Antitumor imidazolyl disulfide IV-2 causes irreversible G(2)/M cell cycle arrest without hyperphosphorylation of cyclin-dependent kinase Cdk1

Aberrant function of redox-regulated proteins is a possible cause for cellu lar transformation and loss of cell cycle control. The small protein thiore doxin has oncogenic properties and controls cell cycle movement through G(1 ), S, and G(2)/M phases. The redox-active, asymmetrical 1-methylpropyl-2-im idazolyl disulfide (IV-2) has previously been shown to react with and inhib it thioredoxin activity in vitro, the proliferation of human tumor cells in culture, and the growth of tumors in mice. We now examined the effects of IV-2 on cell cycle progression. In synchronized tsFT210 mouse mammary carci noma cells, IV-2 halted cells in mitosis, In asynchronously growing MCF-7 h uman breast cancer cells, IV-2 exclusively and irreversibly blocked cells i n G(2)/M at concentrations that correlated with its growth inhibitory activ ity. Neither the closely related, less redox active 2-hydroxy-1-methylpropy l-2-imidazolyl disulfide (AIV-2), which differs from IV-2 only by an additi onal hydroxyl group, nor the symmetrical diallyl disulfide caused a G(2)/M arrest under these conditions. Furthermore, MCF-7 cells treated with IV-2 s howed increased Cdk1 kinase activity and a decrease in Cdk1 tyrosine phosph orylation, indicating that IV-2 did not directly inhibit Cdk1 or Cdc25 acti vities. IV-2 did, however, increase Bcl-2 phosphorylation. These data sugge st that the thioredoxin inhibitor IV-2, despite its simple structure, is ab le to target redox-sensitive processes that are critical for cell cycle pro gression through mitosis. The results are also consistent with a role of th ioredoxin regulating cell cycle progression through G(2)/M.