The role of trophic factors and autocrine/paracrine growth factors in brain metastasis

Pathophysiological aspects of transferrin-A potential nano-based drug delivery signaling molecule in therapeutic target for varied diseases

Transferrin (Tf), widely known for its role as an iron-binding protein, exemplifies multitasking in biological processes. The role of Tf in iron metabolism involves both the uptake of iron from Tf by various cells, as well as the endocytosis mediated by the complex of Tf and the transferrin receptor (TfR). The direct conjugation of the therapeutic compound and immunotoxin studies using Tf peptide or anti-Tf receptor antibodies as targeting moieties aims to prolong drug circulation time and augment efficient cellular drug uptake, diminish systemic toxicity, traverse the blood-brain barrier, restrict systemic exposure, overcome multidrug resistance, and enhance therapeutic efficacy with disease specificity. This review primarily discusses the various biological actions of Tf, as well as the development of Tf-targeted nano-based drug delivery systems. The goal is to establish the use of Tf as a disease-targeting component, accentuating the potential therapeutic applications of this protein.

The Journey of Cancer Cells to the Brain: Challenges and Opportunities

Cancer metastases into the brain constitute one of the most severe, but not uncommon, manifestations of cancer progression. Several factors control how cancer cells interact with the brain to establish metastasis. These factors include mediators of signaling pathways participating in migration, infiltration of the blood-brain barrier, interaction with host cells (e.g., neurons, astrocytes), and the immune system. Development of novel therapies offers a glimpse of hope for increasing the diminutive life expectancy currently forecasted for patients suffering from brain metastasis. However, applying these treatment strategies has not been sufficiently effective. Therefore, there is a need for a better understanding of the metastasis process to uncover novel therapeutic targets. In this review, we follow the journey of various cancer cells from their primary location through the diverse processes that they undergo to colonize the brain. These processes include EMT, intravasation, extravasation, and infiltration of the blood-brain barrier, ending up with colonization and angiogenesis. In each phase, we focus on the pathways engaging molecules that potentially could be drug target candidates.

Cutaneous melanoma dissemination is dependent on the malignant cell properties and factors of intercellular crosstalk in the cancer microenvironment (Review)

The incidence of cutaneous malignant melanoma has been steadily increasing worldwide for several decades. This phenomenon seems to follow the trend observed in many types of malignancies caused by multiple significant factors, including ageing. Despite the progress in cutaneous malignant melanoma therapeutic options, the curability of advanced disease after metastasis represents a serious challenge for further research. In this review, we summarise data on the microenvironment of cutaneous malignant melanoma with emphasis on intercellular signalling during the disease progression. Malignant melanocytes with features of neural crest stem cells interact with non‑malignant populations within this microenvironment. We focus on representative bioactive factors regulating this intercellular crosstalk. We describe the possible key factors and signalling cascades responsible for the high complexity of the melanoma microenvironment and its premetastatic niches. Furthermore, we present the concept of melanoma early becoming a systemic disease. This systemic effect is presented as a background for the new horizons in the therapy of cutaneous melanoma.

Nongenetic Mechanisms of Drug Resistance in Melanoma

Resistance to targeted and immune-based therapies limits cures in patients with metastatic melanoma. A growing number of reports have identified nongenetic primary resistance mechanisms including intrinsic microenvironment- and lineage plasticity–mediated processes serving critical functions in the persistence of disease throughout therapy. There is a temporally shifting spectrum of cellular identities fluidly occupied by therapy-persisting melanoma cells responsible for driving therapeutic resistance and metastasis. The key epigenetic, metabolic, and phenotypic reprogramming events requisite for the manifestation and maintenance of so-called persister melanoma populations remain poorly understood and underscore the need to comprehensively investigate actionable vulnerabilities. Here we attempt to integrate the field's observations on nongenetic mechanisms of drug resistance in melanoma. We postulate that the future design of therapeutic strategies specifically addressing therapy-persisting subpopulations of melanoma will improve the curative potential of therapy for patients with metastatic disease.

Solanine Attenuates Hepatocarcinoma Migration and Invasion Induced by Acetylcholine

AIM

Evidence has provided an explanation of the correlation between the nervous system and the tumor microenvironment. Neurotransmitters may be involved in different aspects of cancer progression. The glycoalkaloid solanine has been reported to suppress neural signaling pathways and exists in numerous plants, including Solanum nigrum, which have been demonstrated to inhibit cancer cell proliferation.

METHODS

We evaluated the potentials of solanine on inhibiting acetylcholine-induced cell proliferation and migration in hepatocellular carcinoma cells.

RESULTS

The results indicated that solanine markedly attenuated cell proliferation and migration via inhibiting epithelial-mesenchymal transition and matrix metalloproteinases in acetylcholine-treated Hep G2 cells. In addition, exosomes derived from acetylcholine-treated Hep G2 cells were isolated, and solanine showed inhibiting effects of extrahepatic metastasis on blocking cell proliferation in exosome-treated A549 lung carcinoma cells through regulating microRNA-21 expression.

CONCLUSION

Solanine has strong potential for application in integrative cancer therapy.

