Bcl-2 inhibitors as anti-cancer therapeutics: The impact of and on calcium signaling

Significance of TRAIL/Apo-2 ligand and its death receptors in apoptosis and necroptosis signalling: Implications for cancer-targeted therapeutics

The human immune defensesystem routinely expresses the tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), which is the most prevalent element for antitumor immunity. TRAIL associates with its death receptors (DRs), DR4 (TRAIL-R1), and DR5 (TRAIL-R2), in cancer cells to initiate the intracellular apoptosis cascade. Accordingly, numerous academic institutions and pharmaceutical companies havetried to exploreTRAIL's capacity to kill tumourcells by producing recombinant versions of it (rhTRAIL) or TRAIL receptor agonists (TRAs) [monoclonal antibody (mAb), synthetic and natural compounds, etc.] and molecules that sensitize TRAIL signalling pathway for therapeutic applications. Recently, several microRNAs (miRs) have been found to activate or inhibit death receptor signalling. Therefore, pharmacological regulation of these miRs may activate or resensitize the TRAIL DRs signal, and this is a novel approach for developing anticancer therapeutics. In this article, we will discuss TRAIL and its receptors and molecular pathways by which it induces various cell death events. We will unravel potential innovative applications of TRAIL-based therapeutics, and other investigated therapeutics targeting TRAIL-DRs and summarize the current preclinical pharmacological studies and clinical trials. Moreover, we will also emphasizea few situations where future efforts may be addressed to modulate the TRAIL signalling pathway.

CYD0281, a Bcl-2 BH4 domain antagonist, inhibits tumor angiogenesis and breast cancer tumor growth

BACKGROUND

B-cell lymphoma 2 (Bcl-2) family proteins are key regulators of apoptosis, which possess four conserved Bcl-2 homologies (BH) domains. Among the BH domains, the BH3 domain is considered as a potent 'death domain' while the BH4 domain is required for anti-apoptotic activity. Bcl-2 can be converted to a pro-apoptotic molecule through the removal or mutation of the BH4 domain. Bcl-2 is considered as an inducer of angiogenesis, which can promote tumor vascular network formation and further afford nutrients and oxygen to promote tumor progression. However, whether disrupting the function of the BH4 domain to convert Bcl-2 into a pro-apoptotic molecule could make Bcl-2 possess the potential for anti-angiogenic therapy remains to be defined.

METHODS

CYD0281 was designed and synthesized according to the lead structure of BDA-366, and its function on inducing a conformational change of Bcl-2 was further evaluated via immunoprecipitation (IP) and immunofluorescence (IF) assays. Moreover, the function of CYD0281 on apoptosis of endothelial cells was analyzed via cell viability, flow cytometry, and western blotting assays. Additionally, the role of CYD0281 on angiogenesis in vitro was determined via endothelial cell migration and tube formation assays and rat aortic ring assay. Chick embryo chorioallantoic membrane (CAM) and yolk sac membrane (YSM) models, breast cancer cell xenograft tumor on CAM and in mouse models as well as the Matrigel plug angiogenesis assay were used to explore the effects of CYD0281 on angiogenesis in vivo.

RESULTS

We identified a novel potent small-molecule Bcl-2-BH4 domain antagonist, CYD0281, which exhibited significant anti-angiogenic effects both in vitro and in vivo, and further inhibited breast cancer tumor growth. CYD0281 was found to induce conformational changes in Bcl-2 through the exposure of the BH3 domain and convert Bcl-2 from an anti-apoptotic molecule into a cell death inducer, thereby resulting in the apoptosis of vascular endothelial cells.

CONCLUSIONS

This study has revealed CYD0281 as a novel Bcl-2-BH4 antagonist that induces conformational changes of Bcl-2 to convert to a pro-apoptotic molecule. Our findings indicate that CYD0281 plays a crucial role in anti-angiogenesis and may be further developed as a potential anti-tumor drug candidate for breast cancer. This work also provides a potential anti-angiogenic strategy for breast cancer treatment.

Calcium's Role in Orchestrating Cancer Apoptosis: Mitochondrial-Centric Perspective

Calcium is an essential intracellular messenger that plays a vital role in controlling a broad range of cellular processes, including apoptosis. This review offers an in-depth analysis of calcium's multifaceted role in apoptosis regulation, focusing on the associated signaling pathways and molecular mechanisms. We will explore calcium's impact on apoptosis through its effects on different cellular compartments, such as the mitochondria and endoplasmic reticulum (ER), and discuss the connection between calcium homeostasis and ER stress. Additionally, we will highlight the interplay between calcium and various proteins, including calpains, calmodulin, and Bcl-2 family members, and the role of calcium in regulating caspase activation and pro-apoptotic factor release. By investigating the complex relationship between calcium and apoptosis, this review aims to deepen our comprehension of the fundamental processes, and pinpointing possible treatment options for illnesses associated with imbalanced cell death is crucial.

The ER-mitochondria interface, where Ca2+ and cell death meet

Endoplasmic reticulum (ER)-mitochondria contact sites are crucial to allow Ca²⁺ flux between them and a plethora of proteins participate in tethering both organelles together. Inositol 1,4,5-trisphosphate receptors (IP₃Rs) play a pivotal role at such contact sites, participating in both ER-mitochondria tethering and as Ca²⁺-transport system that delivers Ca²⁺ from the ER towards mitochondria. At the ER-mitochondria contact sites, the IP₃Rs function as a multi-protein complex linked to the voltage-dependent anion channel 1 (VDAC1) in the outer mitochondrial membrane, via the chaperone glucose-regulated protein 75 (GRP75). This IP₃R-GRP75-VDAC1 complex supports the efficient transfer of Ca²⁺ from the ER into the mitochondrial intermembrane space, from which the Ca²⁺ ions can reach the mitochondrial matrix through the mitochondrial calcium uniporter. Under physiological conditions, basal Ca²⁺ oscillations deliver Ca²⁺ to the mitochondrial matrix, thereby stimulating mitochondrial oxidative metabolism. However, when mitochondrial Ca²⁺ overload occurs, the increase in [Ca²⁺] will induce the opening of the mitochondrial permeability transition pore, thereby provoking cell death. The IP₃R-GRP75-VDAC1 complex forms a hub for several other proteins that stabilize the complex and/or regulate the complex's ability to channel Ca²⁺ into the mitochondria. These proteins and their mechanisms of action are discussed in the present review with special attention for their role in pathological conditions and potential implication for therapeutic strategies.

