Potentiation of adriamycin accumulation and effectiveness in adriamycin-resistant cells by aclacinomycin A.

Variants of Friend leukemia cells (FLC) selected for resistance to either adriamycin (ADM), daunorubicin (DNR) or aclacinomycin A (ACM) by step-wise exposure to each drug, were found to be cross-resistant to ADM and DNR but not to ACM. In addition, an epithelial cell line isolated from normal monkey kidney (CV-1) was found to be intrinsically resistant to ADM and DNR but not to ACM. In contrast, a human breast carcinoma cell line (MCF-7) was found to be sensitive to all three compounds. In these latter cell lines as well as in the FLC variants, lowered intracellular amounts of ADM and DNR correlated with resistance, but ACM levels were the same in sensitive and resistant cells. When cells with either acquired or intrinsic resistance were treated with ACM in combination with ADM or DNR, significant increases in the intracellular amounts of these latter compounds were found. Increased drug accumulation in resistant cells treated this way was accompanied by increased cytotoxicity. When resistant cells were exposed to ACM in combination with other anthracyclines, similar results were obtained. In comparison, these phenomena were not observed when either one of the sensitive cell types (parental FLC and MCF-7) were treated similarly. Since ADM and DNR resistant cells are sensitive to ACM and their resistance circumvented by ACM, this drug may have important clinical applications when used in combination with other anthracyclines.

[Role of cell pharmacokinetics in the modulation of modalities in the administration of anthracyclines]. / Rôle de la pharmacocinétique cellulaire dans la modulation des modalités d'administration des anthracyclines.

The rate of the anthracycline uptake and retention differs with the drug structure and with the cell type. Here we present evidence to show that as compared to carcinoma cells, normal epithelial cells are naturally resistant to adriamycin. Moreover, it is shown that uptake of demethoxy-daunorubicin and THP-ADM is a very rapid process as compared to ADM, epi-ADM or DNR. Cytotoxicity correlates with the intracellular concentration. The relevance of these in vitro findings is considered in the in vivo situation. Resistance to anthracyclines is in part related to decrease accumulation and retention. This resistance can be reversed not only by calcium transport and calmodulin inhibitors but also by co-treatment with aclacinomycin. Wether changes which occurred in acquired resistance can be found in cells with natural resistance to adriamycin remain to be determined.

The effects of N-methyl-N'-nitro-N-nitrosoguanidine on KB cells. II. Cell sensitivity to the lethal effect of the drug as a function of the cell age and of the nature of the culture medium.

We have tested the sensitivity of KB cells to the lethal effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), measured as cell loss within the 20-h period following a 1-h drug treatment, as a function of culture age and of the medium in which treated cells were incubated after elimination of MNNG. We showed that KB cell sensitivity to the lethal effect of the drug decreased with time after seeding when the treated cells were post-incubated in drug-free medium conditioned by untreated cells of the same age as treated ones but not when they were post-incubated in fresh drug-free medium. This difference was due in part to the fact that the conditioned medium had acquired with time a protective activity for treated cells and in part to an increased competence of aging cells to be protected by this medium. By post-incubating treated stationary cells sequentially in both media, we showed that a brief (15 min) post-incubation of the cells in fresh medium was sufficient to trigger cell death even if the cells were afterwards transferred to conditioned medium. In contrast, long post-incubation in fresh medium did not cause cell death if the cells were first post-incubated in conditioned medium for about 3 h. We conclude that: the medium acted on cell sensitivity to the lethal effect of MNNG through its growth regulatory ability; quiescent cells were less sensitive to the drug than growing cells; the sensitive phase of the cell was located before S; cell hypersensitivity might be due to deficient repair of cellular lesions rather than to increased lesion formation.

Progression of spontaneous malignant transformation of epithelial rat liver cell lines.

Cultured epithelial cell lines from normal rat livers were shown to undergo gradual transformation and malignancy which increased with time. Morphological changes appeared both before and after cells had attained a malignant state, as detected by agar tests. The progression of the degree of malignancy was determined by the morphological appearance of the cells, the increase in the number and size of cell colonies in soft agar, the expression of gamma glutamyl transferase (gamma GT) and the shortening of the latency period necessary for tumor formation after transplantation to syngeneic rats of cells from sequential passages.

Promoting effect of biliverdin for liver cells initiated by aflatoxin B1.

In this paper we have studied the participation of biliverdin, a bile pigment produced from hemoglobin catabolism, in a two-stage carcinogenesis model using hepatic cells in culture. The initiation was realised by a short term exposure to low doses of aflatoxin B1. The cells were then cultivated in the presence of biliverdin in the medium. We observed that biliverdin increased the rate and the efficiency of neoplastic transformation of cells. These results suggest that biliverdin may act as a promoting substance.

The effects of N-methyl-N'-nitro-N-nitrosoguanidine on KB cells. I. Growth inhibition and cell killing in relation to inhibition of macromolecular synthesis.

