Synthesis and evaluation of novel mitochondria-specific near-IR stains based on triphenylphosphonium-heptamethine cyanines

Mitochondria play a crucial role in many biological processes that ensure cell viability. Dysfunction of mitochondria can therefore lead to serious disorders, including cardiovascular disease and cancer. This makes mitochondria desirable targets for selective imaging and targeted therapy. Currently, several mitochondria-specific stains have been developed; however, most of them suffer from low specificity and/or poor brightness. Herein, we developed a series of novel near-IR heptamethine cyanine dyes containing mitochondria-specific triphenylphosphonium (TPP⁺) groups. These dyes were investigated in comparison to the recently reported cyanine Cy-TPP for staining mitochondria in human breast cancer SK-BR-3 and MDA-MB-231 cell lines. Several new dyes presented better visualization and higher fluorescence intensity in mitochondria than Cy-TPP. These dyes are considered promising mitochondria-specific stains for biomedical applications based on cell mitochondria visualization.