Neurotrophin system activation in pleural effusions.

Neurotrophins (NTs) expression was assessed in malignant and non-malignant pleural effusions (inflammatory exudates and transudates). Enzyme-linked immunosorbent assay, in malignant exudates from small and non-small cell lung cancer (SCLC and NSCLC), detected nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3), and their levels are higher as compared with inflammatory and transudative effusions. By immunoblots, in cultured cancer cells coming from malignant pleural effusions, NTs and low- and high-affinity NT receptors were detected in a percentage of SCLC and NSCLC. Proliferation assay demonstrated that BDNF significantly increased cancer cell proliferation in vitro, on the contrary, NT-3 reduced cancer cell growth rate and NGF did not modify cell growth. Moreover, NGF protects cells from death during starvation. These effects are reverted by the addition of NT receptor antagonists. Cultured cancer cells injected into the lung of immunodeficient mice generate lung tumors expressing NTs and NT receptors. These findings suggest that NTs may be able to modulate cancer cell behavior and their growth.