Corrigendum: AMPA receptor-mediated regulation of a Gi-protein in cortical neurons.

This corrects the article DOI: 10.1038/39062.

cIAP1 and cIAP2 facilitate cancer cell survival by functioning as E3 ligases that promote RIP1 ubiquitination.

The inhibitor of apoptosis (IAP) family of proteins enhances cell survival through mechanisms that remain uncertain. In this report, we show that cIAP1 and cIAP2 promote cancer cell survival by functioning as E3 ubiquitin ligases that maintain constitutive ubiquitination of the RIP1 adaptor protein. We demonstrate that AEG40730, a compound modeled on BIR-binding tetrapeptides, binds to cIAP1 and cIAP2, facilitates their autoubiquitination and proteosomal degradation, and causes a dramatic reduction in RIP1 ubiquitination. We show that cIAP1 and cIAP2 directly ubiquitinate RIP1 and induce constitutive RIP1 ubiquitination in cancer cells and demonstrate that constitutively ubiquitinated RIP1 associates with the prosurvival kinase TAK1. When deubiquitinated by AEG40730 treatment, RIP1 binds caspase-8 and induces apoptosis. These findings provide insights into the function of the IAPs and provide new therapeutic opportunities in the treatment of cancer.

Cytoprotective effects of IAPs revealed by a small molecule antagonist.

Deregulated expression of members of the IAP (inhibitor of apoptosis) family has been identified in a wide variety of neoplastic cells, and synthetic IAP antagonists represent a promising novel class of chemotherapeutic agents. Early work focused on the ability of these compounds to block the caspase-inhibitory function of XIAP (X-linked IAP). However, recent studies have shown that IAP antagonists, although primarily designed to target XIAP, trigger ubiquitin-mediated degradation of two related proteins, c-IAP (cellular IAP) 1 and c-IAP2, and through this process potentiates the death of tumour cells via autocrine cellular-signalling pathways. In this context, the relative contribution of XIAP as a target of this class of compounds is unclear. In the present study, we examine the involvement of XIAP using a recently described synthetic IAP antagonist, AEG40730, and through comparison of a human XIAP-depleted tumour cell line with its isogenic wild-type control line. Treatment with nanomolar concentrations of AEG40730 resulted in the loss of both XIAP and c-IAP1 proteins, albeit with different kinetics. Although XIAP-deficient HCT116 cells retained some sensitivity to external apoptotic stimuli, the results suggest that IAP antagonists, such as AEG40730, exert their apoptosis-enhancing effects through XIAP in addition to the c-IAPs. These results indicate that IAP antagonists can target multiple IAPs to augment distinct pro-apoptotic signalling pathways, thereby revealing the potential for these compounds in cancer therapy and underscoring the promise of IAP-targeted therapies.

Downregulation of XIAP expression in ovarian cancer cells induces cell death in vitro and in vivo.

A hallmark of cancer cells is an ability to evade apoptosis. Overexpression and/or activating mutations of prosurvival molecules such as the X-linked inhibitor of apoptosis (XIAP) contribute to this inappropriate cell survival. Our objectives were to investigate the effects of downregulation of XIAP in ovarian cancer cells in vitro and in vivo using the clinical candidate antisense oligonucleotide against XIAP, AEG35156 (AS XIAP). Three ovarian cancer cell lines were transfected with AS XIAP in vitro, and the effects on cell survival were assessed. Downregulation of XIAP resulted in significant apoptosis. To investigate the in vivo efficacy of AS XIAP, CD-1 nude mice were xenografted intraperitoneally with A2780-cp cells, treated with intraperitoneal AS XIAP and evaluated for survival time and tumor histology. Mice treated with 10 mg/kg/day AS XIAP showed a significant improvement in survival time compared to animals treated with control oligonucleotides. Histological analysis of the tumors showed significantly fewer viable cells in the AS XIAP-treated tumors. Downregulation of XIAP expression in ovarian cancer cells resulted in apoptosis in vitro and a prolonged survival time of ovarian cancer-bearing mice, which indicate that XIAP may be a valuable therapeutic target in ovarian cancers, and supports the ongoing clinical investigation of AEG35156.

