The HSP90 inhibitor NVP-AUY922-AG inhibits the PI3K and IKK signalling pathways and synergizes with cytarabine in acute myeloid leukaemia cells

Targeting hematological malignancies with isoxazole derivatives

Compounds with a heterocyclic isoxazole ring are well known for their diverse biologic activities encompassing antimicrobial, antipsychotic, immunosuppressive, antidiabetic and anticancer effects. Recent studies on hematological malignancies have also shown that some of the isoxazole-derived compounds feature encouraging cancer selectivity, low toxicity to normal cells and ability to overcome cancer drug resistance of conventional treatments. These characteristics are particularly promising because patients with hematological malignancies face poor clinical outcomes caused by cancer drug resistance or relapse of the disease. This review summarizes the knowledge on isoxazole-derived compounds toward hematological malignancies and provides clues on their mechanism(s) of action (apoptosis, cell cycle arrest, ROS production) and putative pharmacological targets (c-Myc, BET, ATR, FLT3, HSP90, CARM1, tubulin, PD-1/PD-L1, HDACs) wherever known.

Role of Ganetespib, an HSP90 Inhibitor, in Cancer Therapy: From Molecular Mechanisms to Clinical Practice

Heat-shock proteins are upregulated in cancer and protect several client proteins from degradation. Therefore, they contribute to tumorigenesis and cancer metastasis by reducing apoptosis and enhancing cell survival and proliferation. These client proteins include the estrogen receptor (ER), epidermal growth factor receptor (EGFR), insulin-like growth factor-1 receptor (IGF-1R), human epidermal growth factor receptor 2 (HER-2), and cytokine receptors. The diminution of the degradation of these client proteins activates different signaling pathways, such as the PI3K/Akt/NF-κB, Raf/MEK/ERK, and JAK/STAT3 pathways. These pathways contribute to hallmarks of cancer, such as self-sufficiency in growth signaling, an insensitivity to anti-growth signals, the evasion of apoptosis, persistent angiogenesis, tissue invasion and metastasis, and an unbounded capacity for replication. However, the inhibition of HSP90 activity by ganetespib is believed to be a promising strategy in the treatment of cancer because of its low adverse effects compared to other HSP90 inhibitors. Ganetespib is a potential cancer therapy that has shown promise in preclinical tests against various cancers, including lung cancer, prostate cancer, and leukemia. It has also shown strong activity toward breast cancer, non-small cell lung cancer, gastric cancer, and acute myeloid leukemia. Ganetespib has been found to cause apoptosis and growth arrest in these cancer cells, and it is being tested in phase II clinical trials as a first-line therapy for metastatic breast cancer. In this review, we will highlight the mechanism of action of ganetespib and its role in treating cancer based on recent studies.

A novel fatty acid metabolism-related signature identifies features of the tumor microenvironment and predicts clinical outcome in acute myeloid leukemia

Background

Acute myeloid leukemia (AML) is the most common malignancy of the hematological system, and there are currently a number of studies regarding abnormal alterations in energy metabolism, but fewer reports related to fatty acid metabolism (FAM) in AML. We therefore analyze the association of FAM and AML tumor development to explore targets for clinical prognosis prediction and identify those with potential therapeutic value.

Methods

The identification of AML patients with different fatty acid metabolism characteristics was based on a consensus clustering algorithm. The CIBERSORT algorithm was used to calculate the proportion of infiltrating immune cells. We used Cox regression analysis and least absolute shrinkage and selection operator (LASSO) regression analysis to construct a signature for predicting the prognosis of AML patients. The Genomics of Drug Sensitivity in Cancer database was used to predict the sensitivity of patient samples in high- and low-risk score groups to different chemotherapy drugs.

