Interaction of an intercalating antitumoral agent: 9-hydroxy-2-methyl ellipticinium (NMHE) with chromatin

Microspectrofluorometry of the protonation state of ellipticine, an antitumor alkaloid, in single cells

The protonation state and intracellular distribution of ellipticine were investigated in single human mammary T47D cells by confocal laser microspectrofluorimetry. In the cell nucleus, only the protonated form of ellipticine was detected as a direct consequence of its apparent pK increase upon DNA binding. Both protonated and neutral forms were present in the aqueous cytoplasm, where the pH is close to the drug pK. When cells were incubated in high concentrations of K+, a condition that depolarizes the plasma membrane potential, ellipticine cellular accumulation was reduced. In the cytoplasm, ellipticine was mainly bound to mitochondria, and its protonation equilibrium was shifted toward the neutral form. The fluorescence spectrum of ellipticine bound to mitochondria was insensitive to valinomycin, whereas it was markedly shifted toward the protonated form after carbonyl cyanide p-trifluoromethoxy-phenylhydrazone or nigericin addition. Similar studies with ellipticine bound to isolated mitochondria suggest that it behaves as a fluorescent probe of mitochondrial pH in both isolated mitochondria and single living cells.

Interaction between 2N-methyl-9-hydroxyellipticinium and ionizing radiation in CHO cells

Incubation with 2N-methyl-9-hydroxyellipticinium (NMHE) increases the killing of gamma-irradiated CHO cells. The main effect is observed in the case of exponentially growing cells which are also more sensitive to the drug alone than plateau phase cells. Radiosensitivity increases with drug concentration and incubation time in the presence of the drug until a plateau value. However, the presence of NMHE in the culture medium inhibits neither the repair of sublethal nor potentially lethal damage. The influence of different ellipticine derivatives on the cell radiosensitivity was measured. The results show that only the hydroxylated derivatives (NMHE and 9-hydroxyellipticinium), which covalently bind to nucleic acids, increase the cellular sensitivity to ionizing radiations, whereas the non-hydroxylated derivative, 2N-methyl-ellipticinium, has no influence on cell radiosensitivity.