Synergistic antipancreatic tumor effect by simultaneously targeting hypoxic cancer cells with HSP90 inhibitor and glycolysis inhibitor

Silencing heat shock protein 27 decreases metastatic behavior of human head and neck squamous cell cancer cells in vitro

The small heat shock protein 27 (Hsp27) is a molecular chaperone that is involved in a variety of cellular functions in cancer cells. The purpose of this research is to study Hsp27 in vitro metastatic behaviors of head and neck squamous cell carcinoma cells (HNSCC). The expression of Hsp27 in primary and metastatic cell lines derived from the primary HNSCC and a synchronous lymph node metastasis in the same patient was determined using real-time PCR and Western blotting. Proliferation of the primary and metastatic HNSCC cell lines was evaluated using the MTS proliferation assay. Metastatic behavior was assessed using migration and invasion assays. SiRNA knockdown of Hsp27 was performed in the highly migratory metastatic HNSCC cell line. MTS assays showed that the primary (UM-SCC-22A) and metastatic (UM-SCC-22B) HNSCC have similar proliferation rates. However, UM-SCC-22B derived from the metastasis showed 2.3- to 3.6-fold higher migration ability and 2-fold higher invasion ability than UM-SCC-22A. Real-time PCR demonstrated that Hsp27 mRNA is 22.4-fold higher in metastatic UM-SCC-22B than primary UM-SCC-22A. Similarly, Western blotting showed that Hsp27 is rarely detectable in UM-SCC-22A whereas UM-SCC-22B expresses a 25-fold higher level of Hsp27 protein. SiRNA-mediated knockdown of Hsp27 in UM-SCC-22B reduced Hsp27 mRNA expression by nearly 6-fold and protein expression by 23-fold. Furthermore, siRNA knockdown of Hsp27 decreased metastatic behaviors of UM-SCC-22B by 3- to 4-fold in migration and 2-fold in cell invasion reducing cell invasion and migration to levels similar to the primary HNSCC UM-SCC-22A. These data indicate that Hsp27 may regulate metastatic potential of HNSCC cancer cells. Targeting Hsp27 may decrease metastasis in head and neck squamous cell cancer cells.

Glucose metabolism gene polymorphisms and clinical outcome in pancreatic cancer

BACKGROUND

Altered glucose metabolism is the most common metabolic hallmark of malignancies. The authors tested the hypothesis that glucose metabolism gene variations affect clinical outcome in pancreatic cancer.

METHODS

The authors retrospectively genotyped 26 single nucleotide polymorphisms from 5 glucose metabolism genes in 154 patients with localized disease and validated the findings in 552 patients with different stages of pancreatic adenocarcinoma. Association between genotypes and overall survival (OS) was evaluated using multivariate Cox proportional hazard regression models with adjustment for clinical predictors.

RESULTS

Glucokinase (GCK) IVS1 + 9652C > T and hexokinase 2 (HK2) N692N homozygous variants were significantly associated with reduced OS in the training set of 154 patients (P < .001). These associations were confirmed in the validation set of 552 patients and in the combined dataset of all 706 patients (P ≤ .001). In addition, HK2 R844K variant K allele was associated with a better survival in the validation set and the combined dataset (P ≤ .001). When data were further analyzed by disease stage, glutamine-fructose-6-phosphate transaminase (GFPT1) IVS14-3094T>C, HK2 N692N and R844K in patients with localized disease and GCK IVS1 + 9652C>T in patients with advanced disease were significant independent predictors for OS (P ≤ .001). Haplotype CGG of GPI and GCTATGG of HK2 were associated with better OS, respectively, with P values of .004 and .007.

CONCLUSIONS

The authors demonstrated that glucose metabolism gene polymorphisms affect clinical outcome in pancreatic cancer. These observations support a role of abnormal glucose metabolism in pancreatic carcinogenesis.

