scholarly journals Indoxyl Sulfate Induces Renal Fibroblast Activation through a Targetable Heat Shock Protein 90-Dependent Pathway

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Samantha Milanesi ◽  
Silvano Garibaldi ◽  
Michela Saio ◽  
Giorgio Ghigliotti ◽  
Daniela Picciotto ◽  
...  
Keyword(s):  
Heat Shock Protein 90 ◽  
Hsp90 Inhibitor ◽  
Indoxyl Sulfate ◽  
Collagen I ◽  
Hsp90 Inhibition ◽  
Fibroblast Activation ◽  
Tubular Necrosis ◽  
Pathway Activation ◽  
Potential Strategy ◽  
Dependent Pathway

Indoxyl sulfate (IS) accumulation occurs early during chronic kidney disease (CKD) progression and contributes to renal dysfunction by inducing fibrosis, inflammation, oxidative stress, and tissue remodeling. Renal toxicity of high IS concentrations (250 μM) has been widely explored, particularly in resident tubular and glomerular cells, while the effect of a moderate IS increase on kidneys is still mostly unknown. To define the effects of IS accumulation on renal fibroblasts, we first analyzed kidneys of C57BL/6 mice receiving IS (0.1%) in drinking water for 12 weeks. As a next step, we treated renal fibroblasts (NRK-49F) with IS (20 μM) with or without the HSP90 inhibitor 17-AAG (1 μM). In mouse kidneys, IS increased the collagen deposition and HSP90 and α-SMA expression (immunohistochemistry) in interstitial fibroblasts and caused tubular necrosis (histological H&E and picrosirius red staining). In NRK-49F cells, IS induced MCP1, TGF-β, collagen I, α-SMA, and HSP90 gene/protein expression and Smad2/3 pathway activation. IS had no effects on fibroblast proliferation and ROS production. 17-AAG counteracted IS-induced MCP1, TGF-β, collagen I, and α-SMA expression and Smad2/3 phosphorylation. Our study demonstrates that the IS increase promotes renal fibroblast activation by a HSP90-dependent pathway and indicates HSP90 inhibition as a potential strategy to restrain IS-induced kidney inflammation and fibrosis in CKD.

scholarly journals HSP90 is a chaperone for DLK and is required for axon injury signaling

2018 ◽  
Vol 115 (42) ◽  
pp. E9899-E9908 ◽  
Author(s):  
Scott Karney-Grobe ◽  
Alexandra Russo ◽  
Erin Frey ◽  
Jeffrey Milbrandt ◽  
Aaron DiAntonio
Keyword(s):  
Leucine Zipper ◽  
Axon Regeneration ◽  
Heat Shock Protein 90 ◽  
Hsp90 Inhibitor ◽  
Loss Of Function ◽  
Hsp90 Inhibition ◽  
Axon Injury ◽  
Evolutionarily Conserved ◽  
The Stability

Peripheral nerve injury induces a robust proregenerative program that drives axon regeneration. While many regeneration-associated genes are known, the mechanisms by which injury activates them are less well-understood. To identify such mechanisms, we performed a loss-of-function pharmacological screen in cultured adult mouse sensory neurons for proteins required to activate this program. Well-characterized inhibitors were present as injury signaling was induced but were removed before axon outgrowth to identify molecules that block induction of the program. Of 480 compounds, 35 prevented injury-induced neurite regrowth. The top hits were inhibitors to heat shock protein 90 (HSP90), a chaperone with no known role in axon injury. HSP90 inhibition blocks injury-induced activation of the proregenerative transcription factor cJun and several regeneration-associated genes. These phenotypes mimic loss of the proregenerative kinase, dual leucine zipper kinase (DLK), a critical neuronal stress sensor that drives axon degeneration, axon regeneration, and cell death. HSP90 is an atypical chaperone that promotes the stability of signaling molecules. HSP90 and DLK show two hallmarks of HSP90–client relationships: (i) HSP90 binds DLK, and (ii) HSP90 inhibition leads to rapid degradation of existing DLK protein. Moreover, HSP90 is required for DLK stability in vivo, where HSP90 inhibitor reduces DLK protein in the sciatic nerve. This phenomenon is evolutionarily conserved in Drosophila. Genetic knockdown of Drosophila HSP90, Hsp83, decreases levels of Drosophila DLK, Wallenda, and blocks Wallenda-dependent synaptic terminal overgrowth and injury signaling. Our findings support the hypothesis that HSP90 chaperones DLK and is required for DLK functions, including proregenerative axon injury signaling.