Stereotactic radiosurgery (SRS) in the modern management of patients with brain metastases

Stereotactic radiosurgery (SRS) is an established non-invasive ablative therapy for brain metastases. Early clinical trials with SRS proved that tumor control rates are superior to whole brain radiotherapy (WBRT) alone. As a result, WBRT plus SRS was widely adopted for patients with a limited number of brain metastases (“limited number” customarily means 1-4). Subsequent trials focused on answering whether WBRT upfront was necessary at all. Based on current randomized controlled trials (RCTs) and meta-analyses comparing SRS alone to SRS plus WBRT, adjuvant WBRT results in better intracranial control; however, at the expense of neurocognitive functioning and quality of life. These adverse effects of WBRT may also negatively impact on survival in younger patients. Based on the results of these studies, treatment has shifted to SRS alone in patients with a limited number of metastases. Additionally, RCTs are evaluating the role of SRS alone in patients with >4 brain metastases. New developments in SRS include fractionated SRS for large tumors and the integration of SRS with targeted systemic therapies that cross the blood brain barrier and/or stimulate an immune response. We present in this review the current high level evidence and rationale supporting SRS as the standard of care for patients with limited brain metastases, and emerging applications of SRS.

Control of the blood-brain barrier function in cancer cell metastasis

Cerebral metastases are the most common brain neoplasms seen clinically in the adults and comprise more than half of all brain tumours. Actual treatment options for brain metastases that include surgical resection, radiotherapy and chemotherapy are rarely curative, although palliative treatment improves survival and life quality of patients carrying brain-metastatic tumours. Chemotherapy in particular has also shown limited or no activity in brain metastasis of most tumour types. Many chemotherapeutic agents used systemically do not cross the blood-brain barrier (BBB), whereas others may transiently weaken the BBB and allow extravasation of tumour cells from the circulation into the brain parenchyma. Increasing evidence points out that the interaction between the BBB and tumour cells plays a key role for implantation and growth of brain metastases in the central nervous system. The BBB, as the tightest endothelial barrier, prevents both early detection and treatment by creating a privileged microenvironment. Therefore, as observed in several in vivo studies, precise targetting the BBB by a specific transient opening of the structure making it permeable for therapeutic compounds, might potentially help to overcome this difficult clinical problem. Moreover, a better understanding of the molecular features of the BBB, its interrelation with metastatic tumour cells and the elucidation of cellular mechanisms responsible for establishing cerebral metastasis must be clearly outlined in order to promote treatment modalities that particularly involve chemotherapy. This in turn would substantially expand the survival and quality of life of patients with brain metastasis, and potentially increase the remission rate. Therefore, the focus of this review is to summarise the current knowledge on the role and function of the BBB in cancer metastasis.

Imaging of Primary Brain Tumors and Metastases with Fast Quantitative 3-Dimensional Magnetization Transfer

BACKGROUND AND PURPOSE

This study assesses whether magnetization transfer (MT) imaging provides additive information to conventional MRI in brain tumors.

METHODS

MT data of 26 patients with neoplastic and metastatic brain tumors were analyzed at 1.5 T. For the 3 largest tumor groups investigated in this study--glioblastoma multiforme (GBM), meningiomas, and metastases-statistical comparisons were performed. Analyzed MT parameters included the magnetization transfer ratio (MTR) and 4 quantitative MT parameters (qMT): Relaxation times (T1, T2), exchange rate (kf), and macromolecular content (F). Total imaging time of high-resolution whole brain MTR and qMT imaging with balanced steady-state free precession required 9 minutes. Five ROIs were chosen: Contrast-enhancing (T1W-CE), noncontrast-enhancing (T1W-non-CE), proximal hyperintensity (T2W-pSI), distal hyperintensity (T2W-dSI), and a reference (ref).

RESULTS

Pathologies showed significant (P < .05) MT changes (MTR and qMT) compared to the reference. The T1W-CE, T1W-non-CE, and T2W-pSI ROIs of GBMs, meningiomas, and metastases showed significant differences in MTR and qMT estimates. Similar MTR with significant different qMT values were observed in several ROIs among different lesions. MT maps (MTR and qMT) indicated changes in tissue appearing unaffected on MRI in most glial tumors.

CONCLUSIONS

MTR and qMT imaging enables a better differentiation between brain tumors and provides additive information to MRI.

Novel treatments for melanoma brain metastases

BACKGROUND

The development of brain metastases is common in patients with melanoma and is associated with a poor prognosis. Treating patients with melanoma brain metastases (MBMs) is a major therapeutic challenge. Standard approaches with conventional chemotherapy are disappointing, while surgery and radiotherapy have improved outcomes.

METHODS

In this article, we discuss the biology of MBMs, briefly outline current treatment approaches, and emphasize novel and emerging therapies for MBMs.

RESULTS

The mechanisms that underlie the metastases of melanoma to the brain are unknown; therefore, it is necessary to identify pathways to target MBMs. Most patients with MBMs have short survival times. Recent use of immune-based and targeted therapies has changed the natural history of metastatic melanoma and may be effective for the treatment of patients with MBMs.

