Combination Strategy Targeting the Hypoxia Inducible Factor-1α with Mammalian Target of Rapamycin and Histone Deacetylase Inhibitors

Acetylation and Phosphorylation in the Regulation of Hypoxia-Inducible Factor Activities: Additional Options to Modulate Adaptations to Changes in Oxygen Levels

O2 is essential for the life of eukaryotic cells. The ability to sense oxygen availability and initiate a response to adapt the cell to changes in O2 levels is a fundamental achievement of evolution. The key switch for adaptation consists of the transcription factors HIF1A, HIF2A and HIF3A. Their levels are tightly controlled by O2 through the involvement of the oxygen-dependent prolyl hydroxylase domain-containing enzymes (PHDs/EGNLs), the von Hippel-Lindau tumour suppressor protein (pVHL) and the ubiquitin-proteasome system. Furthermore, HIF1A and HIF2A are also under the control of additional post-translational modifications (PTMs) that positively or negatively regulate the activities of these transcription factors. This review focuses mainly on two PTMs of HIF1A and HIF2A: phosphorylation and acetylation.

Development and validation of a microenvironment-related prognostic model for hepatocellular carcinoma patients based on histone deacetylase family

BACKGROUND

Histone deacetylase (HDAC) family can remove acetyl groups from histone lysine residues, and their high expression is closely related to the poor prognosis of hepatocellular carcinoma (HCC) patients. Recently, it has been reported to play an immunosuppressive role in the microenvironment, but little is known about the mechanism.

METHODS

Through machine learning, we trained and verified the prognostic model composed of HDACs. CIBERSORT was used to calculate the percentage of immune cells in the microenvironment. Based on co-expression network, potential targets of HDACs were screened. After that, qRT-PCR was employed to evaluate the expression of downstream genes of HDACs, while HPLC-CAD analysis was applied to detect the concentration of arachidonic acid (AA). Finally, Flow cytometry, WB and IHC experiments were used to detect CD86 expression in RAW246.7.

RESULTS

We constructed a great prognostic model composed of HDAC1 and HDAC11 that was significantly associated with overall survival. These HDACs were related to the abundance of macrophages, which might be attributed to their regulation of fatty-acid-metabolism related genes. In vitro experiments, the mRNA expression of ACSM2A, ADH1B, CYP2C8, CYP4F2 and SLC27A5 in HCC-LM3 was significantly down-regulated, and specific inhibitors of HDAC1 and HDAC11 significantly promoted the expression of these genes. HDAC inhibitors can promote the metabolism of AA, which may relieve the effect of AA on the polarization of M1 macrophages.

CONCLUSIONS

Our study revealed the blocking effect of HDAC1 and HDAC11 on the polarization of macrophages M1 in the microenvironment by inhibiting fatty acid metabolism.

Targeted inhibition of the GRK2/HIF-1α pathway is an effective strategy to alleviate synovial hypoxia and inflammation

G-protein coupled receptor (GPCR) kinases (GRKs) and hypoxia-inducible factor-1α (HIF-1α) play key roles in rheumatoid arthritis (RA). Several studies have demonstrated that HIF-1α expression is positively regulated by GRK2, suggesting its posttranscriptional effects on HIF-1α. In this study, we review the role of HIF-1α and GRK2 in RA pathophysiology, focusing on their proinflammatory roles in immune cells and fibroblast-like synoviocytes (FLS).We then introduce several drugs that inhibit GRK2 and HIF-1α, and briefly outline their molecular mechanisms. We conclude by presenting gaps in knowledge and our prospects for the pharmacological potential of targeting these proteins and the relevant downstream signaling pathways.Future research is warranted and paramount for untangling these novel and promising roles for GRK2 and HIF-1α in RA.

Histone deacetylases: A novel class of therapeutic targets for pancreatic cancer

Pancreatic cancer is the seventh leading cause of cancer death worldwide, with a low 5-year survival rate. Novel agents are urgently necessary to treat the main pathological type, known as pancreatic ductal carcinoma (PDAC). The dysregulation of histone deacetylases (HDACs) has been identified in association with PDAC, which can be more easily targeted by small molecular inhibitors than gene mutations and may represent a therapeutic breakthrough for PDAC. However, the contributions of HDACs to PDAC remain controversial, and pharmacokinetic challenges have limited the application of HDAC inhibitors (HDACis) in PDAC. This review summarizes the mechanisms associated with success and failure of HDACis in PDAC and discusses the recent progress made in HDACi development and application, such as combination therapies designed to enhance efficacy. More precise strategies involving HDACis might eventually improve the outcomes of PDAC treatment.

Hypoxia increases the expression of stem cell markers in human osteosarcoma cells

Osteosarcoma (OS) is the most common primary malignant tumor of bone. It is a common phenomenon that osteosarcoma cells have a hypoxic microenvironment. Hypoxia can dedifferentiate cells of several malignant tumor types into stem cell-like phenotypes. However, the role of hypoxia in stemness induction and the expression of cancer stem cell (CSC) markers in human osteosarcoma cells has not been reported. The present study examined the effects of hypoxia on stem-like cells in the human osteosarcoma MNNG/HOS cells. Under the incubation with 1% oxygen, the expression of CSCs markers (Oct-4, Nanog and CD133) in MNNG/HOS cells were increased. Moreover, MNNG/HOS cells cultured under hypoxic conditions were more likely to proliferate into spheres and resulted in larger xenograft tumor. Hypoxia also increased the mRNA and protein levels of hypoxia-inducible factor (HIF)-1α. Then rapamycin was used, which has been shown to lower HIF-1α protein level, to inhibit the hypoxic response. Rapamycin suppressed the expression of HIF-1α protein and CSCs markers (Oct4, Nanog and CD133) in MNNG/HOS cells. In addition, pretreatment with rapamycin reduced the efficiency of MNNG/HOS cells in forming spheres and xenograft tumors. The results demonstrated that hypoxia (1% oxygen) can dedifferentiate some of the MNNG/HOS cells into stem cell-like phenotypes, and that the mTOR signaling pathway participates in this process via regulating the expression of HIF-1α protein.