MEK inhibition potentiates the activity of Hsp90 inhibitor 17-AAG against pancreatic cancer cells

The Ras/Raf/MEK/ERK signaling has been implicated in uncontrolled cell proliferation and tumor progression in pancreatic cancer. The purpose of this study is to evaluate the antitumor activity of MEK inhibitor U0126 in combination with Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) in pancreatic cancer cells. Western blotting showed that 17-AAG caused a 2- to 3-fold transient activation of MEK/ERK signaling in pancreatic cancer cells. The activation sustained for 6 h before phospho-ERK (p-ERK) destabilization. The selective MEK inhibitor U0126 completely abolished 17-AAG induced ERK1/2 activation and resulted in more than 80% of phospho-ERK degradation after only 15 min treatment. Moreover, U0126 had complementary effect on 17-AAG regulated oncogenic and cell cycle related proteins. Although 17-AAG downregulated cyclin D1, cyclin E, CDK4 and CDK6, it led to cyclin A and CDK2 accumulation, which was reversed by the addition of U0126. Antiproliferation assay showed that combination of U0126 and 17-AAG resulted in synergistic cytotoxic effect. More importantly, 17-AAG alone only exhibited moderate inhibition of cell migration in vitro, while addition of U0126 dramatically enhanced the inhibitory effect by 2- to 5-fold. Taken together, these data demonstrate that MEK inhibitor U0126 potentiates the activity of Hsp90 inhibitor 17-AAG against pancreatic cancer cells. The combination of Hsp90 and MEK inhibition could provide a promising avenue for the treatment of pancreatic cancer.

The pyruvic acid analog 3-bromopyruvate interferes with the tetrazolium reagent MTS in the evaluation of cytotoxicity

3-Bromopyruvate (3BrPA) is a pyruvate analog known for its alkylating property. Recently, several reports have documented the antiglycolytic and anticancer effects of 3BrPA and its potential for therapeutic applications. 3BrPA-mediated cytotoxicity has been evaluated in vitro by various methods including tetrazolium salt (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide)-based assays such as MTT, MTS, and so on. However, growing body of evidences has shown that tetrazolium reagent may interfere with the test compounds. In this study, we investigated whether the tetrazolium reagent interferes with the assessment of 3BrPA cytotoxicity. The results of the tetrazolium-based MTS assay were compared with 3 distinct cell viability detection methods, that is, Trypan Blue staining, ATP depletion, and Annexin V staining in 2 different cell lines, Vx-2 and HepG2. The MTS assay data showed false positive results by indicating increased cell viability at 1 mM and 2 mM 3BrPA whereas the other cell viability assays demonstrated that both Vx-2 and HepG2 cells are not viable at the same treatment conditions. In order to validate the direct interaction of 3BrPA with MTS reagent, we tested cell-free media incubated with different concentrations of 3BrPA. The results of cell-free media showed an increase in absorbance in a dose-dependent manner confirming the interaction of MTS with 3BrPA. Thus, our data clearly demonstrate that 3BrPA interferes with the accuracy of MTS-based cytotoxicity evaluation. Hence, we suggest that employing multiple methods of biochemical as well as morphological cytotoxicity assays is critical to evaluate 3BrPA-mediated cell death.

Mitochondrially targeted anti-cancer agents

Cancer is an ever-increasing problem that is yet to be harnessed. Frequent mutations make this pathology very variable and, consequently, a considerable challenge. Intriguingly, mitochondria have recently emerged as novel targets for cancer therapy. A group of agents with anti-cancer activity that induce apoptosis by way of mitochondrial destabilisation, termed mitocans, have been a recent focus of research. Of these compounds, many are hydrophobic agents that associate with various sub-cellular organelles. Clearly, modification of such structures with mitochondria-targeting moieties, for example tagging them with lipophilic cations, would be expected to enhance their activity. This may be accomplished by the addition of triphenylphosphonium groups that direct such compounds to mitochondria, enhancing their activity. In this paper, we will review agents that possess anti-cancer activity by way of destabilizing mitochondria and their possible targets. We propose that mitochondrial targeting, in particular where the agent associates directly with the target, results in more specific and efficient anti-cancer drugs of potential high clinical relevance.

Targeting mitochondria for cancer therapy

Mitochondria are the cells' powerhouse, but also their suicidal weapon store. Dozens of lethal signal transduction pathways converge on mitochondria to cause the permeabilization of the mitochondrial outer membrane, leading to the cytosolic release of pro-apoptotic proteins and to the impairment of the bioenergetic functions of mitochondria. The mitochondrial metabolism of cancer cells is deregulated owing to the use of glycolytic intermediates, which are normally destined for oxidative phosphorylation, in anabolic reactions. Activation of the cell death machinery in cancer cells by inhibiting tumour-specific alterations of the mitochondrial metabolism or by stimulating mitochondrial membrane permeabilization could therefore be promising therapeutic approaches.

