Increased expression of human aspartyl (asparaginyl) beta-hydroxylase (HAAH) has been observed in multiple tumor types. HAAH in tumor cells is localized to the cell surface. Its over-expression is sufficient to induce cellular transformation, increase motility and invasiveness, and establish tumor formation. As such, HAAH represents an important novel target for cancer therapy. Ideal drugs retain high affinity and strong specificity for their target, characteristics that are often associated with antibodies. Unfortunately, in most cases effective antibody therapeutics have yet to be developed due to inherent problems in antibody selection and relatively low overall affinities. Recent advances in antibody engineering have lead to the "directed evolution" of extremely high affinity single-chain antibody fragments (scFv). The primary goal of this work is the development of high affinity scFv that can inhibit or attenuate the tumor cell phenotype. In this Phase I proposal we will investigate the use of anti-HAAH mAbs for the inhibition of the tumor phenotype, evolve high affinity anti-HAAH scFv and test their ability to inhibit tumor cell function. A future Phase II application will explore the use of these high affinity anti-HAAH scFv for the treatment of malignancies in preclinical animal models and ultimately in human clinical trials.