Download Investigation of animal tissue samples using X

Investigation of animal tissue samples using X-ray fluorescence
Tatjana Paunesku1, Andrew Gordon1, Kathleen Harris1, M. Beau Wanzer1, Andrew
Larson1, Olga Antipova2, Luxi Li2, Si Chen2, Stefan Vogt2, Gayle Woloschak1
1
2
Feinberg School of Medicine, Northwestern University, Chicago IL USA
Microscopy, Advanced Photon Source, Argonne National Lab, Argonne IL USA
Use of animal models is one of the key foundations of cancer research when new
therapies and imaging agents are developed. Thorough investigation of functional cancer
treatment endpoints needs to be complemented with investigation of adjacent normal
cells and tissues, and the use of multiple animal samples is critical to provide an insight
into typical vs. incidental outcomes. In those situations when the therapeutic (or imaging)
agent is made of elementally unique components X-ray fluorescence mapping is an
excellent way to provide information about the tissue/cell and sub-cellular placement of
these agents at different timepoints.
We are currently using a rabbit model of cancer called VX2 caused by cottontail rabbit
papilloma virus. VX2 cells grown in hind limb of “donor” rabbit are transplanted into
liver of recipient animal; once the tumor is detectable by magnetic resonance imaging
(MRI) these animals are used for testing of MR and therapeutic agents. In a recent series
of experiments treatment with TheraSphere® agent was done, and tumor reduction and
similar treatment responses were investigated. In most cases animals were sacrificed 2-4
weeks after treatment and their tissues collected for subsequent analysis. Criosectioned
liver tissue sections including tumor and adjacent healthy tissue were prepared as 5
micron thick, containing, nevertheless, TheraSpheres (that measure 25-30 micron in
diameter) that could not be sectioned due to their rigidity. TheraSpheres are glass beads
embedded with elements that become radioactive upon “activation” in a cyclotron; their
radioactivity
Tissue samples were mounted on Ultralene™ membrane and imaged using a rapid
scanning approach, so called “fly scans” at the X-ray microprobe located at the beamline
2-ID-E at APS, ANL. X-ray energy of 17 keV was used in order to enable imaging of
yttrium, products of radioactive decay of yttrium; in addition, due to large volume of
glass in TheraSpheres they can also be identified by presence of silica. Imaging of several
liver samples identified presence and distribution of TheraSPheres in liver tissue; decay
of radioactive yttrium was also noted, accomplishing the primary goals of the X-ray
fluorescence imaging study. More excitingly, however, we noted semi-“digested”
TheraSpheres in small sub-regions of the tissue (possibly even single cells), overlapping
in all cases with localy increased zinc signal. This finding can be used as a basis for
further evaluation of TheraSphere treated tissues – cytological evaluation of matching
tissue sections with different markers can be done prior to repeated evaluation of these
tissues by X-ray fluorescence. No technique other than X-ray fluorescence can be
expected to detect silica, yttrium and its decay products, however, therefore – all other
complementary studies will have to be done first with X-ray fluorescence microscopy
following as the last step of work.