Tumor interstitial fluid and gastric cancer metastasis: an experimental study to verify the hypothesis of "tumor-phlegm microenvironment".

OBJECTIVE: To extract tumor interstitial fluid (TIF) from MKN-45 gastric cancer which is similar to "muddy phlegm" in Chinese medicine and observe influences of MKN-45 tumor interstitial fluid (MKN-45 TIF) intervention on metastasis of gastric cancer and on the expressions of vascular endothelial growth factor (VEGF), kinase insert domain containing receptor (KDR), epithelial-cadherin (E-cad), cyclooxygenase-2 (COX-2), intercellular adhesion molecule-1 (ICAM-1) and telomerase genes and proteins in primary tumor tissue.

METHODS: An MKN-45 tumor-bearing model was established in 50 nude mice. The modeled animals were equally randomized to 5 groups: the simple tumor-bearing group (model group), the normal saline (NS) via tail vein injection (i.v.) group (NS i.v. group), MKN-45 TIF i.v. group (TIF i.v. group), NS intraperitoneal injection (i.p.) group (NS i.p. group), and MKN-45 TIF i.p. group (TIF i.p. group). The TIF and NS intervention groups received injection (i.p. or i.v.) of MKN-45 TIF or NS twice a week, 0.2 mL at a time. After 8 weeks, the primary tumors were removed, weighed and HE stained to observe tumor metastasis. The primary tumor tissues were analyzed by immunohistochemistry and real-time quantitative PCR to detect expressions of VEGF, KDR, E-cad, COX-2, ICAM-1, and telomerase genes and proteins in different groups.

RESULTS: There were significant differences in tumor weight between TIF intervention groups and the model and NS intervention groups. Tumor metastasis was observed in all 5 groups, but the tumor metastasis rate in TIF intervention groups was significantly higher than those in the model and NS intervention groups. The gene and protein expressions of gastric cancer-related factors VEGF, KDR, COX-2, ICAM-1 and telomerase were unregulated while the gene and protein expressions of E-cad were downregulated in TIF intervention groups.

CONCLUSIONS: TIF promotes tumor growth, invasion and metastasis of gastric cancer. These findings provide preliminary experimental clues for verifying the hypothesis of "tumor-phlegm microenvironment".