The in vitro and in vivo effects of re-expressing methylated von Hippel-Lindau tumor suppressor gene in clear cell renal carcinoma with 5-aza-2'-deoxycytidine

Targeting tumor endothelial cells with methyltransferase inhibitors: Mechanisms of action and the potential of combination therapy

Tumor endothelial cells (TECs) reside in the inner lining of blood vessels and represent a promising target for targeted cancer therapy. DNA methylation is a chemical process that involves the transfer of a methyl group to a specific base in the DNA strand, catalyzed by DNA methyltransferase (DNMT). DNMT inhibitors (DNMTis) can inhibit the activity of DNMTs, thereby preventing the transfer of methyl groups from s-adenosyl methionine (SAM) to cytosine. Currently, the most viable therapy for TECs is the development of DNMTis to release cancer suppressor genes from their repressed state. In this review, we first outline the characteristics of TECs and describe the development of tumor blood vessels and TECs. Abnormal DNA methylation is closely linked to tumor initiation, progression, and cell carcinogenesis, as evidenced by numerous studies. Therefore, we summarize the role of DNA methylation and DNA methyltransferase and the therapeutic potential of four types of DNMTi in targeting TECs. Finally, we discuss the accomplishments, challenges, and opportunities associated with combination therapy with DNMTis for TECs.

Major heritable renal cell carcinoma syndromes: novel treatment options and future perspectives

PURPOSE OF REVIEW

To provide an overview of diagnosis, genetic abnormalities, clinical signs and treatment options for the major heritable renal cell carcinoma (RCC) syndromes.

RECENT FINDINGS

RCC in major hereditary syndromes are disorders which are typically autosomal dominant. They predispose patients to early onset of RCC and may exhibit other extrarenal manifestations. Early recognition of these diseases allows correct screening at appropriate ages as well as early detection of RCC. Moreover, expedient identification may optimize the management of extra renal manifestations as well as allow for genetic testing and screening of at-risk relatives.

SUMMARY

The risk of RCC in these major heritable syndromes is higher than sporadic disease. They occur at earlier age groups and can be multifocal or bilateral. Tumours are observed until at least 3 cm before any intervention, while nephron sparing surgery is widely considered as the treatment of choice except for hereditary leiomyomatosis with renal cell cancer, of which radical nephrectomy is treatment of choice. Intervention should be timeous as there is a highly reported incidence of early metastasis. Molecular therapies have been used in the setting of patients with metastasis, some of which show favourable outcomes.

Differential sensitivity of renal carcinoma cells to doxorubicin and epigenetic therapeutics depends on the genetic background

Differential sensitivity to chemotherapeutics is a limitation in chemotherapy of kidney cancer patients. Role of genetic background in chemotherapy is not fully understood. Therefore, this study evaluated the influence of genetic/epigenetic background of renal cancer cells on the sensitivity to chemotherapeutics. Two renal cell carcinoma (RCC) cell lines, Caki-1 and 786-0, with different genetic makeup of p53 and VHL were treated with doxorubicin either alone or in combination with epigenetic therapeutics 5-aza-2-dc and TSA. Sensitivity of RCC cells to these drugs was evaluated by cell viability and cell cycle analysis and was further confirmed by analysis of selected genes expression. Cell viability data revealed that 786-0 cells were more sensitive than Caki-1 to doxorubicin. Combination of doxorubicin with 5-aza-2-dc or TSA was more effective to inhibit growth of Caki-1 cells but not the 786-0. Data of cell cycle analysis and expression of representative genes for tumor suppressor, cell cycle and survival, drug transporter and DNA repair further provided the molecular basis for differential sensitivity of Caki-1 and 786-0 cell lines to doxorubicin. Important findings of this study suggest that doxorubicin is more cytotoxic to primary renal cancer 786-0 cells with mutant VHL and p53 than the metastatic Caki-1 cells with wild-type VHL and p53, and this differential response was independent of p53 expression level. This study suggests that combination of doxorubicin with epigenetic therapeutics could potentially be beneficial in clinical treatment of renal cancer patients with wild-type VHL and p53 but not in patients with mutant VHL and p53.

Incorporating DNA Methyltransferase Inhibitors (DNMTis) in the Treatment of Genitourinary Malignancies: A Systematic Review

Inhibition of DNA methyltransferases (DNMTs) has emerged as a novel treatment strategy in solid tumors. Aberrant hypermethylation in promoters of critical tumor suppressor genes is the basis for the idea that treatment with hypomethylating agents may lead to the restoration of a "normal" epigenome and produce clinically meaningful therapeutic outcomes. The aim of this review article is to summarize the current state of knowledge of DNMT inhibitors in the treatment of genitourinary malignancies. The efficacy of these agents in genitourinary malignancies was reported in a number of studies and suggests a role of induced DNA hypomethylation in overcoming resistance to conventional cytotoxic treatments. The clinical significance of these findings should be further investigated.

Population Pharmacokinetic Analysis of Decitabine in Pediatric Patients With Acute Myeloid Leukemia

Dacogen, the formulated product of the pharmaceutically active agent decitabine (5 aza-2'-deoxycytidine), is approved for treatment of myelodysplastic syndromes (MDSs) and acute myeloid leukemia (AML). The current analysis was performed to characterize the pharmacokinetics of decitabine in pediatric patients with AML and evaluate their consistency with the PK in adult patients. A population pharmacokinetic model was developed by pooling decitabine concentration-time data from 5 adult (AML and MDS) and 2 pediatric (AML) studies. A total of 840 concentration-time data points obtained from 71 adults and 28 pediatric subjects (1 to 16 years old) were available for analysis. A 2-compartment linear pharmacokinetic (PK) model with allometric scaling using body surface area accounting for body size adequately described the PK of decitabine. After accounting for body size, decitabine pharmacokinetics were not affected by age, sex, race, dosing regimen, renal function (creatinine clearance), bilirubin, or disease type (AML or MDS) and all PK parameters (including clearance, steady-state volume of distribution, maximum concentration, time to reach maximal concentration, and terminal half-life) were comparable between adult and pediatric patients. Simulated concentration-time profiles using the final population PK model suggested that decitabine exposure at steady state was similar in adults and pediatrics for a 20 mg/m² decitabine dose administered as a 1-hour infusion once daily. The current analysis suggests that decitabine PK is similar in pediatric AML patients and a combined adult AML and MDS population.

