Engineered knottin peptide enables noninvasive optical imaging of intracranial medulloblastoma

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 36; pp. 14598 - 14603
• Main Authors: Moore, Sarah J., Gephart, Melanie G. Hayden, Bergen, Jamie M., Su, YouRong S., Rayburn, Helen, Scott, Matthew P., Cochran, Jennifer R.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 03.09.2013; National Acad Sciences
• Subjects: Animals; antibodies; Biological Sciences; brain; Brain cancer; Brain neoplasms; Brain tumors; Cancer; caudal vein; Central nervous system; Cerebellar Neoplasms - diagnosis; Cerebellar Neoplasms - genetics; Cerebellar Neoplasms - metabolism; Chemotherapy; cystine; Cystine-Knot Miniproteins - chemistry; Cystine-Knot Miniproteins - genetics; Cystine-Knot Miniproteins - metabolism; Diagnostic Imaging - methods; drug therapy; Dyes; Female; fluorescence; fluorescent dyes; Fluorescent Dyes - chemistry; Fluorescent Dyes - metabolism; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; image analysis; Imaging; Injection; Integrin alpha5beta1 - metabolism; Integrins; Male; Medulloblastoma; Medulloblastoma - diagnosis; Medulloblastoma - genetics; Medulloblastoma - metabolism; Mice; Mice, Knockout; Mice, Nude; Mice, Transgenic; Microscopy, Fluorescence; Molecular imaging; Molecular Imaging - methods; Molecules; neoplasms; Nervous system; Neuroimaging; Patched Receptors; Peptides; Protein Binding; Protein Engineering; receptors; Receptors, Cell Surface - genetics; Receptors, Cell Surface - metabolism; resection; Rodents; Sensitivity and Specificity; Tissues; Tumors; protein engineering; tumor targeting; miniprotein; Hedgehog pathway
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1311333110

Central nervous system tumors carry grave clinical prognoses due to limited effectiveness of surgical resection, radiation, and chemotherapy. Thus, improved strategies for brain tumor visualization and targeted treatment are critically needed. We demonstrate that mouse cerebellar medulloblastoma (MB) can be targeted and illuminated with a fluorescent, engineered cystine knot (knottin) peptide that binds with high affinity to αvß₃,αvß₅, and α₅ß₁, integrin receptors. This integrin-binding knottin peptide, denoted EETI 2.5F, was evaluated as a molecular imaging probe in both orthotopic and genetic models of MB. Following tail vein injection, fluorescence arising from dye-conjugated EETI 2.5F was localized to the tumor compared with the normal surrounding brain tissue, as measured by optical imaging. The imaging signal intensity correlated with tumor volume. Due to its unique ability to bind to α₅ß₁ integrin, EETI 2.5F showed superior in vivo and ex vivo brain tumor imaging contrast compared with other engineered integrinbinding knottin peptides and with c(RGDfK), a well-studied integrin-binding peptidomimetic. Next, EETI 2.5F was fused to an antibody fragment crystallizable (Fc) domain (EETI 2.5F-Fc) to determine if a larger integrin-binding protein could also target intracranial brain tumors. EETI 2.5F-Fc, conjugated to a fluorescent dye, illuminated MB following i.v. injection and was able to distribute throughout the tumor parenchyma. In contrast, brain tumor imaging signals were not detected in mice injected with EETI 2.5F proteins containing a scrambled integrin-binding sequence, demonstrating the importance of target specificity. These results highlight the potential of using EETI 2.5F and EETI 2.5-Fc as targeted molecular probes for brain tumor imaging.