Peroxisome proliferator-activated receptors (PPARs) have been originally thought to be restricted to lipid metabolism or glucose homeostasis. Recently, evidence is growing that PPARγ ligands have inhibitory effects on tumor growth. To shed light on the potential therapeutic effects on melanoma we tested a panel of PPAR agonists on their ability to block tumor proliferation in vitro. Whereas ciglitazone, troglitazone and WY14643 showed moderate effects on proliferation, 15d-PGJ2 displayed profound anti-tumor activity on four different melanoma cell lines tested. Additionally, 15d-PGJ2 inhibited proliferation of tumor-associated fibroblasts and tube formation of endothelial cells. 15d-PGJ2 induced the tumor suppressor gene p21, a G2/M arrest and inhibited tumor cell migration. Shot gun proteome analysis in addition to 2D-gel electrophoresis and immunoprecipitation of A375 melanoma cells suggested that 15d-PGJ2 might exert its effects via modification and/or downregulation of Hsp-90 (heat shock protein 90) and several chaperones. Applying the recently established CPL/MUW database with a panel of defined classification signatures, we demonstrated a regulation of proteins involved in metastasis, transport or protein synthesis including paxillin, angio-associated migratory cell protein or matrix metalloproteinase-2 as confirmed by zymography. Our data revealed for the first time a profound effect of the single compound 15d-PGJ2 on melanoma cells in addition to the tumor-associated microenvironment suggesting synergistic therapeutic efficiency.

The FDA-approved BRAF inhibitor vemurafenib achieves outstanding clinical response rates in patients with melanoma, but early resistance is common. Understanding the pathologic mechanisms of drug resistance and identification of effective therapeutic alternatives are key scientific challenges in the melanoma setting. Using proteomic techniques, including shotgun analysis and 2D-gel electrophoresis, we identified a comprehensive signature of the vemurafenib-resistant M24met in comparison with the vemurafenib-sensitive A375 melanoma cell line. The resistant cells were characterized by loss of differentiation, induction of transformation, enhanced expression of the lysosomal compartment, increased potential for metastasis, migration, adherence and Ca2(+) ion binding, enhanced expression of the MAPK pathway and extracellular matrix proteins, and epithelial-mesenchymal transformation. The main features were verified by shotgun analysis with QEXACTIVE orbitrap MS, electron microscopy, lysosomal staining, Western blotting, and adherence assay in a VM-1 melanoma cell line with acquired vemurafenib resistance. On the basis of the resistance profile, we were able to successfully predict that a novel resveratrol-derived COX-2 inhibitor, M8, would be active against the vemurafenib-resistant but not the vemurafenib-sensitive melanoma cells. Using high-throughput methods for cell line and drug characterization may thus offer a new way to identify key features of vemurafenib resistance, facilitating the design of effective rational therapeutic alternatives.

To shed light on the multistep process of squamous cell carcinoma development and the underlying pathologic mechanisms, we performed comparative proteome analysis of keratinocytes, keratinocytes stimulated with Il-1beta, and A431 epidermoid carcinoma cells. Fractionation of the cells into supernatant, nucleus, and cytoplasm was followed by protein separation, proteolytic digest, and nano-LC separation, and fragmentation using an ion trap mass spectrometer. Specific bioinformatics tools were used to generate a list of keratinocyte-specific proteins. Ninety percent of these proteins were found to be upregulated in keratinocytes versus the A431 cells. Classification of the identified proteins by biologic function and gene set enrichment analysis revealed that keratinocytes produced more proteins involved in cell differentiation, cell adhesion, cell junction, calcium ion, calmodulin binding, cytoskeleton organization, and cytokinesis, whereas A431 produced more proteins involved in cell cycle checkpoint, cell cycle process, RNA processing and transport, DNA damage and repair, RNA and DNA binding, and chromatin remodeling. The protein signatures of A431 and normal keratinocytes treated with IL-1beta showed marked similarity, confirming that inflammation is an important step in malignant transformation in nonmelanoma skin cancer. Thus, proteome profiling and bioinformatic processing may support the understanding of the underlying mechanisms, with the potential to facilitate development of early biomarkers and patient-tailored therapy.

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<p>Activity of vemurafenib and M8 against A375, M24met and V0, V0.1, V1, V10 (Proliferation assay).*Paulitschke et al. 2010</p>