We recently noted that low doses of sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95, and this drug combination is entering phase I trials. The present studies mechanistically extended our initial observations. Low doses of sorafenib and vorinostat, but not the individual agents, caused an acidic sphingomyelinase and fumonisin B1-dependent increase in CD95 surface levels and CD95 association with caspase 8. Knock down of CD95 or FADD expression reduced sorafenib/vorinostat lethality. Signaling by CD95 caused PERK activation that was responsible for both promoting caspase 8 association with CD95 and for increased eIF2α phosphorylation; suppression of eIF2α function abolished drug combination lethality. Cell killing was paralleled by PERK- and eIF2α-dependent lowering of c-FLIP-s protein levels and over-expression of c-FLIP-s maintained cell viability. In a CD95-, FADD- and PERK-dependent fashion, sorafenib and vorinostat increased expression of ATG5 that was responsible for enhanced autophagy. Expression of PDGFRβ and FLT3 were essential for high dose single agent sorafenib treatment to promote autophagy. Suppression of PERK function reduced sorafenib and vorinostat lethality whereas suppression of ATG5 levels elevated sorafenib and vorinostat lethality. Over-expression of c-FLIP-s blocked apoptosis and enhanced drug-induced autophagy. Thus sorafenib and vorinostat promote ceramide-dependent CD95 activation followed by induction of multiple downstream survival regulatory signals: ceramide-CD95-PERK-FADD-pro-caspase 8 (death); ceramide-CD95-PERK-eIF2α -↓c-FLIP-s (death); ceramide-CD95-PERK-ATG5-autophagy (survival).
Vorinostat; Sorafenib; CD95; c-FLIP-s; PDGFRβ; FLT3; autophagy; ceramide; cell death; ASMase
Purpose and Design
Mechanism(s) by which the multi-kinase inhibitor sorafenib and the histone deacetylase inhibitor vorinostat interact to kill hepatic, renal and pancreatic adenocarcinoma cells have been defined.
Low doses of sorafenib and vorinostat interacted in vitro in a synergistic fashion to kill hepatic, renal and pancreatic adenocarcinoma cells in multiple short term viability (24–96h) and in long term colony formation assays. Cell killing was suppressed by inhibition of cathepsin proteases and caspase 8, and to a lesser extent by inhibition of caspase 9. Twenty four hours after exposure, the activities of ERK1/2, AKT and NFκB were only modestly modulated by sorafenib and vorinostat treatment. However, 24h after exposure, sorafenib and vorinostat- treated cells exhibited markedly diminished expression of c-FLIP-s, full length BID, BCL-2, BCLXL, MCL-1, XIAP, increased expression of BIM, and increased activation of BAX, BAK and BAD. Expression of eIF2α S51A blocked sorafenib and vorinostat –induced suppression of c-FLIP-s levels and over-expression of c-FLIP-s abolished lethality. Sorafenib and vorinostat treatment increased surface levels of CD95 and CD95 association with caspase 8. Knock down of CD95 or FADD expression significantly reduced sorafenib / vorinostat -mediated lethality.
These data demonstrate that combined exposure of epithelial tumor cell types to sorafenib and vorinostat diminishes expression of multiple anti-apoptotic proteins, promotes activation of the CD95 extrinsic apoptotic and the lysosomal protease pathways, and that suppression of c-FLIP-s expression represents a critical event in transduction of the pro-apoptotic signals from CD95 to promote mitochondrial dysfunction and death.
Vorinostat; Sorafenib; CD95; c-FLIP-s; caspase 8; cathepsin; cell death
Sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95, and the present studies have determined individually how sorafenib and vorinostat contribute to CD95 activation. Sorafenib (3-6 μM) promoted a dose-dependent increase in Src Y416, ERBB1 Y845 and CD95 Y232/Y291 phosphorylation, and Src Y527 dephosphorylation. Low levels of sorafenib (3 μM) –induced CD95 tyrosine phosphorylation did not promote surface localization whereas sorafenib (6 μM), or sorafenib (3 μM) and vorinostat (500 nM) treatment promoted higher levels of CD95 phosphorylation that correlated with DISC formation, receptor surface localization and autophagy. CD95 (Y232F, Y291F) was not tyrosine phosphorylated and was unable to plasma membrane localize or induce autophagy. Knock down / knock out of Src family kinases abolished sorafenib –induced: CD95 tyrosine phosphorylation; DISC formation; and the induction of cell death and autophagy. Knock down of PDGFRβ enhanced Src Y416 and CD95 tyrosine phosphorylation that correlated with elevated CD95 plasma membrane levels and autophagy, and with a reduced ability of sorafenib to promote CD95 membrane localization. Vorinostat increased ROS levels; and in a delayed NFκB-dependent fashion, those of FAS ligand and CD95. Neutralization of FAS-L did not alter the initial rapid drug-induced activation of CD95 however, neutralization of FAS-L reduced sorafenib + vorinostat toxicity by ~50%. Thus sorafenib contributes to CD95 activation by promoting receptor tyrosine phosphorylation whereas vorinostat contributes to CD95 activation via initial facilitation of ROS generation and subsequently of FAS-L expression.
