STAT3 inhibition in prostate and pancreatic cancer lines by STAT3 binding sequence oligonucleotides: differential activity between 5' and 3' ends

Exploring Novel Frontiers: Leveraging STAT3 Signaling for Advanced Cancer Therapeutics

Signal Transducer and Activator of Transcription 3 (STAT3) plays a significant role in diverse physiologic processes, including cell proliferation, differentiation, angiogenesis, and survival. STAT3 activation via phosphorylation of tyrosine and serine residues is a complex and tightly regulated process initiated by upstream signaling pathways with ligand binding to receptor and non-receptor-linked kinases. Through downstream deregulation of target genes, aberrations in STAT3 activation are implicated in tumorigenesis, metastasis, and recurrence in multiple cancers. While there have been extensive efforts to develop direct and indirect STAT3 inhibitors using novel drugs as a therapeutic strategy, direct clinical application remains in evolution. In this review, we outline the mechanisms of STAT3 activation, the resulting downstream effects in physiologic and malignant settings, and therapeutic strategies for targeting STAT3. We also summarize the pre-clinical and clinical evidence of novel drug therapies targeting STAT3 and discuss the challenges of establishing their therapeutic efficacy in the current clinical landscape.

Targeting Janus Kinases and Signal Transducer and Activator of Transcription 3 to Treat Inflammation, Fibrosis, and Cancer: Rationale, Progress, and Caution

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

SH003 reverses drug resistance by blocking signal transducer and activator of transcription 3 (STAT3) signaling in breast cancer cells

Overcoming drug resistance is an important task for investigators and clinician to achieve successful chemotherapy in cancer patients. Drug resistance is caused by various factors, including the overexpression of P-glycoprotein (P-gp, MDR1). The development of new, useful compounds that overcome drug resistance is urgent. SH003 is extracted from the mixture of three different herbs, and its anticancer effect has been revealed in different cancer cell types. In the present study, we investigated whether SH003 is able to reverse drug resistance using paclitaxel-resistant breast cancer cells (MCF-7/PAC). In our experiments, SH003 significantly decreased cell growth and colony formation in MCF-7/PAC cells and parental MCF-7 cells. This growth inhibition was related to the accumulation of cells in the sub-G₀/G₁ apoptotic population and an increase in the number of apoptotic cells. SH003 reduced the mRNA expression of multidrug resistance 1 (MDR1) and multidrug resistance-associated proteins (MRPs) in MCF-7/PAC cells. SH003 also down-regulated the expression of P-gp. SH003 reversed drug efflux from MCF-7/PAC cells, resulting in rhodamine123 (Rho123) accumulation. Inhibition of drug resistance by SH003 is related to the suppression of the signal transducer and activator of transcription 3 (STAT3) signaling pathway. SH003 decreased STAT3 activation (p-STAT3) and its nuclear translocation and inhibited the secretion of VEGF and MMP-2, which are STAT3 target genes. An STAT3 inhibitor, JAK inhibitor I and an HIF-1α inhibitor decreased cell growth in MCF-7 and MCF-7/PAC cells. Taken together, these results demonstrate that SH003 can overcome drug resistance, and SH003 might be helpful for chemotherapy in cancer patients.

Apigenin overcomes drug resistance by blocking the signal transducer and activator of transcription 3 signaling in breast cancer cells