Therapeutic advancements in targeting BCL-2 family proteins by epigenetic regulators, natural, and synthetic agents in cancer

Cancer is amongst the deadliest and most disruptive disorders, having a much higher death rate than other diseases worldwide. Human cancer rates continue to rise, thereby posing the most significant concerns for medical health professionals. In the last two decades, researchers have gone past several milestones in tackling cancer while gaining insight into the role of apoptosis in cancer or targeting various biomarker tools for prognosis and diagnosis. Apoptosis which is still a topic full of complexities, can be controlled considerably by B-cell lymphoma 2 (BCL-2) and its family members. Therefore, targeting proteins of this family to prevent tumorigenesis, is essential to focus on the pharmacological features of the anti-apoptotic and pro-apoptotic members, which will help to develop and manage this disorder. This review deals with the advancements of various epigenetic regulators to target BCL-2 family proteins, including the mechanism of several microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Similarly, a rise in natural and synthetic molecules' research over the last two decades has allowed us to acquire insights into understanding and managing the transcriptional alterations that have led to apoptosis and treating various neoplastic diseases. Furthermore, several inhibitors targeting anti-apoptotic proteins and inducers or activators targeting pro-apoptotic proteins in preclinical and clinical stages have been summarized. Overall, agonistic and antagonistic mechanisms of BCL-2 family proteins conciliated by epigenetic regulators, natural and synthetic agents have proven to be an excellent choice in developing cancer therapeutics.

Demethylzeylasteral targets lactate by inhibiting histone lactylation to suppress the tumorigenicity of liver cancer stem cells

Cancer stem cells drive tumor initiation, progression, and recurrence, which compromise the effectiveness of anti-tumor drugs. Here, we report that demethylzeylasteral (DML), a triterpene anti-tumor compound, suppressed tumorigenesis of liver cancer stem cells (LCSCs) by interfering with lactylation of a metabolic stress-related histone. Using RNA sequencing (RNA-seq) and gas chromatography-mass spectrometric (GC-MS) analysis, we showed that the glycolysis metabolic pathway contributed to the anti-tumor effects of DML, and then focused on lactate downstream regulation as the molecular target. Mechanistically, DML opposed the progress of hepatocellular carcinoma (HCC), which was efficiently facilitated by the increase in H3 histone lactylation. Two histone modification sites: H3K9la and H3K56la, which were found to promote tumorigenesis, were inhibited by DML. In addition, we used a nude mouse tumor xenograft model to confirm that the anti-liver cancer effects of DML are mediated by regulating H3 lactylation in vivo. Our findings demonstrate that DML suppresses the tumorigenicity induced by LCSCs by inhibiting H3 histone lactylation, thus implicating DML as a potential candidate for the supplementary treatment of hepatocellular carcinoma.

The multifaceted roles of mitochondria at the crossroads of cell life and death in cancer

Mitochondria are the cytoplasmic organelles mostly known as the "electric engine" of the cells; however, they also play pivotal roles in different biological processes, such as cell growth/apoptosis, Ca²⁺ and redox homeostasis, and cell stemness. In cancer cells, mitochondria undergo peculiar functional and structural dynamics involved in the survival/death fate of the cell. Cancer cells use glycolysis to support macromolecular biosynthesis and energy production ("Warburg effect"); however, mitochondrial OXPHOS has been shown to be still active during carcinogenesis and even exacerbated in drug-resistant and stem cancer cells. This metabolic rewiring is associated with mutations in genes encoding mitochondrial metabolic enzymes ("oncometabolites"), alterations of ROS production and redox biology, and a fine-tuned balance between anti-/proapoptotic proteins. In cancer cells, mitochondria also experience dynamic alterations from the structural point of view undergoing coordinated cycles of biogenesis, fusion/fission and mitophagy, and physically communicating with the endoplasmic reticulum (ER), through the Ca²⁺ flux, at the MAM (mitochondria-associated membranes) levels. This review addresses the peculiar mitochondrial metabolic and structural dynamics occurring in cancer cells and their role in coordinating the balance between cell survival and death. The role of mitochondrial dynamics as effective biomarkers of tumor progression and promising targets for anticancer strategies is also discussed.

Bcl-xL acts as an inhibitor of IP3R channels, thereby antagonizing Ca2+-driven apoptosis

