Altered Angiogenesis Underlying Age-Dependent Changes in Tumor Growth

Cancer incidence increases with age, but the growth and spread of tumors is often slow and prolonged in the elderly. Transplantable murine tumors grow and spread less readily in older mice and can be used as models to study the effect of host age. Neovascularization is crucial for the growth of solid tumors, and alterations in the host vascular response may underlie the changes in tumor growth occurring with age.We have used transplantable tumor cells and tumors, and tumor extracts, to better understand differences in the biology of tumor growth and vascularization as a function of host age.Englebreth-Holm-Swarm (EHS) carcinoma and B16-F10 melanoma cells were injected into C57BL mice of different ages. Tumor growth, histology, and cellular DNA synthesis were compared. Vascularization was determined using basic fibroblast growth factor and an in vivo angiogenesis assay. EHS tumor extracts were assayed for biologic activity in vitro using human endothelial cells and in vivo using mouse EHS-BAM carcinoma and human TSU-Pr1 prostate carcinoma cells.EHS tumors formed larger tumors in young than in old C57BL mice. Rapid tumor growth resumed upon transfer of tumor tissue from old animals into young animals. The rate of DNA synthesis of tumor tissue from old animals in organ culture was lower than in tissue from young animals. Histologically, tumors grown in old animals exhibited a threefold higher ratio of extracellular matrix to tumor cells than those grown in young animals. Tumors from adult animals exhibited numerous small blood vessels; those from old animals contained fewer, much larger vessels. Similar results were observed in young mice fed a reduced-calorie diet. Young animals elicited a greater and more rapid angiogenic response than old animals. Extracts of tumors grown in old animals failed to support endothelial cell differentiation in culture. Tumor cells injected together with such old extracts showed reduced tumor growth in nude mice.The rate of growth and morphology of the EHS tumor were altered with age, partly due to a reduced capacity to vascularize the tumors because of a lack of angiogenic factors or the presence of host inhibitors.Alterations in host factors detected in this tumor model may underlie a variety of age-dependent changes that could influence tumor growth and the repair and regeneration of normal tissue. Reducing the vascularization of tumors represents a potential target to reduce their growth and progression.