Supramolecular Dipeptide-Based Near-Infrared Fluorescent Nanotubes for Cellular Mitochondria Targeted Imaging and Early Apoptosis.

Herein, we have designed and synthesized unsymmetrical visible Cy-3 and near-infrared (NIR) Cy-5 chromophores anchoring mitochondria targeting functional group conjugated with a Phe-Phe dipeptide by a microwave-assisted Fmoc solid phase peptide synthesis method on Wang resin. These dipeptide-based Cy-3-TPP/FF as well as Cy-5-TPP/FF molecules self-assemble to form fluorescent nanotubes in solution, and it has been confirmed by TEM, SEM, and AFM. The Cy-3-TPP/FF and Cy-5-TPP/FF molecules in solution exhibit narrow excitation as well as emission bands in the visible and NIR region, respectively. These lipophilic cationic fluorescent peptide molecules spontaneously and selectively accumulate inside the mitochondria of human carcinoma cells that have been experimentally validated by live cell confocal laser scanning microscopy and display a high Pearson's correlation coefficient in a colocalization assay. Live cell multicolor confocal imaging using the NIR Cy-5-TPP/FF in combination with other organelle specific dye is also accomplished. Moreover, these lipophilic dipeptide-based cationic molecules reach the critical aggregation concentration inside the mitochondria because of the extremely negative inner mitochondrial membrane potential [(ΔΨm)cancer ≈ -220 mV] and form supramolecular nanotubes which are accountable for malignant mitochondria targeted early apoptosis. The early apoptosis is arrested using Cy-5-TPP/FF and confirmed by annexin V-FITC/PI apoptosis detection assay.