AEG3482 is an antiapoptotic compound that inhibits Jun kinase activity and cell death through induced expression of heat shock protein 70.

We describe a group of small-molecule inhibitors of Jun kinase (JNK)-dependent apoptosis. AEG3482, the parental compound, was identified in a screening effort designed to detect compounds that reduce apoptosis of neonatal sympathetic neurons after NGF withdrawal. We show that AEG3482 blocks apoptosis induced by the p75 neurotrophin receptor (p75NTR) or its cytosolic interactor, NRAGE, and demonstrate that AEG3482 blocks proapoptotic JNK activity. We show that AEG3482 induces production of heat shock protein 70 (HSP70), an endogenous inhibitor of JNK, and establish that HSP70 accumulation is required for the AEG3482-induced JNK blockade. We show that AEG3482 binds HSP90 and induces HSF1-dependent HSP70 mRNA expression and find that AEG3482 facilitates HSP70 production while retaining HSP90 chaperone activity. These studies establish that AEG3482 inhibits JNK activation and apoptosis by a mechanism involving induced expression of HSP proteins.

Preclinical characterization of AEG35156/GEM 640, a second-generation antisense oligonucleotide targeting X-linked inhibitor of apoptosis.

PURPOSE: Cancer cells can use X-linked inhibitor of apoptosis (XIAP) to evade apoptotic cues, including chemotherapy. The antitumor potential of AEG35156, a novel second-generation antisense oligonucleotide directed toward XIAP, was assessed in human cancer models when given as a single agent and in combination with clinically relevant chemotherapeutics. EXPERIMENTAL DESIGN: AEG35156 was characterized for its ability to cause dose-dependent reductions of XIAP mRNA and protein in vitro and in vivo, to sensitize cancer cell lines to death stimuli, and to exhibit antitumor activity in multiple human cancer xenograft models as a single agent or in combination with chemotherapy. RESULTS: AEG35156 reduced XIAP mRNA levels with an EC50 of 8 to 32 nmol/L and decreased XIAP protein levels by >80%. Loss of XIAP protein correlated with increased sensitization to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in Panc-1 pancreatic carcinoma cells. AEG35156 exhibited potent antitumor activity relative to control oligonucleotides in three human cancer xenograft models (prostate, colon, and lung) and was capable of inducing complete tumor regression when combined with taxanes. Antitumor effects of AEG35156 correlated with suppression of tumor XIAP levels. CONCLUSIONS: AEG35156 reduces XIAP levels and sensitizes tumors to chemotherapy. AEG35156 is presently under clinical assessment in multiple phase I trials in cancer patients as a single agent and in combination with docetaxel in solid tumors or cytarabine/idarubicin in leukemia.

Loss of XIAP protein expression by RNAi and antisense approaches sensitizes cancer cells to functionally diverse chemotherapeutics.

Stable expression of short-hairpin RNAs (shRNAs) directed against the X-linked inhibitor of apoptosis (XIAP) resulted in the generation of three MDA-MB-231 cell lines (XIAP shRNA cells) with reductions in XIAP mRNA and protein levels > 85% relative to MDA-MB-231 cells stably transfected with the U6 RNA polymerase III promoter alone (U6 cells). This RNA interference (RNAi) approach dramatically sensitized these cells to killing by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Importantly, loss of XIAP also sensitized the cells to killing by taxanes but had no additional effects on killing by carboplatin and doxorubicin. The increased sensitivity of the XIAP shRNA cells to killing by TRAIL and taxanes correlated with enhanced caspase cleavage and activation, including caspase-8, and robust processing of poly(ADP-ribose) polymerase and BID compared to U6 cells. Additionally, increasing XIAP levels by adenovirus-mediated expression protected both XIAP shRNA and U6 cells from TRAIL killing in a dose-dependent manner. The effects observed by stable RNAi with respect to TRAIL sensitization were also achieved following downregulation of XIAP in Panc-1 cells treated with a second-generation, mixed-backbone antisense oligonucleotide, AEG 35156/GEM640. These data indicate that reducing XIAP protein expression by either RNAi or antisense approaches increases cancer cell susceptibility to functionally diverse chemotherapeutic agents and supports the notion that downregulation of XIAP in vivo may synergize with disease-relevant chemotherapeutic regimes, including TRAIL and taxanes, to increase the effectiveness of antineoplastic agents.