Phase I study of the mTOR inhibitor everolimus in combination with the histone deacetylase inhibitor panobinostat in patients with advanced clear cell renal cell carcinoma

Background Preclinical studies suggested synergistic anti-tumor activity when pairing mTOR inhibitors with histone deacetylase (HDAC) inhibitors. We completed a phase I, dose-finding trial for the mTOR inhibitor everolimus combined with the HDAC inhibitor panobinostat in advanced clear cell renal cell carcinoma (ccRCC) patients. We additionally investigated expression of microRNA 605 (miR-605) in serum samples obtained from trial participants. Patients and Methods Twenty-one patients completed our single institution, non-randomized, open-label, dose-escalation phase 1 trial. miR-605 levels were measured at cycle 1/day 1 (C1D1) and C2D1. Delta Ct method was utilized to evaluate miR-605 expression using U6B as an endogenous control. Results There were 3 dosing-limiting toxicities (DLTs): grade 4 thrombocytopenia (n = 1), grade 3 thrombocytopenia (n = 1), and grade 3 neutropenia (n = 1). Everolimus 5 mg PO daily and panobinostat 10 mg PO 3 times weekly (weeks 1 and 2) given in 21-day cycles was the recommended phase II dosing based on their maximum tolerated dose. The 6-month progression-free survival was 31% with a median of 4.1 months (95% confidence internal; 2.0-7.1). There was higher baseline expression of miR-605 in patients with progressive disease (PD) vs those with stable disease (SD) (p = 0.0112). PD patients' miR-605 levels decreased after the 1st cycle (p = 0.0245), whereas SD patients' miR-605 levels increased (p = 0.0179). Conclusion A safe and tolerable dosing regimen was established for combination everolimus/panobinostat therapy with myelosuppression as the major DLT. This therapeutic pairing did not appear to improve clinical outcomes in our group of patients with advanced ccRCC. There was differential expression of miR-605 that correlated with treatment response. Clinical trial information: NCT01582009.

Glycolytic enzyme hexokinase II is a putative therapeutic target in B-cell malignant lymphoma

Hexokinase II (HXKII) is a key regulator of glucose metabolism that converts glucose to glucose 6-phosphate. Furthermore, HXKII blocks mitochondria-dependent apoptosis by inhibiting the release of cytochrome c. HXKII overexpression is frequently observed in several types of cancer and confers chemoresistance to cancer cells. In the present study, we found that compared with cell lines generated from diffuse large-B-cell lymphoma (DLBCL) patients, cell lines with features of Burkitt lymphoma have higher levels of HXKII because of the activation of both c-MYC and HIF-1. Under normoxia, HXKII levels were correlated with the growth ability of each B-cell lymphoma cell line. HXKII levels were further enhanced when the B-cell lymphoma cells were cultured under hypoxia. The high levels of HXKII induced by hypoxia conferred cisplatin resistance in all tested B-cell lymphoma cell lines. The HDAC inhibitor panobinostat significantly suppressed HXKII expression under both normoxic and hypoxic conditions. Importantly, panobinostat reversed the anti-lymphoma action of cisplatin, and this effect was diminished by hypoxia. These data suggest that HXKII plays different roles, including in the regulation of glycolysis and inhibition of apoptosis, depending on its expression levels. Furthermore, inhibition of HXKII expression by panobinostat may represent a new and attractive strategy to overcome cisplatin resistance.

Inhibition of BET Proteins and Histone Deacetylase (HDACs): Crossing Roads in Cancer Therapy

Histone DeACetylases (HDACs) are enzymes that remove acetyl groups from histones and other proteins, regulating the expression of target genes. Pharmacological inhibition of these enzymes re-shapes chromatin acetylation status, confusing boundaries between transcriptionally active and quiescent chromatin. This results in reinducing expression of silent genes while repressing highly transcribed genes. Bromodomain and Extraterminal domain (BET) proteins are readers of acetylated chromatin status and accumulate on transcriptionally active regulatory elements where they serve as scaffold for the building of transcription-promoting complexes. The expression of many well-known oncogenes relies on BET proteins function, indicating BET inhibition as a strategy to counteract their activity. BETi and HDACi share many common targets and affect similar cellular processes to the point that combined inhibition of both these classes of proteins is regarded as a strategy to improve the effectiveness of these drugs in cancer. In this work, we aim to discuss the molecular basis of the interplay between HDAC and BET proteins, pointing at chromatin acetylation as a crucial node of their functional interaction. We will also describe the state of the art of their dual inhibition in cancer therapy. Finally, starting from their mechanism of action we will provide a speculative perspective on how these drugs may be employed in combination with standard therapies to improve effectiveness and/or overcome resistance.

CUDC-907 blocks multiple pro-survival signals and abrogates microenvironment protection in CLL

CUDC‐907, a dual PI3K/HDAC inhibitor, has been proposed to have therapeutic potential in hematopoietic malignancies. However, the molecular mechanisms of its effects in chronic lymphocytic leukaemia (CLL) remain elusive. We show that CLL cells are sensitive to CUDC‐907, even under conditions similar to the protective microenvironment of proliferation centres. CUDC‐907 inhibited PI3K/AKT and HDAC activity, as expected, but also suppressed RAF/MEK/ERK and STAT3 signalling and reduced the expression of anti‐apoptotic BCL‐2 family proteins BCL‐2, BCL‐xL, and MCL‐1. Moreover, CUDC‐907 downregulated cytokines BAFF and APRIL and their receptors BAFFR, TACI, and BCMA, thus blocking BAFF‐induced NF‐κB signalling. T cell chemokines CCL3/4/17/22 and phosphorylation of CXCR4 were also reduced by CUDC‐907. These data indicated that CUDC‐907 abrogates different protective signals and suggested that it might sensitize CLL cells to other drugs. Indeed, combinations of low concentrations of CUDC‐907 with inhibitors of BCL2, BTK, or the NF‐κB pathway showed a potent synergistic effect. Our data indicate that, apart from its known functions, CUDC‐907 blocks multiple pro‐survival pathways to overcome microenvironment protection in CLL cells. This provides a rationale to evaluate the clinical relevance of CUDC‐907 in combination therapies with other targeted inhibitors.

HDAC Inhibition Counteracts Metastatic Re-Activation of Prostate Cancer Cells Induced by Chronic mTOR Suppression

This study was designed to investigate whether epigenetic modulation by histone deacetylase (HDAC) inhibition might circumvent resistance towards the mechanistic target of rapamycin (mTOR) inhibitor temsirolimus in a prostate cancer cell model. Parental (par) and temsirolimus-resistant (res) PC3 prostate cancer cells were exposed to the HDAC inhibitor valproic acid (VPA), and tumor cell adhesion, chemotaxis, migration, and invasion were evaluated. Temsirolimus resistance was characterized by reduced binding of PC3^res cells to endothelium, immobilized collagen, and fibronectin, but increased adhesion to laminin, as compared to the parental cells. Chemotaxis, migration, and invasion of PC3^res cells were enhanced following temsirolimus re-treatment. Integrin α and β receptors were significantly altered in PC3^res compared to PC3^par cells. VPA significantly counteracted temsirolimus resistance by down-regulating tumor cell–matrix interaction, chemotaxis, and migration. Evaluation of integrin expression in the presence of VPA revealed a significant down-regulation of integrin α5 in PC3^res cells. Blocking studies demonstrated a close association between α5 expression on PC3^res and chemotaxis. In this in vitro model, temsirolimus resistance drove prostate cancer cells to become highly motile, while HDAC inhibition reversed the metastatic activity. The VPA-induced inhibition of metastatic activity was accompanied by a lowered integrin α5 surface level on the tumor cells.

