Rational design of mitochondria-targeted fluorescent biosensors for in vivo elucidation of the interaction between breast cancer metastasis and mitochondrial autophagy

Breast cancer lung metastases (BCLM) are a major cause of high mortality in patients. The shortage of therapeutic targets and rapid drug screening tools for BCLM is a major challenge at present. Mitochondrial autophagy, which involves the degradation of proteins associated with cancer cell aggressiveness, represents a possible therapeutic approach for the treatment of BCLM. Herein, four fluorescent biosensors with different alkyl chains were designed and synthesized to monitor mitochondrial autophagy. Among them, PMV-12 demonstrated the highest sensitivity to viscosity variance, the least impact on polarity, and the longest imaging time. The introduction of the C12-chain made PMV-12 anchored in the mitochondrial membrane without being disturbed by changes of the mitochondrial membrane potential (MMP), thereby achieving the long-term monitor in situ for mitochondrial autophagy. Mitochondria stained with PMV-12 induced swelling and viscosity increase after treating with apigenin, which indicated that apigenin is a potential mitochondrial autophagy inducer. Apigenin was subsequently verified to inhibit cancer cell invasion by 92%. Furthermore, PMV-12 could monitor the process of BCLM in vivo and evaluate the therapeutic effects of apigenin. This work provides a fluorescent tool for elucidating the role of mitochondrial autophagy in the BCLM process and for anti-metastatic drug development.