a significant fraction of breast and prostate cancer cells escapes arrest in a lung capillary bed and lodges successfully in other organs and tissues. Monoclonal antibodies and carbohydrate-based compounds (anti-Thomsen-Friedenreich antigen antibody, anti-galectin-3 antibody, modified citrus pectin, and lactulosyl-l-leucine), targeting specifically beta-galactoside-mediated tumor-endothelial cell adhesive interactions, inhibited by >90% the in vivo formation of breast and prostate carcinoma metastatic deposits in mouse lung and bones. Our results indicate that metastatic cell arrest in target organ microvessels is not a consequence of mechanical trapping, but is supported predominantly by intercellular adhesive interactions mediated by cancer-associated Thomsen-Friedenreich glycoantigen and beta-galactoside-binding lectin galectin-3. Efficient blocking of beta-galactoside-mediated adhesion precludes malignant cell lodging in target organs.

The ability to recognize and appreciate from a reproductive standpoint that males and females possess different attributes has been long standing. Only more recently have we begun to look more deeply into both the similarities and differences between men and women, as well as between boys and girls, with respect to the structure and function of other organ systems. This article focuses on the cardiovascular system, with examples of sex differences in the control of coronary function, blood pressure, and volume. Recognizing the differences between the sexes with respect to cardiovascular function facilitates understanding of the mechanisms whereby homeostasis can be achieved using different contributions or components of the living system. Furthermore, recognition of the differences as well as the similarities permits the design of appropriate diagnostic instruments, recognition of sex-specific pathophysiology, and implementation of appropriate treatment of cardiovascular disease in men and women.

Whereas the glycocalyx of endothelial cells has been shown to influence solute flux from capillary microvessels, little is known about its contribution to the movement of macromolecules across the walls of other microvessels. We evaluated the hypothesis that a glycocalyx contributes resistance to protein flux measured in coronary arterioles. Apparent solute permeability (P(s)) to two proteins of different size and similar charge, alpha-lactalbumin (alpha-lactalb) and porcine serum albumin (PSA), was determined in arterioles isolated from the hearts of 43 female Yucatan miniature swine. P(s) was assessed in arterioles with an "intact" glycocalyx under control conditions and again after suffusion with adenosine (Ado, 10(-5) M, n = 42 arterioles, N = 29 pigs). In a second set of experiments (n = 21 arterioles, N = 21 pigs) arteriolar P(s) was determined before and after perfusion with enzyme (pronase or heparinase), which was used to digest the glycocalyx. P(s) was assessed a third time on those microvessels after exposure to Ado. Consistent with the hypothesis, P(s) for PSA (P(PSA)(s)) and P(s) for alpha-lactalb (P(alpha-lactalb)(s)) increased from basal levels following enzyme treatment. Subsequent suffusion with Ado, a significant metabolite known to alter coronary vascular smooth muscle tone and permeability, resulted in a significant reduction of basal P(alpha-lactalb)(s) in both untreated and enzyme-treated arterioles. Furthermore, in untreated arterioles, P(PSA)(s) was unchanged by Ado suffusion, whereas Ado induced a pronounced reduction in P(PSA)(s) of enzyme-treated vessels. These data demonstrate that in intact coronary arterioles an enzyme-sensitive layer, most likely at the endothelial cell surface, contributes significantly to net barrier resistance to solute flux.

Thomsen-Friedenreich antigen (TF-Ag) is expressed in many carcinomas, including those of the breast, colon, bladder, and prostate. TF-Ag is important in adhesion and metastasis and as a potential immunotherapy target. We hypothesized that passive transfer of JAA-F11, an anti-TF-Ag monoclonal antibody, may create a survival advantage for patients with TF-Ag-expressing tumors by cytotoxicity, blocking of tumor cell adhesion, and inhibition of metastasis. This was tested using in vitro models of tumor cell growth; cytotoxicity assays; in vitro, ex vivo, and in vivo models of cancer metastasis; and, finally, in vivo effects in mice with metastatic breast cancer. Unlike some anti-TF-Ag antibodies, JAA-F11 did not enhance breast carcinoma cell growth. JAA-F11 did not induce the killing of 4T1 tumor cells through complement-dependent cytotoxicity or apoptotic mechanisms. However, JAA-F11 blocked the stages of metastasis that involve the adhesion of human breast carcinoma cells to human endothelial cells (human umbilical vein endothelial cells and human bone marrow endothelial cells 60) in in vitro static adhesion models, in a perfused ex vivo model, and in murine lung vasculature in an in vivo metastatic deposit formation assay. JAA-F11 significantly extended the median survival time of animals bearing metastatic 4T1 breast tumors and caused a > 50% inhibition of lung metastasis.

While it is well established that the lymphatic vasculature is central to fluid and solute homeostasis, how it accomplishes this task is not well defined. To clarify the basic mechanisms underlying basal fluid and solute homeostasis, we assessed permeability to rat serum albumin (P RSA s ) in mesenteric collecting lymphatic vessels and venules of juvenile male rats. Using the quantitative microfluorometric technique originally developed for blood capillaries, we tested the hypothesis that as a consequence of venules and collecting lymphatics sharing a common embryological origin, their P RSA s would not differ significantly. Supporting our hypothesis, the median collecting lymphatic P RSA s (3.5 ± 1.0 × 10 −7 cm s −1 , N = 22) did not differ significantly from the median venular P RSA s (4.0 ± 1.0 × 10 −7 cm s −1 , N = 8, P = 0.61). For collecting lymphatics the diffusive permeability (P d = 2.5 × 10 −7 cm s −1 ) was obtained from the relationship of apparent P RSA s and pressure. While the measured P RSA s , P d and estimated hydraulic conductivity of collecting lymphatics and venules were similar, the contribution of convective coupling differs as a result of the higher hydrostatic pressure experienced by venules relative to collecting lymphatics in vivo. In summary, the data demonstrate the capacity for collecting lymphatics to act as exchange vessels, able to extravasate solute and filter fluid. As a consequence these data provide experimental support for the theory that prenodal lymphatic vessels concentrate intraluminal protein. Abbreviations BSA, bovine serum albumin; C, transmural concentration difference; D, vessel diameter; J s , solute flux; J v , volume flux; L p , hydraulic conductivity; P, transmural pressure difference; P c , microvessel lumen pressure; P d , diffusive permeability; P i , interstitial pressure; P lumen , native vessel pressure; P s or P RSA s , apparent solute permeability (to RSA); Pé, Péclet number; RSA, rat serum albumin; S, surface area; π, transmural oncotic pressure difference; π c or π L , microvessel or lymphatic oncotic pressure; π i , interstitial oncotic pressure; σ, reflection coefficient.