Rsedwards1988

Photoacoustic imaging is a nonionizing biomedical imaging modality with higher resolution and imaging depth compared to fluorescence imaging, which has greater sensitivity. The combination of the two imaging modalities could improve the detection of cancer. Integrin αvβ6 is a cell-surface marker overexpressed in many different cancers. Here, we report the development and evaluation of a dye-labeled cystine knot peptide, which selectively recognizes integrin αvβ6 with high affinity, for photoacoustic and fluorescence imaging. The new dual-modality probe may find clinical application in cancer diagnosis and intraoperative imaging of integrin αvβ6-positive tumors. Materials and Methods: An engineered cystine knot peptide, R01, that recognizes integrin αvβ6 was labeled with Atto 740 (A740-R01) and evaluated for its specific cell uptake, and its sensitivity threshold. A740-R01 was injected via the tail vein into nude mice xenografted with A431 (integrin αvβ6-positive) or 293T (integrin αvβ6-negative) tumors. Photoacoustic and fluorescence scans of tumors were acquired before and 0.5, 1, 2 and 4 hours (h) after injection of A740-R01. Dynamic photoacoustic scans of various normal organs were also acquired. Ex vivo fluorescence imaging of tissues was performed 1h post injection (p.i.). Results: The A740-R01 demonstrated integrin αvβ6-dependent binding to A431 cells in culture. Sensitivity studies indicated that the probe may potentially detect lesions as small as 1 mm3 or 6 mm3 by fluorescence or photoacoustic imaging, respectively. The photoacoustic and fluorescence signals of A431 xenografts at 1h p.i. were 1.87 AU ± 0.25 and 8.27 AU ± 0.87, respectively. Target specificity was confirmed by low tumor uptake in 293T tumors at 1h p.i. (1.07 AU ± 0.15 and 1.10 AU ± 0.14 for photoacoustic and fluorescence signals respectively). A740-R01 exhibited hepatobiliary clearance marked by high uptake in the liver, spleen and intestine, but low uptake in the kidney. Conclusion: A740-R01 specifically targeted integrin αvβ6 with low nanomolar affinity. A740-R01 was able to detect integrin αvβ6 both in vitro and in vivo by photoacoustic and fluorescence imaging. A740-R01 is able to detect αvβ6-positive tumors in living subjects and may have clinical application in cancer diagnosis and real-time image guided surgery.