Anti-apoptotic Bcl-2-family members not only act at mitochondria but also at the endoplasmic reticulum, where they impact Ca²⁺ dynamics by controlling IP₃ receptor (IP₃R) function. Current models propose distinct roles for Bcl-2 vs. Bcl-xL, with Bcl-2 inhibiting IP₃Rs and preventing pro-apoptotic Ca²⁺ release and Bcl-xL sensitizing IP₃Rs to low [IP₃] and promoting pro-survival Ca²⁺ oscillations. We here demonstrate that Bcl-xL too inhibits IP₃R-mediated Ca²⁺ release by interacting with the same IP₃R regions as Bcl-2. Via in silico superposition, we previously found that the residue K87 of Bcl-xL spatially resembled K17 of Bcl-2, a residue critical for Bcl-2's IP₃R-inhibitory properties. Mutagenesis of K87 in Bcl-xL impaired its binding to IP₃R and abrogated Bcl-xL's inhibitory effect on IP₃Rs. Single-channel recordings demonstrate that purified Bcl-xL, but not Bcl-xL^K87D, suppressed IP₃R single-channel openings stimulated by sub-maximal and threshold [IP₃]. Moreover, we demonstrate that Bcl-xL-mediated inhibition of IP₃Rs contributes to its anti-apoptotic properties against Ca²⁺-driven apoptosis. Staurosporine (STS) elicits long-lasting Ca²⁺ elevations in wild-type but not in IP₃R-knockout HeLa cells, sensitizing the former to STS treatment. Overexpression of Bcl-xL in wild-type HeLa cells suppressed STS-induced Ca²⁺ signals and cell death, while Bcl-xL^K87D was much less effective in doing so. In the absence of IP₃Rs, Bcl-xL and Bcl-xL^K87D were equally effective in suppressing STS-induced cell death. Finally, we demonstrate that endogenous Bcl-xL also suppress IP₃R activity in MDA-MB-231 breast cancer cells, whereby Bcl-xL knockdown augmented IP₃R-mediated Ca²⁺ release and increased the sensitivity towards STS, without altering the ER Ca²⁺ content. Hence, this study challenges the current paradigm of divergent functions for Bcl-2 and Bcl-xL in Ca²⁺-signaling modulation and reveals that, similarly to Bcl-2, Bcl-xL inhibits IP₃R-mediated Ca²⁺ release and IP₃R-driven cell death. Our work further underpins that IP₃R inhibition is an integral part of Bcl-xL's anti-apoptotic function.

Kaempferol-3-O-rutinoside, a flavone derived from Tetrastigma hemsleyanum, suppresses lung adenocarcinoma via the calcium signaling pathway

Lung cancer has been threatening human health worldwide for a long time. However, the clinic therapies remain unsatisfactory. In this study, the anti-adenocarcinoma lung cancer A549 cell line abilities of Tetrastigma hemsleyanum tuber flavonoids (THTF) were evaluated in vivo, and isobaric tags for relative and absolute quantification (iTRAQ)-based proteomic analysis was conducted to detect the protein alterations in THTF-treated solid tumors. The differentially expressed proteins were related to the cytoskeleton and mostly accumulated in the calcium signaling pathway. The in vitro study illustrated that 80 μg mL-1 THTF significantly suppressed cellular viability to approximately 75% of the control. Further results suggested that kaempferol-3-O-rutinoside (K3R), the major component of THTF, effectively triggered cytoskeleton collapse, mitochondrial dysfunction and consequent calcium overload to achieve apoptosis, which remained consistent with proteomic results. This study uncovers a new mechanism for THTF anti-tumor ability, and suggests THTF and K3R as promising anti-cancer agents, providing new ideas and possible strategies for future anti-lung cancer prevention and therapy.

pH-Responsive Pluronic F127-Lenvatinib-Encapsulated Halogenated Boron-Dipyrromethene Nanoparticles for Combined Photodynamic Therapy and Chemotherapy of Liver Cancer

Combination therapy such as photodynamic therapy (PDT)-enhanced chemotherapy is regarded as a promising strategy for cancer treatment. Boron-dipyrromethene (BODIPY), as close relatives of porphyrins, was widely used in PDT. However, poor water solubility, rapid metabolism by the body and lack of targeting limits its clinical application. Lenvatinib, as the first-line drug for molecular-targeted therapy of liver cancer, restricted its clinical application for its side effects. Herein, to achieve the synergy between PDT and chemotherapy, we synthesized two halogenated BODIPY, BDPBr₂ and BDPCl₂, which were prepared into self-assembly nanoparticles with lenvatinib, and were encapsulated with Pluronic F127 through the nanoprecipitation method, namely, LBPNPs (LBBr₂ NPs and LBCl₂ NPs). The fluorescence quantum yields of LBPNPs were 0.73 and 0.71, respectively. The calculated loading rates of lenvatinib for LBBr₂ NPs and LBCl₂ NPs were 11.8 and 10.2%, respectively. LBPNPs can be hydrolyzed under weakly acidic conditions (pH 5.0) to generate reactive oxygen species (ROS), and the release rate of lenvatinib reached 88.5 and 82.4%. Additionally, LBPNPs can be effectively taken up by Hep3B and Huh7 liver cancer cells, releasing halogenated BODIPY and lenvatinib in the acidic environment of tumor cells to enhance the targeting performance of chemotherapeutics. Compared with free lenvatinib and separate halogenated BODIPY, LBPNPs can inhibit tumor growth more effectively through pH-responsive chemo/photodynamic synergistic therapy and significantly promote the cascade of caspase apoptotic protease. This study shows that LBPNPs can be a promising nanotheranostic agent for synergetic chemo/photodynamic liver cancer therapy.

Progesterone induces apoptosis by activation of caspase-8 and calcitriol via activation of caspase-9 pathways in ovarian and endometrial cancer cells in vitro

Previously we have shown inhibition of endometrial cancer cell growth with progesterone and calcitriol. However, the mechanisms by which the two agents attenuate proliferation have not been well characterized yet. Herein, we investigated how progesterone and calcitriol induce apoptosis in cancer cells. DNA fragmentation was upregulated by progesterone and calcitriol in ovarian and endometrial cancer cells. Time-dependent treatment of ovarian cancer cells, ES-2, and TOV-21G with progesterone enhanced caspase -8 activity after 12 h, whereas OV-90, TOV-112D, HEC-1A, and HEC-59 cells showed increased activity after 24 h. Caspase 9 activity was increased in all cell lines after 24 h treatment with calcitriol. Pretreatment of cancer cells with a caspase-8 inhibitor (z-IETD-fmk) or caspase-9 inhibitor (Z-LEHD-fmk) significantly attenuated progesterone and calcitriol induced caspase-8 and caspase-9 expression, respectively. The expression of FasL, Fas, FAD, and pro-caspase-8, which constitute the death-inducing signaling complex (DISC), was upregulated in progesterone treated cancer cells. Knockdown of FAS or FADD with specific siRNAs significantly blocked progesterone-induced caspase-8. Cleavage of the BID was not affected by caspase-8 activation suggesting the absence of cross-talk between caspase-8 and caspase-9 pathways. Calcitriol treatment decreased mitochondrial membrane potential and increased the release of cancer cytochrome C. These findings indicate that progesterone induces apoptosis through activation of caspase-8 and calcitriol through caspase-9 activation in cancer cells. A combination of progesterone-calcitriol activates both extrinsic and intrinsic apoptotic pathways in cancer cells.

