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Inhibition of tumor growth by solid stress
Vol. 32, Nos. 2-3 F216.
MELANOMA
REQUIRED
Free Communications
CELL-PLATEI.ET
345
INTERACTION
IS
FOR MF.IANOMA CF.IJ. ARREST UNDER FLOW
B. F E L D I N G - H A B E R M A N N , R. H A B E R M A N N , E. SALDIVAR, AND Z. M. RUGGERI The Scripps Research Institute, Department of Molecular and Experimental Medicine, La Jolla, CA 92037, USA Arrest of tumor cells in the vasculature is a prerequisite for extravasation and represents a rate-limiting step during tumor metastasis. We have analyzed h u m a n melanoma cells suspended in h u m a n blood and evaluated their capacity to attach to a surface-immobilized matrix using a flow chamber system combined with confocal laser microscopy. Adherent melanoma cells were detected and quantified based on differential staining. We f o u n d that melanoma cells interact with platelets under flow conditions and that this interaction is required for melanoma cell arrest on to the surface. At a wall shear rate of 50 sec-1, M21 melanoma cells failed to adhere to a collagen type I matrix unless they associated with attached platelet thromhi. Inhibition of platelet activation or functional blockage of platelet integral ¢xIIb~3 (GP IIb-IIIa) inhibited M21 cell arrest. Moreover, we found that [33 integrins expressed by the melanoma cells are required for interaction of the latter with platelets. Wild type M21 cells express ¢xv[$3. The variant M21-L, lacking integrin ¢xv~3 expression, failed to interact with platelets and could not adhere to the collagen surface under flow. However, M21-L4 cells transfected to reconstitute ¢xv[33 expression, or M21-LIIb cells transfected to express ¢xIIbl$3, both interacted with platelet thrombi and attached to the matrix. These results support the existence of a mechanism for melanoma cell arrest u n d e r flow based on [33 integrin-mediated interaction with platelets. This may be relevant in the hematogenous metastasis of melanoma. F217.
INI4rRITION OF TUMOR
GROWTH
BY S O L I D S T R E S S
G. HELMLINGER, P. A. NET-I'I, H. C. LICHTENBELD, R.J. MELDER, AND R. K. JAIN Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA The aim of this study was to experimentally evaluate the effect of mechanical solid stress on tumor growth. To this end, we quantified the in vitro growth kinetics of two tumor cell lines (LS 174T and MCaIV) grown as multicellular spheroids in agarose gels at different gel concentrations (0.3-1.0%). The mechanical properties of the gels were characterized using a cone-and-plate rheometer. For LS174T, spheroid growth rates and final sizes were similar among the 0.3, 0.5, 0.7, 0.8, and 0.9% gel concentrations, and were significandy lower when compared to free suspension controls. The most dramatic result was a marked inhibition of growth and a reduced final size of spheroids at a 1.0% gel concentration. This was in spite of the observation that colony growth efficiencies were remarkably similar (88 to 95%) for all culture conditions tested (free suspension and 0.3-1.0% gels). Thus, average spheroid sizes did not decrease in a progressive fashion with increasing gel concentrations; rather, there was a "switch" to growth inhibition between the 0.9 and 1.0% gels.
346
Vol. 32, Nos. 2-3
Free Communications
Growth of MCaW spheroids was qualitatively similar to the growth of LS 174T; i.e., growth rates and final sizes were not significantly different among the 0.3, 0.5 and 0.7% gels, and growth inhibition was observed at 1.0% gel concentration. Mechanical testing of the gels revealed gel failure at =0.20 strains for all concentrations investigated (0.3-1.0%). Our growth data imply that spheroids impose local strains on the gel which can be an order of magnitude greater than 1; accordingly, breaks in the agarose gels should be induced by tumor spheroid growth. However, growth-induced breaks cannot explain the observed growth kinetics curves. A more realistic model would involve the reversible, slow making and breaking of physical crosslinks within the gel network during cellular growth. At a threshold gel concentration, cells may then be faced with a critical energy barrier which they cannot overcome. These results provide novel insights into the relationship between tumor growth and stress exerted by the surrounding tissue
F218.