CONCLUSIONS

Developing a better understanding of the factors responsible for MBMs will lead to improved management of this disease. In addition, determining the optimal treatments for MBMs and how they can be optimized or combined with other therapies, along with appropriate patient selection, are challenges for the management of this disease.

Melanoma brain colonization involves the emergence of a brain-adaptive phenotype

The brain offers a unique microenvironment that plays an important role in the establishment and progression of metastasis. However, the molecular determinants that promote development of melanoma brain metastases are largely unknown. Utilizing two species of immune-compromised animals, with in vivo cultivated metastatic tissues along with their corresponding host tissues in a metastasis model, we here identify molecular events associated with melanoma brain metastases. We find that the transcriptional changes in the melanoma cells, as induced by the brain-microenvironment in both host species, reveal the opportunistic nature of melanoma in this biological context in rewiring the molecular framework of key molecular players with their associated biological processes. Specifically, we identify the existence of a neuron-like melanoma phenotype, which includes synaptic characteristics and a neurotransmission-like circuit involving glutamate. Regulation of gene transcription and neuron-like plasticity by Ca(2+)-dependent signaling appear to occur through glutamate receptor activation. The brain-adaptive phenotype was found as more prominent in the early metastatic growth phases compared to a later phase, emphasizing a temporal requirement of critical events in the successful colonization of the brain. Analysis of the host tissue uncovered a cooperative inflammatory microenvironment formed by activated host cells that permitted melanoma growth at the expense of the host organism. Combined experimental and computational approaches clearly highlighted genes and signaling pathways being shared with neurodegenerative diseases. Importantly, the identification of essential molecular networks that operate to promote the brain-adaptive phenotype is of clinical relevance, as they represent leads to urgently needed therapeutic targets.

Role of the nervous system in cancer metastasis

The notion that tumors lack innervation was proposed several years ago. However, nerve fibers are irregulatedly found in some tumor tissues. Their terminals interaction with cancer cells are considered to be neuro-neoplastic synapses. Moreover, neural-related factors, which are important players in the development and activity of the nervous system, have been found in cancer cells. Thus, they establish a direct connection between the nervous system and tumor cells. They modulate the process of metastasis, including degradation of base membranes, cancer cell invasion, migration, extravasation and colonization. Peripheral nerve invasion provides another pathway for the spread of cancer cells when blood and lymphatic metastases are absent, which is based on the interactions between the microenvironments of nerve fibers and tumor cells. The nervous system also modulates angiogenesis, the tumor microenvironment, bone marrow, immune functions and inflammatory pathways to influence metastases. Denervation of the tumor has been reported to enhance cancer metastasis. Stress, social isolation and other emotional factors may increase distant metastasis through releasing hormones from the brain, the hypothalamic-pituitary-adrenal axis and autonomic nervous system. Disruption of circadian rhythms will also promote cancer metastasis through direct and indirect actions of the nervous system. Therefore, the nervous system plays an important role in cancer metastasis.

Role of the blood-brain barrier in the formation of brain metastases

The majority of brain metastases originate from lung cancer, breast cancer and malignant melanoma. In order to reach the brain, parenchyma metastatic cells have to transmigrate through the endothelial cell layer of brain capillaries, which forms the morphological basis of the blood-brain barrier (BBB). The BBB has a dual role in brain metastasis formation: it forms a tight barrier protecting the central nervous system from entering cancer cells, but it is also actively involved in protecting metastatic cells during extravasation and proliferation in the brain. The mechanisms of interaction of cancer cells and cerebral endothelial cells are largely uncharacterized. Here, we provide a comprehensive review on our current knowledge about the role of junctional and adhesion molecules, soluble factors, proteolytic enzymes and signaling pathways mediating the attachment of tumor cells to brain endothelial cells and the transendothelial migration of metastatic cells. Since brain metastases represent a great therapeutic challenge, it is indispensable to understand the mechanisms of the interaction of tumor cells with the BBB in order to find targets of prevention of brain metastasis formation.

The biology of brain metastases-translation to new therapies

Brain metastases are a serious obstacle in the treatment of patients with solid tumors and contribute to the morbidity and mortality of these cancers. It is speculated that the frequency of brain metastasis is increasing for several reasons, including improved systemic therapy and survival, and detection of metastases in asymptomatic patients. The lack of preclinical models that recapitulate the clinical setting and the exclusion of patients with brain metastases from most clinical trials have slowed progress. Molecular factors contributing to brain metastases are being elucidated, such as genes involved in cell adhesion, extravasation, metabolism, and cellular signaling. Furthermore, the role of the unique brain microenvironment is beginning to be explored. Although the presence and function of the blood-brain barrier in metastatic tumors is still poorly understood, it is likely that some tumor cells are protected from therapeutics by the blood-tumor barrier, creating a sanctuary site. This Review discusses what is known about the biology of brain metastases, what preclinical models are available to study the disease, and which novel therapeutic strategies are being studied in patients.

