Michael J. Duffy

The urokinase‐type plasminogen activator system in cancer metastasis: A review

The urokinase‐type plasminogen activator (u‐PA) system consists of the serine proteinases plasmin and u‐PA; the serpin inhibitors α2‐anti‐plasmin, PAI‐1 and PAI‐2; and the u‐PA receptor (u‐PAR). Two lines of evidence have strongly suggested an important and apparently causal role for the u‐PA system in cancer metastasis: results from experimental model systems with animal tumor metastasis and the finding that high levels of u‐PA, PAI‐1 and u‐PAR in many tumor types predict poor patient prognosis. We discuss here recent observations related to the molecular and cellular mechanisms underlying this role of the u‐PA system. Many findings suggest that the system does not support tumor metastasis by the unrestricted enzyme activity of u‐PA and plasmin. Rather, pericellular molecular and functional interactions between u‐PA, u‐PAR, PAI‐1, extracellular matrix proteins, integrins, endocytosis receptors and growth factors appear to allow temporal and spatial re‐organizations of the system during cell migration and a selective degradation of extracellular matrix proteins during invasion. Differential expression of components of the system by cancer and non‐cancer cells, regulated by paracrine mechanisms, appear to determine the involvement of the system in cancer cell–directed tissue remodeling. A detailed knowledge of these processes is necessary for utilization of the therapeutic potential of interfering with the action of the system in cancers. Int. J. Cancer 72:1–22, 1997.

Metalloproteinases: role in breast carcinogenesis, invasion and metastasis.

The matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases. Their primary function is degradation of proteins in the extracellular matrix. Currently, at least 19 members of this family are known to exist. Based on substrate specificity and domain organization, the MMPs can be loosely divided into four main groups: the interstitial collagenases, gelatinases, stromelysins and membrane-type MMPs. Recent data from model systems suggest that MMPs are involved in breast cancer initiation, invasion and metastasis. Consistent with their role in breast cancer progression, high levels of at least two MMPs (MMP-2 and stromelysin-3) have been found to correlate with poor prognosis in patients with breast cancer. Because MMPs are apparently involved in breast cancer initiation and dissemination, inhibition of these proteinases may be of value both in preventing breast cancer and in blocking metastasis of established tumours

National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines for use of tumor markers in testicular, prostate, colorectal, breast, and ovarian cancers

BACKGROUND Updated National Academy of Clinical Biochemistry (NACB) Laboratory Medicine Practice Guidelines for the use of tumor markers in the clinic have been developed. METHODS Published reports relevant to use of tumor markers for 5 cancer sites--testicular, prostate, colorectal, breast, and ovarian--were critically reviewed. RESULTS For testicular cancer, alpha-fetoprotein, human chorionic gonadotropin, and lactate dehydrogenase are recommended for diagnosis/case finding, staging, prognosis determination, recurrence detection, and therapy monitoring. alpha-Fetoprotein is also recommended for differential diagnosis of nonseminomatous and seminomatous germ cell tumors. Prostate-specific antigen (PSA) is not recommended for prostate cancer screening, but may be used for detecting disease recurrence and monitoring therapy. Free PSA measurement data are useful for distinguishing malignant from benign prostatic disease when total PSA is <10 microg/L. In colorectal cancer, carcinoembryonic antigen is recommended (with some caveats) for prognosis determination, postoperative surveillance, and therapy monitoring in advanced disease. Fecal occult blood testing may be used for screening asymptomatic adults 50 years or older. For breast cancer, estrogen and progesterone receptors are mandatory for predicting response to hormone therapy, human epidermal growth factor receptor-2 measurement is mandatory for predicting response to trastuzumab, and urokinase plasminogen activator/plasminogen activator inhibitor 1 may be used for determining prognosis in lymph node-negative patients. CA15-3/BR27-29 or carcinoembryonic antigen may be used for therapy monitoring in advanced disease. CA125 is recommended (with transvaginal ultrasound) for early detection of ovarian cancer in women at high risk for this disease. CA125 is also recommended for differential diagnosis of suspicious pelvic masses in postmenopausal women, as well as for detection of recurrence, monitoring of therapy, and determination of prognosis in women with ovarian cancer. CONCLUSIONS Implementation of these recommendations should encourage optimal use of tumor markers.