Delivery of apigenin-loaded magnetic Fe2O3/Fe3O4@mSiO2 nanocomposites to A549 cells and their antitumor mechanism

This study introduces a mesoporous magnetic nano-system for the delivery of apigenin (API). A targeted therapeutic drug delivery system was prepared based on Fe₂O₃/Fe₃O₄@mSiO₂-HA nanocomposites. Magnetic Fe₂O₃/Fe₃O₄ heterogeneous nanoparticles were first prepared via the rapid-combustion process. The effects of solvent type, solvent volume, calcination temperature, and calcination time on the crystal size and magnetism of the Fe₂O₃/Fe₃O₄ heterogeneous nanoparticles were investigated. The mesoporous silica shell was deposited on the Fe₂O₃/Fe₃O₄ heterogeneous nanoparticles using an improved Stöber method. HA was exploited as the targeting ligand. The specific surface area of the Fe₂O₃/Fe₃O₄@mSiO₂ nanocomposites was 369.6 m²/g, which is 19 times higher than that of the magnetic Fe₂O₃/Fe₃O₄ heterogeneous nanoparticle cores. Drug release properties from the Fe₂O₃/Fe₃O₄@mSiO₂-HA nanocomposites were studied, and the result showed that API-loaded nano-system had sustained release effect. Prussian blue staining and electrochemical performance variation showed that an external magnetic field facilitated cell uptake of Fe₂O₃/Fe₃O₄@mSiO₂-HA nanocomposites. MTT assays showed that the cell inhibition effect of API-Fe₂O₃/Fe₃O₄@mSiO₂-HA was stronger than that of free API at the same drug dose under a magnetic field and Fe₂O₃/Fe₃O₄@mSiO₂-HA nanocomposites showed good biocompatibility. Fluorescence imaging, flow cytometry, western blot, reactive oxygen species (ROS), Superoxide dismutase (SOD) and malondialdehyde (MDA) kits verified that the enhanced therapeutic action was due to the promotion of apoptosis, lipid peroxidation, and ferroptosis. The magnetic nano-system (Fe₂O₃/Fe₃O₄@mSiO₂-HA) showed good magnetic targeting and active hyaluronic acid targeting, and has the potential to provide a targeted delivery platform for many antitumor drugs.

Regulation of Cell Death by Mitochondrial Transport Systems of Calcium and Bcl-2 Proteins

Mitochondria represent the fundamental system for cellular energy metabolism, by not only supplying energy in the form of ATP, but also by affecting physiology and cell death via the regulation of calcium homeostasis and the activity of Bcl-2 proteins. A lot of research has recently been devoted to understanding the interplay between Bcl-2 proteins, the regulation of these interactions within the cell, and how these interactions lead to the changes in calcium homeostasis. However, the role of Bcl-2 proteins in the mediation of mitochondrial calcium homeostasis, and therefore the induction of cell death pathways, remain underestimated and are still not well understood. In this review, we first summarize our knowledge about calcium transport systems in mitochondria, which, when miss-regulated, can induce necrosis. We continue by reviewing and analyzing the functions of Bcl-2 proteins in apoptosis. Finally, we link these two regulatory mechanisms together, exploring the interactions between the mitochondrial Ca2+ transport systems and Bcl-2 proteins, both capable of inducing cell death, with the potential to determine the cell death pathway-either the apoptotic or the necrotic one.

BDA-366, a putative Bcl-2 BH4 domain antagonist, induces apoptosis independently of Bcl-2 in a variety of cancer cell models

Several cancer cell types, including chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL) upregulate antiapoptotic Bcl-2 to cope with oncogenic stress. BH3 mimetics targeting Bcl-2's hydrophobic cleft have been developed, including venetoclax as a promising anticancer precision medicine for treating CLL patients. Recently, BDA-366 was identified as a small molecule BH4-domain antagonist that could kill lung cancer and multiple myeloma cells. BDA-366 was proposed to switch Bcl-2 from an antiapoptotic into a proapoptotic protein, thereby activating Bax and inducing apoptosis. Here, we scrutinized the therapeutic potential and mechanism of action of BDA-366 in CLL and DLBCL. Although BDA-366 displayed selective toxicity against both cell types, the BDA-366-induced cell death did not correlate with Bcl-2-protein levels and also occurred in the absence of Bcl-2. Moreover, although BDA-366 provoked Bax activation, it did neither directly activate Bax nor switch Bcl-2 into a Bax-activating protein in in vitro Bax/liposome assays. Instead, in primary CLL cells and DLBCL cell lines, BDA-366 inhibited the activity of the PI3K/AKT pathway, resulted in Bcl-2 dephosphorylation and reduced Mcl-1-protein levels without affecting the levels of Bcl-2 or Bcl-xL. Hence, our work challenges the current view that BDA-366 is a BH4-domain antagonist of Bcl-2 that turns Bcl-2 into a pro-apoptotic protein. Rather, our results indicate that other mechanisms beyond switching Bcl-2 conformation underlie BDA-366's cell-death properties that may implicate Mcl-1 downregulation and/or Bcl-2 dephosphorylation.

Acute toxicity analysis of Disarib, an inhibitor of BCL2

Small molecule inhibitors targeting BCL2 are explored as anticancer therapeutics. Previously, we have reported identification and characterization of a novel BCL2 inhibitor, Disarib. Disarib induced cancer cell death in a BCL2 dependent manner in different cancer cell lines and mouse tumor models when it was administered intraperitoneally. In the present study, using two syngeneic mouse models, breast adenocarcinoma (EAC) and Dalton’s lymphoma (DLA), we show that oral administration of Disarib resulted in significant tumor regression in a concentration dependent manner. Importantly, tumor developed in both female and male mice were equally sensitive to Disarib. Further, we have investigated the toxicity of Disarib in normal cells. Single dose toxicity analysis of Disarib in male and female mice after oral administration revealed no significant variations compared to control group for parameters such as body weight, food and water consumption and behavioural changes which were analysed for the entire period of study. Haematological and histopathological analyses also did not show any significant difference from the control groups. Thus, our results reveal safe use of Disarib as a small molecule inhibitor and provide the foundation for investigation of other preclinical studies.

