Effect of Increased Intracellular pH by HMA on the Cytotoxicity of Combined Treatment of Hyperthermia and Chemotherapy

Hur, Won Joo; Song, Chang Won

Abstract

PURPOSE: The enhanced cytotoxic effect of combined treatement of hyperthermia and chemotherapy by increasing intracellular acidify with HMA was investigated.
MATERIALS AND METHODS
Fsall tumor cells were injected on the hindlegs of female C3H mice. When the tumor volume reached about 200mm3 , experiments were performed on the groups classified as follows : Group I : Control Group II : Melphalan alone (2.5 mg/kg, 5 mg/kg, 10 mg/kg, 15 mg/kg). Group III : Heat alone (42.5degree C for 1 hour) Group IV : Melphalan + Heat (42.5degree C for 1 hour) Group V : HMA(10 mg/kg) + Melphalan (5.0 mg/kg) + Heat (42.5degree C for 1 hour) Each group included 8-12 mice on each experiment. HMA (3-amino-6-chloro-5(1-homopiperidyl)-N-(diaminomethylene)-c-pyrazinecarboxamide), an analog of amiloride which increases intracellular pH(pHi) was dissolved in dimethyl sulfoxide(DMS) and injected into the tumor-bearing mice through the tail vein. 10mg/kg of HMA and each dose of melphalan were injected into peritoneum of the tumor-bearing mice 30 minutes before heating. Tumor growth delay was calculated when the tumor vlme reached at 1500mm3 . Excision assay was performed on each group and repeated 2-4 times.
RESULTS
Tumor growth delay of each experimental groups at 1500 mm3 were 9, 10, 13 and 19 days respectively. In vivo-in vitro excision assay using Fsall tumor cells, the cytotoxicity of each experimental groups was 1.2 X 107 , 1 X 107 , 6 X 106 , 1.7 X 106 and 1 X 105 clonogenic cells/gm respectively. When HMA was added to the combined treatment of heat and chemotherapy, the tumor growth ws delayed more than combined treatment without HMA i.e., 6 days tumor growth delay at 1500 mm3 of tumor volume.
CONCLUSION
he combined effect of cytotoxicity by heat and chemotherapy can be much more enhanced by HMA.