Antitumor activity of a novel STAT3 inhibitor and redox modulator in non-small cell lung cancer cells

Cell Death by Gallotannin Is Associated with Inhibition of the JAK/STAT Pathway in Human Colon Cancer Cells

Background

Gallotannin (GT) is a polyphenol that possesses interesting anticancer properties. However, the mechanisms underlying its antitumor effects have not been well defined.

Objective

This study was designed to clarify the mechanisms underlying GT antitumor effects in colon cancer cell lines.

Methods

Three isogenic HCT116 cell lines (p53^+/+, p53^-/-, and p21^-/-) were treated with GT for different time points then Western blot, flow cytometry, and senescence analysis were performed to examine the effect of GT on Mitogen-activated protein kinase (MAPK) and Janus kinase (JAK)/signal transducer and activator of transcription (STAT) effectors, STAT3 downstream apoptotic targets, Sub-G1 phase, and programmed cell death induction. Transfection using Invitrogen Lipofectamine 2000 Transfection Reagent (Thermo Fisher Scientific, Waltham, Massachusetts) were used to identify the role of p53 and p21 in the p53^-/- and p21^-/- cell lines.

Results

Both low and high GT concentrations caused MAPKs activation marked by upregulation of extracellular signal-regulated kinase (p-ERK). The preincubation with the antioxidant Tiron (Sigma-Aldrich, St Louis, Missouri) showed that GT's antitumor effects were not mediated by reactive oxygen species. We then examined the effect of GT on the JAK/STAT pathway, which is known to be activated in colorectal cancer. GT totally inhibited the JAK/STAT pathway effectors JAK2, STAT1, and STAT3 and their downstream apoptotic regulators B-cell lymphoma-extra large (Bcl-x_L) and c-Myc in all 3 cell lines. HCT116 cancer cells exhibited differential sensitivity to GT with p21^-/- cells being the most sensitive and p53^+/+ cells that express p21 protein being the least sensitive. In p53^+/+ cells, GT induced senescence, whereas in p53^-/- and p21^-/- cells, GT induced apoptosis in a caspase independent manner marked by Poly(ADP-Ribose) Polymerase (PARP) cleavage, Bcl-2 downregulation, and upregulation of the Bcl-2 associated X (Bax) to B-cell lymphoma 2 (Bcl-2) ratio. In addition, the sub-G1 phase exceeded 50% in p21^-/- cells.

Conclusions

Considered together, our results indicate that GT is potent inhibitor of the JAK/STAT pathway in colon cancer irrespective of the p53 and p21 status, which provides insights into its mechanism of anticancer activities and future potential for clinical translation. (Curr Ther Res Clin Exp. 2020; 81:XXX-XXX).

Reactive Oxygen Species and Oncoprotein Signaling-A Dangerous Liaison

SIGNIFICANCE

There is evidence to implicate reactive oxygen species (ROS) in tumorigenesis and its progression. This has been associated with the interplay between ROS and oncoproteins, resulting in enhanced cellular proliferation and survival. Recent Advances: To date, studies have investigated specific contributions of the crosstalk between ROS and signaling networks in cancer initiation and progression. These investigations have challenged the established dogma of ROS as agents of cell death by demonstrating a secondary function that fuels cell proliferation and survival. Studies have thus identified (onco)proteins (Bcl-2, STAT3/5, RAS, Rac1, and Myc) in manipulating ROS level as well as exploiting an altered redox environment to create a milieu conducive for cancer formation and progression.

CRITICAL ISSUES

Despite these advances, drug resistance and its association with an altered redox metabolism continue to pose a challenge at the mechanistic and clinical levels. Therefore, identifying specific signatures, altered protein expressions, and modifications as well as protein-protein interplay/function could not only enhance our understanding of the redox networks during cancer initiation and progression but will also provide novel targets for designing specific therapeutic strategies.

FUTURE DIRECTIONS

Not only a heightened realization is required to unravel various gene/protein networks associated with cancer formation and progression, particularly from the redox standpoint, but there is also a need for developing more sensitive tools for assessing cancer redox metabolism in clinical settings. This review attempts to summarize our current knowledge of the crosstalk between oncoproteins and ROS in promoting cancer cell survival and proliferation and treatment strategies employed against these oncoproteins. Antioxid. Redox Signal.

