Anticancer natural products targeting immune checkpoint protein network.

Normal cells express surface proteins that bind to immune checkpoint proteins on immune cells to turn them off, whereby the immune system does not attack normal healthy cells. Cancer cells can also utilize this same protective mechanism by expressing surface proteins that can interact with checkpoint proteins on immune cells to overcome the immune surveillance. Immunotherapy is making the best use of the body's own immune system to reinforce anti-tumor responses. The most generally used immunotherapy is the control of immune checkpoints including the cytotoxic T lymphocyte-associated molecule 4 (CTLA-4), programmed cell deathreceptor 1 (PD-1), or programmed cell death ligand-1 (PD-L1). In spite of the clinical effectiveness of immune checkpoint inhibitors, the overall response rate still remains low. Therefore, there have been considerable efforts in searching for alternative immune checkpoint proteins that may work as new therapeutic targets for treatment of cancer. Recent studies have identified several additional novel immune checkpoint targets, including lymphocyte activation gene-3, T cell immunoglobulin and mucin-domain containing-3, T cell immunoglobulin and immunoreceptor tyrosine-based inhibition motif domain, V-domain Ig suppressor of T cell activation, B7 homolog 3 protein, B and T cell lymphocyte attenuator, and inducible T cell COStimulator. Natural compounds, especially those present in medicinal or dietary plants, have been investigated for their anti-tumor effects in various in vitro and in vivo models. Some phytochemicals exert anti-tumor activities based on immunoregulatioby blocking interaction between proteins involved in immune checkpoint signal transduction or regulating their expression/activity. Recently, synergistic anti-cancer effects of diverse phytochemicals with anti-PD-1/PD-L1 or anti-CTLA-4 monoclonal antibody drugs have been continuously reported. Considering an increasing attention to noteworthy therapeutic effects of immune checkpoint inhibitors in the cancer therapy, this review focuses on regulatory effects of selected phytochemicals on immune checkpoint protein network and their combinational effectiveness with immune checkpoint inhibitors targeting tumor cells.

Thymoquinone induces oxidative stress-mediated apoptosis through downregulation of Jak2/STAT3 signaling pathway in human melanoma cells.

Melanoma is a highly aggressive and treatment-resistant cancer, and the incidence and mortality rates are increasing worldwide. Thymoquinone (TQ) is the active component of Nigella sativa seed extracts and exerts anticancer effects in various cancer cells. However, the anticancer effects of TQ on melanoma and the underlying molecular mechanisms remain elusive. In this study, TQ treatment induced apoptosis in SK-MEL-28 cells. Interestingly, constitutive phosphorylation of Janus kinase 2 (Jak2) and signal transducer and activator of transcription 3 (STAT3) was markedly decreased following TQ treatment. Furthermore, TQ treatment downregulated STAT3-dependent genes including cyclin D1, D2, and D3 and survivin. Moreover, inhibition of Jak2/STAT3 using AG490, an inhibitor of Jak2 or genetic ablation of STAT3, abrogated the expression of target genes. TQ increased the levels of reactive oxygen species (ROS), whereas pretreatment with N-acetyl cysteine (NAC), a ROS scavenger, prevented the suppressive effect of TQ on Jak2/STAT3 activation and protected SK-MEL-28 cells from TQ-induced apoptosis. TQ administration further attenuated the growth of SK-MEL-28 tumor xenografts. Taken together, TQ induced apoptosis of SK-MEL-28 by hindering the Jak2/STAT3 signaling pathway through ROS generation. Our results support further development of TQ as a potential anticancer therapeutic agent for treating melanoma.

Role of chemopreventive phytochemicals in NRF2-mediated redox homeostasis in humans.

While functioning as a second messenger in the intracellular signaling, ROS can cause oxidative stress when produced in excess or not neutralized/eliminated properly. Excessive ROS production is implicated in multi-stage carcinogenesis. Our body is equipped with a defense system to cope with constant oxidative stress caused by the external insults, including redox-cycling chemicals, radiation, and microbial infection as well as endogenously generated ROS. The transcription factor, nuclear transcription factor erythroid 2-related factor 2 (NRF2) is a master switch in the cellular antioxidant signaling and plays a vital role in adaptive survival response to ROS-induced oxidative stress. Although NRF2 is transiently activated when cellular redox balance is challenged, this can be overwhelmed by massive oxidative stress. Therefore, it is necessary to maintain the NRF2-mediated antioxidant defense capacity at an optimal level. This review summarizes the natural NRF2 inducers/activators, especially those present in the plant-based diet, in relation to their cancer chemopreventive potential in humans. The molecular mechanisms underlying their stabilization or activation of NRF2 are also discussed.

Enhanced viability and function of mesenchymal stromal cell spheroids is mediated via autophagy induction.