Results

The consensus clustering approach identified three molecular subtypes of FAM that exhibited significant differences in genomic features such as immunity, metabolism, and inflammation, as well as patient prognosis. The risk-score model we constructed accurately predicted patient outcomes, with area under the receiver operating characteristic curve values of 0.870, 0.878, and 0.950 at 1, 3, and 5 years, respectively. The validation cohort also confirmed the prognostic evaluation performance of the risk score. In addition, higher risk scores were associated with stronger fatty acid metabolisms, significantly higher expression levels of immune checkpoints, and significantly increased infiltration of immunosuppressive cells. Immune functions, such as inflammation promotion, para-inflammation, and type I/II interferon responses, were also significantly activated. These results demonstrated that immunotherapy targeting immune checkpoints and immunosuppressive cells, such as myeloid-derived suppressor cells (MDSCs) and M2 macrophages, are more suitable for patients with high-risk scores. Finally, the prediction results of chemotherapeutic drugs showed that samples in the high-risk score group had greater treatment sensitivity to four chemotherapy drugs in vitro.

Conclusions

The analysis of the molecular patterns of FAM effectively predicted patient prognosis and revealed various tumor microenvironment (TME) characteristics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-022-01687-x.

NF-κB: A Druggable Target in Acute Myeloid Leukemia

Simple Summary

AML is a highly heterogeneous hematological disease and is the second most common form of leukemia. Around 40% of AML patients display elevated nuclear NF-κB activity, providing a compelling rationale for targeting the NF-κB pathway in AML. Here we summarize the main drivers of the NF-κB pathway in AML pathogenesis as well as the conventional and novel therapeutic strategies targeting NF-κB to improve the survival of AML patients.

Abstract

Acute Myeloid Leukemia (AML) is an aggressive hematological malignancy that relies on highly heterogeneous cytogenetic alterations. Although in the last few years new agents have been developed for AML treatment, the overall survival prospects for AML patients are still gloomy and new therapeutic options are still urgently needed. Constitutive NF-κB activation has been reported in around 40% of AML patients, where it sustains AML cell survival and chemoresistance. Given the central role of NF-κB in AML, targeting the NF-κB pathway represents an attractive strategy to treat AML. This review focuses on current knowledge of NF-κB’s roles in AML pathogenesis and summarizes the main therapeutic approaches used to treat NF-κB-driven AML.

Mutated KIT Tyrosine Kinase as a Novel Molecular Target in Acute Myeloid Leukemia

KIT is a type-III receptor tyrosine kinase that contributes to cell signaling in various cells. Since KIT is activated by overexpression or mutation and plays an important role in the development of some cancers, such as gastrointestinal stromal tumors and mast cell disease, molecular therapies targeting KIT mutations are being developed. In acute myeloid leukemia (AML), genome profiling via next-generation sequencing has shown that several genes that are mutated in patients with AML impact patients’ prognosis. Moreover, it was suggested that precision-medicine-based treatment using genomic data will improve treatment outcomes for AML patients. This paper presents (1) previous studies regarding the role of KIT mutations in AML, (2) the data in AML with KIT mutations from the HM-SCREEN-Japan-01 study, a genome profiling study for patients newly diagnosed with AML who are unsuitable for the standard first-line treatment (unfit) or have relapsed/refractory AML, and (3) new therapies targeting KIT mutations, such as tyrosine kinase inhibitors and heat shock protein 90 inhibitors. In this era when genome profiling via next-generation sequencing is becoming more common, KIT mutations are attractive novel molecular targets in AML.

The heat shock response and small molecule regulators

The heat shock response (HSR) is a highly conserved cellular pathway that is responsible for stress relief and the refolding of denatured proteins [1]. When a host cell is exposed to conditions such as heat shock, ischemia, or toxic substances, heat shock factor-1 (HSF-1), a transcription factor, activates the genes that encode for the heat shock proteins (Hsps), which are a family of proteins that work alongside other chaperones to relieve stress and refold proteins that have been denatured (Burdon, 1986) [2]. Along with the refolding of denatured proteins, Hsps facilitate the removal of misfolded proteins by escorting them to degradation pathways, thereby preventing the accumulation of misfolded proteins [3]. Research has indicated that many pathological conditions, such as diabetes, cancer, neuropathy, cardiovascular disease, and aging have a negative impact on HSR function and are commonly associated with misfolded protein aggregation [4,5]. Studies indicate an interplay between mitochondrial homeostasis and HSF-1 levels can impact stress resistance, proteostasis, and malignant cell growth, which further support the role of Hsps in pathological and metabolic functions [6]. On the other hand, Hsp activation by specific small molecules can induce the heat shock response, which can afford neuroprotection and other benefits [7]. This review will focus on the modulation of Hsps and the HSR as therapeutic options to treat these conditions.

