Downregulation of insulin-like growth factor-binding protein 7 in cisplatin-resistant non-small cell lung cancer.

Cisplatin is an effective anticancer drug used to treat many types of cancer, including non-small cell lung carcinoma (NSCLCs), but development of resistance is the primary impediment in cancer treatment. Insulin-like growth factor-binding protein 7 (IGFBP7) is a secreted tumor suppressor that is inactivated in human lung cancer. IGFBP7 is known to alter sensitivity to interferon-based anticancer therapy, and here, we examined loss of IGFBP7 as a potential contributor to chemo-resistance to cisplatin. The transcriptional level of IGFBP7 was decreased in cisplatin-resistant human cancer cell lines and NSCLC xenografts. IGFBP7 knock-down increased cellular resistance to cisplatin and increased the level of mitogen-activated protein kinase phosphatases (MKP) 3 levels. The expression of MKP3 increased in a cisplatin-resistant NSCLC cell line and lung xenografts. MKP3 knock-down increased IGFBP7 level, indicating that MKP3 regulates IGFBP7. These findings suggest a novel molecular mechanism responsible for the tumor suppressive function of IGFBP7 in cisplatin-resistant human lung cancer and could lead to the development of IGFBP7 as a cisplatin-sensitizing agent.