MMP-7 promotes prostate cancer-induced osteolysis via the solubilization of RANKL.

We developed a rodent model that mimics the osteoblastic and osteolytic changes associated with human metastatic prostate cancer. Microarray analysis identified MMP-7, cathepsin-K, and apolipoprotein D as being upregulated at the tumor-bone interface. MMP-7, which was produced by osteoclasts at the tumor-bone interface, was capable of processing RANKL to a soluble form that promoted osteoclast activation. MMP-7-deficient mice demonstrated reduced prostate tumor-induced osteolysis and RANKL processing. This study suggests that inhibition of MMP-7 will have therapeutic benefit in the treatment of prostate cancer-induced osteolysis.

Hu/Mu ProtIn oligonucleotide microarray: dual-species array for profiling protease and protease inhibitor gene expression in tumors and their microenvironment.

Proteolysis is a critical regulatory mechanism for a wide variety of physiologic and pathologic processes. To assist in the identification of proteases, their endogenous inhibitors, and proteins that interact with proteases or proteolytic pathways in biological tissues, a dual-species oligonucleotide microarray has been developed in conjunction with Affymetrix. The Hu/Mu ProtIn microarray contains 516 and 456 probe sets that survey human and mouse genes of interest (proteases, protease inhibitors, or interactors), respectively. To investigate the performance of the array, gene expression profiles were analyzed in pure mouse and human samples (reference RNA; normal and tumor cell lines/tissues) and orthotopically implanted xenografts of human A549 lung and MDA-MB-231 breast carcinomas. Relative gene expression and "present-call" P values were determined for each probe set using dChip and MAS5 software, respectively. Despite the high level of sequence identity of mouse and human protease/inhibitor orthologues and the theoretical potential for cross-hybridization of some of the probes, >95% of the "present calls" (P<0.01) resulted from same-species hybridizations (e.g., human transcripts to human probe sets). To further assess the performance of the microarray, differential gene expression and false discovery rate analyses were carried out on human or mouse sample groups, and data processing methods to optimize performance of the mouse and human probe sets were identified. The Hu/Mu ProtIn microarray is a valuable discovery tool for the identification of components of human and murine proteolytic pathways in health and disease and has particular utility in the determination of cellular origins of proteases and protease inhibitors in xenograft models of human cancer.

Matrix metalloproteinase-9 from bone marrow-derived cells contributes to survival but not growth of tumor cells in the lung microenvironment.

The role of specific stromal-derived matrix metalloproteinases (MMPs) was analyzed in experimental metastasis assays in wild-type and either MMP-9, MMP-7, or MMP-2 null mice. MMP-9 null mice showed an 81% reduction in Lewis lung carcinoma tumor number, whereas MMP-7 null mice showed a 42% increase in tumor number, and there was no difference in tumor number in MMP-2 null mice compared with wild-type controls. Similarly, in an orthotopic model of lung cancer, 50% fewer MMP-9 null mice were able to establish tumors in the lung compared with control mice, although the size of the tumors was not different. The effect of MMP-9 on lung tumor colonization was dependent on the expression of MMP-9 from bone marrow-derived cells and is most likely contributed by neutrophils. To examine temporal effects of stromal MMP-9, bioluminescence imaging from luciferase-expressing human lung cancer-derived A549 cells revealed that there were fewer tumor cells in the lungs of MMP-9 null mice as early as 19 hours after injection compared with control mice, with no difference in subsequent growth rates. Six hours after injection of tumor cells, MMP-9 null mice showed a 4-fold increase in the percent of tumor cells undergoing apoptosis compared with control mice. We conclude that MMP-9 from the bone marrow contributes to the early survival and establishment of tumors in the lung and has no effect on subsequent growth. These results provide insights into the failure of MMP inhibitors in clinical trials in patients with late-stage lung cancer.

An orthotopic model of lung cancer to analyze primary and metastatic NSCLC growth in integrin alpha1-null mice.

