Retraction of "Identification of Purine-Scaffold Small-Molecule Inhibitors of Stat3 Activation by QSAR Studies"

[This retracts the article DOI: 10.1021/ml100224d.].

Abstract 2782: Small molecule H182 suppresses Stat3 activation in tumor cells and combines with radiation therapy to block breast tumor growth in mouse syngeneic models

Signal transducer and activator of transcription 3 (Stat3) is a latent transcription factor that contributes to tumor cell growth and survival in constitutively-active form in several types of human cancers, and hence, serves as a therapeutic target. The azetidine-based compound, H182 irreversibly binds to Stat3. In cell-free DNA-binding assay, H182 selectively inhibited Stat3 DNA-binding activity (IC50 0.38-0.66 μM) over Stat1 or Stat5 (IC50>15.8 μM) in vitro. In treated pancreatic cancer cells, H182 specifically blocked the association of Stat3 with gp130 and JAK2, and inhibited Stat3 tyrosine phosphorylation and DNA-binding activity. Coimmunoprecipitation and colocalization studies of hemagglutinin (HA)-tagged Stat3 and EGFP-tagged Stat3 expressed in prostate cancer cells showed that treatment with H182 blocked the HA-Stat3:EGFP-Stat3 interactions in intact cells. Immunofluorescence staining with laser-scanning confocal microscopy analysis for the intracellular localization of Stat3 showed treatment of H182 disrupted Stat3 nuclear accumulation and promoted the aggregation of Stat3 at the perinuclear region. H182 consequently suppressed Stat3-dependent transcriptional activity and the expression of Stat3 downstream genes, including Cyclin A, Bcl-2, Cyclin B1, and Mcl-1. Moreover, H182 significantly inhibited the colony survival, migration, and invasion in vitro of breast, pancreatic and prostate cancer cells harboring aberrant Stat3 activation. Significantly, in vivo administration of H182 in combination with radiation induced a strong antitumor response against mouse triple-negative breast cancer in syngeneic models and prolonged survival. Thus, our study provides a novel Stat3 inhibitor with significant antitumor activity against human tumors cancer harboring persistently active STAT3.

Citation Format: Yue Chen, Peibin Yue, Wenzhen Fu, Weiliang Chen, Kathleen M. Kershaw, Stephen L. Shiao, Marcus A. Tius, Francisco Lopez-Tapia, James Turkson. Small molecule H182 suppresses Stat3 activation in tumor cells and combines with radiation therapy to block breast tumor growth in mouse syngeneic models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2782.

Abstract 514: Novel potent azetidine-based inhibitors bind irreversibly to Stat3 DNA-binding domain (DBD) and are efficacious against tumor growth in mice

Unlike classical Signal transducer and activator of transcription (Stat) signaling, which is transient in non-transformed cells, the aberrant activation of the family member, Stat3, occurs in malignant transformation and is implicated in breast, ovarian and many other human cancers. Thus, Stat3 remains a validated and important target for the discovery of novel anticancer drugs. Despite this, the discovery and development of potent Stat3 small molecule inhibitors has proven to be a significant challenge, and no drug is available yet in the market. We have discovered novel Stat3 irreversible azetidine inhibitors with unprecedent submicromolar potency through systematic medicinal chemistry structure activity relationship (SAR). Mechanism of action of most potent azetidine inhibitors depend on whether they are salicylic acids or not, i.e., salicylic acids preferably bind irreversibly to Stat3 Cys426 site in the DNA-binding domain (DBD), and non-salicylic acids, e.g., current lead H182, bind to Stat3 Cys468 DBD site. As expected, the inhibition of Stat3 DNA-binding activity was time dependent, with IC50 in the range of 0.27-0.87 µM at one hour incubation with active Stat3. On the other hand, azetidine salicylic acids also bind to the SH2 domain, although reversibly and at much weaker affinity, as determined in fluorescent polarization (FP) assay, with IC50 of 10-16 µM at one hour incubation, while non-salicylic acids, e.g., lead H182, present no binding affinity up to 600 µM for the SH2 domain. Despite that H182 does not bind to SH2 domain, it still inhibits its phosphorylation. Though lead compound H182 presents significant mouse in vivo efficacy, mouse in vivo pharmacokinetics shows very low plasma AUC, which correlates with quite high mouse in vitro hepatocyte CLint of 138 µL/min/106 cells; however, human in vitro hepatocyte assay gives much better results and is in the middle stability range (CLint of 14.6 µL/min/106 cells). The in vivo PK in other species, e.g., rat, is being determined. H182 represents a plausible molecule for further development.

Citation Format: Yue Chen, Ning Zhai, Yinsong Zhu, Peibin Yue, Nagendra Verma, Christine Brotherton-Pleiss, Wenzhen Fu, Kayo Nakamura, Weiliang Chen, Marcus Tius, Francisco J. Lopez-Tapia, James Turkson. Novel potent azetidine-based inhibitors bind irreversibly to Stat3 DNA-binding domain (DBD) and are efficacious against tumor growth in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 514.

Natural product preferentially targets redox and metabolic adaptations and aberrantly active STAT3 to inhibit breast tumor growth in vivo

Dysregulated gene expression programs and redox and metabolic adaptations allow cancer cells to survive under high oxidative burden. These mechanisms also represent therapeutic vulnerabilities. Using triple-negative breast cancer (TNBC) as a model, we show that compared to normal human breast epithelial cells, the TNBC cells, MDA-MB-231 and MDA-MB-468 that harbor constitutively active STAT3 also express higher glucose-6-phosphate dehydrogenase (G6PD), thioredoxin reductase (TrxR)1, NADPH, and GSH levels for survival. Present studies discover that the natural product, R001, targets these adaptation mechanisms. Treatment of TNBC cells with R001 inhibited constitutively active STAT3, STAT3-regulated gene expression, and the functions of G6PD and TrxR1. Consequently, in the TNBC, but not normal cells, R001 suppressed GSH levels, but raised NADPH levels, reflective of a loss of mitochondrial respiration and which led to reactive oxygen species (ROS) induction, all of which led to loss of viable cells and inhibition of anchorage-dependent and independent growth. R001 treatment further led to early pyroptosis and late DNA damage, cell cycle arrest, and apoptosis only in the TNBC cells. Oral administration of 5 mg/kg R001 inhibited MDA-MB-468 xenografts growth in mice, with reduced pY705-STAT3, G6PD, TrxR1, and GSH levels. R001 serves as a therapeutic entity that targets the vulnerabilities of TNBC cells to inhibit tumor growth in vivo.

Abstract 5476: Novel azetidine-based STAT3 inhibitors induce misfolded protein response, endoplasmic reticulum stress and mitophagy, and inhibit breast tumor growth in vivo

Anticancer drugs that directly target Signal Transducer and Activator of Transcription (Stat)3 have remained elusive. We present azetidine-based small molecules as a new class of potent Stat3 inhibitors. Compounds H172 and H182 have potency (IC50) of 0.38-0.98 µM, H105 and H120 have IC50 of 1.75-2.07 µM against Stat3 DNA-binding activity in vitro, compared to the IC50 of >17 µM against Stat1 or Stat5 activity. Treatment of the triple-negative breast cancer (TNBC), MDA-MB-231 and MDA-MB-468 cells with the new compounds inhibited constitutive Stat3 activation, promoted Stat3 ubiquitination, blocked anchorage-dependent and independent growth, with potency, EC50 of 1.0-1.9 μM, and induced apoptosis of these cells. By contrast, pYStat1, pYStat5, pS727Stat3, pSrc, pJanus kinase, or the induction of other signaling events are not inhibited in compound-treated cells, and normal or tumor cells that do not harbor aberrantly-active Stat3 are only weakly inhibited. In vivo delivery of H120 or H182 as a single agent inhibited growth of human TNBC xenografts, and of H278 (HCl salt of H182) combined with radiation abrogated tumor growth and improved survival in mouse TNBC syngeneic models. These studies provide novel mechanism of disruption of aberrantly-active Stat3 and its dynamics in showing that the azetidine-based Stat3 inhibitors trigger Stat3 ubiquitination, and tumor cell death. H182 and H172 are new entities for further therapeutic development against TNBC and other cancers that harbor aberrantly-active Stat3.

Citation Format: Peibin Yue, Francisco Lopez-Tapia, Yinsong Zhu, Nagendra Verma, Felix Alonso-Valenteen, Simoun Mikhael, Lali Medina-Kauwe, Marcus Tius, James Turkson. Novel azetidine-based STAT3 inhibitors induce misfolded protein response, endoplasmic reticulum stress and mitophagy, and inhibit breast tumor growth in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5476.