Activation of STAT3 and Bcl-2 and reduction of reactive oxygen species (ROS) promote radioresistance in breast cancer and overcome of radioresistance with niclosamide

Radiotherapy significantly improves the therapeutic outcomes and survival of breast cancer patients. However, the acquired resistance to this therapeutic modality is a major clinical challenge. Here we show that ionizing irradiation (IR)-induced phosphorylation of signal transducer and activator of transcription 3 (STAT3) at the Tyr705 residue and the induction of reactive oxygen species (ROS) in wild-type and radioresistant MDA-MB-231 and MDA-MB-468 triple-negative breast cancer (TNBC) cell lines. Comparing with radiosensitive parental TNBC cells, significantly low levels of ROS and higher protein levels of phospho-STAT3 and Bcl-2 were observed in TNBC cells with acquired radioresistance. Moreover, knockdown of STAT3 by shRNA sensitized the TNBC cells to IR. Niclosamide, a potent inhibitor of STAT3, overcame the radioresistance in TNBC cells via inhibition of STAT3 and Bcl-2 and induction of ROS. In combination with radiation, niclosamide treatment resulted in significant increase of ROS generation and induction of apoptosis in parental and radioresistant TNBC cells in vitro and TNBC xenograft tumors in vivo. These findings demonstrate that activation of STAT3 and Bcl-2 and reduction of ROS contribute to the development of radioresistance in TNBC, and niclosamide acts as a potent radiosensitizer via inhibiting STAT3 and Bcl-2 and increasing ROS generation in TNBC cells and xenograft tumors. Our findings suggest that niclosamide in combination with irradiation may offer an effective alternative approach for restoring the sensitivity of radioresistant TNBC cells to IR for improved therapeutic efficacy and outcomes.

Modulation of reactive oxygen species via ERK and STAT3 dependent signalling are involved in the response of mesothelioma cells to exemestane

Pleural mesothelioma is a deadly form of cancer. The prognosis is extremely poor due to the limited treatment modalities. Uptake of asbestos fibres, the leading cause of mesothelioma, lead to the accumulation of reactive-oxygen-species (ROS). Interestingly, increasing ROS production by using ROS-generating drugs may offer a strategy to selectively trigger cell death. Exemestane, an aromatase inhibitor, has previously shown anti-tumor properties in mesothelioma preclinical models suggesting a role of G protein-coupled receptor 30 (GPR30) in the drug response. As exemestane, in addition to blocking estrogen biosynthesis, generates ROS that are able to arrest the growth of breast cancer, we explored the role of ROS, antioxidant defense system, and ROS-induced signalling pathways in mesothelioma cells during exemestane response. Here we report that exemestane treatment reduced cell proliferation with an increase in ROS production and reduction of cyclic adenosine monophosphate (cAMP) levels in MSTO-H211, Ist-Mes1, Ist-Mes2 and MPP89 exemestane-sensitive mesothelioma cell lines, but not in NCI-H2452 exemestane-insensitive mesothelioma cells. Exemestane induced a significant antioxidant response in NCI-H2452 cells, as highlighted by an increase in γ-glutamylcysteine levels, catalase (Cat), superoxide-dismutase and (SOD) and glutathione-peroxidase (GSH-Px) activity and nuclear factor E2-related factor 2 (Nrf2) activation, responsible for drug insensitivity. Conversely, exemestane elevated ROS levels along with increased ERK phosphorylation and a reduction of p-STA3 in exemestane-sensitive mesothelioma cells. ROS generation was the crucial event of exemestane action because ROS inhibitor N-acetyl-L-cysteine (NAC) abrogated p-ERK and p-STAT3 modulation and cellular death. Exemestane also modulates ERK and STAT3 signalling via GPR30. Results indicate an essential role of ROS in the antiproliferative action of exemestane in mesothelioma cells. It is likely that the additional oxidative insults induced by exemestane results in the lethal effects of mesothelioma cells by increasing ROS production. As such, manipulating ROS levels with exemestane seems to be a feasible strategy to selectively kill mesothelioma cells with less toxicity to normal cells by regulating ERK and STAT3 activity.

Anti-leukemia activity of NSC-743380 in SULT1A1-expressing acute myeloid leukemia cells is associated with inhibitions of cFLIP expression and PI3K/AKT/mTOR activities

Our recent study showed that acute myeloid leukemia (AML) cells expressing SULT1A1 are highly sensitive to NSC-743380, a small molecule that inhibits STAT3 activity and induces SULT1A1-dependent apoptosis of various cancer cell lines. In this study, we characterized the molecular mechanisms of NSC-743380-mediated anti-leukemia activity in AML cell lines and antileukemia activity of NSC-743380 in patient-derived primary leukemia cells from AML patients. Our results showed that treatment with NSC-743380 triggered robust apoptosis in SULT1A1-positive AML cells. Treatment with NSC-743380 did not increase intracellular reactive oxygen species or change of STAT3 activity in AML cells, but did dramatically and rapidly decrease cFLIP expression. Proteomic analysis with reverse phase protein microarray revealed that treatment of U937 and THP-1 AML cells with NSC-743380 led to drastic and time-dependent suppression of phosphorylation of several key nodes in the PI3K/AKT/mTOR pathway, including AKT and mTOR. Moreover, primary AML cells expressed SULT1A1 were highly sensitive to treatment with NSC-743380, which was not affected by co-culture with bone marrow mesenchymal stem cells. Thus, our results provide proof-of-concept evidence that AML cells expressing SULT1A1 can be targeted by small molecules that induce apoptosis through inhibiting the expression or activities of multiple targets.

