The novel
nitroxyl,
Tempicol-3 (
nitroxide-N-
oxide) was synthesized and its capacity to act as a scavenger of
hydroxyl radicals was tested. The concentration-dependent reducibility of this novel compound was also examined and compared with those of previously characterized nitroxides,
Tempo and
Tempace. The cytotoxicity of
Tempicol-3 in vitro was measured by the modified tetrazolium assay (MTT), using, model cells for neoplastic phenotype (mouse NIH 3T3 fibroblast line). The ability of
Tempicol-3 to act as an
antitumor agent in vivo was also investigated in a pharmacological test, using rats bearing 3-day old
Yoshida Sarcoma (promotion phase of the disease). Our results clearly indicated that
Tempicol-3 acts as an effective and promising
hydroxyl radical scavenger-
antioxidant. Structure- and concentration-dependent bioreduction of
Tempicol-3 by
ascorbic acid may account for some of its
biological effects, causing modulation of the
antioxidant status of cells. The presence of one nitrone moiety per molecule of
Tempicol-3 caused a significant decrease in
nitroxide cytotoxicity as compared with
Tempo, in vitro. The results clearly confirmed that the toxic effect could result either from the presence or structure of substituent(s) at position 4 of the
free radical piperidine moiety. It can be stated that
Tempicol-3 is a lowtoxicity
nitroxide, which could be effective in providing antioxidative activity. We have also observed that lowtoxic
Tempicol-3, at m.e.d. (minimal effective dose) suppressed
tumorigenesis, acting as a cell proliferation modifier and apoptosis inducer in vivo. This work provides the base for further investigations on
nitroxide-N-
oxide derivatives since the serious question remains to be solved as to what is the molecular mechanism of action of the
nitroxide-N-
oxides.