Induction of hypoxia in experimental murine tumors by the nitric oxide synthase inhibitor, NG-nitro-L-arginine.
The nitric oxide synthase inhibitor NG-nitro-L-arginine (NOARG) was examined for its ability to alter energy metabolism in three murine tumors using 31P magnetic resonance spectroscopy. NOARG (10 mg/kg, i.v.) increased the inorganic phosphate:total phosphate ratio (Pi:total) 2-3-fold in the KHT, RIF-1, and SCCVII/Ha intradermal back tumors from 30 min to 6 h after injection, but the 31P magnetic resonance spectrum from normal tissue on the mouse back was unchanged after this treatment. NOARG (10 mg/kg, i.v.) injected 30 min before X-rays increased tumor cell survival 3-5-fold in SCCVII/Ha and 50-200-fold in RIF-1, measured using an in vivo/in vitro clonogenic assay. These effects were equivalent to those obtained from clamped tumors, indicating full radiobiological hypoxia. In KHT, only a 2-fold increase in radioresistance was observed after NOARG, which was less than the response of clamped tumors. In RIF-1 tumors, NOARG induced full radiobiological hypoxia when given from 30 min to 6 h prior to X-rays, consistent with the time course for the increase in Pi:total, measured by 31P magnetic resonance spectroscopy. Pi:total after NOARG doses of 0.1-10 mg/kg, i.v., increased in a dose-dependent manner in this tumor. Increased RIF-1 tumor radioresistance was similarly dependent on NOARG dose. The combination of the bioreductive agent RB6145 (300 mg/kg, i.p.) 15 min prior to NOARG (10 mg/kg, i.v.) produced greater than 5 decades of KHT tumor cell killing at 24 h after treatment. This combination also increased Pi:total 4.5-fold over the control value at 24 h in the KHT tumor. Histological examination of tumors at this time indicated extensive necrosis.
Wood
P J
PJ
MRC Radiobiology Unit, Chilton, Didcot, Oxon, United Kingdom.
Sansom
J M
JM
Butler
S A
SA
Stratford
I J
IJ
Cole
S M
SM
Szabo
C
C
Thiemermann
C
C
Adams
G E
GE
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology; D002277:Carcinoma / Q000188:drug therapy* / Q000378:metabolism / Q000532:radiotherapy; D015687:Cell Hypoxia; D002470:Cell Survival / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D004734:Energy Metabolism / Q000187:drug effects*; D005260:Female; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D019335:Nitroarginine; D009593:Nitroimidazoles / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism; D011355:Prodrugs / Q000494:pharmacology; D012513:Sarcoma, Experimental / Q000188:drug therapy* / Q000378:metabolism / Q000532:radiotherapy
D009593:Nitroimidazoles; D010710:Phosphates; D011355:Prodrugs; C067834:RB 6145; D019335:Nitroarginine; D001120:Arginine