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1.  MEK1/2 inhibitors and 17AAG synergize to kill human GI tumor cells in vitro via suppression of c-FLIP-s levels and activation of CD95 
Molecular cancer therapeutics  2008;7(9):2633-2648.
Prior studies have noted that inhibitors of MEK1/2 enhanced geldanamycin lethality in malignant hematopoietic cells by promoting mitochondrial dysfunction. The present studies focused on defining the mechanism(s) by which these agents altered survival in carcinoma cells. MEK1/2 inhibitors (PD184352; AZD6244 (ARRY-142886)) interacted in a synergistic manner with geldanamycins (17AAG, 17DMAG) to kill hepatoma and pancreatic carcinoma cells that correlated with inactivation of ERK1/2 and AKT and with activation of p38 MAPK; p38 MAPK activation was ROS-dependent. Treatment of cells with MEK1/2 inhibitors and 17AAG reduced expression of c-FLIP-s that was mechanistically connected to loss of MEK1/2 and AKT function; inhibition of caspase 8 or over-expression of c-FLIP-s abolished cell killing by MEK1/2 inhibitors and 17AAG. Treatment of cells with MEK1/2 inhibitors and 17AAG caused a p38 MAPK-dependent plasma membrane clustering of CD95 without altering the levels or cleavage of FAS ligand. In parallel, treatment of cells with MEK1/2 inhibitors and 17AAG caused a p38 MAPK-dependent association of caspase 8 with CD95. Inhibition of p38 MAPK or knock down of BID, FADD or CD95 expression suppressed MEK1/2 inhibitor and 17AAG lethality. Similar correlative data were obtained using a xenograft flank tumor model system. Our data demonstrate that treatment of tumor cells with MEK1/2 inhibitors and 17AAG induces activation of the extrinsic pathway and that suppression of c-FLIP-s expression is crucial in transduction of the apoptotic signal from CD95 to promote cell death.
doi:10.1158/1535-7163.MCT-08-0400
PMCID: PMC2585522  PMID: 18790746
CD95; caspase; extrinsic; FLIP
2.  MEK inhibition potentiates the activity of Hsp90 inhibitor 17-AAG against pancreatic cancer cells 
Molecular pharmaceutics  2010;7(5):1576-1584.
The Ras/Raf/MEK/ERK signaling has been implicated in uncontrolled cell proliferation and tumor progression in pancreatic cancer. The purpose of this study is to evaluate the antitumor activity of MEK inhibitor U0126 in combination with Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) in pancreatic cancer cells. Western blotting showed that 17-AAG caused a 2- to 3-fold transient activation of MEK/ERK signaling in pancreatic cancer cells. The activation sustained for 6 h before phospho-ERK (p-ERK) destabilization. The selective MEK inhibitor U0126 completely abolished 17-AAG induced ERK1/2 activation and resulted in more than 80% of phosphor-ERK degradation after only 15 min treatment. Moreover, U0126 had complementary effect on 17-AAG regulated oncogenic and cell cycle related proteins. Although 17-AAG downregulated cyclin D1, cyclin E, CDK4 and CDK6, it led to cyclin A and CDK2 accumulation, which was reversed by the addition of U0126. Anti-proliferation assay showed that combination of U0126 and 17-AAG resulted in synergistic cytotoxic effect. More importantly, 17-AAG alone only exhibited moderate inhibition of cell migration in vitro, while addition of U0126 dramatically enhanced the inhibitory effect by 2- to 5-fold. Taken together, these data demonstrate that MEK inhibitor U0126 potentiates the activity of Hsp90 inhibitor 17-AAG against pancreatic cancer cells. The combination of Hsp90 and MEK inhibition could provide a promising avenue for the treatment of pancreatic cancer.
doi:10.1021/mp900321a
PMCID: PMC2992603  PMID: 20669973
Hsp90; MEK; ERK; 17-AAG
3.  Modeling tandem AAG8-MEK inhibition in melanoma cells 
Cancer Medicine  2014;3(3):710-718.
Drug resistance presents a challenge to the treatment of cancer patients, especially for melanomas, most of which are caused by the hyperactivation of MAPK signaling pathway. Innate or acquired drug-resistant relapse calls for the investigation of the resistant mechanisms and new anti-cancer drugs to provide implications for the ultimate goal of curative therapy. Aging-associated gene 8 (AAG8, encoded by the SIGMAR1 gene) is a chaperone protein profoundly elaborated in neurology. However, roles of AAG8 in carcinogenesis remain unclear. Herein, we discover AAG8 antagonists as new MEK inhibitors in melanoma cells and propose a novel drug combination strategy for melanoma therapy by presenting the experimental evidences. We report that specific antagonism of AAG8, efficiently suppresses melanoma cell growth and migration through, at least in part, the inactivation of the RAS-CRAF-MEK signaling pathway. We further demonstrate that melanoma cells that are resistant to AAG8 antagonist harbor refractory CRAF-MEK activity. MEK acts as a central mediator for anti-cancer effects and also for the resistance mechanism, leading to our proposal of tandem AAG8-MEK inhibition in melanoma cells. Combination of AAG8 antagonist and very low concentration of a MEK inhibitor synergistically restricts the growth of drug-resistant cells. These data collectively pinpoint AAG8 as a potential target and delineate a promising drug combination strategy for melanoma therapy.
doi:10.1002/cam4.233
PMCID: PMC4101763  PMID: 24634165
AAG8; drug combination; drug resistance; MEK; melanoma
4.  Targeting GRP75 Improves HSP90 Inhibitor Efficacy by Enhancing p53-Mediated Apoptosis in Hepatocellular Carcinoma 
PLoS ONE  2014;9(1):e85766.
Heat shock protein 90 (HSP90) inhibitors are potential drugs for cancer therapy. The inhibition of HSP90 on cancer cell growth largely through degrading client proteins, like Akt and p53, therefore, triggering cancer cell apoptosis. Here, we show that the HSP90 inhibitor 17-AAG can induce the expression of GRP75, a member of heat shock protein 70 (HSP70) family, which, in turn, attenuates the anti-growth effect of HSP90 inhibition on cancer cells. Additionally, 17-AAG enhanced binding of GRP75 and p53, resulting in the retention of p53 in the cytoplasm. Blocking GRP75 with its inhibitor MKT-077 potentiated the anti-tumor effects of 17-AAG by disrupting the formation of GRP75-p53 complexes, thereby facilitating translocation of p53 into the nuclei and leading to the induction of apoptosis-related genes. Finally, dual inhibition of HSP90 and GRP75 was found to significantly inhibit tumor growth in a liver cancer xenograft model. In conclusion, the GRP75 inhibitor MKT-077 enhances 17-AAG-induced apoptosis in HCCs and increases p53-mediated inhibition of tumor growth in vivo. Dual targeting of GRP75 and HSP90 may be a useful strategy for the treatment of HCCs.
doi:10.1371/journal.pone.0085766
PMCID: PMC3894982  PMID: 24465691
5.  Transcription Inhibition of Heat Shock Proteins: A Strategy for Combination of 17-allylamino-17-demethoxygeldanamycin and Actinomycin D 
Cancer research  2009;69(9):3947-3954.