Synergistic antitumour effects of rapamycin and oncolytic reovirus

There are currently numerous oncolytic viruses undergoing clinical trial evaluation in cancer patients and one agent, Talimogene laherparepvec, has been approved for the treatment of malignant melanoma. This progress highlights the huge clinical potential of this treatment modality, and the focus is now combining these agents with conventional anticancer treatments or agents that enhance viral replication, and thereby oncolysis, in the tumour microenvironment. We evaluated the combination of reovirus with rapamycin in B16F10 cell, a murine model of malignant melanoma, based on potential mechanisms by which mTOR inhibitors might enhance viral oncolysis. Rapamycin was not immunomodulatory in that it had no effect on the generation of an antireovirus-neutralising antibody response in C57/black 6 mice. The cell cycle effects of reovirus (increase G0/G1 fraction) were unaffected by concomitant or sequential exposure of rapamycin. However, rapamycin attenuated viral replication if given prior or concomitantly with reovirus and similarly reduced reovirus-induced apoptotic cell death Annexin V/PI and caspase 3/7 activation studies. We found clear evidence of synergistic antitumour effects of the combination both in vitro and in vivo, which was sequence dependent only in the in vitro setting. In conclusion, we have demonstrated synergistic antitumour efficacy of reovirus and rapamycin combination.

Therapeutic effects of histone deacetylase inhibitors on kidney disease

Increasing evidence has shown the involvement of histone deacetylases (HDACs) in the development and progression of various renal diseases, highlighting its inhibition as a promising therapeutic strategy to prevent kidney diseases. Accordingly, numerous studies have shown that HDAC inhibitors protect the kidneys from various diseases through their effects on multiple pathways, such as suppression of transforming growth factor-β signaling pathway and nuclear factor-κB signaling pathways, augmentation of apoptosis, and inhibition of angiogenesis. To develop more effective and less toxic isoform-selective HDAC inhibitors and further improve clinical outcomes, it is necessary to identify and understand the mechanisms involved in the pathogenesis and progression of renal diseases. This review focuses on the roles of HDAC inhibitors and the mechanisms involved in their therapeutic effects in experimental models of kidney diseases including glomerulosclerosis, tubulointerstitial fibrosis, glomerular and tubulointerstitial inflammation, lupus nephritis, polycystic kidney disease, and renal cell carcinoma (RCC).

Evolving Significance and Future Relevance of Anti-Angiogenic Activity of mTOR Inhibitors in Cancer Therapy

mTOR inhibitors have demonstrated remarkable anti-tumor activity in experimental models, mainly by reducing cancer cell growth and tumor angiogenesis. Their use in cancer patients as monotherapy has, however, generated only limited benefits, increasing median overall survival by only a few months. Likewise, in other targeted therapies, cancer cells develop resistance mechanisms to overcome mTOR inhibition. Hence, novel therapeutic strategies have to be designed to increase the efficacy of mTOR inhibitors in cancer. In this review, we discuss the present and future relevance of mTOR inhibitors in cancer therapy by focusing on their effects on tumor angiogenesis.

PI3K/mTOR dual inhibitor BEZ235 and histone deacetylase inhibitor Trichostatin A synergistically exert anti-tumor activity in breast cancer

Molecule-targeted therapy has achieved great progress in cancer therapy. Effective drug combinations are one way to enhance the therapeutic efficacy and combat resistance. Here, we determined the effect of the PI3K/mTOR dual inhibitor BEZ235 and the histone deacetylase inhibitor Trichostatin A (TSA) on human breast cancer. We demonstrated that the combination of BEZ235 and TSA results in significant synergistic growth inhibition of multiple breast cancer cell lines. Mechanistic studies revealed that the combined therapy induced apoptosis in a caspase-dependent manner, which might be related to the further depression of the PI3K/Akt/mTOR signalling pathway. Additionally, co-treatment with BEZ235 and TSA enhanced autophagic cell death by up-regulating the expression of LC3B-II and Beclin-1. The vivo tumour modelling studies revealed that BEZ235 combined with TSA blocked tumour growth without noticeable side effects. These data suggest that the combination of BEZ235 and TSA may be a new selective strategy, which may have significant clinical application in the treatment of breast cancer patients.

Epigenome Aberrations: Emerging Driving Factors of the Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC), the most common form of Kidney cancer, is characterized by frequent mutations of the von Hippel-Lindau (VHL) tumor suppressor gene in ~85% of sporadic cases. Loss of pVHL function affects multiple cellular processes, among which the activation of hypoxia inducible factor (HIF) pathway is the best-known function. Constitutive activation of HIF signaling in turn activates hundreds of genes involved in numerous oncogenic pathways, which contribute to the development or progression of ccRCC. Although VHL mutations are considered as drivers of ccRCC, they are not sufficient to cause the disease. Recent genome-wide sequencing studies of ccRCC have revealed that mutations of genes coding for epigenome modifiers and chromatin remodelers, including PBRM1, SETD2 and BAP1, are the most common somatic genetic abnormalities after VHL mutations in these tumors. Moreover, recent research has shed light on the extent of abnormal epigenome alterations in ccRCC tumors, including aberrant DNA methylation patterns, abnormal histone modifications and deregulated expression of non-coding RNAs. In this review, we discuss the epigenetic modifiers that are commonly mutated in ccRCC, and our growing knowledge of the cellular processes that are impacted by them. Furthermore, we explore new avenues for developing therapeutic approaches based on our knowledge of epigenome aberrations of ccRCC.

Epigenetic therapy in urologic cancers: an update on clinical trials

Epigenetic dysregulation is one of many factors that contribute to cancer development and progression. Numerous epigenetic alterations have been identified in urologic cancers including histone modifications, DNA methylation changes, and microRNA expression. Since these changes are reversible, efforts are being made to develop epigenetic drugs that restore the normal epigenetic patterns of cells, and many clinical trials are already underway to test their clinical potential. In this review we analyze multiple clinical trials (n=51) that test the efficacy of these drugs in patients with urologic cancers. The most frequently used epigenetic drugs were histone deacetylase inhibitors followed by antisense oligonucleotides, DNA methyltransferase inhibitors and histone demethylase inhibitors, the last of which are only being tested in prostate cancer. In more than 50% of the clinical trials considered, epigenetic drugs were used as part of combination therapy, which achieved the best results. The epigenetic regulation of some cancers is still matter of research but will undoubtedly open a window to new therapeutic approaches in the era of personalized medicine. The future of therapy for urological malignancies is likely to include multidrug regimens in which epigenetic modifying drugs will play an important role.

HDAC 1 and 6 modulate cell invasion and migration in clear cell renal cell carcinoma

Background

Class I histone deacetylases (HDACs) have been reported to be overexpressed in clear cell renal cell carcinoma (ccRCC), whereas the expression of class II HDACs is unknown.

