title: Assessing pH and oxygenation in cryotherapy-induced cytotoxicity and tissue response to freezing.
abstract: The microenvironmental pH and oxygenation is known to influence tumor cell response to heat, radiation, photodynamic and even chemotherapy. We have studied the previously untested influence of acidity and hypoxia on tumor and endothelial cell sensitivity to freezing. In addition, we have measured changes in oxygenation in vivo in murine FSaII fibrosarcomas after freeze injury. A low pH or low oxygenation environment was found to increase the sensitivity of tumor and endothelial cells to freezing at -20 degrees C or -40 degrees C in vitro. However, low pH and low oxygenation combined did not further increase cryosensitivity of the cells. In vivo, tumor oxygenation after freeze injury was studied immediately or 1-3 days after a standard freezing protocol was applied to FSaII tumors ranging from 250-500 mm3 grown in the rear-limb of C3H mice. Tumor oxygenation at the edge of the iceball was found to transiently increase 1-2 hours after freezing. At 1-3 days after freezing, a treatment that delayed FSaII tumor growth by approximately 1.5-fold, the mean tumor oxygenation was significantly increased by up to 2.5-fold from a control level of 5 mmHg partial pressure of oxygen (pO2), especially at the periphery of the tumor. We conclude that manipulation of pH or oxygenation has potential to increase the anti-tumor effects of minimally invasive cryosurgical techniques. Furthermore, the dynamic changes in oxygenation after freeze injury in vivo suggests value in combining cryotherapy with treatments dependent on oxygenation levels. Ultimately, these may be routes to more reliable treatment response with fewer recurrences.
authors.affiliation: University of Minnesota, Department of Therapeutic Radiology, 420 Delaware St. SE, MMC 494, Minneapolis, MN 55455, USA. griff007@umn.edu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Griffin
authors.forename: Brent W
authors.initials: BW
authors.lastname: Williams
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Roberts
authors.forename: David J
authors.initials: DJ
authors.lastname: Swanlund
authors.forename: John C
authors.initials: JC
authors.lastname: Bischof
mesh_terms: D000818:Animals; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D002470:Cell Survival; D002478:Cells, Cultured; D017679:Cryotherapy / Q000379:methods*; D042783:Endothelial Cells / Q000378:metabolism* / Q000473:pathology; D005260:Female; D005354:Fibrosarcoma / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D005615:Freezing; D006614:Hindlimb; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008809:Mice, Inbred C3H; D009368:Neoplasm Transplantation; D010100:Oxygen / Q000032:analysis / Q000378:metabolism; D010101:Oxygen Consumption; D010313:Partial Pressure; D013997:Time Factors; D047368:Tumor Burden
chemical_list: D010100:Oxygen