title: Differential effects of toremifene on doxorubicin, vinblastine and Tc-99m-sestamibi in P-glycoprotein-expressing breast and head and neck cancer cell lines.
abstract: The effect of toremifene on P-glycoprotein-mediated multidrug resistance (MDR) in breast and head and neck cancer cell lines was measured in vitro and in vivo. Pgp expression was low and high, respectively, in drug-sensitive (MCF7-S, KB) and drug-resistant (MCF7-R, MCF7-R1, KBV1) cell lines. Toremifene (7.5 microM) significantly enhanced cytoplasmic and nuclear accumulation of doxorubicin in drug-resistant cells. Toremifene (10 microM) increased the in vitro cytotoxicity of doxorubicin in drug-resistant breast cancer cells (13-fold and 21-fold for MCF7-R and MCF7-R1, respectively) without affecting the sensitivity of MCF7-S cells. Similarly, toremifene (10 microM) caused a 12-fold increase in the sensitivity of KBV1 cells to vinblastine. In contrast, toremifene (5 microM) reduced the net uptake of the radiolabelled Pgp substrate, Tc-99m-sestamibi, in the Pgp-overexpressing cell lines by factors of 0.32 and 0.42 for MCF7-R1 and KBV1 cells, respectively (p < 0.01), and, to a lesser extent, by corresponding factors of 0.89 and 0.86 in the drug-sensitive cell lines (p < 0.05 and p > 0.05, respectively). In nude mice bearing both KB and KBV1 xenograft tumours, significantly higher tumour levels of Tc-99m-sestamibi were recorded in KB tumours compared with KBV1 tumours. After 3 days of treatment with intraperitoneal toremifene (25 mg/kg), tumour levels of Tc-99m-sestamibi were reduced in KB and KBV1 tumours but only statistically significantly for KB tumours. Toremifene is a potent MDR modulating agent with respect to chemotherapeutic agents but has the opposite effect with respect to Tc-99m-sestamibi. This finding is of importance in view of the widespread use of Tc-99m-sestamibi as an imaging surrogate for a chemotherapeutic agent.
authors.affiliation: Department of Imaging, Hammersmith Hospital, London, UK.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Mubashar
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Harrington
authors.forename: Khurram S
authors.initials: KS
authors.lastname: Chaudhary
authors.forename: El-Nasir
authors.initials: el-N
authors.lastname: Lalani
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Stamp
authors.forename: A Michael
authors.initials: AM
authors.lastname: Peters
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis*; D000818:Animals; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000493:pharmacokinetics* / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005260:Female; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008856:Microscopy, Fluorescence; D017256:Technetium Tc 99m Sestamibi / Q000493:pharmacokinetics*; D017312:Toremifene / Q000494:pharmacology*; D014747:Vinblastine / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D014747:Vinblastine; D017312:Toremifene; D004317:Doxorubicin; D017256:Technetium Tc 99m Sestamibi