Early multidrug resistance, defined by changes in intracellular doxorubicin distribution, independent of P-glycoprotein.
Resistance to multiple antitumour drugs, mostly antibiotics or alkaloids, has been associated with a cellular plasma membrane P-glycoprotein (Pgp), causing energy-dependent transport of drugs out of cells. However, in many common chemotherapy resistant human cancers there is no overexpression of Pgp, which could explain drug resistance. In order to characterise early steps in multidrug resistance we have derived a series of P-glycoprotein-positive (Pgp/+) and P-glycoprotein-negative (Pgp/-) multidrug resistant cell lines, from a human non-small cell lung cancer cell line, SW-1573, by stepwise selection with increasing concentrations of doxorubicin. These cells were exposed to doxorubicin and its fluorescence in nucleus (N) and cytoplasm (C) was quantified with laserscan microscopy and image analysis. The fluorescence N/C ratio in parent cells was 3.8 and decreased both in Pgp/+ and Pgp/- cells with increasing selection pressure to 1.2-2.6 for cells with a resistance factor of 7-17. N/C ratios could be restored partly with verapamil only in Pgp/+ cells. N/C ratio measurements may define a general Pgp-independent type of defense of mammalian cells against certain anticancer agents which may precede Pgp expression in early doxorubicin resistance.
Department of Medical Oncology, Amsterdam, The Netherlands.
G J
GJ
Schuurhuis
H J
HJ
Broxterman
J H
JH
de Lange
H M
HM
Pinedo
T H
TH
van Heijningen
C M
CM
Kuiper
G L
GL
Scheffer
R J
RJ
Scheper
C K
CK
van Kalken
J P
JP
Baak
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000493:pharmacokinetics*; D004351:Drug Resistance / Q000235:genetics / Q000502:physiology; D005453:Fluorescence; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000502:physiology*; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D008562:Membrane Glycoproteins; D004317:Doxorubicin