c-Jun NH2-terminal kinase-dependent upregulation of DR5 mediates cooperative induction of apoptosis by perifosine and TRAIL

DR4-Associated Death Receptor Signal Promotes Cartilage Damage in Patients With Kashin-Beck Disease

Purpose. To explore the relationship between the death receptor (DR) and the pathological progression of Kashin-Beck disease (KBD). Design. KBD cartilage samples were collected from 15 patients diagnosed according to the "National Diagnostic Criteria of KBD" in China. In vitro monolayer chondrocytes were cultured in complete medium. Caspase-3 and caspase-8 activities in chondrocytes were analyzed using a kit. Nuclear morphology was observed by Hoechst 33258 staining, apoptosis was verified by flow cytometry analysis, and DR molecules were detected using Western blotting and quantitative real-time reverse transcription polymerase chain reaction analysis. Results. Early apoptotic rates of KBD and osteoarthritis (OA) chondrocytes were higher than those of normal control (NC) cells. Excessive apoptotic nuclei were observed in OA and KBD cells after Hoechst 33258 staining. Activities of both caspase-3 and caspase-8 were higher in KBD and OA cells than in NC cells. The average DR4 mRNA level in KBD cells was 3.301-fold higher than that in NC cells, Fas-associating protein with death domain (FADD) transcript level in KBD cells was 2.528-fold higher than that in NC cells. Western blot analyses showed that FAS, DR4, DR5, caspase-3, and FADD were upregulated in the KBD and OA groups compared with the NC group. High expression of caspase-8 in KBD compared with NC was verified, whereas cellular FLICE-inhibitory protein (c-FLIP) in KBD was significantly downregulated. Conclusions. KBD and OA chondrocytes showed obvious FADD-caspase-dependent apoptosis, which is related to the DR pathway. Apoptosis in KBD articular cartilage is mainly related to FAS/DR4-FADD-caspase signaling, and OA is associated with FAS/DR4/DR5-FADD-caspase signaling.

MET inhibition downregulates DR4 expression in MET-amplified lung cancer cells with acquired resistance to EGFR inhibitors through suppressing AP-1-mediated transcription

Death receptor 4 (DR4) is a cell surface protein that is generally thought to mediate apoptosis upon binding to its ligand named TRAIL. However, its contribution to apoptosis resistance has also been reported. MET (or c-MET) gene amplification represents an important mechanism for acquired resistance to EGFR tyrosine kinase inhibitors (EGFR-TKIs) against EGFR mutant non-small cell lung cancer (NSCLC). This study focuses on demonstrating the impact of MET inhibition on DR4 modulation in MET-amplified EGFR mutant NSCLC cell lines and the underlying mechanisms. Several MET inhibitors decreased DR4 levels in MET-amplified HCC827 cell lines resistant to EGFR-TKIs with no or limited effects on modulating DR5 levels, while increasing DR4 levels in HCC827 parental cells and other NSCLC cell lines. MET inhibitors did not affect DR4 stability, but decreased DR4 mRNA levels with suppression of AP-1-dependent DR4 promoter transactivation. Moreover, these inhibitors suppressed ERK and c-Jun phosphorylation accompanied with decreasing c-Jun levels. Hence, it is likely that MET inhibition downregulates DR4 expression in MET-amplified EGFR mutant NSCLC cells through suppressing AP-1-mediated DR4 transcription. Osimertinib combined with MET inhibition synergistically induces apoptosis in the MET-amplified EGFR mutant NSCLC cells accompanied with augmented DR4 reduction both in vitro and in vivo. Furthermore, MET inhibition combined with TRAIL enhanced killing of MET-amplified EGFR mutant HCC827/AR cells, but not HCC827 parental cells. These data collectively suggest that DR4 may possess an unrecognized anti-apoptotic function, contributing to apoptosis resistance under given conditions.

