title: Soluble factor from murine bladder tumor-2 cell elevates nitric oxide production in macrophages and enhances the taxol-mediated macrophage cytotoxicity on tumor cells.
abstract: The therapeutic mechanism of taxol is believed to reside primarily in its ability to stabilize microtubules and prevent cell progression through mitosis. Taxol also can activate macrophage-mediated antitumor mechanism through a nitric oxide (NO)-dependent pathway. To address whether any mechanisms account for superficial urinary bladder tumor cell killing, we evaluated the effects of taxol on the growth and viability of murine bladder tumor-2 (MBT-2) cells in vitro, both in the absence and presence of murine macrophages. In addition, we evaluated whether a soluble factor generated from MBT-2 cells could modulate the antitumor activity of the taxol-activated macrophages. Although taxol inhibited the growth of MBT-2 cells, it did not kill the tumor cells. However, preincubation of macrophages with taxol significantly decreased the viability of MBT-2 cells. Secretion of NO correlated with MBT-2 cell killing, and the activated macrophages failed to kill tumor cell targets in the presence of NG-monomethyl-L-arginine, a competitive inhibitor of NO synthase. By the co-culture of macrophages and MBT-2 cells, untreated macrophages also released modest amount of NO and this was synergistically augmented by the treatment with taxol, indicating that MBT-2 tumor cells released some unknown factor that activated the macrophages and enhanced NO production. We named this factor the tumor-derived macrophage activating factor (TMAF). The TMAF-mediated activation of macrophages to enhance the NO production was not blocked by treatment of macrophages with oxidized low-density lipoprotein (Ox-LDL), implying that the scavenger receptor of macrophages is not involved. Sodium nitroprusside (SNP), an NO donor given to the MBT-2 cells, increased the activities of c-Jun N-terminal kinase and caspase-3 in MBT-2 cells and associated with nucleosomal fragmentation or apoptosis, whereas taxol had no direct effect on these parameters. Collectively, our results strongly suggest that taxol kills the murine bladder tumor cells through indirect activation of macrophages via NO-dependent apoptosis, instead of its better-known role as the direct antimitotic action. Our results further demonstrate that TMAF acts in synergy with taxol to activate the macrophages to elicit enhanced tumor cell killing ability.
authors: Digestive Disease Research Institute, Wonkwang University School of Medicine, Iksan, Chonbuk, Korea.
authors: Suck-Chei
authors: SC
authors: Choi
authors: Hyun-Mee
authors: HM
authors: Oh
authors: Jae-Sung
authors: JS
authors: Park
authors: Weon-Cheol
authors: WC
authors: Han
authors: Kwon-Ha
authors: KH
authors: Yoon
authors: Tae-Hyeon
authors: TH
authors: Kim
authors: Ki-Jung
authors: KJ
authors: Yun
authors: Eun-Cheol
authors: EC
authors: Kim
authors: Yong-Ho
authors: YH
authors: Nah
authors: Young-Nam
authors: YN
authors: Cha
authors: Hun-Taeg
authors: HT
authors: Chung
authors: Chang-Duk
authors: CD
authors: Jun
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D018450:Disease Progression; D005260:Female; D016166:Free Radical Scavengers / Q000032:analysis*; D008264:Macrophages / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008938:Mitosis; D009569:Nitric Oxide / Q000032:analysis*; D017239:Paclitaxel / Q000494:pharmacology*; D010537:Peritoneum / Q000166:cytology; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms / Q000737:chemistry* / Q000503:physiopathology*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D016166:Free Radical Scavengers; D009569:Nitric Oxide; D017239:Paclitaxel