Abstract 5482: Natural product inhibitor of Stat3, G6PD, and TrxR1 functions induces an early oxidative stress and pyroptosis, and a late-stage DNA damage and cell cycle arrest to block tumor growth in human breast cancer models

Bioactive natural products have led to new drugs or been the inspiration for developing new treatments. Signal transducer and activator of transcription (STAT)3 is a an oncogene that has been implicated in many human cancers. We report that the hirsutinolide natural product, R001, blocks STAT3 DNA-binding activty in vitro. Treatment with R001 of the human triple-negative breast cancer (TNBC) cells, MDA-MB-231 and MDA-MB-468 led to the concurrent inhibition of constitutively-active STAT3 and the expression and activities of glucose-6-phosphate 1-dehydrogenase (G6PD) and thioredoxin reductase (TrxR)1, early suppression of glutathione (GSH), and the induction of reactive oxygen species (ROS), which peaked at 6-24 h post R001-treatment. In the short term, R001-treated TNBC cells showed evidence of pyroptotic cell death. Prolonged treatment of TNBC cells with R001 led to DNA damage and G2/M-phase cell cycle arrest, which are late-stage responses that were preceded by the suppression of ATM-Chk2-Cdc25c pathway, and the induction of p21 and γH2AX phosphorylation by the natural product. Accordingly, R001 suppressed the viable cell numbers, colony formation, growth in 3D-matrigel, and the migration of MDA-MB-231 and MDA-MB-468 cells in vitro. The oral administration of R001 at 5 mg/kg signficantly inhibited growth of human MDA-MB-468 xenografts in mice. Results together show that R001 inhibits STAT3, G6PD and TrxR1 functions that lead to early oxidative stress and pyroptosis and late-stage DNA damage and cell cycle arrest, which collectively cause tumor cell death and tumor growth inhibition in human TNBC models.

Citation Format: Yinsong Zhu, Cody F. Dickinson, Justin Yang, Kyrstin Datanagan, Ning Zhai, Peibin Yue, Francisco Lopez-Tapia, Marcus A. Tius, James Turkson. Natural product inhibitor of Stat3, G6PD, and TrxR1 functions induces an early oxidative stress and pyroptosis, and a late-stage DNA damage and cell cycle arrest to block tumor growth in human breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5482.

Novel potent azetidine-based compounds irreversibly inhibit Stat3 activation and induce antitumor response against human breast tumor growth in vivo

Signal transducer and activator of transcription (Stat)3 is a valid anticancer therapeutic target. We have discovered a highly potent chemotype that amplifies the Stat3-inhibitory activity of lead compounds to levels previously unseen. The azetidine-based compounds, including H172 (9f) and H182, irreversibly bind to Stat3 and selectively inhibit Stat3 activity (IC₅₀ 0.38-0.98 μM) over Stat1 or Stat5 (IC₅₀ > 15.8 μM) in vitro. Mass spectrometry detected the Stat3 cysteine peptides covalently bound to the azetidine compounds, and the key residues, Cys426 and Cys468, essential for the high potency inhibition, were confirmed by site-directed mutagenesis. In triple-negative breast cancer (TNBC) models, treatment with the azetidine compounds inhibited constitutive and ligand-induced Stat3 signaling, and induced loss of viable cells and tumor cell death, compared to no effect on the induction of Janus kinase (JAK)2, Src, epidermal growth factor receptor (EGFR), and other proteins, or weak effects on cells that do not harbor aberrantly-active Stat3. H120 (8e) and H182 as a single agent inhibited growth of TNBC xenografts, and H278 (hydrochloric acid salt of H182) in combination with radiation completely blocked mouse TNBC growth and improved survival in syngeneic models. We identify potent azetidine-based, selective, irreversible Stat3 inhibitors that inhibit TNBC growth in vivo.

SS-4 is a highly selective small molecule inhibitor of STAT3 tyrosine phosphorylation that potently inhibits GBM tumorigenesis in vitro and in vivo

Glioblastoma (GBM) is a highly aggressive cancer with a dismal prognosis. Constitutively active STAT3 has a causal role in GBM progression and is associated with poor patient survival. We rationally designed a novel small molecule, SS-4, by computational modeling to specifically interact with STAT3. SS-4 strongly and selectively inhibited STAT3 tyrosine (Y)-705 phosphorylation in MT330 and LN229 GBM cells and inhibited their proliferation and induced apoptosis with an IC₅₀ of ∼100 nM. The antiproliferative and apoptotic actions of SS-4 were Y-705 phosphorylation dependent, as evidenced by its lack of effects on STAT3 knockout (STAT3^KO) cells or STAT3^KO cells that overexpressed a phospho-Y705 deficient (STAT3Y705F) mutant, and the recovery of effects when wild-type STAT3 or a phospho-serine (S)727 deficient mutant was expressed in STAT3^KO cells. SS-4 increased the expression of tumor suppressive genes, while decreasing the expression of tumor promoting genes. Importantly, SS-4 markedly reduced the growth of GBM intracranial tumor xenografts. These data together identify SS-4 as a potent STAT3 inhibitor that selectively blocks Y705-phosphorylation, induces apoptosis, and inhibits growth of human GBM models in vitro and in vivo.

Discovery of Novel Azetidine Amides as Potent Small-Molecule STAT3 Inhibitors

We optimized our previously reported proline-based STAT3 inhibitors into an exciting new series of (R)-azetidine-2-carboxamide analogues that have sub-micromolar potencies. 5a, 5o, and 8i have STAT3-inhibitory potencies (IC50) of 0.55, 0.38, and 0.34 μM, respectively, compared to potencies greater than 18 μM against STAT1 or STAT5 activity. Further modifications derived analogues, including 7e, 7f, 7g, and 9k, that addressed cell membrane permeability and other physicochemical issues. Isothermal titration calorimetry analysis confirmed high-affinity binding to STAT3, with KD of 880 nM (7g) and 960 nM (9k). 7g and 9k inhibited constitutive STAT3 phosphorylation and DNA-binding activity in human breast cancer, MDA-MB-231 or MDA-MB-468 cells. Furthermore, treatment of breast cancer cells with 7e, 7f, 7g, or 9k inhibited viable cells, with an EC50 of 0.9-1.9 μM, cell growth, and colony survival, and induced apoptosis while having relatively weaker effects on normal breast epithelial, MCF-10A or breast cancer, MCF-7 cells that do not harbor constitutively active STAT3.

RasGRP1 induces autophagy and transformation-associated changes in primary human keratinocytes

Ras mutations are present in only a subset of sporadic human cutaneous squamous cell carcinomas (cSCC) even though Ras is activated in most. This suggests that other mechanisms of Ras activation play a role in the disease. The aberrant expression of RasGRP1, a guanyl nucleotide exchange factor for Ras, is critical for mouse cSCC development through its ability to increase Ras activity. However, the role of RasGRP1 in human keratinocyte carcinogenesis remains unknown. Here we report that RasGRP1 is significantly elevated in human cSCC and that high RasGRP1 expression in human primary keratinocytes triggered activation of endogenous Ras and significant morphological changes including cytoplasmic vacuole formation and growth arrest. Moreover, RasGRP1-expressing cells were autophagic as indicated by LC3-II increase and the formation of LC3 punctae. In an in vitro organotypic skin model, wild type keratinocytes generated a well-stratified epithelium, while RasGRP1-expressing cells failed to do so. Finally, RasGRP1 induced transformation-like changes in skin cells from Li-Fraumeni patients with inactivating p53 mutations, demonstrating the oncogenic potential of this protein. These results support a role for RasGRP1 in human epidermal keratinocyte carcinogenesis and might serve as an important new therapeutic target.

STAT3 and GR Cooperate to Drive Gene Expression and Growth of Basal-Like Triple-Negative Breast Cancer

Breast cancers are divided into subtypes with different prognoses and treatment responses based on global differences in gene expression. Luminal breast cancer gene expression and proliferation are driven by estrogen receptor alpha, and targeting this transcription factor is the most effective therapy for this subtype. By contrast, it remains unclear which transcription factors drive the gene expression signature that defines basal-like triple-negative breast cancer, and there are no targeted therapies approved to treat this aggressive subtype. In this study, we utilized integrated genomic analysis of DNA methylation, chromatin accessibility, transcription factor binding, and gene expression in large collections of breast cancer cell lines and patient tumors to identify transcription factors responsible for the basal-like gene expression program. Glucocorticoid receptor (GR) and STAT3 bind to the same genomic regulatory regions, which were specifically open and unmethylated in basal-like breast cancer. These transcription factors cooperated to regulate expression of hundreds of genes in the basal-like gene expression signature, which were associated with poor prognosis. Combination treatment with small-molecule inhibitors of both transcription factors resulted in synergistic decreases in cell growth in cell lines and patient-derived organoid models. This study demonstrates that GR and STAT3 cooperate to regulate the basal-like breast cancer gene expression program and provides the basis for improved therapy for basal-like triple-negative breast cancer through rational combination of STAT3 and GR inhibitors. SIGNIFICANCE: This study demonstrates that GR and STAT3 cooperate to activate the canonical gene expression signature of basal-like triple-negative breast cancer and that combination treatment with STAT3 and GR inhibitors could provide synergistic therapeutic efficacy.