The Role of HSP70 in the Protective Effects of NVP-AUY922 on Multiple Organ Dysfunction Syndrome in Endotoxemic Rats

Sepsis is defined as a life-threatening organ dysfunction syndrome with high morbidity and mortality caused by bacterial infection. The major characteristics of sepsis are systemic inflammatory responses accompanied with elevated oxidative stress, leading to multiple organ dysfunction syndrome (MODS), and disseminated intravascular coagulation (DIC). As a molecular chaperon to repair unfolded proteins, heat shock protein 70 (HSP70) maintains cellular homeostasis and shows protective effects on inflammatory damage. HSP 90 inhibitors were reported to exert anti-inflammatory effects via activation of the heat shock factor-1 (HSF-1), leading to induction of HSP70. We evaluated the beneficial effect of HSP 90 inhibitor NVP-AUY 922 (NVP) on multiple organ dysfunction syndrome induced by lipopolysaccharide (LPS) and further explored the underlying mechanism. NVP (5 mg/kg, i.p.) was administered 20 h prior to LPS initiation (LPS 30 mg/kg, i.v. infusion for 4 h) in male Wistar rats. Results demonstrated that pretreatment with NVP significantly increased survival rate and prevented hypotension at 6 h after LPS injection. Plasma levels of ALT, CRE and LDH as well as IL-1β and TNF-α were significantly reduced by NVP at 6 h after LPS challenge. The induction of inducible NO synthase in the liver, lung and heart and NF-κB p-p65 and caspase 3 protein expression in the heart were also attenuated by NVP. In addition, NVP markedly induced HSP70 and HO-1 proteins in the liver, lung and heart after LPS injection. These results indicated that NVP possessed the anti-inflammatory and antioxidant effects on LPS-induced acute inflammation, which might be associated with HSP70 and HO-1, leading to prevent MODS in sepsis. NVP might be considered as a novel therapeutic strategy in the prevention of sepsis-induced MODS.

Heat Shock Proteins in Lymphoma Immunotherapy

Immunotherapy harnessing the host immune system for tumor destruction revolutionized oncology research and advanced treatment strategies for lymphoma patients. Lymphoma is a heterogeneous group of cancer, where the central roles in pathogenesis play immune evasion and dysregulation of multiple signaling pathways. Immunotherapy-based approaches such as engineered T cells (CAR T), immune checkpoint modulators and NK cell-based therapies are now in the frontline of lymphoma research. Even though emerging immunotherapies showed promising results in treating lymphoma patients, low efficacy and on-target/off-tumor toxicity are of a major concern. To address that issue it is suggested to look into the emerging role of heat shock proteins. Heat shock proteins (HSPs) showed to be highly expressed in lymphoma cells. HSPs are known for their abilities to modulate immune responses and inhibit apoptosis, which made their successful entry into cancer clinical trials. Here, we explore the role of HSPs in Hodgkin and Non-Hodgkin lymphoma and their involvement in CAR T therapy, checkpoint blockade and NK cell- based therapies. Understanding the role of HSPs in lymphoma pathogenesis and the ways how HSPs may enhance anti-tumor responses, may help in the development of more effective, specific and safe immunotherapy.

Discovery of 2-isoxazol-3-yl-acetamide analogues as heat shock protein 90 (HSP90) inhibitors with significant anti-HIV activity

