Interaction of doxorubicin with nuclei isolated from rat liver and kidney

Chromatin as a target for the DNA-binding anticancer drugs

Chemotherapy has been a major approach to treat cancer. Both constituents of chromatin, chromosomal DNA and the associated chromosomal histone proteins are the molecular targets of the anticancer drugs. Small DNA binding ligands, which inhibit enzymatic processes with DNA substrate, are well known in cancer chemotherapy. These drugs inhibit the polymerase and topoisomerase activity. With the advent in the knowledge of chromatin chemistry and biology, attempts have shifted from studies of the structural basis of the association of these drugs or small ligands (with the potential of drugs) with DNA to their association with chromatin and nucleosome. These drugs often inhibit the expression of specific genes leading to a series of biochemical events. An overview will be given about the latest understanding of the molecular basis of their action. We shall restrict to those drugs, synthetic or natural, whose prime cellular targets are so far known to be chromosomal DNA.

A new antitumor agent amrubicin induces cell growth inhibition by stabilizing topoisomerase II-DNA complex

Amrubicin is a novel, completely synthetic 9-aminoanthracycline derivative. Amrubicin and its C-13 alcohol metabolite, amrubicinol, inhibited purified human DNA topoisomerase II (topo II). Compared with doxorubicin (DXR), amrubicin and amrubicinol induced extensive DNA-protein complex formation and double-strand DNA breaks in CCRF-CEM cells and KU-2 cells. In this study, we found that ICRF-193, a topo II catalytic inhibitor, antagonized both DNA-protein complex formation and double-strand DNA breaks induced by amrubicin and amrubicinol. Coordinately, cell growth inhibition induced by amrubicin and amrubicinol, but not that induced by DXR, was antagonized by ICRF-193. Taken together, these findings indicate that the cell growth-inhibitory effects of amrubicin and amrubicinol are due to DNA-protein complex formation followed by double-strand DNA breaks, which are mediated by topo II.

Transport mechanisms of idarubicin, an anthracycline derivative, in human leukemia HL60 cells and mononuclear cells, and comparison with those of its analogs

Transport mechanisms of idarubicin (IDA) in HL60 cells, as leukemia cells, and human mononuclear cells (MNCs), as normal cells, were investigated, and compared with those of its analogs. The uptake of IDA by both cell types was temperature- and concentration-dependent, was inhibited competitively by daunorubicin (DNR) and noncompetitively by adriamycin (ADR), and was stimulated by preloading of the cells with DNR and ADR, indicating the partial involvement of a carrier-mediated mechanism. On pretreatment of the cells with 2,4-dinitrophenol, IDA uptake by HL60 cells increased, but that by MNCs decreased, suggesting that IDA was partially taken up into HL60 cells via an energy-independent carrier system, and into MNCs via an energy-dependent one. We speculated that in HL60 cells the carrier concerned with IDA uptake was common to DNR and ADR, and that the binding site of IDA on the carrier was the same as that for DNR, but not that for ADR, while in MNCs the carrier system consisted of, at least in part, a carrier for DNR uptake and one for ADR uptake, and the binding site of IDA was identical to that for DNR in the former, but different from that for ADR in the latter. It appeared that the uptake of IDA was greater than those of pirarubicin, DNR and ADR in both HL60 cells and MNCs, and that IDA was incorporated into MNCs more efficiently than into HL60 cells because of the higher uptake efficacy of the carrier(s).

Phosphatidylserine as a determinant for the tissue distribution of weakly basic drugs in rats

Interogan variation in tissue distribution of weakly basic drugs such as quinidine, propranolol, and imipramine was investigated as a function of binding to phosphatidylserine (PhS) in tissues. Tissue distributions of these drugs were determined using 10 different tissues at a steady-state plasma concentration and were expressed as tissue-to-plasma partition coefficients (Kp values). The concentration of PhS in the tissue was determined by two-dimensional thin-layer chromatography. Plotting of Kp values, except for brain, against the tissue PhS concentrations showed a linear relationship, indicating that PhS is a determinant in the interorgan variation of these tissue distributions. Further, differences in tissue distribution among the drugs was considered to be due to the difference in binding potency to PhS. Drug binding parameters to individual standard phospholipid were determined using a hexane-pH 4.0 buffer partition system. Binding was highest to PhS, and a linear relationship was found between the log nK [product of the number of binding sites (n) and the association constant (K) for PhS binding] obtained in vitro and Kp values of drugs in tissues in vivo. The empirically derived equation, Kp = 14.3 x (log nK) x (PhS conc.) - 8.09, was found to predict Kp values in vivo of weakly basic drugs. Thus, a determinant of interorgan variation in the tissue distribution of the weakly basic drugs studied was the tissue concentration of PhS and the drug binding affinity to PhS.

Differential retention of doxorubicin in the organs of two strains of rats

Fluorescence microscopy and high pressure liquid chromatography were used to study the decrease of doxorubicin (DXR) concentrations in the liver, spleen, heart, lung, kidney and skeletal muscle of two strains of rats at various times after a single intravenous injection of the drug (8 mg kg-1). DXR was located within the cell nucleus and was mostly undegraded, it persisted, especially in heart, lungs and spleen where it was detectable 10 days after injection. The DXR/DNA ratio, was used as an index of nuclear fixation of the drug. A major difference in the DXR/DNA ratio between the two strains were observed in heart and spleen results; the DXR/DNA ratio was significantly higher in heart and spleen compared with lung, liver and kidney in both strains.

Tubulin as a major determinant of tissue distribution of vincristine

The tissue distribution of vincristine was correlated with the tubulin content in different mouse tissues. The concentration of tubulin in the mouse tissues was determined by estimation of the tissue binding capacities for colchicine. Significant differences in the tubulin concentration were observed among the tissues. The comparison of the apparent tissue-to-plasma partition coefficients (KPapp) of vincristine (taken from the literature) with the tubulin concentration (expressed by the binding capacities for colchicine) showed a good correlation. These results suggest that the in vivo distribution of vincristine is predicted by the tissue tubulin concentration.

Pharmacokinetic study on the mechanism of tissue distribution of doxorubicin: interorgan and interspecies variation of tissue-to-plasma partition coefficients in rats, rabbits, and guinea pigs

The mechanism of interorgan and interspecies variations in the tissue distribution of doxorubicin was studied in rats, rabbits, and guinea pigs. The permeation properties of doxorubicin were investigated by using isolated rat erythrocytes as a model membrane. A significant dependency of the uptake rate constant on medium pH was observed, suggesting that only un-ionized doxorubicin is diffusible through the plasma membrane. The values of plasma unbound fraction (fp) of doxorubicin were 0.344 for rats, 0.415 for rabbits, and 0.529 for guinea pigs. The tissue DNA concentrations of rats were larger than those of rabbits and smaller than those of guinea pigs in corresponding organs or tissues. An in vitro organ model that described the distribution behavior of doxorubicin in the whole body was constructed, and an equation was derived to estimate the tissue-to-plasma partition coefficients, (Kp) from in vitro experiments. The in vitro Kp values showed comparatively good agreement with the in vivo Kp values for the various organs or tissues in all three species. Doxorubicin is exclusively bound to the nuclei in the cells. The variation of the Kp values in different organs depended on the amount of nuclei per gram of tissue. The primary determinant of the interspecies variation in the Kp values was the difference in tissue DNA concentrations among rats, rabbits, and guinea pigs, and a secondary determinant was the difference in fp values.