Targeting DNA Methyltranferases in Urological Tumors

Urological cancers are a heterogeneous group of malignancies accounting for a considerable proportion of cancer-related morbidity and mortality worldwide. Aberrant epigenetic traits, especially altered DNA methylation patterns constitute a hallmark of these tumors. Nonetheless, these alterations are reversible, and several efforts have been carried out to design and test several epigenetic compounds that might reprogram tumor cell phenotype back to a normal state. Indeed, several DNMT inhibitors are currently under evaluation for therapeutic efficacy in clinical trials. This review highlights the critical role of DNA methylation in urological cancers and summarizes the available data on pre-clinical assays and clinical trials with DNMT inhibitors in bladder, kidney, prostate, and testicular germ cell cancers.

UV-induced proteolysis of RNA polymerase II is mediated by VCP/p97 segregase and timely orchestration by Cockayne syndrome B protein

RNA polymerase II (RNAPII) acts as a damage sensor for transcription-coupled nucleotide excision repair (TC-NER) and undergoes proteolytic clearance from damaged chromatin by the ubiquitin-proteasome system (UPS). Here, we report that Valosin-containing protein (VCP)/p97, a druggable oncotarget, is essential for RNAPII's proteolytic clearance in mammalian cells. We show that inhibition of VCP/p97, or siRNA-mediated ablation of VCP/p97 and its cofactors UFD1 and UBXD7 severely impairs ultraviolet radiation (UVR)-induced RNAPII degradation. VCP/p97 interacts with RNAPII, and the interaction is enhanced by Cockayne syndrome B protein (CSB). However, the VCP/p97-mediated RNAPII proteolysis occurs independent of CSB. Surprisingly, CSB enhances UVR-induced RNAPII ubiquitination but delays its turnover. Additionally, VCP/p97-mediated RNAPII turnover occurs with and without Von Hippel-Lindau tumor suppressor protein (pVHL), a known substrate receptor of Elongin E3 ubiquitin ligase for RNAPII. Moreover, pVHL re-expression improves cell viability following UVR. Whereas, VCP/p97 inhibition decreases cell viability and enhances a low-dose UVR killing in presence of pVHL. These findings reveal a function of VCP/p97 segregase in UVR-induced RNAPII degradation in mammalian cells, and suggest a role of CSB in coordinating VCP/p97-mediated extraction of ubiquitinated RNAPII and CSB itself from chromatin.

Neurological Management of Von Hippel-Lindau Disease

Von Hippel-Lindau disease is a genetic condition due to mutation of the Von Hippel-Lindau gene, which leads to an increased risk in the development of hemangioblastomas of the brain and spinal cord. The pathophysiology of disease and its clinical manifestations, as they pertain to the general neurologist, are discussed. Therapeutic management of central nervous system hemangioblastomas ranging from neurosurgical resection, radiation therapy, and systemic therapies is reviewed.

VHL-deficient renal cancer cells gain resistance to mitochondria-activating apoptosis inducers by activating AKT through the IGF1R-PI3K pathway

We previously developed (2-deoxyglucose)-(ABT-263) combination therapy (2DG-ABT), which induces apoptosis by activating Bak in the mitochondria of highly glycolytic cells with varied genetic backgrounds. However, the rates of apoptosis induced by 2DG-ABT were lower in von Hippel-Lindau (VHL)-deficient cancer cells. The re-expression of VHL protein in these cells lowered IGF1R expression in a manner independent of oxygen concentration. Lowering IGF1R expression via small interfering RNA (siRNA) sensitized the cells to 2DG-ABT, suggesting that IGF1R interfered with the activation of apoptosis by the mitochondria. To determine which of the two pathways activated by IGF1R, the Ras-ERK pathway or the PI3K-AKT pathway, was involved in the impairment of mitochondria activation, the cells were treated with a specific inhibitor of either PI3K or ERK, and 2DG-ABT was added to activate the mitochondria. The apoptotic rates resulting from 2DG-ABT treatment were higher in the cells treated with the PI3K inhibitor, while the rates remained approximately the same in the cells treated with the ERK inhibitor. In 2DG-ABT-sensitive cells, a 4-h 2DG treatment caused the dissociation of Mcl-1 from Bak, while ABT treatment alone caused the dissociation of Bcl-xL from Bak without substantially reducing Mcl-1 levels. In 2DG-ABT-resistant cells, Mcl-1 dissociated from Bak only when AKT activity was inhibited during the 4-h 2DG treatment. Thus, in VHL-deficient cells, IGF1R activated AKT and stabilized the Bak-Mcl-1 complex, thereby conferring cell resistance to apoptosis.

