(2,6-Dimethylphenyl)arsonic Acid Induces Apoptosis through the Mitochondrial Pathway, Downregulates XIAP, and Overcomes Multidrug Resistance to Cytostatic Drugs in Leukemia and Lymphoma Cells In Vitro.

Cancer treatment is greatly challenged by drug resistance, highlighting the need for novel drug discoveries. Here, we investigated novel organoarsenic compounds regarding their resistance-breaking and apoptosis-inducing properties in leukemia and lymphoma. Notably, the compound (2,6-dimethylphenyl)arsonic acid (As2) demonstrated significant inhibition of cell proliferation and induction of apoptosis in leukemia and lymphoma cells while sparing healthy leukocytes. As2 reached half of its maximum activity (AC50) against leukemia cells at around 6.3 µM. Further experiments showed that As2 overcomes multidrug resistance and sensitizes drug-resistant leukemia and lymphoma cell lines to treatments with the common cytostatic drugs vincristine, daunorubicin, and cytarabine at low micromolar concentrations. Mechanistic investigations of As2-mediated apoptosis involving FADD (FAS-associated death domain)-deficient or Smac (second mitochondria-derived activator of caspases)/DIABLO (direct IAP binding protein with low pI)-overexpressing cell lines, western blot analysis of caspase-9 cleavage, and measurements of mitochondrial membrane integrity identified the mitochondrial apoptosis pathway as the main mode of action. Downregulation of XIAP (x-linked inhibitor of apoptosis protein) and apoptosis induction independent of Bcl-2 (B-cell lymphoma 2) and caspase-3 expression levels suggest the activation of additional apoptosis-promoting mechanisms. Due to the selective apoptosis induction, the synergistic effects with common anti-cancer drugs, and the ability to overcome multidrug resistance in vitro, As2 represents a promising candidate for further preclinical investigations with respect to refractory malignancies.

A grape-supplemented diet prevented ultraviolet (UV) radiation-induced cataract by regulating Nrf2 and XIAP pathways.

The purpose of this study is to investigate if grape consumption, in the form of grape powder (GP), could protect against ultraviolet (UV)-induced cataract. Mice were fed with the regular diet, sugar placebo diet, or a grape diet (regular diet supplemented with 5%, 10%, and 15% GP) for 3 months. The mice were then exposed to UV radiation to induce cataract. The results showed that the GP diet dose-dependently inhibited UV-induced cataract and preserved glutathione pools. Interestingly, UV-induced Nrf2 activation was abolished in the groups on the GP diet, suggesting GP consumption may improve redox homeostasis in the lens, making Nrf2 activation unnecessary. For molecular target prediction, a total of 471 proteins regulated by GP were identified using Agilent Literature Search (ALS) software. Among these targets, the X-linked inhibitor of apoptosis (XIAP) was correlated with all of the main active ingredients of GP, including resveratrol, catechin, quercetin, and anthocyanins. Our data confirmed that GP prevented UV-induced suppression of XIAP, indicating that XIAP might be one of the critical molecular targets of GP. In conclusion, this study demonstrated that GP protected the lens from UV-induced cataract development in mice. The protective effects of GP may be attributed to its ability to improve redox homeostasis and activate the XIAP-mediated antiapoptotic pathway.

Systematic analysis of PANoptosis-related genes identifies XIAP as a functional oncogene in breast cancer.

