No abstract

The intracellular steady-state levels of methotrexate were previously shown to be reduced in estrogen receptor (ER)-negative human breast cancer MDA-MB-436 cells and ER-positive human breast cancer MCF7 cells following treatment with pharmacologically relevant concentrations of 17 beta-estradiol (E2). We now report that both E2 and tamoxifen (TMX) significantly decreased the fluidity of MCF7 and MDA-MB-436 cellular membranes. With E2 or TMX at concentrations greater than 1 microM, perturbations in membrane fluidity were accompanied by apparently non-ER-mediated cytotoxicity. Alterations in membrane structure may have contributed to the cytotoxicity of high-dose endocrine therapy and to the ability of E2 to inhibit methotrexate transport and cytotoxicity in some human breast cancer cells.

No abstract

No abstract

SynopsisBased on equilibrium binding studies, as well as on kinetic investigations, two types of interactions of Cu2+ ions with native DNA a t low ionic strength could be characterized, namely, a nondenaturing and a denaturing complex formation. During a fast nondenaturing complex formation a t low relative ligand concentrations and a t low temperatures, different binding sites at the DNA bases become occupied by the metal ions. This type of interaction includes chelate formation of Cu2+ ions with atoms N(7) of purine bases and the oxygens of the corresponding phosphate groups, chelation between atoms N(7) and 0 of C(6) of the guanine bases, as well as the formation of specific interstrand crosslink complexes a t adjacent G.C pairs of the sequence dGpC. CD spectra of the resulting nondenatured complex (DNA-CU~+),,~ may be interpreted in terms of a conformational change of DNA from the B-form to a C-like form on ligand binding. A slow cooperative denaturing complex formation occurs a t increased copper concentrations and/or a t increased temperatures. The uv absorption and CD spectra of the resulting complex, (DNA-Cu2+)denat, indicate DNA denaturation during this type of interaction. Such a conclusion is confirmed by microcalorimetric measurements, which show that the reaction consumes nearly the same amount of heat as acid denaturation of DNA.From these and the kinetic results, the following mechanism for the denaturing action of the ligands is suggested: binding of Cu2+ ions to atoms N(3) of the cytosine bases takes place when the cytosines come to the outside of the double helix as a result of statistical fluctuations. After the completion of the binding process, the bases cannot return to their initial positions, and thus local denaturation at the G-C pairs is brought about. The probability of the necessary fluctuations occurring is increased by chelation of Cu2+ ions between atoms N(7) and 0 of C(6) of the guanine bases during nondenaturing complex formation, which loosens one of the hydrogen bonds within the G-C pairs, as well as by raising the temperature. The implications of the new binding model, which comprises both the sequence-specific interstand crosslinks and the described mechanism of denaturing complex formation, are discussed and some predictions are made. The model is also used to explain the different renaturation properties of the denatured complexes of Cu2+, Cd2+, and Zn2+ ions with DNA.In temperature-jump experiments with the nondenatured complex (DNA-CU~+),,~, a specific kinetic effect is observed, namely, the appearance of a lag in the response to the per-

No abstract

We present possibilities and trends of ELF bioelectromagnetic effects in the mT amplitude range on cancer cells and on mice bearing tumors. In contrast to invasive electrochemotherapy and electrogenetherapy, using mostly needle electrodes and single high-amplitude electropulses for treatment, extremely low-frequency (ELF) pulsating electromagnetic fields (PEMF) and sinusoidal electromagnetic fields (SEMF) induce tumor cell apoptosis, inhibit angiogenesis, impede proliferation of neoplastic cells, and cause necrosis non invasively, whereas human lymphocytes are negligibly affected. Our successful results in killing cancer cells-analyzed by trypan blue staining or by flow cytometry-and of the inhibition of MX-1 tumors in mice by 15-20 mT, 50 Hz treatment in a solenoid coil also in the presence of bleomycin are presented in comparison to similar experimental results from the literature. In conclusion, the synergistic combinations of PEMF or SEMF with hyperthermia (41.5°C) and/or cancerostatic agents presented in the tables for cells and mice offer a basis for further development of an adjuvant treatment for patients suffering from malignant tumors and metastases pending the near-term development of suitable solenoids of 45-60 cm in diameter, producing >20 mT in their cores.

No abstract