Vorinostat; Sorafenib; CD95; c-FLIP-s; FAS-L; cell death; autophagy
The present studies determined in greater detail the molecular mechanisms upstream of the CD95 death receptor by which geldanamycin HSP90 inhibitors and MEK1/2 inhibitors interact to kill carcinoma cells. MEK1/2 inhibition enhanced 17AAG toxicity that was suppressed in cells deleted for mutant active RAS which were non-tumorigenic but was magnified in isogenic tumorigenic cells expressing H-RAS V12 or K-RAS D13. MEK1/2 inhibitor and 17AAG treatment increased intracellular Ca2+ levels and reduced GRP78/BiP expression in a Ca2+ -dependent manner. GRP78/BiP over-expression, however, also suppressed drug-induced intracellular Ca2+ levels. MEK1/2 inhibitor and 17AAG treatment increased ROS levels that were blocked by quenching Ca2+ or over-expression of GRP78/BiP. MEK1/2 inhibitor and 17AAG treatment activated CD95 and inhibition of ceramide synthesis; ROS or Ca2+ quenching blocked CD95 activation. In SW620 cells that are patient matched to SW480 cells, MEK1/2 inhibitor and 17AAG toxicity was significantly reduced that correlated with a lack of CD95 activation and lower expression of ceramide synthase 6 (LASS6). Over-expression of LASS6 in SW620 cells enhanced drug-induced CD95 activation and enhanced tumor cell killing. Inhibition of ceramide signaling abolished drug-induced ROS generation but not drug-induced cytosolic Ca2+ levels. Thus treatment of tumor cells with MEK1/2 inhibitor and 17AAG induces cytosolic Ca2+ and loss of GRP78/BiP function, leading to de novo ceramide synthesis pathway activation that plays a key role in ROS generation and CD95 activation.
Geldanamycin; 17AAG; MEK1/2 inhibitor; CD95; c-FLIP-s; GRP78/BiP; autophagy; cell death; ASMase; de novo
The present studies sought to further understand how the anti-folate pemetrexed and the multi-kinase inhibitor sorafenib interact to kill tumor cells. Sorafenib activated SRC, and via SRC the drug combination activated ERK1/2. Expression of dominant negative SRC or dominant negative MEK1 abolished drug-induced ERK1/2 activation, together with drug-induced autophagy, acidic lysosome formation, and tumor cell killing. Protein phosphatase 2A is an important regulator of the ERK1/2 pathway. Fulvestrant resistant MCF7 cells expressed higher levels of the PP2A inhibitor SET/I2PP2A, had lower endogenous PP2A activity, and had elevated basal ERK1/2 activity compared with their estrogen dependent counterparts. Overexpression of I2PP2A blocked drug-induced activation of ERK1/2 and tumor cell killing. PP2A can be directly activated by ceramide and SET/I2PP2A can be inhibited by ceramide. Inhibition of the de novo ceramide synthase pathway blocked drug-induced ceramide generation, PP2A activation and tumor cell killing. Collectively these findings demonstrate that ERK1/2 plays an essential role downstream of SRC in pemetrexed and sorafenib lethality and that PP2A plays an important role in regulating this process.
ERK; I2PP2A; PP2A; SRC; autophagy; ceramide; pemetrexed; sorafenib
Hepatocellular carcinoma (HCC) is the most common form of liver cancer and the third leading cause of cancer death worldwide. The only approved systemic treatment for unresectable HCC is the oral kinase inhibitor, sorafenib. Recombinant human acid sphingomyelinase (rhASM), which hydrolyzes sphingomyelin to ceramide, is an orphan drug under development for the treatment of Type B Niemann-Pick disease (NPD). Due to the hepatotropic nature of rhASM and its ability to generate pro-apoptotic ceramide, this study evaluated the use of rhASM as an adjuvant treatment with sorafenib in experimental models of HCC.
In vitro, rhASM/sorafenib treatment reduced the viability of Huh7 liver cancer cells more than sorafenib. In vivo, using a subcutaneous Huh7 tumor model, mouse survival was increased and proliferation in the tumors decreased to a similar extent in both sorafenib and rhASM/sorafenib treatment groups. However, combined rhASM/sorafenib treatment significantly lowered tumor volume, increased tumor necrosis, and decreased tumor blood vessel density compared to sorafenib. These results were obtained despite poor delivery of rhASM to the tumors. A second (orthotopic) model of Huh7 tumors also was established, but modest ASM activity was similarly detected in these tumors compared to healthy mouse livers. Importantly, no chronic liver toxicity or weight loss was observed from rhASM therapy in either model.
The rhASM/sorafenib combination exhibited a synergistic effect on reducing the tumor volume and blood vessel density in Huh7 xenografts, despite modest activity of rhASM in these tumors. No significant increases in survival were observed from the rhASM/sorafenib treatment. The poor delivery of rhASM to Huh7 tumors may be due, at least in part, to low expression of mannose receptors. The safety and efficacy of this approach, together with the novel findings regarding enzyme targeting, merits further investigation.