Cytotoxic effects of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on KB cells were analyzed taking into account cell killing and growth inhibition. Attempts to correlate these effects with macromolecular synthesis inhibition were monitored. At low doses (1 X 10(-6) at 1 X 10(-5) M), MNNG acting for 1 h only inhibited cell proliferation in a dose dependent manner and specifically inhibited DNA synthesis. At intermediate doses (1.6 X 10(-5) at 3.2 X 10(-5) M), treatment resulted in detachment and death of the cells during a 20-h post-incubation period. This effect was related to a dose-dependent inhibition of RNA and protein synthesis. At high doses (greater than 3.2 X 10(-5) M) MNNG treatment resulted in cell killing which was distinct from that produced by lower doses, since the cells did not detach from the glass. At these high doses strong inhibition of RNA and protein synthesis was observed early. When cells prelabelled with radioactive uridine or amino acids were treated with MNNG, the release of labelling into the culture medium increased, especially with uridine prelabelled cells. This increase was very high with the intermediate doses of the drug, but more modest with the strong doses. Furthermore, with the moderate doses, cell size showed greater reduction compared to the control than with the high doses. Thus, cell size reduction and loss of cellular material varied parallel to cell detachment. We hypothesize that moderate doses of MNNG may induce cellular degradation, whereas high doses may prevent it. The significance of this finding is discussed.

Cytotoxic and cytostatic effect of T2-toxin on epithelial cell lines derived from rat liver.

Cytotoxic and cytostatic effects of T2-toxin (Fusarium mycotoxin) on cells in culture derived from rat hepatomas and rat livers were investigated. Results showed that these effects appeared to be dependent on both drug concentration and duration of drug exposure. Non-transformed, as well as spontaneous neoplastic transformed liver cells and hepatoma cells were sensitive to its effect. T2-toxin had no selective action on cancer cells; however, a progression appeared in sensitivity to the toxic effect as a function of the degree of tumorigenicity of the cell line. This progression dis not exist for the cytostatic effect, which remained only in relation to the degree of proliferation of the cells in culture.

Hydroxyurea: protection of KB cells against the toxic effect of N-methyl-N'-nitro-N-nitrosoguanidine.

This report shows that hydroxyurea (HU) protected KB cells specifically against the toxic effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). It appears unlikely that this action was due to stimulation of DNA repair since HU neither protected the cells when added after removal of MNNG, nor shielded them against the toxicity of other DNA damaging agents. Similarly, it seems difficult to account for HU protection by its specific effect as an inhibitor of DNA synthesis, because cell protection was found to be maximal when the proliferative activity of the cultures was minimal, and because much higher doses of HU were required to ensure cell protection than to inhibit DNA synthesis. In fact, the shift of the MNNG dose-response curves in the presence of increasing HU concentrations suggests that HU might interfere with the MNNG-molecule. This was confirmed by our finding that HU enhanced the decomposition rate of MNNG, as did other substances like cysteine or ascorbic acid, which also appeared able to protect the cells against the toxic effect of MNNG.

Cytostatic effects of T2 toxin on cultured human neoplastic cells of intestinal origin.

The cytostatic effects of T2 toxin, a sesquiterpenoid mycotoxin produced by some Fusarium strains, were studied on cultured human cells originating from rectal and colonic tumors (HRT18 and HT29). These cells were found to be sensitive to doses of the order of 0.1 to 1 ng/ml medium. Duration of treatment influences the reversibility of cytostatic effect. Brief treatments (1 to 6 hours) at a non toxic concentration of 10 ng/ml induce a cytostatic effect of 24 hours duration, which is reversible after this period. Longer treatments (24 hours or more) induce a cytostatic effect not reversed 3 days after removal of toxin. T2 toxin thus appears to have, in vitro, a powerful cytostatic effect.

Effects of PR toxin on liver cells in culture.

We studied the effects on liver cells in culture of PR toxin, a substance produced from Penicillium roqueforti. PR toxin displayed cytotoxicity which increased as a function of its concentration but the form of such toxicity differed, depending on the toxin's concentration. Thus, cells only underwent quick retraction and intensive vacuolization when treated with low drug concentrations, and they came away from the substrate easily under these conditions. By contrast, the major events observed in the case of high concentrations were loss of structure of the nuclei and strong adhesiveness of dead cells to the support. PR toxin already inhibited cell multiplication at low concentrations and became toxic when the concentration was raised; growth inhibition decreased but the toxic effect increased when cells passed from the exponential growth phase to a phase of slower growth. PR toxin inhibited tritiated precursor incorporation into DNA, RNA and proteins in a similar time and concentration-dependent manner. Inhibition of DNA synthesis persisted even after removal of the drug from the medium.

An inhibitor of hepatoma cells multiplication in the efferent fluid from isolated perfused rat liver.

Efferent fluid from isolated rat livers perfused with a synthetic medium, when concentrated, inhibits the multiplication of hepatoma LF 20 cells "in vitro". The inhibitory factor is thermolabile, and is inactivated at a slow rate by proteolytic enzymes. Sephadex and Acrylamide-agarose chromatographic fractionation leads us to assume a molecular weight around 100,000 for the inhibitory factor. The release of the factor by the perfused liver depends on the temperature of the perfusing fluid. Potential role of this factor in the control of liver cell proliferation is discussed.