BACKGROUND: Breast cancer (BC) is the most prevalent malignant disease affecting women globally. PANoptosis, a novel form of cell death combining features of pyroptosis, apoptosis, and necroptosis, has recently gained attention. However, its precise function in BC and the predictive values of PANoptosis-related genes remain unclear. METHODS: We used the expression data and clinical information of BC tissues or normal breast tissues from public databases, and then successfully developed and verified a BC PANoptosis-related risk model through a combination of univariate Cox regression, least absolute shrinkage and selection operator (LASSO) regression, and Kaplan-Meier (KM) analysis. A nomogram was constructed to estimate survival probability, and its accuracy was assessed using calibration curves. RESULTS: Among 37 PANoptosis-related genes, we identified 4 differentially expressed genes related to overall survival (OS). Next, a risk model incorporating these four PANoptosis-related genes was established. Patients were stratified into low/high-risk groups based on the median risk score, with the low-risk group showing better prognoses and higher levels of immune infiltration. Utilizing the risk score and clinical features, we developed a nomogram to predict 1-, 3- and 5-year survival probability. X-linked inhibitor of apoptosis protein (XIAP) emerged as a potentially risky factor with the highest hazard ratio. In vitro experiments demonstrated that XIAP inhibition enhances the antitumor effect of doxorubicin through the PANoptosis pathway. CONCLUSION: PANoptosis holds an important role in BC prognosis and treatment.

Moracin D suppresses cell growth and induces apoptosis via targeting the XIAP/PARP1 axis in pancreatic cancer.

BACKGROUND: Pancreatic cancer, a tumor with a high metastasis rate and poor prognosis, is among the deadliest human malignancies. Investigating effective drugs for their treatment is imperative. Moracin D, a natural benzofuran compound isolated from Morus alba L., shows anti-inflammation and anti-breast cancer properties and is effective against Alzheimer's disease. However, the effect and mechanism of Moracin D action in pancreatic cancer remain obscure. PURPOSE: To investigate the function and molecular mechanism of Moracin D action in repressing the malignant progression of pancreatic cancer. METHODS: Pancreatic cancer cells were treated with Moracin D, and cell proliferation was evaluated by cell counting kit-8 (CCK-8) and immunofluorescence assays. The clonogenicity of pancreatic cancer cells was assessed based on plate colony formation and soft agar assay. Flow cytometry was used to detect cell apoptosis. The expression of proteins related to the apoptosis pathway was determined by Western blot analysis. Moracin D and XIAP were subjected to docking by auto-dock molecular docking analysis. Ubiquitination levels of XIAP and the interaction of XIAP and PARP1 were assessed by co-immunoprecipitation analysis. Moracin D's effects on tumorigenicity were assessed by a tumor xenograft assay. RESULTS: Moracin D inhibited cell proliferation, induced cell apoptosis, and regulated the protein expression of molecules involved in caspase-dependent apoptosis pathways. Moracin D suppressed clonogenicity and tumorigenesis of pancreatic cancer cells. Mechanistically, XIAP could interact with PARP1 and stabilize PARP1 by controlling its ubiquitination levels. Moracin D diminished the stability of XIAP and decreased the expression of XIAP by promoting proteasome-dependent XIAP degradation, further blocking the XIAP/PARP1 axis and repressing the progression of pancreatic cancer. Moracin D could dramatically improve the chemosensitivity of gemcitabine in pancreatic cancer cells. CONCLUSION: Moracin D repressed cell growth and tumorigenesis, induced cell apoptosis, and enhanced the chemosensitivity of gemcitabine through the XIAP/PARP1 axis in pancreatic cancer. Moracin D is a potential therapeutic agent or adjuvant for pancreatic cancer.

Lymphopenia associated with survivin and its downstream pathway in COVID-19 serving as a potential route in COVID-19 pathogenesis.