Mesenchymal stromal cells (MSCs) have received attention as promising therapeutic agents for the treatment of various diseases. However, poor post-transplantation viability is a major hurdle in MSC-based therapy, despite encouraging results in many inflammatory disorders. Recently, three dimensional (3D)-cultured MSCs (MSC3D) were shown to have higher cell survival and enhanced anti-inflammatory effects, although the underlying mechanisms have not yet been elucidated. In this study, we investigated the molecular mechanisms by which MSC3D gain the potential for enhanced cell viability. Herein, we found that macroautophagy/autophagy was highly induced and ROS production was suppressed in MSC3D as compared to 2D-cultured MSCs (MSC2D). Interestingly, inhibition of autophagy induction caused decreased cell viability and increased apoptotic activity in MSC3D. Furthermore, modulation of ROS production was closely related to the survival and apoptosis of MSC3D. We also observed that HMOX1 (heme oxygenase 1) was significantly up-regulated in MSC3D. In addition, gene silencing of HMOX1 caused upregulation of ROS production and suppression of the genes related to autophagy. Moreover, inhibition of HIF1A (hypoxia inducible factor 1 subunit alpha) caused suppression of HMOX1 expression in MSC3D, indicating that the HIF1A-HMOX1 axis plays a crucial role in the modulation of ROS production and autophagy induction in MSC3D. Finally, the critical role of autophagy induction on improved therapeutic effects of MSC3D was further verified in dextran sulfate sodium (DSS)-induced murine colitis. Taken together, these results indicated that autophagy activation and modulation of ROS production mediated via the HIF1A-HMOX1 axis play pivotal roles in enhancing the viability of MSC3D.Abbreviations: 3D: three dimensional; 3MA: 3 methlyadenine; AMPK: AMP-activated protein kinase; Baf A1: bafilomycin A1; CFSE: carboxyfluorescein succinimidyl ester; CoCl2: cobalt chloride; CoPP: cobalt protoporphyrin; DSS: dextran sulfate sodium; ECM: extracellular matrix; FOXO3/FOXO3A: forkhead box O3; HIF1A: hypoxia inducible factor 1 subunit alpha; HMOX1/HO-1: heme oxygenase 1; HSCs: hematopoietic stem cells; IL1A/IL-1α: interleukin 1 alpha; IL1B/IL-1ß: interleukin 1 beta; IL8: interleukin 8; KEAP1: kelch like ECH associated protein 1; LAMP1: lysosomal associated membrane protein 1; LAMP2: lysosomal associated membrane protein 2; MSC2D: 2D-cultured MSCs; MSC3D: 3D-cultured MSCs; MSCs: mesenchymal stromal cells; NFE2L2/NRF2: nuclear factor, erythroid 2 like 2; PGE2: prostaglandin E2; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PINK1: PTEN induced kinase 1; ROS: reactive oxygen species; siRNA: small interfering RNA; SIRT1: sirtuin 1; SOD2: superoxide dismutase 2; SQSTM1/p62: sequestosome 1; TGFB/TGF-ß: transforming growth factor beta.

Globular adiponectin antagonizes leptin-induced growth of cancer cells by modulating inflammasomes activation: Critical role of HO-1 signaling.

Accumulating evidence suggests that adipokines, a group of hormones secreted from adipose tissue, modulate tumor growth in a complicated manner. Among diverse adipokines, adiponectin exerts potent anti-tumor activities, whereas leptin exhibits pro-tumorigenic properties. Herein, we have examined the opposing effect of adiponectin on leptin-induced growth of cancer cells and investigated the underlying mechanisms, particularly in the context of inflammasomes activation, which plays a role in the growth of cancer cells. Globular adiponectin (gAcrp) significantly suppressed leptin-induced growth of human breast (MCF-7) and hepatic (HepG2) cancer cells by modulating both cell cycle and apoptosis. To elucidate the underlying mechanisms, we examined the modulatory effects of gAcrp and leptin on inflammasomes. Herein, we showed that gAcrp substantially abolished leptin-induced inflammasomes activation, as evidenced by suppression of IL-1ß maturation, caspase-1 activation, and downregulation of inflammasomes components, including NLRP3 and ASC, in both MCF-7 and HepG2 cancer cells. Interestingly, suppression of inflammasomes activation by gAcrp was almost completely restored by blockade of heme oxygenase-1 (HO-1) signaling. In addition, suppressive effects of gAcrp on ROS production and NADPH oxidase activation, both of which critically contribute to leptin-induced inflammasomes activation, disappeared by inhibition of HO-1 signaling. Moreover, gAcrp downregulated estrogen receptor-α (ER-α) expression and blocked leptin-induced ER-α activation, which also plays an important role in inflammasomes activation. Finally, the opposing effects of gAcrp on leptin-induced inflammasomes activation and tumor growth were further confirmed in MCF-7 tumor xenografts. In summary, treatment with gAcrp prevents leptin-induced cancer cell growth by modulating inflammasome activation, which is mediated, at least in part, via HO-1 induction and modulation of ER-α signaling.

Globular Adiponectin Inhibits Breast Cancer Cell Growth through Modulation of Inflammasome Activation: Critical Role of Sestrin2 and AMPK Signaling.

