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Developing Multispecific Biological Agents that Target Tumor Neovasculature for Cancer Imaging and Therapy

Final Report Summary - BISPROT (Developing Multispecific Biological Agents that Target Tumor Neovasculature for Cancer Imaging and Therapy)

We developed rational and combinatorial engineering methods for transforming these ligands: tendamistat, APPI, N-TIMP2 and HTB1 proteins and the natural dimeric VEGF, ANG2, M-CSF and SCF agonists into a bispecific, high affinity receptor antagonists. To achieve this, we screened random mutagenesis libraries of the ligand genes against their receptor targets and selected mutants with highest affinity, specificity and stability. For this affinity maturation process, we used the yeast surface display technology, in which improvement in protein expression, stability, and affinity to the different receptors was accomplished simulta¬neously. We were able to identify residues in the ligands that are important for their conformational stability and interactions with their targets and to generate several variants with increased expression yield, chemical and thermo-stabilities, and high affinity.
We then used these variants for functional experiments. For that we evaluated the interactions between the purified engineered high-affinity antagonists and their receptors and determined the effects of the former on cancer cell activation, proliferation, and angiogenesis in vitro. Our variants showed high stability, affinity, and specificity to recombinant receptors and to receptor-expressing cells. These variants showed significant in vitro antagonistic activity, which was validated in several functional assays.
Next, the antagonistic mutants were tested for their ability to inhibit tumor growth, angiogenesis, and metastasis in vivo. For that, we used non-invasive imaging and immunofluorescent staining of ex¬cised tumor sections to follow disease progression and angiogenesis in response to treatment with our proteins. At this point, we had several leading antagonistic variants with significant in vivo therapeutic potency. These pro¬teins were shown to inhibit tumor growth and reduce multiple metastases in various primary tumor and experi¬mental metastasis models.
We are now following up with the potent proteins for the evaluation of their pharmacokinetic properties (i.e. tumor uptake, biodistribution and body clearance) by using PET imaging several in vivo models. We will be able to measure key pharmacokinetic parameters in the selected variants. We expect our high affinity variants to demonstrate high tumor uptake and stability and minimal degradation in the blood or tumor upon injection.