PURPOSE: Starting in 2019, coronavirus disease 2019 (COVID-19) caused an epidemic that was growing rapidly and has harmed millions of people globally. It has been demonstrated that survivin regulates lymphocyte survival, a main route involved in COVID-19 pathogenesis. Survivin belongs to the inhibitor of apoptosis protein (IAP) family, and its primary functions comprise regulating mitosis and inhibiting apoptosis. Since lower survivin expression has been shown to increase the sensitivity of lymphocytes to apoptotic induction, we looked into the function of survivin and its corresponding pathways in COVID-19 pathogenesis. MATERIALS AND METHODS: The expression of survivin, X-linked inhibitor of apoptosis protein (XIAP), caspases 3, 7, 9, and poly (ADP-ribose) polymerase (PARP) was evaluated at both mRNA and protein levels in peripheral blood mononuclear cells (PBMCs) derived from healthy donors and patients with severe and moderate COVID-19 by qRT-PCR and Western blotting, respectively. Then, we enforced apoptosis to COVID-19 patient-derived lymphocytes, and the percent was assessed by flow cytometry. RESULTS: Survivin and XIAP were less expressed in PBMCs derived from COVID-19 patients as apoptosis inhibitors than PARP, cleaved-PARP, caspase 9, and cleaved caspases 3 and 7, according to the results of real-time PCR and Western blot analysis. Additionally, according to the flow cytometry results, the down-regulation of survivin served as a potential factor in the lymphocyte depletion observed in patients with COVID-19. CONCLUSION: The role of survivin and its related pathway was first discovered in the development of COVID-19 and may serve as a potential prognostic and therapeutic target.

Targeting inhibitor of apoptosis proteins (IAPs) enhances susceptibility of oral squamous carcinoma cells to cisplatin.

PURPOSE: Oral Squamous Cell Carcinoma (OSCC) is the 6th most common cancer worldwide. It is generally aggressive and closely associated with chemoresistance and poor survival. There is accumulating evidence for the involvement of inhibitors of apoptosis proteins (IAPs), including IAP1 and XIAP, in mediating chemotherapy resistance in OSCC. Various strategies for targeting IAPs have been designed and tested in recent years and several small molecule IAP inhibitors are in clinical trials as monotherapies as well as in combination with radiotherapy and chemotherapy. The purpose of this study was to evaluate and compare the efficacy and biological activity of three IAP inhibitors both as stand-alone and sensitising agents to cisplatin in a preclinical model of squamous cell carcinoma of the tongue. METHODS: Cisplatin-sensitive SCC4 and -resistant SCC4cisR cells were utilised in this study. Apoptosis was evaluated by flow cytometric analysis of Annexin V/Propidium Iodide-stained cells. Expression of IAP proteins was determined by western blotting and knockdown of cIAP1, livin and XIAP was conducted by transfection of cells with siRNA. RESULTS: We establish for the first time the therapeutic efficacy of the Smac mimetic, BV6 and the XIAP inhibitor Embelin, for OSCC. Both of these IAP targeting agents synergistically enhanced cisplatin-mediated apoptotic cell death in resistant cells which was mediated in part by depletion of XIAP. In addition, knockdown of XIAP using siRNA enhanced cisplatin-mediated cell death, demonstrating the importance of targeting XIAP in this sensitisation. CONCLUSION: These findings provide pre-clinical evidence that IAP inhibition may be a valuable therapeutic option in OSCC.

Design, in silico evaluation, and in vitro verification of new bivalent Smac mimetics with pro-apoptotic activity.

Bivalent Smac mimetics have been shown to possess binding affinity and pro-apoptotic activity similar to or more potent than that of native Smac, a protein dimer able to neutralize the anti-apoptotic activity of an inhibitor of caspase enzymes, XIAP, which endows cancer cells with resistance to anticancer drugs. We design five new bivalent Smac mimetics, which are formed by various linkers tethering two diazabicyclic cores being the IAP binding motifs. We built in silico models of the five mimetics by the TwistDock workflow and evaluated their conformational tendency, which suggests that compound 3, whose linker is n-hexylene, possess the highest binding potency among the five. After synthesis of these compounds, their ability in tumour cell growth inhibition and apoptosis induction displayed in experiments with SK-OV-3 and MDA-MB-231 cancer cell lines confirms our prediction. Among the five mimetics, compound 3 displays promising pro-apoptotic activity and deserves further optimization.

Enhanced translocation of TRIM32 to mitochondria sensitizes dopaminergic neuronal cells to apoptosis during stress conditions in Parkinson's disease.

