Inhibition of the AURKA/YAP1 axis is a promising therapeutic option for overcoming cetuximab resistance in colorectal cancer stem cells

BACKGROUND

Primary resistance to anti-EGFR therapies affects 40% of metastatic colorectal cancer patients harbouring wild-type RAS/RAF. YAP1 activation is associated with this resistance, prompting an investigation into AURKA's role in mediating YAP1 phosphorylation at Ser397, as observed in breast cancer.

METHODS

We used transcriptomic analysis along with in vitro and in vivo models of RAS/RAF wild-type CRC to study YAP1 Ser397 phosphorylation as a potential biomarker for cetuximab resistance. We assessed cetuximab efficacy using CCK8 proliferation assays and cell cycle analysis. Additionally, we examined the effects of AURKA inhibition with alisertib and created a dominant-negative YAP1 Ser397 mutant to assess its impact on cancer stem cell features.

RESULTS

The RAS/RAF wild-type CRC models exhibiting primary resistance to cetuximab prominently displayed elevated YAP1 phosphorylation at Ser397 primarily mediated by AURKA. AURKA-induced YAP1 phosphorylation was identified as a key trigger for cancer stem cell reprogramming. Consequently, we found that AURKA inhibition had the capacity to effectively restore cetuximab sensitivity and concurrently suppress the cancer stem cell phenotype.

CONCLUSIONS

AURKA inhibition holds promise as a therapeutic approach to overcome cetuximab resistance in RAS/RAF wild-type colorectal cancer, offering a potential means to counter the development of cancer stem cell phenotypes associated with cetuximab resistance.

Choline Kinase α Inhibitors MN58b and RSM932A Enhances the Antitumor Response to Cisplatin in Lung Tumor Cells

Lung cancer is one of the main causes of death in developed countries, and non-small cell lung cancer (NSCLC) is the most frequent type (80% of patients). In advanced NSCLC, platinum-based chemotherapy is the frontline palliative treatment, but less than 5% of patients achieve prolonged survival. Immunotherapy has recently been proposed as the standard of care (SoC) as either monotherapy or in combination with chemotherapy for advanced NSCLC. The levels of expression of PD-L1 are the only predictive biomarkers for patient assessment. Although around 30% of patients receiving immunotherapy achieve 5-year survival, a significant number does not benefit from this novel therapeutic approach. Therefore, there is a need for novel strategies to improve clinical outcomes. The expression level of choline kinase α (ChoKα) is increased in a large number of human tumors, including NSCLC tumors, and constitutes an independent prognostic factor for early-stage NSCLC patients. Thus, ChoKα has been postulated as a new target drug in cancer therapy. The combination of cisplatin with novel targeted drugs such as choline kinase inhibitors may improve both the survival rates and the quality of life of NSCLC patients and may serve as the basis for the development of new therapeutic approaches. To that aim, we developed several in vitro and in vivo approaches to assess the antitumor activity of a novel combination regimen using cisplatin and ChoKα inhibitors. Our results suggest that a proper combination of specific inhibitors of the NSCLC prognostic factor ChoKα and platinum-based conventional chemotherapy might constitute a new, efficient treatment approach for NSCLC patients. This novel approach may help reduce the toxicity profile associated with cisplatin since, despite the advances in NSCLC management in recent years, the overall 5-year survival rate is still poor.

Choline Kinase: An Unexpected Journey for a Precision Medicine Strategy in Human Diseases

Choline kinase (ChoK) is a cytosolic enzyme that catalyzes the phosphorylation of choline to form phosphorylcholine (PCho) in the presence of ATP and magnesium. ChoK is required for the synthesis of key membrane phospholipids and is involved in malignant transformation in a large variety of human tumours. Active compounds against ChoK have been identified and proposed as antitumor agents. The ChoK inhibitory and antiproliferative activities of symmetrical bispyridinium and bisquinolinium compounds have been defined using quantitative structure-activity relationships (QSARs) and structural parameters. The design strategy followed in the development of the most active molecules is presented. The selective anticancer activity of these structures is also described. One promising anticancer compound has even entered clinical trials. Recently, ChoKα inhibitors have also been proposed as a novel therapeutic approach against parasites, rheumatoid arthritis, inflammatory processes, and pathogenic bacteria. The evidence for ChoKα as a novel drug target for approaches in precision medicine is discussed.