Downregulation of death receptor 4 is tightly associated with positive response of EGFR mutant lung cancer to EGFR-targeted therapy and improved prognosis

Death receptor 4 (DR4), a cell surface receptor, mediates apoptosis or induces inflammatory cytokine secretion upon binding to its ligand depending on cell contexts. Its prognostic impact in lung cancer and connection between EGFR-targeted therapy and DR4 modulation has not been reported and thus was the focus of this study. Methods: Intracellular protein alterations were measured by Western blotting. Cell surface protein was detected with antibody staining and flow cytometry. mRNA expression was monitored with qRT-PCR. Gene transactivation was analyzed with promoter reporter assay. Drug dynamic effects in vivo were evaluated using xenografts. Gene modulations were achieved with gene overexpression and knockdown. Proteins in human archived tissues were stained with immunohistochemistry. Results: EGFR inhibitors (e.g., osimertinib) decreased DR4 levels only in EGFR mutant NSCLC cells and tumors, being tightly associated with induction of apoptosis. This modulation was lost once cells became resistant to these inhibitors. Increased levels of DR4 were detected in cell lines with acquired osimertinib resistance and in NSCLC tissues relapsed from EGFR-targeted therapy. DR4 knockdown induced apoptosis and augmented apoptosis when combined with osimertinib in both sensitive and resistant cell lines, whereas enforced DR4 expression significantly attenuated osimertinib-induced apoptosis. Mechanistically, osimertinib induced MARCH8-mediated DR4 proteasomal degradation and suppressed MEK/ERK/AP-1-dependent DR4 transcription, resulting in DR4 downregulation. Moreover, we found that DR4 positive expression in human lung adenocarcinoma was significantly associated with poor patient survival. Conclusions: Collectively, we suggest that DR4 downregulation is coupled to therapeutic efficacy of EGFR-targeted therapy and predicts improved prognosis, revealing a previously undiscovered connection between EGFR-targeted therapy and DR4 modulation.

Gossypol induces apoptosis of multiple myeloma cells through the JUN-JNK pathway

Multiple myeloma (MM) is one of the most common hematologic neoplastic diseases. Gossypol was once used as a male contraceptive but is considered a novel antitumor agent. This study aimed to reveal the gossypol-induced apoptosis mechanism and its hub genes. Gossypol-induced MM cell apoptosis is concentration- and time-dependent. Of a total of 532 differentially expressed genes, 273 genes were upregulated and 259 genes were downregulated in gossypol-treated MM cells. Through KEGG and WGCNA analyses, the apoptosis-associated module was identified, and JUN was identified as the hub gene. The expression of the JUN protein product c-Jun was downregulated in MM cell lines compared to that in normal plasma cells. High-risk MM patients had a lower expression of JUN. High-expression JUN group patients had a lower risk of death. JUN overexpression in MM cells induced potent cell death and growth inhibition by a caspase-dependent apoptotic mechanism. DR5 is one of the upstream receptors of the JNK pathway, and shRNA knockdown of DR5 can partially reverse gossypol-induced apoptosis. A total of 1017 genes were coexpressed with JUN in MM patients. These genes are mainly involved in other JNK-associated signaling pathways, such as the IL6, EGF and PDGF signaling pathways. In conclusion, JUN is identified as the hub gene in gossypol-induced apoptosis, and gossypol can activate caspase-dependent apoptosis through the JNK pathway by targeting c-Jun and other JNK-associated pathways. DR5 and IL6 are also involved in this mechanism.

Targeting Functional Activity of AKT Has Efficacy against Aggressive Neuroblastoma

