Dario Marchetti

The Identification and Characterization of Breast Cancer CTCs Competent for Brain Metastasis

EpCAM− CTCs isolated from breast cancer patients express markers needed to promote brain metastasis. Cancer Cells in Blood, Directed to the Brain Circulating tumor cells (CTCs) have been touted as exciting sources of diagnostic information, where the number of CTCs may correlate with disease progression or treatment success. However, little is known about the biology of these cells and why they are in the bloodstream, mostly because technology has prevented their long-term culture and analysis outside the body. Now, Zhang et al. have figured out how to isolate CTCs from breast cancer patients and study their metastatic potential. Starting with cancer-associated circulating cells isolated from eight patients, the authors ultimately selected a population of CTCs from three patients that was EGFR+/HPSE+/ALDH1+/CD45−/EpCAM−. These CTCs were then grown as cell lines in culture, which allowed the authors to study their cancerous behavior in more detail. Zhang et al. hypothesized that a specific protein signature was present in these cells, essentially “telling” these cells to metastasize to the brain. After identifying the “brain metastasis selected markers (BMSMs)” as HER2+/EGFR+/HPSE+/Notch1+, the authors injected these selected patient CTCs into mice. By 6 weeks, between 60 and 80% of the BMSM CTCs metastasized to brain compared with only 0 to 20% for the parental CTC lines. This protein signature, derived from human cells and tested in mice, could possibly govern brain metastatic breast cancer in patients. The next step will be to validate the presence of this BMSM CTC signature in a large number of breast cancer patients with brain metastases, with the goal of not only predicting disease course but also better understanding metastatic cancer. Brain metastatic breast cancer (BMBC) is uniformly fatal and increasing in frequency. Despite its devastating outcome, mechanisms causing BMBC remain largely unknown. The mechanisms that implicate circulating tumor cells (CTCs) in metastatic disease, notably in BMBC, remain elusive. We characterize CTCs isolated from peripheral blood mononuclear cells of patients with breast cancer and also develop CTC lines from three of these patients. In epithelial cell adhesion molecule (EpCAM)–negative CTCs, we identified a potential signature of brain metastasis comprising “brain metastasis selected markers (BMSMs)” HER2+/EGFR+/HPSE+/Notch1+. These CTCs, which are not captured by the CellSearch platform because of their EpCAM negativity, were analyzed for cell invasiveness and metastatic competency in vivo. CTC lines expressing the BMSM signature were highly invasive and capable of generating brain and lung metastases when xenografted in nude mice. Notably, increased brain metastatic capabilities, frequency, and quantitation were detected in EpCAM− CTCs overexpressing the BMSM signature. The presence of proteins of the BMSM CTC signature was also detected in the metastatic lesions of animals. Collectively, we provide evidence of isolation, characterization, and long-term culture of human breast cancer CTCs, leading to the description of a BMSM protein signature that is suggestive of CTC metastatic competency to the brain.

Heparanase Degrades Syndecan-1 and Perlecan Heparan Sulfate FUNCTIONAL IMPLICATIONS FOR TUMOR CELL INVASION

Heparanase (HPSE-1) is involved in the degradation of both cell-surface and extracellular matrix (ECM) heparan sulfate (HS) in normal and neoplastic tissues. Degradation of heparan sulfate proteoglycans (HSPG) in mammalian cells is dependent upon the enzymatic activity of HPSE-1, an endo-β-d-glucuronidase, which cleaves HS using a specific endoglycosidic hydrolysis rather than an eliminase type of action. Elevated HPSE-1 levels are associated with metastatic cancers, directly implicating HPSE-1 in tumor progression. The mechanism of HPSE-1 action to promote tumor progression may involve multiple substrates because HS is present on both cell-surface and ECM proteoglycans. However, the specific targets of HPSE-1 action are not known. Of particular interest is the relationship between HPSE-1 and HSPG, known for their involvement in tumor progression. Syndecan-1, an HSPG, is ubiquitously expressed at the cell surface, and its role in cancer progression may depend upon its degradation. Conversely, another HSPG, perlecan, is an important component of basement membranes and ECM, which can promote invasive behavior. Down-regulation of perlecan expression suppresses the invasive behavior of neoplastic cells in vitro and inhibits tumor growth and angiogenesis in vivo. In this work we demonstrate the following. 1) HPSE-1 cleaves HS present on the cell surface of metastatic melanoma cells. 2) HPSE-1 specifically degrades HS chains of purified syndecan-1 or perlecan HS. 3) Syndecan-1 does not directly inhibit HPSE-1 enzymatic activity. 4) The presence of exogenous syndecan-1 inhibits HPSE-1-mediated invasive behavior of melanoma cells by in vitro chemoinvasion assays. 5) Inhibition of HPSE-1-induced invasion requires syndecan-1 HS chains. These results demonstrate that cell-surface syndecan-1 and ECM perlecan are degradative targets of HPSE-1, and syndecan-1 regulates HPSE-1 biological activity. This suggest that expression of syndecan-1 on the melanoma cell surface and its degradation by HPSE-1 are important determinants in the control of tumor cell invasion and metastasis.