A
PRESSURE
POROELASTIC
MODEL
FOR
INTERSTITIAL
IN TUMORS
P. A. NETTI, L. T. BAXTER, Y. C O U C H E R , R. K. JAIN
R. K. SKALAK, AND
Department of Radiation Oncology, MGH/Harvard Medical School, Boston MA, 02114, Bioengineering Institute, University of California, San Diego, CA 92093 Jain and Baxter (1988) previously developed a macroscopic fluid transport model to describe the spatial distribution of interstitial fluid pressure (IFP) in solid tumors, thought to be a possible cause of non-uniform distribution of monoclonal antibodies within the tumor mass. The model has been successfully used to explain the steady-state pressure profile in isolated and subcutaneous tumors, but does not apply to transient data on (a) the effect of modulation of systemic blood pressure, and (b) the effect of intratumor fluid infusion on the IFP. In the present study, we have extended this theoretical framework to a poroelastic model capable of describing transient behavior. The tumor tissue is represented by a biphasic continuum model consisting of a gel-like solid phase (collagen and proteoglycans) and a fluid phase (interstitial fluid). The fluid pressure and velocity and the solid stress and deformation profiles are predicted both in steady state and transient conditions. The model predictions are in agreement with the following experimental data: (i) the decrease of interstitial pressure in a tumor subsequent to the sacrifice of the animal occurs through an initial fast decay followed by a slower approach to the equilibrium value, (ii) the increase of IFP after an abrupt increase of blood pressure quickly reaches the final value via a process with a single time constant, and (iii) the decay of IFP registered in isolated tumor by a quick interruption of the artery and vein blood flow occurs via a process with a single very slow time constant . The implication of the predicted fluid dynamics on blood flow in solid tumors will be also discussed. (Supported by CA-56591)
MELANOMA
REQUIRED
Free Communications
CELL-PLATEI.ET
345
INTERACTION
IS
FOR MF.IANOMA CF.IJ. ARREST UNDER FLOW
B. F E L D I N G - H A B E R M A N N , R. H A B E R M A N N , E. SALDIVAR, AND Z. M. RUGGERI The Scripps Research Institute, Department of Molecular and Experimental Medicine, La Jolla, CA 92037, USA Arrest of tumor cells in the vasculature is a prerequisite for extravasation and represents a rate-limiting step during tumor metastasis. We have analyzed h u m a n melanoma cells suspended in h u m a n blood and evaluated their capacity to attach to a surface-immobilized matrix using a flow chamber system combined with confocal laser microscopy. Adherent melanoma cells were detected and quantified based on differential staining. We f o u n d that melanoma cells interact with platelets under flow conditions and that this interaction is required for melanoma cell arrest on to the surface. At a wall shear rate of 50 sec-1, M21 melanoma cells failed to adhere to a collagen type I matrix unless they associated with attached platelet thromhi. Inhibition of platelet activation or functional blockage of platelet integral ¢xIIb~3 (GP IIb-IIIa) inhibited M21 cell arrest. Moreover, we found that [33 integrins expressed by the melanoma cells are required for interaction of the latter with platelets. Wild type M21 cells express ¢xv[$3. The variant M21-L, lacking integrin ¢xv~3 expression, failed to interact with platelets and could not adhere to the collagen surface under flow. However, M21-L4 cells transfected to reconstitute ¢xv[33 expression, or M21-LIIb cells transfected to express ¢xIIbl$3, both interacted with platelet thrombi and attached to the matrix. These results support the existence of a mechanism for melanoma cell arrest u n d e r flow based on [33 integrin-mediated interaction with platelets. This may be relevant in the hematogenous metastasis of melanoma. F217.