The heat shock protein (HSP) 90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) is currently in clinical trials because of its unique mechanism of action and antitumor activity. However, 17-AAG triggers the transcription and elevation of antiapoptotic HSP90, HSP70, and HSP27, which lead to chemoresistance in tumor cells. We hypothesized that inhibiting HSP90, HSP70, and HSP27 transcription may enhance 17-AAG-induced cell death in multiple myeloma (MM) cell lines. Actinomycin D (Act D), a clinically used agent and transcription inhibitor, was combined with 17-AAG. The concentrations for 17-AAG and Act D were selected based on the target actions and plasma levels during therapy. Inducible and constitutive HSP27, HSP70, and HSP90 mRNA and protein levels were measured by real-time RT-PCR and immunoblot assays. Compared to no treatment, Act D alone decreased HSP mRNA levels in the MM.1S and RPMI-8226 cell lines. Combining of Act D with 17-AAG did not attenuate 17-AAG-mediated increases in transcript levels of inducible HSP70; however, constitutive HSP mRNA levels were decreased. In contrast to its effect on mRNA levels, Act D was able to abrogate 17-AAG-mediated increases in all HSP protein levels. The cytotoxicity of combined Act D and 17-AAG was assessed. Treatment with Act D alone caused less than 40% cell death, while the combination of 17-AAG and Act D resulted in an increase of cell death in both MM cell lines. In conclusion, these results indicate that 17-AAG-mediated induction of HSP70 and HSP27 expression can be attenuated by Act D and therefore can potentially improve the clinical treatment of MM.
doi:10.1158/0008-5472.CAN-08-4406
PMCID: PMC2778753  PMID: 19383903
multiple myeloma; 17-AAG; actinomycin D; heat shock proteins; transcription
6.  Oxidative stress plays a critical role in inactivating mutant BRAF by geldanamycin derivatives 
Cancer research  2008;68(15):6324-6330.
The geldanamycin derivatives 17-allylamino-17-demethoxygeldanamycin (17-AAG) and 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) are promising chemotherapeutic drugs that inhibit heat shock protein 90 (HSP90) function. Previous studies have shown that 17-AAG/DMAG treatment induces the degradation of mutant BRAF (V600E) and inhibits the activation of MAP/ERK1/2 (MEK1/2). We have found, however, that HSP90 inhibition alone is not sufficient for efficient BRAF(V600E) degradation in some cells. HSP90 inhibitors structurally unrelated to geldanamycin, radicicol and novobiocin, while inducing the degradation of the HSP90 client protein RAF-1 fail to induce BRAF(V600E) degradation or inhibit MEK1/2 activation in HT29 human colon cancer cells ‥ Moreover, after treatment with 17-DMAG, the kinase activity of residual, un-degraded BRAF(V600E) was also lost. Incubation of cells with a reactive oxygen species (ROS) scavenger, N-acetyl cysteine (NAC), partially restored kinase activity and also partially prevented BRAF(V600E) degradation due to 17-DMAG treatment. Conversely, treatment with the ROS producing drug menadione clearly inhibited MEK1/2 and reduced BRAF(V600E). These results suggest that in addition to direct inhibition of HSP90, the anti-tumor effect of geldanamycin and its derivatives is also mediated though the production of ROS which may directly inactivate tumorigenic mutant BRAF(V600E).
doi:10.1158/0008-5472.CAN-07-6602
PMCID: PMC2693332  PMID: 18676857
BRAF; MAP kinase; geldanamycin; HSP90; ROS
7.  Vorinostat and sorafenib increase CD95 activation in gastrointestinal tumor cells through a Ca2+ - de novo ceramide - PP2A - ROS dependent signaling pathway 
Cancer research  2010;70(15):6313-6324.
The targeted therapeutics sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95, and this drug combination is entering phase I evaluation. In this study we determined how CD95 is activated by treatment with this drug combination. Low doses of sorafenib and vorinostat but not the individual drugs rapidly increased ROS, Ca2+ and ceramide levels in GI tumor cells. The production of ROS was reduced in Rho zero cells. Quenching ROS blocked drug-induced CD95 surface localization and apoptosis. ROS generation, CD95 activation and cell killing was also blocked by quenching of induced Ca2+ levels or by inhibition of PP2A. Inhibition of acidic sphingomyelinase or de novo ceramide generation blocked the induction of ROS however combined inhibition of both acidic sphingomyelinase and de novo ceramide generation was required to block the induction of Ca2+. Quenching of ROS did not impact on drug-induced ceramide/dihydro-ceramide levels whereas quenching of Ca2+ reduced the ceramide increase. Sorafenib and vorinostat treatment radiosensitized liver and pancreatic cancer cells, an effect that was suppressed by quenching ROS or knock down of LASS6. Further, sorafenib and vorinostat treatment suppressed the growth of pancreatic tumors in vivo. Our findings demonstrate that induction of cytosolic Ca2+ by sorafenib and vorinostat is a primary event that elevates dihydroceramide levels, each essential steps in ROS generation that promotes CD95 activation.
doi:10.1158/0008-5472.CAN-10-0999
PMCID: PMC2918282  PMID: 20631069
8.  Targeting Hsp90 with small molecule inhibitors induces the over-expression of the anti-apoptotic molecule, survivin, in human A549, HONE-1 and HT-29 cancer cells 
Molecular Cancer  2010;9:77.
Background
Survivin is a dual functioning protein. It inhibits the apoptosis of cancer cells by inhibiting caspases, and also promotes cancer cell growth by stabilizing microtubules during mitosis. Since the molecular chaperone Hsp90 binds and stabilizes survivin, it is widely believed that down-regulation of survivin is one of the important therapeutic functions of Hsp90 inhibitors such as the phase III clinically trialed compound 17-AAG. However, Hsp90 interferes with a number of molecules that up-regulate the intracellular level of survivin, raising the question that clinical use of Hsp90 inhibitors may indirectly induce survivin expression and subsequently enhance cancer anti-drug responses. The purpose of this study is to determine whether targeting Hsp90 can alter survivin expression differently in different cancer cell lines and to explore possible mechanisms that cause the alteration in survivin expression.
