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Inhibitors of apoptosis (IAPs) are a family of proteins that regulate cell death and inflammation. XIAP (X-linked IAP) is the only family member that suppresses apoptosis by directly binding to and inhibiting caspases. On the other hand, cIAPs suppress the activation of the extrinsic apoptotic pathway by preventing the formation of pro-apoptotic signaling complexes. IAPs are negatively regulated by IAP-antagonist proteins such as Smac/Diablo and ARTS. ARTS can promote apoptosis by binding and degrading XIAP via the ubiquitin proteasome-system (UPS). Smac can induce the degradation of cIAPs but not XIAP. Many types of cancer overexpress IAPs, thus enabling tumor cells to evade apoptosis. Therefore, IAPs, and in particular XIAP, have become attractive targets for cancer therapy. In this review, we describe the differences in the mechanisms of action between Smac and ARTS, and we summarize efforts to develop cancer therapies based on mimicking Smac and ARTS. Several Smac-mimetic small molecules are currently under evaluation in clinical trials. Initial efforts to develop ARTS-mimetics resulted in a novel class of compounds, which bind and degrade XIAP but not cIAPs. Smac-mimetics can target tumors with high levels of cIAPs, whereas ARTS-mimetics are expected to be effective for cancers with high levels of XIAP.

Derived from rosaceous plant seed, amygdalin belongs to aromatic cyanogenic glycoside group, and its anticancer effects have been supported by mounting evidence. In this study, we objected to investigate amygdalin effect on two antiapoptotic genes (Survivin, XIAP) and two lncRNAs (GAS5, MALAT1) in human cancer cells (A549, MCF7, AGS). Employing RT-qPCR analysis, we compared the mRNA levels of the genes related to apoptosis in A549, MCF7, and AGS cancer cells between amygdalin-treated (24, 48 and 72 h) and un-treated groups. RNA was extracted from both cell groups and then cDNAs were synthesized. The changes in the gene expression levels were specified using ΔΔCt method. RT-qPCR analysis has revealed that the expression of Survivin, XIAP, GAS5 and MALAT1 in amygdala-treated cancer cells were significantly different, compared to the un-treated cells. However, these expressions were different depending on the treatment time. According to the results, amygdalin significantly inhibited the expression level of Survivin, and XIAP genes in treated via untreated group. Our findings suggest that amygdalin might have an anticancer effect due to the various gene expressions in A549, MCF7, and AGS human cancer cells, showing it's potential as a natural therapeutic anticancer drug.

Evasion of apoptosis is an important reason for tumor cells to resist the anticancer drugs in cancer therapy. As a critical regulator, the inhibitor of apoptosis proteins (IAPs) can block the apoptosis by inhibiting the activities of caspases. Scientists find that IAPs are over-expressed in many cancer cells, such as leukemia and B-cell lymphoma, which elucidate that high levels of IAPs are closely related to tumorigenesis and cancer development. Thus, targeting IAPs may be an attractive strategy for anti-tumor treatment. As an endogenous antagonist of IAPs, second mitochondria-derived activator of caspases (Smac) can suppress their activities through directly binding to IAPs. Based on structural biology study, Smac interacts with IAPs through the Ala-Val-Pro-Ile (AVPI) tetra-peptide of Smac. Therefore, many agents have been studied to suppress the IAPs which result in the activation of caspases and subsequently induce the apoptosis of tumor cells based on mimicking AVPI peptide strategy. In this review, the functions of IAPs in apoptosis and the recent advance of IAPs antagonists will be discussed.