Oroxylin A reversed Fibronectin-induced glioma insensitivity to Temozolomide by suppressing IP3R1/AKT/β-catenin pathway

AIMS

Cell adhesion mediated-drug resistance (CAM-DR) is one of main reasons for. the limitation to chemotherapy, but the underlying mechanism remains unclear in glioma. In this study, we investigated the mechanism of CAM-DR induced by Fibronectin (Fn). Besides, we studied the reversal effect of Oroxylin A, a natural flavonoid extracted from Scutellaria radix, on Temozolomide (TMZ) insensitivity of glioma cells.

MAIN METHODS

Human Fn protein was used to mimic cell adhesion model and investigate its effect on the insensitivity of glioma cells to TMZ. Moreover, Oroxylin A was studied regarding its reversal effect on TMZ insensitivity of glioma via multiple molecular biological methods such as MTT, cell apoptosis assay, siRNA transfection, western blot, immunofluorescence assay.

KEY FINDINGS

Fn could decrease the apoptosis-inducing effect of TMZ and led to the CAM-DR in glioma cells. Further studies showed that up-regulations of IP₃R1 and intracellular Ca²⁺ level induced the activation of AKT kinase which increased the phosphorylation of GSK-3β and subsequently caused the entry of β-catenin into the nucleus. Knocking down IP₃R1 significantly improved the sensitivity of glioma cells to TMZ. Meanwhile, after treatment with low-toxic concentration of Oroxylin A, the apoptosis induced by TMZ under Fn condition increased dramatically. Furthermore, our results revealed that Oroxylin A markedly inhibited the expression of IP₃R1 and the activation of AKT/β-catenin pathway.

SIGNIFICANCE

Oroxylin A could reverse the insensitivity of TMZ via suppressing IP₃R1/AKT/β-catenin pathway and it might be helpful for enhancing the anti-cancer effect of TMZ in glioma.

Report of the 23rd Meeting on Signal Transduction 2019-Trends in Cancer and Infection

The annual meeting "Signal Transduction-Receptors, Mediators and Genes" of the Signal Transduction Society (STS) is an interdisciplinary conference open to all scientists sharing the common interest in elucidating the signalling pathways underlying the physiological or pathological processes in health and disease of humans, animals, plants, fungi, prokaryotes and protists. The 23rd meeting on signal transduction was held from 4-6 November 2019 in Weimar, Germany, and focused on "Trends in Cancer and Infection". As usual, keynote presentations by invited scientists introduced the respective workshops and were followed by speakers chosen from the submitted abstracts. Ample time had been reserved for discussion of the presented data during the workshops. In this report, we provide a concise summary of the various workshops and further aspects of the scientific program.

Circular RNA has_circ_0000527 participates in proliferation, invasion and migration of retinoblastoma cells via miR-646/BCL-2 axis

Retinoblastoma (RB) is one of the most common primary intraocular malignancies in children. Emerging researches have shown that circular RNAs (circRNAs) play critical roles in a variety of cancers. As a novel circRNA, the function of circ_0000527 in RB remains unknown. In this work, expression level of circ_0000527 and miR-646 in RB tissues and cell lines were detected by quantitative real-time polymerase chain reaction (qRT-PCR). RB cell lines (SO-Rb50 and WERI-Rb-1) were used as cell models in functional experiments. CCK-8 assay, TUNEL assay and transwell assay were employed to detect the biological influence of circ_0000527 and miR-646 on cancer cells in vitro. qRT-PCR, luciferase reporter assay, RIP assay and western blot were used for exploring the interactions among circ_0000527, miR-646 and BCL-2. It was demonstrated that expression level of circ_0000527 in RB samples was significantly up-regulated compared to normal tissues, while miR-646 was markedly down-regulated. Overexpression of circ_0000527 promoted the viability, migration and invasion of RB cells, while miR-646 transfection had the opposite effects. Circ_0000527 sponged miR-646 to regulate the expression of BCL-2. In conclusion, circ_0000527 could promote the development of RB by indirectly modulating BCL-2 via absorbing miR-646. SIGNIFICANCE OF THE STUDY: Expression level of circ_0000527 in RB samples was significantly up-regulated compared to normal tissues, while miR-646 was markedly down-regulated. Overexpression of circ_0000527 promoted the viability, migration and invasion of RB cells, while miR-646 transfection had the opposite effects. Circ_0000527 sponged miR-646 to regulate the expression of BCL-2.

Partners in Crime: Towards New Ways of Targeting Calcium Channels

The characterization of calcium channel interactome in the last decades opened a new way of perceiving ion channel function and regulation. Partner proteins of ion channels can now be considered as major components of the calcium homeostatic mechanisms, while the reinforcement or disruption of their interaction with the channel units now represents an attractive target in research and therapeutics. In this review we will focus on the targeting of calcium channel partner proteins in order to act on the channel activity, and on its consequences for cell and organism physiology. Given the recent advances in the partner proteins’ identification, characterization, as well as in the resolution of their interaction domain structures, we will develop the latest findings on the interacting proteins of the following channels: voltage-dependent calcium channels, transient receptor potential and ORAI channels, and inositol 1,4,5-trisphosphate receptor.

