Advance in intracellular telomerase imaging for cancer diagnosis and therapy

Telomerase is a distinctive reverse transcriptase that can elongate telomere end to preserve the telomere length and maintain chromosome integrity. Telomerase activity is silenced in most normal cells but highly reactivated in almost all types of tumor cells, making it an important hallmark of cancers and a potential target for cancer therapeutics. However, the majority of reported methods are only suitable for telomerase detection in cell extracts, which severely hinders their wider applications in fundamental research and clinical diagnosis. Recently, a series of imaging methods are developed for intracellular telomerase imaging in living cells and even living bodies, providing a non-invasive and real-time approach for better understanding the telomerase-associated carcinogenesis and accurately evaluating the efficiency of telomerase inhibitor drugs. In this review, we introduce the biological functions of telomerase and summarize the recent advances in development of various methods for in vivo telomerase imaging (e.g., fluorescence imaging, dark-field imaging, Raman imaging, and magnetic resonance imaging), and discuss their principles, features, performances, and applications in cancer cell discrimination, telomerase inhibitor screening, and cancer therapy. Moreover, we highlight the challenges and future directions in the field.