The recent burst of explorations on heat shock protein 90 (HSP90) in virus research supports its emergence as a promising target to overcome the drawbacks of current antiviral therapeutic regimen. In continuation of our efforts towards the discovery of novel anti-retroviral molecules, we designed, synthesized fifteen novels 2-isoxazol-3-yl-acetamide based compounds (2a-o) followed by analysis of their anti-HIV activity and cytotoxicity studies. 2a-b, 2e, 2j, and 2l-m were found to be active with inhibitory potentials >80% at their highest non-cytotoxic concentration (HNC). Further characterization of anti-HIV activity of these molecules suggests that 2l has ∼3.5 fold better therapeutic index than AUY922, the second generation HSP90 inhibitor. The anti-HIV activity of 2l is a cell type, virus isolate and viral load independent phenomena. Interestingly, 2l does not significantly modulate viral enzymes like Reverse Transcriptase (RT), Integrase (IN) and Protease (PR) as compared to their known inhibitors in a cell free in vitro assay system at its HNC. Further, 2l mediated inhibition of HSP90 attenuates HIV-1 LTR driven gene expression. Taken together, structural rationale, modeling studies and characterization of biological activities suggest that this novel scaffold can attenuate HIV-1 replication significantly within the host and thus opens a new horizon to develop novel anti-HIV therapeutic candidates.

The role of heat shock protein 90 in regulating pain, opioid signaling, and opioid antinociception

Heat shock protein 90 (Hsp90) is one of the central signal transduction regulators of the cell. Via client interactions with hundreds of proteins, including receptors, receptor regulatory kinases, and downstream signaling regulators, Hsp90 has a crucial and wide-ranging impact on signaling in response to numerous drugs with impacts on resultant physiology and behavior. Despite this importance, however, Hsp90 has barely been studied in the context of pain and the opioid receptor system, leaving open the possibility that Hsp90 could be manipulated to improve pain therapeutic outcomes, a current area of massive medical need. In this review, we will highlight the known roles of Hsp90 in directly regulating the initiation and maintenance of the pain state. We will also explore how Hsp90 regulates signaling and antinociceptive responses to opioid analgesic drugs, with a special emphasis on ERK MAPK signaling. Understanding this new and growing area will improve our understanding of how Hsp90 regulates signaling and physiology, and also may provide new ways to treat pain, and perhaps reduce the severe impact of the ongoing opioid addiction and overdose crisis.

Traditional and Novel Mechanisms of Heat Shock Protein 90 (HSP90) Inhibition in Cancer Chemotherapy Including HSP90 Cleavage

HSP90 is a molecular chaperone that increases the stability of client proteins. Cancer cells show higher HSP90 expression than normal cells because many client proteins play an important role in the growth and survival of cancer cells. HSP90 inhibitors mainly bind to the ATP binding site of HSP90 and inhibit HSP90 activity, and these inhibitors can be distinguished as ansamycin and non-ansamycin depending on the structure. In addition, the histone deacetylase inhibitors inhibit the activity of HSP90 through acetylation of HSP90. These HSP90 inhibitors have undergone or are undergoing clinical trials for the treatment of cancer. On the other hand, recent studies have reported that various reagents induce cleavage of HSP90, resulting in reduced HSP90 client proteins and growth suppression in cancer cells. Cleavage of HSP90 can be divided into enzymatic cleavage and non-enzymatic cleavage. Therefore, reagents inducing cleavage of HSP90 can be classified as another class of HSP90 inhibitors. We discuss that the cleavage of HSP90 can be another mechanism in the cancer treatment by HSP90 inhibition.

Alizarin increase glucose uptake through PI3K/Akt signaling and improve alloxan-induced diabetic mice

Aim: Alizarin (AZ), that can be isolated from Rubia cordifolia, has biological activities such as antioxidation and anti-inflammatory. This study aimed to investigate the effect of AZ on glucose and lipid metabolism disorders in alloxan-induced diabetic mice and also explored the effect of AZ on insulin resistance in 3T3-L1 adipocytes. Results: The research showed that AZ could decrease fasting and postprandial blood glucose, TG, TC and MDA, and it could also increase liver glycogen levels and SOD activity in diabetic mice. AZ could significantly improve the glucose uptake of 3T3-L1 adipocytes under insulin resistance, and could also increase GLUT4 protein expression levels, IRS-1 and Akt protein phosphorylation. Conclusion: These results showed that AZ has the potential to reduce blood sugar and improve insulin resistance.

