M. Osmak et al., INHIBITION OF APOPTOSIS IS THE CAUSE OF RESISTANCE TO DOXORUBICIN IN HUMAN BREAST ADENOCARCINOMA CELLS, Neoplasma, 45(4), 1998, pp. 223-230
In our previous paper we have described the isolation and characteriza
tion of a doxorubicin (DOX) resistant subline of breast adenocarcinoma
SC6 cells. These cells were obtained after the treatment with low, cl
inically relevant doses of doxorubicin. They became cross-resistant to
different wide used cytostatics. The expression of several genes invo
lved in mitotic signal transduction, as well as cathepsins D and L, wa
s similar in both parental and doxorubicin treated cells. The aim of t
his study was to examine the molecular mechanisms involved in resistan
ce of these cells to doxorubicin. Activity of plasma membrane Pgp was
examined in parental and resistant cells due to rhodamine-accumulation
assay. The involvement of glutathione (GSH) and glutathione S-transfe
rase (GST) in resistance to doxorubicin was determined in MTT modified
assay due to the addition of specific inhibitors: buthionine sulfoxim
ine (for GSH) or ethacrynic acid (for GST). The kinetic of apoptosis w
as followed after the treatment with DOX in control and SC6 cells by f
luorescent microscope. The occurrence of apoptosis was confirmed by an
alysing DNA fragmentation in agarose gel. Our results indicate that P-
glycoprotein, glutathione or glutathione transferases were not involve
d in resistance of SC6 cells to doxorubicin. However, the apoptosis wa
s inhibited in doxorubicin-resistant cells. Therefore, even low doses
of doxorubicin can induce the resistance to this drug due to inhibitio
n of apoptosis.