Turning on the Radio: Epigenetic Inhibitors as Potential Radiopriming Agents

First introduced during the late 1800s, radiation therapy is fundamental to the treatment of cancer. In developed countries, approximately 60% of all patients receive radiation therapy (also known as the sixty percenters), which makes radioresistance in cancer an important and, to date, unsolved, clinical problem. Unfortunately, the therapeutic refractoriness of solid tumors is the rule not the exception, and the ubiquity of resistance also extends to standard chemotherapy, molecularly targeted therapy and immunotherapy. Based on extrapolation from recent clinical inroads with epigenetic agents to prime refractory tumors for maximum sensitivity to concurrent or subsequent therapies, the radioresistant phenotype is potentially reversible, since aberrant epigenetic mechanisms are critical contributors to the evolution of resistant subpopulations of malignant cells. Within the framework of a syllogism, this review explores the emerging link between epigenetics and the development of radioresistance and makes the case that a strategy of pre- or co-treatment with epigenetic agents has the potential to, not only derepress inappropriately silenced genes, but also increase reactive oxygen species production, resulting in the restoration of radiosensitivity.

Epigenetic modulators mitigate angiogenesis through a complex transcriptomic network

In this review, we summarize the knowledge pertaining to the role of epigenetics in the regulation of angiogenesis. In particular, we show that lysine acetylation and cytosine methylation are important transcriptional regulators of angiogenic genes in endothelial cells. Lysine acetylation and cytosine methylation inhibitors idiosyncratically tune the transcriptome and affect expression of key modulators of angiogenesis such as VEGF and eNOS. Transcriptomic profiling also reveals a series of novel genes that are concomitantly affected by epigenetic modulators. The reversibility and overall tolerability of currently available epigenetic inhibitors open up the prospect of therapeutic intervention in pathologies where angiogenesis is exacerbated. This type of multitargeted strategy has the major advantage of overcoming the compensatory feedback mechanisms that characterize single anti-angiogenic factors.

Hereditary kidney cancer syndromes

Inherited susceptibility to kidney cancer is a fascinating and complex topic. Our knowledge about types of genetic syndromes associated with an increased risk of disease is continually expanding. Currently, there are 10 syndromes associated with an increased risk of all types of kidney cancer, which are reviewed herein. Clear cell kidney cancer is associated with von Hippel Lindau disease, chromosome 3 translocations, PTEN hamartomatous syndrome, and mutations in the BAP1 gene as well as several of the genes encoding the proteins comprising the succinate dehydrogenase complex (SDHB/C/D). Type 1 papillary kidney cancers arise in conjunction with germline mutations in MET and type 2 as part of hereditary leiomyomatosis and kidney cell cancer (fumarate hydratase [FH] mutations). Chromophone and oncocytic kidney cancers are predominantly associated with Birt-Hogg-Dubé syndrome. Patients with Tuberous Sclerosis Complex (TSC) commonly have angiomyolipomas and rarely their malignant counterpart epithelioid angiomyolipomas. The targeted therapeutic options for the kidney cancer associated with these diseases are just starting to expand and are an area of active clinical research.

Methylation profiling and evaluation of demethylating therapy in renal cell carcinoma

BACKGROUND

Despite therapeutic advances in targeted therapy, metastatic renal cell carcinoma (RCC) remains incurable for the vast majority of patients. Key molecular events in the pathogenesis of RCC include inactivation of the VHL tumour suppressor gene (TSG), inactivation of chromosome 3p TSGs implicated in chromatin modification and remodelling and de novo tumour-specific promoter methylation of renal TSGs. In the light of these observations it can be proposed that, as in some haematological malignancies, demethylating agents such as azacitidine might be beneficial for the treatment of advanced RCC.

RESULTS

Here we report that the treatment of RCC cell lines with azacitidine suppressed cell proliferation in all 15 lines tested. A marked response to azacitidine therapy (>50% reduction in colony formation assay) was detected in the three cell lines with VHL promoter methylation but some RCC cell lines without VHL TSG methylation also demonstrated a similar response suggesting that multiple methylated TSGs might determine the response to demethylating therapies. To identify novel candidate methylated TSGs implicated in RCC we undertook a combined analysis of copy number and CpG methylation array data. Candidate novel epigenetically inactivated TSGs were further prioritised by expression analysis of RCC cell lines pre and post-azacitidine therapy and comparative expression analysis of tumour/normal pairs. Thus, with subsequent investigation two candidate genes were found to be methylated in more than 25% of our series and in the TCGA methylation dataset for 199 RCC samples: RGS7 (25.6% and 35.2% of tumours respectively) and NEFM in (25.6% and 30.2%). In addition three candidate genes were methylated in >10% of both datasets (TMEM74 (15.4% and 14.6%), GCM2 (41.0% and 14.6%) and AEBP1 (30.8% and 13.1%)). Methylation of GCM2 (P = 0.0324), NEFM (P = 0.0024) and RGS7 (P = 0.0067) was associated with prognosis.

CONCLUSIONS

These findings provide preclinical evidence that treatment with demethylating agents such as azacitidine might be useful for the treatment of advanced RCC and further insights into the role of epigenetic changes in the pathogenesis of RCC.

Thrombospondin-1 expression in melanoma is blocked by methylation and targeted reversal by 5-Aza-deoxycytidine suppresses angiogenesis

BACKGROUND

Reversibility of aberrant methylation via pharmacological means is an attractive target for therapies through epigenetic reprogramming. To establish that pharmacologic reversal of methylation could result in functional inhibition of angiogenesis, we undertook in vitro and in vivo studies of thrombospondin-1 (TSP1), a known inhibitor of angiogenesis. TSP1 is methylated in several malignancies, and can inhibit angiogenesis in melanoma xenografts. We analyzed effects of 5-Aza-deoxycytidine (5-Aza-dC) on melanoma cells in vitro to confirm reversal of promoter hypermethylation and restoration of TSP1 expression. We then investigated the effects of TSP1 expression on new blood vessel formation and tumor growth in vivo. Finally, to determine potential for clinical translation, the methylation status of TSP1 promoter regions of nevi and melanoma tissues was investigated.

