Structure–activity analysis of the potentiation by aminothiols of the chromosome‐damaging effect of bleomycin in G₀ human lymphocytes

Abstract

The radioprotective aminothiols 2-[(aminopropyl)amino] ethanethiol (WR-1065) and cysteamine (CSM) potentiate the induction of chromosomal damage by the radiomimetic compound bleomycin (BLM) in G0 human lymphocytes. To investigate the mechanism of potentiation, we measured the clastogenic activity of BLM in the cytokinesis-block micronucleus assay in the presence and absence of amines, thiols, and aminothiols. The hydroxy analog of WR-1065, 2-(3-aminopropylamino) ethanol (WR-OH), potentiates BLM only slightly, indicating the critical nature of the thiol group. As thiols, WR-1065 and CSM may donate electrons for the activation of Fe(+2)-BLM or for the regeneration of Fe(+2)-BLM from inactive Fe(+3)-BLM. The amines putrescine, spermidine, and spermine all potentiate BLM, but they are weaker potentiators than the aminothiols, and they are effective only at high concentrations. Their activity, like that of WR-OH, is probably a consequence of conformational alteration of DNA. Dithioerythritol (DTE) and 2-mercaptoethanol (2-ME), thiols lacking an amino group, are less effective potentiators of BLM than are the aminothiols. The thiol group of WR-1065 and CSM is therefore essential, but insufficient, for explaining the strong enhancement of BLM activity. The cationic nature of CSM and WR-1065, conferred by the amino groups, evidently concentrates the active thiol function at the site of BLM action on DNA. As expected on this basis, the diamine WR-1065 is a more effective potentiator of BLM than is the monoamine CSM, whereas cysteine and N-acetylcysteine (NAC), which lack a net positive charge, potentiate BLM only weakly. These studies suggest that potentiation of the clastogenic action of BLM by aminothiols can be explained by the combination of a thiol-mediated redox mechanism and an amine-mediated targeting of the thiol function to DNA.

Potentiation of the mutagenicity and recombinagenicity of bleomycin in yeast by unconventional intercalating agents

“…In the case of intercalators, however, the interaction appears to be uniformly one of BLM amplification. The generality of BLM enhancement by intercalators does not preclude other possible means of potentiation, including enhanced BLM activation through redox mechanisms, improved BLM uptake, or altered DNA repair [Hoffmann et al, 1995[Hoffmann et al, , 2001Snyder, 2007].…”

“…BLM is a potent mutagen, clastogen, and recombinagen, and earlier studies have shown that its genetic activity can be reduced by antimutagens or enhanced by various agents, including 3-aminobenzamide, aminothiols, caffeine, ethanol, hydroxyurea, isoptin, heterocyclic aromatic intercalating agents, hyperthermia, ß-carotene, triethylenetetramine, and hyperbaric oxygen (reviewed in Hoffmann et al [2001]). Several mechanisms of modulation of BLM have been described in yeast strain D7.…”

“…Chemicals representing diverse structural classes have been found to increase or decrease the genotoxicity of BLM in various assays [Hoffmann et al, 2001. Many agents thought to intercalate between the base pairs of DNA have been studied in combination with BLM in a micronucleus assay in Chinese hamster V79 cells, and they consistently enhance its activity.…”

“…The resultant free radical is processed through defined pathways that lead to single-and double-strand breaks in DNA [Povirk and Austin, 1991;Chen and Stubbe, 2005]. Double-strand breaks are responsible for cytotoxic [Hay et al, 1991;Stubbe et al, 1996;Burger, 1998], clastogenic [Povirk and Austin, 1991;Hoffmann et al, 1994Hoffmann et al, , 2001 and recombinagenic [Kupiec, 2000;Freeman and Hoffmann, 2007] effects of BLM. The induction of point mutations by BLM may involve imperfect repair of breaks [Chen and Stubbe, 2005].…”

A Potential Synergistic Anticancer Effect of Paclitaxel and Amifostine on Endometrial Cancer

“…However, amifostine has also been reported to potentially compromise anticancer therapies. Previous research has indicated that amifostine impaired p53-induced apoptosis in myeloid leukemia cells (17) and potentiated bleomycin-induced DNA damage in human lymphocytes (27). Pretreatment with Figure 6.…”