Choline Kinase Emerges as a Promising Drug Target in Gram-Positive Bacteria

Both nosocomial pathogens, such as Streptococcus pneumoniae and Haemophilus influenzae and food-borne pathogens, such as Bacillus cereus and Clostridium perfringens are known to be detrimental to human and animal health. The effectiveness of currently used treatments for these pathogens becomes limited as resistant strains emerge. Therefore, new methods for eliminating bacterial pathogens must be developed continuously. This includes establishing novel targets to which drug discovery efforts could be focused. A promising method for discovering new drug targets in prokaryotes is to take advantage of the information available regarding the enzymatic pathways that have been established as drug targets in eukaryotic systems and explore the analogous pathways found in bacterial systems. This is an efficient strategy because the same inhibitors developed at considerable expense to block these pathways in eukaryotic systems could also be employed in prokaryotes. Drugs that are used to prevent diseases involving eukaryotic cells could be repurposed as antibiotics and antimicrobials for the control of bacteria pathogens. This strategy could be pursued whenever the primary and tertiary structures of a target are are conserved between eukaryotic and prokaryotes. A possible novel target fitting these parameters is choline kinase (ChoK), whose active site sequences are conserved (Figure 1) and whose tertiary structure (Figure 2) is maintained. Here, we describe why ChoK is a putative drug target by describing its role in the growth and pathogenesis of Gram-positive bacteria S. pneumoniae and the Gram-negative bacteria H. influenzae. Using S. pneumoniae as a model, we also present promising preliminary information that repurposing of drugs known to inhibit the human isoform of ChoK (hChoK), is a promising strategy for blocking the growth of S. pneumoniae cells and inhibiting the activity of the S. pneumoniae isoform of ChoK (sChok), with downstream physiological effects on the cell wall.

Choline Uptake and Metabolism Modulate Macrophage IL-1β and IL-18 Production

Choline is a vitamin-like nutrient that is taken up via specific transporters and metabolized by choline kinase, which converts it to phosphocholine needed for de novo synthesis of phosphatidylcholine (PC), the main phospholipid of cellular membranes. We found that Toll-like receptor (TLR) activation enhances choline uptake by macrophages and microglia through induction of the choline transporter CTL1. Inhibition of CTL1 expression or choline phosphorylation attenuated NLRP3 inflammasome activation and IL-1β and IL-18 production in stimulated macrophages. Mechanistically, reduced choline uptake altered mitochondrial lipid profile, attenuated mitochondrial ATP synthesis, and activated the energy sensor AMP-activated protein kinase (AMPK). By potentiating mitochondrial recruitment of DRP1, AMPK stimulates mitophagy, which contributes to termination of NLRP3 inflammasome activation. Correspondingly, choline kinase inhibitors ameliorated acute and chronic models of IL-1β-dependent inflammation.

Choline uptake and metabolism modulate macrophage immunity

Choline is a vitamin-like nutrient that is taken up via specific transporters and metabolized by choline kinase (ChoKα) which converts it to phosphocholine needed for de novo synthesis of phosphatidylcholine (PC), the main phospholipid of cellular membranes. We found that Toll-like receptor (TLR) activation enhances choline uptake by macrophages through induction of the choline transporter CTL1. Choline is rapidly phosphorylated and mobilized to the Kennedy pathway leading to increased cellular phosphatidylcholine production. Inhibition of choline uptake or phosphorylation attenuated NLRP3 inflammasome activation and IL-1β and IL-18 production in stimulated macrophages. Mechanistically, reduced choline uptake altered mitochondrial lipid profile, attenuated mitochondrial ATP synthesis and activated the energy sensor AMP-activated protein kinase (AMPK). By potentiating mitochondrial recruitment of DRP1, AMPK stimulates mitophagy, which contributes to termination of NLRP3 inflammasome activation. Correspondingly, pharmacological ChoKα inhibition ameliorated acute and chronic macrophage-dependent inflammation in vivo.

