Kinetics of MDR transport in tumor-initiating cells.

Vasilij Koshkin,Burton B Yang,Sergey N Krylov

doi:10.1371/journal.pone.0079222

Vasilij Koshkin, Burton B Yang + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0079222

Copy DOI

Abstract

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.

Highlights

One of the most important aspects of tumor heterogeneity is the existence of tumor-initiating cells (TICs) responsible for both the initiation of cancers and dissemination of metastases [1,2]
We found that activation of Multidrug resistance (MDR) transport in TICs, compared to transport in bulk cells, is highly heterogeneous and realized by two alternative mechanisms
We examined the generality of kinetic MDR features found in TICs of MCF-7 cell line by studying MDR efflux in murine breast cancer cell line 4T1

Summary

Introduction

One of the most important aspects of tumor heterogeneity is the existence of tumor-initiating cells (TICs) responsible for both the initiation of cancers and dissemination of metastases [1,2]. Besides their elevated proliferative and invasive capacity, these cells demonstrate high resistance to anticancer treatments, in particular, to chemotherapy (chemoresistance). The overall functional characterization of MDR in TICs to date has been provided by a widely used flow cytometric side population assay This assay is based on the differential accumulation of a fluorescent MDR substrate, Hoechst 33342, in cancer cells. The cells exhibiting low Hoechst retention are considered as having high MDR capacity and referred to as the “side population”[4]

Objectives

Methods

Results

Conclusion