Heparanase promotes tumor infiltration and antitumor activity of CAR-redirected T-lymphocytes

Adoptive transfer of chimeric antigen receptor (CAR)-redirected T lymphocytes (CAR-T cells) has had less striking therapeutic effects in solid tumors than in lymphoid malignancies. Although active tumor-mediated immunosuppression may have a role in limiting the efficacy of CAR-T cells, functional changes in T lymphocytes after their ex vivo manipulation may also account for the reduced ability of cultured CAR-T cells to penetrate stroma-rich solid tumors compared with lymphoid tissues. We therefore studied the capacity of human in vitro–cultured CAR-T cells to degrade components of the extracellular matrix (ECM). In contrast to freshly isolated T lymphocytes, we found that in vitro–cultured T lymphocytes lack expression of the enzyme heparanase (HPSE), which degrades heparan sulfate proteoglycans, the main components of ECM. We found that HPSE mRNA is downregulated in in vitro–expanded T cells, which may be a consequence of p53 (officially known as TP53, encoding tumor protein 53) binding to the HPSE gene promoter. We therefore engineered CAR-T cells to express HPSE and showed their improved capacity to degrade the ECM, which promoted tumor T cell infiltration and antitumor activity. The use of this strategy may enhance the activity of CAR-T cells in individuals with stroma-rich solid tumors.

MicroRNA-1258 Suppresses Breast Cancer Brain Metastasis by Targeting Heparanase

Heparanase (HPSE) is a potent protumorigenic, proangiogenic, and prometastatic enzyme that is overexpressed in brain metastatic breast cancer (BMBC). However, little is known about the regulation of this potential therapeutic target in BMBC, which remains very poorly managed in the clinic. We hypothesized that HPSE gene expression might be regulated by micro RNA that might be exploited therapeutically. Using miRanda and RNAhybrid, we identified miR-1258 as a candidate micro RNA that may directly target HPSE and suppress BMBC. In support of our hypothesis, we found that miR-1258 levels inversely correlated with heparanase expression, enzymatic activity, and cancer cell metastatic propensities, being lowest in highly aggressive BMBC cell variants compared with either nontumorigenic or nonmetastatic human mammary epithelial cells. These findings were validated by analyses of miR-1258 and heparanase content in paired clinical specimens of normal mammary gland versus invasive ductal carcinoma, and primary breast cancer versus BMBC. In regulatory experiments, miR-1258 inhibited the expression and activity of heparanase in BMBC cells, whereas modulating heparanase blocked the phenotypic effects of miR-1258. In functional experiments, stable expression of miR-1258 in BMBC cells inhibited heparanase in vitro cell invasion and experimental brain metastasis. Together, our findings illustrate how micro RNA mechanisms are linked to brain metastatic breast cancer through heparanase control, and they offer a strong rationale to develop heparanase-based therapeutics for treatment of cancer patients with brain metastases, BMBC in particular.

Rescue of motoneurons from cell death by a purified skeletal muscle polypeptide: Effects of the ChAT development factor, CDF

Rat skeletal muscle contains a 22 kd polypeptide that increases the level of choline acetyltransferase (ChAT) activity in cultures of embryonic rat spinal cord neurons and has been purified to homogeneity. The application of this factor, ChAT development factor or CDF, to developing chick embryos during the period of naturally occurring motoneuron cell death significantly increased the survival of motoneurons but did not affect the survival of dorsal root ganglion neurons or sympathetic preganglionic neurons (column of Terni). These results provide the first demonstration that an isolated, skeletal muscle-derived molecule can selectively enhance the survival of motoneurons in vivo and suggest that CDF may function in vivo to regulate the survival and development of motoneurons.