Clinical relevance of the transcriptional signature regulated by CDC42 in colorectal cancer

CDC42 is an oncogenic Rho GTPase overexpressed in colorectal cancer (CRC). Although CDC42 has been shown to regulate gene transcription, the specific molecular mechanisms regulating the oncogenic ability of CDC42 remain unknown. Here, we have characterized the transcriptional networks governed by CDC42 in the CRC SW620 cell line using gene expression analysis. Our results establish that several cancer-related signaling pathways, including cell migration and cell proliferation, are regulated by CDC42. This transcriptional signature was validated in two large cohorts of CRC patients and its clinical relevance was also studied. We demonstrate that three CDC42-regulated genes offered a better prognostic value when combined with CDC42 compared to CDC42 alone. In particular, the concordant overexpression of CDC42 and silencing of the putative tumor suppressor gene CACNA2D2 dramatically improved the prognostic value. The CACNA2D2/CDC42 prognostic classifier was further validated in a third CRC cohort as well as in vitro and in vivo CRC models. Altogether, we show that CDC42 has an active oncogenic role in CRC via the transcriptional regulation of multiple cancer-related pathways and that CDC42-mediated silencing of CACNA2D2 is clinically relevant. Our results further support the use of CDC42 specific inhibitors for the treatment of the most aggressive types of CRC.

Abstract 4235: Choline metabolism is an early predictor of EGFR-mediated survival in NSCLC

Oncogenic signalling and metabolic reprograming are hallmarks of tumour progression, yet little is known about the regulatory elements that coordinate their interface. Aberrant choline and phospholipid metabolism are strongly correlated to malignant progression in NSCLC and provide the essential components required by both hallmarks and yet mechanistic links to either remain scarce. Choline kinase alpha (ChoKα) regulates the conversion of choline to phosphocholine and although its regulatory cascade has not been described, it is thought to act in conjuction with EGFR. We used an integrated systems approach and queried whether pharmacoproteomic pathway mapping could identify regulators of the cholinic phenotype. Proteomic and phosphoproteomic Stable isotope labelling by amino acids in cell culture (SILAC) analysis was used to describe the interactome following ChoKα or EGFR inhibition. Bioinformatic analysis was used to identify the significant (Significance-B test) subset of targets for each condition. These subsets were clustered according to GeneOntology, Reactome and KEGG databases and the resulting maps identifed the potential regulators of choline metabolism. Choline uptake, phosphorylation and efflux were further evaluated in vitro in response to erlotinib, cisplatin, pemetrexed and paclitaxel using radio-labelled Choline analogues. Derived metabolites were characterised using radio-HPLC. Uptake was further characterised under hypoxic and nutrient deficient conditions. In vivo, [18F]-D4-Choline PET dynamic imaging was performed following treatment. Pharmacoproteomic analysis revealed a 40% overlap between ChoKα and EGFR inhibition providing direct evidence of the pathways and targets involved in, mostly, biosynthesis. Rapid modulation of the cholinic phenotype was directly dependent on ChoKα activity. Intracellular uptake was induced by nutrient deprivation, hypoxia and reversed through second messenger signalling or growth factor stimulation. Choline uptake within 3 hours of treatment correlated to survival at 72 hours. In vivo, [18F]-D4-Choline tracer kinetics were diagnostic of choline kinase expression and sensitive to treatment. Significant correspondence between ChoKα and EGFR inhibition provided mechanistic evidence that ChoKα and lipid metabolism are effectors of the EGFR signalling cascade in NSCLC. Choline can act as a sensor by synchronizing the survival response via metabolic and signalling reprograming and is thus an early predictor of therapeutic efficiency in vitro and in vivo.

Citation Format: Rosy Favicchio, Nicos Angelopoulos, Diana Brickute, Robin Fortt, Frazer Twyman, Georgios Giamas, Juan Carlos Lacal, Eric O. Aboagye. Choline metabolism is an early predictor of EGFR-mediated survival in NSCLC. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4235.

Phospholipid profiling identifies acyl chain elongation as a ubiquitous trait and potential target for the treatment of lung squamous cell carcinoma

Lung cancer is the leading cause of cancer death. Beyond first line treatment, few therapeutic options are available, particularly for squamous cell carcinoma (SCC). Here, we have explored the phospholipidomes of 30 human SCCs and found that they almost invariably (in 96.7% of cases) contain phospholipids with longer acyl chains compared to matched normal tissues. This trait was confirmed using in situ 2D-imaging MS on tissue sections and by phospholipidomics of tumor and normal lung tissue of the L-IkkαKA/KA mouse model of lung SCC. In both human and mouse, the increase in acyl chain length in cancer tissue was accompanied by significant changes in the expression of acyl chain elongases (ELOVLs). Functional screening of differentially expressed ELOVLs by selective gene knockdown in SCC cell lines followed by phospholipidomics revealed ELOVL6 as the main elongation enzyme responsible for acyl chain elongation in cancer cells. Interestingly, inhibition of ELOVL6 drastically reduced colony formation of multiple SCC cell lines in vitro and significantly attenuated their growth as xenografts in vivo in mouse models. These findings identify acyl chain elongation as one of the most common traits of lung SCC discovered so far and pinpoint ELOVL6 as a novel potential target for cancer intervention.

