The objective of this work was to develop a novel dual-modal protein for targeted vascular occlusion of solid tumor neovasculature mediated by in-situ polymer synthesis. Towards this aim two novel constructs were designed; a single-chain variable fragment (ScFv), J591 ScFv, that recognizes an extracellular epitope the tumor neovasculature endothelial marker Prostate Specific Membrane Antigen (PSMA) and a fusion protein composed of the J591 ScFv and the polyhydroxyalkanoate (PHA) synthase enzyme, the sole enzyme required to initiate synthesis of the biocompatible polyhydroxybutyrate (PHB) polymer by conversion of (R)-3-hydroxyacylCoA thioester (3HB-CoA) substrate to PHB. The dual moiety fusion protein was designed to localize to the solid tumor neovasculature by targeting PSMA via the J591 ScFv. Next, 3HBCoA monomer substrate will be locally delivered and vascular occlusion will be mediated via in situ growth of PHB polymer catalyzed by the PHA synthase enzyme moiety of the fusion protein. The resulting obstruction of the tumor neovasculature due to PHB polymer accumulation will restrict the blood supply to the tumor, causing in tissue ischemia and tumor necrosis. Further, conjugating the fusion protein with superparamagnetic iron oxide nanoparticles (SPIONs) allows for monitoring via Magnetic resonance imaging (MRI) and potentially provides a means increasing the valency of the fusion protein. The following chapters detail the design, production, and characterization of the J591 ScFv and J591 ScFv-PHA Synthase proteins. Construction of the J591 ScFv was based on the reported iii complementarity-determining region (CDR) of the PSMA specific J591 monoclonal antibody (mAb). The nucleotide sequence encoding the J591-derived ScFv was codon-optimized for expression in P. pastoris and a 6X his-tag was added to facilitate affinity purification. The J591 ScFv showed binding affinity and specificity to cell extracts containing PSMA and PSMAexpressing prostate cancer cells. The J591ScFv -PHA Synthase fusion protein was expressed in Pichia pastoris. The addition of a linker between the J591 ScFv and PHA Synthase proteins was determined critical to maintain functionality of the ScFv. Our results demonstrate that our J591 ScFv-PHA synthase fusion protein construct is functional and can be produced in P. pastoris for use in diagnostic and targeted therapeutic applications. iv