Specific degradation of subendothelial matrix proteoglycans by brain-metastatic melanoma and brain endothelial cell heparanases

The origin of brain malignancies at the blood-brain barrier

Despite improvements in extracranial therapy, survival rate for patients suffering from brain metastases remains very poor. This is coupled with the incidence of brain metastases continuing to rise. In this review, we focus on core contributions of the blood-brain barrier to the origin of brain metastases. We first provide an overview of the structure and function of the blood-brain barrier under physiological conditions. Next, we discuss the emerging idea of a pre-metastatic niche, namely that secreted factors and extracellular vesicles from a primary tumor site are able to travel through the circulation and prime the neurovasculature for metastatic invasion. We then consider the neurotropic mechanisms that circulating tumor cells possess or develop that facilitate disruption of the blood-brain barrier and survival in the brain's parenchyma. Finally, we compare and contrast brain metastases at the blood-brain barrier to the primary brain tumor, glioma, examining the process of vessel co-option that favors the survival and outgrowth of brain malignancies.

New Era in the Management of Melanoma Brain Metastases

The remarkable advances in the systemic therapy of metastatic melanoma have now extended the 1-year overall survival rate from 25% to nearing 85%. Systemic treatment in the form of BRAF-targeted therapy and immunotherapy is slowly but surely proving its efficacy in the treatment of metatstatic brain metastases (MBM). Single-agent BRAF inhibitors provide an intracranial response rate of 25% to 40%, whereas the combination of BRAFi/MEKi leads to responses in up to 58%. However, the durability of responses induced by BRAFi/MEKi seems to be even shorter than in extracranial disease. On the other hand, single-agent ipilimumab provides comparable clinical benefit in MBMs as it does in extracranial metastases. Single-agent PD-1 anitbodies induce response rates of approximately 20%, and those responses appear durable. Similarly the combination of CTLA-4+ PD-1 antibodies induces durable responses at an impressive rate of 55% and is safe to administer. Although the local treatment approaches with radiation and surgery remain important and are critically needed in the management of MBM, systemic therapy offers a new dimension that can augment the impact of those therapies and come at a potentially lower cost of neurocognitive impairment. Considerations for combining those modalities are direly needed, in addition to considering novel systemic combinations that target mechanisms specific to MBM. In this report, we will discuss the underlying biology of melanoma brain metastases, the clinical outcomes from recent clinical trials of targeted and immunotherapy, and their impact on clinical practice in the context of existing local therapeutic modalities.

Heparan Sulfate Glycosaminoglycans in Glioblastoma Promote Tumor Invasion

Glioblastoma (GBM) is the most common primary malignant brain tumor of adults and confers a poor prognosis due, in part, to diffuse invasion of tumor cells. Heparan sulfate (HS) glycosaminoglycans, present on the cell surface and in the extracellular matrix, regulate cell signaling pathways and cell-microenvironment interactions. In GBM, the expression of HS glycosaminoglycans and the enzymes that regulate their function are altered, but the actual HS content and structure are unknown. However, inhibition of HS glycosaminoglycan function is emerging as a promising therapeutic strategy for some cancers. In this study, we use liquid chromatography-mass spectrometry analysis to demonstrate differences in HS disaccharide content and structure across four patient-derived tumorsphere lines (GBM1, 5, 6, 43) and between two murine tumorsphere lines derived from murine GBM with enrichment of mesenchymal and proneural gene expression (mMES and mPN, respectively) markers. In GBM, the heterogeneous HS content and structure across patient-derived tumorsphere lines suggested diverse functions in the GBM tumor microenvironment. In GBM5 and mPN, elevated expression of sulfatase 2 (SULF2), an extracellular enzyme that alters ligand binding to HS, was associated with low trisulfated HS disaccharides, a substrate of SULF2. In contrast, other primary tumorsphere lines had elevated expression of the HS-modifying enzyme heparanase (HPSE). Using gene editing strategies to inhibit HPSE, a role for HPSE in promoting tumor cell adhesion and invasion was identified. These studies characterize the heterogeneity in HS glycosaminoglycan content and structure across GBM and reveal their role in tumor cell invasion.Implications: HS-interacting factors promote GBM invasion and are potential therapeutic targets. Mol Cancer Res; 15(11); 1623-33. ©2017 AACR.