Auranofin-mediated inhibition of PI3K/AKT/mTOR axis and anticancer activity in non-small cell lung cancer cells

Auranofin, a gold complex that has been used to treat rheumatoid arthritis in clinics and has documented pharmacokinetic and safety profiles in humans, has recently been investigated for its anticancer activity in leukemia and some solid cancers. However, auranofin's single agent activity in lung cancer is not well characterized. To determine whether auranofin has single agent activity in lung cancer, we evaluated auranofin's activity in a panel of 10 non-small cell lung cancer (NSCLC) cell lines. Cell viability analysis revealed that auranofin induced growth inhibition in a subset of NSCLC cell lines with a half maximal inhibitory concentration (IC₅₀) below 1.0 μM. Treatment with auranofin elicited apoptosis and necroptosis in auranofin-sensitive cell lines. Moreover, the susceptibility of NSCLC cells to auranofin was inversely correlated with TXNRD1 expression in the cells. Transient transfection of the TXNRD1-expressing plasmid in auranofin-sensitive Calu3 cells resulted in partial resistance, indicating that high TXNRD level is one of causal factors for resistance to auranofin. Further mechanistic characterization with proteomic analysis revealed that auranofin inhibits expression and/or phosphorylation of multiple key nodes in the PI3K/AKT/mTOR pathway, including S6, 4EBP1, Rictor, p70S6K, mTOR, TSC2, AKT and GSK3. Ectopic expression of TXNRD1 partially reversed auranofin-mediated PI3K/AKT/mTOR inhibition, suggesting that TXNRD1 may participate in the regulation of PI3K/AKT/mTOR pathway. Administration of auranofin to mice with xenograft tumors derived from NSCLC cells significantly suppressed tumor growth without inducing obvious toxic effects. Our results demonstrated feasibility of repurposing auranofin for treatment of lung cancer.

ZYZ451 protects cardiomyocytes from hypoxia-induced apoptosis via enhancing MnSOD and STAT3 interaction

3,5-dimethoxy-4-(2-amino-3-prop-2-ynylsulfanyl-propionyl)-benzoic acid 4-guanidino-butyl ester (ZYZ451) was found to be an excellent cardio-protective agent in the previous research in our lab. However, its potent therapeutic effects on myocardial infarction and the underlying mechanism remain elusive. In the present study, we demonstrate that ZYZ451 protects neonatal rat ventricular cardiomyocytes (NRVCs) from hypoxia-induced apoptosis via increasing manganese-containing superoxide dismutase (MnSOD) activity and inhibiting mitochondrial reactive oxidative species (mitoROS) production. MnSOD knockdown impairs the anti-apoptotic effects of ZYZ451. We report here for the first time that signal transducer and activator of transcription 3 (STAT3), an important nuclear transcriptional factor also identified in mitochondria, co-localizes with MnSOD and interacts with it, as determined by using methods of co-immunofluorescence and co-immunoprecipitation. Knockdown of STAT3 rather than inhibition of STAT3 phosphorylation results in a significant reduction in MnSOD activity. Furthermore, interaction between MnSOD and STAT3 is diminished in STAT3 deficient H9C2 cells. Its novel subcellular localization and interaction with MnSOD suggest that STAT3 may be involved in regulation of MnSOD activity beyond its transcriptional potential. Consistent with the results in vitro, ZYZ451 reduces myocardial infarct size as well as cardiomyocytes apoptosis, inhibits lactate dehydrogenase (LDH) and malondialchehyche (MDA) release, and restores MnSOD activity in peri-infarct hearts. These benefits appear to be attributed to the enhanced interaction between STAT3 and MnSOD. These findings shed a light on a new role of STAT3 in oxidative stress and suggest that ZYZ451 is likely an effective cardio-protective agent.

Expression of sulfotransferase SULT1A1 in cancer cells predicts susceptibility to the novel anticancer agent NSC-743380

The small molecule anticancer agent NSC-743380 modulates functions of multiple cancer-related pathways and is highly active in a subset of cancer cell lines in the NCI-60 cell line panel. It also has promising in vivo anticancer activity. However, the mechanisms underlying NSC-743380's selective anticancer activity remain uncharacterized. To determine biomarkers that may be used to identify responders to this novel anticancer agent, we performed correlation analysis on NSC-743380's anticancer activity and the gene expression levels in NCI-60 cell lines and characterized the functions of the top associated genes in NSC-743380–mediated anticancer activity. We found sulfotransferase SULT1A1 is causally associated with NSC-743380's anticancer activity. SULT1A1 was expressed in NSC-743380–sensitive cell lines but was undetectable in resistant cancer cells. Ectopic expression of SULT1A1 in NSC743380 resistant cancer cells dramatically sensitized the resistant cells to NSC-743380. Knockdown of the SULT1A1 in the NSC-743380 sensitive cancer cell line rendered it resistance to NSC-743380. The SULT1A1 protein levels in cell lysates from 18 leukemia cell lines reliably predicted the susceptibility of the cell lines to NSC-743380. Thus, expression of SULT1A1 in cancer cells is required for NSC-743380's anticancer activity and can be used as a biomarker for identification of NSC-743380 responders.

