Slowed diffusion in tumors revealed by microfiberoptic epifluorescence photobleaching.
It has not been possible to measure diffusion deep in solid tissues such as tumors because of the limited light penetration of conventional optical techniques. Here we report a microfiberoptic epifluorescence photobleaching (MFEP) method in which photobleaching is done by laser epi-illumination through a multimode fiberoptic whose micron-sized tip can be introduced deep into tissues. We applied MFEP to measure the diffusion of fluorescent macromolecules in tumors in living mice, at depths well beyond those accessible by surface optical measurements. Macromolecule diffusion was slowed about twofold within 200 microm of the surface of a solid tumor, but was slowed greater than tenfold beyond 500 microm. Our results reveal a remarkable and previously unrecognized slowing of diffusion deep in tumors, which correlated with the differing tissue architectures of tumor periphery versus core, and with altered tumor vasculature produced by aquaporin-1 deletion. MFEP should have wide applications for measuring diffusion in organs, solid tumors and other light-inaccessible tissue masses.
Department of Medicine, Cardiovascular Research Institute, University of California, San Francisco, California 94143, USA.
Jay R
JR
Thiagarajah
Jung Kyung
JK
Kim
Mazin
M
Magzoub
A S
AS
Verkman
D000818:Animals; D051398:Aquaporin 1 / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003094:Collagen / Q000737:chemistry; D004058:Diffusion; D005336:Fiber Optic Technology / Q000295:instrumentation / Q000379:methods*; D005456:Fluorescent Dyes / Q000737:chemistry*; D005780:Gelatin / Q000737:chemistry; D017353:Gene Deletion; D051379:Mice; D008856:Microscopy, Fluorescence; D009369:Neoplasms / Q000098:blood supply / Q000473:pathology*; D038761:Photobleaching; D013997:Time Factors
D005456:Fluorescent Dyes; D051398:Aquaporin 1; D005780:Gelatin; D003094:Collagen