The manuscripts by Park et al.1 and Zhang et al.2 were initially planned as studies to understand the regulation of cell survival in transformed cells treated with sorafenib and vorinostat, and in primary hepatocytes treated with a bile acid+MEK1/2 inhibitor. In both cell systems we discovered that the toxicity of sorafenib and vorinostat or bile acid+MEK1/2 inhibitor exposure depended on the generation of ceramide and the ligand-independent activation of the CD95 death receptor, with subsequent activation of pro-caspase 8. We noted, however, in these systems that, in parallel with death receptor–induced activation of the extrinsic pathway, CD95 signaling also promoted increased phosphorylation of PKR-like endoplasmic reticulum kinase (PERK) and eIF2α, increased expression of ATG5, and increased processing of LC3 and vesicularization of a GFP-LC3 construct. The knockdown of ATG5 expression blocked GFP-LC3 vesicularization and enhanced cell killing. Thus ceramide-CD95 signaling promoted cell death via activation of pro-caspase 8 and cell survival via autophagy. PERK was shown to signal in a switch-hitting fashion; PERK promoted CD95-DISC formation and an eIF2α-dependent reduction in c-FLIP-s levels that were essential for cell killing to proceed, but in parallel it also promoted autophagy that was protective. The death receptor-induced apoptosis and autophagy occur proximal to the receptor rather than the mitochondrion, and the relative flow of death receptor signaling into either pathway may determine cell fate. Finally, death receptor induced apoptosis and autophagy could be potential targets for therapeutic intervention.
Vorinostat; Sorafenib; bile acid; CD95; autophagy; ceramide; cell death; ASMase
Ceramide is an important second messenger that has diverse cellular and biological effect. It is a specific and potent inducer of apoptosis and suppressor of cell growth. In leukemia, chemoresistance generally developed due to deregulated ceramide metabolism. In combinatorial treatment strategies of leukemia, few components have the capability to increases ceramide production. Manipulation in ceramide production by physiological and pharmacological modulators therefore will give additive effect in leukemia chemotherapy.
Here, we show that Withanolide D (C4β-C5β,C6β-epoxy-1-oxo-,20β, dihydroxy-20S,22R-witha-2,24-dienolide; WithaD), a pure herbal compound isolated from Withania somnifera could effectively induces apoptosis in a dose and time dependant manner both in myeloid (K562) and lymphoid (MOLT-4) cells being nontoxic to normal lymphocytes and control proliferative cells. WithaD potentially augment ceramide production in these cells. Downstream of ceramide, WithaD acted on MKK group of proteins and significantly increased JNK and p38MAPK phosphorylation. Pharmacological inhibition of p38MAPK and JNK proves their cooperative action on WithaD-induced cell death. Dissecting the cause of ceramide production, we found activation of neutral sphingomyelinase and showed neutral-sphingomyelinase 2 (N-SMase 2) is a critical mediator of WithaD-induced apoptosis. Knockdown of N-SMase 2 by siRNA and inhibitor of N-SMase (GW4869) significantly reduced WithaD-induced ceramide generation and phosphorylation of MKK4 and MKK3/6, whereas phosphorylation of MKK7 was moderately regulated in leukemic cells. Also, both by silencing of N-SMase 2 and/or blocking by GW4869 protects these cells from WithaD-mediated death and suppressed apoptosis, whereas Fumonisin B1, an inhibitor of ceramide synthase, did not have any effect. Additionally, WithaD effectively induced apoptosis in freshly isolated lymphoblasts from patients and the potent cell killing activity was through JNK and p38MAPK activation.
Our results demonstrate that WithaD enhance the ceramide accumulation by activating N-SMase 2, modulate phosphorylation of the JNK and p38MAPK and induced apoptosis in both myeloid and lymphoid cells along with primary cells derived from leukemia patients. Taken together, this pure herbal compound (WithaD) may consider as a potential alternative tool with additive effects in conjunction with traditional chemotherapeutic treatment, thereby accelerate the process of conventional drug development.
Vesicular stomatitis virus (VSV) is an oncolytic virus that induces cancer cell death through activation of the apoptotic pathway. Intrinsic resistance to oncolysis is found in some cell lines and many primary tumors as a consequence of residual innate immunity to VSV. In resistant-tumor models, VSV oncolytic potential can be reversibly stimulated by combination with epigenetic modulators, such as the histone deacetylase inhibitor vorinostat. Based on this reversible effect of vorinostat, we reasoned that critical host genes involved in oncolysis may likewise be reversibly regulated by vorinostat. A transcriptome analysis in prostate cancer PC3 cells identified a subset of NF-κB target genes reversibly regulated by vorinostat, as well as a group of interferon (IFN)-stimulated genes (ISGs). Consistent with the induction of NF-κB target genes, vorinostat-mediated enhancement of VSV oncolysis increased hyperacetylation of NF-κB RELA/p65. Additional bioinformatics analysis revealed that NF-κB signaling also increased the expression of several autophagy-related genes. Kinetically, autophagy preceded apoptosis, and apoptosis was observed only when cells were treated with both VSV and vorinostat. VSV replication and cell killing were suppressed when NF-κB signaling was inhibited using pharmacological or genetic approaches. Inhibition of autophagy by 3-methyladenine (3-MA) enhanced expression of ISGs, and either 3-MA treatment or genetic ablation of the autophagic marker Atg5 decreased VSV replication and oncolysis. Together, these data demonstrate that vorinostat stimulates NF-κB activity in a reversible manner via modulation of RELA/p65 signaling, leading to induction of autophagy, suppression of the IFN-mediated response, and subsequent enhancement of VSV replication and apoptosis.