Inhibition and flare patterns of metabolic response to the heat shock protein 90 (Hsp90) inhibitor IPI-504 visualized by FDG-PET in patients (pts) with advanced gastrointestinal stromal tumors (GIST) resistant to tyrosine kinase inhibitor (TKI) therapy

2007 ◽  
Vol 25 (18_suppl) ◽  
pp. 3530-3530 ◽  
Author(s):  
A. D. Van den Abbeele ◽  
J. T. Yap ◽  
D. S. Grayzel ◽  
J. Walker ◽  
G. D. Demetri
Keyword(s):  
Fdg Pet ◽  
Kinase Inhibitor ◽  
Metabolic Response ◽  
Clinical Investigation ◽  
Heat Shock Protein 90 ◽  
Hsp90 Inhibitor ◽  
Resistance Mutations ◽  
Hsp90 Inhibition ◽  
Standardized Uptake Values ◽  
Time Point

3530 Background: We have previously demonstrated the inhibition and rebound of GIST glycolytic metabolism with FDG-PET while pts were on or off TKI in prior trials of imatinib and sunitinib. We tested the same principle in a phase I trial of IPI-504, a novel potent inhibitor of Hsp90 (a chaperone for protein homeostasis) that results in selective destruction of the mutated KIT kinase in human GIST cell lines regardless of TKI-resistance mutations. Methods: Twenty-one patients with metatastic and/or unresectable GIST following failure of prior therapy with TKI were treated with IPI-504. Serial FDG-PET imaging was performed at baseline, during the 1st cycle after at least 2 doses (C1, days 4–11, “ON”, n = 18), and at the end of the 10-day off-treatment period prior to the start of the 2nd cycle (C1, “OFF”, n = 20). A subset of 5 pts also had FDG-PET at the end of the 3rd cycle (C3, day 11, “ON”). Maximum standardized uptake values (SUVmax) were measured in up to 3 lesions/pt with the greatest FDG uptake, and the SUVmax of all lesions was summed at each time point. Percent change in the summed mean SUVmax was calculated at each time point relative to the previous scan. Temporal changes were evaluated in those pts showing more than a 10% decrease in SUVmax during C1 “ON” compared to baseline. Results: We observed a >10% reduction in SUVmax (mean = - 28%) during the 1st cycle (C1, “ON”) in 8/18 pts. All these pts showed an increase in SUVmax (mean = +29%) when off therapy (C1, “OFF”). Three of these 8 pts had a scan during cycle 3. All demonstrated a decrease in SUVmax (mean = -30%) while on the drug (C3, “ON”). Conclusion: These preliminary findings suggest that: (1) tumor metabolic response as measured with FDG-PET parallels the intermittent pattern of IPI-504 administration in this study as early as after the 2nd dose administration; and, (2) IPI-504 has a rapid downstream effect on glucose metabolism similar to that observed with TKIs despite the very different mechanism of action of IPI-504. The pattern of response to Hsp90 inhibition seen in this heavily pretreated population strongly supports further clinical investigation. No significant financial relationships to disclose.

scholarly journals SNX-2112, a selective Hsp90 inhibitor, potently inhibits tumor cell growth, angiogenesis, and osteoclastogenesis in multiple myeloma and other hematologic tumors by abrogating signaling via Akt and ERK

Blood ◽  
2009 ◽  
Vol 113 (4) ◽  
pp. 846-855 ◽  
Author(s):  
Yutaka Okawa ◽  
Teru Hideshima ◽  
Paul Steed ◽  
Sonia Vallet ◽  
Steven Hall ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Bone Marrow ◽  
Cell Growth ◽  
Umbilical Vein ◽  
Conformational Stability ◽  
Heat Shock Protein 90 ◽  
Hsp90 Inhibitor ◽  
Tube Formation ◽  
Osteoclast Formation ◽  
Hsp90 Inhibition