Creating a New Cancer Therapeutic Agent by Targeting the Interaction between Bcl-2 and IP3 Receptors

Bcl-2 is a member of a family of proteins that regulate cell survival. Expression of Bcl-2 is aberrantly elevated in many types of cancer. Within cells of the immune system, Bcl-2 has a physiological role in regulating immune responses. However, in cancers arising from cells of the immune system Bcl-2 promotes cell survival and proliferation. This review summarizes discoveries over the past 30 years that have elucidated Bcl-2's role in the normal immune system, including its actions in regulating calcium (Ca²⁺) signals necessary for the immune response, and for Ca²⁺-mediated apoptosis at the end of an immune response. How Bcl-2 modulates the release of Ca²⁺ from intracellular stores via inositol 1,4,5-trisphosphate receptors (IP₃R) is discussed, and in particular, the role of Bcl-2/IP₃R interactions in promoting the survival of cancer cells by preventing Ca²⁺-mediated cell death. The development and usage of a peptide, referred to as TAT-Pep8, or more recently, BIRD-2, that induces death of cancer cells by inhibiting Bcl-2's control over IP₃R-mediated Ca²⁺ elevation is discussed. Studies aimed at discovering a small molecule that mimics BIRD-2's anticancer mechanism of action are summarized, along with the prospect of such a compound becoming a novel therapeutic option for cancer.

Structure and Function of IP3 Receptors

Inositol 1,4,5-trisphosphate receptors (IP₃Rs), by releasing Ca²⁺ from the endoplasmic reticulum (ER) of animal cells, allow Ca²⁺ to be redistributed from the ER to the cytosol or other organelles, and they initiate store-operated Ca²⁺ entry (SOCE). For all three IP₃R subtypes, binding of IP₃ primes them to bind Ca²⁺, which then triggers channel opening. We are now close to understanding the structural basis of IP₃R activation. Ca²⁺-induced Ca²⁺ release regulated by IP₃ allows IP₃Rs to regeneratively propagate Ca²⁺ signals. The smallest of these regenerative events is a Ca²⁺ puff, which arises from the nearly simultaneous opening of a small cluster of IP₃Rs. Ca²⁺ puffs are the basic building blocks for all IP₃-evoked Ca²⁺ signals, but only some IP₃ clusters, namely those parked alongside the ER-plasma membrane junctions where SOCE occurs, are licensed to respond. The location of these licensed IP₃Rs may allow them to selectively regulate SOCE.

Therapeutic implications of novel peptides targeting ER-mitochondria Ca2+-flux systems

Intracellular Ca²⁺-flux systems located at the ER-mitochondrial axis govern mitochondrial Ca²⁺ balance and cell fate. Multiple yet incurable pathologies are characterized by insufficient or excessive Ca²⁺ fluxes toward the mitochondria, in turn leading to aberrant cell life or death dynamics. The discovery and ongoing molecular characterization of the main interorganellar Ca²⁺ gateways have resulted in a novel class of peptide tools able to regulate relevant protein-protein interactions (PPIs) underlying this signaling scenario. Here, we review peptides, molecularly derived from Ca²⁺-flux systems or their accessory proteins. We discuss how they alter Ca²⁺-signaling protein complexes and modulate cell survival in light of their forthcoming therapeutic applications.

Communication between mitochondria and other organelles: a brand-new perspective on mitochondria in cancer

Mitochondria are energy factories of cells and are important pivots for intracellular interactions with other organelles. They interact with the endoplasmic reticulum, peroxisomes, and nucleus through signal transduction, vesicle transport, and membrane contact sites to regulate energy metabolism, biosynthesis, immune response, and cell turnover. However, when the communication between organelles fails and the mitochondria are dysfunctional, it may induce tumorigenesis. In this review, we elaborate on how mitochondria interact with the endoplasmic reticulum, peroxisomes, and cell nuclei, as well as the relation between organelle communication and tumor development .

ER-mitochondria interactions: Both strength and weakness within cancer cells

ER-mitochondria contact sites represent hubs for signaling that control mitochondrial biology related to several aspects of cellular survival, metabolism, cell death sensitivity and metastasis, which all contribute to tumorigenesis. Altered ER-mitochondria contacts can deregulate Ca²⁺ homeostasis, phospholipid metabolism, mitochondrial morphology and dynamics. MAM represent both a hot spot in cancer onset and progression and an Achilles' heel of cancer cells that can be exploited for therapeutic perspectives. Over the past years, an increasing number of cancer-related proteins, including oncogenes and tumor suppressors, have been localized in MAM and exert their pro- or antiapoptotic functions through the regulation of Ca²⁺ transfer and signaling between the two organelles. In this review, we highlight the central role of ER-mitochondria contact sites in tumorigenesis and focus on chemotherapeutic drugs or potential targets that act on MAM properties for new therapeutic approaches in cancer.

Bcl-2 Inhibition to Overcome Resistance to Chemo- and Immunotherapy

Abstract: According to the World Health Organization (WHO), cancer is a leading cause of death worldwide. The identification of novel targets for cancer treatment is an area of intense work that has led Bcl-2 over-expression to be proposed as one of the hallmarks of cancer and Bcl-2 inhibition as a promising strategy for cancer treatment. In this review, we describe the different pathways related to programmed cell death, the role of Bcl-2 family members in apoptosis resistance to anti-cancer treatments, and the potential utility of Bcl-2 inhibitors to overcome resistance to chemo- and immunotherapy.

ABT-199 (Venetoclax), a BH3-mimetic Bcl-2 inhibitor, does not cause Ca2+ -signalling dysregulation or toxicity in pancreatic acinar cells

BACKGROUND AND PURPOSE

Many cancer cells depend on anti-apoptotic B-cell lymphoma 2 (Bcl-2) proteins for their survival. Bcl-2 antagonism through Bcl-2 homology 3 (BH3) mimetics has emerged as a novel anti-cancer therapy. ABT-199 (Venetoclax), a recently developed BH3 mimetic that selectively inhibits Bcl-2, was introduced into the clinic for treatment of relapsed chronic lymphocytic leukaemia. Early generations of Bcl-2 inhibitors evoked sustained Ca²⁺ responses in pancreatic acinar cells (PACs) inducing cell death. Therefore, BH3 mimetics could potentially be toxic for the pancreas when used to treat cancer. Although ABT-199 was shown to kill Bcl-2-dependent cancer cells without affecting intracellular Ca²⁺ signalling, its effects on PACs have not yet been determined. Hence, it is essential and timely to assess whether this recently approved anti-leukaemic drug might potentially have pancreatotoxic effects.