Glioblastomas are invasive tumors with poor prognosis despite current therapies. Histone deacetylase inhibitors (HDACIs) represent a class of agents that can modulate gene expression to reduce tumor growth, and we and others have noted some antiglioma activity from HDACIs, such as vorinostat, although insufficient to warrant use as mono-therapy. We have recently demonstrated that proteasome inhibitors, such as bortezomib, dramatically sensitized highly resistant glioma cells to apoptosis induction, suggesting that proteasomal inhibition may be a promising combination strategy for glioma therapeutics. In this study, we examined whether bortezomib could enhance response to HDAC inhibition in glioma cells. Although primary cells from glioblastoma multiforme (GBM) patients and established glioma cell lines did not show significant induction of apoptosis with vorinostat treatment alone, the combination of vorino-stat plus bortezomib significantly enhanced apoptosis. The enhanced efficacy was due to proapoptotic mitochondrial injury and increased generation of reactive oxygen species. Our results also revealed that combination of bortezomib with vorinostat enhanced apoptosis by increasing Mcl-1 cleavage, Noxa upregulation, Bak and Bax activation, and cytochrome c release. Further downregulation of Mcl-1 using shRNA enhanced cell killing by the bortezomib/vorinostat combination. Vorinostat induced a rapid and sustained phosphorylation of histone H2AX in primary GBM and T98G cells, and this effect was significantly enhanced by co-administration of bortezomib. Vorinostat/bortezomib combination also induced Rad51 downregulation, which plays an important role in the synergistic enhancement of DNA damage and apoptosis. The significantly enhanced antitumor activity that results from the combination of bortezomib and HDACIs offers promise as a novel treatment for glioma patients.
bortezomib; vorinostat; glioma; synergy; apoptosis
Hepatocellular carcinoma is the fifth most common solid cancer worldwide. Sorafenib, a small multikinase inhibitor, is the only approved therapy for advanced HCC. The clinical benefit of sorafenib is offset by the acquisition of sorafenib resistance. Understanding of the molecular mechanism of STAT3 overexpression in sorafenib resistance is critical if the clinical benefits of this drug are to be improved. In this study, we explored our hypothesis that loss of RFX-1/SHP-1 and further increase of p-STAT3 as a result of sorafenib treatment induces sorafenib resistance as a cytoprotective response effect, thereby, limiting sorafenib sensitivity and efficiency. We found that knockdown of RFX-1 protected HCC cells against sorafenib-induced cell apoptosis and SHP-1 activity was required for the process. SC-2001, a molecule with similar structure to obatoclax, synergistically suppressed tumor growth when used in combination with sorafenib in vitro and overcame sorafenib resistance through up-regulating RFX-1 and SHP-1 resulting in tumor suppression and mediation of dephosphorylation of STAT3. In addition, sustained sorafenib treatment in HCC led to increased p-STAT3 which was a key mediator of sorafenib sensitivity. The combination of SC-2001 and sorafenib strongly inhibited tumor growth in both wild-type and sorafenib-resistant HCC cell bearing xenograft models. These results demonstrate that inactivation of RFX/SHP-1 induced by sustained sorafenib treatment confers sorafenib resistance to HCC through p-STAT3 up-regulation. These effects can be overcome by SC-2001 through RFX-1/SHP-1 dependent p-STAT3 suppression. In conclusion, the use of SC-2001 in combination with sorafenib may constitute a new strategy for HCC therapy.
Ceramide levels are elevated in Mantle Cell Lymphoma cells following treatment with cannabinoids. Here, we investigated the pathways of ceramide accumulation in the MCL cell line Rec-1 using the stable endocannabinoid analogue R(+)-methanandamide (R-MA). We further interfered with the conversion of ceramide into sphingolipids that promote cell growth. Treatment with R-MA led to increased levels of ceramide species C16, C18, C24 and C24:1 and transcriptional induction of ceramide synthases (CerSs) 3 and 6. The effects were attenuated using SR141716A, which has high affinity to cannabinoid receptor 1 (CB1). The CB1-mediated induction of CerS3 and CerS6 mRNA was confirmed using Win-55,212-2. Simultaneous silencing of CerS3 and CerS6 using siRNA abrogated the R-MA-induced accumulation of C16 and C24. Inhibition of either of the enzymes serine palmiotyl transferase, ceramide synthase, and dihydroceramide desaturase within the de novo ceramide pathway reversed ceramide accumulation and cell death induced by R-MA treatment. In order to enhance the cytotoxic effect R-MA, sphingosine kinase-1 (SK-1) and glucosylceramide synthase (GCS), enzymes that convert ceramide to the pro-proliferative sphingolipids sphingosine-1-phospate and glucosylceramide, respectively, were inhibited. Suppression of either enzyme using inhibitors or siRNA potentiated the decreased viability, induction of cell death and ceramide accumulation induced by R-MA treatment. Our findings suggest that R-MA induces cell death in MCL via CB1-mediated upregulation of the de novo ceramide synthesis pathway. Furthermore, inhibition of SK-1 and GCS potentiated ceramide accumulation and cell death induced by R-MA. This is the first study were the cytotoxic effect of a cannabinoid is enhanced by modulation of ceramide metabolism.
While there is significant interest in combining anti-angiogenesis therapy with conventional anti-cancer treatment, clinical trials have as of yet yielded limited therapeutic gain, mainly because mechanisms of anti-angiogenic therapy remain to a large extent unknown. Currently, anti-angiogenic tumor therapy is conceptualized to either “normalize” dysfunctional tumor vasculature, or to prevent recruitment of circulating endothelial precursors into the tumor. An alternative biology, restricted to delivery of anti-angiogenics immediately prior to single dose radiotherapy (radiosurgery), is provided in the present study.
