As a key regulator for hormone activity, human aldo‐keto reductase family 1 member C3 (AKR1C3) plays crucial roles in the occurrence of various hormone‐dependent or independent malignancies. It is a ...promising target for treating castration‐resistant prostate cancer (CRPC). However, the development of AKR1C3 specific inhibitors remains challenging due to the high sequence similarity to its isoform AKR1C2. Here, we performed a combined in silico study to illuminate the inhibitory preference of 3‐(3,4‐dihydroisoquinolin‐2(1H)‐ylsulfonyl)benzoic acids for AKR1C3 over AKR1C2, of which compound 38 can achieve up to 5000‐fold anti‐AKR1C3 selectivity. Our umbrella sampling (US) simulations together with end‐point binding free energy calculation MM/GBSA uncover that the high inhibition selectivity originates from the different binding modes, namely “Inward” and “Outward,” of this compound series in AKR1C3 and AKR1C2, respectively. In AKR1C3/38, the tetrahydroquinoline moiety of 38 is accommodated inside the SP1 pocket and interacts favorably with surrounding residues, while, in AKR1C2/38, the SP1 pocket is too small to hold the bulky tetrahydroquinoline group that instead moves out of the pocket with 38 transitioning from an “Inward” to an “Outward” state. Further 3D‐QSAR and energy decomposition analyses suggest that SP1 in AKR1C3 prefers to bind with a rigid bicyclic moiety and the modification of the R3 group has important implication for the compound's activity. This work is the first attempt to elucidate the selectivity mechanism of inhibitors toward AKR1C3 at the atomic level, which is anticipated to propel the development of next‐generation AKR1C3 inhibitors with enhanced efficacy and reduced “off‐target” effect for CRPC therapy.
STAT3 is constitutively activated in colon cancer but its contributions in cancer-initiating cells have not been explored. In this study, we characterized STAT3 in aldehyde dehydrogenase ...(ALDH)-positive (ALDH(+)) and CD133-positive (CD133(+)) subpopulations of human colon tumor cells that exhibited more potent tumor-initiating ability than ALDH(-)/CD133(-) cells in tumor xenograft assays in mice. We found that ALDH(+)/CD133(+) cells expressed higher levels of the active phosphorylated form of STAT3 than either ALDH(-)/CD133(-) or unfractionated colon cancer cells. STAT3 inhibition by RNA interference-mediated knockdown or small-molecule inhibitors LLL12 or Stattic blocked downstream target gene expression, cell viability, and tumorsphere-forming capacity in cancer-initiating cells. Similarly, treatment of mouse tumor xenografts with STAT3 short hairpin RNA (shRNA), interleukin 6 shRNA, or LLL12 inhibited tumor growth. Our results establish that STAT3 is constitutively activated in colon cancer-initiating cells and that these cells are sensitive to STAT3 inhibition. These findings establish a powerful rationale to develop STAT3 inhibitory strategies for treating advanced colorectal cancers.
Abstract The rapid development of new anticancer drugs that are safe and effective is a common goal shared by basic scientists, clinicians and patients. The current review discusses one such agent, ...namely niclosamide, which has been used in the clinic for the treatment of intestinal parasite infections. Recent studies repeatedly identified niclosamide as a potential anticancer agent by various high-throughput screening campaigns. Niclosamide not only inhibits the Wnt/β-catenin, mTORC1, STAT3, NF-κB and Notch signaling pathways, but also targets mitochondria in cancer cells to induce cell cycle arrest, growth inhibition and apoptosis. A number of studies have established the anticancer activities of niclosamide in both in vitro and in vivo models. Moreover, the inhibitory effects of niclosamide on cancer stem cells provide further evidence for its consideration as a promising drug for cancer therapy. This article reviews various aspects of niclosamide as they relate to its efficacy against cancer and associated molecular mechanisms.
Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are diseases with high mortality. Macrophages and neutrophils are responsible for inflammatory responses in ALI and ARDS, which ...are characterized by excessive production of proinflammatory mediators in bronchoalveolar lavage fluid (BALF) and plasma. Aberrant activation of the JAK/STAT pathway is critical for persistent inflammation in many conditions such as infection and autoimmunity. Given the importance of the STAT3 transcription factor in activating macrophages and neutrophils and augmenting inflammation, we investigated the therapeutic potential of inhibiting STAT3 activity using the small-molecule STAT3 inhibitor, LLL12. Our results demonstrate that LPS induces STAT3 activation in macrophages in vitro and in CD45
CD11b
cells from BALF in the LPS-induced ALI model in vivo. LLL12 treatment inhibits LPS-induced lung inflammation in the ALI model, which is accompanied by suppression of LPS-induced STAT3 activation and an inhibition of macrophage and inflammatory cell infiltration in lung and BALF. LLL12 treatment also suppresses expression of proinflammatory genes including IL-1β, IL-6, TNF-α, iNOS, CCL2, and MHC class II in macrophages and inflammatory cells from BALF and serum as determined by ELISA. Furthermore, hyperactivation of STAT3 in LysMCre-SOCS3
mice accelerates the severity of inflammation in the ALI model. Both pre- and post-LPS treatment with LLL12 decrease LPS-induced inflammatory responses in mice with ALI. Importantly, LLL12 treatment attenuates STAT3 phosphorylation in human peripheral blood mononuclear cells induced by plasma from patients with ARDS, which suggests the feasibility of targeting the STAT3 pathway therapeutically for patients with ALI and ARDS.