EXPERIMENTAL APPROACH

Single-cell Ca²⁺ measurements and cell death analysis were performed on isolated mouse PACs.

KEY RESULTS

Inhibition of Bcl-2 via ABT-199 did not elicit intracellular Ca²⁺ signalling on its own or potentiate Ca²⁺ signalling induced by physiological/pathophysiological stimuli in PACs. Although ABT-199 did not affect cell death in PACs, under conditions that killed ABT-199-sensitive cancer cells, cytosolic Ca²⁺ extrusion was slightly enhanced in the presence of ABT-199. In contrast, inhibition of Bcl-xL potentiated pathophysiological Ca²⁺ responses in PACs, without exacerbating cell death.

CONCLUSION AND IMPLICATIONS

Our results demonstrate that apart from having a modest effect on cytosolic Ca²⁺ extrusion, ABT-199 does not substantially alter intracellular Ca²⁺ homeostasis in normal PACs and should be safe for the pancreas during cancer treatment.

LINKED ARTICLES

This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Extracellular and ER-stored Ca2+ contribute to BIRD-2-induced cell death in diffuse large B-cell lymphoma cells

The anti-apoptotic protein Bcl-2 is upregulated in several cancers, including diffuse large B-cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL). In a subset of these cancer cells, Bcl-2 blocks Ca²⁺-mediated apoptosis by suppressing the function of inositol 1,4,5-trisphosphate (IP₃) receptors (IP₃Rs) located at the endoplasmic reticulum (ER). A peptide tool, called Bcl-2/IP₃ receptor disruptor-2 (BIRD-2), was developed to disrupt Bcl-2/IP₃R complexes, triggering pro-apoptotic Ca²⁺ signals and killing Bcl-2-dependent cancer cells. In DLBCL cells, BIRD-2 sensitivity depended on the expression level of IP₃R2 channels and constitutive IP₃ signaling downstream of the B-cell receptor. However, other cellular pathways probably also contribute to BIRD-2-provoked cell death. Here, we examined whether BIRD-2-induced apoptosis depended on extracellular Ca²⁺ and more particularly on store-operated Ca²⁺ entry (SOCE), a Ca²⁺-influx pathway activated upon ER-store depletion. Excitingly, DPB162-AE, a SOCE inhibitor, suppressed BIRD-2-induced cell death in DLBCL cells. However, DPB162-AE not only inhibits SOCE but also depletes the ER Ca²⁺ store. Treatment of the cells with YM-58483 and GSK-7975A, two selective SOCE inhibitors, did not protect against BIRD-2-induced apoptosis. Similar data were obtained by knocking down STIM1 using small interfering RNA. Yet, extracellular Ca²⁺ contributed to BIRD-2 sensitivity in DLBCL, since the extracellular Ca²⁺ buffer ethylene glycol tetraacetic acid (EGTA) blunted BIRD-2-triggered apoptosis. The protective effects observed with DPB162-AE are likely due to ER Ca²⁺-store depletion, since a similar protective effect could be obtained using the sarco/endoplasmic reticulum Ca²⁺-ATPase inhibitor thapsigargin. Thus, both the ER Ca²⁺-store content and extracellular Ca²⁺, but not SOCE, are critical factors underlying BIRD-2-provoked cell death.

Consensus report of the 8 and 9th Weinman Symposia on Gene x Environment Interaction in carcinogenesis: novel opportunities for precision medicine

The relative contribution of intrinsic genetic factors and extrinsic environmental ones to cancer aetiology and natural history is a lengthy and debated issue. Gene-environment interactions (G x E) arise when the combined presence of both a germline genetic variant and a known environmental factor modulates the risk of disease more than either one alone. A panel of experts discussed our current understanding of cancer aetiology, known examples of G × E interactions in cancer, and the expanded concept of G × E interactions to include somatic cancer mutations and iatrogenic environmental factors such as anti-cancer treatment. Specific genetic polymorphisms and genetic mutations increase susceptibility to certain carcinogens and may be targeted in the near future for prevention and treatment of cancer patients with novel molecularly based therapies. There was general consensus that a better understanding of the complexity and numerosity of G × E interactions, supported by adequate technological, epidemiological, modelling and statistical resources, will further promote our understanding of cancer and lead to novel preventive and therapeutic approaches.

Benzyl isothiocyanate (BITC) triggers mitochondria-mediated apoptotic machinery in human cisplatin-resistant oral cancer CAR cells

Benzyl isothiocyanate (BITC), a component of dietary food, possesses a powerful anticancer activity. Previous studies have shown that BITC produces a large number of intracellular reactive oxygen species (ROS) and increases intracellular Ca²⁺ release from endoplasmic reticulum (ER), leading to the activation of the apoptotic mechanism in tumor cells. However, there is not much known regarding the inhibitory effect of BITC on cisplatin-resistant oral cancer cells. The purpose of this study was to examine the anticancer effect and molecular mechanism of BITC on human cisplatin-resistant oral cancer CAR cells. Our results demonstrated that BITC significantly reduced cell viability of CAR cells in a concentration- and time-dependent manner. BITC was found to cause apoptotic cell shrinkage and DNA fragmentation by morphologic observation and TUNEL/DAPI staining. Pretreatment of cells with a specific inhibitor of pan-caspase significantly reduced cell death caused by BITC. Colorimetric assay analyses also showed that the activities of caspase-3 and caspase-9 were elevated in BITC-treated CAR cells. An increase in ROS production and loss of mitochondria membrane potential (ΔΨm) occurred due to BITC exposure and was observed via flow cytometric analysis. Western blotting analyses demonstrated that the protein levels of Bax, Bad, cytochrome c, and cleaved caspase-3 were up-regulated, while those of Bcl-2, Bcl-xL and pro-caspase-9 were down-regulated in CAR cells after BITC challenge. In sum, the mitochondria-dependent pathway might contribute to BITC-induced apoptosis in human cisplatin-resistant oral cancer CAR cells.