Drug resistance in chemotherapy is a serious obstacle for the successful treatment of cancer. Drug resistance is caused by various factors, including the overexpression of P-glycoprotein (P-gp, MDR1). The development of new, useful compounds that overcome drug resistance is urgent. Apigenin, a dietary flavonoid, has been reported as an anticancer drug in vivo and in vitro. In the present study, we investigated whether apigenin is able to reverse drug resistance using adriamycin-resistant breast cancer cells (MCF-7/ADR). In our experiments, apigenin significantly decreased cell growth and colony formation in MCF-7/ADR cells and parental MCF-7 cells. This growth inhibition was related to the accumulation of cells in the sub-G₀/G₁ apoptotic population and an increase in the number of apoptotic cells. Apigenin reduced the mRNA expression of multidrug resistance 1 (MDR1) and multidrug resistance-associated proteins (MRPs) in MCF-7/ADR cells. Apigenin also downregulated the expression of P-gp. Apigenin reversed drug efflux from MCF-7/ADR cells, resulting in rhodamine 123 (Rho123) accumulation. Inhibition of drug resistance by apigenin is related to the suppression of the signal transducer and activator of transcription 3 (STAT3) signaling pathway. Apigenin decreased STAT3 activation (p-STAT3) and its nuclear translocation and inhibited the secretion of VEGF and MMP-9, which are STAT3 target genes. A STAT3 inhibitor, JAK inhibitor I and an HIF-1α inhibitor decreased cell growth in MCF-7 and MCF-7/ADR cells. Taken together, these results demonstrate that apigenin can overcome drug resistance.

Quercetin induces caspase-dependent extrinsic apoptosis through inhibition of signal transducer and activator of transcription 3 signaling in HER2-overexpressing BT-474 breast cancer cells

Flavonoids are assumed to exert beneficial effects in different types of cancers at high concentrations. Yet, their molecular mechanisms of action remain unknown. The present study aimed to examine the effect of quercetin on proliferation and apoptosis in HER2-expressing breast cancer cells. The anti-proliferative effects of quercetin were examined by proliferation, MTT and clonogenic survival assays. The effect of quercetin on expression of apoptotic molecules was determined by western blotting. Luciferase reporter assay was performed to measure signal transducer and activator of transcription 3 (STAT3) transcriptional activity. ELISA assay was performed to measure intracellular MMP-9 levels. Immunocytochemistry was performed to evaluate the nuclear STAT3 level. The results revealed that quercetin inhibited the proliferation of BT-474 cells in a dose- and time-dependent manner. Quercetin also inhibited clonogenic survival (anchorage-dependent and -independent) of BT-474 cells in a dose-dependent manner. These growth inhibitions were accompanied with an increase in sub-G0/G1 apoptotic populations. Quercetin induced caspase-dependent extrinsic apoptosis upregulating the levels of cleaved caspase-8 and cleaved caspase-3, and inducing the cleavage of poly(ADP‑ribose) polymerase (PARP). In contrast, quercetin did not induce apoptosis via intrinsic mitochondrial apoptosis pathway since this compound did not decrease the mitochondrial membrane potential and did not affect the levels of B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (BAX). Quercetin reduced the expression of phospho-JAK1 and phospho-STAT3 and decreased STAT3-dependent luciferase reporter gene activity in the BT-474 cells. Quercetin inhibited MMP-9 secretion and decreased the nuclear translocation of STAT3. Our study indicates that quercetin induces apoptosis at concentrations >20 µM through inhibition of STAT3 signaling and could serve as a useful compound to prevent or treat HER2-overexpressing breast cancer.

Induction of caspase-dependent extrinsic apoptosis by apigenin through inhibition of signal transducer and activator of transcription 3 (STAT3) signalling in HER2-overexpressing BT-474 breast cancer cells

Phytoestrogen intake is known to be beneficial to decrease breast cancer incidence and progression. But its molecular mechanisms of action are still unknown. The present study aimed to examine the effect of apigenin on proliferation and apoptosis in HER2-expressing breast cancer cells. In our experiments, apigenin inhibited the proliferation of BT-474 cells in a dose- and time-dependent manner. Apigenin also inhibited clonogenic survival (anchorage-dependent and -independent) of BT-474 cells in a dose-dependent manner. These growth inhibitions were accompanied with an increase in sub-G0/G1 apoptotic populations. Apigenin-induced extrinsic a caspase-dependent apoptosis up-regulating the levels of cleaved caspase-8 and cleaved caspase-3, and inducing the cleavage of poly (ADP-ribose) polymerase (PARP). Whereas, apigenin did not induce apoptosis via intrinsic mitochondrial apoptosis pathway since this compound did not decrease mitochondrial membrane potential without affecting the levels of B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (BAX). Apigenin reduced the expression of phospho-JAK1, phospho-JAK2 and phospho-STAT3 and decreased signal transducer and activator of transcription 3 (STAT3) dependent luciferase reporter gene activity in BT-474 cells. Apigenin inhibited CoCl2-induced VEGF secretion and decreased the nuclear translocation of STAT3. Our study indicates that apigenin induces apoptosis through inhibition of STAT3 signalling and could serve as a useful compound to prevent or treat HER2-overexpressing breast cancer.