Targeting c-KIT (CD117) by dasatinib and radotinib promotes acute myeloid leukemia cell death

Dasatinib and radotinib are oral BCR-ABL tyrosine kinase inhibitors that were developed as drugs for the treatment of chronic myeloid leukemia. We report here that the c-KIT (CD117) targeting with dasatinib and radotinib promotes acute myeloid leukemia (AML) cell death, and c-KIT endocytosis is essential for triggering c-KIT-positive AML cell death by dasatinib and radotinib during the early stages. In addition, dasatinib and radotinib reduce heat shock protein 90β (HSP90β) expression and release Apaf-1 in c-KIT-positive AML cells. Finally, this activates a caspase-dependent apoptotic pathway in c-KIT-positive AML cells. Moreover, the inhibition of c-KIT endocytosis by dynamin inhibitor (DY) reversed cell viability and c-KIT expression by dasatinib and radotinib. HSP90β expression was recovered by DY in c-KIT-positive AML cells as well. Furthermore, the effect of radotinib on c-KIT and HSP90β showed the same pattern in a xenograft animal model using HEL92.1.7 cells. Therefore, dasatinib and radotinib promote AML cell death by targeting c-KIT. Taken together, these results indicate that dasatinib and radotinib treatment have a potential role in anti-leukemic therapy on c-KIT-positive AML cells.

HSP90 inhibitor (NVP-AUY922) enhances the anti-cancer effect of BCL-2 inhibitor (ABT-737) in small cell lung cancer expressing BCL-2

Small cell lung cancer (SCLC) cannot be efficiently controlled using existing chemotherapy and radiotherapy approaches, indicating the need for new therapeutic strategies. Although ABT-737, a B-cell lymphoma-2 (BCL-2) inhibitor, exerts anticancer effects against BCL-2-expressing SCLC, monotherapy with ABT-737 is associated with limited clinical activity because of the development of resistance and toxicity. Here, we examined whether combination therapy with ABT-737 and heat shock protein 90 (HSP90) inhibitor NVP-AUY922 exerted synergistic anticancer effects on SCLC. We found that the combination of ABT-737 and NVP-AUY922 synergistically induced the apoptosis of BCL-2-expressing SCLC cells. NVP-AUY922 downregulated the expression of AKT and ERK, which activate MCL-1 to induce resistance against ABT-737. The synergistic effect was also partly due to blocking NF-κB activation, which induces anti-apoptosis protein expressions. However, interestingly, targeting BCL-2 and MCL-1 or BCL2 and NF-κB did not induce the cytotoxicity. In conclusion, our study showed that combination of BCL2 inhibitor with HSP90 inhibitor increased activity in in vitro and in vivo study in only BCL-2 expressing SCLC compared to either single BCL2 inhibitor or HSP inhibitor. The enhanced activity might be led by blocking several apoptotic pathways simultaneously rather than a specific pathway.

Dysfunctional diversity of p53 proteins in adult acute myeloid leukemia: projections on diagnostic workup and therapy

The heterogeneous nature of acute myeloid leukemia (AML) and its poor prognosis necessitate therapeutic improvement. Current advances in AML research yield important insights regarding AML genetic, epigenetic, evolutional, and clinical diversity, all in which dysfunctional p53 plays a key role. As p53 is central to hematopoietic stem cell functions, its aberrations affect AML evolution, biology, and therapy response and usually predict poor prognosis. While in human solid tumors TP53 is mutated in more than half of cases, TP53 mutations occur in less than one tenth of de novo AML cases. Nevertheless, wild-type (wt) p53 dysfunction due to nonmutational p53 abnormalities appears to be rather frequent in various AML entities, bearing, presumably, a greater impact than is currently appreciated. Hereby, we advocate assessment of adult AML with respect to coexisting p53 alterations. Accordingly, we focus not only on the effects of mutant p53 oncogenic gain of function but also on the mechanisms underlying nonmutational wtp53 inactivation, which might be of therapeutic relevance. Patient-specific TP53 genotyping with functional evaluation of p53 protein may contribute significantly to the precise assessment of p53 status in AML, thus leading to the tailoring of a rationalized and precision p53-based therapy. The resolution of the mechanisms underlying p53 dysfunction will better address the p53-targeted therapies that are currently considered for AML. Additionally, a suggested novel algorithm for p53-based diagnostic workup in AML is presented, aiming at facilitating the p53-based therapeutic choices.