Heptaphylline derivatives are carbazoles in Clausena harmandiana, a medicinal plant that is utilized for headache, stomach ache, and other treatments of illness. The present study examined the effects of heptaphylline and 7-methoxyheptaphylline on apoptosis of human colon adenocarcinoma cells (HT-29 cell line). Quantification of cell viability was performed using cell proliferation assay (MTT assay) and of protein expression through immunoblotting. The results showed that only heptaphylline, but not 7-methoxyheptaphylline, significantly significantly activated cleaved of caspase-3 and poly (ADP-ribose) polymerase (PARP-1) which resulted in HT-29 cell death. We found that heptaphylline activated BH3 interacting-domain death agonist (Bid) and Bak, proapoptotic proteins. In contrast, it suppressed X-linked inhibitor-of-apoptosis protein (XIAP), Bcl-xL and survivin, inhibitors of apoptosis. In addition, heptaphylline inhibited activation of NF-κB/p65 (rel), a regulator of apoptotic regulating proteins by suppressing the activation of Akt and IKKα, upstream regulators of p65. The findings suggested that heptaphylline induces apoptosis in human colon adenocarcinoma cells .

Apoptosis deregulation is important for cancer development, chemotherapy response, and prognosis. Survivin and X-linked inhibitor of apoptosis protein (XIAP) are 2 members of the inhibitor of apoptosis proteins family (IAP). We used semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) to determine the levels of expression of survivin and XIAP in 30 patients with de novo acute myeloid leukemia (AML) and 20 age- and sex-matched healthy volunteers. Survivin and XIAP overexpression were detected in 36.7% and 43.3% of cases, respectively. Patients with overexpression of either survivin or XIAP showed unfavorable response to chemotherapy in 81.2% and 91.7%, respectively. Also, these cases showed shorter median survival time (30 days) compared to patients with normal expression of either survivin or XIAP (150 days and 180 days). Patients with overexpression of both survivin and XIAP showed unfavorable response to induction therapy in 100% of the patients and the shortest median survival (30 days). These findings suggest that survivin and XIAP may have a role in leukemogenesis and provide prognostic information.

Evasion of apoptosis is one of the crucial acquired capabilities used by cancer cells to fend off anticancer therapies. Inhibitor of apoptosis (IAP) proteins exert a range of biological activities that promote cancer cell survival and proliferation. X chromosome-linked IAP is a direct inhibitor of caspases - pro-apoptotic executioner proteases - whereas cellular IAP proteins block the assembly of pro-apoptotic protein signalling complexes and mediate the expression of anti-apoptotic molecules. Furthermore, mutations, amplifications and chromosomal translocations of IAP genes are associated with various malignancies. Among the therapeutic strategies that have been designed to target IAP proteins, the most widely used approach is based on mimicking the IAP-binding motif of second mitochondria-derived activator of caspase (SMAC), which functions as an endogenous IAP antagonist. Alternative strategies include transcriptional repression and the use of antisense oligonucleotides. This Review provides an update on IAP protein biology as well as current and future perspectives on targeting IAP proteins for therapeutic intervention in human malignancies.

Melanoma is a highly aggressive malignant tumor with an exceptional ability to develop resistance and no curative therapy is available for patients with distant metastatic disease. The inhibitor of apoptosis protein (IAP) family has been related to therapy resistance in cancer. We examined the importance of the IAPs in the resistance to the commonly used chemotherapeutic agent dacarbazine (DTIC) and the apoptosis inducer TRAIL (TNF-related apoptosis inducing ligand) in malignant melanoma. The data presented show that the expression of IAPs is universal, concomitant and generally high in melanoma cell lines and in patient samples. Depleting IAP expression by siRNA tended to reduce cell viability, with XIAP reduction being the most efficient in all four cell lines examined (FEMX-1, LOX, SKMEL-28 and WM115). The combined treatment of XIAP siRNA and DTIC showed a weak improvement in two of four cell lines, while all four cell lines showed enhanced sensitivity towards TRAIL (AdhCMV-TRAIL) after XIAP depletion. In addition, cIAP-1, cIAP-2 and survivin down-regulation sensitized to TRAIL treatment in several of the cell lines. Cells exposed to TRAIL and XIAP siRNA showed increased DNA-fragmentation and cleavage of Bid, procaspase-8, -9, -7 and -3 and PARP, and change in the balance between pro- and anti-apoptotic proteins, indicating an enhanced level of apoptosis. Furthermore, the combined treatment reduced the ability of melanoma cells to engraft and form tumors in mice, actualizing the combination for future therapy of malignant melanoma.

