James R. Fuchs

Novel STAT3 Phosphorylation Inhibitors Exhibit Potent Growth-Suppressive Activity in Pancreatic and Breast Cancer Cells

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.

Pancreatic Cancer-Associated Stellate Cells Promote Differentiation of Myeloid-Derived Suppressor Cells in a STAT3-Dependent Manner

Pancreatic stellate cells (PSC) are a subset of pancreatic cancer-associated fibroblasts. These cells provide prosurvival signals to tumors; however, little is known regarding their interactions with immune cells within the tumor microenvironment. We hypothesized that factors produced by human PSC could enhance myeloid-derived suppressor cell (MDSC) differentiation and function, which promotes an immunosuppressive microenvironment. Primary PSC cell lines (n = 7) were generated from human specimens and phenotypically confirmed via expression of vimentin, α-smooth muscle actin (α-SMA), and glial fibrillary acidic protein (GFAP). Luminex analysis indicated that PSC but not human fetal primary pancreatic fibroblast cells (HPF; negative controls) produced MDSC-promoting cytokines [interleukin (IL-6), VEGF, macrophage colony-stimulating factor (M-CSF) ] and chemokines (SDF-1, MCP-1). Culture of peripheral blood mononuclear cells [peripheral blood mononuclear cell (PBMC), n = 3 donors] with PSC supernatants or IL-6/granulocyte macrophage colony-stimulating factor (GM-CSF; positive control) for 7 days promoted PBMC differentiation into an MDSC (CD11b+CD33+) phenotype and a subpopulation of polymorphonuclear CD11b+CD33+CD15+ cells. The resulting CD11b+CD33+ cells functionally suppressed autologous T-lymphocyte proliferation. In contrast, supernatants from HPF did not induce an MDSC phenotype in PBMCs. Culture of normal PBMCs with PSC supernatants led to STAT3 but not STAT1 or STAT5 phosphorylation. IL-6 was an important mediator as its neutralization inhibited PSC supernatant-mediated STAT3 phosphorylation and MDSC differentiation. Finally, the FLLL32 STAT3 inhibitor abrogated PSC supernatant-mediated MDSC differentiation, PSC viability, and reduced autocrine IL-6 production indicating these processes are STAT3 dependent. These results identify a novel role for PSC in driving immune escape in pancreatic cancer and extend the evidence that STAT3 acts as a driver of stromal immunosuppression to enhance its interest as a therapeutic target.

Multimode, Cooperative Mechanism of Action of Allosteric HIV-1 Integrase Inhibitors

Background: 2-(Quinolin-3-yl)-acetic-acid derivatives target HIV-1 integrase and inhibit viral replication. Results: The compounds are allosteric integrase inhibitors (ALLINIs) that block integrase interactions with viral DNA and its cellular cofactor LEDGF and cooperatively inhibit HIV-1 replication. Conclusion: ALLINIs block multiple steps of HIV-1 integration. Significance: These new properties of ALLINIs will facilitate their further development as potent antiretroviral compounds. The multifunctional HIV-1 enzyme integrase interacts with viral DNA and its key cellular cofactor LEDGF to effectively integrate the reverse transcript into a host cell chromosome. These interactions are crucial for HIV-1 replication and present attractive targets for antiviral therapy. Recently, 2-(quinolin-3-yl) acetic acid derivatives were reported to selectively inhibit the integrase-LEDGF interaction in vitro and impair HIV-1 replication in infected cells. Here, we show that this class of compounds impairs both integrase-LEDGF binding and LEDGF-independent integrase catalytic activities with similar IC50 values, defining them as bona fide allosteric inhibitors of integrase function. Furthermore, we show that 2-(quinolin-3-yl) acetic acid derivatives block the formation of the stable synaptic complex between integrase and viral DNA by allosterically stabilizing an inactive multimeric form of integrase. In addition, these compounds inhibit LEDGF binding to the stable synaptic complex. This multimode mechanism of action concordantly results in cooperative inhibition of the concerted integration of viral DNA ends in vitro and HIV-1 replication in cell culture. Our findings, coupled with the fact that high cooperativity of antiviral inhibitors correlates with their increased instantaneous inhibitory potential, an important clinical parameter, argue strongly that improved 2-(quinolin-3-yl) acetic acid derivatives could exhibit desirable clinical properties.

Structure–activity relationship studies of curcumin analogues

Two series of curcumin analogues, a total of twenty-four compounds, were synthesized and evaluated. The most potent compound, compound 23, showed potent growth inhibitory activities on both prostate and breast cancer lines with IC(50) values in sub-micromolar range, fifty times more potent than curcumin. Curcumin analogues might be potential anti-tumor agents for breast and prostate cancers.

