Effect of calcitonin gene related peptide vs sodium nitroprusside to increase temperature in spontaneous canine tumours during local hyperthermia.

The objectives of this study were to compare the effects of two vasodilators, sodium nitroprusside (SNP) and calcitonin gene-related peptide (CGRP) on mean arterial pressure (MAP), heart rate (HR) and temperatures in tumour and surrounding normal tissue during local hyperthermia treatment. Eleven tumour-bearing pet dogs with spontaneous soft tissue sarcomas were given SNP intravenously during local hyperthermia. The drug infusion rate was adjusted to maintain a 20% decrease in MAP. The median (95% CI) increase in the temperature distribution descriptors T(90) and T(50) was 0.2 degrees C (0.0-0.4 degrees C, p = 0.02) and 0.4 degrees C (0.1-0.7 degrees C, p = 0.02), respectively, in tumour. Normal subcutaneous tissue temperatures were mildly increased but remained below the threshold for thermal injury. The effects of CGRP were investigated in six tumour-bearing dogs following a protocol similar to that used for SNP. The median (interquartile (IQ) range) decrease in mean arterial pressure was 19% (15-26%) after CGRP administration and a significant increase was seen in tumour but not normal subcutaneous tissue temperatures. The median (95% CI) increase in the temperature distribution descriptors T(90) and T(50) was 0.5 degrees C (0.1-1.6 degrees C, p = 0.03) and 0.8 degrees C (0.1-1.6 degrees C, p = 0.13), respectively. Administration of SNP or CGRP did not result in local or systemic toxicity in tumour-bearing dogs. However, the magnitude of increase in tumour temperatures was not sufficient to improve the likelihood of increased response rates. Therefore, there is little justification for translation of this approach to human trials using conventional local hyperthermia.

Temperature-dependent changes in physiologic parameters of spontaneous canine soft tissue sarcomas after combined radiotherapy and hyperthermia treatment.

PURPOSE: The objectives of this study were to evaluate effects of hyperthermia on tumor oxygenation, extracellular pH (pHe), and blood flow in 13 dogs with spontaneous soft tissue sarcomas prior to and after local hyperthermia. METHODS AND MATERIALS: Tumor pO2 was measured using an Eppendorf polarographic device, pHe using interstitial electrodes, and blood flow using contrast-enhanced magnetic resonance imaging (MRI). RESULTS: There was an overall improvement in tumor oxygenation observed as an increase in median pO2 and decrease in hypoxic fraction (% of pO2 measurements <5 mm Hg) at 24-h post hyperthermia. These changes were most pronounced when the median temperature (T50) during hyperthermia treatment was less than 44 degrees C. Tumors with T50 > 44 degrees C were characterized by a decrease in median PO2 and an increase in hypoxic fraction. Similar thermal dose-related changes were observed in tumor perfusion. Perfusion was significantly higher after hyperthermia. Increases in perfusion were most evident in tumors with T50 < 44 degrees C. With T50 > 44 degrees C, there was no change in perfusion after hyperthermia. On average, pHe values declined in all animals after hyperthermia, with the greatest reduction seen for larger T50 values. CONCLUSION: This study suggests that hyperthermia has biphasic effects on tumor physiologic parameters. Lower temperatures tend to favor improved perfusion and oxygenation, whereas higher temperatures are more likely to cause vascular damage, thus leading to greater hypoxia. While it has long been recognized that such effects occur in rodent tumors, this is the first report to tie such changes to temperatures achieved during hyperthermia in the clinical setting. Furthermore, it suggests that the thermal threshold for vascular damage is higher in spontaneous tumors than in more rapidly growing rodent tumors.

Acute pancreatitis associated with administration of a nitric oxide synthase inhibitor in tumor-bearing dogs.

BACKGROUND: Nitric oxide synthase (NOS) inhibitors have been investigated as potential cytotoxic agents to treat tumors lacking p53 function. Furthermore, their ability to reduce tumor blood flow can be combined with drugs that are specifically designed to kill cells that are hypoxic or to improve temperatures during local heat (hyperthermia) treatment of tumors. This paper reports the unexpected development of acute pancreatitis in two tumor-bearing pet dogs that were treated with the NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) during administration of local hyperthermia. METHODS: Prior to the use of L-NAME in tumor-bearing dogs, purpose-bred beagles were studied. Following induction of inhalation anesthesia, local hyperthermia was applied to either normal thigh muscle (beagles) or tumors (tumor-bearing dogs). Once a thermal steady state was achieved, L-NAME was administered and temperature monitoring continued. Animals were observed after treatment for evidence of toxicity. RESULTS: The beagles tolerated the treatment well, with no side effects noted either clinically or by routine CBC or blood chemistry analyses. In contrast, the first two tumor-bearing dogs accrued onto the phase I study developed acute pancreatitis in the immediate post-treatment period which necessitated hospitalization and intensive care. The trial was stopped. Both dogs had intercurrent risk factors which predisposed them to development of pancreatitis, although neither had a history of symptoms of pancreatitis at the time the hyperthermia + L-NAME treatment was given. CONCLUSIONS: We conclude that caution should be exercised when considering NOS inhibition for cancer treatment. Careful evaluation of history and health status as well as recognition of potential risk factors may be key in avoiding potentially fatal complications. This study demonstrates the value of performing potentially harmful treatments in tumor-bearing dogs prior to introduction into the human clinic.