The
sesquiterpene lactone antineoplastic vernolepin acutely depletes murine
tumor cell
glutathione (GSH), and lyses the cells by an unknown mechanism that is enhanced synergistically by inhibition of GSH synthesis with
buthionine sulfoximine (BSO) (Arrick et al. 1983. J. Clin. Invest. 71:258). We found here that lysis of P815
mastocytoma cells by
vernolepin, with or without BSO, required
cystine in the culture medium. Addition of
catalase markedly suppressed
vernolepin-mediated cytolysis in
cystine-containing media, suggesting the involvement of
hydrogen peroxide in the cytolytic action of
vernolepin. Consistent with this, inhibition of
tumor cell
glutathione disulfide reductase with
1,3-bis(2-chloroethyl)-1-nitrosourea or inhibition of endogenous
catalase with
aminotriazole synergistically augmented cytolysis by
vernolepin. Moreover, H2O2 was released by
suspensions of P815 cells in
cystine-containing
buffer (63 pmol/10(6) cells X h). Omission of
cystine reduced the rate of H2O2 accumulation 10-fold. No H2O2 was detected without cells. Cytolysis by
vernolepin could be restored in
cystine-deficient medium by several other
disulfides, themselves noncytolytic, such as
disulfiram and oxidized
Captopril, as well as by
cysteine. In contrast, withholding two other
essential amino acids (
leucine or
tryptophan) or adding
cycloheximide did not interfere with cytolysis by
vernolepin. These results suggest that cellular uptake of
disulfides of physiologic and pharmacologic interest may be followed by their intracellular reduction and autooxidation with generation of H2O2. This previously unrecognized source of intracellular
oxidant stress may be an important component of injury to GSH-depleted cells.