G. Rappa et al., OVEREXPRESSION OF THE MULTIDRUG-RESISTANCE GENES MDR1, MDR3, AND MRP IN L1210 LEUKEMIA-CELLS RESISTANT TO INHIBITORS OF RIBONUCLEOTIDE REDUCTASE, Biochemical pharmacology, 54(6), 1997, pp. 649-655
L1210 MQ-580 is a murine leukemia cell line resistant to the cytotoxic
activity of the alpha-(N)-heterocyclic carboxaldehyde thiosemicarbazo
ne class of inhibitors of ribonucleotide reductase. The line is cross-
resistant to etoposide, daunomycin, and vinblastine. L1210 MQ-580 cell
s expressed 8-fold resistance to 3-aminopyridine-2-carboxaldehyde thio
semicarbazone (3-AP), a relatively newly developed inhibitor of ribonu
cleotide reductase. The accumulation of [C-14]3-AP by L1210 MQ-580 cel
ls was 5- to 6-fold less than by parental L1210 cells. An increased ra
te of efflux of 3-AP was responsible for the lower steady-state concen
tration of 3-AP in resistant cells. In reverse transcription-polymeras
e chain reaction assays, L1210 MQ-580 cells were found to overexpress
the multidrug resistance genes mdr1, mdr3, and mrp, but not the mdr2 g
ene, compared with parental L1210 cells. Measurement of the steady-sta
te concentration of doxorubicin, a potential substrate for both the md
r and mrp gene products, demonstrated that L1210 MQ-580 cells accumula
ted 4-fold less anthracycline than parental cells. These findings indi
cate that drug efflux is a major determinant of the pattern of cross-r
esistance of L1210 MQ-580 cells. To extrapolate these observations to
the human homologues of the mdr1, mdr3, and mrp murine genes, the effe
cts of 3-AP were measured in L1210/VMDRC0.06 and NIH3T3 36-8-32 cells
transfected with human MDR1 and MRP cDNAs, respectively. The transfect
ants were 2- to 3-fold resistant to the cytotoxic effects of 3-AP and
accumulated less [C-14]3-AP than their parental mock-transfected count
erparts. Moreover, the cytotoxic activity of 3-AP was significantly gr
eater in two double mrp gene knockout cell lines than in parental W 9.
5 embryonic stem cells. Thus, the results suggest that 3-AP is a subst
rate for both the P-glycoprotein and MRP and that baseline MRP express
ion has the capacity to exert a protective role against the toxicity o
f this agent. (C) 1997 Elsevier Science Inc.