Molecular Signature of Small Cell Lung Cancer after Treatment Failure: The MCM Complex as Therapeutic Target

SIMPLE SUMMARY: Small cell lung cancer (SCLC) is a fatal malignant tumor with a poor prognosis for patients who relapse after first-line treatment. There are few effective treatments for SCLC patients with relapse. Elucidation of the molecular network related to treatment resistance is an important issue for this disease. In this study, the molecular signature of SCLC specimens after treatment failure was generated. Several pathways, e.g., “cell cycle”, “homologous recombination”, “DNA replication”, and “p53 signaling” were identified as the enriched pathways in this signature. Aberrant expression of MCM2, MCM4, MCM6, and MCM7 were detected in SCLC clinical specimens after treatment failure. This signature contains molecules involved in treatment resistance and will contribute to the study of SCLC molecular pathogenesis. ABSTRACT: Small cell lung cancer (SCLC) is a highly aggressive cancer, and patients who become refractory to first-line treatment have a poor prognosis. The development of effective treatment regimens is urgently needed. In this study, we identified a gene expression signature of SCLC after treatment failure using SCLC clinical specimens (GEO accession number: GSE162102). A total of 1,136 genes were significantly upregulated in SCLC tissues. These upregulated genes were subjected to KEGG pathway analysis, and “cell cycle”, “Fanconi anemia”, “alcoholism”, “systemic lupus erythematosus”, “oocyte meiosis”, “homologous recombination”, “DNA replication”, and “p53 signaling” were identified as the enriched pathways among the genes. We focused on the cell cycle pathway and investigated the clinical significance of four genes associated with this pathway: minichromosome maintenance (MCM) 2, MCM4, MCM6, and MCM7. The overexpression of these MCM genes was confirmed in SCLC clinical specimens. Knockdown assays using siRNAs targeting each of these four MCM genes showed significant attenuation of cancer cell proliferation. Moreover, siRNA-mediated knockdown of each MCM gene enhanced the cisplatin sensitivity of SCLC cells. Our SCLC molecular signature based on SCLC clinical specimens after treatment failure will provide useful information to identify novel molecular targets for this disease.