Choline kinase inhibition in rheumatoid arthritis

OBJECTIVES

Little is known about targeting the metabolome in non-cancer conditions. Choline kinase (ChoKα), an essential enzyme for phosphatidylcholine biosynthesis, is required for cell proliferation and has been implicated in cancer invasiveness. Aggressive behaviour of fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA) led us to evaluate whether this metabolic pathway could play a role in RA FLS function and joint damage.

METHODS

Choline metabolic profile of FLS cells was determined by (1)H magnetic resonance spectroscopy ((1)HMRS) under conditions of ChoKα inhibition. FLS function was evaluated using the ChoKα inhibitor MN58b (IC₅₀=4.2 μM). For arthritis experiments, mice were injected with K/BxN sera. MN58b (3 mg/kg) was injected daily intraperitoneal beginning on day 0 or day 4 after serum administration.

RESULTS

The enzyme is expressed in synovial tissue and in cultured RA FLS. Tumour necrosis factor (TNF) and platelet-derived growth factor (PDGF) stimulation increased ChoKα expression and levels of phosphocholine in FLS measured by Western Blot (WB) and metabolomic studies of choline-containing compounds in cultured RA FLS extracts respectively, suggesting activation of this pathway in RA synovial environment. A ChoKα inhibitor also suppressed the behaviour of cultured FLS, including cell migration and resistance to apoptosis, which might contribute to cartilage destruction in RA. In a passive K/BxN arthritis model, pharmacologic ChoKα inhibition significantly decreased arthritis in pretreatment protocols as well as in established disease.

CONCLUSIONS

These data suggest that ChoKα inhibition could be an effective strategy in inflammatory arthritis. It also suggests that targeting the metabolome can be a new treatment strategy in non-cancer conditions.

Rho GTPase Rac1: molecular switch within the galectin network and for N-glycan α2,6-sialylation/O-glycan core 1 sialylation in colon cancer in vitro

The Rho GTPase Rac1 is a multifunctional protein working through different effector pathways. The emerging physiological significance of glycanlectin recognition gives reason to testing the possibility for an influence of modulation of Rac1 expression on these molecular aspects. Using human colon adenocarcinoma (SW620) cells genetically engineered for its up- and down-regulation (Rac1+ and Rac1- cells) along with wild-type and mock-transfected control cells, the questions are addressed whether the presence of adhesion/growth-regulatory galectins and distinct aspects of cell surface glycosylation are affected. Proceeding from RT-PCR data to Western blotting after two-dimensional gel electrophoresis and flow cytofluorimetry with non-crossreactive antibodies against six members of this lectin family (i.e. galectins-1, -3, -4, -7, -8 and -9), a reduced extent of the presence of galectins-1, -7 and -9 was revealed in the case of Rac1 cells. Application of these six galectins as probes to determination of cell reactivity for human lectins yielded relative increases in surface labelling of Rac1- cells with galectins-1, -3 and -7. Examining distinct aspects of cell surface glycosylation with a panel of 14 plant/fungal lectins disclosed a decrease in α2,6-sialylation of N-glycans and an increase in PNA-reactive sites (i.e. non-sialylated core 1 O-glycans), two alterations known to favour reactivity for galectins-1 and -3. Thus, manipulation of Rac1 expression selectively affects the expression pattern within the galectin network at the level of proteins and distinct aspects of cell surface glycosylation.

Combined 5-FU and ChoKα inhibitors as a new alternative therapy of colorectal cancer: evidence in human tumor-derived cell lines and mouse xenografts

Background

Colorectal cancer (CRC) is the third major cause of cancer related deaths in the world. 5-fluorouracil (5-FU) is widely used for the treatment of colorectal cancer but as a single-agent renders low response rates. Choline kinase alpha (ChoKα), an enzyme that plays a role in cell proliferation and transformation, has been reported overexpressed in many different tumors, including colorectal tumors. ChoKα inhibitors have recently entered clinical trials as a novel antitumor strategy.