27-Hydroxycholesterol Impairs Plasma Membrane Lipid Raft Signaling as Evidenced by Inhibition of IL6-JAK-STAT3 Signaling in Prostate Cancer Cells

We recently reported that restoring the CYP27A1-27hydroxycholesterol axis had antitumor properties. Thus, we sought to determine the mechanism by which 27HC exerts its anti-prostate cancer effects. As cholesterol is a major component of membrane microdomains known as lipid rafts, which localize receptors and facilitate cellular signaling, we hypothesized 27HC would impair lipid rafts, using the IL6-JAK-STAT3 axis as a model given its prominent role in prostate cancer. As revealed by single molecule imaging of DU145 prostate cancer cells, 27HC treatment significantly reduced detected cholesterol density on the plasma membranes. Further, 27HC treatment of constitutively active STAT3 DU145 prostate cancer cells reduced STAT3 activation and slowed tumor growth in vitro and in vivo. 27HC also blocked IL6-mediated STAT3 phosphorylation in nonconstitutively active STAT3 cells. Mechanistically, 27HC reduced STAT3 homodimerization, nuclear translocation, and decreased STAT3 DNA occupancy at target gene promoters. Combined treatment with 27HC and STAT3 targeting molecules had additive and synergistic effects on proliferation and migration, respectively. Hallmark IL6-JAK-STAT gene signatures positively correlated with CYP27A1 gene expression in a large set of human metastatic castrate-resistant prostate cancers and in an aggressive prostate cancer subtype. This suggests STAT3 activation may be a resistance mechanism for aggressive prostate cancers that retain CYP27A1 expression. In summary, our study establishes a key mechanism by which 27HC inhibits prostate cancer by disrupting lipid rafts and blocking STAT3 activation. IMPLICATIONS: Collectively, these data show that modulation of intracellular cholesterol by 27HC can inhibit IL6-JAK-STAT signaling and may synergize with STAT3-targeted compounds.

Cytotoxic Sesquiterpenoid Quinones and Quinols, and an 11-Membered Heterocycle, Kauamide, from the Hawaiian Marine Sponge Dactylospongia elegans

Several known sesquiterpenoid quinones and quinols (1-9), and kauamide (10), a new polyketide-peptide containing an 11-membered heterocycle, were isolated from the extracts of the Hawaiian marine sponge Dactylospongia elegans. The planar structure of 10 was determined from spectroscopic analyses, and its relative and absolute configurations were established from density functional theory (DFT) calculations of the GIAO NMR shielding tensors, and advanced Marfey's analysis of the N-MeLeu residue, respectively. Compounds 1 and 3 showed moderate inhibition of β-secretase 1 (BACE1), whereas 1-9 exhibited moderate to potent inhibition of growth of human glioma (U251) cells. Compounds 1-2 and 4-7 were also active against human pancreatic carcinoma (Panc-1) cells.

GNAI1 and GNAI3 Reduce Colitis-Associated Tumorigenesis in Mice by Blocking IL6 Signaling and Down-regulating Expression of GNAI2

BACKGROUND & AIMS

Interleukin 6 (IL6) and tumor necrosis factor contribute to the development of colitis-associated cancer (CAC). We investigated these signaling pathways and the involvement of G protein subunit alpha i1 (GNAI1), GNAI2, and GNAI3 in the development of CAC in mice and humans.

METHODS

B6;129 wild-type (control) or mice with disruption of Gnai1, Gnai2, and/or Gnai3 or conditional disruption of Gnai2 in CD11c+ or epithelial cells were given dextran sulfate sodium (DSS) to induce colitis followed by azoxymethane (AOM) to induce carcinogenesis; some mice were given an antibody against IL6. Feces were collected from mice, and the compositions of microbiomes were analyzed by polymerase chain reactions. Dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs) isolated from spleen and colon tissues were analyzed by flow cytometry. We performed immunoprecipitation and immunoblot analyses of colon tumor tissues, MDSCs, and mouse embryonic fibroblasts to study the expression levels of GNAI1, GNAI2, and GNAI3 and the interactions of GNAI1 and GNAI3 with proteins in the IL6 signaling pathway. We analyzed the expression of Gnai2 messenger RNA by CD11c+ cells in the colonic lamina propria by PrimeFlow, expression of IL6 in DCs by flow cytometry, and secretion of cytokines in sera and colon tissues by enzyme-linked immunosorbent assay. We obtained colon tumor and matched nontumor tissues from 83 patients with colorectal cancer having surgery in China and 35 patients with CAC in the United States. Mouse and human colon tissues were analyzed by histology, immunoblot, immunohistochemistry, and/or RNA-sequencing analyses.

RESULTS

GNAI1 and GNAI3 (GNAI1;3) double-knockout (DKO) mice developed more severe colitis after administration of DSS and significantly more colonic tumors than control mice after administration of AOM plus DSS. Development of increased tumors in DKO mice was not associated with changes in fecal microbiomes but was associated with activation of nuclear factor (NF) κB and signal transducer and activator of transcription (STAT) 3; increased levels of GNAI2, nitric oxide synthase 2, and IL6; increased numbers of CD4+ DCs and MDSCs; and decreased numbers of CD8+ DCs. IL6 was mainly produced by CD4+/CD11b+, but not CD8+, DCs in DKO mice. Injection of DKO mice with a blocking antibody against IL6 reduced the expansion of MDSCs and the number of tumors that developed after CAC induction. Incubation of MDSCs or mouse embryonic fibroblasts with IL6 induced activation of either NF-κB by a JAK2-TRAF6-TAK1-CHUK/IKKB signaling pathway or STAT3 by JAK2. This activation resulted in expression of GNAI2, IL6 signal transducer (IL6ST, also called GP130) and nitric oxide synthase 2, and expansion of MDSCs; the expression levels of these proteins and expansion of MDSCs were further increased by the absence of GNAI1;3 in cells and mice. Conditional disruption of Gnai2 in CD11c+ cells of DKO mice prevented activation of NF-κB and STAT3 and changes in numbers of DCs and MDSCs. Colon tumor tissues from patients with CAC had reduced levels of GNAI1 and GNAI3 and increased levels of GNAI2 compared with normal tissues. Further analysis of a public human colorectal tumor DNA microarray database (GSE39582) showed that low Gani1 and Gnai3 messenger RNA expression and high Gnai2 messenger RNA expression were significantly associated with decreased relapse-free survival.

CONCLUSIONS

GNAI1;3 suppresses DSS-plus-AOM-induced colon tumor development in mice, whereas expression of GNAI2 in CD11c+ cells and IL6 in CD4+/CD11b+ DCs appears to promote these effects. Strategies to induce GNAI1;3, or block GNAI2 and IL6, might be developed for the prevention or therapy of CAC in patients.

Consensus report of the 8 and 9th Weinman Symposia on Gene x Environment Interaction in carcinogenesis: novel opportunities for precision medicine

The relative contribution of intrinsic genetic factors and extrinsic environmental ones to cancer aetiology and natural history is a lengthy and debated issue. Gene-environment interactions (G x E) arise when the combined presence of both a germline genetic variant and a known environmental factor modulates the risk of disease more than either one alone. A panel of experts discussed our current understanding of cancer aetiology, known examples of G × E interactions in cancer, and the expanded concept of G × E interactions to include somatic cancer mutations and iatrogenic environmental factors such as anti-cancer treatment. Specific genetic polymorphisms and genetic mutations increase susceptibility to certain carcinogens and may be targeted in the near future for prevention and treatment of cancer patients with novel molecularly based therapies. There was general consensus that a better understanding of the complexity and numerosity of G × E interactions, supported by adequate technological, epidemiological, modelling and statistical resources, will further promote our understanding of cancer and lead to novel preventive and therapeutic approaches.