RESULTS

5-Aza-dC reduced DNA (cytosine-5)-methyltransferase 1 (DNMT1) protein, reversed promoter hypermethylation, and restored TSP1 expression in five melanoma cell lines, while having no effect on TSP1 protein levels in normal human melanocytes. In in vivo neovascularization studies, mice were implanted with melanoma cells (A375) either untreated or treated with 5Aza-dC. Vessels at tumor sites were counted by an observer blinded to treatments and the number of tumor vessels was significantly decreased at pretreated tumor sites. This difference occurred before a significant difference in tumor volumes was seen, yet in further studies the average tumor volume in mice treated in vivo with 5-Aza-dC was decreased by 55% compared to untreated controls. Knockdown of TSP1 expression with shRNA enhanced tumor-induced angiogenesis by 68%. Analyses of promoter methylation status of TSP1 in tumors derived from untreated and treated mice identified 67% of tumors from untreated and 17% of tumors from treated mice with partial methylation consistent with the methylation specific PCR analysis of A375 cells. Examination of methylation patterns in the promoter of TSP1 and comparison of aberrantly methylated TSP1 in melanoma with non-malignant nevi identified a significantly higher frequency of promoter methylation in tumor samples from melanoma patients.

CONCLUSIONS

Pharmacological reversal of methylation silenced TSP1 had functional biological consequences in enhancing angiogenesis inhibition and inducing antitumor effects to decrease murine melanoma growth. Angiogenesis inhibition is an additional mechanism by which epigenetic modulators can have antitumor effects.

The Warburg effect: insights from the past decade

Several decades ago, Otto Warburg discovered that cancer cells produce energy predominantly by glycolysis; a phenomenon now termed "Warburg effect". Warburg linked mitochondrial respiratory defects in cancer cells to aerobic glycolysis; this theory of his gradually lost its importance with the lack of conclusive evidence confirming the presence of mitochondrial defects in cancer cells. Scientists began to believe that this altered mechanism of energy production in cancer cells was more of an effect than the cause. More than 50 years later, the clinical use of FDG-PET imaging in the diagnosis and monitoring of cancers rekindled the interest of the scientific community in Warburg's hypothesis. In the last ten years considerable progress in the field has advanced our understanding of the Warburg effect. However, it still remains unclear if the Warburg effect plays a causal role in cancers or it is an epiphenomenon in tumorigenesis. In this review we aim to discuss the molecular mechanisms associated with the Warburg effect with emphasis on recent advances in the field including the role of epigenetic changes, miRNAs and post-translational modification of proteins. In addition, we also discuss emerging therapeutic strategies that target the dependence of cancer cells on altered energy processing through aerobic glycolysis.

Gene expression profiling of the synergy of 5-aza-2'-deoxycytidine and paclitaxel against renal cell carcinoma

Background

Renal cell carcinoma (RCC) is one of the most common kidney cancers and is highly resistant to chemotherapy. We previously demonstrated that 5-aza-2^′-deoxycytidine (DAC) could significantly increase the susceptibility of renal cell carcinoma (RCC) cells to paclitaxel (PTX) treatment in vitro, and showed the synergy of DAC and PTX against RCC. The purpose of this study is to investigated the gene transcriptional alteration and investigate possible molecular mechanism and pathways implicated in the synergy of DAC and PTX against RCC.

Methods

cDNA microarray was performed and coupled with real-time PCR to identify critical genes in the synergistic mechanism of both agents against RCC cells. Various patterns of gene expression were observed by cluster analysis. IPA software was used to analyze possible biological pathways and to explore the inter-relationships between interesting network genes.

Results

We found that lymphoid enhancer-binding factor 1 (LEF1), transforming growth factor β-induced (TGFBI), C-X-C motif ligand 5 (CXCL5) and myelocytomatosis viral related oncogene (c-myc) may play a pivotal role in the synergy of DAC and PTX. The PI3K/Akt pathway and other pathways associated with cyclins, DNA replication and cell cycle/mitotic regulation were also associated with the synergy of DAC and PTX against RCC.

Conclusion

The activation of PI3K/Akt-LEF1/β-catenin pathway could be suppressed synergistically by two agents and that PI3K/Akt-LEF1/β-catenin pathway is participated in the synergy of two agents.

Von Hippel-Lindau disease (VHL): a need for a murine model with retinal hemangioblastoma

Von Hippel-Lindau (VHL) disease is a highly penetrant autosomal dominant systemic malignancy that gives rise to cystic and highly vascularized tumors in a constellation of organs. Patients with VHL disease commonly present with hemangioblastomas in the central nervous system and the eye while other manifestations include pheochromocytoma, clear cell renal cell carcinoma, endolymphatic sac tumors of the middle ear, pancreatic cystadenomas, epididymal and broad ligament cystadenomas. Animal models inactivating the VHL gene product in various organ tissues have been constructed over the past 15 years to parse its HIF-associated mechanisms and its link to tumorigenesis. These models, despite advancing our understanding the molecular role of VHL, are by and large unable to recapitulate the more common features of human VHL disease. Up to date, no model exists that develop retinal hemangioblastomas, the most common clinical manifestation. The purpose of this review is: (1) to discuss the need for an ocular VHL model, (2) to review the animal models that recapitulate clinical VHL disease and (3) to propose potential mechanisms of tumorigenesis for the development of ocular VHL.