Results
Here, we demonstrated that Hsp90 inhibitors, geldanamycin and 17-AAG, induced the over-expression of survivin in three different human cancer cell lines as shown by Western blotting. Increased survivin mRNA transcripts were observed in 17-AAG and geldanamycin-treated HT-29 and HONE-1 cancer cells. Interestingly, real-time PCR and translation inhibition studies revealed that survivin was over-expressed partially through the up-regulation of protein translation instead of gene transcription in A549 cancer cells. In addition, 17-AAG-treated A549, HONE-1 and HT-29 cells showed reduced proteasomal activity while inhibition of 26S proteasome activity further increased the amount of survivin protein in cells. At the functional level, down-regulation of survivin by siRNA further increased the drug sensitivity to 17-AAG in the tested cancer cell lines.
Conclusions
We showed for the first time that down-regulation of survivin is not a definite therapeutic function of Hsp90 inhibitors. Instead, targeting Hsp90 with small molecule inhibitors will induce the over-expression of survivin in certain cancer cell lines and subsequently enhances the ability of cell survival in drug-treated situations. The current study suggests that dual inhibition of Hsp90 and survivin may be warranted.
doi:10.1186/1476-4598-9-77
PMCID: PMC2873435  PMID: 20398291
9.  Aag DNA Glycosylase Promotes Alkylation-Induced Tissue Damage Mediated by Parp1 
PLoS Genetics  2013;9(4):e1003413.
Alkylating agents comprise a major class of front-line cancer chemotherapeutic compounds, and while these agents effectively kill tumor cells, they also damage healthy tissues. Although base excision repair (BER) is essential in repairing DNA alkylation damage, under certain conditions, initiation of BER can be detrimental. Here we illustrate that the alkyladenine DNA glycosylase (AAG) mediates alkylation-induced tissue damage and whole-animal lethality following exposure to alkylating agents. Aag-dependent tissue damage, as observed in cerebellar granule cells, splenocytes, thymocytes, bone marrow cells, pancreatic β-cells, and retinal photoreceptor cells, was detected in wild-type mice, exacerbated in Aag transgenic mice, and completely suppressed in Aag−/− mice. Additional genetic experiments dissected the effects of modulating both BER and Parp1 on alkylation sensitivity in mice and determined that Aag acts upstream of Parp1 in alkylation-induced tissue damage; in fact, cytotoxicity in WT and Aag transgenic mice was abrogated in the absence of Parp1. These results provide in vivo evidence that Aag-initiated BER may play a critical role in determining the side-effects of alkylating agent chemotherapies and that Parp1 plays a crucial role in Aag-mediated tissue damage.
Author Summary
Alkylating agents are genotoxic chemicals that induce both toxic and mutagenic DNA damage through addition of an alkyl group to DNA. Alkylating agents are routinely and successfully used as chemotherapeutic therapies for cancer patients, with one major disadvantage being the significant toxicity induced in non-tumor tissues. Accordingly, identifying factors that modify susceptibility to alkylation-induced toxicity will provide valuable information in designing cancer therapeutic regimens. This study used mouse genetic experiments to investigate whether proteins important in the base excision repair pathway modulate susceptibility to alkylating agents. In addition to whole-animal toxicity at high doses, treatment of mice with alkylating agents resulted in severe damage to numerous tissues including the cerebellum, retina, bone marrow, spleen, thymus, and the pancreas. We illustrate that the DNA glycosylase Aag can actually confer, rather than prevent, alkylation sensitivity at both the whole-animal and tissue level; i.e., Aag transgenic animals are more susceptible than wild type, whereas Aag-deficient animals are less susceptible than wild type to alkylation-induced toxicity. Further genetic experiments show that the Aag-mediated alkylation sensitivity is dependent on Parp1. Given that we observe a wide range of human AAG expression among healthy individuals, this and other base excision repair proteins may be important factors modulating alkylation susceptibility.
doi:10.1371/journal.pgen.1003413
PMCID: PMC3617098  PMID: 23593019
10.  Sulforaphane Potentiates the Efficacy of 17-Allylamino 17-Demethoxygeldanamycin Against Pancreatic Cancer Through Enhanced Abrogation of Hsp90 Chaperone Function 
Nutrition and cancer  2011;63(7):10.1080/01635581.2011.596645.
Heat shock protein 90 (Hsp90), an essential molecular chaperone that regulates the stability of a wide range of oncogenic proteins, is a promising target for cancer therapeutics. We investigated the combination efficacy and potential mechanisms of sulforaphane, a dietary component from broccoli and broccoli sprouts, and 17-allylamino 17-demethoxygeldanamycin (17-AAG), an Hsp90 inhibitor, in pancreatic cancer. MTS assay demonstrated that sulforaphane sensitized pancreatic cancer cells to 17-AAG in vitro. Caspase-3 was activated to 6.4-fold in response to simultaneous treatment with sulforaphane and 17-AAG, whereas 17-AAG alone induced caspase-3 activity to 2-fold compared to control. ATP binding assay and coimmunoprecipitation revealed that sulforaphane disrupted Hsp90-p50Cdc37 interaction, whereas 17-AAG inhibited ATP binding to Hsp90. Concomitant use of sulforaphane and 17-AAG synergistically downregulated Hsp90 client proteins in Mia Paca-2 cells. Co-administration of sulforaphane and 17-AAG in pancreatic cancer xenograft model led to more than 70% inhibition of the tumor growth, whereas 17-AAG alone only suppressed the tumor growth by 50%. Our data suggest that sulforaphane potentiates the efficacy of 17-AAG against pancreatic cancer through enhanced abrogation of Hsp90 function. These findings provide a rationale for further evaluation of broccoli/broccoli sprout preparations combined with 17-AAG for better efficacy and lower dose-limiting toxicity in pancreatic cancer.
doi:10.1080/01635581.2011.596645
PMCID: PMC3850054  PMID: 21875325
11.  The Kinase Inhibitor Sorafenib Induces Cell Death through a Process Involving Induction of Endoplasmic Reticulum Stress▿ †  
Molecular and Cellular Biology  2007;27(15):5499-5513.
Sorafenib is a multikinase inhibitor that induces apoptosis in human leukemia and other malignant cells. Recently, we demonstrated that sorafenib diminishes Mcl-1 protein expression by inhibiting translation through a MEK1/2-ERK1/2 signaling-independent mechanism and that this phenomenon plays a key functional role in sorafenib-mediated lethality. Here, we report that inducible expression of constitutively active MEK1 fails to protect cells from sorafenib-mediated lethality, indicating that sorafenib-induced cell death is unrelated to MEK1/2-ERK1/2 pathway inactivation. Notably, treatment with sorafenib induced endoplasmic reticulum (ER) stress in human leukemia cells (U937) manifested by immediate cytosolic-calcium mobilization, GADD153 and GADD34 protein induction, PKR-like ER kinase (PERK) and eukaryotic initiation factor 2α (eIF2α) phosphorylation, XBP1 splicing, and a general reduction in protein synthesis as assessed by [35S]methionine incorporation. These events were accompanied by pronounced generation of reactive oxygen species through a mechanism dependent upon cytosolic-calcium mobilization and a significant decline in GRP78/Bip protein levels. Interestingly, enforced expression of IRE1α markedly reduced sorafenib-mediated apoptosis, whereas knockdown of IRE1α or XBP1, disruption of PERK activity, or inhibition of eIF2α phosphorylation enhanced sorafenib-mediated lethality. Finally, downregulation of caspase-2 or caspase-4 by small interfering RNA significantly diminished apoptosis induced by sorafenib. Together, these findings demonstrate that ER stress represents a central component of a MEK1/2-ERK1/2-independent cell death program triggered by sorafenib.
doi:10.1128/MCB.01080-06
PMCID: PMC1952105  PMID: 17548474
12.  Inhibition of constitutive and cxc-chemokine-induced NF-κB activity potentiates ansamycin-based HSP90-inhibitor cytotoxicity in castrate-resistant prostate cancer cells 
British Journal of Cancer  2009;101(9):1620-1629.