Background and Purpose: Nuclear factor-kappaB (NF-kappaB) is an important regulator of inflammation and apoptosis. We showed previously that NF-kappaB inhibition by intraperitoneal TAT-NBD treatment strongly reduced neonatal hypoxic-ischemic (HI) brain damage. Neuroprotection by TAT-NBD was not associated with inhibition of cerebral cytokine production. We investigated how tumor necrosis factor-alpha (TNF-alpha) production is maintained after NF-kappaB inhibition and whether TNF-alpha contributes to brain damage., Methods: Postnatal Day 7 rats were subjected to unilateral carotid artery occlusion and hypoxia. Rats were treated immediately after HI with TAT-NBD, the JNK inhibitor TAT-JBD, and/or the TNF-alpha inhibitor etanercept. We determined brain damage, NF-kappaB and AP-1 activity, Gadd45beta, XIAP, (P-)TAK1, TNF-alpha, and TNF receptor expression., Results: Our data confirm that TAT-NBD treatment reduces brain damage without inhibiting TNF-alpha production. We now show that TAT-NBD treatment increased HI-induced AP-1 activation concomitantly with reduced Gadd45beta, XIAP, and increased (P)-TAK1 expression. Combined inhibition of NF-kappaB and JNK/AP-1 abrogated HI-induced TNF-alpha production. However, this treatment reduced the neuroprotective effect of NF-kappaB inhibition alone. We show that etanercept was detectable in the HI brain after intraperitoneal administration and that etanercept treatment also reduced the neuroprotective effect of NF-kappaB inhibition. Finally, NF-kappaB inhibition decreased HI-induced upregulation of TNF-R1 and increased TNF-R2 expression., Conclusions: When NF-kappaB was inhibited after neonatal cerebral HI, JNK/AP-1 activity was increased and required for increased TNF-alpha expression. Our data indicate that the switch to JNK/AP-1 activation preserves HI-induced TNF-alpha expression and thereby might contribute to the neuroprotective effect of TAT-NBD possibly through a TNF-R2 dependent mechanism.

Because evasion of apoptosis can cause radioresistance of glioblastoma, there is a need to design rational strategies that counter apoptosis resistance. In the present study, we investigated the potential of targeting the antiapoptotic protein XIAP for the radiosensitization of glioblastoma. Here, we report that small-molecule XIAP inhibitors significantly enhance gamma-irradiation-induced loss of viability and apoptosis and cooperate with gamma-irradiation to suppress clonogenic survival of glioblastoma cells. Analysis of molecular mechanisms reveals that XIAP inhibitors act in concert with gamma-irradiation to cause mitochondrial outer membrane permeabilization, caspase activation, and caspase-dependent apoptosis. Importantly, XIAP inhibitors also sensitize primary cultured glioblastoma cells derived from surgical specimens as well as glioblastoma-initiating stemlike cancer stem cells for gamma-irradiation. In contrast, they do not increase the toxicity of gamma-irradiation on some nonmalignant cells of the central nervous system, including rat neurons or glial cells, pointing to some tumor selectivity. In conclusion, by demonstrating for the first time that small-molecule XIAP inhibitors increase the radiosensitivity of glioblastoma cells while sparing normal cells of the central nervous system, our findings build the rationale for further (pre)clinical development of XIAP inhibitors in combination with gamma-irradiation in glioblastoma.