Parkinson's disease (PD) is a chronic neurodegenerative disease characterized by progressive loss of dopamine-producing neurons from the substantia nigra region of the brain. Mitochondrial dysfunction is one of the major causes of oxidative stress and neuronal cell death in PD. E3 ubiquitin ligases such as Parkin (PRKN) modulate mitochondrial quality control in PD; however, the role of other E3 ligases associated with mitochondria in the regulation of neuronal cell death in PD has not been explored. The current study investigated the role of TRIM32, RING E3 ligase, in sensitization to oxidative stress-induced neuronal apoptosis. The expression of TRIM32 sensitizes SH-SY5Y dopaminergic cells to rotenone and 6-OHDA-induced neuronal death, whereas the knockdown increased cell viability under PD stress conditions. The turnover of TRIM32 is enhanced under PD stress conditions and is mediated by autophagy. TRIM32 translocation to mitochondria is enhanced under PD stress conditions and localizes on the outer mitochondrial membrane. TRIM32 decreases complex-I assembly and activity as well as mitochondrial reactive oxygen species (ROS) and ATP levels under PD stress. Deletion of the RING domain of TRIM32 enhanced complex I activity and rescued ROS levels and neuronal viability under PD stress conditions. TRIM32 decreases the level of XIAP, and co-expression of XIAP with TRIM32 rescued the PD stress-induced cell death and mitochondrial ROS level. In conclusion, turnover of TRIM32 increases during stress conditions and translocation to mitochondria is enhanced, regulating mitochondrial functions and neuronal apoptosis by modulating the level of XIAP in PD.

Allogeneic Hematopoietic Cell Transplantation Ameliorated Asymptomatic Granulomatous and Lymphocytic Interstitial Lung Disease in a Patient With XIAP Deficiency.

X-linked inhibitor of apoptosis protein (XIAP) deficiency is an inborn error of immunity (IEI). Allogeneic hematopoietic cell transplantation (HCT) is currently the only curative therapy available for XIAP deficiency. Granulomatous and lymphocytic interstitial lung disease (GLILD) is a common immune-related lung complication of IEIs. We present a 6-year-old boy with XIAP deficiency and GLILD. Computed tomography showed lung nodes but no symptoms. Before HCT, GLILD was not managed with immunosuppressive therapy, because he was asymptomatic. The HCT procedure was subsequently performed. The post-HCT course was uneventful; follow-up computed tomography on day 46 showed nodules had disappeared. HCT could potentially ameliorate GLILD like other inflammatory processes associated with the underlying IEIs.

Understanding the molecular mechanism of pathogenic variants of BIR2 domain in XIAP-deficient inflammatory bowel disease.

X-linked inhibitor of apoptosis protein (XIAP) deficiency causes refractory inflammatory bowel disease. The XIAP protein plays a pivotal role in the pro-inflammatory response through the nucleotide-binding oligomerization domain-containing signaling pathway that is important in mucosal homeostasis. We analyzed the molecular mechanism of non-synonymous pathogenic variants (PVs) of XIAP BIR2 domain. We generated N-terminally green fluorescent protein-tagged XIAP constructs of representative non-synonymous PVs. Co-immunoprecipitation and fluorescence cross-correlation spectroscopy showed that wild-type XIAP and RIP2 preferentially interacted in live cells, whereas all non-synonymous PV XIAPs failed to interact properly with RIP2. Structural analysis showed that various structural changes by mutations, such as hydrophobic core collapse, Zn-finger loss, and spatial rearrangement, destabilized the two loop structures (174-182 and 205-215) that critically interact with RIP2. Subsequently, it caused a failure of RIP2 ubiquitination and loss of protein deficiency by the auto-ubiquitination of all XIAP mutants. These findings could enhance our understanding of the role of XIAP mutations in XIAP-deficient inflammatory bowel disease and may benefit future therapeutic strategies.

Severe adult hemophagocytic lymphohistiocytosis (HLHa) correlates with HLH-related gene variants.

