Expression of α 6 integrin, a laminin receptor, on tumor cell surfaces is associated with reduced patient survival and increased metastasis in a variety of tumors. In prostate cancer, tumor extracapsular escape occurs in part via laminin-coated nerves and vascular dissemination, resulting in clinically significant bone metastases. We previously identified a novel form of α 6 integrin, called α 6 p, generated by urokinase-type plasminogen activator-dependent cleavage of the lamininbinding domain from the tumor cell surface. Cleavage increased laminin-dependent migration. Currently, we used the known conformation sensitivity of integrin function to determine if engagement of the extracellular domain inhibited integrin cleavage and the extravasation step of metastasis. We show that α 6 integrin was present on prostate carcinoma escaping the gland via nerves. Both endogenous and inducible levels of α 6 p were inhibited by engaging the extracellular domain of α 6 with monoclonal antibody J8H. J8H inhibited tumor cell invasion through Matrigel. A severe combined immunodeficient mouse model of extravasation and bone metastasis produced detectable, progressive osteolytic lesions within 3 weeks of intracardiac injections. Injection of tumor cells, pretreated with J8H, delayed the appearance of metastases. Validation of the α 6 cleavage effect on extravasation was confirmed through a genetic approach using tumor cells transfected with uncleavable α 6 integrin. Uncleavable α 6 integrin significantly delayed the onset and progression of osseous metastases out to six weeks post-injection. The results suggest that α 6 integrin cleavage permits extravasation of human prostate cancer cells from circulation to bone and can be manipulated to prevent metastasis.

Thirty-four adult patients with portomesenteric venous occlusion (PVO) were reviewed. In 11 with hepatic cirrhosis, PVO was usually heralded by worsening ascites often with varix hemorrhage; mortality was high. Four with isolated portal block had varix hemorrhage without ascites. All of these patients survived despite recurrent hematemesis when portal decompression was not feasible in two patients. Eight others (5 agnogenic and 3 with hypercoagulability), experienced sudden abdominal pain with a clot typically propagated into mesenteric tributaries with ileojejunal infarction; survival was related to the promptness of operation and the extent of bowel ischemia. Of five patients with intraabdominal sepsis and pylephlebitis, only one survived. In the final six patients, PVO occurred with intraabdominal carcinoma. Five had progressive ascites, cachexia, and an early death. Imaging techniques included plain and contrast roentgenograms, ultrasonography, and for definitive diagnosis direct portography (operative or splenoportogram), indirect portography (splanchnic arteriovenogram), and computed tomography. Thirteen of 34 patients had ascites, and in nine of 11 patients examined, protein concentration of ascitic fluid was extremely low (less than 0.6 g/dl). Clinical presentation of PVO varies, depending on acuteness and extent of visceral venous blockade, severity of portal hypertension, auxiliary venous collateralization, and regional lymph flow. Inciting factors include endothelial damage and blood hypercoagulability from trauma, infection, stagnant circulation, blood dyscrasia, and malignancy. Improved imaging now allows early diagnosis.

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Laminin binding integrin receptors are key mediators of epithelial cell migration and tumor metastasis. Recent studies have demonstrated a role for the alpha 6 integrin (ITGA6/CD49f) in maintaining stem cell compartments within normal bone marrow and in residency of tumors metastatic to bone. In this study, we tested a function-blocking antibody specific for ITGA6, called J8H, to determine if pre-existing cancer lesions in bone could be slowed and/or animal survival improved. Human prostate tumors were established by intracardiac injection into male severe combined immunodeficient (SCID) mice and treatment with J8H antibody was initiated after one week. Tumor progression was monitored by micro computed tomography (CT) imaging of skeletal lesions. Animals that received weekly injections of the anti-ITGA6 antibody showed radiographic progression in only 40% of osseous tumors (femur or tibia), compared to control animals, where 80% of the lesions (femur or tibia) showed progression at 5 weeks. Kaplan-Meier survival analysis demonstrated a significant survival advantage for J8H-treated animals. Unexpectedly, CT image analysis revealed an increased proportion of bone lesions displaying a sclerotic rim of new bone formation, encapsulating the arrested lytic lesions in animals that received the anti-ITGA6 antibody treatment. Histopathology of the sclerotic lesions demonstrated well-circumscribed tumor within bone, surrounded by fibrosis. These data suggest that systemic targeting of the ITGA6-dependent function of established tumors in bone may offer a non-cytotoxic approach to arrest the osteolytic progression of metastatic prostate cancer, thereby providing a new therapeutic strategy for advanced disease.