Fluorinated triphenylphosphonium analogs improve cell selectivity and in vivo detection of mito-metformin

Triphenylphosphonium (TPP(+)) conjugated compounds selectively target cancer cells by exploiting their hyperpolarized mitochondrial membrane potential. To date, studies have focused on modifying either the linker or the cargo of TPP(+)-conjugated compounds. Here, we investigated the biological effects of direct modification to TPP(+) to improve the efficacy and detection of mito-metformin (MMe), a TPP(+)-conjugated probe we have shown to have promising preclinical efficacy against solid cancer cells. We designed, synthesized, and tested trifluoromethyl and methoxy MMe analogs (pCF(3)-MMe, mCF(3)-MMe, and pMeO-MMe) against multiple distinct human cancer cells. pCF(3)-MMe showed enhanced selectivity toward cancer cells compared to MMe, while retaining the same signaling mechanism. Importantly, pCF(3)-MMe allowed quantitative monitoring of cellular accumulation via (19)F-NMR in vitro and in vivo. Furthermore, adding trifluoromethyl groups to TPP(+) reduced toxicity in vivo while retaining anti-tumor efficacy, opening an avenue to de-risk these next-generation TPP(+)-conjugated compounds.