Endocrine Abstracts

Neuroendocrine tumors (NETs) are rare neoplasms showing a wide spectrum of clinical behaviors. The therapeutic options available for NET treatment are rarely curative and most are palliative, as NETs frequently show resistance to pharmacological therapy. Cancers develop in complex tissue environments, which they depend upon for sustained growth, invasion and metastasis. A major characteristic of the tumor microenvironment is inflammatory cell infiltration, where tumor-associated macrophages (TAMs) are a major cellular component. The polarized state of macrophages is classified into two subsets: classically activated M1 (anti-tumor promoting effects) and alternatively activated M2 (pro-tumor promoting effects). Thus the restoration of an M1 phenotype may provide therapeutic value by promoting anti-tumor behavior. The importance of immune microenvironment and the role of macrophages in NET are poorly understood. Aims of the study are: to investigate the effects of the different macrophages subtypes (M1, M2) on biological behavior of primary NET cells and QGP1 (pancreatic-NET) and H727 (pulmonary-NET) cell lines. We found that M1 macrophages significantly decreased the viability of QGP1 cell line (−40±14% P<0.01 vs basal) and H727 cell line (−43±8 P<0.01 vs basal). Moreover, CM (conditioned medium) of M1 macrophages strongly decreased colony formation, colony average area and cell number (QGP1: −42±17% P<0.05 vs basal; H727: −60±15% P<0,001 vs basal) after 7 days of incubation. As shown by flow cytometry analysis, after CM of M1 macrophages treatment, G0/G1 phase was increased in H727 cells (+18±7% P<0.05), whereas G2/M phase was decreased in QGP1 cell (−44±4% P<0.05). Interestingly, as shown by real time analysis, the CM of NET cell lines promoted the differentiation of macrophages into an M2 phenotype, after 24 h of culture. Moreover, as shown in preliminary data of primary pancreatic NET cells, CM of M1 macrophages strongly decreased cell proliferation, whereas CM of M2 macrophages promoted it. In conclusion, M1 macrophages have a potent anti-tumor effect, able to affect the proliferation and the tumorigenicity of NET cell lines. Interestingly, NET cell lines contribute to promote a M2 phenotype of macrophages, suggesting a potential involvement of tumor microenvironment in the behaviour of pulmonary and pancreatic NETs.