The small molecule curcumin analog FLLL32 induces apoptosis in melanoma cells via STAT3 inhibition and retains the cellular response to cytokines with anti-tumor activity

BackgroundWe characterized the biologic effects of a novel small molecule STAT3 pathway inhibitor that is derived from the natural product curcumin. We hypothesized this lead compound would specifically inhibit the STAT3 signaling pathway to induce apoptosis in melanoma cells.ResultsFLLL32 specifically reduced STAT3 phosphorylation at Tyr705 (pSTAT3) and induced apoptosis at micromolar amounts in human melanoma cell lines and primary melanoma cultures as determined by annexin V/propidium iodide staining and immunoblot analysis. FLLL32 treatment reduced expression of STAT3-target genes, induced caspase-dependent apoptosis, and reduced mitochondrial membrane potential. FLLL32 displayed specificity for STAT3 over other homologous STAT proteins. In contrast to other STAT3 pathway inhibitors (WP1066, JSI-124, Stattic), FLLL32 did not abrogate IFN-γ-induced pSTAT1 or downstream STAT1-mediated gene expression as determined by Real Time PCR. In addition, FLLL32 did not adversely affect the function or viability of immune cells from normal donors. In peripheral blood mononuclear cells (PBMCs), FLLL32 inhibited IL-6-induced pSTAT3 but did not reduce signaling in response to immunostimulatory cytokines (IFN-γ, IL 2). Treatment of PBMCs or natural killer (NK) cells with FLLL32 also did not decrease viability or granzyme b and IFN-γ production when cultured with K562 targets as compared to vehicle (DMSO).ConclusionsThese data suggest that FLLL32 represents a lead compound that could serve as a platform for further optimization to develop improved STAT3 specific inhibitors for melanoma therapy.

Modulation of DNA Methylation by a Sesquiterpene Lactone Parthenolide

Hypermethylation of 5′-cytosine-guanosine islands of tumor suppressor genes resulting in their silencing has been proposed to be a hallmark of various tumors. Modulation of DNA methylation with DNA methylation inhibitors has been shown to result in cancer cell differentiation or apoptosis and represents a novel strategy for chemotherapy. Currently, effective DNA methylation inhibitors are mainly limited to decitabine and 5-azacytidine, which still show unfavorable toxicity profiles in the clinical setting. Thus, discovery and development of novel hypomethylating agents, with a more favorable toxicity profile, is essential to broaden the spectrum of epigenetic therapy. Parthenolide, the principal bioactive sesquiterpene lactone of feverfew, has been shown to alkylate Cys38 of p65 to inhibit nuclear factor-κB activation and exhibit anti-tumor activity in human malignancies. In this article, we report that parthenolide 1) inhibits DNA methyltransferase 1 (DNMT1) with an IC50 of 3.5 μM, possibly through alkylation of the proximal thiolate of Cys1226 of the catalytic domain by its γ-methylene lactone, and 2) down-regulates DNMT1 expression possibly associated with its SubG1 cell-cycle arrest or the interruption of transcriptional factor Sp1 binding to the promoter of DNMT1. These dual functions of parthenolide result in the observed in vitro and in vivo global DNA hypomethylation. Furthermore, parthenolide has been shown to reactivate tumor suppressor HIN-1 gene in vitro possibly associated with its promoter hypomethylation. Hence, our study established parthenolide as an effective DNA methylation inhibitor, representing a novel prototype for DNMT1 inhibitor discovery and development from natural structural-diversified sesquiterpene lactones.

STAT3 signaling pathway is necessary for cell survival and tumorsphere forming capacity in ALDH+/CD133+ stem cell-like human colon cancer cells

Persistent activation of Signal Transducers and Activators of Transcription 3 (STAT3) is frequently detected in colon cancer. Increasing evidence suggests the existence of a small population of colon cancer stem or cancer-initiating cells may be responsible for tumor initiation, metastasis, and resistance to chemotherapy and radiation. Whether STAT3 plays a role in colon cancer-initiating cells and the effect of STAT3 inhibition is still unknown. Flow cytometry was used to isolate colon cancer stem-like cells from three independent human colon cancer cell lines characterized by both aldehyde dehydrogenase (ALDH)-positive and CD133-positive subpopulation (ALDH(+)/CD133(+)). The effects of STAT3 inhibition in colon cancer stem-like cells were examined. The phosphorylated or activated form of STAT3 was expressed in colon cancer stem-like cells and was reduced by a STAT3-selective small molecular inhibitor, FLLL32. FLLL32 also inhibited the expression of potential STAT3 downstream target genes in colon cancer stem-like cells including survivin, Bcl-XL, as well as Notch-1, -3, and -4, which may be involved in stem cell function. Furthermore, FLLL32 inhibited cell viability and tumorsphere formation as well as induced cleaved caspase-3 in colon cancer stem-like cells. FLLL32 is more potent than curcumin as evidenced with lower IC50 in colon cancer stem-like cells. In summary, our results indicate that STAT3 is a novel therapeutic target in colon cancer stem-like cells and inhibition of STAT3 in cancer stem-like cells may offer a potential treatment for colorectal cancer.