BACKGROUND: The contribution of genetic factors to the severity of adult hemophagocytic lymphohistiocytosis (HLHa) remains unclear. OBJECTIVE: We sought to assess a potential link between HLHa outcomes and HLH-related gene variants. METHODS: Clinical characteristics of 130 HLHa patients (age ≥ 18 years and HScore ≥ 169) and genotype of 8 HLH-related genes (LYST, PRF1, UNC13-D, STX11, STXBP2, RAB27A, XIAP, and SAP) were collected. A total of 34 variants found in only 6 genes were selected on the basis of their frequency and criteria predicted to impair protein function. Severity was defined by refractory disease to HLH treatment, death, or transfer to an intensive care unit. RESULTS: HLHa-associated diseases (ADs) were neoplasia (n = 49 [37.7%]), autoimmune/inflammatory disease (n = 33 [25.4%]), or idiopathic when no AD was identified (n = 48 [36.9%]). Infectious events occurred in 76 (58.5%) patients and were equally distributed in all ADs. Severe and refractory HLHa were observed in 80 (61.5%) and 64 (49.2%) patients, respectively. HScore, age, sex ratio, AD, and infectious events showed no significant association with HLHa severity. Variants were identified in 71 alleles and were present in 56 (43.1%) patients. They were distributed as follows: 44 (34.4%), 9 (6.9%), and 3 (2.3%) patients carrying 1, 2, and 3 variant alleles, respectively. In a logistic regression model, only the number of variants was significantly associated with HLHa severity (1 vs 0: 3.86 [1.73-9.14], P = .0008; 2-3 vs 0: 29.4 [3.62-3810], P = .0002) and refractoriness (1 vs 0: 2.47 [1.17-5.34], P = .018; 2-3 vs 0: 13.2 [2.91-126.8], P = .0003). CONCLUSIONS: HLH-related gene variants may be key components to the severity and refractoriness of HLHa.

OTU deubiquitinase 7B facilitates the hyperthermia-induced inhibition of lung cancer progression through enhancing Smac-mediated mitochondrial dysfunction.

Hyperthermia, as an adjuvant therapy, has shown promising anti-tumor effects. Ovarian tumor domain-containing 7B (OTUD7B) is a deubiquitinating enzyme that is frequently found in a variety of cancers. The aim of this study is to investigate the role of OTUD7B in lung cancer hyperthermia and the underlying mechanism. A549 and CALU-3 cells were respectively exposed to 42 or 44°C for the indicated times (0, 1, 3, or 6 h) followed by incubation at 37°C for 24 h. We found a temperature- and time-dependent decrease in cell viability and an increase in apoptosis levels. Compared with 0 h, heat treatment for 3 h inhibited the proliferation and invasion of A549 cells, reduced the expression levels of mitochondrial membrane potential, IAP family members (cIAP-1 and XIAP) proteins and ubiquitination of Smac, and increased Smac protein expression. Treatment with 10 µM Smac mimic BV6 further enhanced the anti-tumor effect of hyperthermia. Next, co-IP validation showed that OTUD7B interacted with Smac and stabilized Smac through deubiquitination. OTUD7B overexpression induced damage in A549 and CALU-3 cells, while silencing OTUD7B caused opposite effects. Overexpressing OTUD7B enhanced the anti-cancer effect of hyperthermia, while si-OTUD7B reversed the anti-cancer effect of hyperthermia, which was verified in the xenograft tumor model in nude mice. Taken together, OTUD7B may serve as a potential anticancer factor with potential clinical efficacy in the thermotherapeutic treatment of lung cancer.

Hellebrigenin induces oral cancer cell apoptosis by modulating MAPK signalling and XIAP expression.