Genetic data indicate an acute wave of ceramide-mediated endothelial apoptosis, initiated by acid sphingomyelinase (ASMase), regulates tumor stem cell response to single dose radiotherapy, obligatory for tumor cure. Here we show VEGF prevented radiation-induced ASMase activation in cultured endothelium, occurring within minutes after radiation exposure, consequently repressing apoptosis, an event reversible with exogenous C16-ceramide. Anti-VEGFR2 acts conversely, enhancing ceramide generation and apoptosis. In vivo, MCA/129 fibrosarcoma tumors were implanted in asmase+/+ mice or asmase−/− littermates and irradiated in the presence or absence of anti-VEGFR2 DC101 or anti-VEGF G6-31 antibodies. These anti-angiogenic agents, only if delivered immediately prior to single dose radiotherapy, de-repressed radiation-induced ASMase activation, synergistically increasing the endothelial apoptotic component of tumor response and tumor cure. Anti-angiogenic radiosensitization was abrogated in tumors implanted in asmase−/− mice that provide apoptosis-resistant vasculature, or in wild-type littermates pre-treated with anti-ceramide antibody, indicating that ceramide is necessary for this effect.
These studies show that angiogenic factors fail to suppress apoptosis if ceramide remains elevated while anti-angiogenic therapies fail without ceramide elevation, defining a ceramide rheostat that determines outcome of single dose radiotherapy. Understanding the temporal sequencing of anti-angiogenic drugs and radiation enables optimized radiosensitization and design of innovative radiosurgery clinical trials.
We have recently demonstrated that histone deacetylase inhibitor, Vorinostat, applied as a single therapy or in combination with caspase-8 downregulation exhibits high anti-tumoral activity on endometrial carcinoma cell lines. In the present study, we have assessed the signalling processes underlying anti-tumoral effects of Vorinostat. Increasing evidence suggests that reactive oxygen species are responsible for histone deacetylase inhibitor-induced cell killing. We have found that Vorinostat induces formation of reactive oxygen species and DNA damage. To investigate the role of oxidative stress as anti-neoplastic mechanism, we have evaluated the effects of different antioxidants (Bha, Nac and Tiron) on endometrial carcinoma cell line Ishikawa treated with Vorinostat. We show that Bha, Nac and Tiron markedly inhibited the cytotoxic effects of Vorinostat, increasing cell viability in vitro. We found that all three antioxidants did not inhibited accumulation of acetyl Histone H4, so that antioxidants did not inhibit Vorinostat activity. Finally, we have evaluated the effects of antioxidants on anti-tumoral activity of Vorinostat as monotherapy or in combination with caspase-8 downregulation in vivo. Interestingly, antioxidants blocked the reduction of tumour growth caused by Vorinostat, but they were unable to inhibit anti-tumoral activity of Vorinostat plus caspase-8 inhibition.
Sorafenib is the first and only orally administered drug currently approved to treat advanced hepatocellular carcinoma (HCC). However, concerns have been raised about sorafenib therapy, including acquired drug resistance. This review provides an overview of sorafenib in the treatment of HCC on the basis of data obtained in the laboratory and in clinical studies. Three underlying mechanisms have been found to support sorafenib therapy. First, sorafenib blocks HCC cell proliferation by inhibiting BRaf and Raf1/c-Raf serine/threonine kinase phosphorylation in the mitogen activated protein kinase (MAPK) pathway. Second, sorafenib induces apoptosis by reducing elF4E phosphorylation and down-regulating Mcl-1 levels in tumor cells. Third, sorafenib prevents tumor-associated angiogenesis by inactivating vascular endothelial growth factor receptors (VEGFR-2 and VEGFR-3) and the platelet-derived growth factor receptor-β (PDGFR-β). Clinical trials have demonstrated the effectiveness and relative safety of sorafenib, and thus the drug is used in un-resectable HCC. However, many patients may develop acquired resistance to sorafenib, so their response to sorafenib is eventually lost. Sorafenib may induce autophagy, which leads to apoptosis. However, autophagy can also cause drug resistance. Many studies have combined sorafenib with other treatments in an effort to increase its effects, reduce the necessary dosage, or overcome resistance. It is urgent to study the mechanisms underlying how sorafenib interacts with cellular molecules and other drugs to increase its efficacy and reduce resistance in HCC patients.
Sorafenib; Liver Neoplasms; Carcinoma; Hepatocellular; raf Kinases; Angiogenesis inhibitors; Drug Resistance
Sorafenib is a multi-kinase inhibitor approved for hepatocellular carcinoma, but rarely causes tumor regression in patients with chronic liver diseases. To investigate whether growth factor-mediated signaling is involved in sorafenib resistance, HepG2 and PLC/PRF/5 hepatoma cells were exposed to epidermal growth factor (EGF), hepatocyte growth factor (HGF) or transforming growth factor-β (TGF-β) prior to treatment with sorafenib. Furthermore, to identify an effective combination treatment with sorafenib, growth factor-sensitized cells were treated with sorafenib alone or in combination with celecoxib, lovastatin or valproic acid (VPA). Trypan blue staining and Annexin V assays showed that the cytotoxic effect of sorafenib was inhibited by 15-54% in cells sensitized to TGF-β (P<0.05). Western blotting analysis showed that TGF-β significantly activated extracellular signal-regulated kinase (ERK)-mediated AKT signaling, and sorafenib failed to suppress both ERK and AKT in TGF-β-sensitized cells. The decreased anti-tumor effect of sorafenib was rescued by chemical inhibition of ERK and AKT. When TGF-β-sensitized cells were treated with sorafenib plus VPA, the levels of phosphorylated ERK and AKT were considerably suppressed and the numbers of dead cells were increased by 3.7-5.7-fold compared with those exposed to sorafenib alone (P<0.05). Moreover, low dose sorafenib-induced cell migration was effectively suppressed by combination treatment with sorafenib and VPA. Collectively, TGF-β/ERK/AKT signaling might play a critical role in sorafenib resistance in hepatoma cells, and combination treatment with VPA may be effective against this drug resistance.