Patterns of calcium signaling: A link between chronic emotions and cancer

Intra and inter-cellular calcium signaling is present in all types of cells and body tissues. In the human brain, calcium currents and waves are related to mental activities, including emotions. We present a theoretical interpretation of these phenomena suggesting their involvement in chronic emotional patterns and in the pathology of cancer. Recent developments on biophysics, translational biology and psychoneuroendocrinoimmunology (PNEI) can support explanatory hypotheses about the link between emotional stresses and the origin and development of different types of tumor cells. Chronic stresses may cause perturbations of rhythms of the PNEI system, excessive activation of HPA axis and abnormal activation of calcium signals in somatic tissues, with deleterious effects on different parts of the body. The increasing of calcium signaling inside cells may lead to a deregulation of different pathways and epigenetic systems that promote the production of genomic mutations in a second phase. In particular, the hyperactivation of the transcription nuclear factor kappaB (NF-κB), if is not counterbalanced by the following activation of the nuclear factor (erythroid-derived 2)-like 2 (NFE2L2 or Nrf2), increases the production of oxidative catabolites, as the advanced glycation end products (AGE), which play a key role in the progression of different types of cancer and other degenerative diseases. Cortisol binding to glucocorticoid receptor (GR) reduces the activity of both NF-κB and Nrf2 inside the cells but inhibits the cellular immunity and the anabolic processes of tissue regeneration. The tissue atrophy and the defective anti-ageing mechanisms promotes the tumoral cells growth and their escape from the immune-surveillance.

Targeting Bcl-2-IP3 receptor interaction to treat cancer: A novel approach inspired by nearly a century treating cancer with adrenal corticosteroid hormones

Bcl-2 inhibits cell death by at least two different mechanisms. On the one hand, its BH3 domain binds to pro-apoptotic proteins such as Bim and prevents apoptosis induction. On the other hand, the BH4 domain of Bcl-2 binds to the inositol 1,4,5-trisphosphate receptor (IP₃R), preventing Ca²⁺ signals that mediate cell death. In normal T-cells, Bcl-2 levels increase during the immune response, protecting against cell death, and then decline as apoptosis ensues and the immune response dissipates. But in many cancers Bcl-2 is aberrantly expressed and exploited to prevent cell death by inhibiting IP₃R-mediated Ca²⁺ elevation. This review summarizes what is known about the mechanism of Bcl-2's control over IP₃R-mediated Ca²⁺ release and cell death induction. Early insights into the role of Ca²⁺ elevation in corticosteroid-mediated cell death serves as a model for how targeting IP₃R-mediated Ca²⁺ elevation can be a highly effective therapeutic approach for different types of cancer. Moreover, the successful development of ABT-199 (Venetoclax), a small molecule targeting the BH3 domain of Bcl-2 but without effects on Ca²⁺, serves as proof of principle that targeting Bcl-2 can be an effective therapeutic approach. BIRD-2, a synthetic peptide that inhibits Bcl-2-IP₃R interaction, induces cell death induction in ABT-199 (Venetoclax)-resistant cancer models, attesting to the value of developing therapeutic agents that selectively target Bcl-2-IP₃R interaction, inducing Ca²⁺-mediated cell death.

Isorhamnetin: A hepatoprotective flavonoid inhibits apoptosis and autophagy via P38/PPAR-α pathway in mice

Isorhamnetin, a flavonoid compound extracted from plants' fruit or leaves, like sea buckthorn (Hippophae rhamnoides L.), has many biological functions, including anti-tumor, anti-oxidant and anti-inflammatory effect. The present study is in order to explore the hepatoprotective effect of isorhamnetin on concanavalin A (ConA)-induced acute fulminant hepatitis and the underlying mechanism. Mice were injected with ConA (25 mg/kg) to induce acute fulminant hepatitis, three doses of isorhamnetin (10/30/90 mg/kg) was intraperitoneally administrated about 1 h previously. The serum and liver tissues were harvested at 2, 8, and 24 h after ConA injection. The levels of serum liver enzymes and proinflammatory cytokines were significantly reduced in isorhamnetin administration groups. Besides, isorhamnetin improved pathological damage. Furthermore, isorhamnetin affected P38/PPAR-α pathway, and subsequently regulated the expression of apoptosis and autophagy related proteins. The present study investigated that isorhamnetin inhibits apoptosis and autophagy via P38/PPAR-α pathway in mice.

Emerging molecular mechanisms in chemotherapy: Ca2+ signaling at the mitochondria-associated endoplasmic reticulum membranes

Inter-organellar communication often takes the form of Ca2+ signals. These Ca2+ signals originate from the endoplasmic reticulum (ER) and regulate different cellular processes like metabolism, fertilization, migration, and cell fate. A prime target for Ca2+ signals are the mitochondria. ER-mitochondrial Ca2+ transfer is possible through the existence of mitochondria-associated ER membranes (MAMs), ER structures that are in the proximity of the mitochondria. This creates a micro-domain in which the Ca2+ concentrations are manifold higher than in the cytosol, allowing for rapid mitochondrial Ca2+ uptake. In the mitochondria, the Ca2+ signal is decoded differentially depending on its spatiotemporal characteristics. While Ca2+ oscillations stimulate metabolism and constitute pro-survival signaling, mitochondrial Ca2+ overload results in apoptosis. Many chemotherapeutics depend on efficient ER-mitochondrial Ca2+ signaling to exert their function. However, several oncogenes and tumor suppressors present in the MAMs can alter Ca2+ signaling in cancer cells, rendering chemotherapeutics ineffective. In this review, we will discuss recent studies that connect ER-mitochondrial Ca2+ transfer, tumor suppressors and oncogenes at the MAMs, and chemotherapy.