Heparanase: Potential roles in multiple sclerosis

Heparanase is a heparan sulfate degrading enzyme that cleaves heparan sulfate (HS) chains present on HS proteoglycans (HSPGs), and has been well characterized for its roles in tumor metastasis and inflammation. However, heparanase is emerging as a contributing factor in the genesis and severity of a variety of neurodegenerative diseases and conditions. This is in part due to the wide variety of HSPGs on which the presence or absence of HS moieties dictates protein function. This includes growth factors, chemokines, cytokines, as well as components of the extracellular matrix (ECM) which in turn regulate leukocyte infiltration into the CNS. Roles for heparanase in stroke, Alzheimer's disease, and glioma growth have been described; roles for heparanase in other disease such as multiple sclerosis (MS) are less well established. However, given its known roles in inflammation and leukocyte infiltration, it is likely that heparanase also contributes to MS pathology. In this review, we will briefly summarize what is known about heparanase roles in the CNS, and speculate as to its potential role in regulating disease progression in MS and its animal model EAE (experimental autoimmune encephalitis), which may justify testing of heparanase inhibitors for MS treatment.

Targeting brain metastases in patients with melanoma

Patients with brain metastases from malignant melanoma historically have a very poor outcome. Surgery and radiotherapy can be used, but for the majority of patients the disease will progress quickly. In the recent past, patients with brain metastases derived only minimal benefit from cytotoxic chemotherapy. Novel therapies that have been shown to be superior to chemotherapy in metastatic melanoma have made their way in clinic and data regarding their use in patients with treated or untreated brain metastases are encouraging. In this paper we describe the use of vemurafenib, dabrafenib, and ipilimumab in patients with melanoma disseminated to the brain in addition to other treatments currently in development.

Revisiting the role of systemic therapies in patients with metastatic melanoma to the CNS

The CNS is a common site of metastasis in patients with malignant melanoma. Locoregional control either with surgery or radiotherapy is first-line treatment for patients with brain metastasis should they be suitable candidates. For those patients who are not and those who progress after previous treatment, there is an unmet clinical need for effective systemic therapies. Systemic cytotoxics, such as temozolamide and fotemustine, have only modest activity, resulting in a median progression-free survival ranging from 1-2 months, in patients with metastatic melanoma to the brain. Newer systemic treatments such as vemurafenib and ipilimumab have been approved for the treatment of melanoma, but evidence regarding their activity in brain metastases is inconclusive due to the limited access of patients to clinical trials. This is now being revised and more data are emerging supporting the inclusion of patients with brain metastasis in trials. In this review, the authors present data regarding the efficacy of systemically administered therapies in patients with metastatic melanoma to the brain.

Emerging insights into the molecular biology of brain metastases

One of the foremost challenges in oncology is developing improved therapies for preventing and treating metastases to the brain. Recent research in this area is bringing about a shift in the understanding of brain metastases. Previously, the occurrence and poor outcomes associated with brain metastases have been largely attributed to the exclusion of anticancer drugs from the brain by the blood-brain barrier (BBB). However, studies in multiple tumor types have also demonstrated that brain metastases have significant molecular differences from primary tumors and extracranial metastases. These molecular differences may not only promote the formation of brain metastases, but they may also contribute to these tumors' poor responsiveness to therapies. Such changes may be intrinsic to the cancer cells or driven by unique interactions with the brain microenvironment. An improved understanding of the molecular characteristics of brain metastases that contribute to their aggressive behaviors will facilitate the development of rational, more effective treatments for these tumors.

Cerebral melanoma metastases: a critical review on diagnostic methods and therapeutic options

Malignant melanoma represents the third most common cause for cerebral metastases after breast and lung cancer. Central nervous system (CNS) metastases occur in 10 to 40% of patients with melanoma. Most of the symptoms of CNS melanoma metastases are unspecific and depend on localization of the lesion. All patients with new neurological signs and a previous primary melanoma lesion must be investigated. Although primary diagnosis may rely on computed tomography scan, magnetic resonance images are usually used in order to study more precisely the characteristics of the lesions in and to embase the surgical plan. Other possible complementary exams are: positron emission tomography, iofetamine cintilography, immunohistochemistry of liquor, monoclonal antibody immunocytology, optical coherence tomography, and transcriptase-polymerase chain reaction. Treatment procedures are indicated based on patient clinical status, presence of unique or multiple lesions, and family agreement. Often surgery, radiosurgery, whole brain radiotherapy, and chemotherapy are combined in order to obtain longer remissions and optimal symptom relieve. Corticoids may be also useful in those cases that present with remarkable peritumoral edema and important mass effect. Despite of the advance in therapeutic options, prognosis for patients with melanoma brain metastases remains poor with a median survival time of six months after diagnosis.

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-beta-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.

