RESUMO
PURPOSE: To investigate the roles of melanoma-associated macrophages in melanoma resistance to BRAF inhibitors (BRAFi). EXPERIMENTAL DESIGN: An in vitro macrophage and melanoma cell coculture system was used to investigate whether macrophages play a role in melanoma resistance to BRAFi. The effects of macrophages in tumor resistance were examined by proliferation assay, cell death assay, and Western blot analyses. Furthermore, two mouse preclinical models were used to validate whether targeting macrophages can increase the antitumor activity of BRAFi. Finally, the number of macrophages in melanoma tissues was examined by immunohistochemistry. RESULTS: We demonstrate that in BRAF-mutant melanomas, BRAFi paradoxically activate the mitogen-activated protein kinase (MAPK) pathway in macrophages to produce VEGF, which reactivates the MAPK pathway and stimulates cell growth in melanoma cells. Blocking the MAPK pathway or VEGF signaling then reverses macrophage-mediated resistance. Targeting macrophages increases the antitumor activity of BRAFi in mouse and human tumor models. The presence of macrophages in melanomas predicts early relapse after therapy. CONCLUSIONS: Our findings demonstrate that macrophages play a critical role in melanoma resistance to BRAFi, suggesting that targeting macrophages will benefit patients with BRAF-mutant melanoma.
Assuntos
Resistencia a Medicamentos Antineoplásicos/imunologia , Macrófagos/metabolismo , Melanoma/patologia , Proteínas Proto-Oncogênicas B-raf/antagonistas & inibidores , Transdução de Sinais/efeitos dos fármacos , Animais , Western Blotting , Técnicas de Cocultura , Ensaio de Imunoadsorção Enzimática , Feminino , Citometria de Fluxo , Humanos , Immunoblotting , Imuno-Histoquímica , Macrófagos/efeitos dos fármacos , Macrófagos/imunologia , Melanoma/imunologia , Camundongos , Camundongos Endogâmicos BALB C , Terapia de Alvo Molecular/efeitos adversos , Inibidores de Proteínas Quinases/farmacologia , RNA Interferente Pequeno , Transfecção , Microambiente Tumoral/imunologia , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
Tumor-associated macrophages (TAMs) have essential roles in tumor progression and metastasis. Tumor cells recruit myeloid progenitors and monocytes to the tumor site, where they differentiate into TAMs; however, this process is not well studied in humans. Here we show that human CD7, a T-cell and NK cell receptor, is highly expressed by monocytes and macrophages. Expression of CD7 decreases in M-CSF-differentiated macrophages and in melanoma-conditioned medium-induced macrophages (MCMI/Mφ) in comparison to monocytes. A ligand for CD7, SECTM1 (secreted and transmembrane protein 1), is highly expressed in many tumors, including melanoma cells. We show that SECTM1 binds to CD7 and significantly increases monocyte migration by activation of the PI3K (phosphatidylinositol 3'-kinase) pathway. In human melanoma tissues, tumor-infiltrating macrophages expressing CD7 are present. These melanomas, with CD7-positive inflammatory cell infiltrations, frequently highly express SECTM1, including an N-terminal, soluble form, which can be detected in the sera of metastatic melanoma patients but not in normal sera. Taken together, our data demonstrate that CD7 is present on monocytes and tumor macrophages and that its ligand, SECTM1, is frequently expressed in corresponding melanoma tissues, possibly acting as a chemoattractant for monocytes to modulate the melanoma microenvironment.