Oral squamous cell carcinoma (OSCC), which accounts for 90% of all oral cancers, has become a public health crisis worldwide. despite advances in therapeutic interventions, the prognosis remains poor for advanced-stage OSCC. In this study, we investigate the anticancer activity and the mode of action of hellebrigenin in human OSCC. The findings demonstrated that hellebrigenin exerted cytotoxic effects in OSCC cells through cell cycle arrest at the G2/M phase and downregulation of cell cycle-related proteins (cyclins A2, B1 and D3, Cdc2, CDK4 and CDK6). Moreover, hellebrigenin caused activation of PARP and caspase 3, 8 and 9, followed by downregulation of antiapoptotic proteins (Bcl-2 and Bcl-xL) and upregulation of pro-apoptotic proteins (Bax and Bak). The hellebrigenin treatment also increased Fas, DR5, DcR2 and DcR3 expressions in oral cancer cells, indicating the compound causes oral cancer cell apoptosis through both intrinsic and extrinsic pathways. Regarding upstream signalling, hellebrigenin was found to reduce the phosphorylation of ERK, p38, and JNK, indicating that hellebrigenin triggers caspase-mediated apoptosis by downregulating MAPK signalling pathway. Finally, the human apoptosis array findings revealed that hellebrigenin specifically suppressed the expression of XIAP to execute its pro-apoptotic activities. Taken together, the study suggests that hellebrigenin can act as a potent anticancer compound in human OSCC.

Simultaneous XIAP and cIAP1/2 inhibition by a dimeric SMAC mimetic AZD5582 induces apoptosis in multiple myeloma.

Overexpression of inhibitor of apoptosis (IAP) proteins is associated with poor prognosis. In multiple myeloma (MM), the IAP inhibitors (IAPi), LCL161, have been evaluated in preclinical and clinical settings but are not fully effective. Among IAPs, XIAP has the strongest anti-apoptotic function with direct binding activity to caspases and cIAP1 and cIAP2 are positive regulator of NF-κB signaling. Prior IAPi such as LCL161 has high affinity to cIAP1 and cIAP2 resulting in inferior inhibiting activity against XIAP. A novel dimeric IAPi, AZD5582 (C58H78N8O8), have high binding potency to XIAP with EC50 dose of 15 nM, enabling to simultaneous inhibit XIAP and cIAP1/2. AZD5582 monotherapy showed cell growth inhibition for all MM cell lines, MM1S, RPMI8226, U266 and KMS-5 and induced apoptosis. AZD5582 further showed anti-proliferation effect under the IL-6 additional condition and inhibited JAK-STAT signaling triggered by IL-6. AZD5582 combined with carfilzomib therapy showed a synergistic effect. Enhanced apoptosis was also observed in combination therapy. Synergistic effect was further observed with other conventional therapeutics. Simultaneous XIAP and cIAP1/2 inhibition by the dimeric IAPi AZD5582 is promising. This study provides a rationale of AZD5582 as a new treatment strategy in monotherapy and in combination therapy.

Apoptosis-related factors are relevant to progression of pancreatic neuroendocrine tumors.

BACKGROUND: Multidisciplinary therapy centered on antitumor drugs is indicated in patients with unresectable pancreatic neuroendocrine tumors (PanNET). However, the criteria for selection of optimal therapeutic agents is controversial. The aim of this study was to assess the malignancy of PanNET for optimal therapeutic drug selection. METHODS: Forty-seven patients with PanNET who underwent surgery were reviewed retrospectively, and immunohistochemical characteristics, including expression of GLUT1, SSTR2a, SSTR5, Survivin, X-chromosome-linked inhibitor of apoptosis protein (XIAP), and Caspase3 in the resected specimens, were investigated. Relapse-free survival (RFS) and overall survival (OS) were evaluated with regard to the characteristics using the Kaplan-Meier method and compared with the log-rank test. RESULTS: GLUT1 expression showed significant correlation with sex (p = 0.036) and mitotic rate (p = 0.048). Survivin and XIAP expression showed significant correlation with T-stage (p = 0.014 and 0.009), p-Stage (p = 0.028 and 0.045), and mitotic rate (p = 0.023 and 0.007). XIAP expression also significantly influenced OS (p = 0.044). CONCLUSIONS: Survivin and XIAP correlated with grade of malignancy, and expression of XIAP in particular was associated with a poor prognosis. Expression of these proteins may be a useful indicator to select optimal therapeutic agents in PanNET.

