Background/Objectives: Signal Transducer and Activator of Transcription 3 (STAT3) is a transcription factor that is strongly implicated in various cancers. In its canonical signaling pathway, Janus kinases (JAKs) phosphorylate STAT3 at the Y705 residue in response to cytokines or growth factors, with pY705 serving as a key marker of STAT3 oncogenic activity. Elevated pY705 levels correlate with poor prognosis, and numerous small-molecule inhibitors have been developed to block this phosphorylation site. More recently, phosphorylation at the S727 residue (pS727) has emerged as a critical contributor to STAT3-mediated oncogenesis, particularly due to its role in mitochondrial translocation. Evidence suggests that pS727 may even surpass pY705 in driving oncogenic activity. These findings prompt an important question: Which residue should be prioritized for effective STAT3 inhibition in cancer therapy? Methods: This review compiles and critically analyzes the current literature on STAT3 inhibitors targeting pY705 and/or pS727, evaluating their therapeutic efficacy in vitro, in vivo, and in clinical trials. We assess the unique effects of targeting each residue on downstream signaling, toxicity, and clinical outcomes. Results: Our analysis indicates that inhibitors targeting both pY705 and pS727 achieve the greatest therapeutic effectiveness. However, pS727 targeting is associated with higher toxicity risks. Conclusions: Comprehensive evaluation of STAT3 inhibitors underscores the importance of targeting pY705 for maximum therapeutic benefit. The analysis also shows that co-targeting pS727 may increase overall efficacy. However, pS727 inhibition should be approached with lower affinity to minimize toxicity and enhance the clinical feasibility of dual-targeting strategies.

Live-cell imaging is a powerful technique to study the dynamics and mechanics of various biological molecules like proteins, organelles, DNA, and RNA. With the rapid evolution of optical microscopy, our understanding of how these molecules are implicated in the cells’ most critical physiological roles deepens. In this review, we focus on how spatiotemporal nanoscale live-cell imaging at the single molecule level allows for profound contributions towards new discoveries in life science. This review will start by summarizing how single-molecule tracking has been used to analyze membrane dynamics, receptor–ligand interactions, protein–protein interactions, inner- and extra-cellular transport, gene expression/transcription, and whole organelle tracking. We then move on to how current authors are trying to improve single-molecule tracking and overcome current limitations by offering new ways of labeling proteins of interest, multi-channel/color detection, improvements in time-lapse imaging, and new methods and programs to analyze the colocalization and movement of targets. We later discuss how single-molecule tracking can be a beneficial tool used for medical diagnosis. Finally, we wrap up with the limitations and future perspectives of single-molecule tracking and total internal reflection microscopy.

Background/Objectives: Signal Transducer and Activator of Transcription 3 (STAT3) is a transcription factor strongly implicated in various cancers. In its canonical signaling pathway, Janus kinases (JAKs) phosphorylate STAT3 at the Y705 residue in response to cytokines or growth factors, with pY705 serving as a key marker of STAT3 oncogenic ac-tivity. Elevated pY705 levels correlate with poor prognosis, and numerous small-molecule inhibitors have been developed to block this phosphorylation site. More recently, phos-phorylation at the S727 residue (pS727) has emerged as a critical contributor to STAT3-mediated oncogenesis, particularly due to its role in mitochondrial translocation. Evidence suggests that pS727 may even surpass pY705 in driving oncogenic activity. These findings prompt an important question: Which residue should be prioritized for ef-fective STAT3 inhibition in cancer therapy? Methods: This review compiles and critically analyzes current literature on STAT3 inhibitors targeting pY705 and/or pS727, evaluating their therapeutic efficacy in vitro, in vivo, and in clinical trials. We assess the unique ef-fects of targeting each residue on downstream signaling, toxicity, and clinical outcomes. Results: Our analysis indicates that inhibitors targeting both pY705 and pS727 achieve the greatest therapeutic effectiveness. However, pS727 targeting is associated with higher tox-icity risks. Conclusions: Comprehensive evaluation of STAT3 inhibitors underscores the importance of targeting both pY705 and pS727 for maximum therapeutic benefit. None-theless, pS727 inhibition should be approached with lower affinity to minimize toxic side effects and enhance the clinical feasibility of dual-targeting strategies.

3-Phosphoinositides are essential cellular lipids regulating health and disease. Among them, phosphatidylinositol-3,5-bisphosphate [PI(3,5)P ₂ ] remains the least understood. Using a newly developed ratiometric PI(3,5)P ₂ sensor that enables spatiotemporally resolved PI(3,5)P ₂ quantification, we demonstrate that growth factor stimulation generates a distinct PI(3,5)P ₂ pool on lysosomes and late endosomes. Formed sequentially by class II PI3KC2β and PIKfyve, this PI(3,5)P ₂ pool terminates growth factor–stimulated class I phosphatidylinositol 3-kinase (PI3K) activity through a specific interaction with its regulatory p85 subunit. Disrupting this p85-PI(3,5)P ₂ interaction via a small-molecule inhibitor or cancer-causing mutations blocks feedback inhibition, driving sustained class I PI3K activation and promoting neurite growth. Our findings uncover a spatiotemporally specific regulatory function of PI(3,5)P ₂ that links class I and II PI3Ks to tune growth factor signaling. This mechanism offers therapeutic strategies for treating p85-mutant cancers and advancing tissue regeneration.