Decoding melanoma metastasis

Metastasis accounts for the vast majority of morbidity and mortality associated with melanoma. Evidence suggests melanoma has a predilection for metastasis to particular organs. Experimental analyses have begun to shed light on the mechanisms regulating melanoma metastasis and organ specificity, but these analyses are complicated by observations of metastatic dormancy and dissemination of melanocytes that are not yet fully malignant. Additionally, tumor extrinsic factors in the microenvironment, both at the site of the primary tumor and the site of metastasis, play important roles in mediating the metastatic process. As metastasis research moves forward, paradigms explaining melanoma metastasis as a step-wise process must also reflect the temporal complexity and heterogeneity in progression of this disease. Genetic drivers of melanoma as well as extrinsic regulators of disease spread, particularly those that mediate metastasis to specific organs, must also be incorporated into newer models of melanoma metastasis.

Neurotrophin system activation in pleural effusions

Neurotrophins (NTs) expression was assessed in malignant and non-malignant pleural effusions (inflammatory exudates and transudates). Enzyme-linked immunosorbent assay, in malignant exudates from small and non-small cell lung cancer (SCLC and NSCLC), detected nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3), and their levels are higher as compared with inflammatory and transudative effusions. By immunoblots, in cultured cancer cells coming from malignant pleural effusions, NTs and low- and high-affinity NT receptors were detected in a percentage of SCLC and NSCLC. Proliferation assay demonstrated that BDNF significantly increased cancer cell proliferation in vitro, on the contrary, NT-3 reduced cancer cell growth rate and NGF did not modify cell growth. Moreover, NGF protects cells from death during starvation. These effects are reverted by the addition of NT receptor antagonists. Cultured cancer cells injected into the lung of immunodeficient mice generate lung tumors expressing NTs and NT receptors. These findings suggest that NTs may be able to modulate cancer cell behavior and their growth.

Survival of transplanted neural progenitor cells enhanced by brain irradiation

OBJECT

Authors of previous studies have reported that adult transplanted neural progenitor cells (NPCs) are suitable for brain cell replacement or gene delivery. In this study, the authors evaluated survival and integration of adult rat-derived NPCs after transplantation and explored the potential impact on transplant survival of various mechanical and biological factors of clinical importance.

METHODS

Adult female Fischer 344 rats were used both as a source and recipient of transplanted NPCs. Both 9L and RG2 rat glioma cells were used to generate in vivo brain tumor models. On the 5th day after tumor implantation, NPCs expressing green fluorescent protein (GFP) were administered either intravenously (3.5 x 10(7) cells) or by stereotactic injection (1 x 10(4)-1 x 10(6) cells) into normal or tumor-bearing brain. The authors evaluated the effect of delivery method (sharp compared with blunt needles, normal compared with zero-volume needles, phosphate-buffered saline compared with medium as vehicle), delivery sites (intravenous compared with intratumoral compared with intraparenchymal), and pretreatment with an immunosuppressive agent (cyclosporin) or brain irradiation (20-40 Gy) on survival and integration of transplanted NPCs.

RESULTS

Very few cells survived when less than 10(5) cells were transplanted. When 10(5) cells or more were transplanted, only previously administered brain irradiation significantly affected survival and integration of NPCs. Although GFP-containing NPCs could be readily detected 1 day after injection, few cells survived 4 days to 1 week unless preceded by whole-brain radiation (20 or 40 Gy in a single fraction), which increased the number of GFP-containing NPCs within the tissue more than fivefold.

CONCLUSIONS

The authors' findings indicate that most NPCs, including those from a syngeneic autologous source, do not survive at the site of implantation, but that brain irradiation can facilitate subsequent survival in both normal and tumor-bearing brain. An understanding of the mechanisms of this effect could lead to improved survival and clinical utility of transplanted NPCs.

Expression of MMP2, MMP9 and MMP3 in breast cancer brain metastasis in a rat model

In order to study the expression of MMP2, MMP3 and MMP9 in breast cancer brain metastasis, we used a syngeneic rat model of distant metastasis of ENU1564, a carcinogen-induced mammary adenocarcinoma cell line. At six weeks post inoculation we observed development of micro-metastasis in the brain. Immunohistochemistry and Western Blotting analyses showed that MMP-2, -3 and -9 proteins expressions are consistently significantly higher in neoplastic brain tissue compared to normal brain tissue. These results were confirmed by RT-PCR. In situ zymography revealed gelatinase activity within the brain metastasis. Gel zymography showed increase in MMP2 and MMP3 activity in brain metastasis. Furthermore, we were able to significantly decrease the development of breast cancer brain metastasis in animals by treatment with PD 166793, a selective synthetic MMP inhibitor. In addition, PD 166793 decreased the in vitro invasive cell behavior of ENU1546. Together our results suggest that MMP-2, -3 and -9 may be involved in the process of metastasis of breast cancer to the brain.

