Dynamic monitoring of localized tumor oxygenation changes using RF pulsed electron paramagnetic resonance in conscious mice.
Oxygenation status is a key determinant in both tumor growth and responses to therapeutic interventions. The oxygen partial pressure (pO2) was assessed using a novel pulsed electron paramagnetic resonance (EPR) spectroscopy at 750 MHz. Crystals of lithium phthalocyanine (LiPc) implanted into either squamous cell carcinoma (SCC) tumor or femoral muscle on opposing legs of mice were tested by pulsed EPR. The results showed pO2 of SCC tumor was 2.7 +/- 0.4 mmHg, while in the femoral muscle it was 6.1 +/- 0.9 mmHg. A major advantage of pulsed EPR oximetry over conventional continuous-wave (CW) EPR oximetry is the lack of influence from subject motion, while avoiding artifacts associated with modulation or power saturation. Resonators in pulsed EPR are overcoupled to minimize recovery time. This makes changes in coupling associated with object motion minimal without influencing spectral quality. Consequently, pulsed EPR oximetry enables approximately a temporal resolution of approximately one second in pO2 monitoring in conscious subjects, avoiding significant influence of anesthetics on the physiology being studied. The pO2 in SCC tumor and muscle was found to be higher without anesthesia (3.9 +/- 0.5 mmHg for tumor, 8.8 +/- 1.2 mmHg for muscle). These results support the advantage of pulsed EPR in examining pO2 in conscious animals with LiPc chronically implanted in predetermined regions.
Matsumoto
Shingo
S
Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-1002, USA.
Espey
Michael Graham
MG
Utsumi
Hideo
H
Devasahayam
Nallathamby
N
Matsumoto
Ken-Ichiro
K
Matsumoto
Atsuko
A
Hirata
Hiroshi
H
Wink
David A
DA
Kuppusamy
Periannan
P
Subramanian
Sankaran
S
Mitchell
James B
JB
Krishna
Murali C
MC
D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005260:Female; D006614:Hindlimb; D007211:Indoles; D051379:Mice; D008809:Mice, Inbred C3H; D018482:Muscle, Skeletal / Q000378:metabolism*; D009942:Organometallic Compounds; D010092:Oximetry; D010100:Oxygen / Q000378:metabolism*; D010313:Partial Pressure; D011846:Radio Waves
D007211:Indoles; D009942:Organometallic Compounds; C081756:lithium phthalocyanine; D010100:Oxygen