Matrix metalloproteinases-2 and -9 (MMP-2/-9) are key tissue remodeling enzymes that have multiple overlapping activities critical for wound healing and tumor progression in vivo. To overcome issues of redundancy in studying their functions in vivo, we created MMP-2/-9 double knockout (DKO) mice in the C57BL/6 background to examine wound healing. We then bred the DKO mice into the polyomavirus middle T (PyVmT) model of breast cancer to analyze the role of these enzymes in tumorigenesis. Breeding analyses indicated that significantly fewer DKO mice were born than predicted by Mendelian genetics and weaned DKO mice were growth compromised compared with wild type (WT) cohorts. Epithelial wound healing was dramatically delayed in adult DKO mice and when the DKO was combined with the PyVmT oncogene, we found that the biologically related process of mammary tumorigenesis was inhibited in a site-specific manner. To further examine the role of MMP-2/-9 in tumor progression, tumor cells derived from WT or DKO PyVmT transgenic tumors were grown in WT or DKO mice. Ratiometric activatable cell penetrating peptides (RACPPs) previously used to image cancer based on MMP-2/-9 activity were used to understand differences in MMP activity in WT or knockout syngeneic tumors in WT and KO animals. Analysis of an MMP-2 selective RACPP in WT or DKO mice bearing WT and DKO PyVmT tumor cells indicated that the genotype of the tumor cells was more important than the host stromal genotype in promoting MMP-2/-9 activity in the tumors in this model system. Additional complexities were revealed as the recruitment of host macrophages by the tumor cells was found to be the source of the tumor MMP-2/-9 activity and it is evident that MMP-2/-9 from both host and tumor is required for maximum signal using RACPP imaging for detection. We conclude that in the PyVmT model, the majority of MMP-2/-9 activity in mammary tumors is associated with host macrophages recruited into the tumor rather than that produced by the tumor cells themselves. Thus therapies that target tumor-associated macrophage functions have the potential to slow tumor progression.

Objective Functional imaging of synovitis could improve both early detection of rheumatoid arthritis (RA) and long‐term outcomes. Given the intersection of inflammation with coagulation protease activation, this study was undertaken to examine coagulation protease activities in arthritic mice with a dual‐fluorescence ratiometric activatable cell‐penetrating peptide (RACPP) that has a linker, norleucine (Nle)‐TPRSFL, with a cleavage site for thrombin. Methods K/BxN‐transgenic mice with chronic arthritis and mice with day 1 passive serum‐transfer arthritis were imaged in vivo for Cy5:Cy7 emission ratiometric fluorescence from proteolytic cleavage and activation of RACPPNleTPRSFL. Joint thickness in mice with serum‐transfer arthritis was measured from days 0 to 10. The cleavage‐evoked release of Cy5‐tagged tissue‐adhesive fragments enabled microscopic correlation with immunohistochemistry for inflammatory markers. Thrombin dependence of ratiometric fluorescence was tested by ex vivo application of RACPPNleTPRSFL and argatroban to cryosections obtained from mouse hind paws on day 1 of serum‐transfer arthritis. Results In chronic arthritis, RACPPNleTPRSFL fluorescence ratios of Cy5:Cy7 emission were significantly higher in diseased swollen ankles of K/BxN‐transgenic mice than in normal mouse ankles. A high ratio of RACPPNleTPRSFL fluorescence in mouse ankles and toes on day 1 of serum‐transfer arthritis correlated with subsequent joint swelling. Foci of high ratiometric fluorescence localized to inflammation, as demarcated by immune reactivity for citrullinated histones, macrophages, mast cells, and neutrophils, in soft tissue on day 1 of serum‐transfer arthritis. Ex vivo application of RACPPNleTPRSFL to cryosections obtained from mice on day 1 of serum‐transfer arthritis produced ratiometric fluorescence that was inhibited by argatroban. Conclusion RACPPNleTPRSFL activation detects established experimental arthritis, and the detection of inflammation by RACPPNleTPRSFL on day 1 of serum‐transfer arthritis correlates with disease progression.