Antisense-mediated suppression of Heparanase gene inhibits melanoma cell invasion

Cancer metastasis, is a frequent manifestation of malignant melanoma progression. Successful invasion into distant organs by tumor cells must include attachment to microvessel endothelial cells, and degradation of basement membranes and extracellular matrix (ECM). Heparan sulfate proteoglycans (HSPG) are essential and ubiquitous macromolecules associated with the cell surface and ECM of a wide range of cells and tissues. Heparanase (HPSE-1) is an ECM degradative enzyme, which degrades the heparan sulfate (HS) chains of HSPG at specific intrachain sites. To investigate effects of changes in heparanase gene expression in metastatic melanoma cells, we constructed adenoviral vectors containing the full-length human HPSE-1 cDNA in both sense (Ad-S/hep) and antisense orientations (Ad-AS/hep). We found increased HPSE-1 expression and activity in melanoma cell lines following Ad-S/hep infection by Western blot analyses and specific HPSE-1 activity assay. Conversely, HPSE-1 content was significantly inhibited following infection with Ad-AS/Hep. Importantly, HPSE-1 modulation by these adenoviral constructs correlated with invasive cellular properties in vitro and in vivo. Our results suggest that HPSE-1 not only contributes to the invasive phenotype of melanoma cells, but also that the Ad-AS/hep-mediated inhibition of its enzymatic activity can be efficacious in the prevention and treatment of melanoma metastasis.

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.

Heparanase Degrades Syndecan-1 and Perlecan Heparan Sulfate

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-beta-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.

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

Heparanase, a heparan sulfate-specific endo-beta-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 (IC(50)) were 20-30 microM, or at least 2 times lower than that for suramin. One hundred percent inhibition was observed at concentrations of 100 microM 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 trade mark, 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 microM concentrations of compounds with a significant decrease of invasive values at concentrations as low as 1.5 microM. In addition, NF 127, NF 145 and NF 171 promoted nearly complete inhibition of heparanase-induced angiogenesis at values ranging from 236 microM (for NF 145) to 362 microM (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.

Treatment with the novel anti-angiogenic agent PI-88 is associated with immune-mediated thrombocytopenia

BACKGROUND

The novel molecule PI-88 is a highly sulfonated oligosaccharide which inhibits heparanase activity and competes with heparan sulfate binding of growth factors such as FGF and VEGF. Preclinical data demonstrates that PI-88 inhibits angiogenesis and has anti-metastatic effects. The aim of this phase I study was to determine the recommended dose and toxicity profile of PI-88.

PATIENTS AND METHODS

PI-88 was given intravenously in increasing duration of administration (0.57 mg/kg for 2 h, 0.57 mg/kg/day for 1 day, 4, 7 and 14 consecutive days) and then increasing dose for 14 consecutive days (1.14 mg/kg/day and 2.28 mg/kg/day) in patients with advanced malignancies until dose-limiting toxicity (DLT) was observed. Fourteen assessable patients with advanced malignancies received PI-88 intravenously.

RESULTS

DLT was thrombocytopenia. The thrombocytopenia appeared to be immunologically mediated with the development of anti-heparin platelet factor 4 complex antibodies. There were no other significant toxicities. At the final dose and schedule (2.28 mg/kg/day for 14 days), there was limited evidence of biological activity as measured by the surrogate marker activated partial thromboplastin time (APTT), although two patients had stabilisation of disease.

CONCLUSIONS

In conclusion, PI-88 at a dose of 2.28 mg/kg/day for 14 days resulted in dose-limiting thrombocytopenia which appeared to be immune related. Limited evidence of biological activity was noted. Alternate scheduling and routes of administration are now being explored.

Brain metastases: biology and the role of the brain microenvironment

Metastatic lesions constitute the most frequently occurring malignancy in the brain, and their detection portends a grim prognosis. Efforts to treat these lesions have failed partly because the biologic processes that govern their development are poorly understood. In recent years, it has become evident that metastases occur as a result of a multistep process involving a rigorous natural selection of cells in the primary tumor that bear molecular and biologic characteristics permitting brain metastasis. In addition, recent studies have uncovered the importance of the brain microenvironment and its contribution to the metastatic process. The development of targeted therapies against brain metastases demands a better understanding of these molecular processes and the factors that influence them. This review examines the interplay between tumor cells and host brain tissue in the context of our current understanding of the role of various molecules involved in the metastatic process.