Methodology/Principal Findings

ChoKα specific inhibitors, MN58b and TCD-717, have demonstrated a potent antitumoral activity both in vitro and in vivo against several tumor-derived cell line xenografts including CRC-derived cell lines. The effect of ChoKα inhibitors in combination with 5-FU as a new alternative for the treatment of colon tumors has been investigated both in vitro in CRC-tumour derived cell lines, and in vivo in mouse xenografts models. The effects on thymidilate synthase (TS) and thymidine kinase (TK1) levels, two enzymes known to play an essential role in the mechanism of action of 5-FU, were analyzed by western blotting and quantitative PCR analysis. The combination of 5-FU with ChoKα inhibitors resulted in a synergistic effect in vitro in three different human colon cancer cell lines, and in vivo against human colon xenografts in nude mice. ChoKα inhibitors modulate the expression levels of TS and TK1 through inhibition of E2F production, providing a rational for its mechanism of action.

Conclusion/Significance

Our data suggest that both drugs in combination display a synergistic antitumoral effect due to ChoKα inhibitors-driven modulation of the metabolization of 5-FU. The clinical relevance of these findings is strongly supported since TCD-717 has recently entered Phase I clinical trials against solid tumors.

Acid ceramidase as a chemotherapeutic target to overcome resistance to the antitumoral effect of choline kinase α inhibition

We have analyzed the response of primary cultures derived from tumor specimens of non small cell lung cancer (NSCLC) patients to choline kinase α (ChoKα) inhibitors. ChoKα inhibitors have been demonstrated to increase ceramides levels specifically in tumor cells, and this increase has been suggested as the mechanism that explain its proapoptotic effect in cancer cells. Here, we have investigated the molecular mechanism associated to the intrinsic resistance, and found that other enzyme involved in lipid metabolism, acid ceramidase (ASAH1), is specifically upregulated in resistant tumors. NSCLC cells with acquired resistance to ChoKα inhibitors also display increased levels of ASAH1. Accordingly, ASAH1 inhibition synergistically sensitizes lung cancer cells to the antiproliferative effect of ChoKα inhibitors. Thus, the determination of the levels of ASAH1 predicts sensitivity to targeted therapy based on ChoKα specific inhibition and represents a model for combinatorial treatments of ChoKα inhibitors and ASAH1 inhibitors. Considering that ChoKα inhibitors have been recently approved to enter Phase I clinical trials by the Food and Drug Administration (FDA), these findings are anticipating critical information to improve the clinical outcome of this family of novel anticancer drugs under development.

Sensitization of (colon) cancer cells to death receptor related therapies: a report from the FP6-ONCODEATH research consortium

The objective of the ONCODEATH consortium [EU Research Consortium "ONCODEATH" (2006-2010)] was to achieve sensitization of solid tumor cells to death receptor related therapies using rational mechanism-based drug combinations of targeted therapies. In this collaborative effort, during a period of 42 mo, cell and animal model systems of defined oncogenes were generated. Exploitation of generated knowledge and tools enabled the consortium to achieve the following research objectives: (1) elucidation of tumor components which confer sensitivity or resistance to TRAIL-induced cell death; (2) providing detailed knowledge on how small molecule Hsp90, Aurora, Choline kinase, BRAF inhibitors, DNA damaging agents, HDAC and DNMT inhibitors affect the intrinsic apoptotic amplification and execution machineries; (3) optimization of combined action of TRAIL with these therapeutics for optimum effects with minimum concentrations and toxicity in vivo. These findings provide mechanistic basis for a pharmacogenomic approach, which could be exploited further therapeutically, in order to reach novel personalized therapies for cancer patients.

Upregulation of trefoil factor 3 (TFF3) after rectal cancer chemoradiotherapy is an adverse prognostic factor and a potential therapeutic target

PURPOSE

Management of locally advanced rectal cancer (RC) consists of neoadjuvant chemoradiotherapy (CRT) with fluoropyrimidines, followed by total mesorectal excision. We sought to evaluate the expression of selected genes, some of which were derived from a previous undirected SAGE (serial analysis of gene expression)-based approach, before and after CRT, to identify mechanisms of resistance.

METHODS

This retrospective cohort study included 129 consecutive patients. Quantitative polymerase chain reaction of 53 candidate genes was performed on the biopsy specimen before treatment and on the surgical specimen after CRT. A paired-samples t test was performed to determine genes that were significantly changed after CRT. The result was correlated with patients' disease-free survival.

RESULTS

Twenty-two genes were significantly upregulated, and two were significantly downregulated. Several of the upregulated genes have roles in cell cycle control; these include CCNB1IP1, RCC1, EEF2, CDKN1, TFF3, and BCL2. The upregulation of TFF3 was associated with worse disease-free survival on multivariate analyses (hazard ratio, 2.64; P=.027). Patients whose surgical specimens immunohistochemically showed secretion of TFF3 into the lumen of the tumoral microglands had a higher risk of relapse (hazard ratio, 2.51; P=.014). In vitro experiments showed that DLD-1 cells stably transfected with TFF3 were significantly less sensitive to 5-fluorouracil and showed upregulation of genes involved in the transcriptional machinery and in resistance to apoptosis.

CONCLUSION

Upregulation of TFF3 after CRT for RC is associated with a higher risk of relapse. The physiological role of TFF3 in restoring the mucosa during CRT could be interfering with treatment efficacy. Our results could reveal not only a novel RC prognostic marker but also a therapeutic target.

Approaches for the study of cancer: towards the integration of genomics, proteomics and metabolomics

Recent technological advances, combined with the development of bioinformatic tools, allow us to better address biological questions combining -omic approaches (i.e., genomics, metabolomics and proteomics). This novel comprehensive perspective addresses the identification, characterisation and quantitation of the whole repertoire of genes, proteins and metabolites occurring in living organisms. Here we provide an overview of recent significant advances and technologies used in genomics, metabolomics and proteomics. We also underline the importance and limits of mass accuracy in mass spectrometry-based -omics and briefly describe emerging types of fragmentation used in mass spectrometry. The range of instruments and techniques used to address the study of each -omic approach, which provide vast amounts of information (usually termed "high-throughput" technologies in the literature) is briefly discussed, including names, links and descriptions of the main databases, data repositories and resources used. Integration of multiple -omic results and procedures seems necessary. Therefore, an emerging challenge is the integration of the huge amount of data generated and the standardisation of the procedures and methods used. Functional data integration will lead to answers to unsolved questions, hopefully, applicable to clinical practice and management of patients.

Human urine proteomics: building a list of human urine cancer biomarkers

In the last decade, several reports have focused on the identification and characterization of proteins present in urine. In an effort to build a list of proteins of interest as biomarkers, we reviewed the largest urine proteomes and built two updated lists of proteins of interest (available as supplementary tables). The first table includes a consensus list of 443 proteins found in urine by independent laboratories and reported on the top three largest urine proteomes currently published. This consensus list of proteins could serve as biomarkers to diagnose, monitor and manage a number of diseases. Here, we focus on a reduced list of 35 proteins with potential interest as cancer biomarkers in urine following two criteria: first, proteins previously detected in urine using bottom-up proteomic experiments, and second, those suggested as cancer protein biomarkers in human plasma. In an effort to standardize the information presented and its use in future studies, here we include the updated International Protein Index (v. 3.80) and primary Swiss-Prot accession numbers, official gene symbols and recommended full names. The main variables that influence urine proteomic experiments are also discussed.

Abstract 3514: Combination of 5-FU with ChoKα inhibitors as a new alternative therapy in colorectal cancer

Colorectal cancer (CRC) is the third major cause of cancer related deaths worldwide. 5-fluorouracil (5-FU) is widely used for the treatment of colorectal cancer but as a single-agent renders low response rates. Despite the achieved improvements over the past years in cancer treatment, the design of novel targeted and combined therapies is still necessary. Choline kinase alpha (ChoKα), a phospholipid-related enzyme that plays a role in cell proliferation and transformation, has been found overexpressed in many different tumors, including colorectal tumors. ChoKα specific inhibitors, MN58b and TCD717, have potent antitumoral activity both in vitro and in vivo against several tumor-derived cell lines including CRC-derived tumour cells. TCD717 has recently entered clinical trials (http://clinicaltrials.gov/ct2/show/NCT01215864).

