Bis-bioreductive agents as hypoxia-selective cytotoxins: nitracrine N-oxide

Int J Radiat Oncol Biol Phys. 1992;22(4):693-6. doi: 10.1016/0360-3016(92)90505-c.

Abstract

Drugs with two reducible centers, both of which must be metabolized by oxygen-inhibitable processes for full activation ("bis-bioreductive agents"), offer potential for the development of hypoxia-selective cytotoxins with improved oxygen sensitivity. The sidechain N-oxide (1-NCO) of the (mono)bioreductive agent nitracrine (1-NC) has been synthesized and evaluated as a potential example of such an approach. The association constant for reversible DNA binding of 1-NCO was 15-fold lower than that of 1-NC, as measured by equilibrium dialysis in a low ionic strength buffer, indicating that the N-oxide has the potential to act as a less toxic pro-drug of 1-NC. Cell uptake and aerobic cytotoxicity of 1-NCO were much lower than for 1-NC whereas its hypoxic selectivity as a cytotoxin was greatly increased. In stirred suspension cultures of AA8 cells, pure (less than 0.02% 1-NC) 1-NCO was 1000-1500 times more potent under hypoxia than in 20% O2. For 1-NC the corresponding ratio was 10 +/- 1. 1-NCO had greater hypoxic selectivity in this system than misonidazole (ratio 11), RSU 1069 (ratio 25), 8Me-5NQ (ratio 60), or SR 4233 (ratio 80). Studies of 1-NCO metabolism indicate rapid, O2-inhibited reduction to 1-NC. The data are consistent with a two-step bioactivation mechanism, with reduction of the N-oxide generating a DNA intercalator of increased binding affinity, followed by reduction of the nitro group of this DNA-targeted cytotoxin to form reactive cytotoxic metabolites.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / chemical synthesis
  • Antineoplastic Agents / pharmacology*
  • Cell Hypoxia
  • Cell Survival / drug effects
  • Cricetinae
  • In Vitro Techniques
  • Nitracrine / analogs & derivatives*
  • Nitracrine / chemical synthesis
  • Nitracrine / pharmacology
  • Prodrugs / chemical synthesis
  • Prodrugs / pharmacology*
  • Time Factors

Substances

  • Antineoplastic Agents
  • Prodrugs
  • C 684
  • Nitracrine