Expression of heparanase in oral cancer cell lines and oral cancer tissues

In the process of metastasis, cancer cells secrete several enzymes which degrade extracellular matrices (ECMs) and basement membranes (BMs) of blood vessels. One of them, heparanase, has been reported to be an important enzyme when metastatic cancer cells invade blood vessels. The enzyme cleaves heparan sulfate (HS), a main component of ECM and BM. In the present study, HS-degrading ability of several human oral cancer cell lines (HSC2, HSC3, HSC4, Ca9-22, NA, ACC3 and Ab-J) and tissues derived from human oral squamous cell carcinomas (both metastatic and non-metastatic) were investigated by measuring heparanase activities and levels of heparanase mRNA by a quantitative reverse transcriptase-polymerase chain reaction. The catalytic activities and the mRNA levels of heparanase showed a good agreement. Clinical demonstration of cancer metastasis generally correlated with high levels of heparanase activity and its mRNA. The results suggest that heparanase activity and its mRNA level are good diagnostic parameters for evaluating the metastatic properties of human oral cancer cells.

Correlation of overexpression of the low-affinity p75 neurotrophin receptor with augmented invasion and heparanase production in human malignant melanoma cells

The role of growth factor receptors in regulating the progression of human melanocytes toward tumorigenicity and ultimately a malignant phenotype is poorly understood. In particular, the autocrine and paracrine influences that modulate cellular invasion and extracellular matrix (ECM)-degradative enzymes in melanoma cells remain undefined at the molecular level. The low-affinity p75 neurotrophin receptor (p75NTR), a cysteine-rich transmembrane glycoprotein, is frequently expressed in advanced stages of human melanoma, but the biological consequences of this expression are unknown. p75NTR can enhance the invasive potential of brain-metastatic melanoma cells in vitro. We have extended here these results and related the level of p75NTR in human metastatic melanoma cells to their invasive potential to target organs other than brain. Fluorescence activated cell sorting (FACS) analysis showed that 3 melanoma cell lines (SK-MEL-146, SK-MEL-119, 70W) had differential p75NTR contents, whereas SK-MEL-147 cells had elevated amounts of p75NTR. Two other melanoma cell lines (SK-MEL-94, SK-MEL-110) with point mutations in the p75NTR transmembrane domain had reduced (SK-MEL-94) or absent (SK-MEL-110) p75NTR. We also examined these cell lines for presence of TrkA receptor, the high-affinity receptor for nerve growth factor (NGF), the prototypic neurotrophin. No TrkA receptor expression was detected in any of the cell lines. The extent of p75NTR expression correlated with the capability of NGF to promote cellular invasion and with production of heparanase, an important ECM-degradative enzyme. Melanoma cells sorted for high p75NTR expression (p75NTR-H cells) had markedly greater (9- to 13-fold increase) invasive capabilities in response to NGF exposure than those sorted for low p75NTR expression (p75NTR-L cells). Additionally, NGF induced a 8- to 10-fold increase of heparanase activity in p75NTR-H cells. Thus, we propose that p75NTR-mediated trophic support profoundly affects melanoma cell invasion to neurotrophin-rich organs.

Role of neurotrophins and neurotrophins receptors in the in vitro invasion and heparanase production of human prostate cancer cells

The role of the neurotrophins (NTs) and their corresponding receptors (NTRs) TrkA, TrkB, TrkC, and p75NTR in neoplasia has received relatively little attention. However, because malignant cell migration within the prostate occurs predominantly by direct extension around prostatic nerves, the presence and possible upregulation of NTs from autocrine/paracrine sources and NTR expression within prostate epithelial tumor cells may be important in metastasis. We have been addressing their expression and interactions in human prostate cancer cell lines (LNCaP, PC-3, and DU145) and their role in prostate cancer invasion. In this study, we demonstrated that nerve growth factor (NGF), the prototypic NT, and NT-4/5 increased in vitro invasion through a reconstituted basement membrane and induced time- and dose-dependent expression of heparanase, a heparan sulfate-specific endo-beta-D-glucuronidase, an important molecular determinant of tumor metastasis. The NT effects were most marked in the DU 145 brain-metastatic cells and were detected at NT concentrations sufficient to fully saturate both low- and high-affinity NTRs. Additionally, we characterized the molecular expression of NT high-affinity (Trk) and low-affinity (p75NTR) receptors in these cell lines by reverse transcription-polymerase chain reaction. These lines had negligible trkA and trkC expression, although trkB was expressed in the three prostatic tumor cell lines examined. The brain-metastatic DU 145 cells were also positive for p75NTR. Our data showed that the NTs and NTRs are important in metastasis and that their expression coincides with transformation to a malignant phenotype capable of invasion along the perineural space and extracapsular metastasis to distant sites. These findings set the stage for more research into this area as related to prostate cancer evolution and may improve therapy for prostate cancer metastasis.