Enzyme-targeted fluorescent imaging probes on a multiple antigenic peptide core.
Peptide dendrimers have a variety of applications in biology such as the vehicles for drug and gene delivery, molecular inhibitors, protein mimics, and synthetic vaccines. The multiple antigenic peptide (MAP) system is a well-known example of a discrete, dendrimeric scaffold. We explored a novel application of the MAP-based scaffold by designing molecular probes that fluoresce only after enzymatic treatment. The probes, which were synthesized on solid support, incorporate a cathepsin S dipeptide substrate (Leu-Arg), and a poly(ethylene glycol) (PEG) chain in their dendritic arms. The fluorescence emission of the near-infrared fluorochromes attached to the N-termini of the dendritic arms was quenched. Mechanistic studies revealed formation of H-type dye aggregates within the tetravalent MAP system. By varying the length of the PEG chain, three probes were synthesized, CyPEG-1, CyPEG-2, and CyPEG-3 with 4, 8, and 12 ethylene oxide units, respectively. CyPEG-2 showed optimum aqueous solubility and quenching efficiency for imaging applications. Upon proteolytic activation with cathepsin S (EC 3.4.22.27), CyPEG-2 showed greater than 70-fold increase and more than 95% recovery in fluorescence emission.
Galande
Amit K
AK
Center for Molecular Imaging Research, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Hilderbrand
Scott A
SA
Weissleder
Ralph
R
Tung
Ching-Hsuan
CH
D002403:Cathepsins / Q000737:chemistry; D050091:Dendrimers / Q000138:chemical synthesis* / Q000737:chemistry; D004151:Dipeptides / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D006868:Hydrolysis; D011092:Polyethylene Glycols / Q000737:chemistry*; D012995:Solubility; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship
D050091:Dendrimers; D004151:Dipeptides; D005456:Fluorescent Dyes; C078789:leucylarginine; D011092:Polyethylene Glycols; D002403:Cathepsins; C028217:cathepsin S