Pushpak Bhattacharjee

Curcumin Enhances the Efficacy of Chemotherapy by Tailoring p65NFκB-p300 Cross-talk in Favor of p53-p300 in Breast Cancer

Background: Constitutive activation of NFκB has been found in various cancers, causing resistance to chemotherapeutic drugs. Results: Curcumin pretreatment alleviates p65NFκB activation and hence tailors p65NFκB-p300 cross-talk in favor of p53-p300 in drug-resistant cells. Conclusion: This preclinical study suggests curcumin as a potent chemo-sensitizer to improve the therapeutic index. Significance: These results suggest that curcumin can be developed into an adjuvant chemotherapeutic drug. Breast cancer cells often develop multiple mechanisms of drug resistance during tumor progression, which is the major reason for the failure of breast cancer therapy. High constitutive activation of NFκB has been found in different cancers, creating an environment conducive for chemotherapeutic resistance. Here we report that doxorubicin-induced SMAR1-dependent transcriptional repression and SMAR1-independent degradation of IkBα resulted in nuclear translocation of p65NFκB and its association with p300 histone acetylase and subsequent transcription of Bcl-2 to impart protective response in drug-resistant cells. Consistently SMAR1-silenced drug-resistant cells exhibited IkBα-mediated inhibition of p65NFκB and induction of p53-dependent apoptosis. Interestingly, curcumin pretreatment of drug-resistant cells alleviated SMAR1-mediated p65NFκB activation and hence restored doxorubicin sensitivity. Under such anti-survival condition, induction of p53-p300 cross-talk enhanced the transcriptional activity of p53 and intrinsic death cascade. Importantly, promyelocyte leukemia-mediated SMAR1 sequestration that relieved the repression of apoptosis-inducing genes was indispensable for such chemo-sensitizing ability of curcumin. A simultaneous decrease in drug-induced systemic toxicity by curcumin might also have enhanced the efficacy of doxorubicin by improving the intrinsic defense machineries of the tumor-bearer. Overall, the findings of this preclinical study clearly demonstrate the effectiveness of curcumin to combat doxorubicin-resistance. We, therefore, suggest curcumin as a potent chemo-sensitizer to improve the therapeutic index of this widely used anti-cancer drug. Taken together, these results suggest that curcumin can be developed into an adjuvant chemotherapeutic drug.

FoxP3 Acts as a Cotranscription Factor with STAT3 in Tumor-Induced Regulatory T Cells

FoxP3, a lineage-specification factor, executes its multiple activities mostly through transcriptional regulation of target genes. We identified an interleukin-10 (IL-10)-producing FoxP3(+) T regulatory cell population that contributes to IL-10-dependent type 2 cytokine bias in breast-cancer patients. Although genetic ablation of FOXP3 inhibited IL10 transcription, genome-wide analysis ruled out its role as a transcription factor for IL10. In-depth analysis revealed that histone acetyl transterase-1, in association with FoxP3, modified the IL10 promoter epigenetically, making a space for docking STAT3-FoxP3 complexes. A predictive docking module with target-receptor specificity, along with exon-deletion and site-directed mutagenesis studies, showed that STAT3 binds through its N-terminal floppy domain to the exon 2 β sheet region of FoxP3 to form STAT3-FoxP3 complexes. Such cotranscriptional activity of FoxP3 extended to other STAT3-target genes that lack FoxP3-binding sites. These results suggest a function of FoxP3, where, failing to achieve direct promoter occupancy, FoxP3 promotes transcription in association with the locus-specific transcription factor STAT3.

Curcumin inhibits breast cancer stem cell migration by amplifying the E-cadherin/β-catenin negative feedback loop

