Abstract PR01: Disruption of DDR2-collagen interactions in tumor and stroma with a novel small molecule inhibitor blunts cancer metastasis

Discoidin Domain Receptor 2 (DDR2) is a receptor tyrosine kinase that utilizes the extracellular matrix protein collagen as its ligand. Recently, DDR2 was shown to be critical in facilitating breast cancer metastasis. In tumor cells DDR2 expression, which is absent in normal breast epithelium, is induced during Epithelial Mesenchymal transition (EMT), and serves to stabilize protein levels of the EMT inducing transcription factor, Snail1. DDR2 expression is present in a majority of human invasive ductal breast carcinomas, and expression is predominately localized to the tumor-stroma boundary. In these tumors DDR2 is acting in a positive feedback manner to maintain Snail1 levels and activity at the leading, invasive edge of the tumors, where cells have undergone EMT and come into contact with extracellular matrix (ECM) collagen I. This allows continued invasion through the ECM and contributes to breast cancer metastasis. Interestingly, in genetic models of breast cancer in mice, selectively eliminating DDR2 in either the tumor (MMTV-PyMT; DDR2 fl/fl; K14-Cre) or the fibroblasts within the stroma (MMTV-PyMT; DDR2 fl/fl; FSP-Cre) leads to a dramatic inhibition of tumor metastasis. This indicates that in addition to maintaining EMT in the tumor cells, DDR2 functions within the stromal compartment to facilitate metastasis as well. In culture, the matrix synthesized and remodeled by cancer associated fibroblasts (CAFs) is organized very differently than that of normal fibroblasts. When DDR2 is depleted from CAFS, the matrix more closely resembles that produced by normal fibroblasts, with less organization of matrix proteins. Therefore, it appears that DDR2 engagement by collagen provides a means for both tumor and stromal cells to enhance metastatic potential. As such, DDR2 is a novel RTK target for the treatment of breast cancer metastasis, and we have developed potent and selective small molecule inhibitors of DDR2. These compounds provide a means of blunting breast cancer metastasis by targeting the tumor and stromal cells, thereby disrupting DDR2 signaling in both compartments. The developed inhibitors have nanomolar cellular potency at blocking DDR2 activation. Unlike traditional tyrosine kinase inhibitors (TKIs) that target the intracellular kinase domain, the inhibitors that we have developed act on the extracellular domain of DDR2 and disrupt DDR2 signaling by accelerating the disassembly of the DDR2-collagen complex. Therefore these inhibitors have a unique mode of action that is distinct from the canonical classes of TKIs. These compounds have the ability to attenuate DDR2 signaling both in cell culture, as well as in vivo as demonstrated by using a Snail1-clic beetle green reporter in a syngeneic transplant model. Treating CAFs with the developed inhibitors in culture reverts the organizational phenotype of the resulting matrix to that resembling the matrix produced by normal fibroblasts. Furthermore, using mouse models of late stage breast tumor metastasis, we have shown that these inhibitors reduce metastatic burden in the lungs of mice, to a level comparable to that of genetic knockdown of DDR2. Together these data support further investigation of this novel class of DDR2 inhibitors as anti-metastasis agents, potentially for use in combination with standard of care therapy to halt cancer progression and prevent relapse. Further, it will be important to study the role of these inhibitors in other cancers where DDR2 expression has been shown to promote metastasis, including, but not limited to, ovarian, head and neck, and nonsmall cell lung carcinoma. This abstract is also presented as Poster B13. Citation Format: Whitney R. Grither, Gregory D. Longmore. Disruption of DDR2-collagen interactions in tumor and stroma with a novel small molecule inhibitor blunts cancer metastasis. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr PR01.