Hsp90 inhibitor induces KG-1a cell differentiation and apoptosis via Akt/NF-κB signaling

Heat-shock protein 90 (Hsp 90) acts as a molecular chaperone that maintains protein stability and regulates cell proliferation, survival, differentiation and apoptosis. The present study investigated the effect of Hsp90 inhibition on human acute myeloid leukemia (AML) cells using the novel small-molecule inhibitor SNX-2112. We found that SNX-2112 more potently inhibited KG-1a cell growth than the classical Hsp90 inhibitor 17-(2-dimethylaminoethyl)amino‑17-demethoxygeldanamycin as determined by CCK-8 assay. Flow cytometry was used to examine the cell cycle, differentiation, and apoptosis, and western blotting and qRT-PCR were used to analyze the underlying mechanism. The results revealed that low concentrations of SNX-2112 arrested the cells in the G2/M phase and induced their differentiation and apoptosis, possibly by suppressing Akt and inhibitor of κB kinase, a component of the nuclear factor (NF)-κB signaling pathway. We also found that SNX-2112 increased the expression of the differentiation transcription factors PU.1 and CCAAT‑enhancer-binding protein-α. Thus, SNX-2112 induced KG-1a cell differentiation, cell cycle arrest and apoptosis via modulation of Akt and NF-κB signaling, suggesting that it is a promising therapeutic agent for the treatment of AML.

The novel HSP90 inhibitor NVP-AUY922 shows synergistic anti-leukemic activity with cytarabine in vivo

HSP90 is a molecular chaperone essential for stability, activity and intracellular sorting of many proteins, including oncoproteins, such as tyrosine kinases, transcription factors and cell cycle regulatory proteins. Therefore, inhibitors of HSP90 are being investigated for their potential as anti-cancer drugs. Here we show that the HSP90 inhibitor NVP-AUY922 induced degradation of the fusion oncoprotein FOP2-FGFR1 in a human acute myeloid leukemia (AML) cell line, KG-1a. Concordantly, downstream signaling cascades, such as STAT1, STAT3 and PLCγ were abrogated. At concentrations that caused FOP2-FGFR1 degradation and signaling abrogation, NVP-AUY922 treatment caused significant cell death and inhibition of proliferation of KG-1a cells in vitro. In an animal model for AML, NVP-AUY922 administrated alone showed no anti-leukemic activity. However, when NVP-AUY922 was administered in combination with cytarabine, the two compounds showed significant synergistic anti-leukemic activity in vivo. Thus NVP-AUY922 and cytarabine combination therapy might be a prospective strategy for AML treatment.

The HSP90 inhibitor ganetespib: A potential effective agent for Acute Myeloid Leukemia in combination with cytarabine

HSP90 is a multi-client chaperone involved in regulating a large array of cellular processes and is commonly overexpressed in many different cancer types including hematological malignancies. Inhibition of HSP90 holds promise for targeting multiple molecular abnormalities and is therefore an attractive target for heterogeneous malignancies such as Acute Myeloid Leukemia (AML). Ganetespib is a highly potent second generation HSP90 inhibitor which we show is significantly more effective against primary AML blasts at nanomolar concentrations when compared with cytarabine (p<0.001). Dose dependant cytotoxicity was observed with an apoptotic response coordinate with the loss of pro-survival signaling through the client protein AKT. Combination treatment of primary blasts with ganetespib and cytarabine showed good synergistic interaction (combination index (CI): 0.47) across a range of drug effects with associated reduction in HSP70 feedback and AKT signaling levels. In summary, we show ganetespib to have high activity in primary AMLs as a monotherapy and a synergistic relationship with cytarabine when combined. The combination of cytotoxic cell death, suppression of cytoprotective/drug resistance mechanisms such as AKT and reduced clinical toxicity compared to other HSP90 inhibitors provide strong rationale for the clinical assessment of ganetespib in AML.