Background:
We determined how CXC-chemokine signalling and necrosis factor-κB (NF-κB) activity affected heat-shock protein 90 (Hsp90) inhibitor (geldanamycin (GA) and 17-allylamino-demethoxygeldanamycin (17-AAG)) cytotoxicity in castrate-resistant prostate cancer (CRPC).
Methods:
Geldanamycin and 17-AAG toxicity, together with the CXCR2 antagonist AZ10397767 or NF-κB inhibitor BAY11-7082, was assessed by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay in two CRPC lines, DU145 and PC3. Flow cytometry quantified apoptotic or necrosis profiles. Necrosis factor-κB activity was determined by luciferase readouts or indirectly by quantitative PCR and ELISA-based determination of CXCL8 expression.
Results:
Geldanamycin and 17-AAG reduced PC3 and DU145 cell viability, although PC3 cells were less sensitive. Addition of AZ10397767 increased GA (e.g., PC3 IC20: from 1.67±0.4 to 0.18±0.2 nM) and 17-AAG (PC3 IC20: 43.7±7.8 to 0.64±1.8 nM) potency in PC3 but not DU145 cells. Similarly, BAY11-7082 increased the potency of 17-AAG in PC3 but not in DU145 cells, correlating with the elevated constitutive NF-κB activity in PC3 cells. AZ10397767 increased 17-AAG-induced apoptosis and necrosis and decreased NF-κB activity/CXCL8 expression in 17-AAG-treated PC3 cells.
Conclusion:
Ansamycin cytotoxicity is enhanced by inhibiting NF-κB activity and/or CXC-chemokine signalling in CRPC cells. Detecting and/or inhibiting NF-κB activity may aid the selection and treatment response of CRPC patients to Hsp90 inhibitors.
doi:10.1038/sj.bjc.6605356
PMCID: PMC2778515  PMID: 19809428
prostate cancer; CXC-chemokines; CXCL8; NF-κB; Hsp90 inhibitors
13.  Gefitinib-Induced Killing of NSCLC Cell Lines Expressing Mutant EGFR Requires BIM and Can Be Enhanced by BH3 Mimetics 
PLoS Medicine  2007;4(10):e316.
Background
The epidermal growth factor receptor (EGFR) plays a critical role in the control of cellular proliferation, differentiation, and survival. Abnormalities in EGF-EGFR signaling, such as mutations that render the EGFR hyperactive or cause overexpression of the wild-type receptor, have been found in a broad range of cancers, including carcinomas of the lung, breast, and colon. EGFR inhibitors such as gefitinib have proven successful in the treatment of certain cancers, particularly non-small cell lung cancers (NSCLCs) harboring activating mutations within the EGFR gene, but the molecular mechanisms leading to tumor regression remain unknown. Therefore, we wished to delineate these mechanisms.
Methods and Findings
We performed biochemical and genetic studies to investigate the mechanisms by which inhibitors of EGFR tyrosine kinase activity, such as gefitinib, inhibit the growth of human NSCLCs. We found that gefitinib triggered intrinsic (also called “mitochondrial”) apoptosis signaling, involving the activation of BAX and mitochondrial release of cytochrome c, ultimately unleashing the caspase cascade. Gefitinib caused a rapid increase in the level of the proapoptotic BH3-only protein BIM (also called BCL2-like 11) through both transcriptional and post-translational mechanisms. Experiments with pharmacological inhibitors indicated that blockade of MEK–ERK1/2 (mitogen-activated protein kinase kinase–extracellular signal-regulated protein kinase 1/2) signaling, but not blockade of PI3K (phosphatidylinositol 3-kinase), JNK (c-Jun N-terminal kinase or mitogen-activated protein kinase 8), or AKT (protein kinase B), was critical for BIM activation. Using RNA interference, we demonstrated that BIM is essential for gefitinib-induced killing of NSCLC cells. Moreover, we found that gefitinib-induced apoptosis is enhanced by addition of the BH3 mimetic ABT-737.
Conclusions
Inhibitors of the EGFR tyrosine kinase have proven useful in the therapy of certain cancers, in particular NSCLCs possessing activating mutations in the EGFR kinase domain, but the mechanisms of tumor cell killing are still unclear. In this paper, we demonstrate that activation of the proapoptotic BH3-only protein BIM is essential for tumor cell killing and that shutdown of the EGFR–MEK–ERK signaling cascade is critical for BIM activation. Moreover, we demonstrate that addition of a BH3 mimetic significantly enhances killing of NSCLC cells by the EGFR tyrosine kinase inhibitor gefitinib. It appears likely that this approach represents a paradigm shared by many, and perhaps all, oncogenic tyrosine kinases and suggests a powerful new strategy for cancer therapy.
Andreas Strasser and colleagues demonstrate that activation of the proapoptotic BH3-only protein BIM is essential for tumor cell killing and that shutdown of the EGFR−MEK−ERK signaling cascade is critical for BIM activation.
Editors' Summary
Background.
Normally, cell division (which produces new cells) and cell death are finely balanced to keep the human body in good working order. But sometimes cells acquire changes (mutations) in their genetic material that allow them to divide uncontrollably to form cancers—life-threatening, disorganized masses of cells. One protein with a critical role in cell division that is often mutated in tumors is the epidermal growth factor receptor (EGFR). In normal cells, protein messengers bind to EGFR and activate its tyrosine kinase. This enzyme then adds phosphate groups to tyrosine (an amino acid) in proteins that form part of signaling cascades (for example, the MEK–ERK signaling cascade) that tell the cell to divide. In cancers that have mutations in EGFR, signaling is overactive so the cancer cells divide much more than they should. Some non-small cell lung cancers (NSCLC, the commonest type of lung cancer), for example, have activating mutations within the EGFR tyrosine kinase. Treatment with EGFR tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib induces the cells in these tumors to stop growing and die. This cell death causes tumor shrinkage (regression) and increases the life expectancy of patients with this type of NSCLC.
