Spitzoid melanoma is a rare malignancy with histological characteristics similar to Spitz nevus. It has a diverse genetic background and in adults, a similarly grim clinical outcome as conventional malignant melanoma. We established a spitzoid melanoma cell line (PF130) from the pleural effusion sample of a 37-year-old male patient. We found that the cell line carries a rare MEK1 mutation (pGlu102_Lys104delinsGln) that belongs to the RAF- and phosphorylation-independent subgroup of MEK1 alternations supposedly insensitive to allosteric MEK inhibitors. The in vivo tumorigenicity was tested in three different models by injecting the cells subcutaneously, intravenously or into the thoracic cavity of SCID mice. In the intrapleural model, macroscopic tumors formed in the chest cavity after two months, while subcutaneously and intravenously delivered cells showed limited growth. In vitro, trametinib—but not selumentinib—and the ATP-competitive MEK inhibitor MAP855 strongly decreased the viability of the cells and induced cell death. In vivo, trametinib but not MAP855 significantly reduced tumor growth in the intrapleural model. To the best of our knowledge, this is the first patient-derived melanoma model with RAF- and phosphorylation-independent MEK mutation and we demonstrated its sensitivity to trametinib.

Objective: Uterine carcinosarcoma (UCS) is a rare but highly aggressive malignancy with biphasic growth pattern. This morphology can be attributed to epithelial-mesenchymal transition (EMT) that often associates with tumor invasion and metastasis. Accordingly, we analyzed a novel patient-derived preclinical model to explore whether EMT is a potential target in UCS.Methods: A novel UCS cell line (PF338) was established from the malignant pleural effusion of a 59-year-old patient at time of disease progression. Immunohistochemistry was performed in primary and metastatic tumor lesions. Oncogenic mutations were identified by next-generation sequencing. Viability assays and cell cycle analyses were used to test in vitro sensitivity to different standard and novel treatments. E-cadherin, β-catenin and pSMAD2 expressions were measured by immunoblot.Results: Whereas immunohistochemistry of the metastatic tumor showed a predominantly sarcomatous vimentin positive tumor that has lost E-cadherin expression, PF338 cells demonstrated biphasic growth and carried mutations in KRAS, PIK3CA, PTEN and ARID1A. PF338 tumor cells were resistant to MEK- and TGF-β signaling-inhibition but sensitive to PIK3CA- and PARP-inhibition and first-line chemotherapeutics. Strikingly, histone deacetylase (HDAC) inhibition markedly reduced cell viability by inducing a dose-dependent G0/1 arrest and led to mesenchymal-epithelial transition as evidenced by morphological change and increased E-cadherin and β-catenin expression.Conclusions: Our data suggest that HDAC inhibition is effective in a novel UCS cell line by interfering with both viability and differentiation. These findings emphasize the dynamic manner of EMT/MET and epigenetics and the importance of molecular profiling to pave the way for novel therapies in UCS.

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