Abstract 4984: Generation of an RGD containing soluble pro-inflammatory form of the XL313 cryptic collagen epitope during tumor growth and inflammation.
Authors: Ames Jacquelyn J. , Caron Jennifer , Contois Liangru , Brooks Peter 
Published: August 2014

Evidence indicates that malignant tumor progression depends not only on tumor cells themselves, but also on stromal cells of the malignant lesion including tumor-associated macrophages (TAMs). TAMs have been suggested to contribute to changes in the extracellular matrix (ECM) through remodeling of architectural proteins like type-I collagen. Our previous studies have shown that remodeling of the ECM results in localized triggering of what we have termed “biomechanical ECM switches” resulting in exposure of cryptic ECM epitopes. In this regard, collagen has a number of Arg-Gly-Asp (RGD) containing cryptic sites and soluble RGD containing reagents are currently being developed for the treatment of malignant tumors. However, it is not known if the distinct cryptic RGD elements in type-I collagen are functionally redundant or if specific flanking sequences convey differential control of cellular behavior. In this regard, we previously generated a series of monoclonal antibodies (Mabs) that target distinct RGD containing cryptic sites of type-I collagen. One of these Mabs designated XL313 exhibits selective recognition of the conserved RGDKGE cryptic element and significantly (P&lt;0.05) inhibits B16F10 melanoma tumor growth as well as growth factor induced angiogenesis and inflammation in vivo. Interestingly, Mab XL166, selective for the RGDAPG collagen cryptic eptitope, showed no effect on tumor growth, angiogenesis or inflammation. To evaluate the role of the XL313 epitope in angiogenesis and inflammation in more detail, we examined its exposure in inflammed tissues. While the XL313 epitope was detected in close proximity to angiogenic blood vessels, the majority of the epitope localized to what appeared to be inflammatory infiltrates, suggesting a role for inflammatory cells in generating the XL313 collagen element. Here we provide evidence that a soluble form of the RGD containing XL313 epitope is generated by macrophages through a mechanism dependent in part on cathepsin activity, as a cathepsin inhibitor reduced generation of the XL313 epitope. Importantly, elevated levels of a circulating form of the XL313 epitope were detected, while lower levels of the related XL166 RGD epitope were observed in these samples following FGF-induced inflammation of the Chick CAM. Given these findings, we sought to determine whether the soluble XL313 epitope might induce inflammation in vivo. Our findings indicate that the RGD containing XL313 epitope, but not the XL166, epitope significantly (P&lt;0.05) induced inflammation in vivo, suggesting that generation of distinct RGD containing collagen peptides might have distinct roles in inflammation. Our findings are consistent with a novel mechanism by which generation of a specific highly conserved cryptic RGD collagen peptide might enhance rather than inhibit inflammation in vivo, and thus contribute to tumor progression.

Citation Format: Jacquelyn J. Ames, Jennifer Caron, Liangru Contois, Peter Brooks. Generation of an RGD containing soluble pro-inflammatory form of the XL313 cryptic collagen epitope during tumor growth and inflammation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4984. doi:10.1158/1538-7445.AM2013-4984