Drug resistance remains a major clinical challenge for cancer treatment. One mechanism by which tumor cells develop resistance to cytotoxic agents and radiation is related to resistance to apoptosis. Apoptosis is a well-organised process of cell death pre-programmed inside the cell. Apoptosis can be initiated either by activation of death receptors on the cell surface membranes (extrinsic pathway) or through a series of cellular events primarily processed at mitochondria (intrinsic pathway). Apoptosis has been shown to be important for tumorigenesis and cancer treatment. Defects in apoptosis can result in the expansion of a population of neoplastic cells. However, because the death of tumor cells induced by chemotherapy and radiotherapy is largely mediated by activation of apoptosis, inhibition of apoptosis will make tumor cells resistant to anti-tumor treatment. Herein, we will review the molecular changes that have the potential to cause apoptotic dysregulation, including activation of antiapoptotic factors (Bcl-2, BCLX(L), Bfl1/A1 etc.), inactivation of pro-apoptotic effectors (p53, p53 pathway), and /or reinforcement of survival signals (Survivin, FLIP, NF-kappaB etc). Furthermore, we will discuss therapeutic intervention and/or strategies that can lower the threshold for apoptosis of tumor cells that could became useful approaches to treat cancer with special emphasis placed on the important priority to develop new cancer therapeutics toward tumor stem cells.

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 (XIAP) is a suppressor of apoptosis that supports an increased survival and resistance to chemotherapy of human prostate cancer (PCa) cells. Effects of transient (24 h) and chronic (beyond 1 month) downregulation of XIAP in DU145 hormone refractory prostate cancer (HRPC) cells were studied. We found that transient downregulation of XIAP by siRNAs resulted in an increase of apoptosis and a decrease in Bcl-2 levels and sensitized PCa cells to cisplatin. XIAP downregulation by shRNA vector stable transfection led to upregulation of Bcl-2 protein. Our results identify the adaptability of PCa cells to chronic loss of XIAP in part through upregulation of Bcl-2 and indicate that multitargeting approach is the most effective application in the chemotherapy of human HRPC.

Spongistatin 1 is a new experimental chemotherapeutic agent isolated from marine sponges. Here we show that spongistatin 1 potently induces cell death in patient primary acute leukemic cells with higher efficiency than 8/10 clinically used cytotoxic drugs and prevents long-term survival of leukemic cell lines. Spongistatin 1 triggers caspase-dependent apoptosis in Jurkat T cells by the release of cytochrome c, Smac/DIABLO and Omi/HtrA2. As caspase-9 acts as an initiator caspase and Bcl-2 and Bcl-xL overexpression suppress spongistatin 1-induced apoptosis, cell death is mediated through the mitochondrial apoptosis pathway. Importantly, spongistatin 1 leads to the degradation of the antiapoptotic X-linked inhibitor of apoptosis protein. In apoptosis-resistant leukemic tumor cells overexpressing XIAP, spongistatin 1 effectively causes cell death and potentiates cell death induction by other apoptosis-promoting factors that might be caused by spongistatin 1-mediated degradation of XIAP. Our data show that spongistatin 1 represents a promising novel therapeutic agent for the treatment of leukemic tumor cells especially in the clinically highly relevant situation of chemoresistance due to overexpression of XIAP.

Undecylprodigiosin (UP) is a bacterial bioactive metabolite produced by Streptomyces and Serratia. In this study, we explored the anticancer effect of UP. Human breast carcinoma cell lines BT-20, MCF-7, MDA-MB-231 and T47D and one nonmalignant human breast epithelial cell line, MCF-10A, were tested in this study. We found that UP exerted a potent cytotoxicity against all breast carcinoma cell lines in a dose- and time-dependent manner. In contrast, UP showed limited toxicity to MCF-10A cells, indicating UP's cytotoxic effect is selective for malignant cells. UP's cytotoxic effect was due to apoptosis, as confirmed by positive TUNEL signals, annexin V-binding, caspase 9 activation and PARP cleavage. Notably, UP-induced apoptosis was blocked by the pan-caspase inhibitor z-VAD.fmk, further indicating the involvement of caspase activity. Moreover, UP caused a marked decrease of the levels of antiapoptotic BCL-X(L), Survivin and XIAP while enhancing the levels of proapoptotic BIK, BIM, MCL-1S and NOXA, consequently favoring induction of apoptosis. Additionally, we found that cells with functional p53 (MCF-7, T47D) or mutant p53 (BT-20, MDA-MB-231) were both susceptible to UP's cytotoxicity. Importantly, UP was able to induce apoptosis in MCF-7 cells with p53 knockdown by RNA interference, confirming the dispensability of p53 in UP-induced apoptosis. Overall, our results establish that UP induces p53-independent apoptosis in breast carcinoma cells with no marked toxicity to nonmalignant cells, raising the possibility of its use as a new chemotherapeutic drug for breast cancer irrespective of p53 status.

