Clinical and therapeutic relevance of PIM1 kinase in gastric cancer

Gastric cancer is a leading cause of cancer-related mortality, and chemotherapeutic options are currently limited. PIM1 kinase, an oncogene that promotes tumorigenesis in several cancer types, might represent a novel therapeutic target in gastric cancer. We studied the expression and genomic status of PIM1 in human primary gastric normal and tumor tissue samples by immunohistochemistry and array-based comparative genomic hybridization (aCGH). To ascertain whether PIM1 expression predicted susceptibility to PIM1 kinase-specific inhibition, the cytotoxic effect of a previously reported PIM1-specific small molecular inhibitor (K00135) was investigated in two gastric cancer cell lines with high (IM95) and undetectable (NUGC-4) PIM1 expression levels. PIM1 expression was exclusively nuclear in normal gastric epithelial cells, while aberrant expression/localization (decreased nuclear and/or increased cytoplasmic expression) was observed in 75.6% (68/90) of the human gastric cancer tissue samples, with a significant inverse correlation between nuclear and cytoplasmic expression levels. Clinicopathological analyses revealed that decreased nuclear PIM1 expression correlated with poorer survival and greater depth of tumor invasion, while increased cytoplasmic PIM1 expression correlated inversely with the presence of lymphovascular invasion. High-level PIM1 amplification was identified in 10.5% of gastric cancers by aCGH. K00135 impaired the survival of IM95, while it had no significant effect on NUGC-4 survival. Our findings demonstrate the clinical and therapeutic relevance of PIM1 in gastric cancers, and suggest that PIM1 represents a potential therapeutic target.