The role of matrix metalloproteinase (MMP)9 in lung cancer progression is controversial. MMP9 promotes local tumor progression and distant metastasis in mouse models by enhancing extracellular matrix degradation, releasing VEGF from extracellular matrix and promoting vascular pericyte recruitment. Furthermore, increased plasma MMP9 expression levels in human subjects with metastatic non-small cell lung cancer (NSCLC) inversely correlates with survival. In contrast, MMP9 can benefit the host by generating inhibitors of endothelial cell proliferation such as angiostatin and NC1 domains of collagen IV. To better understand the role of host MMP9 on the primary growth and metastatic potential of NSCLC, we performed an orthotopic model of NSLC in integrin alpha1-null mice (a genetic model for increased MMP9). In these mice we observed decreased number, size and vascularization of primary NSCLC tumors when compared to wild type controls. In addition, decreased number and size of NSCLC-derived metastases were evident in the alpha1-null mice. Furthermore, pharmacological inhibition of MMPs in the alpha1-null mice at the time of tumor cell injection resulted in an increase in the number of both primary and metastatic lung cancer as compared to untreated mice, suggesting that primary growth and metastases of NSCLC are worsened by the early inhibition of MMPs. In conclusion, although MMP9 may potentially promote tumor growth and metastasis, production of MMP-dependent anti-angiogenic factors seems to override these effects and protects the host from NSCL growth and progression.

Analysis of host- and tumor-derived proteinases using a custom dual species microarray reveals a protective role for stromal matrix metalloproteinase-12 in non-small cell lung cancer.

We used a customized Affymetrix protease microarray (Hu/Mu ProtIn chip) designed to distinguish human and mouse genes to analyze the expression of proteases and protease inhibitors in lung cancer. Using an orthotopic lung cancer model, we showed that murine matrix metalloproteinase (MMP)-12, MMP-13, and cathepsin K were up-regulated in tumor tissue compared with normal mouse lung. To determine the relevance of stromal proteases detected using this model system, we compared the results to an analysis of human lung adenocarcinoma specimens using the U133 Plus 2.0 Affymetrix microarray. MMP-12, MMP-13, and cathepsin K showed an increase in expression in human tumors compared with normal lung similar to that seen in the orthotopic model. Immunohistochemical analysis confirmed MMP-12 expression in the stroma of human lung tumor samples. To determine the biological relevance of stromal MMP-12, murine Lewis lung carcinoma cells were injected into the tail vein of syngeneic wild-type (WT) and MMP-12-null mice. MMP-12-null and WT mice developed equivalent numbers of lung tumors; however, there was a 2-fold increase in the number of tumors that reached >2 mm in diameter in MMP-12-null mice compared with WT controls. The increase in tumor size correlated with an increase in CD31-positive blood vessels and a decrease in circulating levels of the K1-K4 species of angiostatin. These results show a protective role for stromal MMP-12 in lung tumor growth. The use of the Hu/Mu ProtIn chip allows us to distinguish tumor- and host-derived proteases and guides the further analysis of the significance of these genes in tumor progression.

Increased plasma MMP9 in integrin alpha1-null mice enhances lung metastasis of colon carcinoma cells.

Inhibitors of matrix metalloproteinases (MMPs) were developed as anticancer agents based on the observation that MMPs facilitate local tumor spread and metastasis by promoting matrix degradation and cell migration. Unfortunately, these inhibitors were unsuccessful in the clinical treatment of several cancers, including lung cancer. A possible reason contributing to their failure is that MMP activity is critical for the generation of inhibitors of tumor angiogenesis, including angiostatin. Thus, MMPs might play opposing roles in tumor vascularization and invasion. To determine which effect of elevated MMP levels dominates in the progression of metastatic cancer, experimental lung metastasis assays were performed in integrin alpha1-null mice, a genetic model for increased plasma levels of MMP9 and MMP9-generated angiostatin (Pozzi et al., Proc. Natl. Acad. Sci. USA 2000;97:2202-7). We show that while the number of lung colonies in integrin alpha1-null mice was significantly increased compared to their wild-type counterparts, tumor volume was markedly reduced. In vivo treatment with the MMP inhibitor doxycycline resulted in a significant decrease in the number of lung colonies in both genotypes, but the tumors that formed were bigger and more vascularized. Increased tumor vascularization paralleled decreased plasma levels of MMP9 and consequent decreased angiostatin synthesis. These results demonstrate that while inhibition of MMPs prevents and/or reduces tumor invasion and lung metastasis, it has the paradoxical effect of increasing the size and vascularization of metastatic tumors due to decreased generation of inhibitors of endothelial cell proliferation. The continued growth of these large well-vascularized tumors may explain the poor efficacy of MMP inhibitors in lung cancer clinical trials.