Methods

Four isogenic cell lines C2/C2VHL and 786-O/786-OVHL with differential VHL expression are used in our studies. Cobalt chloride is used to mimic hypoxia in vitro. HIF-2α knockdowns in C2 and 786-O cells is used to evaluate the effect on HDAC 1 expression and activity. Invasion and migration assays are used to investigate the role of HDAC 1 and HDAC 6 expression in ccRCC cells. Comparisons are made between experimental groups using the paired T-test, the two-sample Student’s T-test or one-way ANOVA, as appropriate. ccRCC and the TCGA dataset are used to observe the clinical correlation between HDAC 1 and HDAC 6 overexpression and overall and progression free survival.

Results

Our analysis of tumor and matched non-tumor tissues from radical nephrectomies showed overexpression of class I and II HDACs (HDAC6 only in a subset of patients). In vitro, both HDAC1 and HDAC6 over-expression increased cell invasion and motility, respectively, in ccRCC cells. HDAC1 regulated invasiveness by increasing matrix metalloproteinase (MMP) expression. Furthermore, hypoxia stimulation in VHL-reconstituted cell lines increased HIF isoforms and HDAC1 expression. Presence of hypoxia response elements in the HDAC1 promoter along with chromatin immunoprecipitation data suggests that HIF-2α is a transcriptional regulator of HDAC1 gene. Conversely, HDAC6 and estrogen receptor alpha (ERα) were co-localized in cytoplasm of ccRCC cells and HDAC6 enhanced cell motility by decreasing acetylated α-tubulin expression, and this biological effect was attenuated by either biochemical or pharmacological inhibition. Finally, analysis of human ccRCC specimens revealed positive correlation between HIF isoforms and HDAC. HDAC1 mRNA upregulation was associated with worse overall survival in the TCGA dataset.

Conclusions

Taking together, these results suggest that HDAC1 and HDAC6 may play a role in ccRCC biology and could represent rational therapeutic targets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2604-7) contains supplementary material, which is available to authorized users.

Panobinostat for the treatment of acute myelogenous leukemia

INTRODUCTION

Therapeutic strategies in patients with acute myeloid leukemia (AML) have not changed significantly over the last decades. Appropriate strategies are ultimately driven by the assessment of patients' fitness to define suitability for intensive induction chemotherapy, which produces high initial remission rates but, increased likelihood of relapse. Old/unfit AML patients still represent an urgent and unmet therapeutic need. Epigenetic deregulation represents a strategic characteristic of AML pathophysiology whereby aberrant gene transcription provides an advantage to leukemic cell survival. Efforts to re-establish impaired epigenetic regulation include hypomethylating agents and histone deacetylase inhibitors (HDACi).

AREAS COVERED

The review discusses the underlying mechanisms leading to disruption of lysine acetyltransferases (KAT or HAT)/deacetylase (KDAC or HDAC) balance and the rationale for using the HDACi panobinostat (LBH-589) in AML.

EXPERT OPINION

Although panobinostat has produced significant results in myeloma, its efficacy remains limited in AML. Panobinostat exerts pleiotropic activity and lack of specificity, which likely contributes to its inadequate safety in elderly AML patients. Phase I-II trials, utilizing panobinostat associated with well-known chemotherapeutic agents are ongoing and combinations with other druggable targets may likely be evaluated in future trials. The clinical use of this HDACi in AML the near future does not appearing promising.

Epigenomics of clear cell renal cell carcinoma: mechanisms and potential use in molecular pathology

Clear cell renal cell carcinoma (ccRCC) is one frequent form of urologic malignancy with numerous genetic and epigenetic alterations. This review summarizes the recent major findings of epigenetic alterations including DNA methylation, histone modifications, microRNAs and recently identified long noncoding RNAs in the development and progression of ccRCC. These epigenetic profilings can provide a promising means of prognostication and early diagnosis for patients with ccRCCs. With the developed high-throughput technologies nowadays, the epigenetic analyses will have possible clinical applications in the molecular pathology of ccRCC.

Lipin-1 regulates cancer cell phenotype and is a potential target to potentiate rapamycin treatment

Lipogenesis inhibition was reported to induce apoptosis and repress proliferation of cancer cells while barely affecting normal cells. Lipins exhibit dual function as enzymes catalyzing the dephosphorylation of phosphatidic acid to diacylglycerol and as co-transcriptional regulators. Thus, they are able to regulate lipid homeostasis at several nodal points. Here, we show that lipin-1 is up-regulated in several cancer cell lines and overexpressed in 50 % of high grade prostate cancers. The proliferation of prostate and breast cancer cells, but not of non-tumorigenic cells, was repressed upon lipin-1 knock-down. Lipin-1 depletion also decreased cancer cell migration through RhoA activation. Lipin-1 silencing did not significantly affect global lipid synthesis but enhanced the cellular concentration of phosphatidic acid. In parallel, autophagy was induced while AKT and ribosomal protein S6 phosphorylation were repressed. We also observed a compensatory regulation between lipin-1 and lipin-2 and demonstrated that their co-silencing aggravates the phenotype induced by lipin-1 silencing alone. Most interestingly, lipin-1 depletion or lipins inhibition with propranolol sensitized cancer cells to rapamycin. These data indicate that lipin-1 controls main cellular processes involved in cancer progression and that its targeting, alone or in combination with other treatments, could open new avenues in anticancer therapy.

Erlotinib-cisplatin combination inhibits growth and angiogenesis through c-MYC and HIF-1α in EGFR-mutated lung cancer in vitro and in vivo

Combination treatment for non–small cell lung cancer (NSCLC) is becoming more popular due to the anticipation that it may be more effective than single drug treatment. In addition, there are efforts to genetically screen patients for specific mutations in light of attempting to administer specific anticancer agents that are most effective. In this study, we evaluate the anticancer and anti-angiogenic effects of low dose erlotinib-cisplatin combination in NSCLC in vitro and in vivo. In NSCLC cells harboring epidermal growth factor receptor (EGFR) mutations, combination erlotinib-cisplatin treatment led to synergistic cell death, but there was minimal efficacy in NSCLC cells with wild-type EGFR. In xenograft models, combination treatment also demonstrated greater inhibition of tumor growth compared to individual treatment. The anti-tumor effect observed was secondary to the targeting of angiogenesis, evidenced by decreased vascular endothelial growth factor (VEGF) levels and decreased levels of CD31 and microvessel density. Combination treatment targets angiogenesis through down-regulation of the c-MYC/hypoxia inducible factor 1-alpha (HIF-1α) pathway. In fact, cell lines with EGFR exon 19 deletions expressed high basal levels of c-MYC and HIF-1α and correlate with robust responses to combination treatment. These results suggest that low dose erlotinib-cisplatin combination exhibits its anti-tumor activity by targeting angiogenesis through the modulation of the c-MYC/HIF-1α/VEGF pathway in NSCLC with EGFR exon 19 deletions. These findings may have significant clinical implications in patients with tumors harboring EGFR exon 19 deletions as they may be particularly sensitive to this regimen.