AbstractHeat-shock protein 90 (Hsp90) acts as a molecular chaperone required for maintaining the conformational stability of client proteins regulating cell proliferation, survival, and apoptosis. Here we investigate the biologic significance of Hsp90 inhibition in multiple myeloma (MM) and other hematologic tumors using an orally available novel small molecule inhibitor SNX-2112, which exhibits unique activities relative to 17-allyamino-17-demethoxy-geldanamycin (17-AAG). SNX-2112 triggers growth inhibition and is more potent than 17-AAG against MM and other malignancies. It induces apoptosis via caspase-8, -9, -3, and poly (ADP-ribose) polymerase cleavage. SNX-2112 inhibits cytokine-induced Akt and extracellular signal-related kinase (ERK) activation and also overcomes the growth advantages conferred by interleukin-6, insulin-like growth factor-1, and bone marrow stromal cells. Importantly, SNX-2112 inhibits tube formation by human umbilical vein endothelial cells via abrogation of eNOS/Akt pathway and markedly inhibits osteoclast formation via down-regulation of ERK/c-fos and PU.1. Finally, SNX-2112, delivered by its prodrug SNX-5422, inhibits MM cell growth and prolongs survival in a xenograft murine model. Our results indicate that blockade of Hsp90 by SNX-2112 not only inhibits MM cell growth but also acts in the bone marrow microenvironment to block angiogenesis and osteoclastogenesis. Taken together, our data provide the framework for clinical studies of SNX-2112 to improve patient outcome in MM and other hematologic malignancies.

A phase I trial of the HSP90 inhibitor, alvespimycin (17-DMAG) administered weekly, intravenously, to patients with advanced, solid tumours

2009 ◽  
Vol 27 (15_suppl) ◽  
pp. 3534-3534 ◽  
Author(s):  
S. C. Pacey ◽  
R. Wilson ◽  
M. Walton ◽  
M. Eatock ◽  
A. Zetterlund ◽  
...  
Keyword(s):  
Mononuclear Cells ◽  
Area Under The Curve ◽  
Heat Shock Protein 90 ◽  
Maximum Tolerated Dose ◽  
Hsp90 Inhibitor ◽  
Maximum Plasma ◽  
Hsp90 Inhibition ◽  
Blurred Vision ◽  
Peripheral Blood Mononuclear ◽  
Client Proteins

3534 Background: alvespimycin (17-dimethylaminoethylamino-17-demethoxygeldanamycin, 17-DMAG) inhibits N-terminal ATPase activity of Heat Shock Protein 90 (HSP90). Chaperone interactions are altered such that client proteins are targeted for degradation. The plethora of HSP90 client proteins offers the potential of simultaneous blockade across multiple, oncogenic signalling pathways. Methods: the maximum tolerated dose, at which ≤ 1/6 patients experienced dose limiting toxicity (DLT) was determined by dose-doubling (3+3) design. PK and PD biomarker data were used to define a biologically effective dose (BED). PK (LC/MS/MS) and PD (western blot) assays were validated and compliant with European clinical trial legislation. Cancer Research UK and the NCI were co-sponsors. Results: twenty five patients, median age 58 (range 38–78) years, received 475 infusions at doses between 2.5 and 106 mg/m2. Dose doubling was possible to 80mg/m2 when grade 2 toxicity, including dry eye and blurred vision (2/5 patients) occurred. At 106mg/m2 DLT were observed (grade 3 fatigue, diarrhoea, dehydration and grade 4 hypotension, AST rise) in 2/4 patients, one patient died from cardiac arrest. PK data were as follows; plasma t = 24.6 ± 8.6 hr, Vss 468 ± 383 L (mean ± SD) and clearance 27.7 L/hr (range 8.26 - 153). Maximum plasma concentration increased proportionally with alvespimycin dose, area under the curve was only linear ≤ 80 mg/m2. PD changes (HSP72 induction) in peripheral blood mononuclear cells were detected ≥ 20 mg/m2. HSP90 inhibition (client protein depletion and HSP72 induction) was not readily detected until 106 mg/m2. Tumour samples confirmed HSP90 inhibition 24 hours after 17-DMAG in 1/1 and 2/4 patients given 106 and 80 mg/m2, respectively. Two partial responses one, confirmed, in a patient with hormone refractory prostate cancer and one, investigator assessed, in a patient with melanoma occurred. Both remain on study after 27 and 18 months, respectively. Nine patients (36%) have been on trial ≥16 weeks. Conclusions: The recommended phase II dose of alvespimycin is 80 mg/m2 weekly. PK and PD data support this as a BED. No significant financial relationships to disclose.

scholarly journals 17-AAG-Induced Activation of the Autophagic Pathway in Leishmania Is Associated with Parasite Death

