Supramolecular β-Sheet Forming Peptide Conjugated with Near-Infrared Chromophore for Selective Targeting, Imaging,...

Herein, conjugation of the amyloid-β (Aβ) peptide fragment, Lys-Leu-Val-Phe-Phe (KLVFF, fragment of Aβ_16-20), with an unsymmetrical near-infrared (NIR) cyanine-5 (Cy-5) chromophore is achieved using microwave-assisted solid phase synthesis on 2-chlorotrityl chloride resin. Selective mitochondria tracking and staining in human carcinoma cells are accomplished by the KLVFF/Cy-5 conjugate containing triphenylphosphonium functionality, and this is compared to a control molecule KLVFF/Cy-5c. Mitochondrial target specificity of KLVFF/Cy-5 is established by the colocalization assay using mitochondria selective probe MitoTracker Red, which is monitored by confocal laser scanning microscope and shows a high Pearson's correlation coefficient. The KLVFF/Cy-5 conjugate has high photostability, NIR absorption/emission, high molar extinction coefficient, narrow absorption/emission band, high fluorescence lifetime, and high fluorescence quantum yield. Moreover, mitochondria targeting KLVFF/Cy-5 conjugate reaches the critical aggregation concentration inside the mitochondria of cancer cells due to the strong negative inner mitochondrial membrane potential [(ΔΨ_m)_cancer -220 mV] and self-assembles to form amyloid fibrils at the target site, which is responsible for the mitochondrial dysfunction and cytotoxicity. Annexin V-FITC/PI apoptosis detection assay is used to determine the signal pathway of mitochondria targeted cellular dysfunction.