Phase I study of the mTOR inhibitor ridaforolimus and the HDAC inhibitor vorinostat in advanced renal cell carcinoma and other solid tumors

INTRODUCTION

Drugs inhibiting the mammalian target of rapamycin (mTOR) are approved in the treatment of renal cell carcinoma (RCC), but resistance inevitably emerges. Proposed escape pathways include increased phosphorylation of Akt, which can be down regulated by histone deacetylase (HDAC) inhibitors. We hypothesized that co-treatment with the mTOR inhibitor ridaforolimus and the HDAC inhibitor vorinostat may abrogate resistance in RCC.

METHODS

This phase 1 study evaluated the co-administration of ridaforolimus and vorinostat in patients with advanced solid tumors. The primary objective was to determine the maximum tolerated dose (MTD) in RCC patients. Although all solid tumors were allowed, prior cytotoxic chemotherapy was limited to 1 regimen. Using a modified 3 + 3 dose escalation design, various dose combinations were tested concurrently in separate cohorts. Efficacy was a secondary endpoint.

RESULTS

Fifteen patients were treated at one of three dose levels, thirteen with RCC (10 clear cell, 3 papillary). Dosing was limited by thrombocytopenia. The MTD was determined to be ridaforolimus 20 mg daily days 1-5 with vorinostat 100 mg BID days 1-3 weekly, however late onset thrombocytopenia led to a lower recommended phase II dose: ridaforolimus 20 mg daily days 1-5 with vorinostat 100 mg daily days 1-3 weekly. Two patients, both with papillary RCC, maintained disease control for 54 and 80 weeks, respectively.

CONCLUSIONS

The combination of ridaforolimus and vorinostat was tolerable at the recommended phase II dose. Two patients with papillary RCC experienced prolonged disease stabilization, thus further study of combined HDAC and mTOR inhibition in this population is warranted.

Epigenetic drugs for cancer treatment and prevention: mechanisms of action

This review provides a brief overview of the basic principles of epigenetic gene regulation and then focuses on recent development of epigenetic drugs for cancer treatment and prevention with an emphasis on the molecular mechanisms of action. The approved epigenetic drugs are either inhibitors of DNA methyltransferases or histone deacetylases (HDACs). Future epigenetic drugs could include inhibitors for histone methyltransferases and histone demethylases and other epigenetic enzymes. Epigenetic drugs often function in two separate yet interrelated ways. First, as epigenetic drugs per se, they modulate the epigenomes of premalignant and malignant cells to reverse deregulated epigenetic mechanisms, leading to an effective therapeutic strategy (epigenetic therapy). Second, HDACs and other epigenetic enzymes also target non-histone proteins that have regulatory roles in cell proliferation, migration and cell death. Through these processes, these drugs induce cancer cell growth arrest, cell differentiation, inhibition of tumor angiogenesis, or cell death via apoptosis, necrosis, autophagy or mitotic catastrophe (chemotherapy). As they modulate genes which lead to enhanced chemosensitivity, immunogenicity or dampened innate antiviral response of cancer cells, epigenetic drugs often show better efficacy when combined with chemotherapy, immunotherapy or oncolytic virotherapy. In chemoprevention, dietary phytochemicals such as epigallocatechin-3-gallate and sulforaphane act as epigenetic agents and show efficacy by targeting both cancer cells and the tumor microenvironment. Further understanding of how epigenetic mechanisms function in carcinogenesis and cancer progression as well as in normal physiology will enable us to establish a new paradigm for intelligent drug design in the treatment and prevention of cancer.

Novel oral histone deacetylase inhibitor, MPT0E028, displays potent growth-inhibitory activity against human B-cell lymphoma in vitro and in vivo

Histone deacetylase (HDAC) inhibitor has been a promising therapeutic option in cancer therapy due to its ability to induce growth arrest, differentiation, and apoptosis. In this study, we demonstrated that MPT0E028, a novel HDAC inhibitor, reduces the viability of B-cell lymphomas by inducing apoptosis and shows a more potent HDAC inhibitory effect compared to SAHA, the first HDAC inhibitor approved by the FDA. In addition to HDACs inhibition, MPT0E028 also possesses potent direct Akt targeting ability as measured by the kinome diversity screening assay. Also, MPT0E028 reduces Akt phosphorylation in B-cell lymphoma with an IC50 value lower than SAHA. Transient transfection assay revealed that both targeting HDACs and Akt contribute to the apoptosis induced by MPT0E028, with both mechanisms functioning independently. Microarray analysis also shows that MPT0E028 may regulate many oncogenes expression (e.g., TP53, MYC, STAT family). Furthermore, in vivo animal model experiments demonstrated that MPT0E028 (50-200 mg/kg, po, qd) prolongs the survival rate of mice bearing human B-cell lymphoma Ramos cells and inhibits tumor growth in BJAB xenograft model. In summary, MPT0E028 possesses strong in vitro and in vivo activity against malignant cells, representing a potential therapeutic approach for cancer therapy.

A novel histone deacetylase 6-selective inhibitor suppresses synovial inflammation and joint destruction in a collagen antibody-induced arthritis mouse model

AIM

To investigate the effects of Tubastatin A, a selective histone deacetylase-6 inhibitor, on synovial inflammation and joint destruction in a collagen antibody-induced arthritis (CAIA) mouse model.

METHODS

Collagen antibody-induced arthritis mice were given daily intraperitoneal injections of various concentrations of Tubastatin A (0, 10, 50, 100 mg/kg). The clinical score and paw thickness were measured. Mice were sacrificed on day 15, and the expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1 and IL-6 in the serum were analyzed using enyme-linked immunosorbent assay (ELISA). Two pathologists independently measured the synovitis score. Micro-computed tomography (CT) scans of the joints were performed to quantify joint destruction. The expression of IL-6 from human fibroblast-like synoviocytes (FLSs) after incubation with various doses of Tubastatin A (0, 0.75, 1.5, 3 μmol/L) was measured using ELISA.

RESULTS

The clinical arthritis score was significantly attenuated and paw thickness was lower in the group treated with 100 mg/kg Tubastatin A compared with those treated with vehicle alone. The synovitis score was significantly reduced in the 100 mg/kg Tubastatin A-treated group compared with the control group. Micro-CT showed that quantitative measures of joint destruction were significantly attenuated in the 100 mg/kg Tubastatin A-treated group compared with the control. The expression of IL-6 in the sera was lower in the mice treated with Tubastatin A compared with the control. The expression of IL-6 in human FLSs decreased dose-dependently after incubation with Tubastatin A without affecting cell viability.

CONCLUSIONS

Tubastatin A successfully ameliorated synovial inflammation and protected against joint destruction in CAIA mice, at least in part, by modulating IL-6 expression.