Apigenin induces caspase-dependent apoptosis by inhibiting signal transducer and activator of transcription 3 signaling in HER2-overexpressing SKBR3 breast cancer cells

Phytoestrogens have been demonstrated to inhibit tumor induction; however, their molecular mechanisms of action have remained elusive. The present study aimed to investigate the effects of a phytoestrogen, apigenin, on proliferation and apoptosis of the human epidermal growth factor receptor 2 (HER2)-expressing breast cancer cell line SKBR3. Proliferation assay, MTT assay, fluorescence-activated cell sorting analysis, western blot analysis, immunocytochemistry, reverse transcription-polymerase chain reaction and ELISA assay were used in the present study. The results of the present study indicated that apigenin inhibited the proliferation of SKBR3 cells in a dose-and time-dependent manner. This inhibition of growth was accompanied by an increase in the sub-G0/G1 apoptotic population. Furthermore, apigenin enhanced the expression levels of cleaved caspase-8 and -3, and induced the cleavage of poly(adenosine diphosphate ribose) polymerase in SKBR3 cells, confirming that apigenin promotes apoptosis via a caspase-dependent pathway. Apigenin additionally reduced the expression of phosphorylated (p)-janus kinase 2 and p-signal transducer and activator of transcription 3 (STAT3), inhibited CoCl2-induced vascular endothelial growth factor (VEGF) secretion and decreased the nuclear localization of STAT3. The STAT3 inhibitor S31-201 decreased the cellular proliferation rate and reduced the expression of p-STAT3 and VEGF. Therefore, these results suggested that apigenin induced apoptosis via the inhibition of STAT3 signaling in SKBR3 cells. In conclusion, the results of the present study indicated that apigenin may be a potentially useful compound for the prevention or treatment of HER2-overexpressing breast cancer.

PYK2 sustains endosomal-derived receptor signalling and enhances epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) is a central developmental process implicated in cancer metastasis. Here we show that the tyrosine kinase PYK2 enhances cell migration and invasion and potentiates EMT in human breast carcinoma. EMT inducer, such as EGF, induces rapid phosphorylation of PYK2 and its translocation to early endosomes where it co-localizes with EGFR and sustains its downstream signals. Furthermore, PYK2 enhances EGF-induced STAT3-phosphorylation, while phospho-STAT3 directly binds to PYK2 promoter and regulates PYK2 transcription. STAT3 and PYK2 also enhance c-Met expression, while c-Met augments their phosphorylation, suggesting a positive feedback loop between PYK2-STAT3-c-Met. We propose that PYK2 sustains endosomal-derived receptor signalling and participates in a positive feedback that links cell surface receptor(s) to transcription factor(s) activation, thereby prolonging signalling duration and potentiating EMT. Given the role of EMT in breast cancer metastasis, we also found a significant correlation between PYK2 expression, tumour grade and lymph node metastasis, thus, demonstrating the clinicopathological implication of our findings.

Novel thiosemicarbazones regulate the signal transducer and activator of transcription 3 (STAT3) pathway: inhibition of constitutive and interleukin 6-induced activation by iron depletion