The role of proteolytic enzymes in cancer invasion and metastasis

The production of metastasis appears to involve a number of different proteases including the urokinase form of plasminogen activator, cathepsin B, cathepsin D and various metalloproteases. Early data implicating these proteases in metastasis were mostly indirect and based on correlation studies in animal models. More recent work, using specific protease inhibitors and antibodies against proteases to block experimental metastasis, have provided more direct evidence that proteases play a role in cancer spread. In addition, transfection of genes encoding certain proteases increases the metastatic phenotype of the recipient cells. In human tumours, a number of different proteases also correlate with metastatic potential. It is concluded that certain proteases may be new prognostic markers in cancer as well as new targets for anti-metastatic therapy.

Survivin: A new target for anti-cancer therapy

Survivin is one of the most cancer-specific proteins identified to date, being upregulated in almost all human tumors. Biologically, survivin has been shown to inhibit apoptosis, enhance proliferation and promote angiogenesis. Because of its upregulation in malignancy and its key role in apoptosis, proliferation and angiogenesis, survivin is currently attracting considerable attention as a new target for anti-cancer therapies. In several animal model systems, downregulation of survivin or inactivation of its function has been shown to inhibit tumor growth. Strategies under investigation to target survivin include antisense oligonucleotides, siRNA, ribozymes, immunotherapy and small molecular weight molecules. The translation of these findings to the clinic is currently ongoing with a number of phase I/II clinical trials targeting survivin in progress. These include use of the antisense oligonucleotide LY2181308, the low molecular weight molecule inhibitor YM155 and survivin-directed autologous cytotoxic T lymphocytes. The optimum use of survivin antagonists in the treatment of cancer is likely to be in combination with conventional cancer therapies.

The Urokinase Plasminogen Activator System: Role in Malignancy

The urokinase plasminogen activator (uPA) system consists of the serine protease uPA, its glycolipid-anchored receptor, uPAR and its 2 serpin inhibitors, plasminogen activator inhibitor-1 (PAI-1) and plasminogen activator inhibitor-2 (PAI-2). Recent findings suggest that the uPA system is causally involved at multiple steps in cancer progression. In particular, uPA has been implicated in remodelling of the extracellular matrix, enhancing both cell proliferation and migration and modulating cell adhesion. Consistent with its role in cancer progression, multiple groups have shown that high levels of uPA in primary breast cancers are independently associated with adverse outcome. Paradoxically, high levels of PAI-1 also correlate with poor prognosis in patients with breast cancer. The prognostic value of uPA/PAI-1 in axillary node-negative breast cancer patients was recently validated using both a prospective randomised trial and a pooled analysis, i.e., in 2 different Level 1 Evidence studies. Assay of uPA and PAI-1 may thus help identify low risk node-negative patients for whom adjuvant chemotherapy is unnecessary. Finally, preclinical studies show that either inhibition of uPA catalytic activity or prevention of uPA binding to its receptor reduces tumor growth, angiogenesis and metastasis.

Cancer invasion and metastasis: changing views†

The formation of distant metastasis is the main cause of morbidity and mortality in patients with cancer. The aim of this article is to review recent advances in molecular and clinical aspects of metastasis. Traditionally, genes encoding extracellular matrix (ECM) processing proteases, adhesion proteins, and motility factors were thought to be amongst the main mediators of metastasis. Recently, however, genes activated during the early stages of tumourigenesis were implicated in the process. Conversely, genes thought to be primarily involved in metastasis such as urokinase plasminogen (uPA) and certain matrix metalloproteases (MMPs) are now known to also play a role in the early steps of tumour progression, perhaps by stimulating cell proliferation and/or promoting angiogenesis. Paradoxically, certain endogenous protease inhibitors such as PAI‐1 and TIMP‐1 appear to promote cancer metastasis rather than inhibiting the process. These recent advances in our understanding should lead to the development of new molecular markers for predicting the likely formation of metastasis as well as the identification of new targets for anti‐metastatic therapies. Copyright

