Monoclonal antibody PAL-M1 recognizes the transferrin receptor and is a progression marker in melanocytic lesions

Ex vivo derived primary melanoma cells: implications for immunotherapeutic vaccines

Transformation of the pigment producing melanocytes into melanoma is a complex multi-step process involving the enhanced expression of various antigens considered as immunotherapeutic targets. Significant progress in melanoma research has been made over the years and has resulted in the identification of various antigens over expressed in melanoma as well as advances in immunotherapeutic treatments, which focus on modulating the immune systems response to melanoma. Despite these advances, incidences of melanoma are still on the rise thus warranting additional research in identifying new therapeutic treatments. Our focus is on developing a multivalent immunotherapeutic vaccine that targets various melanoma associated antigens. The approach focuses on the use of five primary patient derived melanoma cells (MEL-2, MEL-V, 3MM, KFM, and GLM-2, which have been characterized in this study. These cells express differential amounts of various melanoma associated antigens such as MART-1, gp100 (Pmel17), MAGE-A1 and tyrosinase as well a cell surface antigens essential for melanoma cell metastasis, such as CD146 and CD71. In addition these cells display differential in vitro migratory and invasive properties as well as have the ability to form solid tumors when implanted into BALB/c nude mice. The retention of the innate phenotype of these primary patient derived cells together with the expression of a multitude repertoire of melanoma associated antigens offers a novel opportunity to target melanoma so as to avoid immune evasion.

Effective inhibition of melanosome transfer to keratinocytes by lectins and niacinamide is reversible

Skin pigmentation results in part from the transfer of melanized melanosomes synthesized by melanocytes to neighboring keratinocytes. Plasma membrane lectins and their glycoconjugates expressed by these epidermal cells are critical molecules involved in this transfer process. In addition, the derivative of vitamin B(3), niacinamide, can inhibit melanosome transfer and induce skin lightening. We investigated the effects of these molecules on the viability of melanocytes and keratinocytes and on the reversibility of melanosome-transfer inhibition induced by these agents using an in vitro melanocyte-keratinocyte coculture model system. While lectins and neoglycoproteins could induce apoptosis in a dose-dependent manner to melanocytes or keratinocytes in monoculture, similar dosages of the lectins, as opposed to neoglycoproteins, did not induce apoptosis to either cell type when treated in coculture. The dosages of lectins and niacinamide not affecting cell viability produced an inhibitory effect on melanosome transfer, when used either alone or together in cocultures of melanocytes-keratinocytes. Cocultures treated with lectins or niacinamide resumed normal melanosome transfer in 3 days after removal of the inhibitor, while cocultures treated with a combination of lectins and niacinamide demonstrated a lag in this recovery. Subsequently, we assessed the effect of niacinamide on facial hyperpigmented spots using a vehicle-controlled, split-faced design human clinical trial. Topical application of niacinamide resulted in a dose-dependent and reversible reduction in hyperpigmented lesions. These results suggest that lectins and niacinamide at concentrations that do not affect cell viability are reversible inhibitors of melanosome transfer.

Immunohistochemistry in melanocytic proliferative lesions

Melanoma incidence is rising worldwide. Early diagnosis is very important, as the most effective treatment for melanoma still consists of excision of the tumour before onset of the metastatic growth phase. Immunohistochemistry is a valuable tool for (dermato)pathologists to aid establishing diagnosis. Melanoma markers can be classified into two main categories: melanocytic differentiation markers and melanoma progression markers. Melanocytic differentiation markers are mostly used to distinguish poorly differentiated melanomas from non-melanocytic tumours and for staging of melanocytic proliferative lesions. Melanoma progression markers are most suitable to determine the level of malignancy and/or aggressiveness of tumour cells. This review describes the classification of melanoma markers, including commonly used and recently identified antigens with potential marker function. We characterize their expression profile in melanocytic proliferative lesions and their potential usefulness for diagnosis, prognosis, microstaging, immunotherapeutic purposes and evaluation of therapies.