2021 ◽  
Vol 9 (5) ◽  
pp. 1089
Author(s):  
Antonio Luis de O. A. Petersen ◽  
Benjamin Cull ◽  
Beatriz R. S. Dias ◽  
Luana C. Palma ◽  
Yasmin da S. Luz ◽  
...  
Keyword(s):  
Cell Death ◽  
Heat Shock Protein 90 ◽  
Hsp90 Inhibitor ◽  
Lower Sensitivity ◽  
Hsp90 Inhibition ◽  
In Vivo Models ◽  
Ultrastructural Alterations ◽  
Transgenic Parasites

The heat shock protein 90 (Hsp90) is thought to be an excellent drug target against parasitic diseases. The leishmanicidal effect of an Hsp90 inhibitor, 17-N-allylamino-17-demethoxygeldanamycin (17-AAG), was previously demonstrated in both in vitro and in vivo models of cutaneous leishmaniasis. Parasite death was shown to occur in association with severe ultrastructural alterations in Leishmania, suggestive of autophagic activation. We hypothesized that 17-AAG treatment results in the abnormal activation of the autophagic pathway, leading to parasite death. To elucidate this process, experiments were performed using transgenic parasites with GFP-ATG8-labelled autophagosomes. Mutant parasites treated with 17-AAG exhibited autophagosomes that did not entrap cargo, such as glycosomes, or fuse with lysosomes. ATG5-knockout (Δatg5) parasites, which are incapable of forming autophagosomes, demonstrated lower sensitivity to 17-AAG-induced cell death when compared to wild-type (WT) Leishmania, further supporting the role of autophagy in 17-AAG-induced cell death. In addition, Hsp90 inhibition resulted in greater accumulation of ubiquitylated proteins in both WT- and Δatg5-treated parasites compared to controls, in the absence of proteasome overload. In conjunction with previously described ultrastructural alterations, herein we present evidence that treatment with 17-AAG causes abnormal activation of the autophagic pathway, resulting in the formation of immature autophagosomes and, consequently, incidental parasite death.

scholarly journals Heat shock protein 90 inhibitors suppress pyroptosis in THP-1 cells

2020 ◽  
Vol 477 (20) ◽  
pp. 3923-3934
Author(s):  
Zhou Zhou ◽  
Xiuzhen Li ◽  
Yisong Qian ◽  
Cynthia Liu ◽  
Xiaotian Huang ◽  
...  
Keyword(s):  
Therapeutic Strategy ◽  
Inflammatory Diseases ◽  
Heat Shock Protein 90 ◽  
Hsp90 Inhibitor ◽  
Signal Pathway ◽  
Intracellular Pathogens ◽  
Critical Component ◽  
Hsp90 Inhibition ◽  
Potential Therapeutic Target ◽  
Natural Product Library

Pyroptosis is a recently discovered inflammatory form of programmed cell death which is mostly triggered by infection with intracellular pathogens and critically contributes to inflammation. Mitigating pyroptosis may be a potential therapeutic target in inflammatory diseases. However, small chemicals to reduce pyroptosis is still elusive. In the present study, we screened 155 chemicals from a microbial natural product library and found Geldanamycin, an HSP90 inhibitor, profoundly rescued THP-1 cells from pyroptosis induced by LPS plus Nigericin treatment. Consistently, other HSP90 inhibitors, including Radicicol, 17-DMAG and 17-AAG, all ameliorated pyroptosis in THP-1 cells by suppressing the inflammasome/Caspase-1/GSDMD signal pathway in pyroptosis. HSP90 inhibition compromised the protein stability of NLRP3, a critical component of the inflammasome. Moreover, up-regulated HSP70 may also contribute to this effect. HSP90 inhibition may thus be a potential therapeutic strategy in the treatment of inflammatory diseases in which pyroptosis plays a role.

scholarly journals Heat Shock Protein 90 Chaperones E1A Early Protein of Adenovirus 5 and Is Essential for Replication of the Virus

2021 ◽  
Vol 22 (4) ◽  
pp. 2020
Author(s):  
Iga Dalidowska ◽  
Olga Gazi ◽  
Dorota Sulejczak ◽  
Maciej Przybylski ◽  
Pawel Bieganowski
Keyword(s):  
Mrna Level ◽  
Heat Shock Protein 90 ◽  
Human Adenovirus ◽  
Hsp90 Inhibitor ◽  
Hsp90 Inhibition ◽  
Early Protein ◽  
Fold Reduction ◽  
Hsp90 Chaperone ◽  
Adenovirus 5 ◽  
E1a Protein

