Enhancement of hyperthermia effect in vivo by amiloride and DIDS

Int J Radiat Oncol Biol Phys. 1993 Jan;25(1):95-103. doi: 10.1016/0360-3016(93)90150-t.

Abstract

Purpose: Intracellular pH is regulated mainly by Na+/H+ antiport and Cl-/HCO3- exchange through the cell membrane. Amiloride (3,5-diamino-6-chloro-N-(diaminomethylene)pyrazine carboxamide) is a diuretic drug that blocks Na+/H+ antiport and DIDS (4,4-diisothiocyanatostilbene-2,2'-disulfonic acid) is an inhibitor of Cl-/HCO3- exchange. We investigated the potency of these drugs to lower pHi and increase the thermosensitivity of tumors in vivo.

Materials and methods: The cytocidal effect of heat in combination with drug effect in vivo was studied using the in vivo-in vitro clonogenic assay method and the tumor growth delay method with SCK tumors, a mammary adenocarcinoma, on the hind limbs of A/J mice. The effects of amiloride and DIDS on tumor pHi and high energy phosphate levels were investigated using 31P-NMR.

Results: We observed that amiloride or DIDS alone increased the effect of hyperthermia at 42.5 degrees C or 43.5 degrees C to suppress tumor growth. The thermosensitization was greater when the two drugs were combined. For example, hyperthermia at 43.5 degrees C alone resulted in a tumor growth delay of about 4 days. When 10 mg/kg amiloride or 25 mg/kg DIDS was injected prior to heating, the growth delay increased to about 6 days. When both drugs were injected prior to heating, a total growth delay of 8 days was obtained. In vivo-in vitro excision assays for cell survival demonstrated that these drugs enhanced the heat-induced tumor cell death. An i.p. injection of 10 mg/kg amiloride plus 25 mg/kg DIDS did not lower the tumor pHi over a 120 min interval. Heating the tumors at 42.5 degrees C for 1 hr significantly lowered the pHi and when the tumor-bearing mice were injected i.p with amiloride and DIDS, and the tumors were heated 1 hr later, the drop in pHi was greater relative to that by heating alone. Heating alone significantly lowered the tumor energy levels as indicated by PCr/Pi and beta-ATP/Pi ratios and an i.p. injection of 25 mg/kg amiloride prior to heating further reduced the energy status in the tumors.

Conclusion: Amiloride or its analogs and DIDS may be useful in increasing the therapeutic efficacy of hyperthermia treatments by enhancing the reduction in tumor pHi.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid
  • 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / administration & dosage
  • 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / analogs & derivatives*
  • 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / therapeutic use
  • Adenocarcinoma / drug therapy
  • Adenocarcinoma / therapy*
  • Amiloride / administration & dosage
  • Amiloride / therapeutic use*
  • Animals
  • Cell Survival / drug effects
  • Cell Survival / radiation effects
  • Combined Modality Therapy
  • Drug Combinations
  • Female
  • Hyperthermia, Induced*
  • Mammary Neoplasms, Experimental / drug therapy
  • Mammary Neoplasms, Experimental / therapy*
  • Mice
  • Neoplasm Transplantation

Substances

  • Drug Combinations
  • 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid
  • Amiloride
  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid