Enhanced Claudin-9 expression is associated with lung cancer metastasis

Typical metastasis models utilize intravenous injection of tumor cells, thus bypass the egression of malignant cells an obligatory step in metastasis of spontaneous cancers. We herein utilized a unique metastasis model by in vivo passaging the Lewis lung carcinoma (3LL) cells and maintaining them in vivo with 7-11 days of intermittent culture in between passages. When injected subcutaneously parental 3LL cells have minimal metastasis, while in vivo passaged cells show robust metastasis. Most interestingly, parental and passed cell lines if injected i.v., yielded similar metastatic burden suggesting that egression from the primary tumor is facilitated by in vivo passaging. Microarray analysis of RNA from these cells as well as the primary tumors derived from each revealed several novel markers associated with increased metastasis. Expression of a tight junction protein “claudin 9” is highly up regulated in passaged 3LL lines. Enhanced expression of claudin-9 in passaged 3LL lines and tumors derived from these cells was confirmed by real time PCR and Western blot as well as immuno-fluorescence microscopy. Passaged 3LL cells exhibited greater motility and invasiveness relative to parental 3LL cells. Taken together, these data indicate distinct association of claudin 9 expression with metastatic phenotype and suggest that claudin 9 may serve as a biomarker and a potential therapeutic target for preventing lung cancer metastasis.