MYCN-amplified neuroblastoma is one of the deadliest forms of childhood cancer and remains a significant clinical challenge. Direct pharmacological inhibition of MYCN is not currently achievable. One strategy could be to target the AKT/GSK3β pathway, which directly regulates the stability of the MYCN protein. Numerous potent and isoform-specific small-molecule AKT inhibitors have been developed. However, the selection of the right drug combinations in the relevant indication will have a significant impact on AKT inhibitor clinical success. To maximally exploit the potential of AKT inhibitors, a better understanding of AKT isoform functions in cancer is crucial. Here using RNAi to downregulate specific AKT isoforms, we demonstrated that loss of total AKT activity rather than isoform-specific expression was necessary to decrease MYCN expression and cause a significant decrease in neuroblastoma cell proliferation. Consistent with these observations, isoform-specific pharmacological inhibition of AKT was substantially less effective than pan-AKT inhibition in combination with cytotoxic drugs in MYCN-amplified neuroblastoma. The allosteric pan-AKT inhibitor perifosine had promising in vitro and in vivo activity in combination with conventional cytotoxic drugs in MYCN-amplified neuroblastoma cells. Our results demonstrated that perifosine drug combination was able to induce apoptosis and downregulate ABC transporter expression. Collectively, this study shows that selecting pan-AKT inhibitors rather than isoform-specific drugs to synergize with first-line chemotherapy treatment should be considered for clinical trials for aggressive neuroblastoma and, potentially, other MYCN -driven cancers.

Cell death in drug-induced liver injury

Drug-induced liver injury (DILI) is an important cause of liver toxicity which can have varying clinical presentations, the most severe of which being acute liver failure. Hepatocyte death as a cause of drug toxicity is a feature of DILI. There are multiple cell death subroutines; some, like apoptosis, necroptosis, autophagy, and necrosis have been extensively studied, while others such as pyroptosis and ferroptosis have been more recently described. The mode of cell death in DILI depends on the culprit drug, as it largely dictates the mechanism and extent of injury. The main cell death subroutines in DILI are apoptosis and necrosis, with mitochondrial involvement being pivotal for the execution of both. A few drugs such as acetaminophen (APAP) can cause direct, dose-dependent toxicity, while the majority of drugs cause idiosyncratic DILI (IDILI). IDILI is an unpredictable form of liver injury that is not dose dependent, occurs in individuals with a genetic predisposition, and presents with variable latency. APAP-induced programmed necrosis has been extensively studied. However, the mechanisms and pathogenesis of cell death from drugs causing IDILI are harder to elucidate due to the complex and multifactorial nature of the disease. Cell death in IDILI is likely death receptor-mediated apoptosis and the result of an activated innate and adaptive immune system, compounded by other host factors such as genetics, gender, age, and capacity for immune tolerance. This chapter will review the different modes of cell death, namely apoptosis, necrosis, necroptosis, autophagy, pyroptosis, and ferroptosis and their pertinence to DILI.

Monocyte chemotactic protein-induced protein-1 enhances DR5 degradation and negatively regulates DR5 activation-induced apoptosis through its deubiquitinase function

Monocyte chemotactic protein-induced protein-1 (MCPIP1; also called Regnase-1) encoded by the ZC3H12A gene critically regulates inflammatory responses and immune homeostasis primarily by RNase-dependent and -independent mechanisms. However, the relationship of MCPIP1 with apoptosis and cancer and the underlying mechanisms are largely unclear. The current study has demonstrated a previously uncovered connection between MCPIP1 and the negative regulation of death receptor 5 (DR5; also known as TRAIL-R2 or killer/DR5), a cell surface receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which is produced endogenously by various immune cells such as T cells. Our findings have revealed that MCPIP1 decreases both total cellular and cell surface DR5, primarily through modulating DUB-mediated protein autophagic/lysosomal degradation. Suppression of MCPIP1 by gene knockdown induces the formation of death-induced signaling complex (DISC) and enhances TRAIL or DR5 activation-induced apoptosis in cancer cells. Moreover, we demonstrated an inverse correlation between MCPIP1 expression and DR5 expression/cell sensitivity to DR5 activation-induced apoptosis in cancer cells. Our findings warrant future investigation of the roles of negative regulation of DR5 by MCPIP1 in cancer and in T-cell immunity.

Inhibition of Akt and other AGC kinases: A target for clinical cancer therapy?