Uncoupling of epidermal growth factor-dependent proliferation and invasion in a model of squamous carcinoma progression

Cell lines pairs were established from a primary squamous carcinoma of tongue and a lymph node metastasis and their biological behavior characterized. HN12 cells, derived from metastatic SCC, formed tumors upon subcutaneous transplantation to athymic mice, whereas HN4, derived from a primary lesion in the same individual, were non-tumorigenic in this assay. EGF stimulated proliferation of HN4 cells; in comparison, not only were metastatic HN12 cells refractory to the stimulatory effects of this growth factor but showed inhibition at higher growth factor concentrations. However, in contrast to the effects on proliferation, EGF (10 ng/ml) readily induced HN12 cells to invade in Boyden chamber assays whereas HN4 were non-invasive under these conditions. The invasive properties of HN12 cells were apparently independent of MMP-2 activity, as levels of active MMP-2 were higher in the non-invasive cells. However, EGF stimulated MMP-9 activity in invasive cells. Additionally, HN12 cells expressed constitutively high levels of active MMP-7 and MMP-3/10. The pharmacological agents LY294002, PD098059, SP600125, or SB202190 inhibited invasion of HN12 cells, suggesting requirement for phosphoinositide 3-OH kinase- and mitogen activated protein kinase-dependent pathways in the process. The data indicate that distinct biochemical differences distinguish metastatic squamous carcinoma cells from those derived from corresponding primary tumors, resulting in their contrasting biological properties.

Transferrin: structure, function and potential therapeutic actions

There are many proteins that can multi-task. Transferrin, widely known as an iron-binding protein, is one such example of a multi-tasking protein. In this review, the multiple biological actions of transferrin, including its growth and cytoprotective activities, are discussed with the view of highlighting the potential therapeutic applications of this protein.

In vitro growth suppression of human glioma cells by a 16-mer oligopeptide: a potential new treatment modality for malignant glioma

Fibroblast growth factor-2 (FGF-2) is involved as an autocrine growth factor in the autonomous proliferation of glioma cells. To develop a new strategy for treating patients with glioma, we studied the effect on human glioma cells of a 16-mer oligopeptide with conformational similarity to the putative receptor-binding domain of FGF-2. A synthesized oligonucleotide was assessed its receptor-binding activity by BIAcore instrument. Its biological effect on glioma cell lines was examined in vitro by MTT assay. The peptide suppressed the in vitro growth of human glioma cells U87MG, T98G and U251MG cells, but not of A431 cells whose growth is not dependent on FGF-2. Apoptotic bodies were noted after 24-h incubation in the presence of the peptide; Ac-YVAD-CHO, a caspase-3 inhibitor, suppressed apoptosis. Furthermore, we examined the modulation of the cytotoxic effect of anticancer drugs by the oligopeptide. The addition of this oligopeptide to the chemotherapeutic agents CDDP, ACNU and VP16 had additive effects in vitro. These results suggest that the pathway of the FGF-2 autocrine loop through the FGF receptor plays an important role in the proliferation of glioma cells. New drugs targeting this loop may be highly effective in treating FGF-2-dependent tumors. Our results suggest that its addition to the therapeutic arsenal may lead to improved treatment regimens for patients with FGF-2-dependent tumors.

Biological properties associated with the enhanced lung-colonizing potential in a B16 murine melanoma line grown in a medium conditioned by syngeneic Corynebacterium parvum-elicited macrophages

A previous study by our laboratory showed that the peritoneal murine Corynebacterium parnum-elicited macrophages released into their growth medium an activity which enhanced the ability of B16-F10 melanoma cells to form experimental metastases in the lung of syngeneic mice. In the present study, we used a clone of B16-F10 line (F10-M3 cells) to investigate whether the increase in lung-colonizing potential due to the pro-clonogenic activity released by C. parvum-elicited macrophages was associated with biological properties characteristic of a metastatic phenotype. We have found that the pulmonary retention, growth rate in lung parenchyma, invasiveness through Matrigel, adhesiveness to IL-1-activated endothelium and MHC class I expression were increased in F10-M3 cells stimulated by the macrophage pro-clonogenic activity. By using an in vitro experimental protocol, the enhancement of lung-colonizing potential in the stimulated melanoma cells turned out to be a transient phenomenon as was the increase of invasiveness through Matrigel and the higher expression of MHC class I antigens. In conclusion, the melanoma cells stimulated by the pro-clonogenic activity released by C. parvum-elicited macrophages showed changes in biological parameters which are relevant to metastatic diffusion. These changes appeared as a temporary phenomenon which sustains the view that the metastatic phenotype represents a transient biological character influenced by host factors.

TGFalpha and the blood-brain barrier: accumulation in cerebral vasculature

Transforming growth factor alpha (TGFalpha) is a cytokine that belongs to the epidermal growth factor (EGF) family of growth factors. EGF has a fast and saturable entry from blood to brain that is inhibitable by TGFalpha (18). In this report, we studied the passage of TGFalpha from blood to brain after an i.v. bolus injection. Using radioactively labeled peptide, we found that TGFalpha had an apparent rate of entry of 0.7 microl/g/min. However, most of the TGFalpha was trapped in the capillary endothelial cells of the cerebral vasculature rather than entering the brain parenchyma. No saturation was detected. TGFalpha was relatively stable in blood for 20 min after i.v. injection, but dissociation of the isotope 125I was more evident in brain. The accumulation of TGFalpha in the cerebral vasculature was similar to that of amyloid-beta protein1-40. Therefore, we conclude that TGFalpha from the periphery interacts with the blood-brain barrier without substantial uptake into brain parenchyma. This raises the possibility that TGFalpha might be involved in intracranial vascular disorders such as angiopathy.