TP induces hepatic intolerance to FasL-mediated hepatocyte apoptosis by inhibiting XIAP.

Triptolide (TP) is extracted from the traditional Chinese medicine Tripterygium wilfordii Hook. F. (TWHF). Its severe toxic side effects, especially hepatotoxicity, have limited the clinical application of TP-related drugs. In this study, we investigated the mechanism of the hepatotoxic effects of TP from the perspective that TP inhibited the expression of the pro-survival protein X-linked inhibitor of apoptosis protein (XIAP) and enhanced FasL-mediated apoptosis of hepatocytes. TP and CD95/Fas antibody (Jo-2) were administered by gavage to C57BL/6 mice for 7 consecutive days. After co-administration of TP and Jo-2, mouse livers showed large areas of necrosis and apoptosis and significantly increased Caspase-3 activity. KEGG pathway enrichment analysis indicated that TP may cause the development of liver injury through the apoptotic signaling pathway. Proteinprotein interaction networks showed that XIAP played an essential role in this process. TP reduced the protein expression of XIAP after combination treatment with Jo-2/FasL in vivo/in vitro. TP and FasL co-stimulation significantly increased microRNA-137 (miR-137) levels in AML12 cells, while inhibition of miR-137 expression induced a rebound in XIAP protein expression. In conclusion, TP presensitizes hepatocytes and enhances the sensitivity of hepatocytes to the Fas/FasL pathway by inhibiting the protein expression of XIAP, leading to hepatocyte apoptosis.

Targeted Degradation of XIAP is Sufficient and Specific to Induce Apoptosis in MYCN-overexpressing High-risk Neuroblastoma.

XIAP, the most potent mammalian inhibitor of apoptosis protein (IAP), critically restricts developmental culling of sympathetic neuronal progenitors, and is correspondingly overexpressed in most MYCN-amplified neuroblastoma tumors. Because apoptosis-related protein in the TGFß signaling pathway (ARTS) is the only XIAP antagonist that directly binds and degrades XIAP, we evaluated the preclinical effectiveness and tolerability of XIAP antagonism as a novel targeting strategy for neuroblastoma. We found that antagonism of XIAP, but not other IAPs, triggered apoptotic death in neuroblastoma cells. XIAP silencing induced apoptosis while overexpression conferred protection from drug-induced apoptosis. From a screen of IAP inhibitors, first-in-class ARTS mimetic A4 was most effective against high-risk and high XIAP-expressing neuroblastoma cells, and least toxic toward normal liver- and bone marrow-derived cells, compared with pan-IAP antagonists. On target engagement assays and nuclear magnetic resonance spectroscopy, A4 was observed to degrade rather than inhibit XIAP, catalyzing rapid degradation of XIAP through the ubiquitin-proteasome pathway. In MYCN-amplified neuroblastoma patient-derived xenografts, A4 significantly prolonged survival as a single agent, and demonstrated synergism with standard-of-care agents to reduce their effective required doses 3- to 6-fold. Engagement and degradation of XIAP by ARTS mimetics is a novel targeting strategy for neuroblastoma that may be especially effective against MYCN-amplified disease with intrinsically high XIAP expression. First-in-class ARTS mimetic A4 demonstrates preclinical efficacy and warrants further development and study. SIGNIFICANCE: XIAP degradation is sufficient to kill MYCN-amplified neuroblastoma which overexpresses and relies on XIAP as a brake against cell death, without affecting normal cells.

TRAF2/3 deficient B cells resist DNA damage-induced apoptosis via NF-κB2/XIAP/cIAP2 axis and IAP antagonist sensitizes mutant lymphomas to chemotherapeutic drugs.