Targeting metabolic transformation for cancer therapy

Cancer therapy has long relied on the rapid proliferation of tumour cells for effective treatment. However, the lack of specificity in this approach often leads to undesirable side effects. Many reports have described various 'metabolic transformation' events that enable cancer cells to survive, suggesting that metabolic pathways might be good targets. There are currently several drugs under development or in clinical trials that are based on specifically targeting the altered metabolic pathways of tumours. This Review highlights pathways against which there are already drugs in different stages of development and also discusses additional druggable targets.

Withaferin A targets heat shock protein 90 in pancreatic cancer cells

The purpose of this study is to investigate the efficacy and the mechanism of Hsp90 inhibition of Withaferin A (WA), a steroidal lactone occurring in Withania somnifera, in pancreatic cancer in vitro and in vivo. Withaferin A exhibited potent antiproliferative activity against pancreatic cancer cells in vitro (with IC(50)s of 1.24, 2.93 and 2.78 microM) in pancreatic cancer cell lines Panc-1, MiaPaCa2 and BxPc3, respectively. Annexin V staining showed that WA induced significant apoptosis in Panc-1 cells in a dose-dependent manner. Western blotting demonstrated that WA inhibited Hsp90 chaperone activity to induce degradation of Hsp90 client proteins (Akt, Cdk4 and glucocorticoid receptor), which was reversed by the proteasomal inhibitor, MG132. WA-biotin pull down assay of Hsp90 using Panc-1 cancer cell lysates and purified Hsp90 showed that WA-biotin binds to C-terminus of Hsp90 which was competitively blocked by unlabeled WA. Co-immunoprecipitation exhibited that WA (10 microM) disrupted Hsp90-Cdc37 complexes from 1 to 24h post-treatment, while it neither blocked ATP binding to Hsp90, nor changed Hsp90-P23 association. WA (3, 6mg/kg) inhibited tumor growth in pancreatic Panc-1 xenografts by 30% and 58%, respectively. These data demonstrate that Withaferin A binds Hsp90, inhibits Hsp90 chaperone activity through an ATP-independent mechanism, results in Hsp90 client protein degradation, and exhibits in vivo anticancer activity against pancreatic cancer.

Transport by SLC5A8 with subsequent inhibition of histone deacetylase 1 (HDAC1) and HDAC3 underlies the antitumor activity of 3-bromopyruvate

BACKGROUND

3-bromopyruvate is an alkylating agent with antitumor activity. It is currently believed that blockade of adenosine triphosphate production from glycolysis and mitochondria is the primary mechanism responsible for this antitumor effect. The current studies uncovered a new and novel mechanism for the antitumor activity of 3-bromopyruvate.

METHODS

The transport of 3-bromopyruvate by sodium-coupled monocarboxylate transporter SMCT1 (SLC5A8), a tumor suppressor and a sodium (Na+)-coupled, electrogenic transporter for short-chain monocarboxylates, was studied using a mammalian cell expression and the Xenopus laevis oocyte expression systems. The effect of 3-bromopyruvate on histone deacetylases (HDACs) was monitored using the lysate of the human breast cancer cell line MCF7 and human recombinant HDAC isoforms as the enzyme sources. Cell viability was monitored by fluorescence-activated cell-sorting analysis and colony-formation assay. The acetylation status of histone H4 was evaluated by Western blot analysis.

RESULTS

3-Bromopyruvate is a transportable substrate for SLC5A8, and that transport process is Na+-coupled and electrogenic. MCF7 cells did not express SLC5A8 and were not affected by 3-bromopyruvate. However, when transfected with SLC5A8 or treated with inhibitors of DNA methylation, these cells underwent apoptosis in the presence of 3-bromopyruvate. This cell death was associated with the inhibition of HDAC1/HDAC3. Studies with different isoforms of human recombinant HDACs identified HDAC1 and HDAC3 as the targets for 3-bromopyruvate.