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.

Dysregulation of apoptosis has been shown to contribute to many diseases, including cancer formation, development and resistance, as well as neurodegenerative and autoimmune disorders. One mechanism through which tumour cells are believed to acquire resistance to apoptosis is by overexpression of X-linked inhibitor of apoptosis protein (XIAP), which belongs to a family of inhibitor of apoptosis proteins. When XIAP is overexpressed, cancer cells are rendered resistant to apoptosis, both intrinsically and in response to chemotherapy and radiotherapy. Significant progress has been made in targeting XIAP therapeutically, both directly and indirectly through the modulation of other molecules involved in the apoptotic pathway. This review introduces XIAP from its molecular origins, discusses its modulation and potential as a novel drug target, and considers future therapeutic perspectives.

Hepatocyte growth factor (HGF) is one of the most potent survival-promoting factors for motor neurons. We showed that introduction of the HGF gene into neurons of G93A transgenic mice attenuates motor neuron degeneration and increases the lifespan of these mice. Currently, treatment regimens using recombinant protein are closer to clinical application than gene therapy. To examine its protective effect on motor neurons and therapeutic potential we administered human recombinant HGF (hrHGF) by continuous intrathecal delivery to G93A transgenic rats at doses of 40 or 200 microg and 200 microg at 100 days of age (the age at which pathologic changes of the spinal cord appear, but animals show no clinical weakness) and at 115 days (onset of paralysis), respectively, for 4 weeks each. Intrathecal administration of hrHGF attenuates motor neuron degeneration and prolonged the duration of the disease by 63%, even with administration from the onset of paralysis. Our results indicated the therapeutic efficacy of continuous intrathecal administration of hrHGF in transgenic rats and should lead to the consideration for further clinical trials in amyotrophic lateral sclerosis using continuous intrathecal administration of hrHGF.

A small series of peptide mimics was designed and synthesized to contain a heterocyclic ring in place of the potentially labile N-terminal peptide bond of the tetrapeptide containing the Smac-XIAP-binding motif. Two Smac mimics were shown to bind to the BIR3 domain of XIAP with moderate affinity and one displayed increased activity in cells relative to the Smac peptides. The structures of BIR3-XIAP in complex with a Smac peptide and a peptide mimic were solved and analyzed to elucidate the structure-activity relationship surrounding the Smac-binding domain within BIR3-XIAP.

Protein-protein interactions have a key role in transduction pathways that regulate many cellular functions. Structural and functional properties of protein-protein interface are now better understood, therefore offering attractive opportunities for therapeutic intervention. Developping small molecules that modulate protein-protein interactions is challenging. Nethertheless, significant progress in this endeavour has been made on several fronts. Here, we use few illustrative examples to summarize recent work in this emerging field.

The identification of differentially regulated apoptotic signals in normal and tumor cells allows the development of cancer cell-selective therapies. Increasing evidence shows that the inhibitor of apoptosis (IAP) proteins survivin and XIAP are highly expressed in tumor cells but are absent or have very low levels of expression in normal adult tissues. We found that inhibiting AKT activity with 10 to 100 nM deguelin, a small molecule derived from natural products, markedly reduced the levels of both survivin and XIAP, inducing apoptosis in human breast cancer cells but not in normal cells. It is noteworthy that we detected an elevated level of cleaved poly(ADP-ribose) polymerase, a signature of caspase activation, without a significant increase in caspase activity in deguelin-treated cancer cells. Our results suggest that severe down-regulation of the IAPs by deguelin releases their inhibitory activity over pre-existing active caspases present in cancer cells, inducing apoptosis without the need for further caspase activation. Because normal cells have very low levels of p-AKT, XIAP, survivin, and pre-existing caspase activity, deguelin had little effect on those cells. In addition, we found that combining deguelin with chemotherapy drugs enhanced drug-induced apoptosis selectively in human tumor cells, which suggests that deguelin has great potential for chemosensitization and could represent a new therapeutic agent for treatment of breast cancer.

