Abstract 435: MT regulation of tumor-dependent microenvironment remodeling
Authors: Tran Andy D. , Giannakakou Paraskevi 
Published: June 2012

Microtubules (MTs) represent one of the most effective targets in cancer chemotherapy. However, drugs that target MTs, like the taxanes, often fail in the metastatic setting. Most studies are performed in a two-dimensional monoculture thus, overlook the complexity of the tumor microenvironment. Therefore, to gain a better understanding of tumor MT biology within a physiological context we studied the role of MT dynamics in 3D co-cultures closer mimicking the tumor microenvironment. Since tumor cells need to remodel their ECM in order to metastasize we hypothesized that the interphase MT cytoskeleton, through the coordination of cellular signaling regulates this process. To test this hypothesis we first assessed the MT-dependence of tumor-mediated ECM remodeling, using a floating collagen gel contraction assay. In this assay, breast cancer cells were embedded into a floating collagen gel and monitored for their ability to contract the gel as a result of cell generated traction force. We observed that the MDA-MB-231 metastatic breast cancer cells exhibited greater contractility as compared with the MCF-7 non-metastatic breast cancer cells or the non-tumorigenic human breast epithelial cell line MCF10A. However upon disruption of MTs with paclitaxel (PTX), tumor cell contractility was severely inhibited at drug concentrations that did not affect cell number, suggesting that dynamic MTs are essential for cell traction force generation. In addition, we observed that human mammary fibroblasts when co-cultured with breast cancer cells in 3D exhibited increased motility as compared to 3D fibroblast monocultures. Interestingly, fibroblast activation was inhibited in co-cultures with breast cancer cells previously treated with a taxane, suggesting that tumor MT stabilization negatively affects fibroblast activation. To investigate the factors that mediated the tumor cell communication with surrounding fibroblasts we monitored fibroblast motility in 3D monocultures following incubation with conditioned medium collected from either untreated or Taxol pre-treated breast cancer cells. In agreement with our 3D co-culture results, fibroblast 3D motility was inhibited following exposure to conditioned medium from the Taxol-pretreated cells.

These results suggest that the composition of the tumor secretome changes upon MT stabilization, which in turn affects the ability of tumor cells to communicate with stromal fibroblasts. Currently, we are performing proteomic analysis of the conditioned media to identify soluble factors whose secretion is dependent on dynamic microtubules. In addition, to determine whether the effects of taxane treatment is solely due to microtubule stabilization we are performing the 3D co-culture experiments using a Taxol-resistant β-tubulin mutant breast cancer cell line. These findings point to a novel role of interphase MTs in tumor biology and can possibly lead to new avenues for taxane clinical efficacy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 435. doi:10.1158/1538-7445.AM2011-435