MG98, a second-generation DNMT1 inhibitor, in the treatment of advanced renal cell carcinoma

BACKGROUND

In carcinogenesis, methylation of DNA promoter regions results in inactivation of tumor-suppressing genes. MG98 was designed to inhibit DNA methyltransferases enzyme 1 production.

METHODS

This multicenter study explored two schedules of MG98 with Interferon-α-2β to identify schedule and dose for patients with metastatic RCC.

RESULTS

Doses of IFN 9 MIU/MG98 125 mg/m(2) for a continuous schedule and IFN 9 MIU/MG98 200 mg/m(2) for an intermittent schedule were considered the MTDs. Treatment resulted in one PR and eight SD.

CONCLUSION

MG98 combined with IFN was safe and resulted in clinical activity.

Suffocating cancer: hypoxia-associated epimutations as targets for cancer therapy

Lower than normal levels of oxygen (hypoxia) is a hallmark of all solid tumours rendering them frequently resistant to both radiotherapy and chemotherapy regimes. Furthermore, tumour hypoxia and activation of the hypoxia inducible factor (HIF) transcriptional pathway is associated with poorer prognosis. Driven by both genetic and epigenetic changes, cancer cells do not only survive but thrive in hypoxic conditions. Detailed knowledge of these changes and their functional consequences is of great clinical utility and is already helping to determine phenotypic plasticity, histological tumour grading and overall prognosis and survival stratification in several cancer types. As epigenetic changes - contrary to genetic changes - are potentially reversible, they may prove to be potent therapeutic targets to add to the cancer physicians' armorarium in the future.Here, we review the therapeutic potential of epigenetic modifications (including DNA methylation, histone modifications and miRNAs) occurring in hypoxia with particular reference to cancer and tumourigenesis.

Noncytotoxic differentiation treatment of renal cell cancer

Current drug therapy for metastatic renal cell cancer (RCC) results in temporary disease control but not cure, necessitating continued investigation into alternative mechanistic approaches. Drugs that inhibit chromatin-modifying enzymes involved in transcription repression (chromatin-relaxing drugs) could have a role, by inducing apoptosis and/or through differentiation pathways. At low doses, the cytosine analogue decitabine (DAC) can be used to deplete DNA methyl-transferase 1 (DNMT1), modify chromatin, and alter differentiation without causing apoptosis (cytotoxicity). Noncytotoxic regimens of DAC were evaluated for in vitro and in vivo efficacy against RCC cell lines, including a p53-mutated RCC cell line developed from a patient with treatment-refractory metastatic RCC. The cell division-permissive mechanism of action-absence of early apoptosis or DNA damage, increase in expression of HNF4α (hepatocyte nuclear factor 4α), a key driver associated with the mesenchymal to epithelial transition, decrease in mesenchymal marker expression, increase in epithelial marker expression, and late increase in cyclin-dependent kinase inhibitor CDKN1B (p27) protein-was consistent with differentiation-mediated cell-cycle exit. In vivo blood counts and animal weights were consistent with minimal toxicity of therapy. The distinctive mechanism of action of a dose and schedule of DAC designed for noncytotoxic depletion of DNMT1 suggests a potential role in treating RCC.

The Expanding Mi-2/NuRD Complexes: A Schematic Glance

This mini-review will schematically update the progress of the expanding Mi-2/Nucleosome Remodeling Deacetylase (NuRD) complexes in cancer and in normal development such as stemness, with a focus on mammals and the increasingly popular and powerful model organism Caenorhabditis elegans. The Mi-2/NuRD complexes control gene activity during the development of complex organisms. Every Mi-2/NuRD complex contains many different core polypeptides, which form distinct multifunctional complexes with specific context-dependent regulators. The Mi-2/NuRD complexes have unique ATP-dependent chromatin remodeling, histone deacetylase, demethylase activities and higher order chromatin organization. They can regulate the accessibility of transcription factors or repair proteins to DNA. In this review, we summarize our current knowleges in the composition, interaction and function of the subunits within the Mi-2/NuRD complex, the methodology used for the identification of Mi-2/NuRD complexes, as well as the clinical and therapeutic implications targeting the Mi-2/NuRD subunits.

Biological rationale for the use of DNA methyltransferase inhibitors as new strategy for modulation of tumor response to chemotherapy and radiation

Epigenetic modifications play a key role in the patho-physiology of many tumors and the current use of agents targeting epigenetic changes has become a topic of intense interest in cancer research. DNA methyltransferase (DNMT) inhibitors represent a promising class of epigenetic modulators. Research performed yielded promising anti-tumorigenic activity for these agents in vitro and in vivo against a variety of hematologic and solid tumors. These epigenetic modulators cause cell cycle and growth arrest, differentiation and apoptosis. Rationale for combining these agents with cytotoxic therapy or radiation is straightforward since the use of DNMT inhibitor offers greatly improved access for cytotoxic agents or radiation for targeting DNA-protein complex. The positive results obtained with these combined approaches in preclinical cancer models demonstrate the potential impact DNMT inhibitors may have in treatments of different cancer types. Therefore, as the emerging interest in use of DNMT inhibitors as a potential chemo- or radiation sensitizers is constantly increasing, further clinical investigations are inevitable in order to finalize and confirm the consistency of current observations.The present article will provide a brief review of the biological significance and rationale for the clinical potential of DNMT inhibitors in combination with other chemotherapeutics or ionizing radiation. The molecular basis and mechanisms of action for these combined treatments will be discussed herein.

