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Perfusion of single tumor microvessels: application to vascular permeability measurement
H C Lichtenbeld1, F Yuan, C C Michel
1Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
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.
Insights
Convection plays a minor role in macromolecular transport across tumor blood vessels, especially in regions with low pressure differences. This study developed a new method to measure this transport in LS174T tumors.
Area of Science:
- Oncology
- Biomedical Engineering
- Physiology
Background:
- Tumor microvessel permeability is crucial for drug delivery and understanding tumor biology.
- Differentiating convective and diffusive transport mechanisms is essential for targeted therapies.
- Current methods for assessing macromolecular transport in tumors are limited.
Purpose of the Study:
- To establish a novel method for quantifying the relative contributions of convection and diffusion in macromolecular transport across tumor microvessel walls.
- To investigate the pressure-dependent vascular permeability in LS174T human colon adenocarcinoma xenografts.
- To assess the significance of convective transport in solid tumor vasculature.
Main Methods:
- Developed a technique using a dorsal skinfold chamber model in SCID mice with LS174T tumors.
- Isolated and cannulated individual tumor microvessels (20-40 microns diameter).
- Perfusion of fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA) at varying pressures (20-45 cmH2O) and real-time fluorescence intensity recording for permeability analysis.
Main Results:
- Quantified apparent vascular permeability to FITC-BSA in single tumor vessels.
- Observed heterogeneous pressure-dependent permeability within LS174T tumors.
- Found no significant correlation between permeability and perfusion pressure at 20-35 cmH2O (p=0.73), but a significant increase from 20 to 45 cmH2O (p=0.008).
Conclusions:
- Convective transport of albumin is not a major factor in non-peripheral solid tumor regions with minimal pressure gradients.
- The developed preparation allows for studying cell-cell interactions within tumor vessels under controlled flow conditions.
- This method provides insights into the biophysical mechanisms governing macromolecular exchange in tumors.