Targeting of cancer cells using tumor specific peptides has many advantages over similar techniques using antibodies, including reduction in non-specific binding and immunogenicity and smaller size. Using screening of random, one-bead one-compound combinatorial libraries, peptides with specific binding to canine glioma cells (J3TBg) were identified in vitro. Similar peptides have been shown previously to bind to the α3 integrin subunit that plays an important role in tumor cell adhesion, invasion and metastasis. We hypothesized that the peptides would also bind specifically to experimental (J3TBg) gliomas in vivo and to spontaneous canine gliomas.
Using biotin-conjugated peptides and secondary labeling with streptavidin-Alexa-488 fluorochromes, in vivo binding of peptides to control (J3TBg) orthotopic tumors in nude mice and spontaneous canine gliomas was demonstrated on cryostat sections. Delivery of peptides in live animals was investigated using 6-8-week-old nude mice with established J3TBg xenograft tumors. Intravenous administration of peptides labeled with the fluorochrome Alexa-680 was done and tissue distribution was monitored at the near-infrared spectra using the Kodak IS2000MM image station. Mice were serially imaged at 15 minutes, 6 hours, and 24 hours for uptake and washout of peptide. The peptide probe displayed highly specific tumor uptake within 15 min and lasted for 24 hours. Some kidney and bladder signal also was noted at 15 min, but was not detectable at 24 hours.
Preferential binding of peptides to cell surface molecules of canine glioma cells may provide a rational system for the development of targeted therapies for both canine and human gliomas.