Why Was This Study Done?
Unfortunately, treatment with TKIs rarely cures NSCLC, so it would be useful to find a way to augment the effect that TKIs have on cancer cells. To do this, the molecular mechanisms that cause cancer-cell death and tumor regression in response to these drugs need to be fully understood. In this study, the researchers have used a combination of biochemical and genetic approaches to investigate how gefitinib kills NSCLC cells with mutated EGFR.
What Did the Researchers Do and Find?
The researchers first measured the sensitivity of NSCLC cell lines (tumor cells that grow indefinitely in dishes) to gefitinib-induced apoptosis. Gefitinib caused extensive apoptosis in two cell lines expressing mutant EGFR but not in one expressing normal EGFR. Next, they investigated the mechanism of gefitinib-induced apoptosis in the most sensitive cell line (H3255). Apoptosis is activated via two major pathways. Hallmarks of the “intrinsic” pathway include activation of a protein called BAX and cytochrome c release from subcellular compartments known as mitochondria. Gefitinib treatment induced both these events in H3255 cells. BAX (a proapoptotic member of the BCL-2 family of proteins) is activated when proapoptotic BH3-only BCL-2 proteins (for example, BIM; “BH3-only” describes the structure of these proteins) bind to antiapoptotic BCL2 proteins. Gefitinib treatment rapidly increased BIM activity in H3255 and HCC827 cells (but not in gefitinib-resistant cells) by increasing the production of BIM protein and the removal of phosphate groups from it, which increases BIM activity. Pharmacological blockade of the MEK–ERK signaling cascade, but not of other EGFR signaling cascades, also caused the accumulation of BIM. By contrast, blocking BIM expression using a technique called RNA interference reduced gefitinib-induced apoptosis. Finally, a combination of gefitinib and a BH3-mimicking compound called ABT-737 (which, like BIM, binds to antiapoptotic BCL-2 proteins) caused more apoptosis than gefitinib alone.
What Do These Findings Mean?
These findings (and those reported by Gong et al. and Costa et al.) indicate that activation of the proapoptotic BH3-only protein BIM is essential for gefitinib-induced killing of NSCLC cells that carry EGFR tyrosine kinase mutations. They also show that inhibition of the EGFR–MEK–ERK signaling cascade by gefitinib is essential for BIM activation. Because these findings come from studies on NSCLC cell lines, they need confirming in freshly isolated tumor cells and in tumors growing in people. However, the demonstration that a compound that mimics BH3 action enhances gefitinib-induced killing of NSCLC cells suggests that combinations of TKIs and drugs that affect the intrinsic pathway of apoptosis activation might provide a powerful strategy for treating cancers in which tyrosine kinase mutations drive tumor growth.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040316.
A perspective by Ingo Mellinghoff discusses this article and two related research articles
Wikipedia pages on epidermal growth factor receptor, apoptosis, and BCL2 proteins (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
CancerQuest provides information on all aspects of cancer from Emory University (in several languages)
US National Cancer Institute information for patients and professionals on lung cancer (in English and Spanish)
Information for patients from Cancer Research UK on lung cancer including information on treatment with TKIs
Information for patients from Cancerbackup on erlotinib and gefitinib
doi:10.1371/journal.pmed.0040316
PMCID: PMC2043013  PMID: 17973573
14.  Dual targeting of heat shock proteins 90 and 70 promotes cell death and enhances the anticancer effect of chemotherapeutic agents in bladder cancer 
Oncology Reports  2014;31(6):2482-2492.
Heat shock proteins (HSPs), which are molecular chaperones that stabilize numerous vital proteins, may be attractive targets for cancer therapy. The aim of the present study was to investigate the possible anticancer effect of single or dual targeting of HSP90 and HSP70 and the combination treatment with HSP inhibitors and chemotherapeutic agents in bladder cancer cells. The expression of HSP90 and the anticancer effect of the HSP90 inhibitor 17-N-allylamino-17-demethoxygeldanamycin (17-AAG) coupled with cisplatin, docetaxel, or gemcitabine were examined using immunohistochemistry, quantitative real-time PCR, cell growth, flow cytometry, immunoblots and caspase-3/7 assays. The expression of HSP70 under HSP90 inhibition and the additive effect of HSP70 inhibitor pifithrin-μ (PFT-μ) were examined by the same assays and transmission electron microscopy. HSP90 was highly expressed in bladder cancer tissues and cell lines. 17-AAG enhanced the antiproliferative and apoptotic effects of each chemotherapeutic agent. 17-AAG also suppressed Akt activity but induced the upregulation of HSP70. PFT-μ enhanced the effect of 17-AAG or chemotherapeutic agents; the triple combination of 17-AAG, PFT-μ and a chemotherapeutic agent showed the most significant anticancer effect on the T24 cell line. The combination of 17-AAG and PFT-μ markedly suppressed Akt and Bad activities. With HSP90 suppression, HSP70 overexpression possibly contributes to the avoidance of cell death and HSP70 may be a key molecule for overcoming resistance to the HSP90 inhibitor. The dual targeting of these two chaperones and the combination with conventional anticancer drugs could be a promising therapeutic option for patients with advanced bladder cancer.
doi:10.3892/or.2014.3132
PMCID: PMC4055347  PMID: 24718854
HSP90; HSP70; Akt; bladder cancer; chemotherapy
15.  Comparative Study of 17-AAG and NVP-AUY922 in Pancreatic and Colorectal Cancer Cells: Are There Common Determinants of Sensitivity?1 
Translational Oncology  2014;7(5):590-604.
The use of heat shock protein 90 (Hsp90) inhibitors is an attractive antineoplastic therapy. We wanted to compare the effects of the benzoquinone 17-allylamino-17-demethoxygeldanamycin (17-AAG, tanespimycin) and the novel isoxazole resorcinol–based Hsp90 inhibitor NVP-AUY922 in a panel of pancreatic and colorectal carcinoma cell lines and in colorectal primary cultures derived from tumors excised to patients. PANC-1, CFPAC-1, and Caco-2 cells were intrinsically resistant to 17-AAG but sensitive to NVP-AUY922. Other cellular models were sensitive to both inhibitors. Human epidermal growth factor receptor receptors and their downstream signaling pathways were downregulated in susceptible cellular models, and concurrently, Hsp70 was induced. Intrinsic resistance to 17-AAG did not correlate with expression of ATP-binding cassette transporters involved in multidrug resistance. Some 17-AAG-resistant, NVP-AUY922–sensitive cell lines lacked NAD(P)H:quinone oxidoreductase 1 (NQO1) enzyme and activity. However, colorectal LoVo cells still responded to both drugs in spite of having undetectable levels and activity of NQO1. Pharmacological and biologic inhibition of NQO1 did not confer resistance to 17-AAG in sensitive cell lines. Therefore, even though 17-AAG sensitivity is related to NQO1 protein levels and enzymatic activity, the absence of NQO1 does not necessarily convey resistance to 17-AAG in these cellular models. Moreover, NVP-AUY922 does not require NQO1 for its action and is a more potent inhibitor than 17-AAG in these cells. More importantly, we show in this report that NVP-AUY922 potentiates the inhibitory effects of chemotherapeutic agents, such as gemcitabine or oxaliplatin, and other drugs that are currently being evaluated in clinical trials as antitumor agents.
doi:10.1016/j.tranon.2014.08.001
PMCID: PMC4225658  PMID: 25389454
16.  OSU-03012 suppresses GRP78/BiP expression that causes PERK-dependent increases in tumor cell killing 
Cancer Biology & Therapy  2012;13(4):224-236.