Curcumin induces proapoptotic effects against human melanoma cells and modulates the cellular response to immunotherapeutic cytokines

Curcumin has potential as a chemopreventative and chemotherapeutic agent, but its interactions with clinically relevant cytokines are poorly characterized. Because cytokine immunotherapy is a mainstay of treatment for malignant melanoma, we hypothesized that curcumin could modulate the cellular responsiveness to interferons and interleukins. As a single agent, curcumin induced a dose-dependent increase in apoptosis of human melanoma cell lines, which was most prominent at doses >10 μmol/L. Immunoblot analysis confirmed that curcumin induced apoptosis and revealed caspase-3 processing, poly ADP ribose polymerase cleavage, reduced Bcl-2, and decreased basal phosphorylated signal transducers and activators of transcription 3 (STAT3). Despite its proapoptotic effects, curcumin pretreatment of human melanoma cell lines inhibited the phosphorylation of STAT1 protein and downstream gene transcription following IFN-α and IFN-γ as determined by immunoblot analysis and real time PCR, respectively. Pretreatment of peripheral blood mononuclear cells from healthy donors with curcumin also inhibited the ability of IFN-α, IFN-γ, and interleukin-2 to phosphorylate STAT proteins critical for their antitumor activity (STAT1 and STAT5, respectively) and their respective downstream gene expression as measured by real time PCR. Finally, stimulation of natural killer (NK) cells with curcumin reduced the level of interleukin-12–induced IFN-γ secretion, and production of granzyme b or IFN-γ upon coculture with A375 melanoma cells or NK-sensitive K562 cells as targets. These data show that although curcumin can induce apoptosis of melanoma cells, it can also adversely affect the responsiveness of immune effector cells to clinically relevant cytokines that possess antitumor properties. [Mol Cancer Ther 2009;8(9):2726–35]

New curcumin analogues exhibit enhanced growth-suppressive activity and inhibit AKT and signal transducer and activator of transcription 3 phosphorylation in breast and prostate cancer cells.

Curcumin, the active component of turmeric, has been shown to protect against carcinogenesis and prevent tumor development in cancer. To enhance its potency, we tested the efficacy of synthetic curcumin analogues, known as FLLL11 and FLLL12, in cancer cells. We examined the impact of FLLL11 and FLLL12 on cell viability in eight different breast and prostate cancer cell lines. FLLL11 and FLLL12 (IC50 values 0.3–5.7 and 0.3–3.8 µmol/L, respectively) were substantially more potent than curcumin (IC50 values between 14.4–50 µmol/L). FLLL11 and FLLL12 were also found to inhibit AKT phosphorylation and downregulate the expression of HER2/neu. In addition, we demonstrate for the first time that FLLL11 and FLLL12 inhibit phosphorylation of signal transducer and activator of transcription (STAT) 3, an oncogene frequently found to be persistently active in many cancer types. The inhibition of STAT3 signaling was confirmed by the inhibition of STAT3 DNA binding and STAT3 transcriptional activity. Furthermore, FLLL11 and FLLL12 were more effective than curcumin in inhibiting cell migration and colony formation in soft agar as well as inducing apoptosis in cancer cells. These results indicate that FLLL11 and FLLL12 exhibit more potent activities than curcumin on the inhibition of STAT3, AKT, and HER‐2/neu, as well as inhibit cancer cell growth and migration, and may thus have translational potential as chemopreventive or therapeutic agents for breast and prostate cancers. (Cancer Sci 2009; 100: 1719–1727)

HRP2 Determines the Efficiency and Specificity of HIV-1 Integration in LEDGF/p75 Knockout Cells but Does Not Contribute to the Antiviral Activity of a Potent LEDGF/p75-Binding Site Integrase Inhibitor

The binding of integrase (IN) to lens epithelium-derived growth factor (LEDGF)/p75 in large part determines the efficiency and specificity of HIV-1 integration. However, a significant residual preference for integration into active genes persists in Psip1 (the gene that encodes for LEDGF/p75) knockout (KO) cells. One other cellular protein, HRP2, harbors both the PWWP and IN-binding domains that are important for LEDGF/p75 co-factor function. To assess the role of HRP2 in HIV-1 integration, cells generated from Hdgfrp2 (the gene that encodes for HRP2) and Psip1/Hdgfrp2 KO mice were infected alongside matched control cells. HRP2 depleted cells supported normal infection, while disruption of Hdgfrp2 in Psip1 KO cells yielded additional defects in the efficiency and specificity of integration. These deficits were largely restored by ectopic expression of either LEDGF/p75 or HRP2. The double-KO cells nevertheless supported residual integration into genes, indicating that IN and/or other host factors contribute to integration specificity in the absence of LEDGF/p75 and HRP2. Psip1 KO significantly increased the potency of an allosteric inhibitor that binds the LEDGF/p75 binding site on IN, a result that was not significantly altered by Hdgfrp2 disruption. These findings help to rule out the host factor-IN interactions as the primary antiviral targets of LEDGF/p75-binding site IN inhibitors.