Abstract 4880: Novel nano-molar small-molecule STAT3 inhibitor series with antitumor activities against human breast cancer

Constitutively-active Signal transducer and activator of transcription (STAT) 3 has been well validated as a significant mechanistic underpinning of many human cancers and a target for anticancer therapy. To date, no small molecule STAT3 inhibitor has been successfully developed for clinical application as a therapeutic agent, despite the discovery of many molecular entities that inhibit the protein. To advance the therapeutic development of small molecule STAT3 inhibitors, we focused on the existing lead compounds, BP-1-102, SH4-54, and SH5-07 (all three showing IC50 of 4-7 μM). All three leads are based on an N-methylglycinamide scaffold, with its two amine groups condensed with three different functionalities. Intensive medicinal chemistry campaign was directed towards understanding and optimizing the molecular determinants critical for enhanced STAT3-inhibitory potency and strong antitumor effects. We report the development of nanomolar potent inhibitors of STAT3 DNA-binding activity. Most notably, the analogs H127, H145, H171, H174, H181, and H182 preferentially inhibit STAT3 activity in DNA-binding assay in vitro, with IC50 of 300 - 800 nM, compared to little or no observed effect on STAT1 and STAT5 DNA-binding activity at concentrations up to 20 μM. Treatment of human breast cancer MDA-MB-231 and MDA-MB-468 cells with H171, H174 or H182 inhibited constitutive STAT3 DNA-binding activity and phosphorylation at Tyr705 in both time- and dose-dependent manner. H171, H174 or H182 further blocked the growth and viability, colony formation, and oncogenic transformation of the human breast cancer cells that harbor persistently active STAT3, with IC50 of 1.0 - 1.9 μM, compared to the IC50 of 3.8 - 8.1 μM against the viability of the immortalized breast epithelial cells that do not harbor persistently active STAT3. These compounds represent some of the first nanomolar potent small molecules observed to directly inhibit STAT3 activity, with potent antitumor cell effects.

Citation Format: Peibin Yue, Francisco Lopez-Tapia, Christine Brotherton-Pleiss, Casie Kubota, Jasmine Chen, Marcus Tius, James Turkson. Novel nano-molar small-molecule STAT3 inhibitor series with antitumor activities against human breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4880.

Linker Variation and Structure-Activity Relationship Analyses of Carboxylic Acid-based Small Molecule STAT3 Inhibitors

The molecular determinants for the activities of the reported benzoic acid (SH4-54), salicylic acid (BP-1-102), and benzohydroxamic acid (SH5-07)-based STAT3 inhibitors were investigated to design optimized analogues. All three leads are based on an N-methylglycinamide scaffold, with its two amine groups condensed with three different functionalities. The three functionalities and the CH₂ group of the glycinamide scaffold were separately modified. The replacement of the pentafluorobenzene or cyclohexylbenzene, or replacing the benzene ring of the aromatic carboxylic or hydroxamic acid motif with heterocyclic components (containing nitrogen and oxygen elements) all decreased potency. Notably, the Ala-linker analogues, 1a and 2v, and the Pro-based derivative 5d, all with (R)-configuration at the chiral center, had improved inhibitory activity and selectivity against STAT3 DNA-binding activity in vitro, with IC₅₀ of 3.0 ± 0.9, 1.80 ± 0.94, and 2.4 ± 0.2 μM, respectively. Compounds 1a, 2v, 5d, and other analogues inhibited constitutive STAT3 phosphorylation and activation in human breast cancer and melanoma lines, and blocked tumor cell viability, growth, colony formation, and migration in vitro. Pro-based analogue, 5h, with a relatively polar tetrahydropyranyl (THP) ring, instead of the cyclohexyl, showed improved permeability. In general, the (R)-configuration Pro-based analogs showed the overall best profile, including physicochemical properties (e.g., microsomal metabolic stability, Caco-2 permeability), and in particular, 5d showed improved tumor-cell specificity.

Abstract B137: Novel potent salicylic, benzoic, and benzohydroxamic acid-based small-molecule STAT3 inhibitors induce antitumor effects in breast cancer xenografts

We investigated the molecular determinants for the activity of the previously reported salicylic BP-1-102 (IC50 6.8 ± 2.5 μM), benzoic SH4-54 (IC50 4.4 ± 0.3 μM), and benzohydroxamic acid SH5-07 (IC50 3.9 ± 0.6 μM) small-molecule STAT3 inhibitors in order to derive structurally optimum analogs with improved potency and pharmacokinetic parameters. All three leads are based on N-methylglycinamide scaffold, with its two amine groups condensed with three different functionalities. The three functionalities were separately modified to generate various series of new analogs. The inhibitory activities of the new analogs against STAT3 DNA-binding in vitro were determined by electrophoretic motility shift assay. Some new analogs show dramatically improved potency compared to the corresponding lead compounds. Notably, analogs H098, H127, H142, H145, H152, and H155 showed more than 10-fold improved potency in inhibiting STAT3 DNA-binding activity in vitro, with IC50 of 300 - 600 nM. Using analogs H105 and H120, we show that the new analogs decreased STAT3 DNA-binding activity and phosphorylation at Tyr705 in MDA-MB-231 and MDA-MB-468 cells, two human triple-negative breast cancer lines harboring constitutively active STAT3, within as early as 30 min. Furthermore, the new analogs potently inhibited the growth and viability of the human cancer cells with persistently active STAT3, with IC50 of 1.2 - 2.0 µM. The potent analogs specifically disrupted STAT3 DNA-binding activity in vitro over that of STAT1 and STAT5, and they further showed minimum inhibitory effect on the proliferation of human cancer cells that do not harbor persistently active STAT3. Initial in vivo efficacy study in nude mouse model showed that oral administration of H105 and H120 suppressed the growth of tumor xenografts generated from human breast cancer line harboring constitutively active STAT3. Thus, we have made substantial progress and broken the nanomolar barrier in developing STAT3 inhibitors, and these compounds are the first nanomolar STAT3 inhibitors reported to date that are direct disruptors of STAT3 activation, which show in vivo activity.

Citation Format: Peibin Yue, Francisco Lopez-Tapia, Christine Brotherton-Pleiss, Marcus Tius, James Turkson. Novel potent salicylic, benzoic, and benzohydroxamic acid-based small-molecule STAT3 inhibitors induce antitumor effects in breast cancer xenografts [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B137.

NF-κB inhibitors, unique γ-pyranol-γ-lactams with sulfide and sulfoxide moieties from Hawaiian plant Lycopodiella cernua derived fungus Paraphaeosphaeria neglecta FT462

LC-UV/MS-based metabolomic analysis of the Hawaiian endophytic fungus Paraphaeosphaeria neglecta FT462 led to the identification of four unique mercaptolactated γ-pyranol-γ-lactams, paraphaeosphaerides E-H (1-4) together with one γ-lactone (5) and the methyl ester of compound 2 (11). The structures of the new compounds (1-5 and 11) were elucidated through the analysis of HRMS and NMR spectroscopic data. The absolute configuration was determined by chemical reactions with sodium borohydride, hydrogen peroxide, α-methoxy-α-(trifluoromethyl)phenylacetyl chlorides (Mosher reagents), and DP4 + NMR calculations. All the compounds were tested against STAT3, A2780 and A2780cisR cancer cell lines, E. coli JW2496, and NF-κB. Compounds 1 and 3 strongly inhibited NF-κB with IC50 values of 7.1 and 1.5 μM, respectively.

Anti-proliferative ambuic acid derivatives from Hawaiian endophytic fungus Pestalotiopsis sp. FT172

Five previously undescribed ambuic acid derivatives, pestallic acids A-E and three known analogs were isolated from the cultured broth of Pestalotiopsis sp. FT172. The structures of the pestallic acids A-E were determined through the analysis of HRMS and NMR spectroscopic data. The absolute configurations (ACs) of pestallic acids B-E were assigned by comparison of the experimental electric circular dichroism (ECD) spectra or the optical rotations with those in the literature. All compounds were tested against A2780 and cisplatin resistant A2780 (A2780CisR) cell lines. Pestallic acid E and (+)-ambuic acid showed potent activities with IC₅₀ values from 3.3 to 17.0 μM.

