Discoidin domain receptor (DDR) belongs to the receptor tyrosine kinase family l and is activated by binding to its ligand (collagen). Once activated, DDR undergoes autophosphorylation and triggers cellular signaling for proliferation and invasion. While studies have shown that high grade glioma expressed high levels of DDR1 and signifies poor clinical outcome, the underlying mechanism(s) is not known. We attempted to exploit this pathway for future treatment. DDR comprises of 2 members (DDR1 and DDR2). DDR1 is composed of five isoforms, i.e. a,b,c,d, and e. (d and e are inactive). We have studied the expression of both DDR1 (a,b,c) and DDR2 in 6 glioma cell lines (U118, Glioma1, SW1783, U87, A172, and U373). All 6 cell lines express all three subtypes of DDR1 as well as DDR2 by RT-PCR . DDR1 protein was also detected in all 6 cell lines. Knockdown DDR1 inhibited glioma cell migration by scratch assay and deactivated MMP9 by zymography analysis, which was best seen in Glioma1, U-118, and much less in A-172 and U-373. Knock down DDR1 also decreased AKT, ERK, and Bcl-xl which suggests positive regulation of these prosurvival proteins by DDR1. Since there is no inhibitor of DDR1, we have used Brefeldin A (BFA), which can block procollagen (ligand for DDR1 and DDR2) secretion. Treatment with BFA results in decreased DDR 1a,b and c mRNA in U-118, Glioma SW1783 and U-87 and no change in A-172 and U373. A decrease in DDR2 also was seen in U-118 and SW1783 and no change was seen in the other 4 cell lines. The ID50 of BFA ranged from 6 to 13 ng/ml in U-118, Glioma1 SW1783 and U-87 and 23 ng/ml in A-172. Treatment with BFA also inhibited cell migration (scratch assay) in Glioma 1, U-118 and SW1783 but not in U-373 and A-172. A-172 and U-373 did not possess procollagen alpha 1 type 1 which may explain the insensitivity to BFA. Silencing DDR1 does not significantly alter the growth inhibitory effect of Glioma1 U-118 or A-172. This may be due to the compensatory increase of DDR2. Thus, our data showed that glioma cells possess all DDR 1 subtypes as well as DDR2. Silencing DDR1 results in decreased AKT, ERK and antiapoptotic protein Bcl-xl and migration, suggesting its role in cellular proliferation and invasion. However, decreasing the available ligand (procollagen) from exiting the cells only affected DDR1 and DDR2 expression in certain cell lines (U-118 , SW1783). Interestingly, these 2 cell lines are also very sensitive to BFA (ID50 of 6 ng/mL) and possess high levels of procollagen type1 (both alpha1 and alpha 2 ) which are the ligands for both DDR1 and DDR2, while the cell line which had the least effect (A-172) did not express procollagen alpha 1 type 1. Overall, the presence of DDR family in malignant gliomas may not indicate that this is a major pathway for proliferation /survival and invasion . However, the presence of both ligand(s) and receptor(s) are important for future application to treat malignant gliomas targeting this pathway.

Citation Format: Shumei Chen, Chunjing Wu, Min You, Minh Tran, Medhi Wangpaichitr, Ying Ying Li, Ronald J. Benveniste, Macus T. Kuo, Niramol Savaraj, Lynn G. Feun. Exploiting discoidin domain receptor (DDR) and collagen signaling as a new approach to treat human malignant gliomas. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4192. doi:10.1158/1538-7445.AM2014-4192