Prognostic immunohistochemical markers of primary human melanomas

BACKGROUND

Several clinical and histological factors of primary melanomas comprise a relatively large quantity of prognostic information.

OBJECTIVE

To find immunohistochemical markers that can improve the prognostic accuracy achieved by factors that are available without extra laboratory work, i.e. mitotic rate, tumour thickness, ulceration, localization, gender and age.

METHODS

Immunohistochemical markers were determined on frozen sections. Univariate and multivariate Cox regression analyses were performed after 5-10 years follow-up.

RESULTS

Seven immunohistochemical markers were related to disease-free and overall survival in univariate Cox regression analysis: Ki-67, human leucocyte antigen (HLA) -DQ, HLA-DP, Muc 18, A-10-33, transferrin receptor, and H-2-8-10. Only Ki-67 (n = 399) and HLA-DQ (n = 452) retained prognostic significance when evaluated in multivariate analyses in several models together with tumour thickness alone and with tumour thickness, gender, mitotic rate, age, localization and ulceration.

CONCLUSIONS

Ki-67 and HLA-DQ may be useful for risk assessments in primary melanomas.

The roles of iron in health and disease

Iron is vital for almost all living organisms by participating in a wide variety of metabolic processes, including oxygen transport, DNA synthesis, and electron transport. However, iron concentrations in body tissues must be tightly regulated because excessive iron leads to tissue damage, as a result of formation of free radicals. Disorders of iron metabolism are among the most common diseases of humans and encompass a broad spectrum of diseases with diverse clinical manifestations, ranging from anemia to iron overload and, possibly, to neurodegenerative diseases. The molecular understanding of iron regulation in the body is critical in identifying the underlying causes for each disease and in providing proper diagnosis and treatments. Recent advances in genetics, molecular biology and biochemistry of iron metabolism have assisted in elucidating the molecular mechanisms of iron homeostasis. The coordinate control of iron uptake and storage is tightly regulated by the feedback system of iron responsive element-containing gene products and iron regulatory proteins that modulate the expression levels of the genes involved in iron metabolism. Recent identification and characterization of the hemochromatosis protein HFE, the iron importer Nramp2, the iron exporter ferroportin1, and the second transferrin-binding and -transport protein transferrin receptor 2, have demonstrated their important roles in maintaining body's iron homeostasis. Functional studies of these gene products have expanded our knowledge at the molecular level about the pathways of iron metabolism and have provided valuable insight into the defects of iron metabolism disorders. In addition, a variety of animal models have implemented the identification of many genetic defects that lead to abnormal iron homeostasis and have provided crucial clinical information about the pathophysiology of iron disorders. In this review, we discuss the latest progress in studies of iron metabolism and our current understanding of the molecular mechanisms of iron absorption, transport, utilization, and storage. Finally, we will discuss the clinical presentations of iron metabolism disorders, including secondary iron disorders that are either associated with or the result of abnormal iron accumulation.

Transferrin receptor overexpression enhances transferrin responsiveness and the metastatic growth of a rat mammary adenocarcinoma cell line