LW6, a novel HIF-1 inhibitor, promotes proteasomal degradation of HIF-1alpha via upregulation of VHL in a colon cancer cell line

Hypoxia-inducible factor HIF-1 is responsible for radiation resistance and poor prognosis in cancer therapy. As part of our drug discovery program, a novel HIF inhibitor, LW6, was identified as a small compound that inhibits the accumulation of HIF-1alpha. We found that LW6 decreased HIF-1alpha protein expression without affecting HIF-1beta expression. MG132, a proteasome inhibitor, protected HIF-1alpha from LW6-induced proteasomal degradation, indicating that LW6 affects the stability of the HIF-1alpha protein. We found that LW6 promoted the degradation of wild type HIF-1alpha, but not of a DM-HIF-1alpha with modifications of P402A and P564A, at hydroxylation sites in the oxygen-dependent degradation domain (ODDD). LW6 did not affect the activity of prolyl hydroxylase (PHD), but induced the expression of von Hippel-Lindau (VHL), which interacts with prolyl-hydroxylated HIF-1alpha for proteasomal degradation. In the presence of LW6, knockdown of VHL did not abolish HIF-1alpha protein accumulation, indicating that LW6 degraded HIF-1alpha via regulation of VHL expression. In mice carrying xenografts of human colon cancer HCT116 cells, LW6 demonstrated strong anti-tumor efficacy in vivo and caused a decrease in HIF-1alpha expression in frozen-tissue immunohistochemical staining. These data suggest that LW6 may be valuable in the development of a HIF-1alpha inhibitor for cancer treatment.

5-Aza-2'-deoxycytidine suppresses human renal carcinoma cell growth in a xenograft model via up-regulation of the connexin 32 gene

BACKGROUND AND PURPOSE

The connexin (Cx) 32 gene, a member of the gap junction gene family, acts as a tumour suppressor gene in human renal cell carcinoma (RCC) and is down-regulated by the hypermethylation of CpG islands in a promoter region of the Cx gene. The current study investigated whether the restoration of Cx32 silenced by hypermethylation in RCC by a DNA demethylating agent could be an effective treatment against RCC.

EXPERIMENTAL APPROACH

Using nude mice bearing Caki-1 cells (a human metastatic RCC cell line), the effects of 5-aza-2'-deoxycytidine (5-aza-CdR), a DNA demethylase inhibitor, on Cx32 mRNA expression and tumour growth were examined by RT-PCR, and by measuring tumour weight and volume. Cx32 expression in Caki-1 tumours was inhibited by Cx32 short interfering (si) RNA, and the effect of siRNA on 5-aza-CdR-dependent suppression of tumour growth in nude mice was evaluated.

KEY RESULTS

5-aza-CdR treatment inhibited the growth of Caki-1 cells in nude mice by 70% and increased 7-fold the level of Cx32 mRNA. The intratumour injection of Cx32 siRNA almost totally inhibited the expression of Cx32 mRNA and significantly reduced the suppression of tumour growth in 5-aza-CdR-treated nude mice.

CONCLUSIONS AND IMPLICATIONS

5-aza-CdR suppressed the growth of Caki-1 tumours in a xenograft model, by restoring Cx32 expression. This finding suggests that treatment with 5-aza-CdR could be a new effective therapy against human metastatic RCC and that Cx32 could be a potential target for the treatment of RCC.

Inhibition of DNA methylation by antisense oligonucleotide MG98 as cancer therapy

Results of preclinical studies and clinical phase I/II trials suggest that the antisense oligodeoxynucleotide and DNA methyltransferase inhibitor MG98 can safely and effectively lead to reactivation of methylation silence tumor suppressor genes. It is possible that daily or continuous dosing of MG98 might be more active and less toxic than intermittent dosing. Combination of MG98 with other agents having completely different mechanisms of action seems reasonable. One clinical trial now under way is evaluating the use of MG98 in combination with interferon-alpha in patients with advanced renal cell carcinoma (RCC). Because of the current preclinical and clinical evidence, further trials of MG98 as therapy for RCC would be of interest.

Modulation by decitabine of gene expression and growth of osteosarcoma U2OS cells in vitro and in xenografts: identification of apoptotic genes as targets for demethylation

Background

Methylation-mediated silencing of genes is one epigenetic mechanism implicated in cancer. Studies regarding the role of modulation of gene expression utilizing inhibitors of DNA methylation, such as decitabine, in osteosarcoma (OS) have been limited. A biological understanding of the overall effects of decitabine in OS is important because this particular agent is currently undergoing clinical trials. The objective of this study was to measure the response of the OS cell line, U2OS, to decitabine treatment both in vitro and in vivo.

Results

Microarray expression profiling was used to distinguish decitabine-dependent changes in gene expression in U2OS cells, and to identify responsive loci with demethylated CpG promoter regions. U2OS xenografts were established under the sub-renal capsule of immune-deficient mice to study the effect of decitabine in vivo on tumor growth and differentiation. Reduced nuclear methylation levels could be detected in xenografts derived from treated mice by immunohistochemistry utilizing a 5-methylcytidine antibody. Decitabine treatment reduced tumor xenograft size significantly (p < 0.05). Histological analysis of treated U2OS xenograft sections revealed a lower mitotic activity (p < 0.0001), increased bone matrix production (p < 0.0001), and a higher number of apoptotic cells (p = 0.0329). Microarray expression profiling of U2OS cultured cells showed that decitabine treatment caused a significant induction (p < 0.0025) in the expression of 88 genes. Thirteen had a ≥2-fold change, 11 of which had CpG-island-associated promoters. Interestingly, 6 of these 11 were pro-apoptotic genes and decitabine resulted in a significant induction of cell death in U2OS cells in vitro (p < 0.05). The 6 pro-apoptotic genes (GADD45A, HSPA9B, PAWR, PDCD5, NFKBIA, and TNFAIP3) were also induced to ≥2-fold in vivo. Quantitative methylation pyrosequencing confirmed that the tested pro-apoptotic genes had CpG-island DNA demethylationas a result of U2OS decitabine treatment both in vitro and in xenografts

Conclusion

These data provide new insights regarding the use of epigenetic modifiers in OS, and have important implications for therapeutic trials involving demethylation drugs. Collectively, these data have provided biological evidence that one mode of action of decitabine may be the induction of apoptosis utilizing promoter-CpG demethylation of specific effectors in cell death pathways in OS.

