Abstract A43: Lysyl oxidases are poor therapeutic targets in pancreatic cancer

Abstract

Abstract A characteristic feature of pancreatic cancer is the predominant stroma, which consists of fibroblasts, immune cells and a significant deposition of extracellular matrix (ECM). The stroma accounts for over eighty percent of the pancreatic tumor mass and plays significant, yet poorly understood, roles in tumor progression and therapeutic response. One major component of the ECM in pancreatic cancer is fibrillar type I collagen, which has been shown to serve as a barrier to chemotherapy and to facilitate metastatic dissemination of breast cancer cells through integrin-mediated signaling. The cross-linking of type I collagen mediated by the lysyl oxidases (LOX) is elevated in invasive cancers and inversely correlates with metastatic free survival in breast cancer patients. Moreover, inhibition of LOX enzymes in mouse models of breast cancer decreases tumor size, latency, and metastasis. Given the abundance of type I collagen and the high expression of several LOX family members in pancreatic cancer, we examined whether inhibiting these enzymes could limit the progression of pancreatic cancer in mouse models. Using syngeneic, orthotopic transplantation models of pancreatic cancer - with significant fibrosis - we determined the effects of lysyl oxidases on pancreatic cancer. First, we established that both LOX and LOX-like 2 (LOXL2) were expressed much higher in tumors than in normal pancreatic tissue. However, inhibition of LOX activity, using the small molecule inhibitor β-aminoproprionitirile, significantly increased tumor wet weight and metastasis to the liver and spleen – the exact opposite results of those reported in breast cancer mouse models. Similarly, silencing the expression of LOXL2 in cancer cells, using RNA interference, also resulted in increased tumor growth. To examine why LOX inhibition has this surprisingly negative effect on pancreatic cancer progression, we tested the effects of LOX enzyme inhibition on collagen structure by picrosirius red stains, which visualize fibrillar collagens when tissues are observed under cross-polarized light. LOX inhibition promoted the deposition of fibrillar collagen in the tumor. To determine how this altered collagen deposition influenced cell behavior, we performed confocal microscope imaging in live tumor-bearing mice that express a fusion protein in which GFPtopaz is inserted into the N-terminus of α2(I)- collagen and expression is driven by the 3.6kb Col1a1 promoter [α2(I)-col-GFP mice]. Live imaging of red fluorescent protein expressing cancer cells in pancreatic tumors in the α2(I)-col-GFP mice showed a rich deposit of collagen and migration of cancer cells on linear collagen. Imaging confirmed that administration of the LOX inhibitor for just 3 days resulted in thicker collagen fibers than the control treated tumors. We are currently examining the underlying mechanisms responsible for the opposite responses of LOX targeting in breast and pancreatic cancer. In conclusion, our data strongly suggest that targeting collagen cross-linking enzymes would be a poor strategy for the treatment of pancreatic cancer. Citation Format: Mario A. Shields, Pascal Maguin, Priyanka Kumar, Sarah L. Dallas, Mikala Egeblad. Lysyl oxidases are poor therapeutic targets in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr A43.