title: Structural determinants of phenoxazine type compounds required to modulate the accumulation of vinblastine and vincristine in multidrug-resistant cell lines.
abstract: Phenoxazine and seven other structurally related compounds were investigated to determine whether they would increase accumulation of Vinca alkaloids in multidrug-resistant (MDR) GC3/C1 (human colon adenocarcinoma) and KB-ChR-8-5 (HeLa variant) cell lines. Among eight compounds examined, phenoxazine caused greater accumulations of vincristine (VCR) and vinblastine (VLB) than the other chemosensitizers. The structure-activity relationship of these compounds for anti-MDR activity suggested an ideal tricyclic ring structure with a basic nitrogen atom at position 10 for modulating the accumulation of Vinca alkaloids. Addition of oxygen to position 5 of the tricyclic ring system further increased the activity, implying that a highly electronegative element with one, or more, lone pair of electrons in the nucleus opposite to heterocyclic nitrogen was a requirement for better anti-MDR activity. The relationship between the concentration of phenoxazine and the potentiation of Vinca alkaloid accumulation in comparison to verapamil was examined. For VCR in GC3/C1 cells, maximal modulation indices were: for verapamil, 1.8; phenoxazine, 8.6; and for VLB, 1.3 for verapamil compared to 3.3 for phenoxazine. In KB-ChR-8-5 cells, for VCR the maximal modulating index values were 9.0 and 4.3, respectively, and for phenoxazine and verapamil and for VLB were 5.0 and 3.7, respectively. Accumulations of VLB in GC3/C1 cells were similar in the presence of 1 microM phenoxazine or 10 mM sodium azide plus 10 mM 2-deoxyglucose. The effects of verapamil and phenoxazine on the accumulation of Vinca alkaloid were additive. Further, phenoxazine decreased the efflux of VLB by 30% in KB-ChR-8-5 cell line and 10% in GC3/C1 cells. In addition to enhancing the cytotoxicities of VCR and VLB, phenoxazine competed relatively weakly for binding to P-glycoprotein with [3H]azidopine and moderately with [3H]azidoverapamil, at equal concentrations, suggesting that the multidrug transporter may be the primary target for phenoxazine.
authors.affiliation: Department of Biochemical and Clinical Pharmacology, St. Jude Children's Research Hospital, Memphis, TN 38101-0318.
authors.forename: K N
authors.initials: KN
authors.lastname: Thimmaiah
authors.forename: J K
authors.initials: JK
authors.lastname: Horton
authors.forename: X D
authors.initials: XD
authors.lastname: Qian
authors.forename: W T
authors.initials: WT
authors.lastname: Beck
authors.forename: J A
authors.initials: JA
authors.lastname: Houghton
authors.forename: P J
authors.initials: PJ
authors.lastname: Houghton
mesh_terms: D000230:Adenocarcinoma; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D003110:Colonic Neoplasms; D004351:Drug Resistance / Q000502:physiology*; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015394:Molecular Structure; D010078:Oxazines / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000378:metabolism*; D014750:Vincristine / Q000378:metabolism*; D014966:Xanthenes / Q000494:pharmacology*
chemical_list: D010078:Oxazines; D014966:Xanthenes; D014750:Vincristine; D014747:Vinblastine; C039203:phenoxazine; D014700:Verapamil