Pharmacologic manipulation of metal pools in tumor cells is a promising strategy for cancer treatment. Here, we reveal how the iron-binding ligands desferrioxamine (DFO), di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT), and di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) inhibit constitutive and interleukin 6-induced activation of signal transducer and activator of transcription 3 (STAT3) signaling, which promotes proliferation, survival, and metastasis of cancer cells. We demonstrate that DFO, Dp44mT, and DpC significantly decrease constitutive phosphorylation of the STAT3 transcription factor at Tyr705 in the pancreatic cancer cell lines PANC-1 and MIAPaCa-2 as well as the prostate cancer cell line DU145. These compounds also significantly decrease the dimerized STAT3 levels, the binding of nuclear STAT3 to its target DNA, and the expression of downstream targets of STAT3, including cyclin D1, c-myc, and Bcl-2. Examination of upstream mediators of STAT3 in response to these ligands has revealed that Dp44mT and DpC could significantly decrease activation of the nonreceptor tyrosine kinase Src and activation of cAbl in DU145 and MIAPaCa-2 cells. In contrast to the effects of Dp44mT, DpC, or DFO on inhibiting STAT3 activation, the negative control compound di-2-pyridylketone 2-methyl-3-thiosemicarbazone, or the DFO:Fe complex, which cannot bind cellular iron, had no effect. This demonstrates the role of iron-binding in the activity observed. Immunohistochemical staining of PANC-1 tumor xenografts showed a marked decrease in STAT3 in the tumors of mice treated with Dp44mT or DpC compared with the vehicle. Collectively, these studies demonstrate suppression of STAT3 activity by iron depletion in vitro and in vivo, and reveal insights into regulation of the critical oncogenic STAT3 pathway.

STAT3 Inhibition Induces Apoptosis in Cancer Cells Independent of STAT1 or STAT2

Signal transducers and activators of transcription (STATs) were originally discovered as mediators of signal transduction. Persistent aberrant activation of STAT3 is part of the malignant phenotype of hormone-refractory prostate cancer and pancreatic cancer; this is thought to be mediated by homodimers of phosphorylated STAT3, which translocate to the nucleus. One consequence of persistently-activated STAT3 in malignant cells is that they depend upon it for survival. STAT3 is observed to heterodimerize with STAT1 and STAT2; however the contributions of STAT3:STAT1 and STAT3:STAT2 heterodimers to the survival of malignant cells have not been investigated in detail. Previously we reported that single-stranded oligonucleotides containing consensus STAT3 binding sequences (13410 and 13411) were more effective for inducing apoptosis in prostate cancer cells than antisense STAT3 oligonucleotides. Control oligonucleotides (scrambled sequences) had no effect. STAT3-inhibiting oligonucleotide 13410, but not scrambled-sequence oligonucleotides, induced apoptosis in pancreatic cancer cells as well. Here we report that 13410 and derivative olignucleotides induced apoptosis in STAT1-null and STAT2-null fibrosarcoma cell lines U3A and U6A, as well as in the parental fibrosarcoma cell line 2fTGH. The cell lines expressed constitutively-activated STAT3 and depended on its activity for survival. Forty-eight hr after transfection of 13410 or related oligonucleotides, significant apoptosis was observed in 2fTGH, U3A and U6A cells. Scrambled-sequence oligonucleotides had no effect on survival. These data indicate that neither STAT1 nor STAT2 play significant roles in the maintenance of these cells, and by extension that STAT3:STAT1 and STAT3:STAT2 heterodimers regulate a different set of genes from STAT3:STAT3 homodimers.

Potential use of STAT3 inhibitors in targeted prostate cancer therapy: future prospects

In 2012, prostate cancer will once again be the second-leading cause of cancer death of American males. Although initially treatable, prostate cancer can recur in a hormone refractory form that is not responsive to current available therapies. The mortality rate associated with hormone refractory prostate cancer is high, and there is an urgent need for new therapeutic agents to treat prostate cancer. A common feature of prostate cancer is the dependence on activated signal transducer and activator of transcription 3 (STAT3), a transcription factor, for survival. More important, inhibition of STAT3 has been shown to induce apoptosis in prostate cancer cells. In recent years, inhibitors of STAT3 have emerged as promising molecular candidates for targeted prostate cancer therapy. The aim of this review is to examine the role of STAT3 in prostate cancer and how inhibitors of STAT3 could advance the quest for treatment of the disease. Janus kinase 2 (JAK2)-targeted therapy appears very promising in the treatment of prostate cancer. It has been shown to decrease symptoms associated with myeloproliferative disorders and increase overall survival of patients compared with the best available therapy. In addition to improved outcome, many JAK2 inhibitors have been found to be tolerable with no adverse impact on quality of life. As such, JAK2 inhibitors may play an important role in the management of patients with prostate cancer. Current studies are evaluating the role of JAK2 inhibitors in solid tumors. Pending clinical trial results will determine the future direction of JAK2 inhibitors in the treatment of patients with prostate cancer.

