The proliferation of neoplastic cells in a confined space collapses blood vessels thus restricting the penetration and uniform distribution of therapeutic agents in tumors. Our recent data also shows that growth of tumor spheroids in a confined space can upregulate the expression of hyaluronan an interstitial matrix (IM) molecule that hinders interstitial fluid movement and molecular diffusion. The induction of apoptosis by taxol alleviates the confined space effects, thus improving vascular perfusion and fluid flow through the tumor IM. In contrast, radiation reduces fluid flow through the tumor IM. Thus the objectives of the proposed study will be to determine: 1) the effects of taxol and radiation on interstitial transport, and on the production of IM molecules, 2) test the hypothesis that growth in a confined space upregulates the expression of glycosaminoglycans by tumor cells and reduces diffusive transport and 3) determine if the void spaces induced by apoptosis produce interstitial pathways that favor a rapid and more uniform penetration of viruses. Fluorescence recovery after photobleaching and measurements of hydraulic conductivity will test the hypothesis that taxol enhances interstitial transport in tumors. The transport data will be related to the levels of IM matrix molecules and apoptosis. The effects of growth in a confined space on the expression of hyaluronan will be tested in vitro by growing tumor spheroids in increasing concentrations of collagen or agarose gels. To test the hypothesis that apoptosis enhances the distribution volume of viral particles and gene transfection in tumors, apoptosis will be induced with taxol and in cells transfected with a caspase-8 inducible promoter. Multiphoton laser-scanning microscopy will be used to measure in tumors the distribution volume of viral vectors and determine if the void spaces induced by apoptosis form interconnected interstitial pathways that enhance the movement of viral particles. Sense constructs of hyaluronan synthase 2 will test the hypothesis that hyaluronan participates in the remodeling and obstruction of the void spaces following apoptotic death, thus reducing interstitial transport and the movement of viral vectors. The hypothesis that taxol-induced apoptosis (void space formation) enhances the antitumor efficacy of gene therapy will be tested. The results will provide insight on how to best combine viral vectors and cytotoxic agents.