A New N-methoxypyridone from the Co-Cultivation of Hawaiian Endophytic Fungi Camporesia sambuci FT1061 and Epicoccum sorghinum FT1062

A new N-methoxypyridone analog (1), together with four known compounds, was isolated from the co-culture of Hawaiian endophytic fungi Camporesia sambuci FT1061 and Epicoccum sorghinum FT1062. The structure of the new compound was elucidated as 11S-hydroxy-1-methoxyfusaricide (1) by extensive spectroscopic analysis and comparison with the literature. The absolute configuration of 1 was determined by comparison with the experimental and calculated ECD spectra. The absolute configuration of compound 3 was investigated and renamed as (+)-epipyridone by comparison of the optical rotation and CD spectrum with those of 1. The other known compounds were identified as epicoccarine B (2), D8646-2-6 (4), and iso-D8646-2-6 (5). Compounds 4 and 5 showed modest inhibitory activity towards pathogenic fungi. Epicoccarine B (2) inhibited A2780 and TK-10 with an IC₅₀ value of 22 μM.

Bioactive polyprenylated benzophenone derivatives from the fruits extracts of Garcinia xanthochymus

Two new polycyclic prenylated xanthones (1 and 2) and a new phenylpropanoid glycoside (3), along with seven known compounds (4-10) were isolated from the fruits of Garcinia xanthochymus. The structures were elucidated by 1D- and 2D-NMR, and HRMS experiments. The isolates were evaluated for their inhibitory effects against the viability of U251MG glioblastoma and MDA-MB-231 breast cancer cells that harbor an aberrantly active signal transducer and exhibit activation of transcription 3 (STAT3), and compared to normal NIH3T3 mouse fibroblasts. Among the isolates, compounds 1, 2, 5, and 6-9 inhibited the viability of glioma cancer cells with IC₅₀ values in the range of 1.6-6.5μM. Furthermore, treatment of U251MG with 6 and 7 inhibited intracellular STAT3 tyrosine phosphorylation and glioma cell migration in vitro, respectively.

Verbenanone, an octahydro-5H-chromen-5-one from a Hawaiian-Plant Associated Fungus FT431

A new secondary metabolite verbenanone (1) with a unique (4aS,8aS)-octahydro-5H-chromen-5-one moiety has been obtained from the endophytic fungus FT431, which was isolated from the native Hawaiian plant Verbena sp. The structure of compound 1 was characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of compound 1 was determined by Mosher acids. Compound 1 was tested against A2780 and A2780cisR, but it was inactive.

15α-methoxypuupehenol Induces Antitumor Effects In Vitro and In Vivo against Human Glioblastoma and Breast Cancer Models

Studies with 15α-methoxypuupehenol (15α-MP), obtained from the extracts of Hyrtios species, identified putative targets that are associated with its antitumor effects against human glioblastoma and breast cancer. In the human glioblastoma (U251MG) or breast cancer (MDA-MB-231) cells, treatment with 15α-MP repressed pY705Stat3, pErk1/2, pS147CyclinB1, pY507Alk (anaplastic lymphoma kinase), and pY478ezrin levels and induced pS10merlin, without inhibiting pJAK2 (Janus kinase) or pAkt induction. 15α-MP treatment induced loss of viability of breast cancer (MDA-MB-231, MDA-MB-468) and glioblastoma (U251MG) lines and glioblastoma patient-derived xenograft cells (G22) that harbor aberrantly active Stat3, with only moderate or little effect on the human breast cancer, MCF7, colorectal adenocarcinoma Caco-2, normal human lung fibroblast, WI-38, or normal mouse embryonic fibroblast (MEF Stat3^fl/fl) lines that do not harbor constitutively active Stat3 or the Stat3-null (Stat3^-/-) mouse astrocytes. 15α-MP-treated U251MG cells have severely impaired F-actin organization and altered morphology, including the cells rounding up, and undergo apoptosis, compared with a moderate, reversible morphology change observed for similarly treated mouse astrocytes. Treatment further inhibited U251MG or MDA-MB-231 cell proliferation, anchorage-independent growth, colony formation, and migration in vitro while only moderately or weakly affecting MCF7 cells or normal mouse astrocytes. Oral gavage delivery of 15α-MP inhibited the growth of U251MG subcutaneous tumor xenografts in mice, associated with apoptosis in the treated tumor tissues. Results together suggest that the modulation of Stat3, CyclinB1, Alk, ezrin, merlin, and Erk1/2 functions contributes to the antitumor effects of 15α-MP against glioblastoma and breast cancer progression. Mol Cancer Ther; 16(4); 601-13. ©2017 AACR.

A novel nuclear Src and p300 signaling axis controls migratory and invasive behavior in pancreatic cancer

The presence of Src in the nuclear compartment has been previously reported, although its significance has remained largely unknown. We sought to delineate the functions of the nuclear pool of Src within the context of malignant progression. Active Src is localized within the nuclei of human pancreatic cancer cells and mouse fibroblasts over-expressing c-Src where it is associated with p300. Nuclear Src additionally promotes the tyrosine phosphorylation of p300 in pancreatic cancer Panc-1 cells. Src, together with p300, is associated with the high-mobility group AT-hook (HMGA)2 and SET and MYND domain-containing protein (SMYD)3 gene promoters and regulates their expression in a Src-dependent manner. These nuclear Src-dependent events correlate with anchorage-independent soft-agar growth and the migratory properties in both pancreatic Panc-1 cells and mouse fibroblasts over-expressing Src. Moreover, analyses of human pancreatic ductal adenocarcinoma (PDAC) tumor tissues detected the association of nuclear Src with the HMGA2 and SMYD3 gene promoters. Our findings for the first time show the critical importance of nuclear Src and p300 function in the migratory properties of pancreatic cancer cells. Further, data together identify a previously unknown role of nuclear Src in the regulation of gene expression in association with p300 within the context of cells harboring activated or over-expressing Src. This novel mechanism of nuclear Src-p300 axis in PDAC invasiveness and metastasis may provide an opportunity for developing more effective early clinical interventions for this lethal disease.

Active Src is complexed with and phosphorylates p300 in the nucleus, and the complex is bound to HMGA2 and SMYD3 genes, thereby regulating their expression to promote pancreatic tumor cell migration and invasiveness.

Abstract LB-058: Linker variation and structure-activity relationship analyses of salicylic, benzoic and hydroxamic acid-based small molecule Stat3 inhibitors

Benzoic acid, salicylic acid and hydroxamic acid-based small molecules have been reported that inhibit Stat3 activation. However, the structural basis for their Stat3-inhibitory activities are not clearly defined. To investigate the molecular determinants for activity and to derive structurally optimized analogs of improved pharmacokinetic parameters and potency, we conducted a computer-aided molecule optimization program and synthesized new analogs of the previously reported lead Stat3 inhibitors, BP-1-102 (IC50, 6.8 ± 2.5), SH4-54 (IC50 4.4 ± 0.3), and SH5-07 (IC50 3.9 ± 0.6). All three leads are based on N-methylglycinamide scaffold with its two amine moieties condensed with three different functionalities. The three functionalities or the CH2 group of the glycolamide scaffold were separately modified to generate a series of compounds, some of which show improved potency compared to the corresponding parental compounds. Specifically, H012, H070 and H072 had improved inhibitory activity against Stat3 DNA-binding activity in vitro, with IC50 of 3.0 ± 0.9, 2.4 ± 0.4, and 2.2 ± 0.9 μM, respectively. The replacement of the pentafluorobenzene or the cyclohexylbenzene with other components was detrimental to activity and led to decreased potency of the new analogues, as did the substitution of the benzene of the pTyr-mimetic moiety with heterocyclic components containing nitrogen and oxygen elements. Pharmacokinetic study showed that analog H058 has improved permeability in Caco-2 bidirectional permeability studies, compared to the lower relative permeability of the lead agents. Ala-based analogs, such as H048 and H058, were low in microsomal stability, presumably due to the labile methyl groups of the Ala. Select active analogs inhibited constitutive Stat3 activation and the DNA-binding activity of Stat3 in cancer cells, and they further decreased the growth, colony formation, and migration of human cancer cells harboring persistently active Stat3. Studies together demonstrate a significant progress towards developing a more suitable Stat3 inhibitor with drug-like features. Additional efforts are focused on refining the physicochemical properties to further improve the activity and efficacy and ultimately furnish suitable Stat3-inhibiting candidates for clinical application.

Citation Format: Peibin Yue, Francisco Lopez-Tapia, Christine Brotherton-Pleiss, Marcus Tius, James Turkson. Linker variation and structure-activity relationship analyses of salicylic, benzoic and hydroxamic acid-based small molecule Stat3 inhibitors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-058.

