title: Synergistic activity of letrozole and sorafenib on breast cancer cells.
abstract: Estrogens induce breast tumor cell proliferation by directly regulating gene expression via the estrogen receptor (ER) transcriptional activity and by affecting growth factor signaling pathways such as mitogen-activated protein kinase (MAPK) and AKT/mammalian target of rapamycin Complex1 (mTORC1) cascades. In this study we demonstrated the preclinical therapeutic efficacy of combining the aromatase inhibitor letrozole with the multi-kinase inhibitor sorafenib in aromatase-expressing breast cancer cell lines. Treatment with letrozole reduced testosterone-driven cell proliferation, by inhibiting the synthesis of estrogens. Sorafenib inhibited cell proliferation in a concentration-dependent manner; this effect was not dependent on sorafenib-mediated inhibition of Raf1, but involved the down-regulation of mTORC1 and its targets p70S6K and 4E-binding protein 1 (4E-BP1). At concentrations of 5-10 μM the growth-inhibitory effect of sorafenib was associated with the induction of apoptosis, as indicated by release of cytochrome c and Apoptosis-Inducing Factor into the cytosol, activation of caspase-9 and caspase-7, and PARP-1 cleavage. Combination of letrozole and sorafenib produced a synergistic inhibition of cell proliferation associated with an enhanced accumulation of cells in the G(0)/G(1) phase of the cell cycle and with a down-regulation of the cell cycle regulatory proteins c-myc, cyclin D1, and phospho-Rb. In addition, longer experiments (12 weeks) demonstrated that sorafenib may be effective in preventing the acquisition of resistance towards letrozole. Together, these results indicate that combination of letrozole and sorafenib might constitute a promising approach to the treatment of hormone-dependent breast cancer.
authors.affiliation: Department of Experimental Medicine, University of Parma, Via Volturno 39, 43100 Parma, Italy.
authors.forename: Mara A
authors.initials: MA
authors.lastname: Bonelli
authors.forename: Claudia
authors.initials: C
authors.lastname: Fumarola
authors.forename: Roberta R
authors.initials: RR
authors.lastname: Alfieri
authors.forename: Silvia
authors.initials: S
authors.lastname: La Monica
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavazzoni
authors.forename: Maricla
authors.initials: M
authors.lastname: Galetti
authors.forename: Rita
authors.initials: R
authors.lastname: Gatti
authors.forename: Silvana
authors.initials: S
authors.lastname: Belletti
authors.forename: Adrian L
authors.initials: AL
authors.lastname: Harris
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Fox
authors.forename: Dean B
authors.initials: DB
authors.lastname: Evans
authors.forename: Mitch
authors.initials: M
authors.lastname: Dowsett
authors.forename: Lesley-Ann
authors.initials: LA
authors.lastname: Martin
authors.forename: Alberto
authors.initials: A
authors.lastname: Bottini
authors.forename: Daniele
authors.initials: D
authors.lastname: Generali
authors.forename: Pier Giorgio
authors.initials: PG
authors.lastname: Petronini
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D001141:Aromatase / Q000235:genetics / Q000378:metabolism; D047072:Aromatase Inhibitors / Q000494:pharmacology; D001557:Benzenesulfonates / Q000494:pharmacology; D001943:Breast Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D053179:Caspase 7 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D019938:Cyclin D1 / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D004958:Estradiol / Q000378:metabolism; D005260:Female; D006801:Humans; D000077289:Letrozole; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D009536:Niacinamide / Q000031:analogs & derivatives; D009570:Nitriles / Q000494:pharmacology; D010671:Phenylurea Compounds; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D016160:Retinoblastoma Protein / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D000077157:Sorafenib; D058570:TOR Serine-Threonine Kinases; D013739:Testosterone / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014230:Triazoles / Q000494:pharmacology
chemical_list: C494829:AIFM1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D051033:Apoptosis Inducing Factor; D047072:Aromatase Inhibitors; D001557:Benzenesulfonates; C530104:CCND1 protein, human; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; C489427:MYC protein, human; D046912:Multiprotein Complexes; D009570:Nitriles; D010671:Phenylurea Compounds; D010750:Phosphoproteins; D047428:Protein Kinase Inhibitors; D011506:Proteins; D016271:Proto-Oncogene Proteins c-myc; D011725:Pyridines; D016160:Retinoblastoma Protein; D014230:Triazoles; D019938:Cyclin D1; D009536:Niacinamide; D013739:Testosterone; D004958:Estradiol; D000077289:Letrozole; D045304:Cytochromes c; D000077157:Sorafenib; D001141:Aromatase; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D000076222:Mechanistic Target of Rapamycin Complex 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C505520:CASP7 protein, human; C506433:CASP9 protein, human; D053179:Caspase 7; D053453:Caspase 9