MG624, an α7-nAChR antagonist, inhibits angiogenesis via the Egr-1/FGF2 pathway.

Small cell lung cancer (SCLC) demonstrates a strong etiological association with smoking. Although cigarette smoke is a mixture of about 4,000 compounds, nicotine is the addictive component of cigarette smoke. Several convergent studies have shown that nicotine promotes angiogenesis in lung cancers via the α7-nicotinic acetylcholine receptor (α7-nAChR) on endothelial cells. Therefore, we conjectured that α7-nAChR antagonists may attenuate nicotine-induced angiogenesis and be useful for the treatment of human SCLC. For the first time, our study explores the anti-angiogenic activity of MG624, a small-molecule α7-nAChR antagonist, in several experimental models of angiogenesis. We observed that MG624 potently suppressed the proliferation of primary human microvascular endothelial cells of the lung (HMEC-Ls). Furthermore, MG624 displayed robust anti-angiogenic activity in the Matrigel, rat aortic ring and rat retinal explant assays. The anti-angiogenic activity of MG624 was assessed by two in vivo models, namely the chicken chorioallantoic membrane model and the nude mice model. In both of these experimental models, MG624 inhibited angiogenesis of human SCLC tumors. Most importantly, the administration of MG624 was not associated with any toxic side effects, lethargy or discomfort in the mice. The anti-angiogenic activity of MG624 was mediated via the suppression of nicotine-induced FGF2 levels in HMEC-Ls. MG624 decreased nicotine-induced early growth response gene 1 (Egr-1) levels in HMEC-Ls, and reduced the levels of Egr-1 on the FGF2 promoter. Consequently, this process decreased FGF2 levels and angiogenesis. Our findings suggest that the anti-angiogenic effects of MG624 could be useful in anti-angiogenic therapy of human SCLCs.

The α7-nicotinic acetylcholine receptor and MMP-2/-9 pathway mediate the proangiogenic effect of nicotine in human retinal endothelial cells.

PURPOSE: Nicotine, the active component of cigarette smoke, has been found to stimulate angiogenesis in several experimental systems. In this study, the Matrigel duplex assay (Matrigel; BD Biosciences, Franklin Lakes, NJ) and the rat retinal explant assay were used to explore the molecular mechanisms underlying the proangiogenic effects of nicotine in endothelial cells. METHODS: Western blot analysis was performed to determine the nicotinic acetylcholine receptor (nAChR) subtypes expressed on primary human retinal microvascular endothelial cells (HRMECs). The angiogenic effect of nicotine in the retina was evaluated with the duplex assay. The results obtained from the assay were confirmed by the rat retinal explant angiogenesis assay. ELISAs were used to measure MMP-2, -9, and -13 levels in HRMEC culture supernatants. The role of α7-nAChRs in nicotine-induced angiogenesis was examined by siRNA techniques. RESULTS: Nicotine-induced angiogenesis required nAChR function and was associated with the upregulation of MMP-2 and -9 in HRMECs. Specifically, α7-nAChRs mediated the stimulatory effects of nicotine on retinal angiogenesis and MMP levels. Treatment of HRMECs with α7-nAChR antagonists ablated nicotine-induced angiogenesis. The inhibitory actions of α7-nAChR antagonists correlated with the suppression of MMP-2 and -9 levels in HRMECs. CONCLUSIONS: The α7-nAChR is vital for the proangiogenic activity of nicotine. The α7-nAChRs expressed on HRMECs upregulate levels of MMP-2 and -9, which stimulate retinal angiogenesis. The data also suggest that α7-nAChR antagonists could be useful agents for the therapy of angiogenesis-related retinal diseases.