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Introduction: Cancer metastases are responsible for the majority of cancer-related deaths. The process of tumor metastasis is highly selective and consists of a series of sequential, inter-related steps which include invasion through extracellular matrix, intravasation, survival in the circulation, extravasation into a distant site, and progressive growth at that site. The goal of this project is to identify individual genes or family of genes that are involved in lung cancer invasion and metastatic processes, using an orthotopic lung model in nude rats and Affymetrix microarray analysis.
 Method: Human lung cancer cell line H2122 adenocarcinoma was tagged with GFP and implanted subcutaneously or orthotopically in athymic nude rats. In vivo fluorescent imaging was used to follow patterns of tumor growth and metastasis formation. When animals showed signs heavy breathing due to metastases, tumor tissues were isolated aseptically from primary sites of implantations, plus metastases in the right lung and distant metastases and were allowed to grow in tissue culture. Early generations of these cells were chipped with Affymetrix HG U133 plus 2, or re-implanted subcutaneously and orthotopically in nude rats again for further comparison studies.
 Results: When implanted subcutaneously in nude rats, human lung cancer cells such as H2122 grew very aggressively but rarely found to metastasize to distant sites. On the other hand, when H2122 were implanted inside the left lung of nude rats, primary tumors established quickly and they frequently metastasized within weeks contra-laterally to the right lungs, followed by mediastinal lymph nodes, then to distant sites including lumbar lymph nodes, adrenal glands, kidneys and sometimes in pancreas. When normalized with gene signals from parental H2122, a broad spectrum of genes that are known to involve in the invasion and metastatic process such as proliferative growth factors/receptors, MMPs, inflammatory cytokines / chemokines, apoptosis and angiogenesis, are found to be up-regulated or down-regulated progressively from parental → primary → metastases → distant metastases, while subcutaneous tumors responded differently.
 Conclusions: Our orthotopic lung model in rats offers a clinically relevant model for the delineation of lung metastastic process. We showed that gene expressions are influenced by sites of tumor environment and that all the involved genes seemed to contribute some roles in the overall invasion and metastatic cascades.


99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA