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Because of the lack of facile and accurate methods to track stress granule (SG) dynamics in live cells and in vivo, in-depth studies of the biological roles of this attractive membraneless organelle have been limited. Herein, we report the first small-molecule probe, TASG, for the selective, convenient and real-time monitoring of SGs. This novel molecule can simultaneously bind to SG RNAs, the core SG protein G3BP1, and their complexes, triggering a significant enhancement in fluorescence intensity, making TASGbroadly applicable to SG imaging under various stress conditions in fixed and live cells, ex vivoand in vivo. Using TASG, the complicated endogenous SG dynamics were revealed in both live cells and C. elegans. Collectively, our work provides an ideal probe that has thus far been absent in the field of SG investigations. We anticipate that this powerful tool may create exciting opportunities to investigate the underlying roles of SGs in different organisms.

Mitochondrion–lysosome interactions have garnered significant attention in recent research. Numerous studies have shown that mitochondrion–lysosome interactions, including mitochondrion–lysosome contact (MLC) and mitophagy, are involved in various biological processes and pathological conditions. Single fluorescent probes are termed a pivotal chemical tool in unraveling the intricate spatiotemporal interorganelle interplay in live cells. However, current chemical tools are insufficient to deeply understand mitochondrion–lysosome dynamic interactions and related diseases, Moreover, the rational design of mitochondrion–lysosome dual-targeting fluorescent probes is intractable. Herein, we designed and synthesized a pH-sensitive fluorescent probe called INSA, which could simultaneously light up mitochondria (red emission) and lysosomes (green emission) for their internal pH differences. Employing INSA, we successfully recorded long-term dynamic interactions between lysosomes and mitochondria. More importantly, the increasing mitochondrion–lysosome interactions in ferroptotic cells were also revealed by INSA. Further, we observed pH variations in mitochondria and lysosomes during ferroptosis for the first time. In brief, this work not only introduced a pH-sensitive fluorescent probe INSAfor the disclosure of the mitochondrion–lysosome dynamic interplays but also pioneered the visualization of the organellar pH alternation in a specific disease model.

Mutations in NRASpromote tumorigenesis and drug resistance. As this protein is often considered an undruggable target, it is urgent to develop novel strategies to suppress NRASfor anticancer therapy. Recent reports indicated that a G-quadruplex (G4) structure formed in the untranslated region of NRASmRNA can downregulate NRAStranslation, suggesting a potential NRASsuppression strategy. Here, we developed a novel cell-based method for large-scale screening of NRASG4 ligand using the G-quadruplex-triggered fluorogenic hybridization probe and successfully identified the clinically used agent Octenidine as a potent NRASrepressor. This compound suppressed NRAStranslation, blocked the MAPK and PI3K-AKT signaling, and caused concomitant cell cycle arrest, apoptosis, and autophagy. It exhibited better antiproliferation effects over clinical antimelanoma agents and could inhibit the growth of NRAS-mutant melanoma in a xenograft mouse model. Our results suggest that Octenidine may be a prominent anti-NRAS-mutant melanoma agent and represent a new NRAS-mutant melanoma therapy option.

Developing c-MYCtranscription inhibitors that target the G-quadruplex has generated significant interest; however, few compounds have demonstrated specificity for c-MYCG-quadruplex and cancer cells. In this study, we designed and synthesized a series of benzoazole derivatives as potential G-quadruplex ligand-based c-MYCtranscription inhibitors. Surprisingly, benzoselenazole derivatives, which are rarely reported as G-quadruplex ligands, demonstrated greater c-MYCG-quadruplex selectivity and cancer cell specificity compared to their benzothiazole and benzoxazole analogues. The most promising compound, benzoselenazole m-Se3, selectively inhibited c-MYCtranscription by specifically stabilizing the c-MYCG-quadruplex. This led to selective inhibition of hepatoma cell growth and proliferation by affecting the MYC target gene network, as well as effective tumor growth inhibition in hepatoma xenografts. Collectively, our study demonstrates that m-Se3holds significant promise as a potent and selective inhibitor of c-MYCtranscription for cancer treatment. Furthermore, our findings inspire the development of novel selenium-containing heterocyclic compounds as c-MYCG-quadruplex-specific ligands and transcription inhibitors.