Deletion of TRAF2 or TRAF3 in B cells prolongs their survival. However, it remains unknown whether deletion of such factors affects B cells' ability to tolerate DNA damage, which can be induced by chemotherapeutics and cause apoptosis. Genetic alterations of TRAF2 or TRAF3 are observed in subsets of human B-cell lymphomas and B cell-specific deletion of TRAF3 led to lymphoma development in aged mice. However, it remains unknown whether double deficiency of TRAF2 and TRAF3 accelerates B-cell lymphomagenesis. Here, we showed that B cell-specific TRAF2/3 double deficient (B-TRAF2/3-DKO) B cells were remarkably more resistant to DNA damage-induced apoptosis via upregulating cIAP2 and XIAP, which in turn attenuates caspase-3 activation. Mechanistically, resistance to DNA damage-induced apoptosis required NF-κB2, which effects by upregulating XIAP and cIAP2 transcription. B-TRAF2/3-DKO mice exhibited a shorter lifespan and succumbed to splenomegaly and lymphadenopathy. Unexpectedly, the incidence of B-cell lymphoma development in B-TRAF2/3-DKO mice was relatively rare (∼10%). Sequencing B cell receptor repertoire of diseased B cells revealed that TRAF2/3 deficiency caused abnormal oligoclonal or clonal expansion of B cells. While a fraction of mutant B cells (25-43%) from aged diseased mice harbored recurrent chromosomal translocations, primary B cells isolated from young B-TRAF2/3-DKO mice had no detectable chromosomal alterations, suggesting that TRAF2/3 deficiency per se does not cause evident genomic instability in B cells. Chemo-resistant TRAF3-deficient B-cell lymphomas were sensitized to chemotherapeutic drugs by blocking IAP activity using IAP antagonist. We conclude that double deficiency of TRAF2 and TRAF3 does not accelerate B-cell lymphomagenesis. Our studies provide insight into mechanisms regulating DNA damage-induced apoptosis and may help develop effective therapies targeting mutant B-cell lymphomas using IAP antagonist.

Ehrlichia Notch signaling induction promotes XIAP stability and inhibits apoptosis.

Ehrlichia chaffeensis has evolved multiple strategies to evade innate defenses of the mononuclear phagocyte. Recently, we reported the E. chaffeensis tandem repeat protein (TRP)120 effector functions as a Notch ligand mimetic and a ubiquitin ligase that degrades the nuclear tumor suppressor, F-box and WD repeat domain-containing 7, a negative regulator of Notch. The Notch intracellular domain (NICD) is known to inhibit apoptosis primarily by interacting with X-linked inhibitor of apoptosis protein (XIAP) to prevent degradation. In this study, we determined that E. chaffeensis activation of Notch signaling increases XIAP levels, thereby inhibiting apoptosis through both the intrinsic and executioner pathways. Increased NICD and XIAP levels were detected during E. chaffeensis infection and after TRP120 Notch ligand mimetic peptide treatment. Conversely, XIAP levels were reduced in the presence of Notch inhibitor DAPT. Cytoplasmic and nuclear colocalization of NICD and XIAP was observed during infection and a direct interaction was confirmed by co-immunoprecipitation. Procaspase levels increased temporally during infection, consistent with increased XIAP levels; however, knockdown (KD) of XIAP during infection significantly increased apoptosis and Caspase-3, -7, and -9 levels. Furthermore, treatment with SM-164, a second mitochondrial activator of caspases (Smac/DIABLO) antagonist, resulted in decreased procaspase levels and increased caspase activation, induced apoptosis, and significantly decreased infection. In addition, RNAi KD of XIAP also decreased infection and significantly increased apoptosis. Moreover, ectopic expression of TRP120 HECT Ub ligase catalytically defective mutant in HeLa cells decreased NICD and XIAP levels and increased caspase activation compared to HeLa cells with functional HECT Ub ligase catalytic activity (TRP120-WT). This investigation reveals a mechanism whereby E. chaffeensis modulates Notch signaling to stabilize XIAP and inhibit apoptosis.