We previously found that breast cancer cell transferrin receptor expression and proliferative response to transferrin often correlated with metastatic capability. To further explore this, we transfected mammary tumor cells with a cDNA coding for the transferrin receptor and examined the effects of its overexpression on various cellular properties. A human transferrin receptor expression plasmid was made by excising the cDNA for the receptor from pcDTR1 and ligating it into the multiple cloning site of pcDNAINeo. The resulting construct was transfected into the poorly metastatic rat MTLn2 line that expresses low endogenous levels of rat transferrin receptor, and transfection-induced receptor expression was ascertained using antibodies specific for the human protein. Approximately 50% of the initial geneticin-resistant transfected MTLn2 cells overexpressed human transferrin receptor protein. High expressors were further isolated by four sequential FACS sorts. The final cell population expressed approximately 3-7 times more cell surface transferrin receptor than did vector transfected controls. Both lines proliferated at the same rate in normal (medium plus 5% FBS) culture conditions. However, in serum-free conditions, the transferrin receptor overexpressor cells displayed a pronounced proliferative response to transferrin whereas the control line did not. When injected into the mammary fat pads of female nude mice, cells from both lines formed micrometastases to the lung that were specifically visualized by immunohistochemical staining of rat cytokeratin 17. This revealed that the transferrin receptor transfected line formed larger lesions of this nature than did cells from the vector transfected controls. When injected into the tail vein of female nude mice, the transferrin receptor overexpressors likewise formed gross lung metastases of remarkably greater size than did the vector only transfectants. Overexpression of cell surface human transferrin receptor on MTLn2 cells appeared to affect their in vitro growth response to transferrin and their ability to grow at a secondary site in vivo.

ATF-1 is activated in response to UV irradiation in B16 melanoma cells

We have found that the transferrin receptor gene promoter is strongly activated by exposure of B16 melanoma cells to UV light. This is a delayed event occurring more than 6 h after exposure and requires an AP-1/CRE-like element in the promoter as demonstrated by site-specific mutagenesis. UV irradiation enhances the binding of a nuclear factor to this element and supershift analysis demonstrates that this DNA-protein complex involves ATF-1. No other members of either the AP-1 or CREB/ATF families of transcription factors were found to bind to this DNA element in UV-irradiated B16 cells. Western blots show that the level of ATF-1 does not change following exposure to UV light, indicating that the increased binding of this factor is most likely mediated by posttranslational modifications in response to UV-mediated signaling pathways.

Selection of highly metastatic rat MTLn2 mammary adenocarcinoma cell variants using in vitro growth response to transferrin

We previously found that the proliferative response to transferrin and the expression of transferrin receptors (TfR) on the cell surface of various rat 13762NF mammary adenocarcinoma cell sublines correlated with their spontaneous metastatic capability. To further assess the involvement of transferrin and TfR in metastasis, transferrin-responsive cells were selected from the poorly-metastatic, low-transfferin responsive 13762NF MTLn2 subline. When maintained in low serum (0.3%) conditions, MTLn2 cells failed to survive. However, if like medium was supplemented with 0.5 microgram/ml rat transferrin, some colonies emerged, presumably due to their ability to proliferate in response to the added transferrin. The surviving cells were expanded and exposed to ten or 20 similar cycles of transferrin growth selection to obtain the sublines MTLn2-Tf10 and MTLn2-Tf20, respectively. The MTLn2-Tf20 cells proliferated in response to transferrin at a rate similar to that of the high metastatic 13762NF sublines. Using immunofluorescent staining, Scatchard analysis, and affinity isolation of TfR, we discovered that the MTLn2-Tf20 cells had 5 to 6 times more TfR than did the parental MTLn2 line. When injected into the mammary fat pads of rats, the MTLn2-Tf20 line metastasized to the axillary lymph node in seven out of ten animals and to the lungs in six out of ten (median number = 13). No metastases were seen in the MTLn2 parental line. The MTLn2-Tf10 cells showed intermediate properties compared with the MTLn2 and MTLn2-Tf20 cells. The results indicate that variant cells with a high response to transferrin may be more metastatic than the bulk cells in a poorly metastatic population. The selection of cells with high levels of TfR and a higher proliferative response to transferrin results in sublines with greater potentials for spontaneous metastasis.