Epigenetic drugs as pleiotropic agents in cancer treatment: biomolecular aspects and clinical applications

In the last three decades huge efforts have been made to characterize genetic defects responsible for cancer development and progression, leading to the comprehensive identification of distinct cellular pathways affected by the alteration of specific genes. Despite the undoubtable role of genetic mechanisms in triggering neoplastic cell transformation, epigenetic modifications (i.e., heritable changes of gene expression that do not derive from alterations of the nucleotide sequence of DNA) are rapidly emerging as frequent alterations that often occur in the early phases of tumorigenesis and that play an important role in tumor development and progression. Epigenetic alterations, such as modifications in DNA methylation patterns and post-translational modifications of histone tails, behave extremely different from genetic modifications, being readily revertable by "epigenetic drugs" such as inhibitors of DNA methyl transferases and inhibitors of histone deacetylases. Since epigenetic alterations in cancer cells affect virtually all cellular pathways that have been associated to tumorigenesis, it is not surprising that epigenetic drugs display pleiotropic activities, being able to concomitantly restore the defective expression of genes involved in cell cycle control, apoptosis, cell signaling, tumor cell invasion and metastasis, angiogenesis and immune recognition. Prompted by this emerging clinical relevance of epigenetic drugs, this review will focus on the large amount of available data, deriving both from in vitro experimentations and in vivo pre-clinical and clinical studies, which clearly indicate epigenetic drugs as effective modifiers of cancer phenotype and as positive regulators of tumor cell biology with a relevant therapeutic potential in cancer patients.

Demethylating Agent 5-Aza-2′-Deoxycytidine Enhances Susceptibility of Renal Cell Carcinoma to Paclitaxel

OBJECTIVES

To examine the effect of 5-aza-2'-deoxycytidine (DAC), a DNA methyltransferase inhibitor, on the growth of renal cell carcinoma (RCC) and examine the synergistic growth suppression by DAC and chemotherapeutic agents.

METHODS

The synergy of DAC and chemotherapeutic agents against RCC cell lines was analyzed by isobolographic analysis. The induction of apoptosis and cell cycle arrest by each single agent or the combination of agents was examined by flow cytometric analysis. Caspase activity assays and proliferating cell nuclear antigen protein expression were also examined to clarify the mechanism of the synergism of DAC and chemotherapeutic agents against RCC.

RESULTS

We demonstrated that DAC combined with paclitaxel (PTX) synergistically inhibited the growth of all the RCC cell lines tested, but DAC did not show such synergism with 5-fluorouracil, vinblastine, or Adriamycin. DAC suppressed RCC cell proliferation by inducing G2/M cell cycle arrest without inducing apoptosis, and PTX induced both apoptosis and G2/M cell cycle arrest in a dosage-dependent manner. DAC could enhance the PTX-induced upregulation of caspase activity and antiproliferative effect to increase the fraction of cells in the sub-G1 and G2/M phase.

CONCLUSIONS

DAC and PTX caused synergistic growth suppression of RCC, suggesting that DAC could strikingly increase the susceptibility of RCC to PTX and that combination chemotherapy with DAC and PTX might be a novel strategy to improve the clinical response rate of RCC.

Targeted therapy for renal cell carcinoma: a new therapeutic paradigm

Renal cell carcinoma is the most common tumor of the kidney. It has an unpredictable behavior and poor response to systemic therapy. Developing newer therapy for this disease is a priority considering the high recurrence rate and the small subset of patients who benefit from the use of cytokines such as interferon-alpha or interleukin-2. Identifying molecular targets and targeting various biomarkers has revolutionized the therapeutic approach to advanced and metastatic renal cell carcinoma. Although some of the antiangiogenic agents and receptor tyrosine kinase inhibitors appear promising, further understanding of their mechanism of action and the patient population who would benefit most from such agents is still being explored. As numerous targeted agents are entering the clinical investigation arena in a relatively short period of time, newer challenges in renal cell carcinoma therapeutics are emerging. Some of the future challenges in using targeted antineoplastic agents in renal cell carcinoma will include evaluating their long-term safety and benefit, using the particular drug in the appropriate patient population after appropriate stratification and studying the combination of some of these drugs for synergy or additive effects.

Epigenetic regulation of the expression of the novel stem cell marker CDCP1 in cancer cells

CDCP1 is a novel stem cell marker that is expressed in several types of cancer. The mechanisms by which CDCP1 expression is regulated, and the clinical implications of this marker, have not been clarified. In this report, we examine the epigenetic regulation of CDCP1 expression in cell lines and clinical samples from patients with breast cancer. Many CpG sequences were localized around the transcription initiation site of CDCP1. These CpG motifs were found to be poorly methylated in cell lines with high levels of CDCP1 expression and heavily methylated in cell lines with low levels of CDCP1 expression. The in vitro methylation of CpG sites decreased CDCP1 promoter activity, and the addition of a demethylating reagent restored activity. In 25 breast cancer samples, an inverse correlation was noted between the CDCP1 expression level and the proportion of methylated to non-methylated CpG sites. Tumours with high-level CDCP1 expression showed higher levels of proliferation, as revealed by immunohistochemical detection of the MIB-1 antigen, than tumours with low-level CDCP1 expression. These findings indicate that the expression of CDCP1 is regulated by methylation of its promoter region in tumours. CDCP1 expression may prove to be useful in the further characterization of cancers.

