Dose escalated chemotherapy regimens are now known to damage cells of the hematopoietic microenvironment. Work completed during the previous period of funding demonstrated that exposure of bone marrow stromal cells to VP-16 resulted in reduced ability to support migration and survival of hematopoietic progenitor cells. During the recent period of funding, we also demonstrated that VP-16 exposure altered expression and activity of stromal cell matrix metalloproteinase-2 (MMP-2). Acute exposure to VP-16 resulted in immediate, transient activation of pro-MMP-2 protein. In contrast, long-term exposure resulted in down regulation of MMP-2 protein expression. The varied responses to acute and chronic exposure on MMP-2 have distinct consequences on stromal cell function. Activation of MMP-2 was correlated with release of TGF-beta, which has potential to alter stromal cell phenotype and function in an autocrine manner. Reduced MMP-2 protein expression, associated with sustained exposure of stromal cells to VP-16, resulted in diminished SDF-1 protein in stromal cell supernatants and failure of chemotactic support of hematopoietic cells. These studies underscore a role for MMP-2 in influencing the bone marrow microenvironment that exceeds its well-characterized function in extracellular matrix regulation. The current application will address the mechanism(s) by which chemotherapy-induced effects on MMP-2 alter obligatory components of the hematopoietic microenvironment through completion of the following specific aims: (1) to evaluate the autocrine effects of MMP-2-dependent TGF-beta release on stromal cell hematopoietic support capacity, (2) to investigate the mechanisms by which diminished MMP-2 reduces stromal cell support of chemotaxis, and (3) to develop a murine in vivo model to investigate the effects of modulation of chemotherapy induced-signaling to enhance bone marrow microenvironment support of hematopoietic reconstitution. Our working hypothesis is that inefficient hematopoietic reconstitution following VP-16 chemotherapy is, in part, due to deregulated activation and expression of stromal cell MMP-2 protein. Results of these experiments will aid in tailoring high dose chemotherapy regimens to maintain efficacy of tumor eradication while reducing microenvironment damage to the hematopoietic microenvironment.