Agaricus blazei is well known as a traditional medicinal mushroom and it has been shown to exhibit immunostimulatory and anti-cancer activity. However, the cellular and molecular mechanism of cell cycle arrest and apoptosis of cancer cells is poorly understood. In this study, we have investigated whether A. blazei extract (ABE) exerts anti-proliferative and apoptotic effects on human gastric epithelial AGS cells. It was found that ABE could inhibit cell growth in a dose-dependent manner, which was associated with the arrest of G2/M phase and the induction of apoptotic cell death. Flow cytometric analysis showed that ABE could cause an arrest at the G2/M phase of the cell cycle, which is closely correlated to decreased cyclin B1 and cdc2 levels. Furthermore, this compound induced apoptosis through up-regulation of Bax and the activation of caspases with down-regulation of XIAP and cIAP-1, but not cIAP-2, and a capase-3 inhibitor could block cell death and apoptotic body formation. These data clearly indicate that ABE-induced apoptosis is associated with caspase-3 activation. In summary, the growth inhibition of ABE is highly related to cell cycle arrest at the G2/M phase and the induction of caspase-3-dependent apoptosis in human gastric epithelial AGS cells.

A common feature of cancer cells is their ability to evade apoptosis as a result of alterations that block cell death signaling pathways. The extensive research efforts that elucidated these signaling pathways over the past decade have set the stage for the development of therapeutic agents that either kill cancer cells selectively or reset their apoptotic threshold. Over the past two years a number of these agents have been evaluated in preclinical and clinical trials. The results of these studies suggest that it might soon be possible to modulate apoptosis in cancer cells for therapeutic benefit.

Triptolide, a diterpenoid isolated from the Chinese herb Tripterygium wilfordii Hook.f, has shown antitumor activities in a broad range of solid tumors. Here, we examined its effects on leukemic cells and found that, at 100 nM or less, it potently induced apoptosis in various leukemic cell lines and primary acute myeloid leukemia (AML) blasts. We then attempted to identify its mechanisms of action. Triptolide induced caspase-dependent cell death accompanied by a significant decrease in XIAP levels. Forced XIAP overexpression attenuated triptolide-induced cell death. Triptolide also decreased Mcl-1 but not Bcl-2 and Bcl-X(L) levels. Bcl-2 overexpression suppressed triptolide-induced apoptosis. Further, triptolide induced loss of the mitochondrial membrane potential and cytochrome C release. Caspase-9 knock-out cells were resistant, while caspase-8-deficient cells were sensitive to triptolide, suggesting criticality of the mitochondrial but not the death receptor pathway for triptolide-induced apoptosis. Triptolide also enhanced cell death induced by other anticancer agents. Collectively, our results demonstrate that triptolide decreases XIAP and potently induces caspase-dependent apoptosis in leukemic cells mediated through the mitochondrial pathway at low nanomolar concentrations. The potent antileukemic activity of triptolide in vitro warrants further investigation of this compound for the treatment of leukemias and other malignancies.