AGC kinases have been identified to contribute to cancer development and progression. Currently, most AGC inhibitors in clinical development are Akt inhibitors such as MK-2206 or GDC-0068, which are known to promote cell growth arrest and to sensitize cancer cells to radiotherapy. Response rates in clinical trials with single agent Akt inhibitors are typically low. The observed adverse events are within the expected limits for compounds inhibiting the PI3K-mTOR axis. Preclinical and early clinical data for combination therapies are accumulating. Based on these data, several Akt inhibitors are about to enter phase 3 trials. Besides drugs that target Akt, p70S6K inhibitors have entered clinical development. Again, the response rates were rather low. In addition, relevant toxicities were identified, including a risk for coagulopathies with these compounds. Multi-AGC kinase inhibitors are also in early clinical development but the data is not sufficient yet to draw conclusions regarding their efficacy and side-effect profile. PKC inhibitors have been tested in the phase 3 setting but were found to lack efficacy. More trials with isoform-specific PKC inhibitors are expected. Taken together, therapies with AGC kinase inhibitors as single agents are unlikely to meet success. However, combination therapies and a precise stratification of patients according to the activation of signaling axes may increase the probability to see relevant efficacy with these compounds. The emergence of onco-immunotherapies holds some new challenges for these agents.

Expression of Death Receptor 4 Is Positively Regulated by MEK/ERK/AP-1 Signaling and Suppressed upon MEK Inhibition

Death receptor 4 (DR4) is a cell surface receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and triggers apoptosis upon ligation with TRAIL or aggregation. MEK/ERK signaling is a well known and the best-studied effector pathway downstream of Ras and Raf. This study focuses on determining the impact of pharmacological MEK inhibition on DR4 expression and elucidating the underlying mechanism. We found that several MEK inhibitors including MEK162, AZD6244, and PD0325901 effectively decreased DR4 protein levels including cell surface DR4 in different cancer cell lines. Accordingly, pre-treatment of TRAIL-sensitive cancer cell lines with a MEK inhibitor desensitized them to TRAIL-induced apoptosis. These results indicate that MEK inhibition negatively regulates DR4 expression and cell response to TRAIL-induced apoptosis. MEK inhibitors did not alter DR4 protein stability, rather decreased its mRNA levels, suggesting a transcriptional regulation. In contrast, enforced activation of MEK/ERK signaling by expressing ectopic B-Raf (V600E) or constitutively activated MEK1 (MEK1-CA) or MEK2 (MEK2-CA) activated ERK and increased DR4 expression; these effects were inhibited when a MEK inhibitor was present. Promoter analysis through deletion and mutation identified the AP-1 binding site as an essential response element for enhancing DR4 transactivation by MEK1-CA. Furthermore, inhibition of AP-1 by c-Jun knockdown abrogated the ability of MEK1-CA to increase DR4 promoter activity and DR4 expression. These results suggest an essential role of AP-1 in mediating MEK/ERK activation-induced DR4 expression. Our findings together highlight a previously undiscovered mechanism that positively regulates DR4 expression through activation of the MEK/ERK/AP-1 signaling pathway.

Delivery of tumor-homing TRAIL sensitizer with long-acting TRAIL as a therapy for TRAIL-resistant tumors

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) has attracted great interest as a cancer therapy because it selectively induces death receptor (DR)-mediated apoptosis in cancer cells while sparing normal tissue. However, recombinant human TRAIL demonstrates limited therapeutic efficacy in clinical trials, possibly due to TRAIL-resistance of primary cancers and its inherent short half-life. Here we introduce drug delivery approaches to maximize in vivo potency of TRAIL in TRAIL-resistant tumor xenografts by (1) extending the half-life of the ligand with PEGylated TRAIL (TRAILPEG) and (2) concentrating a TRAIL sensitizer, selected from in vitro screening, in tumors via tumor-homing nanoparticles. Antitumor efficacy of TRAILPEG with tumor-homing sensitizer was evaluated in HCT116 and HT-29 colon xenografts. Western blot, real-time PCR, immunohistochemistry and cell viability assays were employed to investigate mechanisms of action and antitumor efficacy of the combination. We discovered that doxorubicin (DOX) sensitizes TRAIL-resistant HT-29 colon cancer cells to TRAIL by upregulating mRNA expression of DR5 by 60% in vitro. Intravenously administered free DOX does not effectively upregulate DR5 in tumor tissues nor demonstrate synergy with TRAILPEG in HT-29 xenografts, but rather introduces significant systemic toxicity. Alternatively, when DOX was encapsulated in hyaluronic acid-based nanoparticles (HAC/DOX) and intravenously administered with TRAILPEG, DR-mediated apoptosis was potentiated in HT-29 tumors by upregulating DR5 protein expression by 70% and initiating both extrinsic and intrinsic apoptotic pathways with reduced systemic toxicity compared to HAC/DOX or free DOX combined with TRAILPEG (80% vs. 40% survival rate; 75% vs. 34% tumor growth inhibition). This study demonstrates a unique approach to overcome TRAIL-based therapy drawbacks using sequential administration of a tumor-homing TRAIL sensitizer and long-acting TRAILPEG.

