Brent D. G. Page

Orally bioavailable small-molecule inhibitor of transcription factor Stat3 regresses human breast and lung cancer xenografts

Computer-aided lead optimization derives a unique, orally bioavailable inhibitor of the signal transducer and activator of transcription (Stat)3 Src homology 2 domain. BP-1-102 binds Stat3 with an affinity (KD) of 504 nM, blocks Stat3–phospho-tyrosine (pTyr) peptide interactions and Stat3 activation at 4–6.8 μM, and selectively inhibits growth, survival, migration, and invasion of Stat3-dependent tumor cells. BP-1-102–mediated inhibition of aberrantly active Stat3 in tumor cells suppresses the expression of c-Myc, Cyclin D1, Bcl-xL, Survivin, VEGF, and Krüppel-like factor 8, which is identified as a Stat3 target gene that promotes Stat3-mediated breast tumor cell migration and invasion. Treatment of breast cancer cells with BP-1-102 further blocks Stat3–NF-κB cross-talk, the release of granulocyte colony-stimulating factor, soluble intercellular adhesion molecule 1, macrophage migration-inhibitory factor/glycosylation-inhibiting factor, interleukin 1 receptor antagonist, and serine protease inhibitor protein 1, and the phosphorylation of focal adhesion kinase and paxillin, while enhancing E-cadherin expression. Intravenous or oral gavage delivery of BP-1-102 furnishes micromolar or microgram levels in tumor tissues and inhibits growth of human breast and lung tumor xenografts.

Signal transducer and activator of transcription 3 inhibitors: a patent review

Importance of the field: Aberrant activation of signal transducer and activator of transcription (Stat) 3, a member of the STAT family of proteins, is prevalent in numerous human cancers and is now widely recognized as a critical molecular abnormality and a master regulator of tumor processes. Thus, the identification of potent and selective Stat3 inhibitors will have a high commercial potential as anticancer drugs, given the many tumors in which Stat3 is implicated. Areas covered in this review: This review covers the structures and activities of direct inhibitors of Stat3 protein activity described in the patent literature since the research fields inception in 2001. The patents reviewed include peptide and peptidomimetic compounds, small molecules, oligonucleotides and platinum-based Stat3 inhibitors. What the reader will gain: Readers will gain an understanding of how Stat3 protein function has been inhibited by a wide variety of structurally diverse therapeutic compounds. Readers will learn about which classes of patented Stat3 inhibitors are most advanced toward clinical trials, and will be exposed to the proposed mechanisms of inhibition and scope of their application in treating human cancers. Take home message: Numerous groups have shown that in vivo administration of inhibitors of activated Stat3 induce human tumor regression in xenograft models. Indeed, the growing number of preclinical studies in numerous cancer types, as well as the first Phase 0 clinical trial of a Stat3 inhibitor, suggest that Stat3 is a valid and exciting therapeutic target for molecular inhibitors.

Disruption of Transcriptionally Active Stat3 Dimers with Non‐phosphorylated, Salicylic Acid‐Based Small Molecules: Potent in vitro and Tumor Cell Activities

Signal transducer and activator of transcription 3 (Stat3) protein is a cytosolic transcription factor that relays signals from receptors in the plasma membrane directly to the nucleus, and is routinely hyperactivated in many human cancers and diseases.[1] Regarded as an oncogene, Stat3 is well-recognized as a master regulator of cellular events that lead to the cancer phenotype, making this protein viable target for molecular therapeutic design.[2] Stat3 inhibitors have included peptides,[3–4] peptidomimetics,[5–9] small molecules[10–14] and metal complexes.[15] Despite significant advances in Stat3 inhibition,[1] truly potent (in vivo), isoform-selective, small molecule Stat3 agents have not been readily forthcoming; this is likely due in part to the challenge of disrupting protein–protein interactions.[16]

Combined STAT3 and BCR-ABL1 inhibition induces synthetic lethality in therapy-resistant chronic myeloid leukemia