CONCLUSIONS

3-Bromopyruvate was transported into cells actively through the tumor suppressor SLC5A8, and the process was energized by an electrochemical Na+ gradient. Ectopic expression of the transporter in MCF7 cells led to apoptosis, and the mechanism involved the inhibition of HDAC1/HDAC3.

Heat shock proteins, cell survival and drug resistance: the mitochondrial chaperone TRAP1, a potential novel target for ovarian cancer therapy

BACKGROUND

Protein homeostasis is a highly complex network of molecular interactions governing the health and life span of the organism. Molecular chaperones, mainly heat shock proteins (HSP) and other stress-inducible proteins abundantly expressed in multiple compartments of the cell, are major modulators of protein homeostasis. TRAP1 is a mitochondrial HSP involved in protection against oxidant-induced DNA damage and apoptosis. It was recently described as a component of a mitochondrial pathway selectively up-regulated in tumor cells which antagonizes the proapoptotic activity of cyclophilin D, a mitochondrial permeability transition pore regulator, and is responsible for the maintenance of mitochondrial integrity, thus favoring cell survival. Interestingly, novel TRAP1 antagonists cause sudden collapse of mitochondrial function and selective tumor cell death, suggesting that this pathway may represent a novel molecular target to improve anticancer therapy. Preliminary data suggest that TRAP1 may be a valuable biomarker in ovarian cancers: in fact, TRAP1 levels are significantly higher in cisplatin-resistant ovarian tumors and ovarian carcinoma cell lines.

CONCLUSIONS

While major advances have been made in understanding the genetics and molecular biology of cancer, given the considerable heterogeneity of ovarian cancer, the introduction of novel targeted therapies and the consequent selection of treatments based on the molecular profile of each tumor may have a major impact on the management of this malignancy and might contribute to building a new era of personalized medicine.

Metabolic approaches to treatment of melanoma

PURPOSE

Lactate dehydrogenase (LDH) levels in blood of patients with melanoma have proven to be an accurate predictor of prognosis and response to some treatments. Exclusion of patients with high LDH levels from many trials of new treatments has created a need for treatments aimed at patients with high LDH levels. This article reviews the metabolic basis for the association of LDH with prognosis and the treatment initiatives that may be successful in this patient group.

EXPERIMENTAL DESIGN

Review of current literature on the topic.

RESULTS

A number of new treatment initiatives based on manipulation of metabolic pathways in melanoma cells are now available and await evaluation in well-designed clinical trials.

CONCLUSIONS

Different cancers may require different metabolic approaches for effective treatment. In view of the high rate of glycolysis in most melanoma cells, approaches based on inhibition of acid excretion from the cells seem particularly attractive.

New developments in Hsp90 inhibitors as anti-cancer therapeutics: mechanisms, clinical perspective and more potential

The molecular chaperone Hsp90 (heat shock protein 90) is a promising target in cancer therapy. Preclinical and clinical evaluations of a variety of Hsp90 inhibitors have shown anti-tumor effect as a single agent and in combination with chemotherapy. Current Hsp90 inhibitors are categorized into several classes based on distinct modes of inhibition, including (i) blockade of ATP binding, (ii) disruption of co-chaperone/Hsp90 interactions, (iii) antagonism of client/Hsp90 associations and (iv) interference with post-translational modifications of Hsp90. The different functions of Hsp90 isoforms and the isoform selectivity of drugs need further investigation. The correlation of cell surface Hsp90 with cancer metastasis and the emerging involvement of Hsp90 inhibition in cancer stem cells have become exciting areas that could be exploited. Therefore, the aim of this review is (1) to summarize the up-to-date knowledge of mechanistic studies and clinical prospect of currently available Hsp90 inhibitors, (2) to enhance our perspectives for designing and discovering novel Hsp90 inhibitors, and (3) to provide an insight into less-understood potential of Hsp90 inhibition in cancer therapy.