IntroductionThe existence of cancer stem cells (CSCs) has been associated with tumor initiation, therapy resistance, tumor relapse, angiogenesis, and metastasis. Curcumin, a plant ployphenol, has several anti-tumor effects and has been shown to target CSCs. Here, we aimed at evaluating (i) the mechanisms underlying the aggravated migration potential of breast CSCs (bCSCs) and (ii) the effects of curcumin in modulating the same.MethodsThe migratory behavior of MCF-7 bCSCs was assessed by using cell adhesion, spreading, transwell migration, and three-dimensional invasion assays. Stem cell characteristics were studied by using flow cytometry. The effects of curcumin on bCSCs were deciphered by cell viability assay, Western blotting, confocal microscopy, and small interfering RNA (siRNA)-mediated gene silencing. Evaluations of samples of patients with breast cancer were performed by using immunohistochemistry and flow cytometry.ResultsHere, we report that bCSCs are endowed with aggravated migration property due to the inherent suppression of the tumor suppressor, E-cadherin, which is restored by curcumin. A search for the underlying mechanism revealed that, in bCSCs, higher nuclear translocation of beta-catenin (i) decreases E-cadherin/beta-catenin complex formation and membrane retention of beta-catenin, (ii) upregulates the expression of its epithelial-mesenchymal transition (EMT)-promoting target genes (including Slug), and thereby (iii) downregulates E-cadherin transcription to subsequently promote EMT and migration of these bCSCs. In contrast, curcumin inhibits beta-catenin nuclear translocation, thus impeding trans-activation of Slug. As a consequence, E-cadherin expression is restored, thereby increasing E-cadherin/beta-catenin complex formation and cytosolic retention of more beta-catenin to finally suppress EMT and migration of bCSCs.ConclusionsCumulatively, our findings disclose that curcumin inhibits bCSC migration by amplifying E-cadherin/beta-catenin negative feedback loop.

Restoration of p53/miR-34a regulatory axis decreases survival advantage and ensures Bax-dependent apoptosis of non-small cell lung carcinoma cells.

Tumor‐suppressive miR‐34a, a direct target of p53, has been shown to target several molecules of cell survival pathways. Here, we show that capsaicin‐induced oxidative DNA damage culminates in p53 activation to up‐regulate expression of miR‐34a in non‐small cell lung carcinoma (NSCLC) cells. Functional analyses further indicate that restoration of miR‐34a inhibits B cell lymphoma‐2 (Bcl‐2) protein expression to withdraw the survival advantage of these resistant NSCLC cells. In such a proapoptotic cellular milieu, where drug resistance proteins are also down‐regulated, p53‐transactivated Bcl‐2 associated X protein (Bax) induces apoptosis via the mitochondrial death cascade. Our results suggest that p53/miR‐34a regulatory axis might be critical in sensitizing drug‐resistant NSCLC cells.

Targeting RET to induce medullary thyroid cancer cell apoptosis: an antagonistic interplay between PI3K/Akt and p38MAPK/caspase-8 pathways.

Mutations in REarranged during Transfection (RET) receptor tyrosine, followed by the oncogenic activation of RET kinase is responsible for the development of medullary thyroid carcinoma (MTC) that responds poorly to conventional chemotherapy. Targeting RET, therefore, might be useful in tailoring surveillance of MTC patients. Here we showed that theaflavins, the bioactive components of black tea, successfully induced apoptosis in human MTC cell line, TT, by inversely modulating two molecular pathways: (i) stalling PI3K/Akt/Bad pathway that resulted in mitochondrial transmembrane potential (MTP) loss, cytochrome-c release and activation of the executioner caspases-9 and -3, and (ii) upholding p38MAPK/caspase-8/caspase-3 pathway via inhibition of Ras/Raf/ERK. Over-expression of either constitutively active myristoylated-Akt-cDNA (Myr-Akt-cDNA) or dominant-negative-caspase-8-cDNA (Dn-caspase-8-cDNA) partially blocked theaflavin-induced apoptosis, while co-transfection of Myr-Akt-cDNA and Dn-caspase-8-cDNA completely eradicated the effect of theaflavins thereby negating the possibility of existence of other pathways. A search for the upstream signaling revealed that theaflavin-induced disruption of lipid raft caused interference in anchorage of RET in lipid raft that in turn stalled phosphorylation of Ras and PI3Kinase. In such anti-survival cellular micro-environment, pro-apoptotic signals were triggered to culminate into programmed death of MTC cell. These findings not only unveil a hitherto unexplained mechanism underlying theaflavin-induced MTC death, but also validate RET as a promising and potential target for MTC therapy.