Sorafenib; TGF-β; hepatocellular carcinoma
The de novo pathway of ceramide synthesis has been implicated in the pathogenesis of excessive lung apoptosis and murine emphysema. Intracellular and paracellular-generated ceramides may trigger apoptosis and propagate the death signals to neighboring cells, respectively. In this study we compared the sphingolipid signaling pathways triggered by the paracellular- versus intracellular-generated ceramides as they induce lung endothelial cell apoptosis, a process important in emphysema development. Intermediate–chain length (C8:0) extracellular ceramides, used as a surrogate of paracellular ceramides, triggered caspase-3 activation in primary mouse lung endothelial cells, similar to TNF-α–generated endogenous ceramides. Inhibitory siRNA against serine palmitoyl transferase subunit 1 but not acid sphingomyelinase inhibited both C8:0 ceramide– and TNF-α (plus cycloheximide)–induced apoptosis, consistent with the requirement for activation of the de novo pathway of sphingolipid synthesis. Tandem mass spectrometry analysis detected increases in both relative and absolute levels of C16:0 ceramide in response to C8:0 and TNF-α treatments. These results implicate the de novo pathway of ceramide synthesis in the apoptotic effects of both paracellular ceramides and TNF-α–stimulated intracellular ceramides in primary lung endothelial cells. The serine palmitoyl synthase-regulated ceramides synthesis may contribute to the amplification of pulmonary vascular injury induced by excessive ceramides.
apoptosis; lung; cytokines; signaling; sphingolipids
β-cell mass is regulated by a balance between β-cell growth and β-cell death, due to apoptosis. We previously reported that apoptosis of INS-1 insulinoma cells due to thapsigargin-induced ER stress was suppressed by inhibition of the Group VIA Ca2+-independent phospholipase A2 (iPLA2β), associated with increased ceramide generation, and that the effects of ER stress were amplified in INS-1 cells in which iPLA2β was over expressed (OE INS-1 cells). These findings suggested that iPLA2β and ceramides participate in ER stress-induced INS-1 cell apoptosis. Here, we addressed this possibility and also the source of the ceramides by examining the effects of ER stress in empty vector (V)-transfected and iPLA2β-OE INS-1 cells using apoptosis assays and immunoblotting, quantitative PCR, and mass spectrometry analyses. ER stress induced expression of ER stress factors GRP78 and BiP, cleavage of apoptotic factor PARP, and apoptosis in V and OE INS-1 cells. Ceramide accumulation during ER stress was not associated with changes in mRNA levels of serine palmitoyl-transferase (SPT), the rate-limiting enzyme in de novo synthesis of ceramides but both message and protein levels of neutral sphingomyelinase (NSMase), which hydrolyzes sphingomyelins to generate ceramides, temporally increased in the INS-1 cells. The increases in NSMase expression in the ER-stressed INS-1 cells were associated with corresponding temporal elevations in ER-associated iPLA2β protein and catalytic activity. Pretreatment with BEL inactivated iPLA2β and prevented induction of NSMase message and protein in ER-stressed INS-1 cells. Relative to V INS-1 cells, the effects of ER stress were accelerated and/or amplified in the OE INS-1 cells. However, inhibition of iPLA2β or NSMase (chemically or with siRNA) suppressed induction of NSMase message, ceramide generation, sphingomyelin hydrolysis, and apoptosis in both V and OE INS-1 cells during ER stress. In contrast, inhibition of SPT did not suppress ceramide generation or apoptosis in either V or OE INS-1 cells. These findings indicate that iPLA2β activation participates in ER stress-induced INS-1 cell apoptosis by promoting ceramide generation via NSMase-catalyzed hydrolysis of sphingomyelins, raising the possibility that this pathway contributes to β-cell apoptosis due to ER stress.
Aberrant Ras/Raf/MEK/ERK signaling is one of the most prevalent oncogenic alterations and confers survival advantage to tumor cells. Inhibition of this pathway can effectively suppress tumor cell growth. For example, sorafenib, a multi-kinase inhibitor targeting c-Raf and other oncogenic kinases, has been used clinically for treating advanced liver and kidney tumors, and also has shown efficacy against other malignancies. However, how inhibition of oncogenic signaling by sorafenib and other drugs suppresses tumor cell growth remains unclear. In this study, we found that sorafenib kills cancer cells by activating PUMA, a p53 target and a BH3-only Bcl-2 family protein. Sorafenib treatment induces PUMA in a variety of cancer cells irrespective of their p53 status. Surprisingly, the induction of PUMA by sorafenib is mediated by IκB-independent activation of NF-κB, which directly binds to the PUMA promoter to activate its transcription. NF-κB activation by sorafenib requires GSK3β activation, subsequent to ERK inhibition. Deficiency in PUMA abrogates sorafenib-induced apoptosis and caspase activation, and renders sorafenib resistance in colony formation and xenograft tumor assays. Furthermore, the chemosensitization effect of sorafenib is dependent on PUMA, and involves concurrent PUMA induction through different pathways. BH3 mimetics potentiate the anticancer effects of sorafenib, and restore sorafenib sensitivity in resistant cells. Together, these results demonstrate a key role of PUMA-dependent apoptosis in therapeutic inhibition of Ras/Raf/MEK/ERK signaling. They provide a rationale for manipulating the apoptotic machinery to improve sensitivity and overcome resistance to the therapies that target oncogenic kinase signaling.
