Mechanistic aspects of the delay in the G2 phase of the cell cycle caused by tumor promoter 12-O-tetradecanoylphorbol-13-acetate in HeLa cells

Abstract

In order to gain an insight into the nature of the radiomimetic activity by which the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) alters cell cycle parameters in HeLa cells, possibilities of modifying the TPA-induced G ₂ block and recovery from it were studied. TPA-induced G ₂ blockage was analysed by counting mitotic figures. It was not influenced by hydroxyurea (10 ⁻³ M) thus indicating that it is independent of DNA synthesis. TPA-induced decrease of mitotic activity occurred faster than that caused by cycloheximide (10 ⁻⁵ M) indicating that the TPA-sensitive transition point in G ₂ is closer to mitosis than that for cycloheximide. Superoxide dismutase, catalase, α-tocopherol, the radioprotector S-(2-aminoethyl)isothiuroniumbromide.HBr (AET), caffeine and indomethacin and eicosatetraynoic acid (ETYA), both inhibitors of oxygenases in the arachidonic acid cascade, were not capable of reducing the TPA-induced G ₂ response. Under certain conditions small concentrations of AET (10 ⁻⁸ M) and ETYA (10 ⁻⁸ M) appeared to improve recovery slightly. Mannitol and sorbitol, however, both hydroxyl radical scavengers at 0.1 M concentration reduced TPA-effectiveness to a large degree (0.1 M D- and L-mannose were ineffective). Dimethylsulfoxide (0.1 M), another hydroxyl radical scavenger, was ineffective.