Capsaicin-Induced Activation of p53-SMAR1 Auto-Regulatory Loop Down-Regulates VEGF in Non-Small Cell Lung Cancer to Restrain Angiogenesis

Lung cancer is the leading cause of cancer-related deaths worldwide. Despite decades of research, the treatment options for lung cancer patients remain inadequate, either to offer a cure or even a substantial survival advantage owing to its intrinsic resistance to chemotherapy. Our results propose the effectiveness of capsaicin in down-regulating VEGF expression in non-small cell lung carcinoma (NSCLC) cells in hypoxic environment. Capsaicin-treatment re-activated p53-SMAR1 positive feed-back loop in these cells to persuade p53-mediated HIF-1α degradation and SMAR1-induced repression of Cox-2 expression that restrained HIF-1α nuclear localization. Such signal-modulations consequently down regulated VEGF expression to thwart endothelial cell migration and network formation, pre-requisites of angiogenesis in tumor micro-environment. The above results advocate the candidature of capsaicin in exclusively targeting angiogenesis by down-regulating VEGF in tumor cells to achieve more efficient and cogent therapy of resistant NSCLC.

Non-migratory tumorigenic intrinsic cancer stem cells ensure breast cancer metastasis by generation of CXCR4 + migrating cancer stem cells

Although the role of metastatic cancer stem cells (mCSCs) in tumor progression has been well documented, our study reveals a hitherto unidentified role of tumorigenic intrinsic CSCs (iCSCs) in breast cancer metastasis. We show that unlike highly migratory mCSCs residing in the breast tumor disseminating/peripheral regions, iCSCs populate the inner mass of the tumor and are non-migratory. However iCSCs, via paracrine signaling, induce conversion of non-stem cancer cells to CSCs that (i) are identical to the previously reported mCSCs, and (ii) in contrast to iCSCs, express chemokine receptor, chemokine (C-X-C motif) receptor 4 (CXCR4), which is crucial for their metastatic potential. These mCSCs also demonstrate high in vivo tumorigenicity. Physical non-participation of iCSCs in metastasis is further validated in vivo, where only mCSCs are found to exist in the metastatic sites, lymph nodes and bone marrow, whereas the primary tumor retains both iCSCs and mCSCs. However, iCSCs ensure metastasis since their presence is crucial for deliverance of highly metastatic CXCR4+ mCSCs to the migrating fraction of cells. Cumulatively, these results unveil a novel role of iCSCs in breast cancer metastasis as parental regulators of CXCR4+ mCSCs, and highlight the therapeutic requisite of targeting iCSCs, but not CXCR4+ mCSCs, to restrain breast cancer metastasis from the root by inhibiting the generation of mCSCs from iCSCs. Considering the pivotal role of iCSCs in tumor metastasis, the possibility of metastasis to be a ‘stem cell phenomena’ is suggested.

MEK inhibition prevents tumour-shed transforming growth factor-β-induced T-regulatory cell augmentation in tumour milieu.

Tumour progression is associated with immune‐suppressive conditions that facilitate the escape of tumour cells from the regimen of immune cells, subsequently paralysing the host defence mechanisms. Induction of CD4+ CD25+ FoxP3+ T regulatory (Treg) cells has been implicated in the tumour immune escape mechanism, although the novel anti‐cancer treatment strategies targeting Treg cells remain unknown. The focus of this study is to define the interaction between tumour and immune system, i.e. how immune tolerance starts and gradually leads to the induction of adaptive Treg cells in the tumour microenvironment. Our study identified hyperactivated mitogen‐activated protein kinase kinase (MEK)/extracellular signal‐regulated kinase (ERK) ‐signalling as a potential target for reversing Treg cell augmentation in breast cancer patients. In more mechanistic detail, pharmacological inhibitors of MEK/ERK signalling inhibited transforming growth factor‐β (TGF‐β) production in tumour cells that essentially blocked TGF‐β‐SMAD3/SMAD4‐mediated induction of CD25/interleukin‐2 receptor α on CD4+ T‐cell surface. As a result high‐affinity binding of interleukin‐2 on those cells was prohibited, causing lack of Janus kinase 1 (JAK1)/JAK3‐mediated signal transducer and activator of transcription 3 (STAT3)/STAT5 activation required for FoxP3 expression. Finally, for a more radical approach towards a safe MEK inhibitor, we validate the potential of multi‐kinase inhibitor curcumin, especially the nano‐curcumin made out of pure curcumin with greater bioavailability; in repealing tumour‐shed TGF‐β‐induced Treg cell augmentation.