Adiponectin, an adipokine predominantly derived from adipose tissue, exhibits potent antitumor properties in breast cancer cells. However, its mechanisms of action remain elusive. Inflammasomes-intracellular multimeric protein complexes-modulate cancer cell growth in a complicated manner, as well as playing a role in the innate immune system. Herein, we examined the potential role of inflammasomes in the antitumor activity of adiponectin and found that globular adiponectin (gAcrp) significantly suppressed inflammasomes activation in breast cancer cells both in vitro and in vivo conditions, as determined by decreased expression of inflammasomes components, including NOD-like receptor pyrin domain-containing protein 3 (NLRP3) and the apoptosis-associated speck-like protein containing a CARD (ASC), and inhibition of interleukin-1ß and caspase-1 activation. Treatment with pharmacological inhibitors of inflammasomes caused decrease in cell viability, apoptosis induction, and G0/G1 cell cycle arrest, suggesting that inflammasomes activation is implicated in the growth of breast cancer cells. In addition, treatment with gAcrp generated essentially similar results to those of inflammasomes inhibitors, further indicating that suppression of breast cancer cell growth by gAcrp is mediated via modulation of inflammasomes. Mechanistically, gAcrp suppressed inflammasomes activation through sestrin2 (SESN2) induction, liver kinase B1 (LKB-1)-dependent AMP-activated protein kinase (AMPK) phosphorylation, and alleviation of endoplasmic reticulum (ER) stress. Taken together, these results demonstrate that gAcrp inhibits growth of breast cancer cells by suppressing inflammasomes activation, at least in part, via SESN2 induction and AMPK activation-dependent mechanisms.

Growth of breast cancer cells by leptin is mediated via activation of the inflammasome: Critical roles of estrogen receptor signaling and reactive oxygen species production.

Leptin, a hormone primarily derived from adipose tissue, is known to induce tumor growth, but its underlying mechanisms of action are not clearly understood. Inflammasomes, acting as signaling platforms for controlling inflammatory responses, modulate tumor growth in a complicated manner. In this study, we investigated the role of inflammasomes in leptin-induced growth of breast cancer cells. Herein, we showed that leptin activated NLRP3 inflammasomes in MCF-7 breast cancer cells, as determined by activation of caspase-1, maturation of interleukin-1ß, and increased expression of the inflammasome components, including NLRP3 and ASC. Interestingly, inhibition of the inflammasome by treatment with a pharmacological inhibitor of caspase-1 or gene silencing of NLRP3 prevented leptin-induced increase in cell viability. Moreover, suppression of apoptosis and cell cycle promotion by leptin were also significantly abolished by gene silencing of NLRP3, clearly indicating a crucial role of NLRP3 inflammasomes in leptin-induced breast cancer growth. In addition, inhibition of estrogen receptor signaling or ROS production markedly blocked leptin-induced activation of NLRP3 inflammasomes, suggesting that estrogen receptor signaling and ROS production mediate inflammasomes activation by leptin. The stimulatory effect of leptin on inflammasomes activation was also observed in MCF-7 tumor xenograft model. Furthermore, the critical roles of inflammasomes activation in leptin-induced tumor growth, suppression of apoptotic gene expression, and induction of the genes stimulating cell cycle were confirmed in a tumor xenograft model. Taken together, these results demonstrate that inflammasomes activation plays a pivotal role in leptin-induced growth of breast cancer cells via modulation of both apoptosis and cell cycle.

Estrogen receptor signaling mediates leptin-induced growth of breast cancer cells via autophagy induction.

Leptin, a hormone derived from adipose tissue, promotes growth of cancer cells via multiple mechanisms. Estrogen receptor signaling is also known to stimulate the growth of breast cancer cells. However, the involvement of estrogen receptor signaling in the oncogenic actions of leptin and its underlying mechanisms are not clearly understood. Herein, we investigated mechanisms for estrogen receptor signaling-mediated growth of breast cancer cells, particularly focusing on autophagy, which plays a crucial role in leptin-induced tumor growth. Inhibition of estrogen receptor signaling via gene silencing or treatment with a pharmacological inhibitor (tamoxifen) abolished leptin-induced growth of MCF-7 human breast cancer cells. Interestingly, leptin-induced autophagy activation, determined by up-regulation of autophagy-related genes and autophagosome formation, was also significantly suppressed by inhibiting estrogen receptor signaling. Moreover, inhibition of estrogen receptor markedly prevented leptin-induced activation of AMPK/FoxO3A axis, which plays a crucial role in autophagy induction. Leptin-induced cell cycle progression and Bax down-regulation were also prevented by treatment with tamoxifen. The pivotal roles of estrogen receptor signaling in leptin-induced cell cycle progression, apoptosis suppression, and autophagy induction were further confirmed in MCF-7 tumor xenograft model. Taken together, these results demonstrate that estrogen receptor signaling plays a key role in leptin-induced growth of breast cancer cells via autophagy activation.