We have evaluated the effect of ChoKα inhibitors in combination with 5-FU as a new alternative for the treatment of colon tumors. The sequential combination of ChoKα inhibitors with 5-FU resulted in a synergistic effect in vitro in three different human colon cancer cell lines, and in vivo against human colon xenografts in nude mice.

Key enzymes in the metabolic pathway of 5-FU such as Thymidylate synthase (TS) and Thymidine kinase (TK1) have been related to drug resistance, one of the major problems for the lack of success of 5-FU chemotherapy. TS is a key enzyme in the synthesis of DNA and the target enzyme of 5-FU. Several studies have demonstrated that the expression of TS mRNA or protein, predicts overall survival for colon cancer and correlates with resistance to 5-FU. Acquired resistance to 5-FU can also be caused by overproduction of TS that results from gene amplification. Regarding to 5-FU developed resistance, a salvaged pathway has been reported in which TK1 plays an important role. Thus, both TS and TK1 are directly involved in resistance to 5-FU therapy.

To elucidate the mechanism of the observed synergistic effect, we examined the modulation of ChoKα inhibitors on the expression levels of TS and TK1. CRC cell lines treated with the sequential combination of ChoKα inhibitors and 5-FU show both mechanisms of TS inactivation, a formation of ternary complex due to 5-FU mechanism and a significant down-regulation of TS active due to ChoKα inhibitors, resulting in a total depletion of TS protein. We also observed that ChoKα inhibitors affects the levels of TK1, and provide the basis to support a new therapy focused on the combination of ChoKα inhibitors and 5-FU as a new approach for colorectal cancer patients. In addition, we suggest a promising role for ChoKα inhibitors as a new treatment for patients who had failed 5-FU chemotherapy or display high expression levels of TS.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3514. doi:10.1158/1538-7445.AM2011-3514

Abstract 2644: Inhibition of choline kinase increases endoplasmic reticulum stress proteins

Choline kinase (ChoK), the first enzyme in the Kennedy pathway, is responsible for the generation of phosphorylcholine (PCho) that renders phosphatidylcholine, the most abundant phospholipid of plasma membrane. ChoK overexpression has been detected in several cancer types and may act as a prognostic factor in lung, bladder and breast tumors, suggesting its important role in proliferation and cell growth. Specific pharmacologic or siRNA ChoKα inhibition have been proposed as a novel broad-spectrum antitumor strategy. Indeed, ChoKα inhibition induces cell death in several tumor cell lines but is a cytostatic drug in primary cells. In order to exploit their full potential as novel anticancer drugs, it is essential to understand the mechanism implicated in the differential cytotoxic effects induced by ChoK inhibitors on cancer cells. Here we investigate this mechanism using as a model cells from a ductal mammary carcinoma, T47D, and the non-tumorigenic epithelial gland mammary cells, MCF10A.

Cells were treated with two chemical ChoK inhibitors, MN58b and TCD717, the latter recently approved by the FDA to begin a Phase I clinical study for the treatment of solid tumors (http://clinicaltrials.gov/ct2/show/NCT01215864). First, cell viability and proliferation was evaluated to confirm the previous differential effect described in other cell types. By flow cytometry and MTT assay both inhibitors induced cell death in the T47D cells but caused G0/G1 cell cycle arrest in the non-tumorigenic MCF10A cells. Protein levels of several cell cycle (cyclins, phosphor-Rb, E2F) and cell death related proteins (caspase3, PARP) were studied, confirming that ChoK inhibitors caused cell cycle arrest in normal cells but cell death in breast cancer cells. To further investigate the mechanism implicated in this specific cytotoxic effect, the expression levels of some of the most relevant ER stress related genes such as C/EBPβ, ATF4 and CHOP were investigated by QPCR. These genes have been recently involved in apoptosis induced by cytotoxic agents such as tocotrienol and delta(9)-tetrahydrocannabinol. C/EBPβ gene expression levels were significantly increased in tumor cells treated with either inhibitor compared to the non-tumourigenic cells, and this increase was maintained from at least 6 to 48 hours. CHOP overexpression was also significantly increased at earlier times after treatment in T47D cells than in MCF10A cells. Moreover, treatment with ChoK inhibitors significantly increased the production of CHOP and the major ER chaperone BIP in T47D cells compared with non-tumourigenic cells. These data suggest a differential effect of ChoK inhibitors on the induction of ER stress factors in normal vs. tumor cells.