Targeting death receptors for TRAIL by agents designed by Mother Nature

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

Ischemic tolerance modulates TRAIL expression and its receptors and generates a neuroprotected phenotype

TNF-related apoptosis inducing ligand (TRAIL), a member of the TNF superfamily released by microglia, appears to be involved in the induction of apoptosis following focal brain ischemia. Indeed, brain ischemia is associated with progressive enlargement of damaged areas and prominent inflammation. As ischemic preconditioning reduces inflammatory response to brain ischemia and ameliorates brain damage, the purpose of the present study was to evaluate the role of TRAIL and its receptors in stroke and ischemic preconditioning and to propose, by modulating TRAIL pathway, a new therapeutic strategy in stroke. In order to achieve this aim a rat model of harmful focal ischemia, obtained by subjecting animals to 100 min of transient occlusion of middle cerebral artery followed by 24 h of reperfusion and a rat model of ischemic preconditioning in which the harmful ischemia was preceded by 30 mins of tMCAO, which represents the preconditioning protective stimulus, were used. Results show that the neuroprotection elicited by ischemic preconditioning occurs through both upregulation of TRAIL decoy receptors and downregulation of TRAIL itself and of its death receptors. As a counterproof, immunoneutralization of TRAIL in tMCAO animals resulted in significant restraint of tissue damage and in a marked functional recovery. Our data shed new light on the mechanisms that propagate ongoing neuronal damage after ischemia in the adult mammalian brain and provide new molecular targets for therapeutic intervention. Strategies aimed to repress the death-inducing ligands TRAIL, to antagonize the death receptors, or to activate the decoy receptors open new perspectives for the treatment of stroke.

Role of the eIF4E binding protein 4E-BP1 in regulation of the sensitivity of human pancreatic cancer cells to TRAIL and celastrol-induced apoptosis

BACKGROUND INFORMATION

Tumour cells can be induced to undergo apoptosis after treatment with the tumour necrosis factor α-related death-inducing ligand (TRAIL). Although human pancreatic cancer cells show varying degrees of response they can be sensitised to the pro-apoptotic effects of TRAIL in the presence of celastrol, a natural compound extracted from the plant Tripterygium wilfordii Hook F. One important aspect of the cellular response to TRAIL is the control of protein synthesis, a key regulator of which is the eukaryotic initiation factor 4E-binding protein, 4E-BP1.

RESULTS

We examined the effects of celastrol and TRAIL in several pancreatic cancer cell lines. In cells that are normally resistant to TRAIL, synergistic effects of TRAIL plus celastrol on commitment to apoptosis and inhibition of protein synthesis were observed. These were associated with a strong up-regulation and dephosphorylation of 4E-BP1. The enhancement of 4E-BP1 expression, which correlated with a threefold increase in the level of the 4E-BP1 transcript, was blocked by inhibitors of reactive oxygen species and the JNK protein kinase. When the expression of 4E-BP1 was reduced by an inducible micro-RNA, TRAIL-mediated apoptosis was inhibited.

CONCLUSION

These results suggest that 4E-BP1 plays a critical role in the mechanism by which TRAIL and celastrol together cause apoptotic cell death in human pancreatic tumour cells.

