Synergistic effects of light-emitting probes and peptides for targeting and monitoring integrin expression

Samuel Achilefu, Sharon Bloch, Mary A. Markiewicz, Tuoxiu Zhong, Yunpeng Ye, Richard B. Dorshow, Britton Chance, Kexian Liang

Research output: Contribution to journalArticlepeer-review

115 Scopus citations


Integrins mediate many biological processes, including tumor-induced angiogenesis and metastasis. The arginine-glycine-aspartic acid (RGD) peptide sequence is a common recognition motif by integrins in many proteins and small peptides. While evaluating a small library of RGD peptides for imaging αvβ3 integrin (ABI)-positive tumor cell line (A549) by optical methods, we discovered that conjugating a presumably inactive linear hexapeptide GRDSPK with a near-infrared carbocyanine molecular probe (Cypate) yielded a previously undescribed bioactive ligand (Cyp-GRD) that targets ABI-positive tumors. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay with A549 cells showed that Cyp-GRD was not cytotoxic up to 100 μM in cell culture. The compound was internalized by cells, and this internalization was blocked by coincubation with a cyclic RGD peptide (cyclo[RGDfV], f is D-phenylalanine) that binds ABI with high affinity. In vivo, Cyp-GRD selectively accumulated in tumors relative to surrounding normal tissues. Blocking studies with cyclo[RGDfV] inhibited the in vivo uptake of Cyp-GRD, suggesting that both compounds target the same active site of the protein. A strong correlation between the Cyp-GRD peptide and mitochondrial NADH concentration suggests that the new molecule could also report on the metabolic status of cells ex vivo. Interestingly, neither a Cypate-labeled linear RGD peptide nor an 111In-labeled DOTA-GRD conjugate was selectively retained in the tumor. These results clearly demonstrate the synergistic effects of Cypate and GRD peptide for molecular recognition of integrin expression and suggest the potential of using carbocyanines as optical scaffolds for designing biologically active molecules.

Original languageEnglish (US)
Pages (from-to)7976-7981
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number22
StatePublished - May 31 2005
Externally publishedYes


  • Mouse
  • Near-infrared
  • Optical imaging
  • RGD peptides
  • Tumor

ASJC Scopus subject areas

  • General


Dive into the research topics of 'Synergistic effects of light-emitting probes and peptides for targeting and monitoring integrin expression'. Together they form a unique fingerprint.

Cite this