Targeting HSP90 for cancer therapy

Heat-shock proteins (HSPs) are molecular chaperones that regulate protein folding to ensure correct conformation and translocation and to avoid protein aggregation. Heat-shock proteins are increased in many solid tumours and haematological malignancies. Many oncogenic proteins responsible for the transformation of cells to cancerous forms are client proteins of HSP90. Targeting HSP90 with chemical inhibitors would degrade these oncogenic proteins, and thus serve as useful anticancer agents. This review provides an overview of the HSP chaperone machinery and the structure and function of HSP90. We also highlight the key oncogenic proteins that are regulated by HSP90 and describe how inhibition of HSP90 could alter the activity of multiple signalling proteins, receptors and transcriptional factors implicated in carcinogenesis.

Hexokinase-2 bound to mitochondria: cancer's stygian link to the "Warburg Effect" and a pivotal target for effective therapy

The most common metabolic hallmark of malignant tumors, i.e., the "Warburg effect" is their propensity to metabolize glucose to lactic acid at a high rate even in the presence of oxygen. The pivotal player in this frequent cancer phenotype is mitochondrial-bound hexokinase [Bustamante E, Pedersen PL. High aerobic glycolysis of rat hepatoma cells in culture: role of mitochondrial hexokinase. Proc Natl Acad Sci USA 1977;74(9):3735-9; Bustamante E, Morris HP, Pedersen PL. Energy metabolism of tumor cells. Requirement for a form of hexokinase with a propensity for mitochondrial binding. J Biol Chem 1981;256(16):8699-704]. Now, in clinics worldwide this prominent phenotype forms the basis of one of the most common detection systems for cancer, i.e., positron emission tomography (PET). Significantly, HK-2 is the major bound hexokinase isoform expressed in cancers that exhibit a "Warburg effect". This includes most cancers that metastasize and kill their human host. By stationing itself on the outer mitochondrial membrane, HK-2 also helps immortalize cancer cells, escapes product inhibition and gains preferential access to newly synthesized ATP for phosphorylating glucose. The latter event traps this essential nutrient inside the tumor cells as glucose-6-P, some of which is funneled off to serve as carbon precursors to help promote the production of new cancer cells while much is converted to lactic acid that exits the cells. The resultant acidity likely wards off an immune response while preparing surrounding tissues for invasion. With the re-emergence and acceptance of both the "Warburg effect" as a prominent phenotype of most clinical cancers, and "metabolic targeting" as a rational therapeutic strategy, a number of laboratories are focusing on metabolite entry or exit steps. One remarkable success story [Ko YH, Smith BL, Wang Y, Pomper MG, Rini DA, Torbenson MS, et al. Advanced cancers: eradication in all cases using 3-bromopyruvate therapy to deplete ATP. Biochem Biophys Res Commun 2004;324(1):269-75] is the use of the small molecule 3-bromopyruvate (3-BP) that selectively enters and destroys the cells of large tumors in animals by targeting both HK-2 and the mitochondrial ATP synthasome. This leads to very rapid ATP depletion and tumor destruction without harm to the animals. This review focuses on the multiple roles played by HK-2 in cancer and its potential as a metabolic target for complete cancer destruction.

Glycolytic enzyme inhibitors in cancer treatment

BACKGROUND

The radio- and chemotherapeutics currently used for the treatment of cancer are widely known to be characterized by a low therapeutic index. An interesting approach to overcoming some of the limits of these techniques is the exploitation of the so-called Warburg effect, which typically characterizes neoplastic cells. Interestingly, this feature has already been utilized with good results, but only for diagnostic purposes (PET and SPECT). From a pharmacological point of view, drugs able to perturb cancer cell metabolism, specifically at the level of glycolysis, may display interesting therapeutic activities in cancer.

OBJECTIVE

The pharmacological actions of these glycolytic enzyme inhibitors, based primarily on ATP depletion, could include: i) amelioration of drug selectivity by exploiting the particular glycolysis addiction of cancer cell; ii) inhibition of energetic and anabolic processes; iii) reduction of hypoxia-linked cancer-cell resistance; iv) reduction of ATP-dependent multi-drug resistance; and v) cytotoxic synergism with conventional cancer treatments.

CONCLUSION

Several glycolytic inhibitors are currently in preclinical and clinical development. Their clinical value as anticancer agents, above all in terms of therapeutic index, strictly depends on a careful reevaluation of the pathophyiological role of the unique metabolism of cancer cells in general and of Warburg effect in particular.