Mutations in the BCR-ABL1 kinase domain are an established mechanism of tyrosine kinase inhibitor (TKI) resistance in Philadelphia chromosome-positive leukemia, but fail to explain many cases of clinical TKI failure. In contrast, it is largely unknown why some patients fail TKI therapy despite continued suppression of BCR-ABL1 kinase activity, a situation termed BCR-ABL1 kinase-independent TKI resistance. Here, we identified activation of signal transducer and activator of transcription 3 (STAT3) by extrinsic or intrinsic mechanisms as an essential feature of BCR-ABL1 kinase-independent TKI resistance. By combining synthetic chemistry, in vitro reporter assays, and molecular dynamics-guided rational inhibitor design and high-throughput screening, we discovered BP-5-087, a potent and selective STAT3 SH2 domain inhibitor that reduces STAT3 phosphorylation and nuclear transactivation. Computational simulations, fluorescence polarization assays and hydrogen–deuterium exchange assays establish direct engagement of STAT3 by BP-5-087 and provide a high-resolution view of the STAT3 SH2 domain/BP-5-087 interface. In primary cells from chronic myeloid leukemia (CML) patients with BCR-ABL1 kinase-independent TKI resistance, BP-5-087 (1.0 μM) restored TKI sensitivity to therapy-resistant CML progenitor cells, including leukemic stem cells. Our findings implicate STAT3 as a critical signaling node in BCR-ABL1 kinase-independent TKI resistance, and suggest that BP-5-087 has clinical utility for treating malignancies characterized by STAT3 activation.

Potent Targeting of the STAT3 Protein in Brain Cancer Stem Cells: A Promising Route for Treating Glioblastoma

The STAT3 gene is abnormally active in glioblastoma (GBM) and is a critically important mediator of tumor growth and therapeutic resistance in GBM. Thus, for poorly treated brain cancers such as gliomas, astrocytomas, and glioblastomas, which harbor constitutively activated STAT3, a STAT3-targeting therapeutic will be of significant importance. Herein, we report a most potent, small molecule, nonphosphorylated STAT3 inhibitor, 31 (SH-4-54) that strongly binds to STAT3 protein (K D = 300 nM). Inhibitor 31 potently kills glioblastoma brain cancer stem cells (BTSCs) and effectively suppresses STAT3 phosphorylation and its downstream transcriptional targets at low nM concentrations. Moreover, in vivo, 31 exhibited blood-brain barrier permeability, potently controlled glioma tumor growth, and inhibited pSTAT3 in vivo. This work, for the first time, demonstrates the power of STAT3 inhibitors for the treatment of BTSCs and validates the therapeutic efficacy of a STAT3 inhibitor for GBM clinical application.

Small Molecule STAT5-SH2 Domain Inhibitors Exhibit Potent Antileukemia Activity

A growing body of evidence shows that Signal Transducer and Activator of Transcription 5 (STAT5) protein, a key member of the STAT family of signaling proteins, plays a pivotal role in the progression of many human cancers, including acute myeloid leukemia and prostate cancer. Unlike STAT3, where significant medicinal effort has been expended to identify potent direct inhibitors, Stat5 has been poorly investigated as a molecular therapeutic target. Thus, in an effort to identify direct inhibitors of STAT5 protein, we conducted an in vitro screen of a focused library of SH2 domain binding salicylic acid-containing inhibitors (∼150) against STAT5, as well as against STAT3 and STAT1 proteins for SH2 domain selectivity. We herein report the identification of several potent (K(i) < 5 μM) and STAT5 selective (>3-fold specificity for STAT5 cf. STAT1 and STAT3) inhibitors, BP-1-107, BP-1-108, SF-1-087, and SF-1-088. Lead agents, evaluated in K562 and MV-4-11 human leukemia cells, showed potent induction of apoptosis (IC(50)s ∼ 20 μM) which correlated with potent and selective suppression of STAT5 phosphorylation, as well as inhibition of STAT5 target genes cyclin D1, cyclin D2, C-MYC, and MCL-1. Moreover, lead agent BP-1-108 showed negligible cytotoxic effects in normal bone marrow cells not expressing activated STAT5 protein. Inhibitors identified in this study represent some of the most potent direct small molecule, nonphosphorylated inhibitors of STAT5 to date.

Identification of a non-phosphorylated, cell permeable, small molecule ligand for the Stat3 SH2 domain

Signal transducer and activator of transcription 3 (Stat3) protein is a cytosolic transcription factor that is aberrantly activated in numerous human cancers. Inhibitors of activated Stat3-Stat3 protein complexes have been shown to hold therapeutic promise for the treatment of human cancers harboring activated Stat3. Herein, we report the design and synthesis of a focused library of salicylic acid containing Stat3 SH2 domain binders. The most potent inhibitor, 17o, effectively disrupted Stat3-phosphopeptide complexes (K(i)=13 μM), inhibited Stat3-Stat3 protein interactions (IC(50)=19 μM) and silenced intracellular Stat3 phosphorylation and Stat3-target gene expression profiles. Inhibition of Stat3 function in both breast and multiple myeloma (MM) tumor cells correlated with induced cell death (EC(50)=10 and 16 μM, respectively).