RAS signaling and anti-RAS therapy: lessons learned from genetically engineered mouse models, human cancer cells, and patient-related studies

Activating mutations of oncogenic RAS genes are frequently detected in human cancers. The studies in genetically engineered mouse models (GEMMs) reveal that Kras-activating mutations predispose mice to early onset tumors in the lung, pancreas, and gastrointestinal tract. Nevertheless, most of these tumors do not have metastatic phenotypes. Metastasis occurs when tumors acquire additional genetic changes in other cancer driver genes. Studies on clinical specimens also demonstrated that KRAS mutations are present in premalignant tissues and that most of KRAS mutant human cancers have co-mutations in other cancer driver genes, including TP53, STK11, CDKN2A, and KMT2C in lung cancer; APC, TP53, and PIK3CA in colon cancer; and TP53, CDKN2A, SMAD4, and MED12 in pancreatic cancer. Extensive efforts have been devoted to develop therapeutic agents that target enzymes involved in RAS posttranslational modifications, that inhibit downstream effectors of RAS signaling pathways, and that kill RAS mutant cancer cells through synthetic lethality. Recent clinical studies have revealed that sorafenib, a pan-RAF and VEGFR inhibitor, has impressive benefits for KRAS mutant lung cancer patients. Combination therapy of MEK inhibitors with either docetaxel, AKT inhibitors, or PI3K inhibitors also led to improved clinical responses in some KRAS mutant cancer patients. This review discusses knowledge gained from GEMMs, human cancer cells, and patient-related studies on RAS-mediated tumorigenesis and anti-RAS therapy. Emerging evidence demonstrates that RAS mutant cancers are heterogeneous because of the presence of different mutant alleles and/or co-mutations in other cancer driver genes. Effective subclassifications of RAS mutant cancers may be necessary to improve patients' outcomes through personalized precision medicine.

Small-molecule targeting of signal transducer and activator of transcription (STAT) 3 to treat non-small cell lung cancer

OBJECTIVE

Lung cancer is the leading cause of cancer death in both men and women. Non-small cell lung cancer (NSCLC) has an overall 5-year survival rate of 15%. While aberrant STAT3 activation has previously been observed in NSCLC, the scope of its contribution is uncertain and agents that target STAT3 for treatment are not available clinically.

METHODS

We determined levels of activated STAT3 (STAT3 phosphorylated on Y705, pSTAT3) and the two major isoforms of STAT3 (α and β) in protein extracts of 8 NSCLC cell lines, as well as the effects of targeting STAT3 in vitro and in vivo in NSCLC cells using short hairpin (sh) RNA and two novel small-molecule STAT3 inhibitors, C188-9 and piperlongumine (PL).

RESULTS

Levels of pSTAT3, STAT3α, and STATβ were increased in 7 of 8 NSCLC cell lines. Of note, levels of pSTAT3 were tightly correlated with levels of STAT3β, but not STAT3α. Targeting of STAT3 in A549 cells using shRNA decreased tSTAT3 by 75%; this was accompanied by a 47-78% reduction in anchorage-dependent and anchorage-independent growth and a 28-45% reduction in mRNA levels for anti-apoptotic STAT3 gene targets. C188-9 and PL (@30 μM) each reduced pSTAT3 levels in all NSCLC cell lines tested by ≥50%, reduced anti-apoptotic protein mRNA levels by 25-60%, and reduced both anchorage-dependent and anchorage-independent growth of NSCLC cell lines with IC50 values ranging from 3.06 to 52.44 μM and 0.86 to 11.66 μM, respectively. Treatment of nude mice bearing A549 tumor xenografts with C188-9 or PL blocked tumor growth and reduced levels of pSTAT3 and mRNA encoding anti-apoptotic proteins.

CONCLUSION

STAT3 is essential for growth of NSCLC cell lines and tumors and its targeting using C188-9 or PL may be a useful strategy for treatment.

