Human breast adenocarcinoma (MDA-231) and human lung squamous cell carcinoma (Hara) do not have the ability to cause bone resorption by themselves during the establishment of bone metastasis.

Osteolysis is an important process in the establishment of bone metastasis. The role which cancer cells play in this process is not fully understood. In this study, we first established a reproducible in vivo bone metastasis model using two types of tumor cells, human breast adenocarcinoma (MDA-231) and human lung squamous cell carcinoma (Hara cells), and examined in vitro characteristics of the tumor cells. Tumor cells injected into the left heart ventricle of nude mice preferentially metastasized to bone, 6 weeks after the inoculation. Histological observation of the bone metastatic lesion showed that tumor cells invaded the bone marrow, and osteoclasts adjacent to fibroblasts were actively resorbing the bone matrix. In vitro analysis of the tumor cells showed that MDA-231 cells express cathepsin K, matrix metalloproteinase 9 (MMP-9), and membrane type-1 matrix metalloproteinase (MT1-MMP), all of which are believed to play an important role in osteoclastic bone resorption. In contrast, Hara cells do not express cathepsin K and MT1-MMP. MMP-9 was expressed at a low level. To assess the osteolytic activity of the tumor cells, an in vitro pit assay was performed. The rabbit osteoclasts formed numerous pits on a dentin slice after 18 h of incubation, whereas tumor cells by themselves did not. Taken together, we conclude that MDA-231 and Hara cells, which metastasize to the bone in vivo, do not have enough ability to achieve bone resorption by themselves, but rather achieve it through activation of fibroblast like cells and osteoclasts.

Structural recognition by recombinant human heparanase that plays critical roles in tumor metastasis. Hierarchical sulfate groups with different effects and the essential target disulfated trisaccharide sequence.

Human heparanase is an endo-beta-d-glucuronidase that degrades heparan sulfate/heparin and has been implicated in a variety of biological processes, such as inflammation, tumor angiogenesis, and metastasis. Although the cloned enzyme has been demonstrated to have a critical role in tumor metastasis, the substrate specificity has been poorly understood. In the present study, the specificity of the purified recombinant human heparanase was investigated for the first time using a series of structurally defined oligosaccharides isolated from heparin/heparan sulfate. The best substrates were deltaHexUA(+/-2S)-GlcN(NS,6S)-GlcUA-GlcN(NS,6S)-GlcUA-GlcN(NS,6S) and deltaHexUA(2S)-GlcN(NS,6S)-GlcUA-GlcN(NS,6S) (where deltaHexUA, GlcN, GlcUA, NS, 2S, and 6S represent unsaturated hexuronic acid, d-glucosamine, d-glucuronic acid, 2-N-sulfate, 2-O-sulfate, and 6-O-disulfate, respectively). Based on the percentage conversion of the substrates to products under identical assay conditions, several aspects of the recognition structures were revealed. 1) The minimum recognition backbone is the trisaccharide GlcN-GlcUA-GlcN. 2) The target GlcUA residues are in the sulfated region. 3) The -GlcN(6S)-GlcUA-GlcN(NS)- sequence is essential but not sufficient as the cleavage site. 4) The IdoUA(2S) residue, located two saccharides away from the target GlcUA residue, claimed previously to be essential, is not indispensable. 5) The 3-O-sulfate group on the GlcN is dispensable and even has an inhibitory effect when located in a highly sulfated region. 6) Based on these and previous results, HexUA(2S)-GlcN(NS,6S)-IdoUA-GlcNAc(6S)-GlcUA-GlcN(NS,+/-6S)-IdoUA(2S)-GlcN(NS,6S) (where HexUA represents hexuronic acid) has been proposed as a probable physiological target octasaccharide sequence. These findings will aid establishing a quantitative assay method using the above tetrasaccharide and designing heparan sulfate-based specific inhibitors of the heparanase for new therapeutic strategies.