The mammalian bromodomain and extra-terminal domain (BET) family of proteins consists of four conserved members (Brd2, Brd3, Brd4, and Brdt) that regulate numerous cancer-related and ...immunity-associated genes. They are epigenetic readers of histone acetylation with broad specificity. BET proteins are linked to cancer progression due to their interaction with numerous cellular proteins including chromatin-modifying factors, transcription factors, and histone modification enzymes. The spectacular growth in the clinical development of small-molecule BET inhibitors underscores the interest and importance of this protein family as an anticancer target. Current approaches targeting BET proteins for cancer therapy rely on acetylation mimics to block the bromodomains from binding chromatin. However, bromodomain-targeted agents are suffering from dose-limiting toxicities because of their effects on other bromodomain-containing proteins. In this review, we provided an updated summary about the evolution of small-molecule BET inhibitors. The design of bivalent BET inhibitors, kinase and BET dual inhibitors, BET protein proteolysis-targeting chimeras (PROTACs), and Brd4-selective inhibitors are discussed. The novel strategy of targeting the unique C-terminal extra-terminal (ET) domain of BET proteins and its therapeutic significance will also be highlighted. Apart from single agent treatment alone, BET inhibitors have also been combined with other chemotherapeutic modalities for cancer treatment demonstrating favorable clinical outcomes. The investigation of specific biomarkers for predicting the efficacy and resistance of BET inhibitors is needed to fully realize their therapeutic potential in the clinical setting.
Interleukin-6 (IL-6) is a multifunctional cytokine, which may block apoptosis during inflammation to protect cells under very toxic conditions. However, IL-6 also activates STAT3 in many types of ...human cancer. Recent studies demonstrate that high levels of IL-6 are associated with hepatocellular carcinoma, the most common type of liver cancer. Here we reported that IL-6 promoted survival of human liver cancer cells through activating STAT3 in response to doxorubicin treatment. Endogenous IL-6 levels in SNU-449 cells were higher than in Hep3B cells. Meanwhile, SNU-449 cells were more resistant to doxorubicin than Hep3B cells. Addition of IL-6 induced STAT3 activation in Hep3B cells and led to protection against doxorubicin. In contrast, neutralizing IL-6 with anti-IL-6 antibody decreased survival of SNU-449 cells in response to doxorubicin. To elucidate the mechanism of the anti-apoptotic function of IL-6, we investigated if STAT3 mediated this drug resistance. Targeting STAT3 with STAT3 siRNA reduced the protection of IL-6 against doxorubicin-induced apoptosis, indicating that STAT3 signaling contributed to the anti-apoptotic effect of IL-6. Moreover, we further explored if a STAT3 small molecule inhibitor could abolish this anti-apoptotic effect. LLL12, a STAT3 small molecule inhibitor, blocked IL-6-induced STAT3 phosphorylation, resulting in attenuation of the anti-apoptotic activity of IL-6. Finally, neutralization of endogenous IL-6 with anti-IL-6 antibody or blockade of STAT3 with LLL12 lowered the recovery in SNU-449 cells after doxorubicin treatment. Therefore, our results demonstrated that targeting STAT3 signaling could interrupt the anti-apoptotic function of IL-6 in human liver cancer cells.
Interleukin (IL)-6 overexpression and constitutive STAT3 activation occur in many cancers, including prostate cancer. However, their contribution to prostate stem and progenitor cells has not been ...explored. In this study, we show that stem-like cells from patients with prostate cancer secrete higher levels of IL-6 than their counterparts in non-neoplastic prostate. Tumor grade did not influence the levels of expression or secretion. Stem-like and progenitor cells expressed the IL-6 receptor gp80 with concomitant expression of pSTAT3. Blockade of activated STAT3, by either anti-IL-6 antibody siltuximab (CNTO 328) or LLL12, a specific pSTAT3 inhibitor, suppressed the clonogenicity of the stem-like cells in patients with high-grade disease. In a murine xenograft model used to determine the in vivo effects of pSTAT3 suppression, LLL12 treatment effectively abolished outgrowth of a patient-derived castrate-resistant tumor. Our results indicate that the most primitive cells in prostate cancer require pSTAT3 for survival, rationalizing STAT3 as a therapeutic target to treat advanced prostate cancer.
Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 is a novel and highly pathogenic coronavirus and is the causative agent of the coronavirus disease 2019 (COVID-19). The high morbidity and ...mortality associated with COVID-19 and the lack of an approved drug or vaccine for SARS-CoV-2 underscores the urgent need for developing effective antiviral therapies. Therapeutics that target essential viral proteins are effective at controlling virus replication and spread. Coronavirus Spike glycoproteins mediate viral entry and fusion with the host cell, and thus are essential for viral replication. To enter host cells, the Spike proteins of SARS-CoV-2 and related coronavirus, SARS-CoV, bind the host angiotensin-converting enzyme 2 (ACE2) receptor through their receptor binding domains (RBDs). Here, we rationally designed a panel of ACE2-derived peptides based on the RBD-ACE2 binding interfaces of SARS-CoV-2 and SARS-CoV. Using SARS-CoV-2 and SARS-CoV Spike-pseudotyped viruses, we found that a subset of peptides inhibits Spike-mediated infection with IC50 values in the low millimolar range. We identified two peptides that bound Spike RBD in affinity precipitation assays and inhibited infection with genuine SARS-CoV-2. Moreover, these peptides inhibited the replication of a common cold causing coronavirus, which also uses ACE2 as its entry receptor. Results from the infection experiments and modeling of the peptides with Spike RBD identified a 6-amino-acid (Glu37-Gln42) ACE2 motif that is important for SARS-CoV-2 inhibition. Our work demonstrates the feasibility of inhibiting SARS-CoV-2 with peptide-based inhibitors. These findings will allow for the successful development of engineered peptides and peptidomimetic-based compounds for the treatment of COVID-19.
The constitutive activation of signal transducer and activator of transcription 3 (STAT3) is frequently detected in most types of human cancer where it plays important roles in survival, drug ...resistance, angiogenesis, and other functions. Targeting constitutive STAT3 signaling is thus an attractive therapeutic approach for these cancers. We have recently developed novel small-molecule STAT3 inhibitors, known as FLLL31 and FLLL32, which are derived from curcumin (the primary bioactive compound of turmeric). These compounds are designed to bind selectively to Janus kinase 2 and the STAT3 Src homology-2 domain, which serve crucial roles in STAT3 dimerization and signal transduction. Here we show that FLLL31 and FLLL32 are effective inhibitors of STAT3 phosphorylation, DNA-binding activity, and transactivation in vitro, leading to the impediment of multiple oncogenic processes and the induction of apoptosis in pancreatic and breast cancer cell lines. FLLL31 and FLLL32 also inhibit colony formation in soft agar and cell invasion and exhibit synergy with the anticancer drug doxorubicin against breast cancer cells. In addition, we show that FLLL32 can inhibit the induction of STAT3 phosphorylation by IFNalpha and interleukin-6 in breast cancer cells. We also show that administration of FLLL32 can inhibit tumor growth and vascularity in chicken embryo xenografts as well as substantially reduce tumor volumes in mouse xenografts. Our findings highlight the potential of these new compounds and their efficacy in targeting pancreatic and breast cancers that exhibit constitutive STAT3 signaling.
An androgen receptor (AR) is an intensively studied treatment target for castration-resistant prostate cancer that is irresponsive to conventional antiandrogen therapeutics. Binding function 3 (BF3) ...inhibitors with alternative modes of action have emerged as a promising approach to overcoming antiandrogen resistance. However, how these BF3 inhibitors modulate AR function remains elusive, hindering the development of BF3-targeting agents. Here, we performed an integrated computational study to interrogate the binding mechanism of several known BF3 inhibitors with ARs. Our results show that the inhibitory effect of the BF3 antagonists arises from their allosteric modulation of the activation function (AF2) site, which alters the dynamic coupling between the BF3 and AF2 sites as well as the AF2-coactivator (SRC2-3) interaction. Moreover, the per-residue binding energy analyses reveal the “anchor” role of the linker connecting the phenyl ring and benzimidazole/indole in these BF3 inhibitors. Furthermore, the allosteric driver-interacting residues are found to include both “positive”, e.g., Phe673 and Asn833, and “negative” ones, e.g., Phe826, and the differential interactions with these residues provide an explanation why stronger binding does not necessarily result in higher inhibitory activities. Finally, our allosteric communication pathway analyses delineate how the allosteric signals triggered by BF3 binding are propagated to the AF2 pocket through multiple short- and/or long-ranged transmission pathways. Collectively, our combined computational study provides a comprehensive structural mechanism underlying how the selected set of BF3 inhibitors modulate AR function, which will help guide future development of BF3 antagonists.
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