Before it was molecularly cloned in 1994, acute-phase response factor or signal transducer and activator of transcription (STAT)3 was the focus of intense research into understanding the mammalian response to injury, particularly the acute-phase response. Although known to be essential for liver production of acute-phase reactant proteins, many of which augment innate immune responses, molecular cloning of acute-phase response factor or STAT3 and the research this enabled helped establish the central function of Janus kinase (JAK) family members in cytokine signaling and identified a multitude of cytokines and peptide hormones, beyond interleukin-6 and its family members, that activate JAKs and STAT3, as well as numerous new programs that their activation drives. Many, like the acute-phase response, are adaptive, whereas several are maladaptive and lead to chronic inflammation and adverse consequences, such as cachexia, fibrosis, organ dysfunction, and cancer. Molecular cloning of STAT3 also enabled the identification of other noncanonical roles for STAT3 in normal physiology, including its contribution to the function of the electron transport chain and oxidative phosphorylation, its basal and stress-related adaptive functions in mitochondria, its function as a scaffold in inflammation-enhanced platelet activation, and its contributions to endothelial permeability and calcium efflux from endoplasmic reticulum. In this review, we will summarize the molecular and cellular biology of JAK/STAT3 signaling and its functions under basal and stress conditions, which are adaptive, and then review maladaptive JAK/STAT3 signaling in animals and humans that lead to disease, as well as recent attempts to modulate them to treat these diseases. In addition, we will discuss how consideration of the noncanonical and stress-related functions of STAT3 cannot be ignored in efforts to target the canonical functions of STAT3, if the goal is to develop drugs that are not only effective but safe. Significance Statement Key biological functions of Janus kinase (JAK)/signal transducer and activator of transcription (STAT)3 signaling can be delineated into two broad categories: those essential for normal cell and organ development and those activated in response to stress that are adaptive. Persistent or dysregulated JAK/STAT3 signaling, however, is maladaptive and contributes to many diseases, including diseases characterized by chronic inflammation and fibrosis, and cancer. A comprehensive understanding of JAK/STAT3 signaling in normal development, and in adaptive and maladaptive responses to stress, is essential for the continued development of safe and effective therapies that target this signaling pathway.

Signal transducer and activator of transcription (STAT) 3 plays a central role in the host response to injury. It is activated rapidly within cells by many cytokines, most notably those in the IL-6 family, leading to pro-proliferative and pro-survival programs that assist the host in regaining homeostasis. With persistent activation, however, chronic inflammation and fibrosis ensue, leading to a number of debilitating diseases. This review summarizes advances in our understanding of the role of STAT3 and its targeting in diseases marked by chronic inflammation and/or fibrosis with a focus on those with the largest unmet medical need.

Small-molecule inhibition of STAT3 in radioresistant head and neck squamous cell carcinoma

The folding of newly synthesized proteins and the maintenance of pre-existing proteins are essential in sustaining a living cell. A network of molecular chaperones tightly guides the folding, intracellular localization, and proteolytic turnover of proteins. Many of the key regulators of cell growth and differentiation have been identified as clients of molecular chaperones, which implies that chaperones are potential mediators of oncogenesis. In this review, we briefly provide an overview of the role of chaperones, including HSP70 and HSP90, in cancer. We further summarize and highlight the emerging the role of chaperonin TRiC (T-complex protein-1 ring complex, also known as CCT) in the development and progression of cancer mediated through its critical interactions with oncogenic clients that modulate growth deregulation, apoptosis, and genome instability in cancer cells. Elucidation of how TRiC modulates the folding and function of oncogenic clients will provide strategies for developing novel cancer therapies.

Purpose: Signal transducer and activator of transcription 3 is a transcription factor that is essential for the survival and immune sequestration of cancer cells. We conducted a phase I study of TTI-101, a first-in-class, selective small-molecule inhibitor of signal transducer and activator of transcription 3, in patients with advanced metastatic cancer. Patients and Methods: Patients were treated with TTI-101 orally twice daily in 28-day cycles at four dose levels (DL): 3.2 (DL1), 6.4 (DL2), 12.8 (DL3), and 25.6 (DL4) mg/kg/day (“3+3” design). Three TTI-101 formulations were used in a stepwise manner (NCT03195699). Results: Sixty-four patients were treated (median age, 63 years; male sex, 52%; median number of prior therapies, 3). No dose-limiting toxicities or fatal treatment-related adverse events (TRAE) were observed. Diarrhea (mostly grade 1/2) was the only TRAE observed in ≥30% of subjects. Five patients experienced grade 3 TRAEs that resolved. TTI-101 showed linear pharmacokinetics from DL1 to DL3, with the pharmacokinetics plateauing at DL3. The recommended phase II dose is 12.8 mg/kg/day (DL3). Of the 41 patients who were evaluable for response, five (12%) had confirmed partial responses (cPR) and 17 (41%) had stable disease. Three (18%) of the 17 patients with hepatocellular carcinoma had a cPR (median time to treatment failure, 10.6 months). Two other cPRs were noted in one patient with ovarian cancer and one patient with gastric cancer. Conclusions: TTI-101 was well tolerated. cPRs were observed across tumor types. The antitumor activity of TTI-101 monotherapy in patients with advanced, metastatic solid tumors is promising. A phase II study of TTI-101 in hepatocellular carcinoma is currently underway.