Loss-of-function RNAi screens in breast cancer cells identify AURKB, PLK1, PIK3R1, MAPK12, PRKD2, and PTK6 as sensitizing targets of rapamycin activity

The use of molecularly targeted drugs as single agents has shown limited utility in many tumor types, largely due to the complex and redundant nature of oncogenic signaling networks. Targeting of the PI3K/AKT/mTOR pathway through inhibition of mTOR in combination with aromatase inhibitors has seen success in particular sub-types of breast cancer and there is a need to identify additional synergistic combinations to maximize the clinical potential of mTOR inhibitors. We have used loss-of-function RNAi screens of the mTOR inhibitor rapamycin to identify sensitizers of mTOR inhibition. RNAi screens conducted in combination with rapamycin in multiple breast cancer cell lines identified six genes, AURKB, PLK1, PIK3R1, MAPK12, PRKD2, and PTK6 that when silenced, each enhanced the sensitivity of multiple breast cancer lines to rapamycin. Using selective pharmacological agents we confirmed that inhibition of AURKB or PLK1 synergizes with rapamycin. Compound-associated gene expression data suggested histone deacetylation (HDAC) inhibition as a strategy for reducing the expression of several of the rapamycin-sensitizing genes, and we tested and validated this using the HDAC inhibitor entinostat in vitro and in vivo. Our findings indicate new approaches for enhancing the efficacy of rapamycin including the use of combining its application with HDAC inhibition.

The role of HIF1α in renal cell carcinoma tumorigenesis

The transcription factor HIF1α is implicated in the development of clear cell renal cell carcinoma (ccRCC). Although HIF1α was initially believed to be essential for ccRCC development, recent studies hypothesize an oncogenic role for HIF2α in ccRCC, but a tumor suppressor role for HIF1α, leading to uncertainty as to the precise roles of the different HIF transcription factors in this disease. Using evidence available from studies with human ccRCC cell lines, mouse xenografts, murine models of ccRCC, and human ccRCC specimens, we evaluate the roles of HIF1α and HIF2α in the pathogenesis of ccRCC. We present a convergence of clinical and mechanistic data supporting an important role for HIF1α in promoting tumorigenesis in a clinically important and large subset of ccRCC. This indicates that current understanding of the exact roles of HIF1α and HIF2α is incomplete and that further research is required to determine the diverse roles of HIF1α and HIF2α in ccRCC.

KEY MESSAGES

The TRACK mouse ccRCC model with constitutively active HIF1α but not HIF2α expressed in proximal tubules develops RCC. HIF1α protein is expressed in the majority of human ccRCC specimens. Elevated HIF1α in ccRCC correlates with a worse prognosis. Many publications do not support a tumor suppressor role for HIF1α in ccRCC. HIF1α, but not HIF2α, is expressed in some types of cancer stem cells.

mTORC1/C2 and pan-HDAC inhibitors synergistically impair breast cancer growth by convergent AKT and polysome inhibiting mechanisms

Resistance of breast cancers to targeted hormone receptor (HR) or human epidermal growth factor receptor 2 (HER2) inhibitors often occurs through dysregulation of the phosphoinositide 3-kinase, protein kinase B/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway. Presently, no targeted therapies exist for breast cancers lacking HR and HER2 overexpression, many of which also exhibit PI3K/AKT/mTOR hyper-activation. Resistance of breast cancers to current therapeutics also results, in part, from aberrant epigenetic modifications including protein acetylation regulated by histone deacetylases (HDACs). We show that the investigational drug MLN0128, which inhibits both complexes of mTOR (mTORC1 and mTORC2), and the hydroxamic acid pan-HDAC inhibitor TSA synergistically inhibit the viability of a phenotypically diverse panel of five breast cancer cell lines (HR-/+, HER2-/+). The combination of MLN0128 and TSA induces apoptosis in most breast cancer cell lines tested, but not in the non-malignant MCF-10A mammary epithelial cells. In parallel, the MLN0128/TSA combination reduces phosphorylation of AKT at S473 more than single agents alone and more so in the 5 malignant breast cancer cell lines than in the non-malignant mammary epithelial cells. Examining polysome profiles from one of the most sensitive breast cancer cell lines (SKBR3), we demonstrate that this MLN0128/TSA treatment combination synergistically impairs polysome assembly in conjunction with enhanced inhibition of 4eBP1 phosphorylation at S65. Taken together, these data indicate that the synergistic growth inhibiting consequence of combining a mTORC1/C2 inhibitor like MLN0128 with a pan-HDAC inhibitor like TSA results from their mechanistic convergence onto the PI3K/AKT/mTOR pathway, profoundly inhibiting both AKT S473 and 4eBP1 S65 phosphorylation, reducing polysome formation and cancer cell viability.

Histone deacetylase inhibitors and epigenetic modifications as a novel strategy in renal cell carcinoma

Recent investigations of renal cell carcinoma (RCC) have revealed several epigenetic modifications, as well as alterations in the genes and enzymes that regulate these changes. Preclinical models have revealed that histone gene modifiers and epigenetic alterations may play a critical role in RCC tumorigenesis. Specific changes in DNA methylation and mutations of histone modifiers have been identified and may be associated with an aggressive phenotype. In addition, the potential of reversing the effects of these enzymes and hence reversing the cellular epigenetic landscape to a "normal phenotype" have led to an increasing interest in developing targeted chromatin remodeling agents. However, the translation of the understanding of these changes to the clinic for the treatment of RCC has posed significant challenges, partly due to tumor heterogeneity. This review describes the aberrant histone and DNA alterations recently reported in RCC and highlights the potential targeted chromatin remodeling therapies in the management of this disease.

TORC1 and class I HDAC inhibitors synergize to suppress mature B cell neoplasms

Enhanced proliferative signaling and loss of cell cycle regulation are essential for cancer progression. Increased mitogenic signaling through activation of the mTOR pathway, coupled with deregulation of the Cyclin D/retinoblastoma (Rb) pathway is a common feature of lymphoid malignancies, including plasmacytoma (PCT), multiple myeloma (MM), Burkitt's lymphoma (BL), and mantle cell lymphoma (MCL). Here we evaluate the synergy of pharmacologically affecting both of these critical pathways using the mTOR inhibitor sirolimus and the histone deacetylase inhibitor entinostat. A dose-matrix screening approach found this combination to be highly active and synergistic in a panel of genetically diverse human MM cell lines. Synergy and activity was observed in mouse PCT and human BL and MCL cell lines tested in vitro, as well as in freshly isolated primary MM patient samples tested ex vivo. This combination had minimal effects on healthy donor cells and retained activity when tested in a co-culture system simulating the protective interaction of cancer cells with the tumor microenvironment. Combining sirolimus with entinostat enhanced cell cycle arrest and apoptosis. At the molecular level, entinostat increased the expression of cell cycle negative regulators including CDKN1A (p21) and CDKN2A (p16), while the combination decreased critical growth and survival effectors including Cyclin D, BCL-XL, BIRC5, and activated MAPK.