sorafenib; PUMA; apoptosis; NF-κB; GSK3β; colon cancer
Gastric cancer continues to be one of the deadliest cancers in the world and therefore identification of new drugs targeting this type of cancer is thus of significant importance. The purpose of this study was to identify and validate a therapeutic agent which might improve the outcomes for gastric cancer patients in the future.
Using microarray technology, we generated a gene expression profile of human gastric cancer–specific genes from human gastric cancer tissue samples. We used this profile in the Broad Institute's Connectivity Map analysis to identify candidate therapeutic compounds for gastric cancer. We found the histone deacetylase inhibitor vorinostat as the lead compound and thus a potential therapeutic drug for gastric cancer. Vorinostat induced both apoptosis and autophagy in gastric cancer cell lines. Pharmacological and genetic inhibition of autophagy however, increased the therapeutic efficacy of vorinostat, indicating that a combination of vorinostat with autophagy inhibitors may therapeutically be more beneficial. Moreover, gene expression analysis of gastric cancer identified a collection of genes (ITGB5, TYMS, MYB, APOC1, CBX5, PLA2G2A, and KIF20A) whose expression was elevated in gastric tumor tissue and downregulated more than 2-fold by vorinostat treatment in gastric cancer cell lines. In contrast, SCGB2A1, TCN1, CFD, APLP1, and NQO1 manifested a reversed pattern.
We showed that analysis of gene expression signature may represent an emerging approach to discover therapeutic agents for gastric cancer, such as vorinostat. The observation of altered gene expression after vorinostat treatment may provide the clue to identify the molecular mechanism of vorinostat and those patients likely to benefit from vorinostat treatment.
Vorinostat, a histone deacetylase (HDAC) inhibitor currently in a clinical phase III trial for multiple myeloma (MM) patients, has been reported to cause bone loss. The purpose of this study was to test whether, and to what extent, vorinostat influences the osteogenic differentiation of mesenchymal stem cells (MSCs) in vitro and bone formation in vivo.
Bone marrow-derived MSCs were prepared from both normal donors and MM patients. The MSCs were cultured in an osteogenic differentiation induction medium to induce osteogenic differentiation, which was evaluated by alkaline phosphatase (ALP) staining, Alizarin Red S staining and the mRNA expression of osteogenic markers. Naïve mice were administered vorinostat (100 mg/kg, ip) every other day for 3 weeks. After the mice were sacrificed, bone formation was assessed based on serum osteocalcin level and histomorphometric analysis.
Vorinostat inhibited the viability of hMSCs in a concentration-dependent manner (the IC50 value was 15.57 μmol/L). The low concentration of vorinostat (1 μmol/L) did not significantly increase apoptosis in hMSCs, whereas pronounced apoptosis was observed following exposure to higher concentrations of vorinostat (10 and 50 μmol/L). In bone marrow-derived hMSCs from both normal donors and MM patients, vorinostat (1 μmol/L) significantly increased ALP activity, mRNA expression of osteogenic markers, and matrix mineralization. These effects were associated with upregulation of the bone-specifying transcription factor Runx2 and with the epigenetic alterations during normal hMSCs osteogenic differentiation. Importantly, the mice treated with vorinostat did not show any bone loss in response to the optimized treatment regimen.
Vorinostat, known as a potent anti-myeloma drug, stimulates MSC osteogenesis in vitro. With the optimized treatment regimen, any decrease in bone formation was not observed in vivo.
histone deacetylase (HDAC); vorinostat; mesenchymal stem cell; osteogenesis; alkaline phosphatase (ALP); Runx2; osteocalcin; multiple myeloma
AIM: To clarify whether histone deacetylase inhibitors histone deacetylase inhibitors (HDACIs) can sensitize hepatocellular carcinoma (HCC) cells to sorafenib treatment.
METHODS: Bax, Bcl-2, ATG5-ATG12, p21, and p27 protein levels in Hep3B, HepG2, and PLC/PRF/5 cells were examined by Western blot. CCK8 and a fluorometric caspase-3 assay were used to examine cellular viability and apoptosis levels. The effect of Beclin-1 on sensitization of HCC cells to sorafenib was examined by transfecting Beclin-1 siRNA into Hep3B, HepG2, and PLC/PRF/5 cells.
RESULTS: Autophagy inhibition enhances the inhibitory effects of vorinostat and sorafenib alone or in combination on HCC cell growth. Vorinostat and sorafenib synergistically induced apoptosis and cell cycle alterations. Western blot data indicated that HDACIs and Beclin-1 knockdown increased the p53 acetylation level. The knockdown of Beclin-1 enhanced the synergistic effect of the combination of vorinostat with sorafenib.