Nifetepimine, a Dihydropyrimidone, Ensures CD4+ T Cell Survival in a Tumor Microenvironment by Maneuvering Sarco(endo)plasmic Reticulum Ca2+ ATPase (SERCA)

Background: Tumor-induced SERCA3 up-regulation is a major cause of death of CD4+T lymphocytes leading to immune suppression in cancer bearers. Results: Nifetepimine down-modulates SERCA3 expression and thereby protects the lymphocytes from tumor-induced apoptosis. Conclusion: The present finding strongly suggests nifetepimine as a potent immuno-restoring agent that protects T lymphocytes from tumor insult. Significance: The results suggest that nifetepimine may be developed into a potent immuno-restoring agent in tumor-bearers. Multiple mechanisms have been proposed by which tumors induce T cell apoptosis to circumvent tumor immune-surveillance. Although sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) have long been known to regulate intracellular Ca2+ homeostasis, few studies have examined the role of SERCA in processes of T lymphocyte survival and activation. In this context it remains largely unexplored as to how tumors jeopardize SERCA function to disable T cell-mediated anti-tumor immunity. Here, we show that human CD4+ T cells in the presence of tumor conditions manifested an up-regulation of SERCA3 expression that resulted in development of endoplasmic reticulum stress leading to CD4+ T cell apoptosis. Prostaglandin E2 produced by the tumor cell plays a critical role in up-regulating SERCA3 by enhancing the binding of its transcription factor Sp1. Gene manipulation and pharmacological approaches further established that an increase in SERCA expression also resulted in subsequent inhibition of PKCα and -θ and retention of NFκB in the cytosol; however, down-modulation of SERCA3 expression by a dihydropyrimidone derivative, ethyl-4-(3-nitro)-phenyl-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5 carboxylate (nifetepimine), protected the CD4+ T cells from tumor-induced apoptosis. In fact, nifetepimine-mediated restoration of PKC activity resulted in nuclear translocation of p65NFκB, thereby ensuring its survival. Studies further undertaken in a tumor-bearing mice model revalidated the immunoprotective role of nifetepimine. Our present study thus strongly suggests that imbalance in cellular calcium homeostasis is an important factor leading to CD4+ T cell death during cancer and holds promise that nifetepimine may have the potential to be used as an immunorestoring agent in cancer bearers.

Contribution of the ROS-p53 feedback loop in thuja-induced apoptosis of mammary epithelial carcinoma cells

The adverse side-effects associated with chemotherapy during cancer treatment have shifted considerable focus towards therapies that are targeted but devoid of toxic side-effects. In the present study, the antitumorigenic activity of thuja, the bioactive derivative of the medicinal plant Thuja occidentalis, was evaluated, and the molecular mechanisms underlying thuja-induced apoptosis of functional p53-expressing mammary epithelial carcinoma cells were elucidated. Our results showed that thuja successfully induced apoptosis in functional p53-expressing mammary epithelial carcinoma cells. Abrogation of intracellular reactive oxygen species (ROS), prevention of p53-activation, knockdown of p53 or inhibition of its functional activity significantly abridged ROS generation. Notably, under these conditions, thuja-induced breast cancer cell apoptosis was reduced, thereby validating the existence of an ROS-p53 feedback loop. Elucidating this feedback loop revealed bi-phasic ROS generation as a key mediator of thuja-induced apoptosis. the first phase of ROS was instrumental in ensuring activation of p53 via p38MAPK and its nuclear translocation for transactivation of Bax, which induced a second phase of mitochondrial ROS to construct the ROS-p53 feedback loop. Such molecular crosstalk induced mitochondrial changes i) to maintain and amplify the thuja signal in a positive self-regulatory feedback manner; and ii) to promote the mitochondrial death cascade through cytochrome c release and caspase-driven apoptosis. These results open the horizon for developing a targeted therapy by modulating the redox status of functional p53-expressing mammary epithelial carcinoma cells by thuja.