Brain metastases in melanoma: roles of neurotrophins.

Brain metastasis, which occurs in 20% to 40% of all cancer patients, is an important cause of neoplastic morbidity and mortality. Successful invasion into the brain by tumor cells must include attachment to microvessel endothelial cells, penetration through the blood-brain barrier, and, of relevance, a response to brain survival and growth factors. Neurotrophins (NTs) are important in brain-invasive steps. Human melanoma cell lines express low-affinity NT receptor p75NTR in relation to their brain-metastatic propensity with their invasive properties being regulated by NGF, or nerve growth factor, the prototypic NT. They also express functional TrkC, the putative receptor for the invasion-promoting NT-3. In brain-metastatic melanoma cells, NTs promote invasion by enhancing the production of extracellular matrix (ECM)-degradative enzymes such as heparanase, an enzyme capable of locally destroying both ECM and the basement membrane of the blood-brain barrier. Heparanase is an endo-beta-d-glucuronidase that cleaves heparan sulfate (HS) chains of ECM HS proteoglycans, and it is a unique metastatic determinant because it is the dominant mammalian HS degradative enzyme. Brain-metastatic melanoma cells also produce autocrine/paracrine factors that influence their growth, invasion, and survival in the brain. Synthesis of these factors may serve to regulate NT production by brain cells adjacent to the neoplastic invasion front, such as astrocytes. Increased NT levels have been observed in tumor-adjacent tissues at the invasion front of human brain melanoma. Additionally, astrocytes may contribute to the brain-metastatic specificity of melanoma cells by producing NT-regulated heparanase. Trophic, autocrine, and paracrine growth factors may therefore determine whether metastatic cells can successfully invade, colonize, and grow in the CNS.

Role of ω-3 polyunsaturated fatty acids on cyclooxygenase-2 metabolism in brain-metastatic melanoma

Cyclooxygenase-2 (COX-2) is important in the progression of epithelial tumors. Evidence indicates that ω-6 PUFAs such as arachidonic acid (AA) promote the growth of tumor cells; however, ω-3 fatty acids [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] inhibit tumor cell proliferation. We investigated the effects of ω-3 PUFA on the expression and function of COX-2 in 70W, a human melanoma cell line that metastasizes to the brain in nude mice. We show that 1) tumor necrosis factor-α upregulates the expression of both COX-2 mRNA and prostaglandin E2 (PGE2) production, and 2) ω-3 and ω-6 PUFA regulate COX-2 mRNA expression and PGE2 production. AA increased COX-2 mRNA expression and prostaglandin production in ω-6-stimulated 70W cells. Conversely, COX-2 mRNA expression decreased in cells incubated with EPA or DHA. AA increased Matrigel™ invasion 2.4-fold, whereas EPA or DHA did not. Additionally, PGE2 increased in vitro invasion 2.5-fold, whereas exposure to PGE3 significantly decreased invasion. Our results demonstrate that incubation of 70W cells with either AA or PGE2 increased invasiveness, whereas incubation with EPA or DHA downregulated both COX-2 mRNA and protein expression, with a subsequent decrease in Matrigel™ invasion. Taken together, these results indicate that ω-3 PUFA regulate COX-2-mediated invasion in brain-metastatic melanoma.

MicroRNA and protein profiling of brain metastasis competent cell-derived exosomes.

