OBJECTIVETo establish a homoharringtonine (HHT)-resistant SKM-1 cell line and explore its biologic characteristics and mechanisms for drug resistance.

METHODSThe HHT-resistant SKM-1 cell line was established by repeatedly exposing the cells to comparatively large doses of HHT with a short-time duration, and gradually elevating the drug concentration to an endurable level. The morphology of the resistant and parental cell lines was observed through optical microscope. The MTT assay was used to determine the doubling time and the resistance index to draw growth curve. The immunophenotype, cell cycle distribution and DNR accumulation between SKM-1 and SKM-1/HHT were analyzed by flow cytometry, and the karyotypes by R-banding. Semi-quantitative real-time PCR was performed to evaluate the expression levels of mdr1, MRP and topo-IIa.

RESULTSThe HHT-resistant cell line SKM-1/HHT was eventually established following 7-month drug induction. Both the resistant and the parental cell lines were similar with regard to morphology and immunophenotype. The karyotypes of the former was more complicated with differences located in chromosome 20, X, 4, 5, 9 and 11. The resistant cell line had more G(1) phase cells (64.04% vs 41.91%), less S phase cells (34.92% vs 53.53%), and less G(2) phase cells (1.04% vs 4.56%) compared with the parental cell line. The SKM-1/HHT cell line showed significant drug resistance to HHT, VCR, DNR and etoposide, the resistance indices of HHT, VCR, DNR and etoposide were 17.94, 8.75, 5.99 and 13.76 respectively. DNR accumulation was impaired in SKM-1/HHT cell line as less fluorescence of DNR (698 ± 36 vs 858 ± 54). The expression of mdr1 increased dramatically in the resistant cell line, its 2(-ΔCt) value was 20.1 higher than that of the parental cell line \[(3.42 ± 0.46)×10(-2) vs (0.17 ± 0.01)×10(-2), P < 0.05\], while MRP also increased in the resistant by 3.56 folds \[(4.77 ± 0.87)×10(-3) vs (1.34 ± 0.56)×10(-3), P < 0.05\]; However there was a slightly decrease of topo-IIa, the ratio of the resistant to the parental calculated by their 2(-ΔCt) values was 0.619:1 \[(1.91 ± 0.30)×10(-4) vs (3.08 ± 0.21)×10(-4), P < 0.05\].

CONCLUSIONA HHT-resistant cell line SKM-1/HHT was established. The prominent overexpression of mdr1 may be the main cause for multidrug resistance.