Application of XIAP antisense to cancer and other proliferative disorders: development of AEG35156/ GEM640.

Targeting apoptosis control provides a novel therapeutic approach to the treatment of cancer and other proliferative disorders. We summarize the evidence for apoptosis deregulation in cancer and describe the pivotal role of XIAP, the X-linked Inhibitor-of-APoptosis. XIAP is the predominant inhibitor of caspases 3, 7 and 9 in cells, which suppresses the programmed cell death effector capability of these proteases. Evidence is presented validating XIAP as a cancer target. The inhibition or downregulation of XIAP in cancer cells lowers the apoptotic threshold, thereby inducing cell death and/or enhancing the cytotoxic action of chemotherapeutic agents. We describe the development of AEG35156 (also named GEM640), a second generation antisense compound targeting XIAP, from concept to in vivo preclinical proof-of-principle studies, through formal toxicology, and to a phase 1 clinical trial in cancer patients.

Longitudinal evaluation of memory performance and peripheral neuropathy in the Ins2C96Y Akita mice.

Ins2C96Y Akita mice represent a model of spontaneous early-onset diabetes mellitus, expressing a mutant non-functional isoform of insulin. These mice are characterized by a reduced number of pancreatic beta cells resulting in hypoinsulinemia and hyperglycemia. We obtained longitudinal measures of morning fasting blood glucose levels and gait performance. Sciatic nerve electrophysiology was also performed and the performance of these mice on spatial memory tasks was measured longitudinally. We observed a progressive increase in fasting blood glucose levels that was proportionally associated with increased gait disturbances. Diabetes induced a decrease in the sensory nerve conduction velocity up to the age of 40 weeks. Glucose transporter (GLUT) 3 levels were reduced in the hippocampus of the aged Ins2C96Y Akita mice. However, we failed to detect any significant deficits during reference, reversal or probe tests in the Morris water maze or in a spontaneous alternation task up to the age of 34 weeks old. We found that, up to the age of 34 weeks old, uncontrolled hyperglycemia produced peripheral neuropathy and reduced hippocampal GLUT3 levels in the absence of any effect on spatial memory processing.

Antisense oligonucleotides targeting XIAP induce apoptosis and enhance chemotherapeutic activity against human lung cancer cells in vitro and in vivo.

Activation of programmed cell death in cancer cells offers novel and potentially useful approaches to improving patient responses to conventional chemotherapy. X-linked inhibitor of apoptosis (XIAP), is the most potent member of the IAP gene family in terms of its ability to inhibit caspases and suppress apoptosis. In this study, we investigated the effect of XIAP down-regulation by antisense oligonucleotides (AS ODNs) on human non-small cell lung cancer (NIH-H460) growth in vitro and in vivo. In cultured H460 cells, G4 AS ODN was identified as the most potent compound. It down-regulated XIAP mRNA by 55% and protein levels up to 60% as determined by real-time quantitative reverse transcription-PCR and Western blotting, respectively, and induced 60% cell death. In contrast, the scrambled control ODN caused minimal XIAP loss and less than 10% cell death. Treatment with G4 AS ODN induced apoptosis as revealed by degradation of procaspase-3 and poly(ADP-ribose) polymerase proteins with significant nuclear DNA condensation and fragmentation. In addition, G4 AS ODNs sensitized H460 cells to the cytotoxic effects of doxorubicin, Taxol, vinorelbine, and etoposide. In animal models, administration of G4 AS ODN had significant sequence-specific inhibitory effects on H460 solid tumor establishment in a xenograft model. This antitumor activity was associated with an 85% down-regulation of XIAP protein in the tumors. In addition, the combination of 15 mg/kg G4 AS ODN with 5 mg/kg vinorelbine significantly delayed tumor establishment, more than either agent alone. These studies support the contention that XIAP is a viable target for cancer therapy in human non-small cell lung cancer.

