Decoding Potassium Homeostasis in Cancer Metastasis and Drug Resistance: Insights from a Highly Selective DNAzyme-Based Intracellular K⁺ Sensor

Potassium ions (K⁺) within the tumor microenvironment, along with dysregulation of K⁺ channels, play critical roles in supporting cancer cell survival and preventing their elimination. Directly monitoring changes in K⁺ homeostasis within cancer cells is invaluable for understanding these processes. However, achieving high selectivity over other biological metal ions, a detection dynamic range that aligns with intracellular K⁺ levels, and broad accessibility to research laboratories remain technically challenging for current K⁺ imaging probes. In this study, we report the <i>in vitro</i> selection of the first K⁺-specific RNA-cleaving DNAzyme and the development of a K⁺-specific DNAzyme fluorescent sensor with exceptional selectivity, achieving over 1000-fold selectivity against Na⁺ and more than 100-fold selectivity over other major biologically relevant metal ions. This sensor has an apparent dissociation constant (105 mM) that is close to the intracellular level of K⁺, and it has a broad detection range from 21 to 200 mM K⁺. Using this tool, we reveal a progressive decline in intracellular K⁺ levels in breast cancer cells with more advanced progression states. Moreover, we demonstrate that elevated extracellular K⁺ levels interfere with the efficacy of anticancer compounds like ML133 and Amiodarone, suggesting an underappreciated role of microenvironmental K⁺ in chemoresistance. Notably, blocking the Kir2.1 channel activity restored treatment sensitivity, presenting a potential strategy to overcome chemoresistance in aggressive cancers. These findings underscore the role of K⁺ homeostasis in tumor progression and support further exploration of ion-channel-targeted cancer therapies.