Histone modifications: implications in renal cell carcinoma

In 2012, an estimated 64,770 men and women were diagnosed with malignancy of the kidney and renal pelvis, of which 13,570 succumbed to their disease. Common genetic aberrations in renal cell carcinomas (RCCs) include loss of function of the VHL gene in clear-cell RCC, overexpression of the c-MET gene in papillary RCC type I, deficiency in the FH gene in papillary RCC type II and loss of heterozygozity of the BHD gene in chromophobe RCC. Recent studies illustrate epigenetic silencing of VHL, as well as alterations in histone modifications and their governing enzymes. The possibility of reversing these epigenetic marks has resulted in efforts to target these changes by utilizing inhibitors of HDACs, DNA methyltransferases and, recently, histone methyltransferases in preclinical and clinical studies. This article focuses on potential therapeutic interventions, and the implications of histone modifications and related enzyme alterations in RCC.

Panobinostat synergizes with zoledronic acid in prostate cancer and multiple myeloma models by increasing ROS and modulating mevalonate and p38-MAPK pathways

Patients with advanced prostate cancer (PCa) and multiple myeloma (MM) have limited long-term responses to available therapies. The histone deacetylase inhibitor panobinostat has shown significant preclinical and clinical anticancer activity in both hematological and solid malignancies and is currently in phase III trials for relapsed MM. Bisphosphonates (BPs), such as zoledronic acid (ZOL), inhibit osteoclast-mediated bone resorption and are indicated for the treatment of bone metastasis. BPs, including ZOL, have also shown anticancer activity in several preclinical and clinical studies. In the present report, we found a potent synergistic antiproliferative effect of panobinostat/ZOL treatment in three PCa and three MM cell lines as well as in a PCa ZOL-resistant subline, independently of p53/KRAS status, androgen dependency, or the schedule of administration. The synergistic effect was also observed in an anchorage-independent agar assay in both ZOL-sensitive and ZOL-resistant cells and was confirmed in vivo in a PCa xenograft model. The co-administration of the antioxidant N-acetyl-L-cysteine blocked the increased reactive oxygen species generation and apoptosis observed in the combination setting compared with control or single-agent treatments, suggesting that oxidative injury plays a functional role in the synergism. Proapoptotic synergy was also partially antagonized by the addition of geranyl-geraniol, which bypasses the inhibition of farnesylpyrophosphate synthase by ZOL in the mevalonate pathway, supporting the involvement of this pathway in the synergy. Finally, at the molecular level, the inhibition of basal and ZOL-induced activation of p38-MAPK by panobinostat in sensitive and ZOL-resistant cells and in tumor xenografts could explain, at least in part, the observed synergism.

Targeting epigenetics for the treatment of prostate cancer: recent progress and future directions

Epigenetic aberrations contribute to prostate cancer carcinogenesis and disease progression. Efforts have been made to target DNA methyltransferase and histone deacetylases (HDACs) in prostate cancer and other solid tumors but have not had the success that was seen in the hematologic malignancies. Oral, less toxic, and more specific agents are being developed in solid tumors including prostate cancer. Combinations of epigenetic agents alone or with a targeted agent such as androgen receptor signaling inhibitors are promising approaches and will be discussed further.

Recent agents targeting HIF-1α for cancer therapy

The discovery of hypoxia-inducible factor-1 (HIF-1) has led to an increasing understanding of the mechanism of tumor hypoxia in the past two decades. As a key transcriptional regulator, HIF-1 plays a central role in the adaptation of tumor cells to hypoxia by activating the transcription of targeting genes, which regulate several biological processes including angiogenesis, cell proliferation, survival, glucose metabolism and migration. The inhibitors of HIF-1 in cancer have provided us a new clue for the targeting cancer therapy. This review will introduce the general knowledge of the biology characteristic of HIF-1 and mechanism of O(2)-dependent regulation. Moreover, a number of chemical inhibitors plus protein and nucleic acid inhibitors are included and classified mainly based on their different mechanism of inhibiting action. We also prefer to discuss the advantages of protein and nucleic acid inhibitors compared with chemical inhibitors.

Phase Ia/II, two-arm, open-label, dose-escalation study of oral panobinostat administered via two dosing schedules in patients with advanced hematologic malignancies

Panobinostat is a potent oral pandeacetylase inhibitor that leads to acetylation of intracellular proteins, inhibits cellular proliferation and induces apoptosis in leukemic cell lines. A phase Ia/II study was designed to determine the maximum-tolerated dose (MTD) of daily panobinostat, administered on two schedules: three times a week every week or every other week on a 28-day treatment cycle in patients with advanced hematologic malignancies. The criteria for hematologic dose-limiting toxicities differed between patients with indications associated with severe cytopenias at baseline (leukemia and myeloid disorders) and those less commonly associated with baseline cytopenias (lymphoma and myeloma). In patients with leukemia and myeloid disorders, 60 mg was the MTD for weekly as well as biweekly panobinostat. In patients with lymphoma and myeloma, 40 mg was the recommended dose for phase II evaluation (formal MTD not determined) of weekly panobinostat, and 60 mg was the MTD for biweekly panobinostat. Overall, panobinostat-related grade 3-4 adverse events included thrombocytopenia (41.5%), fatigue (21%) and neutropenia (21%). Single-agent activity was observed in several indications, including Hodgkin lymphoma and myelofibrosis. This phase Ia/II study provided a broad analysis of the safety profile and efficacy of single-agent panobinostat in patients with hematologic malignancies.

A phase I dose-escalation study of intravenous panobinostat in patients with lymphoma and solid tumors

PURPOSE

Panobinostat, a pan-deacetylase inhibitor, is a promising anti-cancer agent that increases acetylation of proteins associated with growth and survival pathways of malignant cells. The primary objective of this phase I dose-escalation study was to determine the maximum tolerated dose (MTD) of intravenous (i.v.) panobinostat administered on different dosing schedules in patients with advanced solid tumors or lymphoma. Secondary objective was to characterize safety and tolerability, pharmacokinetic profiles, and activities of the i.v. formulation.

METHODS

i.v. panobinostat was administered at escalating doses on a daily (days 1-3 and 8-10 of a 21-day cycle; days 1-3 and 15-17 of a 28-day cycle) or weekly (days 1, 8, and 15 of a 28-day cycle; days 1 and 8 of a 21-day cycle) schedule, and safety and tolerability were monitored. Serial blood samples were collected following dosing for pharmacokinetic and pharmacodynamic analyses.

RESULTS

The MTD for the daily administration schedule was 7.2 g/m(2), whereas the MTD for the weekly schedule was 20.0 mg/m(2). In addition to fatigue and cardiac arrhythmias, including prolonged QTcF, DLTs associated with the study drug were principally due to myelosuppressive effects. Maximum concentrations and bioavailability of i.v. panobinostat increased dose-proportionally across all doses evaluated.

CONCLUSIONS

Based on the results of this study and others, the i.v. formulation of panobinostat was well tolerated in many patients, but concerns remain regarding its potential suitability outside the study setting due to potential electrocardiogram abnormalities. Therefore, further development will focus on the panobinostat oral formulation.