Phase I trial of AEG35156 administered as a 7-day and 3-day continuous intravenous infusion in patients with advanced refractory cancer.

PURPOSE: To establish the maximum-tolerated dose and evaluate tolerability, pharmacokinetics, pharmacodynamic effects, and antitumor activity of AEG35156, a second-generation antisense to X-linked inhibitor of apoptosis (XIAP) protein, in patients with advanced refractory malignant tumors. PATIENTS AND METHODS: This was a first-in-man, open-label, phase I dose-escalation study. AEG35156 was administered by continuous intravenous infusion over 7 days (7DI) or 3 days (3DI) of a 21-day treatment cycle. Dose escalation started at 48 mg/m(2)/d and continued until consistent dose-limiting toxicity (DLT) was observed. RESULTS: Thirty-eight patients were entered in seven cohorts. Grade 3 to 4 adverse events were uncommon and were predominantly abnormal laboratory values: elevated ALT, thrombocytopenia, and lymphopenia. DLTs comprised elevated hepatic enzymes, hypophosphatemia, and thrombocytopenia. The maximum-tolerated doses were defined as 125 mg/m(2)/d for the 7DI regimen and < or = 213 mg/m(2)/d for the 3DI schedule. AEG35156 area under the plasma concentration curve and peak plasma concentration increased proportionally with dose. Suppression of XIAP mRNA levels was maximal at 72 hours (mean suppression, 21%), and this coincided with a dramatic decrease in circulating tumor cells in a patient with non-Hodgkin's lymphoma. Two further patients had unconfirmed partial responses. Circulating biomarkers of cell death and apoptosis altered in association with drug infusion and toxicity. CONCLUSION: In this first-in-man study, AEG35156 was well tolerated, with predictable toxicities, pharmacokinetic properties, and clinical evidence of antitumor activity in patients with refractory lymphoma, melanoma, and breast cancer. Phase I/II trials of AEG35156 chemotherapy combinations are ongoing in patients with pancreatic, breast, non-small-cell lung cancer, acute myeloid leukemia, lymphoma, and solid tumors for which docetaxel is indicated.

X-linked inhibitor of apoptosis regulates T cell effector function.

To understand how the balance between pro- and anti-apoptotic signals influences effector function in the immune system, we studied the X-linked inhibitor of apoptosis (XIAP), an endogenous regulator of cellular apoptosis. Real-time PCR showed increased XIAP expression in blood of mice with experimental autoimmune encephalomyelitis, correlating with disease severity. Daily administration (10 mg/kg/day i.p.) of a 19-mer antisense oligonucleotide specific for XIAP (ASO-XIAP) abolished disease-associated XIAP mRNA and protein expression, and given from day of onset, alleviated experimental autoimmune encephalomyelitis and prevented relapses. Prophylactic treatment also reduced XIAP expression and prevented disease. Random or 5-base mismatched ASO was not inhibitory, and ASO-XIAP did not affect T cell priming. In ASO-XIAP-treated animals, infiltrating cells and inflammatory foci were dramatically reduced within the CNS. Flow cytometry showed an 88-93% reduction in T cells. The proportion of TUNEL(+) apoptotic CD4(+) T cells in the CNS was increased from <1.6 to 26% in ASO-XIAP-treated mice, and the proportion of Annexin V-positive CD4(+) T cells in the CNS increased. Neurons and oligodendrocytes were not affected; neither did apoptosis increase in liver, where XIAP knockdown also occurred. ASO-XIAP increased susceptibility of T cells to activation-induced apoptosis in vitro. Our results identify XIAP as a critical controller of apoptotic susceptibility of effector T cell function.