title: Characterization of paclitaxel (Taxol) sensitivity in human glioma- and medulloblastoma-derived cell lines.
abstract: Paclitaxel (Taxol), a cytotoxic natural product that disrupts microtubule integrity, is being clinically evaluated for use against gliomas. We examined paclitaxel-induced killing in seven cell lines derived from human malignant astrocytic gliomas and medulloblastomas with the goal of characterizing range of sensitivity, contribution of P-glycoprotein 170-mediated drug efflux to resistance, and cross-resistance with alkylating agents. Exposure to paclitaxel for 8 h or less produced biphasic survival curves for all lines, with 40-75% of cells comprising a subpopulation that was 9-26 times more resistant to paclitaxel than the more sensitive fraction. Increasing exposure to 24 h eliminated the resistant subpopulation, increasing sensitivity 50- to 400-fold. The dose producing one log of kill (LD10) after a 24-h exposure ranged from 4 to 18 nM, comparable to concentrations in the cerebrospinal fluid of brain tumor patients given a 3-h infusion of paclitaxel. Concurrent exposure to paclitaxel and either nimodipine or verapamil, inhibitors of P-glycoprotein activity, did not increase sensitivity, demonstrating that the fivefold range in sensitivity was not due to P-glycoprotein-mediated drug efflux. Importantly, there was no correlation between LD10 for paclitaxel and LD10 for 1,3-bis(2-chloroethyl)-1-nitrosourea, streptozotocin, and temozolomide, indicating no expression of cross-resistance to these different classes of tumoricidal agents. Our results suggest that greater clinical efficacy of paclitaxel against malignant brain tumors may be obtained by infusion for 24 h or longer and support the use of paclitaxel in combination with alkylating agents.
authors.affiliation: Department of Neurological Surgery, University of Washington, Box 356470, 1959 N.E. Pacific St., Seattle, WA 98195-6470, USA.
authors.forename: S H
authors.initials: SH
authors.lastname: Tseng
authors.forename: M S
authors.initials: MS
authors.lastname: Bobola
authors.forename: M S
authors.initials: MS
authors.lastname: Berger
authors.forename: J R
authors.initials: JR
authors.lastname: Silber
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001254:Astrocytoma / Q000473:pathology*; D001932:Brain Neoplasms / Q000473:pathology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002453:Cell Cycle; D004273:DNA, Neoplasm / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D006801:Humans; D008527:Medulloblastoma / Q000473:pathology*; D008870:Microtubules / Q000187:drug effects; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D017239:Paclitaxel / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018906:Antineoplastic Agents, Alkylating; D000972:Antineoplastic Agents, Phytogenic; D002121:Calcium Channel Blockers; D004273:DNA, Neoplasm; D009363:Neoplasm Proteins; D017239:Paclitaxel