Prognostic parameters in uveal melanoma: a review

Histologic cell type, largest tumor diameter and tumor location have traditionally been regarded as the leading predictors of survival for uveal melanoma. Morphological cell typing is, however, subjective to variations in interpretation. More objective classification parameters have emerged from extensive cytomorphometrical and DNA flow cytometrical studies. For patients with uveal melanoma there is no effective therapy if metastases have developed, and the median survival after clinical diagnosis of hepatic metastases is extremely poor. Current research focuses on the mechanisms underlying the metastatic process, including tumor vasculature, cytogenetics, oncogene activation, immunology, melanoma-associated antigens and tumor cell migration (cell-cell and cell-matrix interaction). Several new prognostic parameters have emerged from these studies, such as closed vascular patterns, loss of one chromosome 3, and different indices of cell proliferation. Furthermore, considerable genotypical and phenotypical differences have been found between uveal and cutaneous melanoma. In prospective studies on large series of melanomas a combination of histopathological and/or clinical prognostic parameters might be selected with high sensitivity and specificity, providing a way of selecting patients at high risk of developing metastatic disease, who might be eligible for adjuvant therapy.

Limited loss of nine tumor-associated surface antigenic determinants after tryptic cell dissociation

Disodium ethylenediaminetetraacetic acid (EDTA) or trypsin/EDTA are frequently used for the dispersion of monolayer cells into single cell suspensions allowing flow cytometric analysis of surface antigenic determinants. A disadvantage of EDTA is the slow action of this agent, whereas trypsin might affect the antigenic determinants under focus. We studied the possible deleterious effect of trypsin on three different ovarian carcinoma cell lines, COV413b, COV362.c14, and NIH:OVCAR-3, on cell surface antigenic determinants by flow cytometry. Either EDTA or trypsin/EDTA was used for detachment and dissociation of monolayer ovarian cancer cell lines, followed by indirect immunofluorescence with a panel of monoclonal antibodies directed against nine different surface antigenic determinants, including six markers directed against widely distributed antigens. Compared to EDTA, trypsin/EDTA resulted in higher total cell yields and rapid detachment and dissociation into single cell suspensions with significantly lower amounts of dead cells detected by both trypan blue and propidium iodide (PI). Large differences in antigen expression were observed for the different cell lines. However, all antigenic determinants tested could still be detected after tryptic proteolysis. Three antigenic determinants were significantly decreased after trypsin/EDTA compared to EDTA detachment. CA 125 was decreased on COV362.c14 and NIH: OVCAR-3 cells, respectively. BMA 180 and ICAM-1 were decreased on COV413b cells. This cell line-dependent decrease might be caused by differences in glycosylation. We conclude that trypsin/EDTA can be used for rapid monolayer cell detachment with high cell yields and limited loss of antigenic determinants tested.

nmb, a novel gene, is expressed in low-metastatic human melanoma cell lines and xenografts

From a subtractive cDNA library, we isolated several cDNA clones which showed differential expression between highly and lowly metastatic human melanoma cell lines. One clone, designated nmb, showed preferential expression in the low-metastatic cell lines and was chosen for further characterization. Sequence analysis revealed that this clone represents a novel gene, encoding a putative transmembrane glycoprotein which showed the highest homology to the precursor of pMEL17, a melanocyte-specific protein. nmb RNA expression was absent in most tumor-cell lines tested and not restricted to the melanocytic lineage. Transfection of a partial nmb cDNA into a highly metastatic melanoma cell line (BLM) resulted, in 2 of 3 transfectants, in slower subcutaneous tumor growth and, in 1 of 3 transfectants, in reduction of the potential for spontaneous metastasis in nude mice.

Differences in transferrin response and numbers of transferrin receptors in rat and human mammary carcinoma lines of different metastatic potentials