Hsp90 inhibitor as a sensitizer of cancer cells to different therapies (review)

Hsp90 is a molecular chaperone that maintains the structural and functional integrity of various client proteins involved in signaling and many other functions of cancer cells. The natural inhibitors, ansamycins influence the Hsp90 chaperone function by preventing its binding to client proteins and resulting in their proteasomal degradation. N- and C-terminal inhibitors of Hsp90 and their analogues are widely tested as potential anticancer agents in vitro, in vivo as well as in clinical trials. It seems that Hsp90 competitive inhibitors target different tumor types at nanomolar concentrations and might have therapeutic benefit. On the contrary, some Hsp90 inhibitors increased toxicity and resistance of cancer cells induced by heat shock response, and through the interaction of survival signals, that occured as side effects of treatments, could be very effectively limited via combination of therapies. The aim of our review was to collect the data from experimental and clinical trials where Hsp90 inhibitor was combined with other therapies in order to prevent resistance as well as to potentiate the cytotoxic and/or antiproliferative effects.

Small molecule inhibitors in acute myeloid leukemia: from the bench to the clinic

Many patients with acute myeloid leukemia will eventually develop refractory or relapsed disease. In the absence of standard therapy for this population, there is currently an urgent unmet need for novel therapeutic agents. Targeted therapy with small molecule inhibitors represents a new therapeutic intervention that has been successful for the treatment of multiple tumors (e.g., gastrointestinal stromal tumors, chronic myelogenous leukemia). Hence, there has been great interest in generating selective small molecule inhibitors targeting critical pathways of proliferation and survival in acute myeloid leukemia. This review highlights a selective group of intriguing therapeutic agents and their presumed targets in both preclinical models and in early human clinical trials.

Targeting Hsp90 and its co-chaperones to treat Alzheimer's disease

INTRODUCTION

Alzheimer's disease, characterized by the accumulation of hyperphosphorylated tau and β amyloid (Aβ), currently lacks effective treatment. Chaperone proteins, such as the heat shock protein (Hsp) 90, form macromolecular complexes with co-chaperones, which can regulate tau metabolism and Aβ processing. Although small molecule inhibitors of Hsp90 have been successful at ameliorating tau and Aβ burden, their development into drugs to treat disease has been slow due to the off- and on-target effects of this approach as well as challenges with the pharmacology of current scaffolds. Thus, other approaches are being developed to improve these compounds and to target co-chaperones of Hsp90 in an effort to limit these liabilities.

AREAS COVERED

This article discusses the most current developments in Hsp90 inhibitors including advances in blood-brain barrier permeability, decreased toxicity and homolog-specific small-molecule inhibitors. In addition, we discuss current strategies targeting Hsp90 co-chaperones rather than Hsp90 itself to reduce off-target effects.

EXPERT OPINION

Although Hsp90 inhibitors have proven their efficacy at reducing tau pathology, they have yet to meet with success in the clinic. The development of Hsp90/tau complex-specific inhibitors and further development of Hsp90 co-chaperone-specific drugs should yield more potent, less toxic therapeutics.

Primary cilium-associated genes mediate bone marrow stromal cell response to hypoxia

Currently there is intense interest in using mesenchymal stem cells (MSC) for therapeutic interventions in many diseases and conditions. To accelerate the therapeutic use of stem cells we must understand how they sense their environment. Primary cilia are an extracellular sensory organelle present on most growth arrested cells that transduce information about the cellular environment into cells, triggering signaling cascades that have profound effects on development, cell cycle, proliferation, differentiation and migration. Migrating cells likely encounter differing oxygen tensions, therefore we investigated the effect of oxygen tension on cilia. Using bone marrow stromal cells (BMSCs, also known as bone marrow-derived mesenchymal stem cells) we found that oxygen tension significantly affected the length of cilia in primary BMSCs. Chronic exposure to hypoxia specifically down-regulated genes involved in hedgehog signaling and re-localized the Smo and Gli2 proteins to cilia. Investigating the effects of chemotactic migration on cilia, we observed significantly longer cilia in migrating cells which was again, strongly influenced by oxygen tension. Finally, using computational modeling we identified links between migration and ciliation signaling pathways, characterizing the novel role of HSP90 and PI3K signaling in regulating BMSC cilia length. These findings enhance our current understanding of BMSC adaptions to hypoxia and advance our knowledge of BMSC biology and cilia regulation.