Prostaglandin E2 affects T cell responses through modulation of CD46 expression

The ubiquitous protein CD46, a regulator of complement activity, promotes T cell activation and differentiation toward a regulatory Tr1-like phenotype. The CD46-mediated differentiation pathway is defective in several chronic inflammatory diseases, underlying the importance of CD46 in controlling T cell function and the need to understand its regulatory mechanisms. Using an RNA interference-based screening approach in primary T cells, we have identified that two members of the G protein-coupled receptor kinases were involved in regulating CD46 expression at the surface of activated cells. We have investigated the role of PGE(2), which binds to the E-prostanoid family of G protein-coupled receptors through four subtypes of receptors called EP 1-4, in the regulation of CD46 expression and function. Conflicting roles of PGE(2) in T cell functions have been reported, and the reasons for these apparent discrepancies are not well understood. We show that addition of PGE(2) strongly downregulates CD46 expression in activated T cells. Moreover, PGE(2) differentially affects T cell activation, cytokine production, and phenotype depending on the activation signals received by the T cells. This was correlated with a distinct pattern of the PGE(2) receptors expressed, with EP4 being preferentially induced by CD46 activation. Indeed, addition of an EP4 antagonist could reverse the effects observed on cytokine production after CD46 costimulation. These data demonstrate a novel role of the PGE(2)-EP4 axis in CD46 functions, which might at least partly explain the diverse roles of PGE(2) in T cell functions.

Apigenin induces apoptosis via extrinsic pathway, inducing p53 and inhibiting STAT3 and NFκB signaling in HER2-overexpressing breast cancer cells

Phytoestrogens are known to prevent tumor induction. But their molecular mechanisms of action are still unknown. This study aimed to examine the effect of apigenin on proliferation and apoptosis in HER2-expressing breast cancer cells. In our experiments, apigenin inhibited the proliferation of MCF-7 vec and MCF-7 HER2 cells. This growth inhibition was accompanied with an increase of sub G(0)/G(1) apoptotic fractions. Overexpression of HER2 did not confer resistance to apigenin in MCF-7 cells. Apigenin-induced extrinsic apoptosis pathway up-regulating the levels of cleaved caspase-8, and inducing the cleavage of poly (ADP-ribose) polymerase, whereas apigenin did not induce apoptosis via intrinsic mitochondrial apoptosis pathway since this compound did not decrease mitochondrial membrane potential maintaining red fluorescence and did not affect the levels of B-cell lymphoma 2 (BCL2) and Bcl-2-associated X protein. Moreover, apigenin reduced the tyrosine phosphorylation of HER2 (phospho-HER2 level) in MCF-7 HER2 cells, and up-regulated the levels of p53, phospho-p53 and p21 in MCF-7 vec and MCF-7 HER2 cells. This suggests that apigenin induces apoptosis through p53-dependent pathway. Apigenin also reduced the expression of phospho-JAK1 and phospho-STAT3 and decreased STAT3-dependent luciferase reporter gene activity in MCF-7 vec and MCF-7 HER2 cells. Apigenin decreased the phosphorylation level of IκBα in the cytosol, and abrogated the nuclear translocation of p65 within the nucleus suggesting that it blocks the activation of NFκB signaling pathway in MCF-7 vec and MCF-7 HER2 cells. Our study indicates that apigenin could be a potential useful compound to prevent or treat HER2-overexpressing breast cancer.