We previously found that transferrin (Tf) differentially stimulated the growth of highly metastatic variant lines of murine melanoma and that these highly metastatic cells also had greater numbers of Tf receptors on their cell surfaces. In the present study we found that highly metastatic rat mammary adenocarcinoma cell lines also responded differentially to Tf in proliferation assays, and cell monolayers bound Tf in relation to their metastatic potential (MTPaB10 > MTPaB5 > MTLn3 > MTLn2 > MTC > MTF7 > MTPa). The brain-colonizing lines PaB10 and PaB5 were the most responsive to Tf and had the highest numbers of Tf receptors. Different human breast cancer cell lines also responded differentially to Tf in proliferation assays and bound different amounts of Tf to their cell surface Tf receptors. Transferrin binding, but not growth response, correlated with metastatic and invasive properties of lines selected from the human MCF-7 series (MCF7/LCC2 > MCF7/LCC1 > MCF7). In examining the transferrin binding and growth response of lines from the human MDA series, the Tf binding and growth response was MDA231 > MDA435 > MDA468. The lines MDA435 and MDA231 were metastatic in nude mouse assays, whereas the line MDA468 was not. Scatchard analysis indicated the presence of a single class of receptor for Tf on the rat and human mammary cell lines. The results suggest that neoplastic cells displaying various metastatic properties may express differing numbers of Tf receptors and respond differently to growth factors such as Tf.

Presence or absence of melanocytes in vitiligo lesions: an immunohistochemical investigation

There is a long-standing controversy over whether melanocytes in vitiligo lesions are actually lost or are still present but inactivated. Resolving this matter is essential for understanding the underlying pathology and for the development of treatment. Standard methods of detecting melanocytes are based on active melanin synthesis. However, it is possible that inactive melanocytes remain in the lesions. There are no methods presently available to detect such dormant melanocytes. Using a panel of one polyclonal and 17 monoclonal antibodies directed against melanocytic cells (largely selected by the European Organisation for Research and Treatment of Cancer Melanoma Group for diagnostic and therapeutic purposes), we investigated the absence or inactivation of melanocytes in vitiligo by immunohistochemistry. Results using this panel of antibodies on frozen skin sections suggest that melanocytes are indeed absent in the lesions. However, in epidermal split-skin preparations, residual staining was occasionally observed. To determine whether the staining obtained was due to degenerated melanocytes, confocal laser scanning microscopy was used. Immunofluorescent staining using the antibody NKI-beteb confirmed this to be the case. The results presented here strongly suggest that melanocytes are indeed lost in vitiligo lesions.

Macrophages in melanocytic naevi

Whereas the inflammatory infiltrates of malignant melanoma have been widely investigated, little is known about the infiltrates accompanying benign melanocytic naevi. Using monoclonal antibodies directed against HLA-DR antigens, the CD1 antigen, the transferrin receptor and functionally divergent macrophage subpopulations, frozen fresh material of 87 melanocytic naevi (MN), ten primary cutaneous melanomas (PCM) and ten samples of normal skin were studied. Compared with normal skin, abundant HLA-DR+ cells were found in the stroma of MN equivalent to the quantity present in PCM. In MN we found higher numbers of dermal CD1+ dendritic cells compared with PCM and normal skin. There were more macrophages that expressed the transferrin receptor or the antigens 27E10, RM3/1 and 25F9 in MN than in normal skin but fewer than in PCM. No significant differences were found between congenital MN (n = 40), common acquired MN (n = 27) and dysplastic MN (n = 20) macrophage subpopulations. Also, no correlations were evident between macrophage infiltrates and naevus location or patients' age. Our data show that potential melanoma precursors among melanocytic naevi cannot be identified by the pattern of macrophage infiltrates.

The EORTC Melanoma Group exchange program: evaluation of a multicenter monoclonal antibody study

