[Studies on the microtubules assembly of multidrug-resistant human leukemic cells].

The development of drug resistance in cancer cells is a significant clinical problem for the successful cancer chemotherapy. Since the cytoskeleton, including microtubules, may be involved in modulating cellular signal transduction, morphological and structural changes, the microtubules assembly of multidrug resistant cells was examined using Confocal Laser Microscope MRC500 system (Bio Rad). In this study, multidrug resistant cells were established by the continuous exposure to ADR(adriamycin) starting with 20 nM up to 1 microM. The expression of MDR-1 (multidrug resistance) gene was detected in K562 leukemia cells and to more extent in the multidrug resistant K562/ADR cells, but not in HL-60 leukemia cells and multidrug resistant HL-60/ADR cells by RT-PCR method. The chronological features of microtubules assembly in the parent cell lines were lost on day 3, after incubation with 20nM of ADR. In accordance with development of drug resistance, the microtubules assembly appeared to be more dense and stronger than that of parent cells. During the development of drug resistant cells, the ADR-accumulation in the nucleus was decreased according to the increase of microtubules assembly. In the case of incubation with 0.5 microM colcemid, an inhibitor of microtubules polymerization, for 3 hours, the stainings of microtubules were lost their fine network and appeared to be diffuse and dot-like pattern. At the same time, both untreated HL-60/ADR and K562/ADR showed the decrease of ADR-accumulation, but the accumulations both colcemid treated resistant cells were increased the same level of their parent cells at the point of 120 min. These results suggested that the resistance to ADR in human leukemia cells correlated with microtubules assembly, and the microtubules assembly played an important role of drug resistance with or without MDR-1 gene overexpression.