title: In vitro and in vivo chemosensitizing effect of cyclosporin A on an intrinsic multidrug-resistant rat colon tumour.
abstract: Colon tumours are intrinsically resistant to chemotherapy and most of them express the multidrug transporter P glycoprotein (Pgp). Whether this Pgp expression determines their resistance to anticancer agents in patients is not known. We report here on the reversibility of intrinsic multidrug resistance in a syngeneic, solid tumour model. CC531 is a rat colon carcinoma that expresses Pgp, as was shown with the monoclonal antibody C-219. In vitro the sensitivity to doxorubicin, daunorubicin and colchicine was enhanced by the addition of the chemosensitizers verapamil and cyclosporin A (CsA), while the sensitivity to cisplatin was not enhanced. In a daunorubicin accumulation assay verapamil and CsA enhanced the daunorubicin content of CC531 cells. In vivo CsA was injected intramuscularly for 3 consecutive days at a dose of 20 mg kg-1 day-1. This resulted in whole-blood CsA levels above 2 mumol/l, while intratumoral CsA levels amounted to 3.6 mumol/kg. In a subrenal capsule assay the maximal tolerable dose of doxorubicin (4 mg/kg) significantly reduced tumour growth. Doxorubicin at 3 mg/kg was not effective, but in combination with CsA this dose was as effective as 4 mg/kg doxorubicin. These experiments show that adequate doses of the chemosensitizing drug CsA can be obtained in vivo, resulting in increased antitumoral activity of doxorubicin in vivo. The in vitro and in vivo data together suggest that the chemosensitization by CsA is mediated by Pgp. This finding may have implications for the application of CsA and CsA-like chemosensitizers in the clinical setting.
authors.affiliation: Department of Surgical Oncology, Rotterdam Cancer Institute, The Netherlands.
authors.forename: W
authors.initials: W
authors.lastname: Van de Vrie
authors.forename: E E
authors.initials: EE
authors.lastname: Gheuens
authors.forename: N M
authors.initials: NM
authors.lastname: Durante
authors.forename: E A
authors.initials: EA
authors.lastname: De Bruijn
authors.forename: R L
authors.initials: RL
authors.lastname: Marquet
authors.forename: A T
authors.initials: AT
authors.lastname: Van Oosterom
authors.forename: A M
authors.initials: AM
authors.lastname: Eggermont
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000230:Adenocarcinoma / Q000188:drug therapy* / Q000378:metabolism; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D002352:Carrier Proteins / Q000096:biosynthesis; D003078:Colchicine / Q000008:administration & dosage; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D016572:Cyclosporine / Q000493:pharmacokinetics / Q000627:therapeutic use*; D004351:Drug Resistance / Q000235:genetics; D004357:Drug Synergism; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis; D009363:Neoplasm Proteins / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014700:Verapamil / Q000008:administration & dosage
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D016572:Cyclosporine; D014700:Verapamil; D003078:Colchicine