title: A reexamination of PSC 833 (Valspodar) as a cytotoxic agent and in combination with anticancer agents.
abstract: BACKGROUND
  The cyclosporins have been thought as being mainly immunosuppressive agents which interfere with the function of the MDR pump and thus play a role in resistance to drug anticancer effects. We reexamined their cytotoxicity in defined cell lines both as single agents and in combination with agents which may be of value in human malignant disease.
  
  
  METHODS
  Cells were grown to confluence following inoculation at 5,000-8,000 cells/well in 96-well dishes, and growth patterns and death were determined by an MTT assay. Median effect analysis was used to look for synergy, additive effects, or antagonism between the cyclosporins and drugs with antitumor effects in humans.
  
  
  RESULTS
  Cyclosporin A and PSC 833 were found to have cytotoxic activity at clinically achievable concentrations in breast, leukemia, and prostate cell lines. Synergistic or additive effects were demonstrated in all three prostate cell lines when PSC 833 was combined with estramustine, etoposide, ketoconazole, suramin, or vinorelbine in the prostate cancer cell lines. Cell line-selective additive effects or synergism were also identified with bicalutamide, carboplatin, cisplatinum, cis-retinoic acid, dexamethasone, 5-fluorouracil, liarozole, and trans-retinoic acid.
  
  
  CONCLUSIONS
  PSC 833 or cyclosporin alone or in combination with other agents may have an anticancer effect independently of their modulatory action on MDR. Several of the synergistic combinations which are not mediated by the MDR pump need to be tested in vivo for efficacy.
authors.affiliation: Don Monti Division of Oncology, North Shore University Hospital, Manhasset, NY 11030, USA.
authors.forename: W
authors.initials: W
authors.lastname: Kreis
authors.forename: D R
authors.initials: DR
authors.lastname: Budman
authors.forename: A
authors.initials: A
authors.lastname: Calabro
mesh_terms: D000970:Antineoplastic Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D016572:Cyclosporine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D003524:Cyclosporins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D006801:Humans; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D003524:Cyclosporins; D016572:Cyclosporine; C070272:valspodar