title: A synergistic interaction between lapatinib and chemotherapy agents in a panel of cell lines is due to the inhibition of the efflux pump BCRP.
abstract: Lapatinib is a specific HER1 and 2 targeted tyrosine kinase inhibitor now widely used in combination with chemotherapy in the clinical setting. In this work, we investigated the interactions between lapatinib and specific chemotherapy agents (cisplatin, SN-38, topotecan) in a panel of cell lines [breast (n = 2), lung (n = 2), testis (n = 4)]. A high-sensitivity cell proliferation/cytotoxicity ATP assay and flow cytometry were used to determine cell viability, apoptosis, and the effect of the drugs on cell-cycle distribution. CalcuSyn analysis was employed to formally identify synergistic interactions between drugs. Intracellular concentrations of SN-38 were measured using a novel high-performance liquid chromatography (HPLC) technique. Flow cytometry and HPLC techniques were used to identify the effect of lapatinib on drug influx and efflux pumps, using specific substrates and inhibitors of these pumps. Results showed significant synergy between SN-38, and lapatinib in the majority of cell lines (combination index < 0.75), associated with increased apoptosis. This synergy was not universal but, when observed (Susa S/R, H1975, H358, and MDA-MB-231 cell lines), was related to SN-38 intracellular accumulation (2.2- to 4.8-fold increase, P < 0.05 for each), attributable to the inhibition of the breast cancer-related protein (BCRP) efflux pump by lapatinib. Flow cytometry analysis showed that lapatinib (10 μmol/L) inhibited the efflux of mitoxantrone, a specific substrate of the BCRP pump, in a manner similar to fumitremorgin C, a known BCRP inhibitor, confirming lapatinib as a BCRP inhibitor. This work shows that lapatinib has a direct inhibitory effect on BCRP accounting for the synergistic findings. The synergy is cell line dependent and related to the activity of specific efflux pumps.
authors.affiliation: Centre for Experimental Cancer Medicine, Institute of Cancer, John Vane Science Centre, Barts and the London School of Medicine, Queen Mary College, Charterhouse Square, London EC1M 6BQ, UK.
authors.forename: Jackie
authors.initials: J
authors.lastname: Perry
authors.forename: Essam
authors.initials: E
authors.lastname: Ghazaly
authors.forename: Christiana
authors.initials: C
authors.lastname: Kitromilidou
authors.forename: Eva H
authors.initials: EH
authors.lastname: McGrowder
authors.forename: Simon
authors.initials: S
authors.lastname: Joel
authors.forename: Thomas
authors.initials: T
authors.lastname: Powles
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D002945:Cisplatin / Q000494:pharmacology; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D005434:Flow Cytometry; D006801:Humans; D007191:Indazoles; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D000077341:Lapatinib; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology; D011799:Quinazolines / Q000737:chemistry / Q000494:pharmacology*; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D007191:Indazoles; D009363:Neoplasm Proteins; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D011799:Quinazolines; D013449:Sulfonamides; D000077341:Lapatinib; C516667:pazopanib; D002945:Cisplatin