Abstract 3712: The relationship of Procollagen alpha 1 type 1 (Col1A1) / DDR2 signaling in malignant glioma and sensitivity to STAT 3/5 inhibitor

We have previously shown that Procollagen alpha 1 type 1 (Col1A1) is found in low and intermediate grade glioma and in less aggressive glioblastoma multiforme (GBM) (Cancer Invest. 23:577, 2005). However, these tumor cells are more prone to ER stress -inducing agents such as Befeldine (BFA) which block the transport of Procollagen to the cell surface. We also found that GBM cells which possess Col1A1 also express DDR2. The role of Col1A1/ DDR2 signaling in glioma is not known. We have used three GBM cell lines: Glioma1 established in our laboratory from a patient who progressed from grade 3 to grade 4, U-118, A-172 and U-373 to study this signaling pathway. Both Glioma1 and U-118 express Col1A1 and DDR1 and 2. A-172 and U-373 do not express Col1A1 but express both DDR2. U-373 does not express HSP47 which is an essential protein to fold collagen. In order to define the function of DDR2/ Col1A1 in GBM, we have used knock down COL1A1 and DDR2. Silencing Col1A1 leads to a significant increase in invasiveness by Matrigel assay which indicated that Col1A1 is important in preventing invasion in GBM and hence is found more in low and intermediate grade glioma. However, it has minimal effect on cell cycle or cell proliferation. Next, we have silenced DDR2 in all 4 cell lines and studied the biochemical changes. We found that silencing DDR2 does not affect cell proliferation, cell death or cell cycle. However, it does affect the sensitivity to BFA. In cell lines which possess Col1A1, the cell viability increased by 20 -30% (p <0.05). In contrast, cell lines which do not express Col1A1, the cell viability decreased by 25-30% (p<0.01). However, there is no difference in sensitivity to the DNA damaging agent cisplatin. Thus, DDR2 may function differently depending on the presence of Col1A1. To explore this further, we have performed a limited phoshoprotein kinase array in Glioma 1 with siCol1A1 or siDDR2. We found increase in STAT3, 5 and STAT6 upon silencing either Col1A1 or DDR2 which is further confirmed by immunoblot in Glioma 1 for pSTAT 3 and 5. We then tested the antitumor effect of STAT3/5 inhibitor (SH4-54) a benzoic acid based inhibitor (provided by Dr. James Turkson) which interferes with the SH2 and DNA binding domains as well as tyr705 phosphorylation in Glioma1 and U-118 w/wo SiCol1A1. At 0.5 uM the cell viability in Glioma 1 is 55.65 + 1.35 and 74.2 + 4.6 in U-118 while SiCol1A1 it decreased to 44.5 + 3.53% in Glioma 1 and 58.2+ 1.9, respectively, with minimal activity in A-172 which does not possess Col1A1. In contrast, there is no effect with another commercially available STAT 3 inhibitor S31-201 which only interferes with DNA binding domain. Overall, our data suggest that Col1A1/DDR2/ STAT signaling may be important in certain GBM cell lines and can be exploited for future treatment in brain tumor (Supported by Wanfang Hospital-Taipei Medical University Fellowship and VA Research Fund).

Citation Format: Shumei Chen, Chunjing Wu, Ying-Ying Li, Medhi Wangpaichitr, Ronald J. Benveniste, James Turkson, Niramol Savaraj, Lynn G. Feun. The relationship of Procollagen alpha 1 type 1 (Col1A1) / DDR2 signaling in malignant glioma and sensitivity to STAT 3/5 inhibitor. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3712.

Abstract 4847: Discovery, semisynthesis, and structure-activity relationship studies of hirsutinolide derivatives as new STAT3 inhibitors and anti-glioma agents

Clinically, natural product has played a pivotal role in anticancer drug discovery and development. Cancer chemotherapy and/or radiotherapy due to glioma treatment are not ideal, frequently cause unwanted adverse effects, and justify further research and development of alternative, novel, safe, and effective agents. In our continued efforts to identify new signal transducer and activator of transcription 3 (STAT3) and antiglioma agents with enhanced efficacy and specificity, we have initiated a collaborative and multidisciplinary natural product drug discovery project and the goal was to isolate, semisynthesize, and evaluate the potential of Vernonia cinerea-derived phytochemicals as STAT3 inhibitors with therapeutic remedy of human glioma and may be even more effective than the existing ones. To date, our preliminary studies have been conducted and resulted in the discovery of a class of sesquiterpene lactone hirsutinolide series with an á,â-unsaturated-ã-lactone ring as new STAT3 inhibitors. Specifically, on the basis of encouraging biological data and to expand the existing structure activity relationship (SAR) of isolated natural hirsutinolide analogues, chemical modifications were performed using conventional Steglich esterification protocol to produce a series of semisynthetic hirsutinolide derivatives in moderate to high yields. Thus far, biological evaluation revealed that several semisynthetic analogues showed low micromolar inhibitory activities against constitutively-active STAT3 and malignant glioma phenotype. SAR showed that a bulky and lipophilic ester functionality at position 13 is essential for STAT3 inhibition as well as whole cell based anticancer activity. A lipophilic side chain at position 8 also plays an important role in anticancer activity and may contribute a detrimental effect on specificity. In addition, the methoxy group at position 1 enhances the cell-type specificity and selectivity. Finally, selected promising lead candidates also demonstrated in vivo efficacy following oral gavage delivery, inhibiting human glioma tumor growth in subcutaneous mouse xenografts. Together, natural and chemically modified hirsutinolide-type sesquiterpene lactones represent a promising natural product class of new anticancer agents for the treatment of malignant human glioma.

Citation Format: Mingming Zhang, Ui Joung Youn, Gabriella Miklossy, Supakit Wongwiwatthananukit, James Turkson, Leng Chee Chang, Dianqing Sun. Discovery, semisynthesis, and structure-activity relationship studies of hirsutinolide derivatives as new STAT3 inhibitors and anti-glioma agents. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4847.

Eremophilane sesquiterpenes from Hawaiian endophytic fungus Chaetoconis sp. FT087

Seven sesquiterpene derivatives, including chaetopenoids A-F and dendryphiellin A1, and 6-methyl-(2E, 4E, 6S) octadienoic acid were isolated from the culture broth of Chaetoconis sp. FT087. Their structures were determined through the analysis of HRMS and NMR spectroscopic data. The absolute configurations of chaetopenoids A-D were elucidated by comparison of their CD and optical rotation data with those in the literature. Chaetopenoids A-C and E belong to the eremophilane type of sesquiterpenoids, while chaetopenoids D and F and dendryphiellin A1 have a trinor-eremophilane skeleton. All compounds were tested against A2780 and cisplatin resistant A2780CisR cell lines, and dendryphiellin A1 was moderately active with IC50 values of 6.6 and 9.1 μg/mL, respectively.

Meroterpenoids with Antiproliferative Activity from a Hawaiian-Plant Associated Fungus Peyronellaea coffeae-arabicae FT238

Three unusual polyketide-sesquiterpene metabolites peyronellins A-C (1-3), along with the new epoxyphomalin analog 11-dehydroxy epoxyphomalin A (4), have been isolated from the endophytic fungus Peyronellaea coffeae-arabicae FT238, which was isolated from the native Hawaiian plant Pritchardia lowreyana. The structures of compounds 1-4 were characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of the compounds was determined by electronic circular dichroism (ECD). Compound 4 showed antiproliferative activity with an IC50 of 0.5 μM against OVCAR3, and it also strongly inhibited Stat3 at 5 μM.

Bromotyrosine-derived metabolites from an Indonesian marine sponge in the family Aplysinellidae (Order Verongiida)

Seven new bromotyrosine-derived metabolites, purpuramine M-N (1-2), araplysillin VII-XI (3-7) and six known compounds (8-13) were isolated from an Indonesian sponge belonging to the family Aplysinellidae (Order Verongiida). The structures of the new compounds were determined by extensive NMR experiments and mass spectrometric measurements. These compounds were screened against BACE1 and five cancer cell lines.

Hirsutinolide Series Inhibit Stat3 Activity, Alter GCN1, MAP1B, Hsp105, G6PD, Vimentin, TrxR1, and Importin α-2 Expression, and Induce Antitumor Effects against Human Glioma

We report that hirsutinolide series, 6, 7, 10, 11, 20, and 22, and the semisynthetic analogues, 30, 31, 33, and 36, inhibit constitutively active signal transducer and activator of transcription (Stat)3 and malignant glioma phenotype. A position 13 lipophilic ester group is required for activity. Molecular modeling and nuclear magnetic resonance structural analyses reveal direct hirsutinolide:Stat3 binding. One-hour treatment of cells with 6 and 22 also upregulated importin subunit α-2 levels and repressed translational activator GCN1, microtubule-associated protein (MAP)1B, thioredoxin reductase (TrxR)1 cytoplasmic isoform 3, glucose-6-phosphate 1-dehydrogenase isoform a, Hsp105, vimentin, and tumor necrosis factor α-induced protein (TNAP)2 expression. Active hirsutinolides inhibited anchorage-dependent and three-dimensional spheroid growth, survival, and migration of human glioma lines and glioma patients' tumor-derived xenograft cells harboring constitutively active Stat3. Oral gavage delivery of 6 or 22 inhibited human glioma tumor growth in subcutaneous mouse xenografts. The inhibition of Stat3 signaling represents part of the hirsutinolide-mediated mechanisms to induce antitumor effects.