STAT3 silencing enhances the efficacy of the HSV.tk suicide gene in gastrointestinal cancer therapy

Aberrant activation of Signal Transducer and Activator of Transcription 3 (STAT3) signaling has been shown to be associated with uncontrolled cell proliferation and suppression of host-immune surveillance. Conversely, silencing STAT3 can have the dual effects of inhibiting cancer cell proliferation and inducing anti-tumor immune responses. Here, we report on the effects of STAT3 silencing on suicide gene therapy with thymidine kinase (tk). STAT3 silencing by siRNA inhibited the proliferation of AGS human gastric cancer cells through G1 cell cycle arrest, decreased levels of immune-suppressive cytokines, and increased levels of immune-activating cytokines. CT26 mouse colon adenocarcinoma cells, in which STAT3 expression was knocked-down by a STAT3 shRNA-containing lentivirus, grew more slowly in syngenic model Balb/c mice than control CT26 cells. Moreover, we found that STAT3 silencing augmented the efficacy of suicide gene therapy in CT26 cell xenografted mice. When we administrated adenoviruses harboring the herpes simplex virus thymidine kinase gene (Ad5.CMV.HSV.tk) into STAT3-silenced CT26 cell tumors, extensive apoptosis was observed and there was a significant reduction in the size of CT26 cell tumors. STAT3 silencing also enhanced the recruitment and cytotoxic activity of CD3(+)CD8(+) T-cells, and changed the cytokine expression pattern of CT26 cell tumors, reflecting augmentation of anti-cancer immune responses. We conclude that combining suicide gene therapy with STAT3 silencing can result in enhanced anti-cancer effects.

Down-regulation of STAT3 expression by vector-based small interfering RNA inhibits pancreatic cancer growth

AIM: To evaluate the effect of RNA interference (RNAi) mediated silence of signal transduction and activation of transcription (STAT)3 on the growth of human pancreatic cancer cells both in vitro and in vivo.

METHODS: STAT3 specific shRNA was used to silence the expression of STAT3 in pancreatic cancer cell line SW1990. The anti-growth effects of RNAi against STAT3 were studied in vitro and in experimental cancer xenografts in nude mice. The potential pathways involved in STAT3 signaling were detected using reverse transcription polymerase chain reaction and western blotting.

RESULTS: The expression of the STAT3 was inhibited using RNAi in SW1990 cells. RNAi against STAT3 inhibited cell proliferation, induced cell apoptosis and significantly reduced the levels of CyclinD1 and Bcl-xL when compared with parental and control vector-transfected cells. In vivo experiments showed that RNAi against STAT3 inhibited the tumorigenicity of SW1990 cells and significantly suppressed tumor growth when it was directly injected into tumors.

CONCLUSION: STAT3 signaling pathway plays an important role in the progression of pancreatic cancer, and silence of STAT3 gene using RNAi technique may be a novel therapeutic option for treatment of pancreatic cancer.

Creation of a novel peptide with enhanced nuclear localization in prostate and pancreatic cancer cell lines

Background

For improved uptake of oligonucleotide-based therapy, the oligonucleotides often are coupled to peptides that facilitate entry into cells. To this end, novel cell-penetrating peptides (CPPs) were designed for mediating intracellular uptake of oligonucleotide-based therapeutics. The novel peptides were based on taking advantage of the nuclear localization properties of transcription factors in combination with a peptide that would bind putatively to cell surfaces. It was observed that adding a glutamate peptide to the N-terminus of the nuclear localization signal (NLS) of the Oct6 transcription factor resulted in a novel CPP with better uptake and better nuclear colocalization than any other peptide tested.

Results

Uptake of the novel peptide Glu-Oct6 by cancer cell lines was rapid (in less than 1 hr, more than 60% of DU-145 cells were positive for FITC), complete (by 4 hr, 99% of cells were positive for FITC), concentration-dependent, temperature-dependent, and inhibited by sodium azide (NaN₃). Substitution of Phe, Tyr, or Asn moieties for the glutamate portion of the novel peptide resulted in abrogation of novel CPP uptake; however none of the substituted peptides inhibited uptake of the novel CPP when coincubated with cells. Live-cell imaging and analysis by imaging flow cytometry revealed that the novel CPP accumulated in nuclei. Finally, the novel CPP was coupled to a carboxyfluorescein-labeled synthetic oligonucleotide, to see if the peptide could ferry a therapeutic payload into cells.