We have further defined mechanism(s) by which the drug OSU-03012 (OSU) kills tumor cells. OSU lethality was suppressed by knock down of PERK and enhanced by knock down of ATF6 and IRE1α. OSU treatment suppressed expression of the chaperone, BiP/GRP78, and did so through reduced stability of the protein. Knock down of BiP/GRP78 further enhanced OSU lethality. Overexpression of BiP/GRP78 abolished OSU toxicity. Pre-treatment of cells with OSU enhanced radiosensitivity to a greater extent than concomitant or sequential drug treatment with radiation exposure. Expression of a mutant active p110 PI3K, or mutant active forms of the EGFR in GBM cells did not differentially suppress OSU killing. In contrast loss of PTEN function reduced OSU lethality, without altering AKT, p70 S6K or mTOR activity, or the drug's ability to radiosensitize GBM cells. Knock down of PTEN protected cells from OSU and radiation treatment whereas re-expression of PTEN facilitated drug lethality and radiosensitization. In a dose-dependent fashion OSU prolonged the survival of mice carrying GBM tumors and interacted with radiotherapy to further prolong survival. Collectively, our data show that reduced BiP/GRP78 levels play a key role in OSU-3012 toxicity in GBM cells, and that this drug has in vivo activity against an invasive primary human GBM isolate.
doi:10.4161/cbt.13.4.18877
PMCID: PMC3336069  PMID: 22354011
OSU-03012; BiP/GRP78; ER stress; PERK; ionizing radiation; ceramide
17.  Sublethal concentrations of 17-AAG suppress homologous recombination DNA repair and enhance sensitivity to carboplatin and olaparib in HR proficient ovarian cancer cells 
Oncotarget  2014;5(9):2678-2687.
The promise of PARP-inhibitors(PARPis) in the management of epithelial ovarian cancer(EOC) is tempered by the fact that approximately 50% of patients with homologous recombination (HR)-proficient tumors do not respond well to these agents. Combination of PARPis with agents that inhibit HR may represent an effective strategy to enhance their activity in HR-proficient tumors. Using a bioinformatics approach, we identified that heat shock protein 90 inhibitors(HSP90i) may suppress HR and thus revert HR-proficient to HR-deficient tumors. Analysis of publicly available gene expression data showed that exposure of HR-proficient breast cancer cell lines to HSP90i 17-AAG(17-allylamino-17-demethoxygeldanamycin) downregulated HR, ATM and Fanconi Anemia pathways. In HR-proficient EOC cells, 17-AAG suppressed HR as assessed using the RAD51 foci formation assay and this was further confirmed using the Direct Repeat-GFP reporter assay. Furthermore, 17-AAG downregulated BRCA1 and/or RAD51 protein levels, and induced significantly more γH2AX activation in combination with olaparib compared to olaparib alone. Finally, sublethal concentrations of 17-AAG sensitized HR-proficient EOC lines to olaparib and carboplatin but did not affect sensitivity of the HR-deficient OVCAR8 line arguing that the 17-AAG mediated sensitization is dependent on suppression of HR. These results provide a preclinical rationale for using a combination of olaparib/17-AAG in HR-proficient EOC.
PMCID: PMC4058036  PMID: 24798692
Epithelial ovarian cancer; platinum; PARP inhibitors; Heat Shock Protein 90 inhibitors; homologous recombination
18.  A Novel Therapeutic Strategy for the Treatment of Glioma, Combining Chemical and Molecular Targeting of Hsp90α 
Cancers  2011;3(4):4228-4244.
Hsp90α's vital role in tumour survival and progression, together with its highly inducible expression profile in gliomas and its absence in normal tissue and cell lines validates it as a therapeutic target for glioma. Hsp90α was downregulated using the post-transcriptional RNAi strategy (sihsp90α) and a post-translational inhibitor, the benzoquinone antibiotic 17-AAG. Glioblastoma U87-MG and normal human astrocyte SVGp12 were treated with sihsp90α, 17-AAG and concurrent sihsp90α/17-AAG (combined treatment). Both Hsp90α gene silencing and the protein inhibitor approaches resulted in a dramatic reduction in cell viability. Results showed that sihsp90α, 17-AAG and a combination of sihsp90α/17-AAG, reduced cell viability by 27%, 75% and 88% (p < 0.001), respectively, after 72 h. hsp90α mRNA copy numbers were downregulated by 65%, 90% and 99% after 72 h treatment with sihsp90α, 17-AAG and sihsp90α/17-AAG, respectively. The relationship between Hsp90α protein expression and its client Akt kinase activity levels were monitored following treatment with sihsp90α, 17-AAG and sihsp90α/17-AAG. Akt kinase activity was downregulated as a direct consequence of Hsp90α inhibition. Both Hsp90α and Akt kinase levels were significantly downregulated after 72 h. Although, 17-AAG when used as a single agent reduces the Hsp90α protein and the Akt kinase levels, the efficacy demonstrated by combinatorial treatment was found to be far more effective. Combination treatment reduced the Hsp90α protein and Akt kinase levels to 4.3% and 43%, respectively, after 72 h. hsp90α mRNA expression detected in SVGp12 was negligible compared to U87-MG, also, the combination treatment did not compromise the normal cell viability. Taking into account the role of Hsp90α in tumour progression and the involvement of Akt kinase in cell signalling and the anti-apoptotic pathways in tumours, this double targets treatment infers a novel therapeutic strategy.
doi:10.3390/cancers3044228
PMCID: PMC3763420  PMID: 24213135
sihsp90α; 17-AAG; glioblastoma; Hsp90α; Akt kinase; combinational treatment
19.  OSU-03012 interacts with lapatinib to kill brain cancer cells 
Cancer Biology & Therapy  2012;13(14):1501-1511.
