title: Pharmacologic interactions between the resistance-modifying cyclosporine SDZ PSC 833 and etoposide (VP 16-213) enhance in vivo cytostatic activity and toxicity.
abstract: Cyclosporin A reverses multidrug resistance (MDR) and increases the in vivo cytostatic activity and toxicity of the anticancer agent etoposide (VP 16-213). SDZ PSC 833 (PSC 833), a non-immunosuppressive, non-toxic cyclosporin and very active modifier of P-gp 170-mediated MDR, elicits similar effects when administered with adriamycin. The underlying mechanisms, however, are not yet understood. The present pharmacological interaction study with PSC 833 and VP 16-213 was carried out to reveal the nature of this enhancement of cytostatic activity and toxicity. Rats pre-treated with either PSC-833 or solvent received a single dose of VP 16-213. Plasma levels of VP 16-213 were measured by high-performance liquid chromatography (HPLC). The resulting increase in cytostatic activity and toxicity of VP 16-213 mediated by PSC 833 was paralleled by marked changes in the pharmacokinetic parameters of VP 16-213 in vivo. Bioavailability and blood levels of VP 16-213 were significantly increased 30 min after administration if PSC 833 had been given before. The disappearance rate of VP 16-213 from the intravascular compartment was considerably slowed down by PSC 833. In drug-sensitive xenografts of human colon carcinoma, the PSC-833-induced pharmacologic changes in vivo could be counteracted by dose reduction of VP 16-213 while a full therapeutic potential was maintained. Doses of VP 16-213, 1.5 to 2 times smaller, combined with PSC 833, were as effective in terms of tumor-growth inhibition as the maximum tolerated dose of VP 16-213 alone. Thus, pharmacologic interactions between PSC 833 or other resistance modifiers and VP 16-213 and other cytostatic agents require careful attention if they are to be used in humans to overcome MDR.
authors.affiliation: Sandoz Pharma Ltd., Basel, Switzerland.
authors.forename: R P
authors.initials: RP
authors.lastname: Keller
authors.forename: H J
authors.initials: HJ
authors.lastname: Altermatt
authors.forename: P
authors.initials: P
authors.lastname: Donatsch
authors.forename: H
authors.initials: H
authors.lastname: Zihlmann
authors.forename: J A
authors.initials: JA
authors.lastname: Laissue
authors.forename: P C
authors.initials: PC
authors.lastname: Hiestand
mesh_terms: D000230:Adenocarcinoma / Q000097:blood*; D000328:Adult; D000818:Animals; D003110:Colonic Neoplasms / Q000097:blood*; D003524:Cyclosporins / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004334:Drug Administration Schedule; D004347:Drug Interactions; D004354:Drug Screening Assays, Antitumor; D005047:Etoposide / Q000008:administration & dosage / Q000493:pharmacokinetics*; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D013047:Specific Pathogen-Free Organisms
chemical_list: D003524:Cyclosporins; D005047:Etoposide; C070272:valspodar