Inverse regulation of neuronal cellular adhesion molecule (NCAM) by IFN-gamma in melanoma cell cultures established from CNS lesions

In advanced stages of malignant melanoma (MM), metastases to the CNS are frequently observed. Few results are available on trophic factors and immunological features involved in the process of invasion and adhesion of circulating metastatic cells into the CNS. A direct comparison of remote metastases found in different locations of the same patient might help to identify such properties. For this purpose, we screened a panel of MM cell cultures, which had been established from patients with surgically removed MM lesions of the CNS, for expression and regulation of immunorelevant molecules. The results were compared with standard controls and cultures established from non-CNS metastatic lesions of the same patients. No significant differences were observed for expression of HLA-I, HLA-II, ICAM-1 and the melanoma-associated antigens Mage-3, MelanA and tyrosinase. Constitutive expression of the neuronal cell adhesion molecule (NCAM) was found in all CNS-derived samples and in fewer than 50% of non-CNS derived cultures. IFN-gamma was found to have a weak up-regulating effect in all non-CNS-derived cultures, except normal melanocytes. However, in 6/7 CNS-derived cultures, pre-treatment with IFN-gamma reduced expression of NCAM to 28% to 77% of the level in untreated cultures. The presence and regulation of NCAM differs between MM cells derived from CNS metastases and non-CNS-derived melanocytic cells. Thus, NCAM might be a candidate immunoregulating molecule involved in the formation of CNS metastases of MM.

Induction of electrical excitability by NGF requires autocrine action of a CNTF-like factor

The overlapping expression of neurotrophin and neural cytokine receptors indicates that most neuronal populations are responsive to both classes of factors, yet relatively little is known about how these two trophic signaling systems interact to regulate neuronal phenotype. We report here that one hallmark of NGF's effects on target cells, the induction of membrane electrical excitability, requires the intermediary action of a CNTF-like factor. We found that NGF's regulation of voltage-gated potassium channels, unlike its regulation of voltage-gated sodium and calcium channels, involves a CNTF-like autocrine/paracrine loop. We showed that NGF induces secretion of a soluble factor that mimics the action of exogenous CNTF in regulating voltage-gated potassium channels and that NGF's ability to regulate this potassium channel is blocked by three independent reagents that inhibit the signaling of CNTF and/or related factors. The identity of this autocrine factor does not appear to be CNTF itself. Thus, a CNTF-like autocrine/paracrine factor is both necessary and sufficient for the regulation of potassium channels by NGF and is a key determinant of the type of electrical excitability that NGF induces in target cells.

Divergent cellular differentiation pathways during the invasive stage of cutaneous malignant melanoma progression

Melanocytic nevus cells in the dermis adopt many morphological features of Schwann cells. These differentiation-related changes typically are not observed in melanomas. However, nevus cells do not fully recapitulate a Schwann cell phenotype, because they lack expression of mature myelin-associated proteins. In this study, melanocytic nevi and malignant melanomas were examined by immunohistochemistry for expression of low-affinity nerve growth factor receptor (p75NGFR), neural cell adhesion molecule (CD56/N-CAM), and growth-associated phosphoprotein-43 (GAP-43). These three proteins define the earliest stages of Schwann cell development but are not expressed in myelinated Schwann cells or normal melanocytes. p75NGFR was expressed in 25 of 25 (100%) and CD56/N-CAM and GAP-43 in 23 of 25 (92%) nevi, predominantly in type C nevus cells and nevic corpuscles. Most (84%) of the nevi expressed all three proteins. In primary invasive and metastatic melanoma, expression of each of the three proteins was limited to </=20% of lesions but was not observed in any melanoma in situ (chi(2 )P < 0.0001). None of the melanomas expressed all three proteins (ANOVA P < 0.0001). These data confirm and extend earlier studies by showing that terminal differentiation of melanocytes in the dermis recapitulates some aspects observed in the earliest stages of Schwann cell development and that invasive melanomas follow a divergent pathway. Studying these early differentiation events may help to identify specific defects in the relevant signaling pathways and establish tenable targets for therapy of advanced-stage melanoma.

Cellular and molecular mechanisms of metastasis as applied to carcinomatous meningitis

Cancer cells as well as bacteria metastasize to the subarachnoidal space (SAS) causing meningitis. Primary brain tumors, although not forming distant metastases, disseminate via the cerebrospinal fluid and occupy the meninges. The multistep process of cancer or bacterial dissemination is regulated through molecular crosstalk between invaders and host cells. Such crosstalks establish invasion-promoter and invasion-suppressor complexes. In carcinomatous and bacterial meningitis, the participation of host cells is prominent since leukocytes and inflammatory cytokines are the major determinants of malignancy. We propose a model in which bacterial breakdown products activate endothelial cells, a process leading to leukocyte extravasation. This initiates a cascade of inflammatory processes opening up the blood cerebrospinal fluid barrier and producing access for new invaders.

