Liposome-mediated modulation of multidrug resistance in human HL-60 leukemia cells

Aquilur Rahman, Syed R. Husain, Javed Siddiqui, Madhu Verma, Michael Agresti, Melvin Center, Ahmad R. Safa, Robert I. Glazer

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Background: Multidrug resistance (MDR) is a major obstacle in cancer treatment. Resistance of cultured tumor cells to major classes of cytotoxic drugs is frequently due to expression of a plasma membrane P-glycoprotein encoded by MDR genes. We have demonstrated that liposome-encapsulated doxorubicin is more toxic than the free drug and that it modulates MDR in Chinese hamster LZ cells and human colon cancer cells. Purpose: To investigate further the association between expression of P-glycoprotein and modulation of MDR by liposome-encapsulated doxorubicin, we studied vincristine-resistant HL-60/VCR leukemia cells, which express P-glycoprotein, and doxorubicin-resistant HL-60/ADR leukemia cells, which do not. Methods: Cells were exposed to various concentrations of free doxorubicin and liposome-encapsulated doxorubicin. The cellular content of doxorubicin was determined by fluorescence analysis, and cytotoxicity was determined by cell growth inhibition. Photoaffinity-labeling studies of P-glycoprotein binding were performed on HL-60/VCR and HL-60/ADR cells and KB-GSV2 cells transfected with the MDR1 gene (also known as PGY1). Results: The concentrations that caused 50% inhibition of growth (IC50) for free doxorubicin in HL-60, HL-60/ADR, and HL-60/VCR cells were 30 nM, 9 μM, and 0.9 μM, respectively. The values for liposome-encapsulated doxorubicin in parental HL-60 cells and HL-60/ADR cells were 20 nM and 9 μM, respectively, indicating little or no sensitization. In contrast, HL-60/VCR cells were fivefold more sensitive to liposome-encapsulated doxrubicin than to free doxorubicin, and IC50 was reduced to 0.17 μM. In HL-60 cells exposed to liposome-encapsulated doxorubicin, intracellular doxorubicin accumulation was less than that seen with free drug. In contrast, in HL-60/VCR cells, accumulation was twofold to threefold higher than that with free doxorubicin. Liposome-encapsulated doxorubicin completely inhibited the photoaffinity labeling of P-glycoprotein by azidopine in membrane vesicles of HL-60/VCR cells, with a potency comparable to that of azidopine, suggesting that circumvention of MDR by liposomes is related to their specific interaction with P-glycoprotein. The studies with KB-GSV2 cells indicated that blank liposomes can directly inhibit photoaffinity labeling of P-glycoprotein. Conclusions: These results demonstrate the effectiveness of liposome-encapsulated doxorubicin in overcoming resistance in the multidrug-resistant phenotype of HL-60/VCR cells by direct interaction with P-glycoprotein. Furthermore, they in dicate that liposome-encapsulated doxorubicin may be an effective tretment for human cancers. [J Natl Cancer Inst 84:1909-1915, 1992]

Original languageEnglish (US)
Pages (from-to)1909-1915
Number of pages7
JournalJournal of the National Cancer Institute
Issue number24
StatePublished - Dec 16 1992
Externally publishedYes

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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    Rahman, A., Husain, S. R., Siddiqui, J., Verma, M., Agresti, M., Center, M., Safa, A. R., & Glazer, R. I. (1992). Liposome-mediated modulation of multidrug resistance in human HL-60 leukemia cells. Journal of the National Cancer Institute, 84(24), 1909-1915.