title: Spontaneous reversal of p-glycoprotein expression in multidrug resistant cell lines.
abstract: Increased expression of P-glycoprotein encoded by the mdr-1 gene is a well-characterised mechanism for resistance to cancer chemotherapeutic drugs in cell lines. However, the P-glycoprotein expression after removal of the selection pressure has not fully been elucidated. The stability of P-glycoprotein expression in the presence (+) and absence (-) of vincristine (30 or 150 nM) was studied in multidrug resistant K562 cell lines (VCR30+, VCR150+, VCR30- and VCR150-) for 11 months. The P-glycoprotein protein and mdr-1 mRNA levels were determined at regular intervals using flow cytometry and real-time PCR, respectively. Chemosensitivity to a panel of antineoplastic drugs was measured using an MTT assay. The presence of vincristine (VCR30+ and VCR150+) resulted in high and stable levels of P-glycoprotein and mdr-1 mRNA during the whole period compared to wild type. As for the VCR30- and VCR150- subcultures, the expressions of P-glycoprotein and mdr-1 mRNA were stable for five months, and then the levels decreased rapidly. Concomitantly, the sensitivity to drugs known as P-glycoprotein substrates was restored. In conclusion, resistant cells growing in the presence of the inducing drug have a stable P-glycoprotein expression and resistance level, but removing the inducing drug may result in a sudden and rapid lowering of P-glycoprotein and mdr-1 mRNA levels as long as five months after drug withdrawal.
authors.affiliation: Division of Clinical Pharmacology, Department of Medicine and Care, Faculty of Health Sciences, Linköping University, SE-581 85 Linköping, Sweden. henrik.green@imv.liu.se
authors.forename: Henrik
authors.initials: H
authors.lastname: Gréen
authors.forename: Kourosh
authors.initials: K
authors.lastname: Lotfi
authors.forename: Anna-Lena
authors.initials: AL
authors.lastname: Zackrisson
authors.forename: Curt
authors.initials: C
authors.lastname: Peterson
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor / Q000187:drug effects*; D005434:Flow Cytometry; D019450:Genes, MDR / Q000187:drug effects*; D006801:Humans; D012313:RNA / Q000302:isolation & purification
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D012313:RNA