Kinetics of MDR transport in tumor-initiating cells.
Multidrug resistance (MDR) driven by ABC (ATP binding cassette) membrane transporters is one of the major causes of treatment failure in human malignancy. MDR capacity is thought to be unevenly distributed among tumor cells, with higher capacity residing in tumor-initiating cells (TIC) (though opposite finding are occasionally reported). Functional evidence for enhanced MDR of TICs was previously provided using a "side population" assay. This assay estimates MDR capacity by a single parameter - cell's ability to retain fluorescent MDR substrate, so that cells with high MDR capacity ("side population") demonstrate low substrate retention. In the present work MDR in TICs was investigated in greater detail using a kinetic approach, which monitors MDR efflux from single cells. Analysis of kinetic traces obtained allowed for the estimation of both the velocity (V max) and affinity (K M) of MDR transport in single cells. In this way it was shown that activation of MDR in TICs occurs in two ways: through the increase of V max in one fraction of cells, and through decrease of K M in another fraction. In addition, kinetic data showed that heterogeneity of MDR parameters in TICs significantly exceeds that of bulk cells. Potential consequences of these findings for chemotherapy are discussed.
Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada.
Vasilij
V
Koshkin
Burton B
BB
Yang
Sergey N
SN
Krylov
D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002455:Cell Division; D045744:Cell Line, Tumor; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005434:Flow Cytometry; D019793:Fluorescein / Q000378:metabolism; D016193:G1 Phase; D016195:G2 Phase; D005905:Glyburide / Q000494:pharmacology; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism; D007700:Kinetics; D061986:MCF-7 Cells; D008856:Microscopy, Fluorescence; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D051918:Sialic Acid Binding Ig-like Lectin 2 / Q000378:metabolism; D018874:Spheroids, Cellular / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D019793:Fluorescein; D005905:Glyburide; D018960:Hyaluronan Receptors; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D051918:Sialic Acid Binding Ig-like Lectin 2; C421109:multidrug resistance-associated protein 1