Previously, this laboratory demonstrated that ethanol reduces the number of developing serotonin (5-HT)-containing neurons by increasing apoptosis. We also found that 5-HT(1A) agonists attenuate the proapoptotic effects of ethanol and the ethanol-mediated reduction of fetal 5-HT neurons. These neuroprotective effects are mediated in part by the ability of 5-HT(1A) agonists to activate the phosphatidyl 3'-kinase (PI-3K) prosurvival pathway. NF-kappaB is one of the downstream effectors activated by this pathway. In the present study, we used quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) to determine the effects of 50mM ethanol and 100nM of ipsapirone, a 5-HT(1A) agonist, on the expression of several NF-kappaB-dependent antiapoptotic genes: X-linked inhibitor of apoptosis protein (XIAP), cIAP1, cIAP2, Bcl-2, and Bcl-xl. We also investigated the effects of ethanol and ipsapirone on the expression of the gene encoding the 5-HT(1A) receptor. The results demonstrate that ethanol reduces the expression of several prosurvival genes: XIAP, cIAP1, cIAP2, Bcl-2, and Bcl-xl. Importantly, the ethanol-mediated reduction in the expression of XIAP and Bcl-xl was prevented by co-treatment with ipsapirone. Thus, the damaging effects of ethanol are likely to involve a reduction in several prosurvival proteins. Moreover, the protective effects of ipsapirone on ethanol-treated neurons might involve their ability to prevent the reduction of XIAP and Bcl-xl. Although ipsapirone treatment decreased the expression of cIAP1, Bcl-2, and Bcl-xl in control neurons, our prior studies suggest that their survival is not reduced by ipsapirone. We also observed an increased expression of the 5-HT(1A) receptor in ipsapirone-treated control neurons.

The protein transduction domain (PTD) of HIV-1 TAT has been extensively documented with regard to its membrane transduction potential, as well as its efficient delivery of biomolecules in vivo. However, the majority of PTD and PTD-conjugated molecules translocate to the nucleus rather than to the cytoplasm after transduction, due to the functional nuclear localization sequence (NLS). Here, we report a cytoplasmic transduction peptide (CTP), which was deliberately designed to ensure the efficient cytoplasmic delivery of the CTP-fused biomolecules. In comparison with PTD, CTP and its fusion partners exhibited a clear preference for cytoplasmic localization, and also markedly enhanced membrane transduction potential. Unlike the mechanism underlying PTD-mediated transduction, CTP-mediated transduction occurs independently of the lipid raft-dependent macropinocytosis pathway. The CTP-conjugated Smac/DIABLO peptide (Smac-CTP) was also shown to be much more efficient than Smac-PTD in the blockage of the antiapoptotic properties of XIAP, suggesting that cytoplasmic functional molecules can be more efficiently targeted by CTP-mediated delivery. In in vivo trafficking studies, CTP-fused beta-gal exhibited unique organ tropisms to the liver and lymph nodes when systemically injected into mice, whereas PTD-beta-gal exhibited no such tropisms. Taken together, our findings implicate CTP as a novel delivery peptide appropriate for (i) molecular targeting to cytoplasmic compartments in vitro, (ii) the development of class I-associated CTL vaccines, and (iii) special drug delivery in vivo, without causing any untoward effects on nuclear genetic material.

Due to their tremendous apoptosis-inducing potential, proteasomal inhibitors (PIs) have recently entered clinical trials. Here we show, however, that various PIs rescued proliferating tumor cells from death receptor-induced apoptosis. This protection correlated with the stabilization of X-linked IAP (XIAP) and c-FLIP and the inhibition of caspase activation. Together with the observation that PIs could not protect cells expressing XIAP or c-FLIP short interfering RNAs (siRNAs) from death receptor-induced apoptosis, our results demonstrate that PIs mediate their protective effect via the stabilization of these antiapoptotic proteins. Furthermore, we show that once these proteins were eliminated, either by long-term treatment with death receptor ligands or by siRNA-mediated suppression, active caspases accumulated to an even larger extent in the presence of PIs. Together, our data support a biphasic role for the proteasome in apoptosis, as they show that its constitutive activity is crucial for the rapid initiation of the death program by eliminating antiapoptotic proteins, whereas at later stages, the proteasome acts in an antiapoptotic manner due to the proteolysis of caspases. Thus, for a successful PI-based tumor therapy, it is crucial to carefully evaluate basal proteasomal activity and the status of antiapoptotic proteins, as their PI-mediated prolonged stability might even cause adverse effects, leading to the survival of a tumor.