Aberrant promoter methylation of the ABCG2 gene in renal carcinoma

ABCG2 is a ubiquitous ATP-binding cassette transmembrane protein that is important in clinical drug resistance. Little is known about the mechanism(s) regulating the expression of ABCG2. We hypothesized that DNA methylation could play a role in the epigenetic regulation of ABCG2 gene expression. The promoter methylation status of three renal carcinoma cell lines was assessed with restriction enzyme digestion-coupled PCR and bisulfite genomic sequencing. Both UOK121 and UOK143, with known methylation of the VHL promoter, showed induction of ABCG2 expression after 5-aza-2'-deoxycytidine (5-aza-dC) treatment, suggesting that aberrant methylation of the ABCG2 gene was associated with gene silencing. In vitro methylation of the ABCG2 promoter-driven luciferase reporter vector resulted in a significant inhibition of transcription. Our data suggested that the ABCG2 gene is regulated coordinately at both histone and DNA levels. A chromatin immunoprecipitation assay demonstrated that the methylated promoter in UOK121 and UOK143, but not the unmethylated one in UOK181, is associated with the methyl CpG binding domain proteins (MBDs), MBD2 and MeCP2. Histone deacetylase 1 and a corepressor, mSin3A, were identified binding to the promoter region containing the CpG island, thereby suppressing ABCG2 transcription. Reactivation of ABCG2 was achieved by treatment with 5-aza-dC, a demethylating agent, concomitant with the release of MBDs from the promoter. Furthermore, the association of methylated lysine 9 on histone H3, a hallmark of promoter methylation, with the promoter was reduced following 5-aza-dC treatment. These data suggest that DNA methylation-dependent formation of a repressor complex in the CpG island contributes to inactivation of ABCG2.

Development of a cell-based reporter assay for screening of inhibitors of hypoxia-inducible factor 2-induced gene expression

Reporter cell lines have been developed for the identification of inhibitors of gene expression enhanced by hypoxia-inducible factor 2, which has been implicated as a transcription factor involved in the tumorigenesis of clear cell renal carcinoma. Stably transformed reporter clones of the human renal clear cell carcinoma cell line 786-O were generated by transfection or retroviral infection. Luciferase reporter expression in the vectors used was driven by either the natural human vascular endothelial growth factor (VEGF) promoter-enhancer or by the VEGF and the human endothelial nitric oxide synthase enhancers modulating minimal human cytomegalovirus promoter. Utility of the generated reporter cell lines was validated by introducing the von Hippel-Lindau protein complex and testing for reporter inducibility by hypoxia. The dynamic range in reporter activity under hypoxic stress was found to be at least 30- to 40-fold, with a signal-to-noise ratio of 60:1. Properties of the cell lines such as tolerance to up to 3% DMSO, signal stability with multiple in vitro passages, and utility in both 96- and 384-well plate formats indicated their suitability for use in a high-throughput screen. In addition, the potential use of these reporter lines in the evaluation of high-throughput screening hits in vivo in various mice models has been demonstrated.

Emerging drugs for renal cell carcinoma

Renal cell carcinoma (RCC) still represents a therapeutic challenge when patients have advanced or metastatic disease. Treatment using IL-2 and IFN-alpha continues to be the standard of care in patients who are able to tolerate such regimens. Targeted therapy may become the first-line treatment for patients resistant or intolerant to cytokines as new emerging drugs continue to be investigated. Understanding the genetic abnormalities related to the development of RCC (e.g., VHL gene abnormalities) and identifying molecular targets (e.g., epidermal growth factor, vascular endothelial growth factor and carbonic anhydrase IX) are playing a major role in the emergence of these novel agents for the treatment of this malignancy. Overall, these drugs are better tolerated and more acceptable to use by patients than the traditional cytokine-based regimens. The use of oral drugs to treat various malignancies including RCC seems to be the new paradigm of the future. Further understanding of their mechanisms of action and confirmation of their benefits on the clinical outcome is needed.

Heat-shock protein 90 inhibitors in antineoplastic therapy: is it all wrapped up?

Heat-shock protein (Hsp)-90 belongs to the class of molecular chaperone proteins that are capable of sensing cellular stress. Although Hsp90 is essential for viability, the pharmacological inhibition of this chaperone has emerged as an attractive means to inhibit tumorigenesis. This phenomenon is due to a unique property of Hsp90; its 'client proteins' are universally involved in signal transduction pathways commonly dysregulated in, and contributing to, cancer. The natural product geldanamycin, a potent ansamycin Hsp90 inhibitor, has served as a lead compound for the development of several derivatives that are currently undergoing clinical trials. Inhibition of Hsp90 with geldanamycin simultaneously depletes Hsp90-associated clients and impairs numerous signalling cascades that depend on chaperone function. Importantly, tumour cells are exquisitely sensitive to Hsp90 inhibition, lending credence to the feasibility of selectively targeting cancer tissue via the pharmacological modulation of Hsp90 function. Even more remarkably, Hsp90 inhibitors sensitise tumour cells to the cytotoxic effects of a variety of standard therapeutics, and thus, they are likely to have broad utility in combination therapy. Although these are promising developments, much remains to be discovered about client-chaperone biology and the tumour-specific effects of Hsp90 blockade. This information is required to fully grasp the multi-faceted roles of Hsp90 in cancer biology towards the goal of optimising the use of these agents in the clinic. Elucidation of these nuances will undoubtedly lead to better targeting of relevant oncogenic pathways and translate into the development of more effective anticancer regimens.