We have further defined mechanism(s) by which the drug OSU-03012 (OSU) kills brain cancer cells. OSU toxicity was enhanced by the HSP90 inhibitor 17-N-Allylamino-17-demethoxygeldanamycin (17AAG) that correlated with reduced expression of ERBB1 and ERBB2. Inhibition of the extrinsic apoptosis pathway blocked the interaction between 17AAG and OSU. OSU toxicity was enhanced by the inhibitor of ERBB1/2/4, lapatinib. Knock down of ERBB1/2/4 in a cell line specific fashion promoted OSU toxicity. Combined exposure of cells to lapatinib and OSU resulted in reduced AKT and ERK1/2 activity; expression of activated forms of AKT and to a lesser extent MEK1 protected cells from the lethal effects of the drug combination. Knock down of PTEN suppressed, and expression of PTEN enhanced, the lethal interaction between OSU and lapatinib. Downstream of PTEN, inhibition of mTOR recapitulated the effects of lapatinib. Knock down of CD95, NOXA, PUMA, BIK or AIF, suppressed lapatinib and OSU toxicity. Knock down of MCL-1 enhanced, and overexpression of MCL-1 suppressed, drug combination lethality. Lapatinib and OSU interacted in vivo to suppress the growth of established tumors. Collectively our data argue that the inhibition of ERBB receptor function represents a useful way to enhance OSU lethality in brain tumor cells.
doi:10.4161/cbt.22275
PMCID: PMC3542242  PMID: 22990204
glioblastoma; medulloblastoma; lapatinib; OSU-03012; apoptosis; autophagy; ERBB1; PTEN
20.  Chemotherapeutic Potential of 17-AAG against Cutaneous Leishmaniasis Caused by Leishmania (Viannia) braziliensis 
Background
Leishmaniasis remains a worldwide public health problem. The limited therapeutic options, drug toxicity and reports of resistance, reinforce the need for the development of new treatment options. Previously, we showed that 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), a Heat Shock Protein 90 (HSP90)-specific inhibitor, reduces L. (L.) amazonensis infection in vitro. Herein, we expand the current knowledge on the leishmanicidal activity of 17-AAG against cutaneous leishmaniasis, employing an experimental model of infection with L. (V.) braziliensis.
Methodology/Principal findings
Exposure of axenic L. (V.) braziliensis promastigotes to 17-AAG resulted in direct dose-dependent parasite killing. These results were extended to L. (V.) braziliensis-infected macrophages, an effect that was dissociated from the production of nitric oxide (NO), superoxide (O−2) or inflammatory mediators such as TNF-α, IL-6 and MCP-1. The leishmanicidal effect was then demonstrated in vivo, employing BALB/c mice infected with L. braziliensis. In this model, 17-AAG treatment resulted in smaller skin lesions and parasite counts were also significantly reduced. Lastly, 17-AAG showed a similar effect to amphotericin B regarding the ability to reduce parasite viability.
Conclusion/Significance
17-AAG effectively inhibited the growth of L. braziliensis, both in vitro and in vivo. Given the chronicity of L. (V.) braziliensis infection and its association with mucocutaneous leishmaniasis, 17-AAG can be envisaged as a new chemotherapeutic alternative for cutaneous Leishmaniasis.
Author Summary
Antimony-containing compounds are the main drugs used to treat leishmaniasis but the severe associated side effects pose the need for alternative chemotherapeutic options. Herein, we evaluated the ability of 17-AAG (a Heat Shock Protein 90 inhibitor) to kill Leishmania (Viannia) braziliensis parasites, a species that causes both cutaneous and mucocutaneous Leishmaniasis in Brazil. Heat Shock Protein 90 (HSP90) is associated with important biological processes; inhibition of this molecule interferes with parasite survival and, hence, it can be exploited as a chemotherapeutic target. We show that exposure to 17-AAG induced killing of L. brazilensis parasites in both its extracellular and intracellular forms. This effect was not dependent on the activation of the host cell. More importantly, treatment of mice infected with L. (V.) braziliensis also modulated lesion development and decreased parasite growth at the infection site. Collectively, our results show that targeting HSP90 is a promising alternative for development of novel chemotherapeutic options for leishmaniasis.
doi:10.1371/journal.pntd.0003275
PMCID: PMC4207694  PMID: 25340794
21.  Can RNAi-mediated hsp90α knockdown in combination with 17-AAG be a therapy for glioma?☆ 
FEBS Open Bio  2013;3:271-278.
Heat shock protein 90 promotes tumor progression and survival and has emerged as a vital therapeutic target. Previously we reported that the combinatorial treatment of 17AAG/sihsp90α significantly downregulated Hsp90α mRNA and protein levels in Glioblastoma Multiforme (GBM). Here we investigated the ability of cell penetrating peptide (Tat48–60 CPP)-mediated siRNA-induced hsp90α knockdown as a single agent and in combination with 17-allylamino-17-demethoxygeldanamycin (17-AAG) to induce tumor growth inhibition in GBM and whether it possessed therapeutic implications. GBM and non-tumorigenic cells exposed to siRNA and/or 17-AAG were subsequently assessed by qRT-PCR, immunofluorescence, FACS analysis, quantitative Akt, LDH leakage and cell viability assays. PAGE was performed for serum stability assessment. A combination of siRNA/17-AAG treatment significantly induced Hsp90α gene and protein knockdown by 95% and 98%, respectively, concomitant to 84% Akt kinase activity attenuation, induced cell cycle arrest and tumor-specific cytotoxicity by 88%. Efficient complex formation between CPP and siRNA exhibited improved serum stability of the siRNA with minimal intrinsic toxicity in vitro. The preliminary in vivo results showed that combination therapy induced hsp90α knockdown and attenuated Akt kinase activity in intracranial glioblastoma mouse models. The results imply that RNAi-mediated hsp90α knockdown increases 17-AAG treatment efficacy in GBM. In addition, the cytotoxic response observed was the consequence of downregulation of hsp90α gene expression, reduced Akt kinase activity and S-G2/M cell cycle arrest. These results are novel and highlight the ability of Tat to efficiently deliver siRNA in GBM and suggest that the dual inhibition of Hsp90 has therapeutic potentials.
Highlights
•17-AAG–siRNA dual treatment exhibits significant anti-cancer activity in GBM.•Combination therapy induced Hsp90α gene/protein knockdown causing Akt inactivation.•Hsp90α inhibition causes S-G2/M cell cycle arrest and GBM-specific cytotoxicity.•Efficient siRNA/CPP interaction improves serum stability of siRNA.•RNAi-mediated hsp90α knockdown increases GBM sensitivity to 17-AAG.
doi:10.1016/j.fob.2013.06.002
PMCID: PMC3722647  PMID: 23905009
Hsp90α; Tat; sihsp90α/CPP complex; Cell penetrating peptides; Glioblastoma; GBM; Hsp90 inhibitor; Akt; Cell-cycle arrest
22.  † THE GROUP VIA CALCIUM-INDEPENDENT PHOSPHOLIPASE A2 (iPLA2β)1 PARTICIPATES IN ER STRESS-INDUCED INS-1 INSULINOMA CELL APOPTOSIS BY PROMOTING CERAMIDE GENERATION VIA HYDROLYSIS OF SPHINGOMYELINS BY NEUTRAL SPHINGOMYELINASE 
Biochemistry  2007;46(35):10170-10185.
