The common experimental use of B16-F10 melanoma cells focuses on exploring their metastatic potential following intravenous injection into mice. In this study, B16-F10 cells are used to develop a primary tumor model by implanting them directly into the ears of C57BL/6J mice. The model represents a reproducible and easily traceable tool for local tumor growth and for making additional in vivo observations, due to the localization of the tumors. This model is relatively simple and involves (i) surgical opening of the ear skin, (ii) removal of a square-piece of cartilage followed by (iii) the implantation of tumor cells with fibrin gel. The remodeling of the fibrin gel within the cartilage chamber, accompanying tumor proliferation, results in the formation of blood vessels, lymphatics and tissue matrix that can be readily distinguished from the pre-existing skin structures. Moreover, this method avoids the injection-enforced artificial spread of cells into the pre-existing lymphatic vessels. The tumors have a highly reproducible exponential growth pattern with a tumor doubling time of around 1.8 days, reaching an average volume of 85mm3 16 days after implantation. The melanomas are densely cellular with proliferative indices of between 60 and 80%. The induced angiogenesis and lymphangiogenesis resulted in the development of well-vascularized tumors. Different populations of immunologically active cells were also present in the tumor; the population of macrophages decreases with time while the population of T cells remained quasi constant. The B16-F10 tumors in the ear frequently metastasized to the cervical lymph nodes, reaching an incidence of 75% by day 16. This newly introduced B16-F10 melanoma model in the ear is a powerful tool that provides a new opportunity to study the local tumor growth and metastasis, the associated angiogenesis, lymphangiogenesis and tumor immune responses. It could potentially be used to test different treatment strategies.

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Characterization of a B16-F10 melanoma model locally implanted into the ear pinnae of C57BL/6 mice.

Comparison of different methodologies and cryostat versus paraffin sections for chromogenic immunohistochemistry

Background 
Treatment of advanced cutaneous melanoma remains challenging, and new data on melanoma biology are required. The most widely accepted criteria for the prognostic evaluation of melanoma are histopathological and clinical parameters, and the identification of additional tumor markers is thus of paramount importance. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI), an important tool in cancer research, is useful for unraveling the molecular profile of melanoma.


Methodology/Principal findings 
In this report, we used the melanoma-bearing Libechov minipig (MeLiM), a unique animal model that allows observation of the complete spontaneous regression of invasive cutaneous melanoma, to investigate i) the differences between melanoma and healthy skin protein profiles and ii) the proteins potentially involved in spontaneous regression. The MeLiM tissues were cryosected, histologically characterized, analyzed by MALDI MSI, and immunohistologically stained. Multivariate statistical analyses of the MALDI MSI data revealed ten relevant m/z ions, of which the expression levels varied significantly among the studied MeLiM tissues. These ion peaks were used to create mass ion images/maps and visualize the differences between tumor and healthy skin specimens, as well as among histologically characterized tissue regions.


Conclusions/Significance 
Protein profiles comprising ten statistically significant mass ion peaks useful for differentiating cutaneous melanoma and healthy skin tissues were determined. Peaks at m/z 3044, 6011, 6140 and 10180 were overexpressed in melanoma compared with healthy skin tissue. More specifically, m/z 6140 was expressed at significantly (p < 0.05) higher levels in normally growing melanoma regions than in regions with early and late spontaneous regression. This study demonstrates the clinical utility of MALDI MSI for the analysis of tissue cryosections at a molecular level.

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MALDI MSI of MeLiM melanoma: Searching for differences in protein profiles

Cyclooxygenase 2 (COX-2) and phosphorylated Akt1 (p-Akt1) are associated with tumor spreading, cell proliferation, high metabolism, and angiogenesis in solid tumors. This study aimed to investigate COX-2 and p-Akt1 expression in primary and metastatic melanomas by correlating with the cellular proliferation index (as revealed by minichromosome maintenance 2 expression) and the outcome of patients with malignant melanomas. Seventy-seven biopsies of malignant melanomas, including 42 primary nonmetastatic melanomas (PNMMs), 12 primary metastatic melanomas (PMMs), and 23 metastatic melanomas (MMs), were retrospectively selected. Tissue microarrays were developed and submitted for immunohistochemical staining for COX-2, p-Akt1, and minichromosome maintenance 2. Increased COX-2 cytoplasmic staining patterns were observed in PMM and MM when compared with PNMM (P=0.0011). Higher nuclear and cytoplasmic expression of p-Akt1 was more closely associated with PMM than with MM and PNMM (P<0.00001). Coexpression of these biomarkers was closely correlated with lower overall survival rates in melanomas. Furthermore, we observed a statistically significant positive correlation between the mitosis index and increased COX-2 expression (P=0.0135) and between p-Akt1 (P=0.0038) and the cellular proliferation index (P=0.0060). Taken together, our findings demonstrate that COX-2 and p-Akt1 play an important combined role during melanoma progression and are associated with highly metastatic tumors and survival rates in patients with MM. In addition, these biomarkers can be used to predict melanoma prognosis independently of metastatic status. However, further studies are required to elucidate the biological role of these biomarkers during the progression of MM events.