Neurotrophin stimulation of human melanoma cell invasion: selected enhancement of heparanase activity and heparanase degradation of specific heparan sulfate subpopulations

Heparanase is an endo-beta-D-glucuronidase whose enzymatic targets are the glycosaminoglycan chains of heparan sulfate proteoglycans (50). Elevated levels of heparanase are associated with the metastatic potential of melanoma cells, and treatment of murine and human melanoma cells with the prototypic neurotrophin nerve growth factor (NGF) increases the production of heparanase by melanoma cells. We previously reported that physiological concentrations of NGF increased invasion of early passage human brain-metastatic 70W melanoma cells but not melanoma cells metastatic to other sites or nonmetastatic melanoma cells as measured in Matrigel invasion assays. Here we found that treatment of 70W melanoma cells with neurotrophin-3 (NT-3) increased Matrigel invasion, whereas treatment with neurotrophins other than NGF or NT-3 did not influence invasion. Mutants of NGF that do not bind to the neurotrophin receptor p75NTR or other nonneuronal growth factors were not able to enhance the invasion of 70W melanoma cells. When 70W cells were exposed to antisense oligonucleotides directed against p75NTR mRNA, there was a reduction in NGF and NT-3 binding, and the neurotrophins failed to enhance Matrigel invasion. To study the properties of heparanase in neurotrophin-regulated malignant melanoma invasive processes, we developed a sensitive heparanase assay consisting of purified [35S]HS subpopulations separated by agarose gel electrophoresis. Incubation of 70W cells with NGF or NT-3 but not brain-derived neurotrophic factor, neurotrophin-4/5 or mutant NGF resulted in increased release of heparanase activity that was capable of degrading a subpopulation of heparan sulfate molecules.

Tumor cell motility and metastasis : Autocrine motility factor as an example of ecto/exoenzyme cytokines

Cellular locomotion plays a critical role in such normal processes as embryonic development, tissue segregation, as well as the infiltration of fibroblasts and vascular cells during wound repair and the inflammatory responses of the adult immune system. During tumor invasion and metastasis the processes of cell migration achieve dire significance. Disruption of normal homeostatic mechanisms to benefit the survival of the individual tumor cell is a common theme discovered during the characterization of factors once thought to be tumor-specific. One such molecule, tumor cell autocrine motility factor, was so described and has only recently been identified as a normal protein involved in intracellular glycolysis as well as implicated as an extracellular effector of normal cell functions including survival of certain populations of neurons. This molecule represents a member of the newly emerging family of intracellular enzymes whose disparate functions as extracellular mediators of cellular responses defines a new class of ecto/exoenzymes which play a role in normal cellular processes and are inappropriately utilized by tumor cells to elicit new survival strategies.

Growth factor activity of endothelin-1 in primary astrocytes mediated by adhesion-dependent and -independent pathways

Endothelin-1 (ET-1) has been shown to induce DNA synthesis in primary astrocytes by stimulating the extracellular signal-regulated kinase (ERK) pathway. To clarify the mechanisms responsible for the anchorage-dependent growth of astrocytes, the relationships between cell adhesion and ERK activation were investigated. Here it is reported that ET-1 promotes the formation of stress fibers and focal adhesions and the tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin, as well as Src activation and association of phosphorylated FAK with Grb2. Pretreatment of astrocytes with cytochalasin D or C3-transferase, which inhibits actin polymerization or Rho activity, respectively, prevented the activation/phosphorylation of Src, FAK, and paxillin after ET-1 stimulation; by contrast, the ERK pathway was not significantly affected. This differential activation of FAK/Src and ERK pathways was also observed with astrocytes 10 and 60 min after replating on poly-L-ornithine-precoated dishes. Collectively, these findings indicate that activation of FAK and Src is dependent on actin cytoskeleton integrity, Rho activation, and adhesion to extracellular matrix, whereas ERK activation is independent of these intracellular events and seems to correlate with activation of the newly identified protein tyrosine kinase PYK2. Induction of DNA synthesis by ET-1, however, was reduced dramatically in astrocytes pretreated with either cytochalasin D or C3-transferase. This study provides a demonstration of Rho- and adhesion-dependent activation of FAK/Src, which collaborates with adhesion-independent activation of PYK2/ERK for DNA synthesis in ET-1-stimulated astrocytes.

Transferrin promotes endothelial cell migration and invasion: implication in cartilage neovascularization

During endochondral bone formation, avascular cartilage differentiates to hypertrophic cartilage that then undergoes erosion and vascularization leading to bone deposition. Resting cartilage produces inhibitors of angiogenesis, shifting to production of angiogenic stimulators in hypertrophic cartilage. A major protein synthesized by hypertrophic cartilage both in vivo and in vitro is transferrin. Here we show that transferrin is a major angiogenic molecule released by hypertrophic cartilage. Endothelial cell migration and invasion is stimulated by transferrins from a number of different sources, including hypertrophic cartilage. Checkerboard analysis demonstrates that transferrin is a chemotactic and chemokinetic molecule. Chondrocyte-conditioned media show similar properties. Polyclonal anti-transferrin antibodies completely block endothelial cell migration and invasion induced by purified transferrin and inhibit the activity produced by hypertrophic chondrocytes by 50-70% as compared with controls. Function-blocking mAbs directed against the transferrin receptor similarly reduce the endothelial migratory response. Chondrocytes differentiating in the presence of serum produce transferrin, whereas those that differentiate in the absence of serum do not. Conditioned media from differentiated chondrocytes not producing transferrin have only 30% of the endothelial cell migratory activity of parallel cultures that synthesize transferrin. The angiogenic activity of transferrins was confirmed by in vivo assays on chicken egg chorioallantoic membrane, showing promotion of neovascularization by transferrins purified from different sources including conditioned culture medium. Based on the above results, we suggest that transferrin is a major angiogenic molecule produced by hypertrophic chondrocytes during endochondral bone formation.

