Growth and characterization of a cell line from a human primary neuroendocrine carcinoma of the skin (Merkel cell carcinoma) in culture and as xenograft

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Abstract
The primary neuroendocrine carcinoma of the skin or Merkel cell carcinoma (MCC) is a skin tumor with aggressive biological behaviour. Experimental models for investigating the biological properties of the tumor are prerequisite for developing new therapeutic approaches. In this study, we report the establishment and characterisation of a cell line derived from the lymph‐node metastasis of a patient with highly aggressive MCC. Merkel carcinoma cells (MCC‐1) grew as floating aggregates in suspension cultures for more than two years and over 70 subcultures. The proliferation rate in suspension cultures was rather moderate with a population doubling time of 69 h. The immunocytochemical pattern of the cultured MCC‐1 was similar to that of the original tumor with expression of cytokeratin 18, neuron‐specific enolase, neurofilaments, and synaptophysin. In addition, reverse transcriptase polymerase chain reaction (RT‐PCR) revealed presence of chromogranin A mRNA in the MCC‐1 cell line. Furthermore, electron microscopy yielded the rare finding of neuroendocrine granules in the cytoplasm of the cultured cells. The cell line MCC‐1 was able to form colonies in soft agar. Nude mice developed solid tumors with similar histology to the original tumor after subcutaneous and intravenous injections of cultured MCC‐1, and malignant ascites was seen after intraperitoneal injection. Also, two MCC‐1 sublines were established by reculturing cells from the xenografts grown in vivo and immunocytochemistry confirmed their neuroendocrine origin. The MCC‐1 line may thus serve as a model for studying the biology and the metastatic potential of Merkel cell carcinoma.