The hallmark of CML (chronic myeloid leukaemia) is the BCR (breakpoint cluster region) –ABL fusion gene. CML evolves through three phases, based on both clinical and pathological features: a chronic phase, an accelerated phase and blast crisis. TKI (tyrosine kinase inhibitors) are the treatment modality for patients with chronic phase CML. The therapeutic potential of the TKI imatinib is affected by BCR–ABL dependent an independent mechanisms. Development of MDR (multidrug resistance) contributes to the overall clinical resistance. MDR involves overexpression of ABC -transporters (ATP-binding-cassette transporter) among other features. MDR studies include the analysis of cancer cell lines selected for resistance. CML blast crisis is accompanied by increased resistance to apoptosis. This work reviews the role played by the influx transporter OCT1 (organic cation transporter 1), by efflux ABC transporters, molecules involved in the modulation of apoptosis (p53, Bcl-2 family, CD95, IAPs (inhibitors of apoptosis protein)], Hh and Wnt/β-catenin pathways, cytoskeleton abnormalities and other features described in leukaemic cells of clinical samples and CML cell lines. An MDR cell line, Lucena-1, generated from K562 by stepwise exposure to vincristine, was used as our model and some potential anticancer drugs effective against the MDR cell line and patients’ samples are presented.
The present report shows that thymocyte death, induced by glucocorticoids, may be modulated in vivo by ouabain. Young, ten days old, mice injected with 140 mg/kg sodium succcinate of hydrocortisone (HC) intraperitonially (i.p.) displayed, 24 h after the injection, a decrease in thymus size and cellular content, an effect that was magnified when ouabain (OUA) 0.56 mg/kg, i.p. was given 1 h prior to the HC injection. Ouabain per se was not capable of producing these changes. Both HC and the combination OUA plus HC induced the death of immature double positive lymphocytes (CD4 + CD8 + ) whereas CD69 + cells survived both treatments. An increase in annexin positive cells and a decrease in mitochondrial membrane potential, assessed by cytofluorimetry, using the fluorescent dye DiOC 6 , was observed in thymocytes from HC treated animals indicating apoptosis of these cells. Furthermore, a synergistic effect between OUA and HC was also observed using this parameter. The synergy observed in the thymus of animals treated with glucocorticoids and OUA might occur under stress, when both hormones are released, or in situations when ouabain is administered exogenously in a moment of the circadian cycle when glucocorticoid levels are elevated. However the impact of this effect on the immune response is still unknown.
P -glycoprotein has a widespread expression on normal tissues. The protein has also been strongly associated with the multidrug resistance phenotype (MDR) on tumor cells. The employment of flow cytometry and confocal microscopy has contributed to the discovery and application of new particular fluorescent dyes. Nevertheless, several studies are being performed in different cellular types neglecting the expression activity of MDR proteins. Because many fluorochromes have been reported as P -glycoprotein substrates, an especial attention must be given to the properties of new dyes in the presence of MDR proteins. Flow cytometric analyzes of Mitotracker Green (MTG) fluorescence profile were performed in a human erythroleukemic cell line and its resistant counterpart. In this report we demonstrated that MTG, a probe used to evaluate the mitochondrial mass, is a P -glycoprotein substrate and its staining profile is dependent on the activity of this protein. In vitro studies on a human erythroleukemic cell line and its resistant counterpart revealed that MDR modulators (Cyclosporin A, Verapamil, and Trifluoperazine) alter the MTG fluorescence pattern on a resistant cell line. The findings suggest that attention should be given to the expression of P -glycoprotein when performing an evaluation of mitochondria properties with MTG.
Apoptotic cell death plays a critical role in immune system homeostasis, and c- myc protooncogene deregulated expression is a component of this programmed genomic response. Pharmacological intervention and modulation of peripheral lymphocytes apoptosis would have important implications. The present results indicate that ouabain, a specific inhibitor of Na + K + -ATPase, promotes an increased expression of c- myc mRNA, and induces apoptosis in PHA-stimulated lymphocytes. Furthermore, this ouabain-induced apoptosis cannot be counteracted by the addition of exogenous IL-2.