CLDN5 and lung carcinoma: Contrary to these results, a study revealed that the activation of adenosine A2A receptors inhibits lung cancer BM by interfering with SDF-1/CXCR4 signaling pathway involved in promoting cancer metastasis, and through upregulating the expression level of tight junction proteins; claudin-5, occludin, and ZO-1, thereby preserving the integrity of BBB [136].