title: Effects of mitomycin C and carboplatin pretreatment on multidrug resistance-associated P-glycoprotein expression and on subsequent suppression of tumor growth by doxorubicin and paclitaxel in human metastatic breast cancer xenografted nude mice.
abstract: Overexpression of P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP), and several other proteins has been associated with development of multidrug resistance by cancer cells, which represents a significant obstacle to successful treatment by chemotherapy. We had previously demonstrated that a single noncytotoxic dose of mitomycin C (MMC), carboplatin, or one of several other DNA cross-linking agents suppressed mRNA expression of the mdr1 gene coding for Pgp, leading to a subsequent suppression of Pgp protein levels and a concomitant decrease in drug efflux. Pretreatment with MMC led to a 5- to 10-fold decrease in the ED50 for cell killing by a subsequent agent such as the Pgp substrate, doxorubicin, but did not affect killing by the non-Pgp substrate, cisplatin. In this study, we report that MMC and carboplatin each significantly suppressed Pgp protein levels in human MDA-MB-435 cells xenografted as solid tumors into the lateral mammary fat pads of female nude mice, with a similar time course as had previously been observed in cell culture. Pretreatment of mice with MMC or carboplatin 48-72 h prior to receiving either doxorubicin or paclitaxel caused a significantly greater reduction in tumor growth rate compared to either agent alone or the combination given simultaneously. These data suggest that a combination chemotherapy regimen consisting of a DNA cross-linking agent given to modulate the MDR phenotype, followed by a second cytotoxic agent, may be an effective treatment for human patients with de novo or late stage acquired multidrug-resistant malignancies.
authors.affiliation: Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, NH 03755-3835, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Ihnat
authors.forename: A M
authors.initials: AM
authors.lastname: Nervi
authors.forename: S P
authors.initials: SP
authors.lastname: Anthony
authors.forename: R C
authors.initials: RC
authors.lastname: Kaltreider
authors.forename: A J
authors.initials: AJ
authors.lastname: Warren
authors.forename: C A
authors.initials: CA
authors.lastname: Pesce
authors.forename: S A
authors.initials: SA
authors.lastname: Davis
authors.forename: J P
authors.initials: JP
authors.lastname: Lariviere
authors.forename: J W
authors.initials: JW
authors.lastname: Hamilton
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D016190:Carboplatin / Q000494:pharmacology / Q000627:therapeutic use*; D004317:Doxorubicin / Q000627:therapeutic use; D004347:Drug Interactions; D018432:Drug Resistance, Multiple / Q000502:physiology; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D016685:Mitomycin / Q000627:therapeutic use*; D009363:Neoplasm Proteins / Q000187:drug effects* / Q000378:metabolism; D017239:Paclitaxel / Q000627:therapeutic use; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D009363:Neoplasm Proteins; D016685:Mitomycin; D004317:Doxorubicin; D016190:Carboplatin; D017239:Paclitaxel