In the framework of the European Organisation for Research and Treatment of Cancer (EORTC), the Immunology and Pathology Subgroups of the Malignant Melanoma Cooperative Group undertook a large multicenter monoclonal antibody (MAb) study. Fourteen laboratories from 7 European countries tested a panel of 23 MAbs for immunohistological staining reactivity for malignant and non-malignant lesions involving the melanocytic lineage. A standardized immunoperoxidase procedure was used and the results were evaluated using a standard protocol and data evaluation form developed in collaboration with the EORTC Data Center. According to this analysis, the antibodies in the panel could be classified into 3 main groups. The first group of MAbs includes those antibodies which stained the majority (greater than 80%) of all primary tumors, irrespective of their Breslow thickness and the majority of metastatic lesions. In addition, these MAbs stained a high percentage of cells within a given lesion. Several antibodies of Group I were likewise reactive with the majority of naevoblasts and with normal melanocytes. The second group of MAbs included antibodies reacting only with a limited number of primary melanomas and metastatic lesions. Antibodies of Group II reacted only weakly, if at all, with normal melanocytes or naevocytes. The percentage of cells within a malignant lesion stained by these MAbs was always rather low. The MAb group III detected surface structures whose expression appeared to be related to tumor progression; they did not react or reacted only weakly with naevi, and they all reacted with a small number of early primary melanomas (less than 0.75 mm). The number of lesions stained increased with increasing Breslow thickness. Our study suggests that the application of a panel of well defined MAbs might be of diagnostic and prognostic value in evaluating malignant melanoma.

Antigen expression of metastasizing and non-metastasizing human melanoma cells xenografted into nude mice

In order to study differences in antigen expression related to the different stages of the process of metastasis of human melanoma cell lines, we determined the expression pattern of a series of well-characterized genes in a set of human melanoma cell lines with different metastatic behavior in nude mice. This set included non-metastatic (IF6, 530), sporadically metastatic (M14, Mel 57), and frequently metastatic (BLM, MV3) cell lines after subcutaneous inoculation. To study the phenotype of these cell lines both the cultured cells and representative samples of local tumors at the inoculation site and their metastases in the lungs were immunostained with a panel of monoclonal antibodies directed against melanocytic differentiation or progression antigens. Although most cell lines (IF6, 530, M14 and Mel 57) showed HLA-DR expression in vitro, these antigens were lacking in all xenografted lesions studied with exception of the 530 cell line. 530 Xenografts, however, showed a dramatic down-regulation of HLA-DR compared with the cell line in vitro. The same phenomenon was seen with respect to ICAM-1 expression. The expression of all other antigens studied in xenografts, both in subcutaneous tumors and in lung lesions, was in general comparable to that in the melanoma cell lines in vitro, with exception of the 530 cell line. In all melanoma cell lines except 530 the degree of intra- and interlesional heterogeneity regarding the expression of all antigens studied was limited. Remarkably, comparison of the immunophenotype of the frequently metastasizing (BLM, MV3) and the sporadically (M14, Mel 57) or non-metastasizing (IF6, 530) cell lines showed that the two frequently metastasizing cell lines had marked expression of the progression antigens VLA-2 and epidermal growth factor receptor, and lack of expression of the differentiation antigen NKI-beteb. These findings warrant further studies on the role of these antigens in the process of metastasis of human melanoma cells in nude mice.

Establishment and characterization of a human melanoma cell line (MV3) which is highly metastatic in nude mice

To select human melanoma cells that are highly tumorigenic and metastatic in nude mice we have implanted fragments of a fresh human melanoma metastasis subcutaneously (s.c.) into a nude mouse. After 3 passages in nude mice, part of the xenograft was cultured and a new melanoma cell line, MV3, was established. After intravenous (i.v.) inoculation of 2 x 10(6) MV3 cells, 95% of the nude mice (n = 20) developed lung colonies within 6 weeks. S.c. inoculation of 2 x 10(6) MV3 cells resulted in 95% tumor take, while 90% of the mice (n = 20) showed spontaneous metastases in the lungs within 7 weeks. Histological and immunohistological features of the original tumor of the patient were largely retained in the tumors of the mice and in the cell line in vitro. As shown by Alcian blue staining, MV3 cells contain large quantities of glycosaminoglycans (GAGs) and/or proteoglycanes (PGs), both in vivo and in vitro. The cells showed a marked expression of transferrin receptor, ICAM-1, EGF-receptor, and VLA-2 integrin. As only few human melanoma cell lines are available that frequently show metastasis in nude mice, the highly metastatic MV3 cell line represents a useful tool for studying the expression and regulation of molecules on human melanoma cells involved in the process of metastasis.