INI4rRITION OF TUMOR
GROWTH
BY S O L I D S T R E S S
G. HELMLINGER, P. A. NET-I'I, H. C. LICHTENBELD, R.J. MELDER, AND R. K. JAIN Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA The aim of this study was to experimentally evaluate the effect of mechanical solid stress on tumor growth. To this end, we quantified the in vitro growth kinetics of two tumor cell lines (LS 174T and MCaIV) grown as multicellular spheroids in agarose gels at different gel concentrations (0.3-1.0%). The mechanical properties of the gels were characterized using a cone-and-plate rheometer. For LS174T, spheroid growth rates and final sizes were similar among the 0.3, 0.5, 0.7, 0.8, and 0.9% gel concentrations, and were significandy lower when compared to free suspension controls. The most dramatic result was a marked inhibition of growth and a reduced final size of spheroids at a 1.0% gel concentration. This was in spite of the observation that colony growth efficiencies were remarkably similar (88 to 95%) for all culture conditions tested (free suspension and 0.3-1.0% gels). Thus, average spheroid sizes did not decrease in a progressive fashion with increasing gel concentrations; rather, there was a "switch" to growth inhibition between the 0.9 and 1.0% gels.
346
Vol. 32, Nos. 2-3
Free Communications
Growth of MCaW spheroids was qualitatively similar to the growth of LS 174T; i.e., growth rates and final sizes were not significantly different among the 0.3, 0.5 and 0.7% gels, and growth inhibition was observed at 1.0% gel concentration. Mechanical testing of the gels revealed gel failure at =0.20 strains for all concentrations investigated (0.3-1.0%). Our growth data imply that spheroids impose local strains on the gel which can be an order of magnitude greater than 1; accordingly, breaks in the agarose gels should be induced by tumor spheroid growth. However, growth-induced breaks cannot explain the observed growth kinetics curves. A more realistic model would involve the reversible, slow making and breaking of physical crosslinks within the gel network during cellular growth. At a threshold gel concentration, cells may then be faced with a critical energy barrier which they cannot overcome. These results provide novel insights into the relationship between tumor growth and stress exerted by the surrounding tissue
F218.
A
PRESSURE
POROELASTIC
MODEL
FOR
INTERSTITIAL
IN TUMORS
P. A. NETTI, L. T. BAXTER, Y. C O U C H E R , R. K. JAIN
R. K. SKALAK, AND
Department of Radiation Oncology, MGH/Harvard Medical School, Boston MA, 02114, Bioengineering Institute, University of California, San Diego, CA 92093 Jain and Baxter (1988) previously developed a macroscopic fluid transport model to describe the spatial distribution of interstitial fluid pressure (IFP) in solid tumors, thought to be a possible cause of non-uniform distribution of monoclonal antibodies within the tumor mass. The model has been successfully used to explain the steady-state pressure profile in isolated and subcutaneous tumors, but does not apply to transient data on (a) the effect of modulation of systemic blood pressure, and (b) the effect of intratumor fluid infusion on the IFP. In the present study, we have extended this theoretical framework to a poroelastic model capable of describing transient behavior. The tumor tissue is represented by a biphasic continuum model consisting of a gel-like solid phase (collagen and proteoglycans) and a fluid phase (interstitial fluid). The fluid pressure and velocity and the solid stress and deformation profiles are predicted both in steady state and transient conditions. The model predictions are in agreement with the following experimental data: (i) the decrease of interstitial pressure in a tumor subsequent to the sacrifice of the animal occurs through an initial fast decay followed by a slower approach to the equilibrium value, (ii) the increase of IFP after an abrupt increase of blood pressure quickly reaches the final value via a process with a single time constant, and (iii) the decay of IFP registered in isolated tumor by a quick interruption of the artery and vein blood flow occurs via a process with a single very slow time constant . The implication of the predicted fluid dynamics on blood flow in solid tumors will be also discussed. (Supported by CA-56591)