Novel 2-Carbonylbenzo[b]thiophene 1,1-Dioxide Derivatives as Potent Inhibitors of STAT3 Signaling Pathway

Signal transducer and activator of transcription 3 (STAT3) is considered to be an attractive therapeutic target for cancer therapy. In this study, a series of 2-carbonylbenzo[b]thiophene 1,1-dioxide derivatives (CBT) were designed to inhibit the STAT3 SH2 domain phosphorylation site Try 705. We demonstrated that incorporation of basic flexible groups through amide bond linkage to benzo[b]thiophene 1,1-dioxide (BTP) achieved compounds with higher antiproliferative potency than BTP itself. The most potent compound 6o, as indicated from luciferase reporter gene assay, inhibited the STAT3 pathway by decreasing the phosphorylation level of STAT3 Tyr705, while the phosphorylation level of other upstream tyrosine kinases in this pathway was not significantly inhibited. Compound 6o was also shown to trigger ROS generation and accumulation, thus consequently attributed partially to the observed cell apoptosis. This study provided important structural information for the development of inhibitors targeting the STAT3 pathway.

Predictive biomarkers in precision medicine and drug development against lung cancer

The molecular characterization of various cancers has shown that cancers with the same origins, histopathologic diagnoses, and clinical stages can be highly heterogeneous in their genetic and epigenetic alterations that cause tumorigenesis. A number of cancer driver genes with functional abnormalities that trigger malignant transformation and that are required for the survival of cancer cells have been identified. Therapeutic agents targeting some of these cancer drivers have been successfully developed, resulting in substantial improvements in clinical symptom amelioration and outcomes in a subset of cancer patients. However, because such therapeutic drugs often benefit only a limited number of patients, the successes of clinical development and applications rely on the ability to identify those patients who are sensitive to the targeted therapies. Thus, biomarkers that can predict treatment responses are critical for the success of precision therapy for cancer patients and of anticancer drug development. This review discusses the molecular heterogeneity of lung cancer pathogenesis; predictive biomarkers for precision medicine in lung cancer therapy with drugs targeting epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK), c-ros oncogene 1 receptor tyrosine kinase (ROS1), and immune checkpoints; biomarkers associated with resistance to these therapeutics; and approaches to identify predictive biomarkers in anticancer drug development. The identification of predictive biomarkers during anticancer drug development is expected to greatly facilitate such development because it will increase the chance of success or reduce the attrition rate. Additionally, such identification will accelerate the drug approval process by providing effective patient stratification strategies in clinical trials to reduce the sample size required to demonstrate clinical benefits.

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.

Characterization of acute biliary hyperplasia in Fisher 344 rats administered the indole-3-carbinol analog, NSC-743380

NSC-743380 (1-[(3-chlorophenyl)-methyl]-1H-indole-3-carbinol) is in early stages of development as an anticancer agent. Two metabolites reflect sequential conversion of the carbinol functionality to a carboxaldehyde and the major metabolite, 1-[(3-chlorophenyl)-methyl]-1H-indole-3-carboxylic acid. In an exploratory toxicity study in rats, NSC-743380 induced elevations in liver-associated serum enzymes and biliary hyperplasia. Biliary hyperplasia was observed 2 days after dosing orally for 2 consecutive days at 100mg/kg/day. Notably, hepatotoxicity and biliary hyperplasia were observed after oral administration of the parent compound, but not when major metabolites were administered. The toxicities of a structurally similar but pharmacologically inactive molecule and a structurally diverse molecule with a similar efficacy profile in killing cancer cells in vitro were compared to NSC-743380 to explore scaffold versus target-mediated toxicity. Following two oral doses of 100mg/kg/day given once daily on two consecutive days, the structurally unrelated active compound produced hepatic toxicity similar to NSC-743380. The structurally similar inactive compound did not, but, lower exposures were achieved. The weight of evidence implies that the hepatotoxicity associated with NSC-743380 is related to the anticancer activity of the parent molecule. Furthermore, because biliary hyperplasia represents an unmanageable and non-monitorable adverse effect in clinical settings, this model may provide an opportunity for investigators to use a short-duration study design to explore biomarkers of biliary hyperplasia.

Selective antitumor activity of ibrutinib in EGFR-mutant non-small cell lung cancer cells

Ibrutinib, which irreversibly inhibits Bruton tyrosine kinase, was evaluated for antitumor activity in a panel of non-small cell lung cancer (NSCLC) cell lines and found to selectively inhibit growth of NSCLC cells carrying mutations in the epidermal growth factor receptor (EGFR) gene, including T790M mutant and erlotinib-resistant H1975 cells. Ibrutinib induced dose-dependent inhibition of phosphor-EGFR at both Y1068 and Y1173 sites, suggesting ibrutinib functions as an EGFR inhibitor. Survival was analyzed by Kaplan-Meier estimation and log-rank test. All statistical tests were two-sided. In vivo study showed that ibrutinib statistically significantly suppressed H1975 tumor growth and prolonged survival of the tumor bearing mice (n = 5 per group). The mean survival times for solvent- and erlotinib-treated mice were both 17.8 days (95% confidence interval [CI] = 14.3 to 21.3 days), while the mean survival time for ibrutinib-treated mice was 29.8 days (95% CI = 26.0 to 33.6 days, P = .008). Our results indicate that ibrutinib could be a candidate drug for treatment of EGFR-mutant NSCLC, including erlotinib-resistant tumors.