CONCLUSION: HDACIs can sensitize HCC cells to sorafenib treatment by regulating the acetylation level of Beclin-1.
Hepatocellular carcinoma; Histone deacetylase inhibitors; Autophagy; Sorafenib; Chemoresistance
Resistance to imatinib (Gleevec®) in cancer cells is frequently because of acquired point mutations in the kinase domain of BCR-ABL. Ponatinib, also known as AP24534, is an oral multi-targeted tyrosine kinase inhibitor (TKI), and it has been investigated in a pivotal phase 2 clinical trial. The histone deacetylase inhibitor vorinostat (suberoylanilide hydroxamic acid) has been evaluated for its significant clinical activity in hematological malignancies. Thus, treatments combining ABL TKIs with additional drugs may be a promising strategy in the treatment of leukemia. In the current study, we analyzed the efficacy of ponatinib and vorinostat treatment by using BCR-ABL-positive cell lines. Treatment with ponatinib for 72 h inhibited cell growth and induced apoptosis in K562 cells in a dose-dependent manner. We found that ponatinib potently inhibited the growth of Ba/F3 cells ectopically expressing BCR-ABL T315I mutation. Upon BCR-ABL phosphorylation, Crk-L was decreased, and poly (ADP-ribose) polymerase (PARP) was activated in a dose-dependent manner. Combined treatment of Ba/F3 T315I mutant cells with vorinostat and ponatinib resulted in significantly increased cytotoxicity. Additionally, the intracellular signaling of ponatinib and vorinostat was examined. Caspase 3 and PARP activation increased after combination treatment with ponatinib and vorinostat. Moreover, an increase in the phosphorylation levels of γH2A.X was observed. Previously established ponatinib-resistant Ba/F3 cells were also resistant to imatinib, nilotinib, and dasatinib. We investigated the difference in the efficacy of ponatinib and vorinostat by using ponatinib-resistant Ba/F3 cells. Combined treatment of ponatinib-resistant cells with ponatinib and vorinostat caused a significant increase in cytotoxicity. Thus, combined administration of ponatinib and vorinostat may be a powerful strategy against BCR-ABL mutant cells and could enhance the cytotoxic effects of ponatinib in those BCR-ABL mutant cells.
The aim of this study was to investigate the effect of the combination of vorinostat and epigallocatechin-3-gallate against HuCC-T1 human cholangiocarcinoma cells. A novel chemotherapy strategy is required as cholangiocarcinomas rarely respond to conventional chemotherapeutic agents. Both vorinostat and EGCG induce apoptosis and suppress invasion, migration, and angiogenesis of tumor cells. The combination of vorinostat and EGCG showed synergistic growth inhibitory effects and induced apoptosis in tumor cells. The Bax/Bcl-2 expression ratio and caspase-3 and -7 activity increased, but poly (ADP-ribose) polymerase expression decreased when compared to treatment with each agent alone. Furthermore, invasion, matrix metalloproteinase (MMP) expression, and migration of tumor cells decreased following treatment with the vorinostat and EGCG combination compared to those of vorinostat or EGCG alone. Tube length and junction number of human umbilical vein endothelial cells (HUVECs) decreased as well as vascular endothelial growth factor expression following vorinostat and EGCG combined treatment. These results indicate that the combination of vorinostat and EGCG had a synergistic effect on inhibiting tumor cell angiogenesis potential. We suggest that the combination of vorinostat and EGCG is a novel option for cholangiocarcinoma chemotherapy.
Sphingolipids have emerged as bioeffector molecules, controlling various aspects of cell growth and proliferation in cancer, which is becoming the deadliest disease in the world. These lipid molecules have also been implicated in the mechanism of action of cancer chemotherapeutics. Ceramide, the central molecule of sphingolipid metabolism, generally mediates antiproliferative responses, such as cell growth inhibition, apoptosis induction, senescence modulation, endoplasmic reticulum stress responses and/or autophagy. Interestingly, recent studies suggest de novo-generated ceramides may have distinct and opposing roles in the promotion/suppression of tumors, and that these activities are based on their fatty acid chain lengths, subcellular localization and/or direct downstream targets. For example, in head and neck cancer cells, ceramide synthase 6/C16-ceramide addiction was revealed, and this was associated with increased tumor growth, whereas downregulation of its synthesis resulted in ER stress-induced apoptosis. By contrast, ceramide synthase 1-generated C18-ceramide has been shown to suppress tumor growth in various cancer models, both in situ and in vivo. In addition, ceramide metabolism to generate sphingosine-1-phosphate (S1P) by sphingosine kinases 1 and 2 mediates, with or without the involvement of G-protein-coupled S1P receptor signaling, prosurvival, angiogenesis, metastasis and/or resistance to drug-induced apoptosis. Importantly, recent findings regarding the mechanisms by which sphingolipid metabolism and signaling regulate tumor growth and progression, such as identifying direct intracellular protein targets of sphingolipids, have been key for the development of new chemotherapeutic strategies. Thus, in this article, we will present conclusions of recent studies that describe opposing roles of de novo-generated ceramides by ceramide synthases and/or S1P in the regulation of cancer pathogenesis, as well as the development of sphingolipid-based cancer therapeutics and drug resistance.
apoptosis; autophagy; chemoresistance; endoplasmic reticulum stress; sphingolipid; sphingolipid; protein binding