A Resveratrol Analogue Promotes ERKMAPK-Dependent Stat3 Serine and Tyrosine Phosphorylation Alterations and Antitumor Effects In Vitro against Human Tumor Cells

(E)-4-(3,5-dimethoxystyryl)phenyl acetate (Cmpd1) is a resveratrol analog that preferentially inhibits glioma, breast, and pancreatic cancer cell growth, with IC50 values of 6-19 μM. Notably, the human U251MG glioblastoma tumor line is the most sensitive, with an IC50 of 6.7 μM, compared with normal fibroblasts, which have an IC50 > 20 μM. Treatment of U251MG cells that harbor aberrantly active signal transducer and activator of transcription (Stat) 3 with Cmpd1 suppresses Stat3 tyrosine705 phosphorylation in a dose-dependent manner in parallel with the induction of pserine727 Stat3 and extracellular signal-regulated kinase/mitogen-activated protein kinase 1/2 (pErk1/2(MAPK)). Inhibition of pErk1/2(MAPK) induction by the mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] blocked both the pserine727 Stat3 induction and ptyrosine705 Stat3 suppression by Cmpd1, indicating dependency on the mitogen-activated protein/extracellular signal-regulated kinase kinase-Erk1/2(MAPK) pathway for Cmpd1-induced modulation of Stat3 signaling. Cmpd1 also blocked epidermal growth factor-stimulated pStat1 induction, whereas upregulating pSrc, pAkt, p-p38, pHeat shock protein 27, and pmammalian target of rapamycin levels. However, pJanus kinase 2 and pEpidermal growth factor receptor levels were not significantly altered. Treatment of U251MG cells with Cmpd1 reduced in vitro colony formation, induced cell cycle arrest in the G2/M phase and cleavage of caspases 3, 8, and 9 and poly(ADP ribose) polymerase, and suppressed survivin, myeloid cell leukemia 1, Bcl-xL, cyclin D1, and cyclin B1 expression. Taken together, these data identify a novel mechanism for the inhibition of Stat3 signaling by a resveratrol analog and suggest that the preferential growth inhibitory effects of Cmp1 occur in part by Erk1/2(MAPK)-dependent modulation of constitutively active Stat3.

A New Metabolite with a Unique 4-Pyranone-γ-Lactam-1,4-Thiazine Moiety from a Hawaiian-Plant Associated Fungus

An endophytic fungus Paraphaeosphaeria neglecta FT462 isolated from the Hawaiian-plant Lycopodiella cernua (L.) Pic. Serm produced one unusual compound (1, paraphaeosphaeride A) with the 4-pyranone-γ-lactam-1,4-thiazine moiety, along with two new compounds (2 and 3, paraphaeosphaerides B and C, respectively) and the known compound (4). Compounds 1-3 were characterized by NMR and MS spectroscopic analysis. The absolute configuration of the 3-position of compound 1 was determined as S by electronic circular dichroism (ECD) calculations. Compound 3 also showed STAT3 inhibition at 10 μM.

Hydroxamic Acid and Benzoic Acid-Based STAT3 Inhibitors Suppress Human Glioma and Breast Cancer Phenotypes In Vitro and In Vivo

STAT3 offers an attractive target for cancer therapy, but small-molecule inhibitors with appealing pharmacologic properties have been elusive. Here, we report hydroxamic acid-based and benzoic acid-based inhibitors (SH5-07 and SH4-54, respectively) with robust bioactivity. Both inhibitors blocked STAT3 DNA-binding activity in vitro and in human glioma, breast, and prostate cancer cells and in v-Src-transformed murine fibroblasts. STAT3-dependent gene transcription was blocked along with Bcl-2, Bcl-xL, Mcl-1, cyclin D1, c-Myc, and survivin expression. Nuclear magnetic resonance analysis of STAT3-inhibitor complexes defined interactions with the SH2 and DNA-binding domains of STAT3. Ectopic expression of the SH2 domain in cells was sufficient to counter the STAT3-inhibitory effects of SH4-54. Neither compound appreciably affected STAT1 or STAT5 DNA-binding activities, STAT3-independent gene transcription, or activation of a panel of oncogenic kinases in malignant cells. Each compound decreased the proliferation and viability of glioma, breast, and prostate cancer cells and v-Src-transformed murine fibroblasts harboring constitutively active STAT3. Further, in mouse xenograft models of glioma and breast cancer, administration of SH5-07 or SH4-54 effectively inhibited tumor growth. Our results offer preclinical proof of concept for SH5-07 and SH4-54 as candidates for further development as cancer therapeutics.

Abstract 1783: Puupehenol natural product inhibits STAT3 signaling and induces antitumor cell effects in vitro against human glioblastoma cells

Glioblastoma multiforme (GBM) is a malignant brain tumor that lacks effective therapeutics and has a high mortality rate. Constitutively-activated signal transducer and activator of transcription 3 (STAT3) protein is prevalent and implicated in GBM phenotype and represents a valid anti-GBM target. To discover novel STAT3 inhibitors suitable for GBM therapy, natural product extracts were investigated. Whole extracts from marine organisms were first screened for effects against cell viability using the human glioma model line, U251MG that harbors aberrantly-active STAT3 and normal fibroblasts that do not. The screening campaign identified the puupehenol, CC-1-2 from the whole extracts of leiodermatium sp as a bioactive compound that suppressed U251MG cell viability, with an IC50 4.1±0.1 µM, compared to an IC50 value of 7.3±0.3 µM against normal NIH3T3 mouse fibroblasts. Western blot analysis showed pSTAT3 levels in U251MG cells substantially decreased in a time-dependent manner in response to CC-1-2. Decreased pSTAT3 in treated cells occurred in parallel with partial suppression of both phospho- Janus kinase (Jak) 2 and pSrc levels and no induction of protein tyrosine phosphatase, PTP1B. Phosphorylated extracellular signal-regulated kinase (Erk) 1/2 levels also decreased in time-dependent manner, while pAkt remained unchanged in U251MG cells under the same treatment conditions. Furthermore, treatment of U251MG cells with CC-1-2 led to dramatic morphological changes that occurred in a dose- and time-dependent manner, compared to minimal changes observed for similarly-treated MCF-7 breast cancer cells that do not harbor aberrantly-active STAT3. Colony survival assay of U251MG cells revealed single treatment with 1-10 µM CC-1-2 decreased colony sizes and numbers in a dose-dependent manner, compared to moderate effects on MCF-7. In vitro wound-healing assay further showed reduced U251MG cell migration into the denuded area in response to CC-1-2 treatment. CC-1-2 further induced apoptosis in U251MG cells in a dose-dependent manner and suppressed the expression of c-Myc, Cyclin D1, and Bcl-2 levels, which are known STAT3-regulated genes. Studies together identify CC-1-2 as a natural product inhibitor of STAT3 that preferentially induces antitumor cell effects against human glioblastoma cells.

Citation Format: Tyvette S. Hilliard, Christopher Chock, Philip Williams, James Turkson. Puupehenol natural product inhibits STAT3 signaling and induces antitumor cell effects in vitro against human glioblastoma cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1783. doi:10.1158/1538-7445.AM2014-1783

Abstract 3801: Small molecule inhibitor of Stat3 induces antitumor cell effects in vitro and antitumor effects in vivo against human glioma or breast cancer model

Aberrant activation of signal transducer and activator of transcription 3 (Stat3) is prevalent in many human cancers. Compelling evidence shows that constitutively-active Stat3 constitutes a point of convergence in oncogenic tyrosine kinase signaling, functioning as a master regulator of events crucial for tumorigenesis and malignant progression. We show herein that the small-molecule, SH5-07 abrogates constitutive activation of Stat3 and Stat3-dependent functions in human glioma and breast cancer cells. SH5-07 inhibits in vitro Stat3 DNA-binding activity with an IC50 value of 3.9 μM. Treatment of human glioma U251MG and breast cancer MDA-MB-231 cells that harbor aberrantly-active Stat3 with low micromolar SH5-07 blocks Stat3 phosphorylation, DNA-binding, and transcriptional activities in a time and dose-dependent manner. By contrast, SH5-07 shows little or no effect on the induction of pJAK2, pSrc, pErk1/2, and pShc in glioma and breast cancer cells. SH5-07 preferentially inhibited viability of human glioma and breast cancer cells that harbor aberrant Stat3 activity, with IC50 of 1.1-5.2 µM, compared to IC50 of 6.0-10.8 µM for cells that do not. Inhibition of aberrantly-active Stat3 by SH5-07 preferentially suppresses the anchorage-dependent and independent growth, induces apoptosis, and blocks migration and invasion in vitro of human glioma and breast cancer cells that harbor constitutively-active Stat3. Moreover, oral administration of SH5-07 inhibits the growth of human breast tumor xenografts in mice. Data together indicates SH5-07 is a promising small-molecule Stat3 inhibitor and a suitable drug candidate for clinical development.