Brucine, an indole alkaloid from Strychnos nux-vomica attenuates VEGF-induced angiogenesis via inhibiting VEGFR2 signaling pathway in vitro and in vivo

In this study, we investigated the mechanism of brucine in tumor angiogenesis. We found that brucine inhibits VEGF-induced cell proliferation, chemotactic motility, and the formation of capillary-like structures in HUVECs in a dose-dependent manner. Brucine suppresses VEGF- induced p-VEGFR2 kinase activity and inhibits neovascularization in vivo. Brucine inhibits the downstream protein kinases of VEGFR2, including Src, FAK, ERK, AKT and mTOR. And further downregulates levels of VEGF, NO, IL-6, IL-8, TNF-α and IFN-γ in HUVECs. Taken together, our study suggests that brucine potently suppresses angiogenesis by targeting VEGFR2 activation and may be a viable drug candidate in anti-angiogenesis and anti-cancer therapies.

Treating breast cancer in the 21st century: emerging biological therapies

For many years, the medical treatment of breast cancer was reliant solely on cytotoxic chemotherapy. However, over the past twenty years, treatment has evolved to a more target-directed approach. We now employ tailored therapy based on the presence or absence of receptors for estrogen, progesterone, and human epidermal growth factor 2 (HER2). We expect this trend to continue, as agents that use novel approaches to target HER2, as well as targeting different portions of the HER signaling pathway, are in various stages of development. Notably, pertuzumab, a humanized monoclonal antibody that binds to a different domain of the extracellular portion of the HER2 receptor than trastuzumab, was recently approved for use, as was lapatinib, a small-molecule tyrosine kinase inhibitor. Patients with triple negative breast cancer, particularly those with the BRCA mutation, have more limited treatment options and carry a worse prognosis than those who are hormone receptor positive. However, recent data has shown that PARP inhibitors may have significant anti-tumor effect in those with this subtype of breast cancer. Novel agents that inhibit mTOR, PI3K, the insulin-like growth factor, heat shock protein 90, and histone deacetylase have shown promise in phase I-III trials and offer exciting new possibilities for the treatment of this often fatal disease. As we are presented with an ever increasing number of treatment options, the timing and combinations of therapeutic agents used becomes ever more complex in the age of personalized care, but we are hopeful that ultimately this will lead to improved patient outcomes.

HDAC inhibitors in kidney development and disease

The discovery that histone deacetylase inhibitors (HDACis) can attenuate acute kidney injury (AKI)-mediated damage and reduce fibrosis in kidney disease models has opened the possibility of utilizing HDACis as therapeutics for renal injury. Studies to date have made it abundantly clear that HDACi treatment results in a plethora of molecular changes, which are not always linked to histone acetylation, and that there is an essential need to understand the specific target(s) of any HDACi of interest. New lines of investigation are beginning to delve more deeply into target identification of specific HDACis and to address the relative toxicity of different HDACi classes. This review will focus on the utilization of HDACis during kidney organogenesis, injury, and disease, as well as on the development of these compounds as therapeutics.

Dual targeting of mTOR and aurora-A kinase for the treatment of uterine Leiomyosarcoma

PURPOSE

The significance of mTOR activation in uterine leiomyosarcoma (ULMS) and its potential as a therapeutic target were investigated. Furthermore, given that effective therapies likely require combination mTOR blockade with inhibition of other targets, coupled with recent observations suggesting that Aurora-A kinase (Aurk-A) deregulations commonly occur in ULMS, the preclinical impact of dually targeting both pathways was evaluated.

EXPERIMENTAL DESIGN

Immunohistochemical staining was used to evaluate expression of activated mTOR components in a large (>200 samples) ULMS tissue microarray. Effects of mTOR blockade (using rapamycin) and Aurk-A inhibition (using MLN8237) alone and in combination on human ULMS cell growth, cell-cycle progression, and apoptosis were assessed in cellular assays. Drug interactions were determined via combination index analyses. The antitumor effects of inhibitors alone or in combination were evaluated in vivo.

RESULTS

Enhanced mTOR activation was seen in human ULMS samples. Increased pS6RP and p4EBP1 expression correlated with disease progression; p4EBP1 was found to be an independent prognosticator of patient outcome. Rapamycin inhibited growth and cell-cycle progression of ULMS cell strains/lines in culture. However, only a cytostatic effect on tumor growth was found in vivo. Combining rapamycin with MLN8237 profoundly (and synergistically) abrogated ULMS cells' growth in culture; interestingly, these effects were seen only when MLN8237 was preadministered. This novel therapeutic combination and scheduling regimen resulted in marked tumor growth inhibition in vivo.

CONCLUSIONS

mTOR and Aurk-A pathways are commonly deregulated in ULMS. Preclinical data support further exploration of dual mTOR and Aurk-A therapeutic blockade for human ULMS.

Epigenetics of kidney cancer and bladder cancer

This article focuses on the epigenetic alterations of aberrant promoter hypermethylation of genes, and histone modifications or RNA interference in cancer cells. Current knowledge of the hypermethylation of allele(s) in classical tumor suppressor genes in inherited and sporadic cancer, candidate tumor suppressor and other cancer genes is summarized gene by gene. Global and array-based studies of tumor cell hypermethylation are discussed. The importance of standardization of scoring of the methylation status of a gene is highlighted. The histone marks associated with hypermethylated genes, and the miRNAs with dysregulated expression, in kidney or bladder tumor cells are also discussed. Kidney cancer has the highest mortality rate of the genito-urinary cancers. There are management issues associated with the high recurrence rate of superficial bladder cancer, while muscle-invasive bladder cancer has a poor prognosis. These clinical problems are the basis for the translational application of gene hypermethylation in the diagnosis and prognosis of kidney and bladder cancer.

Molecular pathways: old drugs define new pathways: non-histone acetylation at the crossroads of the DNA damage response and autophagy

Histone deacetylases (HDAC) modulate acetylation and the function of histone and non-histone proteins. HDAC inhibitors have been developed to block the aberrant action of HDACs in cancer, and several are in clinical use (vorinostat, romidepsin, and valproic acid). Detailed understanding of their action is lacking, however, and their clinical activity is limited in most cases. Recently, HDACs have been involved in the control of the DNA damage response (DDR) at several levels and in directly regulating the acetylation of a number of DDR proteins (including CtIP and Exo1). Mechanistically, acetylation leads to the degradation of double-strand break repair enzymes through autophagy, providing a novel, direct link between DDR and autophagy. These observations, obtained in yeast cells, should now be translated to mammalian model systems and cancer cells to reveal whether this acetylation link is maintained in mammals, and if and how it is deregulated in cancer. In addition to HDACs, DDR and autophagy have been addressed pharmacologically, suggesting that the acetylation link, if involved in cancer, can be exploited for the design of new anticancer treatments.