Resistance to etoposide in human leukemia HL-60 cells: reduction in drug-induced DNA cleavage associated with hypophosphorylation of topoisomerase II phosphopeptides.
Tumor cell resistance to anthracyclines and epipodophyllotoxins can be due to reduced drug accumulation and/or alterations in the activity of topoisomerase II (TOPO II). HL-60 cells selected in 0.05 micrograms/ml doxorubicin (DOX) are 10-fold and > 20-fold resistant to DOX and etoposide (VP-16), respectively. The accumulation of [3H]VP-16 was 2-3-fold lower in the resistant cells (HL-60/DOX 0.05) than in similarly treated parent-sensitive cells (HL-60/S). However, compared with HL-60/S cells, the HL-60/DOX 0.05 cells required > 20-fold higher concentrations of VP-16 to produce equivalent damage to DNA. The reduced formation of VP-16-stabilized DNA cleavable complex in the HL-60/DOX 0.05 cells was not due to differences in the amount of 170-kDa TOPO (alpha) II protein or enzyme catalytic activity between HL-60/S and HL-60/DOX 0.05 cells. Metabolic labeling with [32P]orthophosphoric acid and immunoprecipitation indicated that the level of phosphorylated 170-kDa TOPO II alpha protein in the HL-60-/S cells was 2.2 +/- 0.4-fold higher than that in HL-60/DOX 0.05 cells. Hypophosphorylation (3-fold) of 170-kDa TOPO II protein in HL-60/S cells treated with the calcium chelator 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester produced a > 2-fold reduction in VP-16-induced TOPO II-mediated DNA cleavable complex formation. Two-dimensional mapping of phosphopeptides in complete tryptic digests demonstrated that the reduced phosphorylation of the 170-kDa TOPO II alpha in HL-60/DOX 0.05 cells was due to the hypophosphorylation of at least three phosphopeptides characteristic of HL-60/S cells. Thus, the attenuated ability of TOPO II to form drug-stabilized DNA cleavable complex is related to the phosphorylated state of 170-kDa TOPO II, and in HL-60/DOX 0.05 cells, resistance may be related to hypophosphorylation of three phosphopeptides characteristic of HL-60/S cells.
Ganapathi
R
R
Department of Cancer Biology, Cleveland Clinic Foundation, Ohio 44195, USA.
Constantinou
A
A
Kamath
N
N
Dubyak
G
G
Grabowski
D
D
Krivacic
K
K
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D004247:DNA / Q000187:drug effects*; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004317:Doxorubicin / Q000494:pharmacology; D004351:Drug Resistance; D005047:Etoposide / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans; D010766:Phosphorylation
D000972:Antineoplastic Agents, Phytogenic; D005047:Etoposide; D004317:Doxorubicin; D004247:DNA; D004250:DNA Topoisomerases, Type II