Complement 5a controls motility of murine microglial cells in vitro via activation of an inhibitory G-protein and the rearrangement of the actin cytoskeleton

Microglial cells respond to most pathological events by rapid transformation from a quiescent to an activated phenotype characterized by increased cytotoxicity and motile activity. To investigate the regulation of microglial motility by different inflammatory mediators, we studied cultured murine microglia by time-lapse video microscopy and a computer-based motility assay. Microglial cells exhibited a high resting motility. The acute application of complement 5a (C5a) immediately induced intense ruffling of microglial membranes followed by lamellipodia extension within few seconds, while formyl-Met-Leu-Phe-OH, bacterial endotoxin (lipopolysaccharide) or inflammatory cytokines did not increase motility. This process was accompanied by a rapid rearrangement of the actin cytoskeleton as demonstrated by labelling with fluorescein isothiocyanate-phalloidin and could be inhibited by cytochalasin B. A GTP-binding protein was involved in the signal cascade, since pertussis toxin inhibited motility and actin assembly in response to C5a. Chemotactic migration in a gradient of C5a was also completely blocked by pertussis toxin and cytochalasin B. The C5a-induced motility reaction was accompanied by an increase in intracellular calcium ([Ca2+]i) as measured by a Fluo-3 based imaging system. Ca2+ transients were, however, not a prerequisite for triggering the increase in motility; motility could be repeatedly evoked by C5a in nominally Ca(2+)-free solution, while Ca2+ signals occurred only upon the first stimulation. Moreover, conditions mimicking intracellular Ca2+ transients, like incubation with thapsigargin or Ca2+ ionophore A23187, were not able to induce any motility reaction, suggesting that Ca2+ transients are not necessary for, but are associated with, microglial motility. Motile activity was shown to be restricted to a defined concentration range of [Ca2+]i as revealed by lowering [Ca2+]i with BAPTA-AM or increasing [Ca2+]i with A23187. Since complement factors are released at pathological sites, this signal cascade could serve to increase motility and to direct microglial cells to the lesioned or damaged area by means of a G-protein-dependent pathway and via the rearrangement of the actin cytoskeleton.

Trophic factors and central nervous system metastasis

To metastasize to the central nervous system (CNS) malignant cells must attach to brain microvessel endothelial cells, respond to brain endothelial cell-derived motility factors, respond to CNS-derived invasion factors and invade the blood-brain barrier (BBB), and finally, respond to CNS survival and growth factors. Trophic factors such as the neurotrophins play an important role in tumor cell invasion into the CNS and in the survival of small numbers of malignant cells under stress conditions. Trophic factors promote BBB invasion by enhancing the production of basement membrane-degrading enzymes in neurotrophin-responsive cells. The expression of certain neurotrophin receptors on brain-metastasic neuroendocrine cells occurs in relation to their invasive and survival properties. For example, CNS-metastatic melanoma cells respond to particular neurotrophins (nerve growth factor, neurotrophin-2) that can be secreted by normal cells within the CNS. In addition, a paracrine form of transferrin is important in CNS metastasis, and brain-metastatic cells respond to low levels of transferrin and express high levels of transferrin receptors. CNS-metastatic tumor cells can also produce autocrine factors and inhibitors that influence their growth, invasion and survival in the brain. Synthesis of paracrine factors and cytokines may influence the production of trophic factors by normal brain cells adjacent to tumor cells. Moreover, we found increased amounts of neurotrophins in brain tissue at the invasion front of human melanoma tumors in CNS biopsies. Thus the ability to form metastatic colonies in the CNS is dependent on tumor cell responses to trophic factors as well as autocrine and paracrine growth factors and probably other underdescribed factors.

Modulation of tumor cell gene expression and phenotype by the organ-specific metastatic environment

The mechanistic basis of a metastatic cell's ability to proliferate in the parenchyma of certain organs and develop organ-specific metastases is under intense investigation. Signals from paracrine or autocrine pathways, alone or in combination, may regulate tumor cell proliferation with the eventual outcome dependent on the net balance of stimulatory and inhibitory factors. This article summarizes recent reports from our laboratory and others demonstrating that the organ microenvironment can profoundly influence the pattern of gene expression and the biological phenotype of metastatic tumor cells, including induction of melanocyte stimulating hormone receptor and production of melanin, regulation of terminal differentiation and apoptosis, resistance to chemotherapy, and regulation of growth at the organ-specific metastatic site. These recent data from both murine and human tumor models support the concept that the microenvironment of different organs can influence the pattern of gene expression and hence the phenotype of tumor cells at different steps of the metastatic process. These findings have obvious implications for the therapy of neoplasms in general and metastases in particular.