title: Cross-resistance studies of isogenic drug-resistant breast tumor cell lines support recent clinical evidence suggesting that sensitivity to paclitaxel may be strongly compromised by prior doxorubicin exposure.
abstract: Less than half of breast cancer patients respond to second-line chemotherapy with paclitaxel after failing treatment with anthracyclines such as doxorubicin. A recent clinical trial by Paridaens et al. [J. Clin. Oncol. 18 : 724-733, 2000] examined whether patients may derive a better clinical benefit if paclitaxel was administered before doxorubicin. While overall survival was similar regardless of the order of drug administration, a >4-fold reduction in the response rate to paclitaxel was observed after late crossover from doxorubicin, compared to the response rate to doxorubicin after late crossover from paclitaxel. This may be related to differences in the ability of the drugs to induce cross-resistance to each other. To test this hypothesis, we examined whether isogenic breast tumor cells selected for resistance to doxorubicin exhibit greater cross-resistance to paclitaxel and other drugs than identical cells selected for resistance to paclitaxel. We found that cells selected for resistance to paclitaxel showed strong resistance (>/=40-fold) to paclitaxel and docetaxel, with little cross-resistance (4-fold) to doxorubicin. In contrast, cells selected for resistance to doxorubicin exhibited 50-fold resistance to doxorubicin and a dramatic 4700-fold and 14,600-fold cross-resistance to paclitaxel and docetaxel, respectively. Doxorubicin-resistant cells exhibited higher P-glycoprotein and breast cancer resistance protein (BCRP) levels than paclitaxel-resistant cells. In addition, procaspase-9 was strongly downregulated in doxorubicin-resistant cells but not in paclitaxel-resistant cells. These differences may account for the contrasting cross-resistance profiles observed for the two cell lines and may help to explain why treatment of breast cancer patients with paclitaxel appears to be compromized by prior doxorubicin exposure.
authors.affiliation: Tumor Biology Research Program, Northeastern Ontario Regional Cancer Centre, Sudbury, Ont., Canada.
authors.forename: Baoqing
authors.initials: B
authors.lastname: Guo
authors.forename: David J
authors.initials: DJ
authors.lastname: Villeneuve
authors.forename: Stacey L
authors.initials: SL
authors.lastname: Hembruff
authors.forename: Angie F
authors.initials: AF
authors.lastname: Kirwan
authors.forename: David E
authors.initials: DE
authors.lastname: Blais
authors.forename: Michel
authors.initials: M
authors.lastname: Bonin
authors.forename: Amadeo M
authors.initials: AM
authors.lastname: Parissenti
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000187:drug effects; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000187:drug effects; D000230:Adenocarcinoma / Q000188:drug therapy* / Q000503:physiopathology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000503:physiopathology; D053453:Caspase 9; D020169:Caspases / Q000187:drug effects; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000494:pharmacology*; D004347:Drug Interactions / Q000502:physiology; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D006801:Humans; D009363:Neoplasm Proteins / Q000187:drug effects; D017239:Paclitaxel / Q000494:pharmacology*
chemical_list: C116614:ABCG2 protein, human; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D009363:Neoplasm Proteins; D004317:Doxorubicin; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; D017239:Paclitaxel