Effects of all-trans-retinoic acid incorporated into low-density lipoprotein on invasive properties of multidrug-resistant MCF-7 spheroids.

Cultured cells grown as spheroids provide an in vitro model that is closer to an in vivo tumour than conventional monolayer techniques. Previous work from our laboratory has demonstrated that spheroids formed from multidrug-resistant MCF-7 cells exhibit invasive characteristics which were not present in their sensitive counterparts. The treatment of these spheroids by all-trans-retinoic acid (ATRA), a potent inducer of in vitro and in vivo differentiation, decreases their proteolytic activity and ability to invade Matrigel-coated filters. The efficiency of ATRA is enhanced by its incorporation into low-density lipoprotein (LDL) (LDL-ATRA). Indeed, invasion through a reconstituted basement membrane was reduced by 73% with 10(-6) M ATRA and 3 x 10(-8) M LDL-ATRA. Furthermore, inhibition of invasion was correlated with a decrease in several factors: (1) secreted matrix metalloproteinase-9 and enzymes degrading type IV collagen and Matrigel films, and (2) tissue plasminogen activator. The results observed were found with a concentration of LDL-ATRA 30 times lower than that of ATRA. This could be due to the protective effect of LDL and to a better targeting of cancer cells through their LDL receptors. LDL-ATRA may therefore represent a new and potent inhibitor of invasion that could be developed for clinical trials.

[The multidrug resistance phenotype: some morphological and biological characteristics except efflux pump]. / Le phénotype de résistance multidrogue: quelques caractéristiques morphologiques et biologiques autres que la pompe à efflux.

Recent data from the literature together with personal results strongly suggest that multidrug resistance phenotype is overwhelming the sole expression of P170 glycoprotein efflux pump. Morphological alterations have been put in evidence in MDR cells after transmission and scanning electron microscopy. They include presence of osmiophilic vesicles and modifications of nuclear and nucleolar chromatin. Biological characteristics include the hypersecretory pattern of lysosomal enzymes from MDR cells. Such a fact could be more or less related to the increased occurrence of mdr1 RNA in metastasis, especially in breast cancers, compared to primary tumors. If the P170-mediated efflux is one of the key mechanism of MDR, a decreased influx of anticancer drugs cannot be excluded. Liposomes, for instance made of cardiolipin, are thus able to increase the intracellular drug uptake of vinblastine without any action upon efflux mechanism.

Increased accumulation of drugs in multidrug-resistant cells induced by liposomes.

A multidrug-resistant cell such as the human lymphoblastic leukemic cell CEM/VLB100 accumulates far less vinblastine (VLB) than its drug-sensitive parent, CEM. When CEM/VLB100 cells are exposed to liposomes consisting of the phospholipids cardiolipin, dioleoylphosphatidic acid, or phosphatidylinositol bearing unsaturated fatty acids and then tested for uptake of VLB, accumulation of drug rapidly rises to levels approaching those of CEM cells, which are relatively unaffected by the liposome treatment. The liposomes are not carriers of entrapped drug. Phosphatidylserine, phosphatidylcholine, and phosphatidylethanolamine are inactive, and the addition of cholesterol to liposomes inhibits uptake. Exposure of cells to liposomes does not appear to alter the efflux of drugs. We suggest that the liposomal lipids, introduced into the plasma membranes of CEM/VLB100 cells, change their properties so that accumulation of drugs by cells is largely restored. The cytotoxicity of VLB in CEM/VLB100 cells is increased approximately 10-fold by cardiolipin liposomes.

Inhibition of collagenolytic activity in human leukemic K562 cells by tamoxifen.

Presence of a collagenolytic activity has been demonstrated in the human leukemic cell line K562. Among various effectors studied, tamoxifen, a well-known antiestrogenic compound, exhibited a strong inhibitory effect. After 3 days of culture in the presence of 10(-7) M of tamoxifen, 75% of the collagenolytic activity was inhibited. Hydroxytamoxifen and N-desmethyltamoxifen were equally potent inhibitors though devoid of the direct cytotoxic effect. Cis-tamoxifen was less efficient. K562 cells have no binding sites for estrogens but they possess high affinity binding sites for 3H-tamoxifen (295 fmol/mg of proteins, KD = 0.25 x 10(-9) M). Tamoxifen had no effect on cellular differentiation or enzyme secretion. Anticollagenolytic activity of tamoxifen (10(-7)-10(-6) M) could be related to its inhibitory action on plasmin and plasminogen activator.

Quantitative morphological analysis of adriamycin-resistant human K562 leukemic cells.

The morphological changes associated with Adriamycin resistance in a human leukemic cell line have been investigated by image analysis. An Adriamycin-resistant subline of the human erythroleukemic K562 cell line has been established. Three sets of cells have been analysed: sensitive cells, resistant cells cultured in the continuous presence of Adriamycin, and resistant cells cultured without the drug. Image analysis shows that Adriamycin-resistant K562 cells display significant morphological changes as compared with sensitive cells, at both the nuclear and cytoplasmic levels. These changes make it possible to separate sensitive and resistant cells automatically and with a classification accuracy of 76% and only four cytological parameters. Image analysis may therefore offer an interesting tool for studying drug resistance in leukemic cells, from both an experimental and a clinical point of view.

Collagenolytic activity in the human leukemic K-562 cell line before and after induction of erythroid differentiation.

K-562 cells were studied for their ability to produce collagenolytic enzymes in culture. Collagenolytic activity has been assayed by a fluorescamine method, it requires Ca2+ ions and is optimal at pH 7.5. It is present within the cells in the cytoplasm and bound to membranes, in addition it is excreted into the medium. Cellular collagenolytic activity is activated by trypsin and inhibited by cysteine and serum. Total cellular activity of K-562 cells corresponds to 30 and 60% of that found respectively in human granulocytes and promyelocytic human HL 60 cells. Induction by hemin of erythroid differentiation in K-562 cells leads to a reversible decrease in collagenolytic activity which is concomitant with the recruitment of hemoglobin-synthesizing cells. The use of spontaneously low and highly hemoglobinized clones of K-562 cells confirms that collagenolytic activity is inversely correlated with the hemoglobin content.