Prognostic significance of cyclooxygenase 2 and phosphorylated Akt1 overexpression in primary nonmetastatic and metastatic cutaneous melanomas.

// Sivan Izraely 1 , Shlomit Ben-Menachem 1 , Orit Sagi-Assif 1 , Tsipi Meshel 1 , Diego M. Marzese 2 , Shuichi Ohe 2 , Inna Zubrilov 1 , Metsada Pasmanik-Chor 3 , Dave S.B. Hoon 2 and Isaac P. Witz 1 1 Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel 2 Department of Translational Molecular Medicine, John Wayne Cancer Institute at Providence Saint John’s Health Center, Santa Monica, CA, USA 3 Bioinformatics Unit, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel Correspondence to: Isaac P. Witz, email: // Keywords : ANGPTL4, melanoma, brain, metastasis, TGFβ1 Received : March 15, 2017 Accepted : June 10, 2017 Published : July 05, 2017 Abstract In an ongoing effort to identify molecular determinants regulating melanoma brain metastasis, we previously identified Angiopoietin-like 4 (ANGPTL4) as a component of the molecular signature of such metastases. The aim of this study was to determine the functional significance of ANGPTL4 in the shaping of melanoma malignancy phenotype, especially in the establishment of brain metastasis. We confirmed that ANGPTL4 expression is significantly higher in cells metastasizing to the brain than in cells from the cutaneous (local) tumor from the same melanoma in a nude mouse xenograft model, and also in paired clinical specimens of melanoma metastases than in primary melanomas from the same patients. In vitro experiments indicated that brain-derived soluble factors and transforming growth factor β1 (TGFβ1) up-regulated ANGPTL4 expression by melanoma cells. Forced over-expression of ANGPTL4 in cutaneous melanoma cells promoted their ability to adhere and transmigrate brain endothelial cells. Over-expressing ANGPTL4 in cells derived from brain metastases resulted in the opposite effects. In vivo data indicated that forced overexpression of ANGPTL4 promoted the tumorigenicity of cutaneous melanoma cells but did not increase their ability to form brain metastasis. This finding can be explained by inhibitory activities of brain-derived soluble factors. Taken together these findings indicate that ANGPTL4 promotes the malignancy phenotype of primary melanomas of risk to metastasize to the brain.

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ANGPTL4 promotes the progression of cutaneous melanoma to brain metastasis.

Melanin may interfere with immunohistochemical staining. The goal of this study was to investigate the effects of trichloroisocyanuric acid (TCCA) bleaching, potassium permanganate bleaching, and potassium dichromate bleaching on melanin, tissue antigen, and 3,3'-diaminobenzidine (DAB) using melanin-containing and melanin-free tissue samples. Our results demonstrated that all 3 bleaching methods efficiently bleached melanin and partially destroyed tissue antigen. In addition, potassium permanganate bleaching and potassium dichromate bleaching clearly destroyed DAB, whereas TCCA bleaching had no significant effect on DAB. Therefore, neither potassium permanganate nor potassium dichromate is an ideal solution, whereas TCCA might be an ideal solution for melanin bleaching after the immunohistochemical staining of melanin-containing tissues. After immunostaining followed by TCCA bleaching, the melanin could be completely removed in all 120 malignant melanoma tissue sections. Compared with the control, the DAB intensity was clear, and the tissue structure and cellular nuclei were well maintained. It is worth noting that TCCA should be freshly prepared before each experiment, and used within 2 hours of its preparation. In addition, sections should not be incubated with TCCA for over 30 minutes.

Wenqiao Wu

Papers

Study of Melanin Bleaching After Immunohistochemistry of Melanin-containing Tissues