FN3: a new protein scaffold reaches the clinic

A fibronectin scaffold approach to bispecific inhibitors of epidermal growth factor receptor and insulin-like growth factor-I receptor

“…12 Phase I studies on CT-322 showed that it was well tolerated and produced pharmacological effects expected from the inhibition of the VEGFR-2 pathway. 13 The first example of a bispecific Adnectin, which targets cell signaling through EGFR and IGF-IR, is described here. EGFR is validated as a target for cancer therapy and numerous anti-EGFR drugs, including cetuximab, panitumumab, erlotinib and lapatinib, are approved by the United States Food and Drug Administration.…”

“…2 The design of a dual specific antibody targeting human epidermal growth factor receptor 2 (HER2 or Erb-B2) and vascular endothelial growth factor (VEGF) by the mutation Engineered domains of human fibronectin (Adnectins TM ) were used to generate a bispecific Adnectin targeting epidermal growth factor receptor (EGFR) and insulin-like growth factor-I receptor (IGF-IR), two transmembrane receptors that mediate proliferative and survival cell signaling in cancer. Single-domain Adnectins that specifically bind EGFR or IGF-IR were generated using mRNA display with a library containing as many as 10 13 Adnectin variants. mRNA display was also used to optimize lead Adnectin affinities, resulting in clones that inhibited EGFR phosphorylation at 7 to 38 nM compared to 2.6 μM for the parental clone.…”

Ubiquibodies, Synthetic E3 Ubiquitin Ligases Endowed with Unnatural Substrate Specificity for Targeted Protein Silencing

“…This has led to the concept of intracellular antibody fragments (intrabodies) and antibody mimics such as the human fibronectin type III domain (FN3) 2 and DARPins (designed ankyrin repeat proteins), all of which can be engineered to bind their antigens inside living cells (2)(3)(4). These designer binding proteins (DBPs) exhibit the high specificity and affinity of conventional monoclonal antibodies, but are much smaller, can fold efficiently in a reducing environment, and can be manipulated and delivered as genes, which makes them particularly useful as drug discovery tools and next-generation therapeutics (5)(6)(7).…”

A Novel Engineered Anti-CD20 Tracer Enables Early Time PET Imaging in a Humanized Transgenic Mouse Model of B-cell Non-Hodgkins Lymphoma

“…The FN3-based protein scaffold system has been explored by various research groups and demonstrates potential as a useful scaffold for imaging agents (20,40). FN3 domains can be readily engineered for specific, high-affinity binding, retain good stability, and are derived from a human parental sequence, which may limit immunogenicity (40).…”