title: Synergistic suppression of microtubule dynamics by discodermolide and paclitaxel in non-small cell lung carcinoma cells.
abstract: Discodermolide is a new microtubule-targeted antimitotic drug in Phase I clinical trials that, like paclitaxel, stabilizes microtubule dynamics and enhances microtubule polymer mass in vitro and in cells. Despite their apparently similar binding sites on microtubules, discodermolide acts synergistically with paclitaxel to inhibit proliferation of A549 human lung cancer cells (L. Martello et al., Clin. Cancer Res., 6: 1978-1987, 2000). To understand their synergy, we examined the effects of the two drugs singly and in combination in A549 cells and found that, surprisingly, their antiproliferative synergy is related to their ability to synergistically inhibit microtubule dynamic instability and mitosis. The combination of discodermolide and paclitaxel at their antiproliferative IC(50)s (7 nm for discodermolide and 2 nm for paclitaxel) altered all of the parameters of dynamic instability synergistically except the time-based rescue frequency. For example, together the drugs inhibited overall microtubule dynamicity by 71%, but each drug individually inhibited dynamicity by only 24%, giving a combination index (CI) of 0.23. Discodermolide and paclitaxel also synergistically blocked cell cycle progression at G(2)-M (41, 9.6, and 16% for both drugs together, for discodermolide alone, and for paclitaxel alone, respectively; CI = 0.59), and they synergistically enhanced apoptosis (CI = 0.85). Microtubules are unique receptors for drugs. The results suggest that ligands that bind to large numbers of binding sites on an individual microtubule can interact in a poorly understood manner to synergistically suppress microtubule dynamic instability and inhibit both mitosis and cell proliferation, with important consequences for combination clinical therapy with microtubule-targeted drugs.
authors.affiliation: FRE-CNRS 2737, Université de la Méditerranée, Marseille, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Honore
authors.forename: Kathy
authors.initials: K
authors.lastname: Kamath
authors.forename: Diane
authors.initials: D
authors.lastname: Braguer
authors.forename: Susan Band
authors.initials: SB
authors.lastname: Horwitz
authors.forename: Leslie
authors.initials: L
authors.lastname: Wilson
authors.forename: Claudette
authors.initials: C
authors.lastname: Briand
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Jordan
mesh_terms: D000473:Alkanes / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001665:Binding Sites; D002219:Carbamates / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D004357:Drug Synergism; D016195:G2 Phase / Q000187:drug effects; D006801:Humans; D020128:Inhibitory Concentration 50; D007783:Lactones / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008870:Microtubules / Q000187:drug effects* / Q000378:metabolism; D008938:Mitosis / Q000187:drug effects; D017239:Paclitaxel / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D011753:Pyrones
chemical_list: D000473:Alkanes; D002219:Carbamates; D007783:Lactones; D011753:Pyrones; C071229:discodermolide; D017239:Paclitaxel