DNA alterations induced by the carbon-centered radical derived from the oxidation of 2-phenylethylhydrazine

The possible significance of carbon-centered radicals in hydrazine-induced carcinogenesis is explored by studies of the interaction between the 2-phenylethyl radical and DNA. The radical is efficiently generated during oxidation of phenelzine (2-phenylethyl-hydrazine) promoted by oxyhemoglobin or ferricyanide, as demonstrated by spin-trapping experiments and analysis of the reaction products. In the ferricyanide promoted oxidation, ethylbenzene formation accounts for about 40% of the initial drug concentration, from 5 to 100 m m phenelzine. By contrast, product formation in the presence of oxyhemoglobin depends on the enzyme concentration due to the fact that the prosthetic heme is destroyed during catalytic turnover. Covalent binding of the 2-phenylethyl radical to oxyhemoglobin is demonstrated by experiments with 2-[ 3 H]phenelzine, where tritium incorporation to the protein is inhibited by the spin-trap, α-(4-pyridyl-1-oxide)- N - tert -butylnitrone. The 2-phenylethyl radical is also able to alkylate DNA as suggested by electrophoretic studies with plasmid DNA, and proved by experiments with 2-[ 3 H]-phenelzine. The carbon-centered radical has a preference for attacking guanine residues as demonstrated by the use of sequencing techniques with 32 P-DNA probes. The results indicate that the 2-phenylethyl radical is an important product of phenelzine oxidation and that this species can directly damage protein and DNA.