Induction of death receptor 5 expression in tumor vasculature by perifosine restores the vascular disruption activity of TRAIL-expressing CD34(+) cells

The proapoptotic death receptor 5 (DR5) expressed by tumor associated endothelial cells (TECs) mediates vascular disrupting effects of human CD34(+) cells engineered to express membrane-bound tumor necrosis factor-related apoptosis-inducing ligand (CD34-TRAIL (+) cells) in mice. Indeed, lack of DR5 on TECs causes resistance to CD34-TRAIL (+) cells. By xenografting in nonobese diabetic/severe combined immunodeficient mice the TRAIL-resistant lymphoma cell line SU-DHL-4V, which generates tumors lacking endothelial DR5 expression, here we demonstrate for the first time that the Akt inhibitor perifosine induces in vivo DR5 expression on TECs, thereby overcoming tumor resistance to the vascular disruption activity of CD34-TRAIL (+) cells. In fact, CD34-TRAIL (+) cells combined with perifosine, but not CD34-TRAIL (+) cells alone, exerted marked antivascular effects and caused a threefold increase of hemorrhagic necrosis in SU-DHL-4V tumors. Consistent with lack of DR5 expression, CD34-TRAIL (+) cells failed to affect the growth of SU-DHL-4V tumors, but CD34-TRAIL (+) cells plus perifosine reduced tumor volumes by 60 % compared with controls. In view of future clinical studies using membrane-bound TRAIL, our results highlight a strategy to rescue patients with primary or acquired resistance due to the lack of DR5 expression in tumor vasculature.

Involvement of de novo ceramide synthesis in gamma-tocopherol and gamma-tocotrienol-induced apoptosis in human breast cancer cells

SCOPE

This study further examines mechanisms involved in the pro-apoptotic action of gamma-tocopherol (γT) and gamma-tocotrienol (γT3) in human breast cancer cell lines.

METHODS AND RESULTS

γT upregulates phospho-JNK (pJNK), CCAAT/enhancer-binding protein homologous protein (CHOP), and death receptor-5 (DR5) protein expression as detected by Western blot assays. siRNA knockdown of JNK, CHOP, or DR5 shows that γT-induced apoptosis is JNK/CHOP/DR5 signaling dependent, which is similar to γT3-mediated apoptotic signaling. Furthermore, both γT and γT3 induce increased levels of cellular ceramides and dihydroceramides as determined by LC-MS/MS analyses. Inhibition of de novo ceramide synthesis using chemical inhibitors blocked the ability of γT and γT3 to induce apoptosis as detected by Annexin V-FITC/PI assay and to activate JNK/CHOP/DR5 pro-apoptotic signaling thereby demonstrating the involvement of de novo ceramide synthesis in γT- and γT3-induced apoptosis.

CONCLUSION

Taken together, data show that both γT and γT3 induce apoptosis via de novo ceramide synthesis dependent activation of JNK/CHOP/DR5 pro-apoptotic signaling.

TRAIL and vitamins: opting for keys to castle of cancer proteome instead of open sesame

Cancer is a multifaceted molecular disorder that is modulated by a combination of genetic, metabolic and signal transduction aberrations, which severely impair the normal homeostasis of cell growth and death. Accumulating findings highlight the fact that different genetic alterations, such as mutations in tumor suppressor genes, might be related to distinct and differential sensitivity to targeted therapies. It is becoming increasingly apparent that a multipronged approach that addresses genetic milieu (alterations in upstream and/or parallel pathways) eventually determines the response of individual tumors to therapy. Cancerous cells often acquire the ability to evade death by attenuating cell death pathways that normally function to eliminate damaged and harmful cells. Therefore impaired cell death nanomachinery and withdrawal of death receptors from cell surface are some of major determinants for the development of chemotherapeutic resistance encountered during treatment. It is therefore essential to emphasize underlying factors which predispose cells to refractoriness against TRAIL mediated cell death pathway and the relevant regulatory components involved. We bring to limelight the strategies to re-sensitize TRAIL resistant cells via vitamins to induce apoptosis.