Prodrug oncrasin-266 improves the stability, pharmacokinetics, and safety of NSC-743380

Through synthetic lethality screening of isogenic cell lines with and without the oncogenic KRAS gene and through lead compound optimization, we recently developed a novel anticancer agent designated NSC-743380 (oncrasin-72) that has promising in vitro and in vivo anticancer activity in a subset of cancer cell lines, including KRAS-mutant cancer cells. However, NSC-743380 tends to form dimers, which dramatically reduces its anticancer activity. To improve the physicochemical properties of NSC-743380, we synthesized a prodrug of NSC-743380, designated oncrasin-266, by modifying NSC-743380 with cyclohexylacetic acid and evaluated its in vitro and in vivo properties. Oncrasin-266 spontaneously hydrolyzed in phosphate-buffered saline in a time-dependent manner and was more stable than NSC-743380 in powder or stock solutions. In vivo administration of oncrasin-266 in mice led to the release of NSC-743380 which improved the pharmacokinetics of NSC-743380. Tissue distribution analysis revealed that oncrasin-266 was deposited in liver, whereas released NSC-743380 was detected in liver, lung, kidney, and subcutaneous tumor. Oncrasin-266 was better tolerated in mice at a higher dose level treatment (150-300 mg/kg, ip) than the parent agent was, suggesting that the prodrug reduced the acute toxicity of the parent agent. Our results demonstrated that the prodrug strategy could improve the stability, pharmacokinetic properties, and safety of NSC-743380.

Development of synthetic lethality anticancer therapeutics

The concept of synthetic lethality (the creation of a lethal phenotype from the combined effects of mutations in two or more genes) has recently been exploited in various efforts to develop new genotype-selective anticancer therapeutics. These efforts include screening for novel anticancer agents, identifying novel therapeutic targets, characterizing mechanisms of resistance to targeted therapy, and improving efficacies through the rational design of combination therapy. This review discusses recent developments in synthetic lethality anticancer therapeutics, including poly ADP-ribose polymerase inhibitors for BRCA1- and BRCA2-mutant cancers, checkpoint inhibitors for p53 mutant cancers, and small molecule agents targeting RAS gene mutant cancers. Because cancers are caused by mutations in multiple genes and abnormalities in multiple signaling pathways, synthetic lethality for a specific tumor suppressor gene or oncogene is likely cell context-dependent. Delineation of the mechanisms underlying synthetic lethality and identification of treatment response biomarkers will be critical for the success of synthetic lethality anticancer therapy.

Genetic Interactions of STAT3 and Anticancer Drug Development

Signal transducer and activator of transcription 3 (STAT3) plays critical roles in tumorigenesis and malignant evolution and has been intensively studied as a therapeutic target for cancer. A number of STAT3 inhibitors have been evaluated for their antitumor activity in vitro and in vivo in experimental tumor models and several approved therapeutic agents have been reported to function as STAT3 inhibitors. Nevertheless, most STAT3 inhibitors have yet to be translated to clinical evaluation for cancer treatment, presumably because of pharmacokinetic, efficacy, and safety issues. In fact, a major cause of failure of anticancer drug development is lack of efficacy. Genetic interactions among various cancer-related pathways often provide redundant input from parallel and/or cooperative pathways that drives and maintains survival environments for cancer cells, leading to low efficacy of single-target agents. Exploiting genetic interactions of STAT3 with other cancer-related pathways may provide molecular insight into mechanisms of cancer resistance to pathway-targeted therapies and strategies for development of more effective anticancer agents and treatment regimens. This review focuses on functional regulation of STAT3 activity; possible interactions of the STAT3, RAS, epidermal growth factor receptor, and reduction-oxidation pathways; and molecular mechanisms that modulate therapeutic efficacies of STAT3 inhibitors.

Assessment of drug delivery and anticancer potentials of nanoparticles-loaded siRNA targeting STAT3 in lung cancer, in vitro and in vivo

Activation of signal transducer and activator of transcription3 (STAT3) is a hallmark of several types of cancer. Failure to inhibit STAT3 expression by injection of siRNA for STAT3 directly to Balb/c mice led us to adopt alternative means. We formulated nanoparticle-based encapsulation of siRNA (NsiRNA) with polyethylenimine (PEI) and poly(lactide-co-glycolide) (PLGA) and characterized them. The siRNA treated and NsiRNA-treated cells were subjected separately to different assay systems. We also checked if NsiRNA could cross the blood brain barrier (BBB). Cell viability reduced dramatically in A549 cells after NsiRNA administration (23.89% at 24 h), thereby implicating considerable silencing of STAT3 by NsiRNA, but not after siRNA administration. Compared to controls, a significant decrease in expression of IL-6 and the angiogenic factor (VEGF) and increase in Caspase 3 activity was observed with corresponding regression in tumor growth in mice treated with NsiRNA. NsiRNA induced apoptosis of cells and arrested cells at G1/G0 stage, both in vitro and in vivo. Apoptosis was also verified by Annexin-V-FITC/Propidium-iodide staining. NsiRNA could cross blood brain barrier. Overall results revealed PEI-PLGA to be a promising carrier for delivery of siRNA targeting STAT3 expression, which can be utilized as an effective strategy for cancer therapy.

