Rapid doxorubicin efflux from the nucleus of drug-resistant cancer cells following extracellular drug clearance.
OBJECTIVE
Following extracellular drug clearance, we analyzed the rate of doxorubicin efflux from the nucleus of three human leukemic cells (K562, Molt4 and CCRF-CEM) and related it to their differential sensitivity to this drug, after a short drug pulse.


RESULTS
For many pulse-chase regimes, K562 cell viability was least affected by doxorubicin. In K562 cells, nuclear drug accumulation was greatest, but nuclear drug egress was also greatest. P-glycoprotein over-expression in a doxorubicin-resistant, K562/DOX sub-line did not facilitate doxorubicin efflux from the nucleus. In K562 cells, doxorubicin accumulated in multivesicular bodies (MVBs) through a pH-dependent mechanism. Inhibiting drug sequestration in MVBs did not affect nuclear efflux. The rates of doxorubicin efflux from the nuclei of live and digitonin-permeabilized K562 cells were similar. However, extracting cytoplasmic membranes with Triton X-100 significantly inhibited nuclear drug efflux following extracellular drug clearance.


CONCLUSIONS
Our results are consistent with drug efflux from the nucleus being primarily mediated by an ATP-independent, passive diffusion mechanism. The effect of membrane extraction suggests that nonspecific drug absorption to cytoplasmic membranes plays a role in facilitating nuclear efflux in K562 cells, perhaps by lowering the concentration of free doxorubicin from a perinuclear diffusion boundary layer.
Department of Pharmaceutical Sciences, University of Michigan College of Pharmacy, 428 Church St., Ann Arbor, MI 48109, USA.
Vivien Y
VY
Chen
Maria M
MM
Posada
Lili
L
Zhao
Gus R
GR
Rosania
D021581:Active Transport, Cell Nucleus; D000255:Adenosine Triphosphate / Q000502:physiology; D000643:Ammonium Chloride / Q000494:pharmacology; D000903:Antibiotics, Antineoplastic / Q000378:metabolism*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D003593:Cytoplasm / Q000378:metabolism; D004317:Doxorubicin / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D004705:Endocytosis; D006801:Humans; D020014:K562 Cells; D008561:Membrane Fusion; D008657:Metabolic Clearance Rate
D000903:Antibiotics, Antineoplastic; D000643:Ammonium Chloride; D004317:Doxorubicin; D000255:Adenosine Triphosphate