Abstract 557: Single-chain type IV collagen (SCCOL-IV), an alternative gene product of COL4A1 as a therapeutic target in tumor tissue expansion as well as a diagnostic marker

Abstract

Abstract Type IV collagen (COL-IV) is a major component of basement membrane (BM), comprising a polygonal meshwork structure underlying the basal side of polarized epithelia in normal tissues. Modulation of BM due to COL-IV degradation by matrix metalloproteinases is often associated with tumor aggravation and metastasis; Degradation products of BM components, including laminin and type IV collagen e.g., are involved in promoting tumor cell motility. Our previous studies showed that cultured human cells, in particular under ascorbate-deficiency, secrete single-chain COL-IV (SCCOL-IV), which is not derived from the denatured polypeptide of COL-IV triple-helical molecule. SCCOL-IV undergoes posttranslational modifications distinct from triple-helical COL-IV; SCCOL-IV has prolyl- and lysyl-hydroxylation to a lower extent than triple-helical COL-IV. SCCOL-IV contains the O-glycan structure of Galβ1-3GalNAc with a positive reaction to Agaricus bisporus agglutinin. The lectin does not recognize the triple-helical COL-IV-derived polypeptide. The alternative form of COL4A1 gene product is detected in vivo by the antibody that recognizes only SCCOL-IV. The polypeptide is isolated from human placenta as well as cultured media. In the present study, we demonstrate that SCCOL-IV is expressed specifically by cultured tumor cells and in tumor tissues. One of the antibodies against SCCOL-IV repressed tumor growth in an in vivo mouse model. The culture cell production of SCCOL-IV was demonstrated by Western blotting of cultured media, with an anti-SCCOL IV antibody, JK132 (Connective Tissue 31:161-168, 1999) for human cancer cell lines; Lu65A and NCI-H460 (pulmonary cancer), HLF (hepatoma), UO31 and A498 (renal cancer), and Panc-1 (pancreatic cancer). SCCOL-IV expression level was as high in tumor tissues of Lu65A-bearing nude mice as in tumor lesions of pulmonary cancer patients. One of the monoclonal antibodies against purified SCCOL-IV, NK46141, which exhibits a higher affinity compared with JK132, has no cross-reactivity with triple-helical COL-IV. Prophylactic interventions with NK46141 suppressed tumor growth in Lu65A-bearing nude mice. NK46141 had no effect, however, on the proliferation of cultured Lu65A cells. In order to obtain a clue for a mechanism how the antibody suppresses in vivo tumor growth, biological properties of SCCOL-IV in tumor interstitium were examined. SCCOL-IV was localized predominantly in vessel lumens in an in vitro vasculogenesis model, suggesting that SCCOL-IV may play a critical role for vasculogenesis in tumor progression. Prevention tumor growth by the antibody might be due to vasculogenesis inhibition. We propose that SCCOL-IV is a useful target in tumor diagnosis and therapy. Anti-SCCOL-IV antibodies including NK46141 could be potential therapeutics for tumor progression involving vasculogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 557. doi:10.1158/1538-7445.AM2011-557