IGFBP2/FAK pathway is causally associated with dasatinib resistance in non-small cell lung cancer cells

Insulin-like growth factor (IGF)-binding protein-2 (IGFBP2) expression is increased in various types of cancers, including in a subset of patients with lung cancer. Because IGFBP2 is involved in signal transduction of some critical cancer-related pathways, we analyzed the association between IGFBP2 and response to pathway-targeted agents in seven human non-small cell lung cancer (NSCLC) cell lines. Western blot analysis and ELISA showed that four of the seven NSCLC cell lines analyzed expressed high levels of IGFBP2, whereas the remaining three had barely detectable IGFBP2. Susceptibilities of those seven cell lines to nine anticancer agents targeting to IGF1R, Src, FAK, MEK, and AKT were determined by a dose-dependent cell viability assay. The results showed that high IGFBP2 levels were associated with resistance to dasatinib and, to a lesser degree, to sacaratinib, but not to other agents. Ectopic IGFBP2 overexpression or knockdown revealed that changing IGFBP2 expression levels reversed dasatinib susceptibility phenotype, suggesting a causal relationship between IGFBP2 expression and dasatinib resistance. Molecular characterization revealed that focal adhesion kinase (FAK) activation was associated with increased IGFBP2 expression and partially contributed to IGFBP2-mediated dasatinib resistance. Treatment with a combination of dasatinib and FAK inhibitor led to enhanced antitumor activity in IGFBP2-overexpressing and dasatinib-resistant NSCLC cells in vitro and in vivo. Our results showed that the IGFBP2/FAK pathway is causally associated with dasatinib resistance and may be used as biomarkers for identification of dasatinib responders among patients with lung cancer. Simultaneous targeting on Src and FAK will likely improve the therapeutic efficacy of dasatinib for treatment of lung cancer.

Oxidative metabolism in cancer: A STAT affair?

STAT3 and STAT5 (STAT3/5) proteins are crucial mediators of cytokine- or growth factor-induced cell survival and proliferation. These transcription factors are frequently overactivated in a variety of solid tumors and hematopoietic neoplasms and are targets of various oncogenes with tyrosine kinase activity. STAT3/5 proteins regulate expression of genes involved in survival and proliferation in the nucleus and interact with signaling pathways in the cytoplasm. Evidences for a cross-talk between STAT3/5 and oxidative metabolism have recently emerged. This review summarizes the current knowledge on the cross-regulation between STAT3/5 and oxidative metabolism in normal and cancer cells.

Rebuilding pluripotency from primordial germ cells

Mammalian primordial germ cells (PGCs) are unipotent progenitors of the gametes. Nonetheless, they can give rise directly to pluripotent stem cells in vitro or during teratocarcinogenesis. This conversion is inconsistent, however, and has been difficult to study. Here, we delineate requirements for efficient resetting of pluripotency in culture. We demonstrate that in defined conditions, routinely 20% of PGCs become EG cells. Conversion can occur from the earliest specified PGCs. The entire process can be tracked from single cells. It is driven by leukemia inhibitory factor (LIF) and the downstream transcription factor STAT3. In contrast, LIF signaling is not required during germ cell ontogeny. We surmise that ectopic LIF/STAT3 stimulation reconstructs latent pluripotency and self-renewal. Notably, STAT3 targets are significantly upregulated in germ cell tumors, suggesting that dysregulation of this pathway may underlie teratocarcinogenesis. These findings demonstrate that EG cell formation is a robust experimental system for exploring mechanisms involved in reprogramming and cancer.