Adenovirus infections tend to be mild, but they may pose a serious threat for young and immunocompromised individuals. The treatment is complicated because there are no approved safe and specific drugs for adenovirus infections. Here, we present evidence that 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG), an inhibitor of Hsp90 chaperone, decreases the rate of human adenovirus 5 (HAdV-5) replication in cell cultures by 95%. 17-AAG inhibited the transcription of early and late genes of HAdV-5, replication of viral DNA, and expression of viral proteins. 6 h after infection, Hsp90 inhibition results in a 6.3-fold reduction of the newly synthesized E1A protein level without a decrease in the E1A mRNA level. However, the Hsp90 inhibition does not increase the decay rate of the E1A protein that was constitutively expressed in the cell before exposure to the inhibitor. The co-immunoprecipitation proved that E1A protein interacted with Hsp90. Altogether, the presented results show, for the first time. that Hsp90 chaperones newly synthesized, but not mature, E1A protein. Because E1A serves as a transcriptional co-activator of adenovirus early genes, the anti-adenoviral activity of the Hsp90 inhibitor might be explained by the decreased E1A level.

A phase I trial of the heat shock protein 90 (HSP90) inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17- DMAG, alvespimycin) administered weekly

2007 ◽  
Vol 25 (18_suppl) ◽  
pp. 3568-3568 ◽  
Author(s):  
S. C. Pacey ◽  
R. Wilson ◽  
M. Walton ◽  
M. Eatock ◽  
J. Moreno-Farre ◽  
...  
Keyword(s):  
Phase I ◽  
Mononuclear Cells ◽  
Heat Shock Protein 90 ◽  
Hsp90 Inhibitor ◽  
Toxicity Assessment ◽  
Biologically Active ◽  
Hsp90 Inhibition ◽  
Multiple Cancer ◽  
Peripheral Blood Mononuclear ◽  
Client Proteins

3568 Background: The geldanamycin analogue 17-DMAG inhibits the ATPase activity of HSP90, thus altering client protein & chaperone interactions and targeting client proteins for degradation. The plethora of oncogenic HSP90 client proteins offers the potential of combinatorial blockade across multiple, cancer causing signalling pathways in cancer. Methods: 17-DMAG was administered weekly to patients with advanced, solid tumours using a dose-doubling 3 + 3 Phase I design. The pharmacokinetic (PK) and pharmacodynamic (PD) analyses undertaken were validated to comply with U.K clinical trial legislation. Results: 10 patients, 7 male and 3 female with a mean age of 60 years (range 38 - 78) have received 107 infusions (mean 10.7 weeks, range 2 - 30) at dose levels of 2.5mg/m2, 5mg/m2 & 20mg/m2. No dose-limiting or drug related grade 3 or 4 toxicity has occurred in 9 patients eligible for toxicity assessment. A linear relationship exists between dose and AUC and Cmax (see table ). Hsp72 induction and CDK4 depletion (consistent with HSP90 inhibition) have been detected at doses of 20mg/m2 in peripheral blood mononuclear cells. A confirmed partial response (by PSA and RECIST) has occurred in a patient with hormone refractory prostate cancer (HRPC). Conclusions: We have shown linear PK for 17-DMAG up to 20mg/m2. No dose-limiting toxicity has been encountered. A robust biologically active dose has not been reached but evidence of the pharmacological signature of HSP90 inhibition has been detected in surrogate tissue and a confirmed PR seen in a patient with HRPC. These data support dose escalation to 40mg/m2 and paired tumor biopsies will be taken to further define the PK-PD-clinical relationships. [Table: see text] [Table: see text]

First-in-human phase I study: Results of a second-generation non-ansamycin heat shock protein 90 (HSP90) inhibitor AT13387 in refractory solid tumors.

2012 ◽  
Vol 30 (15_suppl) ◽  
pp. 3028-3028 ◽  
Author(s):  
Daruka Mahadevan ◽  
Diane M Rensvold ◽  
Sandra E Kurtin ◽  
James M. Cleary ◽  
Leena Gandhi ◽  
...  
Keyword(s):  
Dose Escalation ◽  
Second Generation ◽  
Single Agent ◽  
Heat Shock Protein 90 ◽  
Dose Dependence ◽  
Hsp90 Inhibitor ◽  
Hsp90 Inhibition ◽  
Blurred Vision ◽  
Phase Ii Studies ◽  
Study Results

