Matrix Metalloproteinase Activity and Osteoclasts in Experimental Prostate Cancer Bone Metastasis Tissue

Abstract

Previously, we and others showed that broad spectrum pharmaceutical inhibition of matrix metalloproteinase (MMP) activity reduces intraosseous tumor burden and bone degradation in animal models of bone metastasis. Herein, we used specific assays to measure net enzymatic activities of individual MMPs during colonization of bone by prostate cancer cells. PC3 cells were injected into the marrow of human fetal femurs previously implanted in SCID mice. Net MMP-9 activity in bone tissues peaked 2 weeks after injection, coinciding with a wave of osteoclast recruitment. In contrast, MMP-2 and MT1-MMP activity did not change. In vitro, co-culture of PC3 cells with bone tissue led to activation of pro-MMP-9 and increases in secreted net MMP-9 activity. Activation of pro-MMP-9 was prevented by metalloprotease inhibitors but not by inhibitors of other classes of proteases. Ribozyme suppression of MMP-9 expression in PC3 cells did not affect pro-MMP-9 activation or net MMP-9 activity and did not affect the phenotype of bone tumors. siRNA targeting of MMP-9 expression in preosteoclasts in vitro demonstrated that tumorinduced preosteoclast motility was dependent on MMP-9 expression. These data suggest that osteoclastderived MMP-9 may represent a potential therapeutic target in bone metastasis and provide a rationale for the development of MMP-9-specific inhibitors. Prostate cancer is the most common cancer and second leading cause of cancer death in American males.1 The overwhelming majority of prostate cancer deaths occurs in patients with metastases, and up to 90% of prostate cancer metastases occurs at skeletal sites. 2 Patients with bone metastasis frequently suffer from pain, pathological fractures, spinal cord compression, hypercalcemia, and bone marrow suppression.3,4 Although prostate cancer metastases typically appear osteosclerotic on radiographical imaging studies, multiple lines of evidence demonstrate clearly that both bone degradation and bone formation are present within the metastatic deposits. Importantly, there is now evidence that therapies that specifically target skeletal metastases, as opposed to general metastases, may extend survival in patients with prostate cancer.

CXCL12/CXCR4 Transactivates HER2 in Lipid Rafts of Prostate Cancer Cells and Promotes Growth of Metastatic Deposits in Bone

“…Several studies further suggest that MMP-9 plays a key role in tumor cell migration and invasion by remodeling the matrix; this fact is further supported by MMP-9 knockdown studies (41)(42)(43). In prostate cancer bone metastasis, MMP-9 plays a key role in the initial establishment of metastatic formation by fostering the tumor cell -induced pathophysiologic matrix remodeling and subsequent expansion of tumor deposits in bone tissue (42). Thus, targeting the CXCL12/CXCR4/HER2 pathway as an upstream activator of MMP-9 expression is an attractive avenue for the clinical management of prostate cancer bone metastasis.…”

“…Furthermore, these data suggest that CXCL12/CXCR4 transactivation of HER2 is an upstream event of Akt activation in prostate cancer cells. Several studies further suggest that MMP-9 plays a key role in tumor cell migration and invasion by remodeling the matrix; this fact is further supported by MMP-9 knockdown studies (41)(42)(43). In prostate cancer bone metastasis, MMP-9 plays a key role in the initial establishment of metastatic formation by fostering the tumor cell -induced pathophysiologic matrix remodeling and subsequent expansion of tumor deposits in bone tissue (42).…”

Proteases as modulators of tumor–stromal interaction: Primary tumors to bone metastases

“…As PC3 prostate cancer cells colonize the bone, there is an observed increase in MMP-9 enzymatic activity. Peak MMP-9 activity correlated with osteoclast numbers and primary cellular sources of MMP-9 in this model were the host osteoclasts [56]. In addition, MMP activity, likely MMP-9, is required to recruit osteoclasts at metastatic sites, as treatment with MMP inhibitors or antisense oligonucleotides directed at MMP-9 abrogated osteoclast recruitment [57;58].…”

Obesity-related systemic factors promote an invasive phenotype in prostate cancer cells

“…Studies have shown that cancer cells increase secretion of matrix metalloproteinases (MMPs), which are enzymes that degrade the basement membrane, thereby facilitating their ability to invade. [15][16][17][18] However, the role of obesity in initiating EMT and invasion remains unknown.…”