Ma. Izquierdo et al., OVERLAPPING PHENOTYPES OF MULTIDRUG-RESISTANCE AMONG PANELS OF HUMAN CANCER-CELL LINES, International journal of cancer, 65(2), 1996, pp. 230-237
In addition to P-glycoprotein (Pgp), 2 proteins related to multidrug r
esistance (MDR) have recently been described. The Multidrug-Resistance
-associated protein (MRP) is one of the ATP-binding-cassette (ABC) tra
nsporters. The Lung-Resistance Protein (LRP) is the major component of
human vaults, which are newly described cellular organelles and thoug
ht to mediate intracellular transport processes. Using immunocytochemi
cal methods, we have examined the expression of MRP and LRP among pane
ls of human cancer-cell lines not selected for drug resistance which h
ave been previously characterized for expression of Pgp, and in vitro
response to a variety of anti-cancer drugs. Expression of MRP and LRP
was observed in 47/55 (87%) and 46/59 (78%) cell lines, respectively.
Statistically significant correlations were observed between expressio
n of each of these 3 proteins and in vitro sensitivity to at least one
drug classically associated with MDR. LRP showed the greatest individ
ual predictive value, which also applied to several nonclassical MDR d
rugs. Co expression of 2-3 MDR-related proteins was observed in 64% of
the lines and was, in general, associated with high relative levels o
f drug resistance. Previously identified ''classic'' MDR lines as well
as ''pan-resistant'' lines concurrently expressed all 3 MDR-related p
roteins. Some highly drug-resistant cell lines without detectable MDRI
/Pgp were found to express relatively high levels of MRP and LRP. The
high prevalence of MRP and LRP expression observed in this large set o
f cell lines, which have not been subjected to laboratory drug selecti
on, suggests that MDR mechanisms associated with these proteins may be
widespread in human malignancies. Moreover, the overlapping of these
more recently recognized MDR phenotypes with Pgp-type MDR results in a
complex phenotype, the understanding of which may be of importance in
the development of new drugs and design of clinical treatment protoco
ls, particularly those seeking to employ strategies to reverse the MDR
phenotype. (C) 1996 Wiley-Liss, Inc.