Published ahead of print on August 25, 2005, doi:10.1165/rcmb.2004-0355OC Am. J. Respir. Cell Mol. Biol., Volume 33, Number 6, December 2005, 541-548 A more recent version of this article appeared on December 1, 2005
Submitted on November 14, 2004 A Novel In Vitro Model of Human Mesothelioma for Studying Tumor Biology and Apoptotic ResistanceKi-Up Kim1,1 Lung Biology Center, Universitiy of California San Francisco, San Francisco General Hospital, San Francisco, CA, USA, 2 Department of Pathology, Universitiy of California San Francisco, San Francisco General Hospital, San Francisco, CA, USA, 3 Cancer Research Institute, University of California San Francisco, Comprehensive Cancer Center, San Francisco General Hospital, Universitiy of California San Francisco, CA, USA * To whom correspondence should be addressed. E-mail: cbroaddus{at}medsfgh.ucsf.edu.
Like many tumors, malignant mesothelioma exhibits significant chemoresistance and resistance to apoptosis in vivo that is not seen in current in vitro models. To study the mechanisms of this multicellular resistance, biologically relevant in vitro models are necessary. Therefore, we characterized and tested human mesothelioma tissue grown in vitro as tumor fragment spheroids. After 5-10 days in culture, fragments from each of 15 human mesothelioma tumors rounded into spheroids. The tumor fragment spheroids maintained multiple characteristics of the original tumors for up to 3 months including the presence of viable mesothelioma cells, macrophages and a collagen-rich stroma. In 14-day old spheroids, mesothelioma cells showed the same proliferation rate and expression of a death receptor, DR5, as in the original tumor. To determine responses to treatment, we treated tumor fragment spheroids grown from 3 separate tumors with agents, TRAIL plus cycloheximide, that induced near total apoptosis in 3 human mesothelioma cell lines (M28, REN, MS-1) grown as monolayers (94 ± 6% apoptosis; mean ± SEM). Compared to mesothelioma cells in monolayers, mesothelioma cells in the spheroids were resistant to TRAIL plus cycloheximide (32 ± 4% apoptosis; mean ±SEM). Apoptotic resistance of mesothelioma cells was significantly reduced by inhibiting either the PI3K/Akt pathway with LY294002 (47 ± 6% apoptosis) or the mTOR pathway with rapamycin (50 ± 17% apoptosis). We conclude that human mesothelioma can be maintained in vitro in a biologically relevant model that exhibits apoptotic resistance, thereby permitting study of its tumor biology and of novel approaches to therapy.
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