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A defined system for generation of pluripotent EG cells at high efficiency

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20% of single primordial germ cells become EG cells

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Stimulation with LIF but not FGF drives conversion to pluripotency

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LIF/STAT3 targets are upregulated in pluripotent germ cell tumors

Stattic V, a STAT3 inhibitor, affects human spermatozoa through regulation of mitochondrial activity

We have recently shown that many mediators of the JAK/STAT signaling pathway are present in ejaculated human spermatozoa. Among them, STAT3 is detected mainly in membranes and flagellar cytoskeletal fractions. In order to determine the importance of STAT3-mediated signaling, sperm were incubated with Stattic V, a specific inhibitor. Effects on motility were evaluated by CASA, sperm acrosomal integrity was evaluated by FITC conjugated lectin (PSA or PNA) staining, and protein phosphotyrosine content was assessed by Western blot using a monoclonal anti-phosphotyrosine antibody. INDO1-AM and JC-1 were used to measure sperm intracellular calcium and mitochondrial membrane potential, respectively, by flow cytometry, and reactive oxygen species (ROS) production was investigated by luminol-based assay. Percentages of motility and motility parameters were significantly affected by Stattic V. This later also significantly increased intracellular Ca(2+) levels, progesterone- and calcium ionophore (A23187)-induced acrosome reaction. On the other hand, a significant decrease in ATP content was measured when sperm were treated with Stattic V, associated with depolarization of mitochondrial membrane and elevated ROS production. These results suggest that STAT3 is involved in sperm functions, at least through regulation of mitochondrial activity. This further emphasizes that STAT3 mediates cellular activities in a manner different than strictly the activation of gene transcription.

Lung cancer genotype-based therapy and predictive biomarkers: present and future

CONTEXT

The advent of genotype-based therapy and predictive biomarkers for lung cancer has thrust the pathologist into the front lines of precision medicine for this deadly disease.

OBJECTIVE

To provide the clinical background, current status, and future perspectives of molecular targeted therapy for lung cancer patients, including the pivotal participation of the pathologist.

DATA SOURCES

Data were obtained from review of the pertinent peer-reviewed literature.

CONCLUSIONS

First-generation tyrosine kinase inhibitors have produced clinical response in a limited number of non-small cell lung cancers demonstrated to have activating mutations of epidermal growth factor receptor or anaplastic lymphoma kinase rearrangements with fusion partners. Patients treated with first-generation tyrosine kinase inhibitors develop acquired resistance to their therapy. Ongoing investigations of second-generation tyrosine kinase inhibitors and new druggable targets as well as the development of next-generation genotyping and new antibodies for immunohistochemistry promise to significantly expand the pathologist's already crucial role in precision medicine of lung cancer.

Biologic activity of the novel small molecule STAT3 inhibitor LLL12 against canine osteosarcoma cell lines

BACKGROUND

STAT3 [1] has been shown to be dysregulated in nearly every major cancer, including osteosarcoma (OS). Constitutive activation of STAT3, via aberrant phosphorylation, leads to proliferation, cell survival and resistance to apoptosis. The present study sought to characterize the biologic activity of a novel allosteric STAT3 inhibitor, LLL12, in canine OS cell lines.

RESULTS

We evaluated the effects of LLL12 treatment on 4 canine OS cell lines and found that LLL12 inhibited proliferation, induced apoptosis, reduced STAT3 phosphorylation, and decreased the expression of several transcriptional targets of STAT3 in these cells. Lastly, LLL12 exhibited synergistic anti-proliferative activity with the chemotherapeutic doxorubicin in the OS lines.

CONCLUSION

LLL12 exhibits biologic activity against canine OS cell lines through inhibition of STAT3 related cellular functions supporting its potential use as a novel therapy for OS.

Spirooxindole derivative SOID-8 induces apoptosis associated with inhibition of JAK2/STAT3 signaling in melanoma cells

Melanoma is generally refractory to current chemotherapy, thus new treatment strategies are needed. In this study, we synthesized a series of spirooxindole derivatives (SOID-1 to SOID-12) and evaluated their antitumor effects on melanoma. Among the 12 spirooxindole derivatives, SOID-8 showed the strongest antitumor activity by viability screening. SOID-8 inhibited viability of A2058, A375, SK-MEL-5 and SK-MEL-28 human melanoma cells in a dose- and time-dependent manner. SOID-8 also induced apoptosis of these tumor cells, which was confirmed by positive Annexin V staining and an increase of poly(ADP-ribose) polymerase cleavage. The antiapoptotic protein Mcl-1, a member of the Bcl-2 family, was downregulated and correlated with SOID-8 induced apoptosis. In addition, SOID-8 reduced tyrosine phosphorylation of Signal Tansducer and Activator of Transcription 3 (STAT3) in both dose- and time-dependent manners. This inhibition was associated with decreased levels of phosphorylation of Janus-activated kinase-2 (JAK2), an upstream kinase that mediates STAT3 phosphorylation at Tyr705. Accordingly, SOID-8 inhibited IL-6-induced activation of STAT3 and JAK2 in melanoma cells. Finally, SOID-8 suppressed melanoma tumor growth in a mouse xenograft model, accompanied with a decrease of phosphorylation of JAK2 and STAT3. Our results indicate that the antitumor activity of SOID-8 is at least partially due to inhibition of JAK2/STAT3 signaling in melanoma cells. These findings suggest that the spirooxindole derivative SOID-8 is a promising lead compound for further development of new preventive and therapeutic agents for melanoma.