Secretion of gelatinases and tissue inhibitors of metalloproteinases by human lung cancer cell lines and revertant cell lines: Not an invariant correlation with metastasis

Numerous studies have reported a correlation between production of 72-kDa (MMP-2) and 92-kDa (MMP-9) type-IV collagenases/gelatinases and the metastatic potential of cancer cells. An abrogating effect of tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) on metastases has also been noted. In this report we have used sensitive enzyme-linked immunoassays to measure MMP-2, MMP-9, TIMP-1 and TIMP-2 levels in eight human lung-cancer cell lines which were characterized for biological behavior in nude mice. We demonstrated that the Calu-6 and A549 cell lines with the highest metastatic, invasive and tumorigenic potential secreted the highest levels of MMP-2. MMP-9 and TIMP-1 secretions were comparatively low in all cell lines. TIMP-2 secretion, which exceeded MMP-2 secretion for all cell lines, did not correlate with metastatic potential. To further explore these correlations, the metastatic Calu-6 cell line was transfected with a K-rev-1 cDNA expression construct. The K-rev revertant cell lines demonstrated a more differentiated phenotype and were less tumorigenic, invasive and metastatic in nude mice. Nonetheless, the Calu-6 revertant cell lines secreted higher levels of MMP-2 than the parent cell line. In conclusion, invasion and metastasis by lung-cancer cells requires not only enhanced MMP production, but also other less well-understood tumorigenic characteristics. The multiplicity of factors required by cancer cells for dissemination helps to explain the minute fraction of cancer cells from a primary tumor that ever develop into a metastasis.