3028 Background: AT13387 is a second-generation potent, novel non-ansamycin HSP90 inhibitor (IC50 0.71 nM). AT13387 has good tissue distribution, long tumor t1/2 resulting in extended knockdown of client proteins in cells and animal models of gastric, prostate and melanoma. Methods: AT13387 was administered as a 1-hr IV infusion twice weekly on Days 1, 4, 8, 11, 15 and 18 (Part A) and then subsequently, weekly on Days 1, 8 and 15 (Part B) of a 28-day cycle in a standard 3+3 dose-escalation design. The primary endpoint was to determine the MTD; secondary endpoints included PK, PD, safety and tolerability. Results: As of 1 Dec 2011, 53 patients received 1–12 cycles of AT13387 (median 2). In Part A, AT13387 was evaluated at 5 doses (10, 20, 40, 80, 120 mg/m2). In Part B, 4 additional doses (150, 220, 260 and 310 mg/m2) were explored. Common treatment related toxicities (≥ 10%) included transient and reversible GI disturbance (vomiting, nausea, dry mouth, diarrhea, abdominal pain), fatigue, local infusion site irritation and systemic infusion-related symptoms including chills, rash, itch, cardiovascular (tachycardia, bradycardia, hypertension, hypotension), and visual changes (diplopia, transient flashes, delayed light/dark accommodation, blurred vision). Severity of infusion-related symptoms, GI toxicities, and fatigue at 310 mg/m2 prevented further dose escalation. A dose of 260 mg/m2 has been identified as the once weekly MTD and the study is currently accruing at this dose. Biological evidence of HSP90 inhibition, demonstrated by an increase in HSP70 in PBMCs, was detected at all doses and exhibited evidence of dose dependence. PK demonstrated dose proportionality, without significant accumulation. One durable RECIST PR (8 months) in an imatinib relapsed metastatic GIST patient with c-kit mutations in exons 11 and 17 was observed. Three SD ≥ 6 months (follicular cell thyroid carcinoma, metastatic uveal melanoma, GIST) were also observed. Conclusions: The MTD of AT13387, administered as a once weekly IV, is 260 mg/m2. All drug-related toxicities were generally reversible. Single-agent activity was observed. Dose expansion at MTD and phase II studies are ongoing.

scholarly journals Heat shock protein 90 inhibition sensitizes acute myelogenous leukemia cells to cytarabine

Blood ◽  
2005 ◽  
Vol 106 (1) ◽  
pp. 318-327 ◽  
Author(s):  
Ruben A. Mesa ◽  
David Loegering ◽  
Heather L. Powell ◽  
Karen Flatten ◽  
Sonnet J. H. Arlander ◽  
...  
Keyword(s):  
Heat Shock ◽  
Heat Shock Protein ◽  
Acute Myelogenous Leukemia ◽  
Nucleoside Analogs ◽  
Heat Shock Protein 90 ◽  
Hsp90 Inhibitor ◽  
S Phase ◽  
Myelogenous Leukemia ◽  
Hsp90 Inhibition ◽  
Acute Myelogenous

Previous studies demonstrated that ataxia telangiectasia mutated– and Rad3-related (ATR) kinase and its downstream target checkpoint kinase 1 (Chk1) facilitate survival of cells treated with nucleoside analogs and other replication inhibitors. Recent results also demonstrated that Chk1 is depleted when cells are treated with heat shock protein 90 (Hsp90) inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG). The present study examined the effects of 17-AAG and its major metabolite, 17-aminogeldanamycin (17-AG), on Chk1 levels and cellular responses to cytarabine in human acute myelogenous leukemia (AML) cell lines and clinical isolates. Cytarabine, at concentrations as low as 30 nM, caused activating phosphorylation of Chk1, loss of the phosphatase Cdc25A, and S-phase slowing. Conversely, treatment with 100 to 300 nM 17-AAG for 24 hours caused Chk1 depletion that was accompanied by diminished cytarabine-induced S-phase accumulation, decreased Cdc25A degradation, and enhanced cytotoxicity as measured by inhibition of colony formation and induction of apoptosis. Additional studies demonstrated that small inhibitory RNA (siRNA) depletion of Chk1 also sensitized cells to cytarabine, whereas disruption of the phosphatidylinositol 3-kinase (PI3k) signaling pathway, which is also blocked by Hsp90 inhibition, did not. Collectively, these results suggest that treatment with 17-AAG might represent a means of reversing checkpoint-mediated cytarabine resistance in AML.

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