Conclusions

These studies document the creation of a novel CPP consisting of a glutamate peptide coupled to the N-terminus of the Oct6 NLS; the novel CPP exhibited nuclear colocalization as well as uptake by prostate and pancreatic cancer cell lines.

Inhibition of pancreatic cancer cell growth by cucurbitacin B through modulation of signal transducer and activator of transcription 3 signaling

OBJECTIVES

Pancreatic cancer is a serious disease worldwide for its high mortality. Gemcitabine has become the frontline option for the treatment of this disease since its approval. However, resistance to the drug has been on the rise in recent years. Searching for other chemotherapeutic agents therefore has attracted much attention. Cucurbitacin B (CuB) is a member of the triterpenoid family and has shown inhibitory effect on various cancer cells. In this study, we have assessed the effect of CuB on pancreatic cancer cells.

METHODS

The growth of human pancreatic cancer cells (PANC-1) was monitored using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Cell cycle distribution and apoptosis were evaluated with fluorescence-activated cell sorter and fluorescent microscopy. Western blot was used to determine the expression of relevant genes including phosphorylated signal transducer and activator of transcription 3 (pSTAT3), STAT3, p53, p21, Bcl-2, survivin, and caspase 3.

RESULTS

Our results showed that CuB can inhibit the growth of PANC-1 cells in a dose- and time-dependent manner, resulting in accumulation of G2/M phase cells and apoptosis. Furthermore, CuB treatment inhibited STAT3 phosphorylation, activated caspase 3, up-regulated the expression of p53 and p21, and down-regulated the expression of Bcl-2 and survivin.

CONCLUSIONS

Our results suggested that CuB may provide an effective regimen for the treatment of pancreatic cancers.

Inhibitory effect of cucurbitacin E on pancreatic cancer cells growth via STAT3 signaling

PURPOSE

Pancreatic cancer has been a serious disease worldwide for its high mortality. Cucurbitacin E is a member of triterpenoid family isolated from plants showing antiproliferative activity on various cancer cells. In this study, we have explored whether cucurbitacin E also has an anti-tumor effect on pancreatic cancer cells.

METHODS

Human pancreatic cancer cells PANC-1 were used to explore the effect and possible mechanisms of cucurbitacin E on cell cycle progression, apoptosis and proliferation.

RESULTS

Cucurbitacin E has inhibited the growth of PANC-1 cells in a dose- and time-dependent manner, and has caused accumulation of cells at the G(2)/M phase as well as apoptosis. Western blotting also showed that cucurbitacin E treatment can inhibit STAT3 phosphorylation while upregulate p53 expression.

CONCLUSIONS

Our results suggested that cucurbitacin E may be an effective regimen for the chemotherapy of pancreatic cancer.

Challenges in developing targeted therapy for pancreatic adenocarcinoma

BACKGROUND

Pancreatic adenocarcinoma is a leading cause of cancer deaths in the US. Gemcitabine-based chemotherapy remains the cornerstone treatment for advanced pancreatic cancers. Research into the molecular pathogenesis of pancreatic cancers has allowed scientists to understand the complex heterogeneous signals associated with them. Targeting these pathways with chemical inhibitors could improve patient outcome.

OBJECTIVE

To describe the molecular heterogeneity typical of pancreatic cancers and to discuss targeted therapies in development, and the challenges facing these agents.

METHODS

We reviewed Pub Med. literature, clinical trial database (clinicaltrials.gov), American Society of Clinical Oncology (ASCO) and American Association of Cancer Research (AACR) websites.

CONCLUSIONS

Molecular pathogenesis of pancreatic cancer involves multiple pathways and defined mutations. This molecular heterogeneity is a major reason for failure of targeted therapy. Targeting multiple oncogenic pathways using novel targeted therapies could improve patient survival.