Midkine Promotes Tumor Growth and Attenuates the Effect of Cisplatin in Small Cell Lung Cancer.

PURPOSE: Small cell lung cancer (SCLC) is a highly aggressive disease associated with poor patient survival rates. The addition of an anti-programmed death ligand 1 antibody to platinum combination chemotherapy can improve its prognosis. However, only a few patients achieve a long-term response; thus, establishing new therapies for SCLC is crucial. Midkine (MDK) is a heparin-binding growth factor involved in various biological processes, including cell proliferation and chemotherapeutic resistance, in diverse cancers. MDK has garnered attention as a therapeutic and diagnostic target for several cancers; however, only a few studies have evaluated its expression and function in SCLC. This study aimed to evaluate the MDK expression in human SCLC tissue and human SCLC cell lines, and to clarify its function in tumorigenesis. METHODS: MDK expression was analyzed in vitro and in vivo through ELISA, immunohistochemistry, and western blotting. Its effects on cell proliferation, as well as the effects of cisplatin, were evaluated using the MTT assay. RESULTS: MDK was pathologically expressed in human SCLC tumor tissues but not in normal lung tissues. Serum MDK concentrations in patients with SCLC reflected the SCLC tumor burden and were correlated with response to treatment. Moreover, MDK induced cell proliferation and attenuated the effects of cisplatin in SCLC cell lines. An MDK inhibitor and cisplatin exerted synergistic antitumor effects both in vitro and in vivo. Furthermore, MDK positively regulated the AKT pathway. CONCLUSION: Our findings indicate that MDK promotes cell proliferation and chemotherapeutic resistance by activating the AKT pathway in SCLC cells. Therefore, MDK may be a potential therapeutic and diagnostic target for SCLC.