Perifosine sensitizes UVB-induced apoptosis in skin cells: new implication of skin cancer prevention?

We demonstrate here that a relative low dose of perifosine significantly enhanced UVB-induced apoptosis in skin cells (keratinocytes and fibroblasts), associated with a significant increase of reactive oxygen species (ROS) and ceramide production as well as multiple perturbations of diverse cell signaling pathways, shifting to a significant pro-apoptosis outcomes. Perifosine inhibited UVB-induced pro-survival Akt/mammalian target of rapamycin (mTOR) and ERK activation, while facilitating pro-apoptotic AMP-activated protein kinas (AMPK), c-Jun-NH(2)-kinase (JNK), and p53 activation; these signaling changes together promoted a striking increase in skin cell apoptosis and a significantly reduced amount of DNA damages. Our results suggest that perifosine may represent a novel skin cancer prevention strategy.

AW00179 potentiates TRAIL-mediated death of human lung cancer H1299 cells through ROS-JNK-c-Jun-mediated up-regulation of DR5 and down-regulation of anti-apoptotic molecules

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers apoptosis in tumor cells, but when used alone, it is not effective at treating TRAIL-resistant tumors. This resistance is challenging for TRAIL-based anti-cancer therapies. In this study, we found that 1-(4-trifluoromethoxy-phenyl)-3-[4-(5-trifluoromethyl-2,5-dihydro-pyrazol-1-yl)-phenyl]-urea (AW00179) sensitized human lung cancer H1299 cells to TRAIL-mediated apoptosis. Even in the absence of TRAIL, AW00179 strongly induced DR5 expression and decreased the expression of anti-apoptotic proteins, suggesting that the sensitizing effect of AW00179 on TRAIL-mediated apoptosis is due to increased levels of DR5 protein and decreased anti-apoptotic molecules. AW00179 also induced the activation of c-Jun and ERK; however, a pharmacologic inhibition study revealed that JNK-c-Jun signaling is involved in the induction of DR5 expression. In addition, reactive oxygen species (ROS) appear to be involved in AW00179 activity. In conclusion, AW00179 has the potential to sensitize H1299 cells to TRAIL-mediated apoptosis through two distinct mechanisms: ROS-JNK-c-Jun-mediated up-regulation of DR5, and down-regulation of anti-apoptotic molecules.

Verticillin A overcomes apoptosis resistance in human colon carcinoma through DNA methylation-dependent upregulation of BNIP3

Drug resistance is a major cause of failure in cancer chemotherapy. Therefore, identification and combined use of adjuvant compounds that can overcome drug resistance may improve the efficacy of cancer therapy. We screened extracts of Verticillium species-infected mushrooms for antitumor compounds and identified the compound Verticillin A as an inducer of hepatoma cell apoptosis in vitro and an inhibitor of tumor xenograft growth in vivo. Verticillin A exhibited a potent apoptosis-sensitizing activity in human colon carcinoma cells exposed to TRAIL or Fas in vitro. Furthermore, Verticillin A effectively sensitized metastatic human colon carcinoma xenograft to TRAIL-mediated growth inhibition in vivo. At the molecular level, we observed that Verticillin A induces cell-cycle arrest in the G₂ phase of the cell cycle in human colon carcinoma cells, markedly upregulating BNIP3 in both hepatoma and colon carcinoma cells. Notably, silencing BNIP3 decreased the sensitivity of tumor cells to Verticillin A-induced apoptosis in the absence or presence of TRAIL. We found that the BNIP3 promoter is methylated in both human hepatoma and colon carcinoma cells and tumor specimens. Verticillin A upregulated the expression of a panel of genes known to be regulated at the level of DNA methylation, in support of the concept that Verticillin A may act by demethylating the BNIP3 promoter to upregulate BNIP3 expression. Taken together, our findings identify Verticillin A as a potent apoptosis sensitizer with great promise for further development as an adjuvant agent to overcome drug resistance in human cancer therapy.