Urokinase-plasminogen activator, a marker for aggressive breast carcinomas. Preliminary report

Plasminogen activator is a serine protease which exists in two forms, known as tissue‐type plasminogen activator and urokinase‐type plasminogen activator. Here, we show that urokinase‐type plasminogen activator activity in primary breast carcinomas correlates with both size of tumor and number of axillary nodes with metastases. Patients with primary carcinomas containing high levels of urokinase‐type plasminogen activator activity had a significantly shorter disease‐free interval than patients with low levels of activity. It is concluded that urokinase‐plasminogen activator may be a new prognostic marker in breast cancer.

Tumor Markers in Breast Cancer – European Group on Tumor Markers Recommendations

Recommendations are presented for the routine clinical use of serum and tissue-based markers in the diagnosis and management of patients with breast cancer. Their low sensitivity and specificity preclude the use of serum markers such as the MUC-1 mucin glycoproteins (CA 15.3, BR 27.29) and carcinoembryonic antigen in the diagnosis of early breast cancer. However, serial measurement of these markers can result in the early detection of recurrent disease as well as indicate the efficacy of therapy. Of the tissue-based markers, measurement of estrogen and progesterone receptors is mandatory in the selection of patients for treatment with hormone therapy, while HER-2 is essential in selecting patients with advanced breast cancer for treatment with Herceptin (trastuzumab). Urokinase plasminogen activator and plasminogen activator inhibitor 1 are recently validated prognostic markers for lymph node-negative breast cancer patients and thus may be of value in selecting node-negative patients that do not require adjuvant chemotherapy.

Activated Phosphoinositide 3-Kinase/AKT Signaling Confers Resistance to Trastuzumab but not Lapatinib

Trastuzumab and lapatinib provide clinical benefit to women with human epidermal growth factor receptor 2 (HER)–positive breast cancer. However, not all patients whose tumors contain the HER2 alteration respond. Consequently, there is an urgent need to identify new predictive factors for these agents. The aim of this study was to investigate the role of receptor tyrosine kinase signaling and phosphoinositide 3-kinase (PI3K)/AKT pathway activation in conferring resistance to trastuzumab and lapatinib. To address this question, we evaluated response to trastuzumab and lapatinib in a panel of 18 HER2-amplified cell lines, using both two- and three-dimensional culture. The SUM-225, HCC-1419, HCC-1954, UACC-893, HCC-1569, UACC-732, JIMT-1, and MDA-453 cell lines were found to be innately resistant to trastuzumab, whereas the MDA-361, MDA-453, HCC-1569, UACC-732, JIMT-1, HCC-202, and UACC-893 cells are innately lapatinib resistant. Lapatinib was active in de novo (SUM-225, HCC-1419, and HCC-1954) and in a BT-474 cell line with acquired resistance to trastuzumab. In these cells, trastuzumab had little effect on AKT phosphorylation, whereas lapatinib retained activity through the dephosphorylation of AKT. Increased phosphorylation of HER2, epidermal growth factor receptor, HER3, and insulin-like growth factor IR correlated with response to lapatinib but not trastuzumab. Loss of PTEN or the presence of activating mutations in PI3K marked resistance to trastuzumab, but lapatinib response was independent of these factors. Thus, increased activation of the PI3K/AKT pathway correlates with resistance to trastuzumab, which can be overcome by lapatinib. In conclusion, pharmacologic targeting of the PI3K/AKT pathway may provide benefit to HER2-positive breast cancer patients who are resistant to trastuzumab therapy. Mol Cancer Ther; 9(6); 1489–502. ©2010 AACR.