Chemistry Reference
In-Depth Information
FIGURE 14.22
Oxygen pressure maps of the region containing two laser coagulation spots
(left) and a region centered on one of the spots (right). Reproduced with permission from the
Optical Society of America. (See the color version of this figure in Color Plates section.)
The regions of the injury can be easily seen as circular areas. The absence of
significant leakage of the probe from the vessels was confirmed by measurements
made over a 1 h period following the injection, during which the size and the oxygen
profile of the region of hypoxia remained constant. As expected, the oxygen pressure
in the injury core is extremely low.
These results demonstrate that dendritic phosphors, such as Oxyphor G2, are very
useful for obtaining maps of oxygen distribution in the eye, opening up possibilities
for studies of experimental rodent models of eye diseases.
14.10.3 Imaging Tumor Hypoxia
There is a large amount of evidence that hypoxia plays a central role in proliferation of
cancer. Uncontrollable growth of blood vessels in tumors is associated with poor
tissue oxygenation, the degree of which reflects physiological status of tumors,
correlates with their metastatic potential and affects outcomes of various therapies.
Hypoxia is widely spread in both primary tumors and in their metastases [122].
During tumor growth, an increasingly compromised blood supply generally results in
a tumor oxygen tension of 0-20 mmHg, compared to 30-70 mmHg in normal
tissues [123]. In addition to chronic diffusion-limited hypoxia, tumors also frequently
exhibit transient hypoxia—a transient state caused by fluctuations in individual vessel
perfusion.
Phosphorescence quenching has been used to image hypoxia in tumors using
dendritic probes Oxyphor R2 [124] and G2 [125]. Dorsal window tumor model in
small rodents is especially well suited for optical imaging [126], since the tumor
grows between two thin glass slides in a chamber clipped to the back of a live animal,
allowing for effective optical sectioning.
In recent experiments in collaboration with the Dewhirst laboratory (Duke), the
dorsal window model was used to image hypoxia in mice using a gen 2 Pd
tetrabenzoporphyrin-AG dendrimer (Figure 14.23), modified with PEG residues. The
probe was injected iv, and the imaging was performed in wide-field epiluminescent