Exosomes are small membrane vesicles released by most cell types including tumor cells. The intercellular exchange of proteins and genetic material via exosomes is a potentially effective approach for cell-to-cell communication and it may perform multiple functions aiding to tumor survival and metastasis. We investigated microRNA and protein profiles of brain metastatic (BM) versus non-brain metastatic (non-BM) cell-derived exosomes. We studied the cargo of exosomes isolated from brain-tropic 70W, MDA-MB-231BR, and circulating tumor cell brain metastasis-selected markers (CTC1BMSM) variants, and compared them with parental non-BM MeWo, MDA-MB-231P and CTC1P cells, respectively. By performing microRNA PCR array we identified one up-regulated (miR-210) and two down-regulated miRNAs (miR-19a and miR-29c) in BM versus non-BM exosomes. Second, we analyzed the proteomic content of cells and exosomes isolated from these six cell lines, and detected high expression of proteins implicated in cell communication, cell cycle, and in key cancer invasion and metastasis pathways. Third, we show that BM cell-derived exosomes can be internalized by non-BM cells and that they effectively transport their cargo into cells, resulting in increased cell adhesive and invasive potencies. These results provide a strong rationale for additional investigations of exosomal proteins and miRNAs towards more profound understandings of exosome roles in brain metastasis biogenesis, and for the discovery and application of non-invasive biomarkers for new therapies combating brain metastasis.

Inhibition of heparanase activity and heparanase‐induced angiogenesis by suramin analogues

Heparanase, a heparan sulfate‐specific endo‐β‐D‐glucuronidase, plays an important role in tumor cell metastasis through the degradation of extracellular matrix heparan sulfate proteoglycans (ECM HSPG). Heparanase activity correlates with the metastatic propensity of tumor cells. Suramin, a polysulfonated naphthylurea, is an inhibitor of heparanase with suramin analogues shown to possess antiangiogenic and antiproliferative properties. We investigated the effects of selected suramin analogues (NF 127, NF 145 and NF 171) on heparanase activity and heparanase‐driven angiogenesis. Studies of the ability of cellular extracts and purified heparanase from human, highly invasive and brain‐metastatic melanoma (70W) cells revealed that heparanase expressed by these cells was effectively inhibited by suramin analogues in a dose‐dependent manner. These analogues possessed more potent heparanase inhibitory activities than suramin: The concentrations required for 50% heparanase inhibition (IC50) were 20–30 μM, or at least 2 times lower than that for suramin. One hundred percent inhibition was observed at concentrations of 100 μM and higher. Of relevance, these compounds significantly decreased (i) the invasive capacity of human 70W cells by chemoinvasion assays performed with filters coated with purified HSPG or Matrigel™, and (ii) blood vessel formation by in vivo angiogenic assays, thus linking their antiangiogenic properties with impedance of heparanase‐induced angiogenesis. Specifically, inhibition of invasion by NF 127, NF 145 and NF 171 was found at 10 μM concentrations of compounds with a significant decrease of invasive values at concentrations as low as 1.5 μM. In addition, NF 127, NF 145 and NF 171 promoted nearly complete inhibition of heparanase‐induced angiogenesis at values ranging from 236 μM (for NF 145) to 362 μM (for NF 127). These results further emphasize the importance of heparanase in invasive and angiogenic mechanisms and the potential clinical application of heparanase inhibitors such as suramin analogues in cancers and angiogenesis‐dependent diseases.

Cell surface heparan sulfate released by heparanase promotes melanoma cell migration and angiogenesis.

Heparan sulfate (HS) proteoglycans are essential components of the cell‐surface and extracellular matrix (ECM) which provide structural integrity and act as storage depots for growth factors and chemokines, through their HS side chains. Heparanase (HPSE) is the only mammalian endoglycosidase known that cleaves HS, thus contributing to matrix degradation and cell invasion. The enzyme acts as an endo‐β‐D‐glucuronidase resulting in HS fragments of discrete molecular weight size. Cell‐surface HS is known to inhibit or stimulate tumorigenesis depending upon size and composition. We hypothesized that HPSE contributes to melanoma metastasis by generating bioactive HS from the cell‐surface to facilitate biological activities of tumor cells as well as tumor microenvironment. We removed cell‐surface HS from melanoma (B16B15b) by HPSE treatment and resulting fragments were isolated. Purified cell‐surface HS stimulated in vitro B16B15b cell migration but not proliferation, and importantly, enhanced in vivo angiogenesis. Furthermore, melanoma cell‐surface HS did not affect in vitro endothelioma cell (b.End3) migration. Our results provide direct evidence that, in addition to remodeling ECM and releasing growth factors and chemokines, HPSE contributes to aggressive phenotype of melanoma by releasing bioactive cell‐surface HS fragments which can stimulate melanoma cell migration in vitro and angiogenesis in vivo. J. Cell. Biochem. 106: 200–209, 2009.