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.
doi:10.1021/bi700017z
PMCID: PMC2530898  PMID: 17685585
23.  Selective BRAFV600E Inhibitor PLX4720, Requires TRAIL Assistance to Overcome Oncogenic PIK3CA Resistance 
PLoS ONE  2011;6(6):e21632.
Documented sensitivity of melanoma cells to PLX4720, a selective BRAFV600E inhibitor, is based on the presence of mutant BRAFV600E alone, while wt-BRAF or mutated KRAS result in cell proliferation. In colon cancer appearance of oncogenic alterations is complex , since BRAF, like KRAS mutations, tend to co-exist with those in PIK3CA and mutated PI3K has been shown to interfere with the successful application of MEK inhibitors. When PLX4720 was used to treat colon tumours, results were not encouraging and herein we attempt to understand the cause of this recorded resistance and discover rational therapeutic combinations to resensitize oncogene driven tumours to apoptosis. Treatment of two genetically different BRAFV600E mutant colon cancer cell lines with PLX4720 conferred complete resistance to cell death. Even though p-MAPK/ ERK kinase (MEK) suppression was achieved, TRAIL, an apoptosis inducing agent, was used synergistically in order to achieve cell death by apoptosis in RKOBRAFV600E/PIK3CAH1047 cells. In contrast, for the same level of apoptosis in HT29BRAFV600E/PIK3CAP449T cells, TRAIL was combined with 17-AAG, an Hsp90 inhibitor. For cells where PLX4720 was completely ineffective, 17-AAG was alternatively used to target mutant BRAFV600E. TRAIL dependence on the constitutive activation of BRAFV600E is emphasised through the overexpression of BRAFV600E in the permissive genetic background of colon adenocarcinoma Caco-2 cells. Pharmacological suppression of the PI3K pathway further enhances the synergistic effect between TRAIL and PLX4720 in RKO cells, indicating the presence of PIK3CAMT as the inhibitory factor. Another rational combination includes 17-AAG synergism with TRAIL in a BRAFV600E mutant dependent manner to commit cells to apoptosis, through DR5 and the amplification of the apoptotic pathway. We have successfully utilised combinations of two chemically unrelated BRAFV600E inhibitors in combination with TRAIL in a BRAFV600E mutated background and provided insight for new anti-cancer strategies where the activated PI3KCA mutation oncogene should be suppressed.
doi:10.1371/journal.pone.0021632
PMCID: PMC3124547  PMID: 21738740
24.  The Hsp90 inhibitor 17-(allylamino)-17-demethoxygeldanamycin increases cisplatin antitumor activity by inducing p53-mediated apoptosis in head and neck cancer 
Cell Death & Disease  2013;4(12):e956-.
The tumor suppressor p53 is often inactivated in head and neck cancer (HNC) through TP53 mutations or overexpression of mouse double minute 2 or mouse double minute X. Restoration of p53 function by counteracting these p53 repressors is a promising strategy for cancer treatment. The present study assessed the ability of a heat shock protein 90 (Hsp90) inhibitor, 17-(Allylamino)-17-demethoxygeldanamycin (17AAG), to induce apoptosis in HNC by restoring p53 function. The effect of 17AAG, alone or in combination with Nutlin-3a or cisplatin, was assessed in HNC cells using growth and apoptosis, immunoblotting, quantitative reverse transcription-polymerase chain reaction, and preclinical tumor xenograft models. 17AAG activated and stabilized p53 in HNC cells bearing wild-type TP53 by disrupting the p53–MDMX interaction. 17AAG upregulated p21 and proapoptotic gene expression, and promoted apoptosis in a concentration-dependent manner. Growth inhibition by 17AAG was highest in tumor cells with MDMX overexpression. The apoptotic response was blocked by inhibition of p53 expression, demonstrating that the effect of 17AAG depended on p53 and MDMX. 17AAG synergized in vitro with Nutlin-3a and in vitro and in vivo with cisplatin to induce p53-mediated apoptosis. 17AAG effectively induced p53-mediated apoptosis in HNC cells through MDMX inhibition and increased the antitumor activity of cisplatin synergistically, suggesting a promising strategy for treating HNC.
doi:10.1038/cddis.2013.488
PMCID: PMC3877559  PMID: 24336076
17AAG; p53; MDMX; head and neck cancer; apoptosis
25.  HSP90 Inhibitors Suppress Aryl Hydrocarbon Receptor-Mediated Activation of CYP1A1 and CYP1B1 Transcription and DNA Adduct Formation 
The aryl hydrocarbon receptor (AhR), a client protein of heat shock protein 90 (HSP90), plays a significant role in polycyclic aromatic hydrocarbon (PAH) induced carcinogenesis. Tobacco smoke, a source of PAHs, activates the AhR leading to enhanced transcription of CYP1A1 and CYP1B1, which encode proteins that convert PAHs to genotoxic metabolites. The main objectives of this study were to determine whether HSP90 inhibitors suppress PAH-mediated induction of CYP1A1 and CYP1B1 or block benzo[a]pyrene (B[a]P) induced formation of DNA adducts. Treatment of cell lines derived from oral leukoplakia (MSK-Leuk1) or esophageal squamous cell carcinoma (KYSE450) with a saline extract of tobacco smoke, B[a]P or dioxin induced CYP1A1 and CYP1B1 transcription resulting in enhanced levels of message and protein. Inhibitors of HSP90 (17-allylamino-demethoxygeldanamycin, 17-AAG; celastrol) suppressed these inductive effects of PAHs. Treatment with 17-AAG and celastrol also caused a rapid and marked decrease in amounts of AhR protein without modulating levels of HSP90. The formation of B[a]P induced DNA adducts in MSK-Leuk1 cells was inhibited by 17-AAG, celastrol and α-naphthoflavone, a known AhR antagonist. The reduction in B[a]P induced DNA adducts was due, at least in part, to reduced metabolic activation of B[a]P. Collectively, these results suggest that 17-AAG and celastrol, inhibitors of HSP90, suppress the activation of AhR-dependent gene expression leading, in turn, to reduced formation of B[a]P induced DNA adducts. Inhibitors of HSP90 may have a role in chemoprevention in addition to cancer therapy.
doi:10.1158/1940-6207.CAPR-08-0149
PMCID: PMC2680610  PMID: 19138996
Heat Shock Protein 90 Inhibitors; Aryl Hydrocarbon Receptor; Tobacco Smoke; Cytochrome P450; DNA adduct

Results 1-25 (1338107)