Citation Format: Peibin Yue, Francisco Lopez-Tapia, Marcus Tius, James Turkson. Small molecule inhibitor of Stat3 induces antitumor cell effects in vitro and antitumor effects in vivo against human glioma or breast cancer model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3801. doi:10.1158/1538-7445.AM2014-3801

Abstract 2694: Novel sesquiterpene lactones derived from Vernonia cinerea inhibit STAT3 activity and suppress human glioblastoma phenotype

Constitutively-active STAT3 is prevalent in glioblastoma multiforme, breast cancer and many other human tumors and is a valid target for the discovery of novel anticancer therapeutics. Screening of whole plant extracts from Vernonia cinerea identified sesquiterpene lactones of the hirsutinolide type that inhibit aberrant STAT3 activity and suppress human glioma phenotype in vitro and in vivo. Compounds 6, 10, 20 and 22 suppressed the viability of human glioma, U251MG cells that harbor aberrantly-active STAT3, with IC50 of 2.4-6 µM. Treatment of U251MG cells with any of the four natural product agents inhibited STAT3 phosphorylation in a time-dependent manner, with little or no effects on pErk1/2 and pAkt levels. By contrast, other hirsutinolides, including compounds 8, 9, 11, 18, 19 and 28 showed modest or undetectable effects on U251MG cell viability or on pSTAT3 in U251MG cells. Furthermore, treatment with compounds 6, 10 or 22 had moderate or no effects on phospho-JAK2 or phospho-Src or on the protein tyrosine phosphatase, PTP1B level, as measured by Western blot. Moreover, combined treatment with sodium orthovanadate had minimal effect on compound 6-induced decrease in pSTAT3 levels, altogether suggesting that protein tyrosine phosphatases are less likely to be the primary mechanism for down-regulation of pSTAT3 in treated U251MG cells. By contrast, co-treatment with compund 6 repressed the robust induction of pSTAT3 levels by sodium orthovanadate. Furthermore, treatment with compound 6, 10, 20 or 22 inhibited colony formation and the migration of U251MG cells in vitro, and repressed the expression of STAT3 regulated genes, including Mcl-1 in U251MG cells. In vivo anti-tumor efficacy studies of compound 6 revealed dose-dependent inhibition of the growth of human glioma tumor xenografts in mice. Our studies have identified natural product-based small molecules that potently inhibit STAT3 activity and preferentially induce antitumor cell effects in vitro and antitumor response in vivo against human glioma.

Citation Format: Gabriella Miklossy, Ui Joung Youn, Peibin Yue, Leng Chee Chang, James Turkson. Novel sesquiterpene lactones derived from Vernonia cinerea inhibit STAT3 activity and suppress human glioblastoma phenotype. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2694. doi:10.1158/1538-7445.AM2014-2694

Bioactive sesquiterpene lactones and other compounds isolated from Vernonia cinerea

Four new sesquiterpene lactones, 8α-(2'Z-tigloyloxy)-hirsutinolide (1), 8α-(2'Z-tigloyloxy)-hirsutinolide-13-O-acetate (2), 8α-(4-hydroxytigloyloxy)-hirsutinolide (3), and 8α-hydroxy-13-O-tigloyl-hirsutinolide (4), along with seven known derivatives (5-11), three norisoprenoids (12-14), a flavonoid (15), and a linoleic acid derivative (16), were isolated from the chloroform partition of a methanol extract from the combined leaves and stems of Vernonia cinerea. Their structures were established by 1D and 2D NMR, UV, and MS analyses. Compounds 1-16 were evaluated for their inhibitory effects against the viability of U251MG glioblastoma and MDA-MB-231 breast cancer cells that harbour aberrantly-active STAT3, compared to normal NIH3T3 mouse fibroblasts that show no evidence of activated STAT3. Among the isolates, compounds 2 and 7 inhibited the aberrant STAT3 activity in glioblastoma or breast cancer cells. Further, compounds 7 and 8 inhibited viability of all three cell lines, compounds 2, 4, and 9 predominantly inhibited the viability of the U251MG glioblastoma cell line.

Abstract 3253: A novel small-molecule inhibitor of Stat3 induces antitumor cell effects in human glioma and breast cancer cells

Constitutive activation of Stat3, a member of signal transducer and activator of transcription (Stat) family of proteins, occurs with a high frequency in human tumors and contributes to carcinogenesis and tumor progression. Compelling evidence shows aberrant activation of Stat3 constitutes a point of convergence in oncogenic tyrosine kinase signaling, functioning as a master regulator of events crucial for tumorigenesis and malignant progression. We present a series of novel small-molecules that abrogate constitutive activation of Stat3 in human tumors, including glioma and breast cancer. The small-molecule, SH5-07, inhibits in vitro Stat3 DNA-binding activity, with IC50 value of 3.9 μM. Further, treatment with SH5-07 induces dose-dependent inhibition of constitutively-active Stat3 in human glioma U251MG and U373MG and breast cancer MDA-MB-231 cells. Moreover, treatment with low micromolar SH5-07 of U251MG, U373MG, and MDA-MB-231 cells blocks constitutive Stat3 phosphorylation, DNA-binding, and transcriptional activities by as early as 30 minutes. Furthermore, the inhibition of aberrantly-active Stat3 by SH5-07 blocks the anchorage-dependent and independent growth, survival, migration, and invasion in vitro of human glioma and breast cancer cells. Data together indicates SH5-07 is a promising small-molecule Stat3 inhibitor and a suitable drug candidate for clinical development.

Citation Format: Peibin Yue, Sina Haftchenary, Patrick T. Gunning, James Turkson. A novel small-molecule inhibitor of Stat3 induces antitumor cell effects in human glioma and breast cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3253. doi:10.1158/1538-7445.AM2013-3253

Buffer-stable chitosan-polyglutamic acid hybrid nanoparticles for biomedical applications

In spite of their attractive features, widespread biomedical applications of CS nanoparticles are yet to be realized due to their poor stability in physiological conditions, such as in buffer system at pH 7.4. Buffer-stable chitosan-based hybrid NPs (HNPs) are reported and characterized. Buffer stability is achieved by introducing polyglutamic acid to chitosan. The effect of PGA to CS molar ratio and crosslinking on HNP integrity, buffer stability, and biodegradability are studied. Preliminary in vitro studies are carried out to evaluate targeted uptake efficiency of folate conjugated HNPs. Successful demonstration of buffer stability and cancer cell targeting by HNPs achieves important milestones for chitosan-based nanoparticle technology.

Sensitization of pancreatic cancer cells to radiation by cerium oxide nanoparticle-induced ROS production

Side effect of radiation therapy (RT) remains the most challenging issue for pancreatic cancer treatment. In this report we determined whether and how cerium oxide nanoparticles (CONPs) sensitize pancreatic cancer cells to RT. CONP pretreatment enhanced radiation-induced reactive oxygen species (ROS) production preferentially in acidic cell-free solutions as well as acidic human pancreatic cancer cells. In acidic environments, CONPs favor the scavenging of superoxide radical over the hydroxyl peroxide resulting in accumulation of the latter whereas in neutral pH CONPs scavenge both. CONP treatment prior to RT markedly potentiated the cancer cell apoptosis both in culture and in tumors and the inhibition of the pancreatic tumor growth without harming the normal tissues or host mice. Taken together, these results identify CONPs as a potentially novel RT-sensitizer as well as protectant for improving pancreatic cancer treatment.

FROM THE CLINICAL EDITOR

Pancreatic tumors remain some of the most notoriously treatment-unresponsive malignancies. Cerium oxide nanoparticles may be capable of sensitizing such cells to radiotherapy, as demonstrated in this study.