Antagonism of the Stat3–Stat3 Protein Dimer with Salicylic Acid Based Small Molecules

More than 50 new inhibitors of the oncogenic Stat3 protein were identified through a structure–activity relationship (SAR) study based on the previously identified inhibitor S3I‐201 (IC50=86 μM, Ki>300 μM). A key structural feature of these inhibitors is a salicylic acid moiety, which, by acting as a phosphotyrosine mimetic, is believed to facilitate binding to the Stat3 SH2 domain. Several of the analogues exhibit higher potency than the lead compound in inhibiting Stat3 DNA binding activity, with an in vitro IC50 range of 18.7–51.9 μM, and disruption of Stat3–pTyr peptide interactions with Ki values in the 15.5–41 μM range. One agent in particular exhibited potent inhibition of Stat3 phosphorylation in both breast and multiple myeloma tumor cells, suppressed the expression of Stat3 target genes, and induced antitumor effects in tumor cells harboring activated Stat3 protein.

Dynamic Reprogramming of Signaling Upon Met Inhibition Reveals a Mechanism of Drug Resistance in Gastric Cancer

Understanding how inhibitors rewire the Met receptor pathway points to a strategy for more effective gastric cancer treatment. Met with Resistance in Gastric Cancer The hepatocyte growth factor receptor Met is associated with poor prognosis in various cancers, but the efficacy of Met inhibitors is often impeded by resistance. By comparing transcriptional changes at multiple time points after stimulation or inhibition of Met, Lai et al. identified critical mediators of Met-induced proliferation and Met inhibitor resistance in gastric cancer cell lines. Cancer cells or tumors exposed to Met inhibitors had decreased abundance of phosphatases, and this correlated with reactivation of the pro-proliferative MEK-ERK pathway and the emergence of drug resistance. Combining Met and MEK inhibitors was more cytotoxic to gastric cancer cells in culture than was either inhibitor alone, suggesting that this combination strategy may be effective in gastric cancer. The Met receptor tyrosine kinase is activated or genetically amplified in some gastric cancers, but resistance to small-molecule inhibitors of Met often emerges in patients. We found that Met abundance correlated with a proliferation marker in patient gastric tumor sections, and gastric cancer cell lines that have MET amplifications depended on Met for proliferation and anchorage-independent growth in culture. Inhibition of Met induced temporal changes in gene expression in the cell lines, initiated by a rapid decrease in the expression of genes encoding transcription factors, followed by those encoding proteins involved in epithelial-mesenchymal transition, and finally those encoding cell cycle–related proteins. In the gastric cancer cell lines, microarray and chromatin immunoprecipitation analysis revealed considerable overlap between genes regulated in response to Met stimulation and those regulated by signal transducer and activator of transcription 3 (STAT3). The activity of STAT3, extracellular signal–regulated kinase (ERK), and the kinase Akt was decreased by Met inhibition, but only inhibitors of STAT3 were as effective as the Met inhibitor in decreasing tumor cell proliferation in culture and in xenografts, suggesting that STAT3 mediates the pro-proliferative program induced by Met. However, the phosphorylation of ERK increased after prolonged Met inhibition in culture, correlating with decreased abundance of the phosphatases DUSP4 and DUSP6, which inhibit ERK. Combined inhibition of Met and the mitogen-activated protein kinase kinase (MEK)–ERK pathway induced greater cell death in cultured gastric cancer cells than did either inhibitor alone. These findings indicate combination therapies that may counteract resistance to Met inhibitors.

Inhibiting Aberrant Signal Transducer and Activator of Transcription Protein Activation with Tetrapodal, Small Molecule Src Homology 2 Domain Binders: Promising Agents against Multiple Myeloma

The signal transducer and activator of transcription (STAT) proteins represent a family of cytoplasmic transcription factors that regulate a pleiotropic range of biological processes. In particular, Stat3 protein has attracted attention as it regulates the expression of genes involved in a variety of malignant processes, including proliferation, survival, migration, and drug resistance. Multiple myeloma (MM) is an incurable hematologic malignancy that often exhibits abnormally high levels of Stat3 activity. Although current treatment strategies can improve the clinical management of MM, it remains uniformly incurable with a dismal median survival time post-treatment of 3-4 years. Thus, novel targeted therapeutics are critically needed to improve MM patient outcomes. We herein report the development of a series of small molecule Stat3 inhibitors with potent anti-MM activity in vitro. These compounds showed high-affinity binding to Stat3s SH2 domain, inhibited intracellular Stat3 phosphorylation, and induced apoptosis in MM cell lines at low micromolar concentrations.