In summary, ChoK inhibition has a profound differential effect in cell cycle regulation and in ER stress response in tumor vs. normal cells, suggesting that ER stress could mediate the specific cytotoxic effects of ChoK inhibitors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2644. doi:10.1158/1538-7445.AM2011-2644

Involvement of human choline kinase alpha and beta in carcinogenesis: a different role in lipid metabolism and biological functions

We have summarized here the importance of ChoKα1 in human carcinogenesis. ChoKα1 displays its oncogenic activity through activation of specific signaling pathways that influence on cell proliferation and survival. It is overexpressed in a large number of human tumors with an incidence of 40-60% of all tumors investigated. Currently, there is an active effort in the development of strategies to knockdown the activity of ChoKα through specific siRNA or small molecules inhibitors. Results from genetic silencing or from treatment with MN58b, a well characterized ChoKα inhibitor showing antiproliferative and antitumoral effect in mice xenografts, provide strong support to this concept, indicating that the design of new antitumoral drugs must be selective against this isoform. However, affecting the other two known isoforms of ChoK may have also therapeutic consequences since the physiologically active form of ChoK may be constituted by homo or heterodimers. Furthermore, alteration of the ChoKβ activity might lead to a change in the lipid content of the cells of particular tissues such as skeletal muscle as described in the ChoKβ null mice (Sher et al., 2006). Finally, the identification of the ChoKα1 isoform as an excellent novel tool for the diagnosis and prognosis of cancer patients may have clinical consequences of immediate usefulness. On one hand, the use of specific monoclonal antibodies against ChoKα1 as a tool for diagnosis in paraffin embedded samples from patient biopsies, through standard immunohistochemistry techniques, can now be achieved (Gallego-Ortega et al., 2006). On the other hand, it has been recently described the prognostic value of determination of ChoKα1 expression levels in non-small cell lung cancer using real time quantitative PCR technology (Ramírez de Molina et al., 2007). Therefore, further research should be supported on the utility of ChoK isoforms as a promising area to improve cancer diagnosis and treatment.

Abstract 1545: Combinatorial efficacy of TRAIL and MN58b against colon cancer to overcome TRAIL resistance

BACKGROUND: Tumor resistance is one of the major problems for cancer treatment and new approaches to overcome resistance are required. TNF-Related Apoptosis Inducing Ligand (TRAIL) has recently emerged as a promising therapy due to its selectivity towards tumor cells and is currently being evaluated in phase I and phase II clinical trials. Choline kinase alpha (ChoKα) inhibition has also recently proven to be an efficient strategy to specifically induce tumor cell death without affecting normal cells. The aim of this study is to investigate the potential use of combinatorial treatment of TRAIL and MN58b, a specific ChoKα inhibitor, to potentiate tumor cell death. EXPERIMENTAL PROCEDURES: Two different colon cancer-derived cell lines were used: DLD-1 and SW620. The antiproliferative effect of MN58b, TRAIL, or both was determined using MTT method. Western blots were carried out to measure PARP degradation and caspase-3 activation, and Annexin V- PI staining was used to verify cell death induction in response to drugs by flow cytometry. The results obtained in vitro were verified in vivo using xenograft models for both cell lines. RESULTS: Using different concentrations of both drugs, it has been established that the best strategy of combination is a simultaneous treatment. Our data shows that when MN58b and TRAIL are simultaneously combined, a strong synergistic effect is observed in DLD-1 cells, with a combination index (CI) of 0.196. Moreover, MN58b treatment is able to overcome TRAIL resistance in SW620 cell line (CI=0.155). The synergistic effect was verified by both PARP and Caspase-3 analysis as apoptosis markers. Cell death was also analyzed by flow cytometry. This in vitro synergistic effect was confirmed in vivo using xenograft models of both cell lines. DLD-1 induced tumor growth was inhibited by 42% and 51% when treated with MN58b or TRAIL respectively. When both drugs were combined the effect was much stronger, reaching 78% inhibition. These findings suggest that MN58b cooperates with TRAIL in suppressing tumor growth in DLD-1 xenograft model. SW620 xenograft response to MN58b was weaker, with 26% inhibition. TRAIL alone produced no significant decrease of tumor growth in keeping with the observation of this cell line being resistant to TRAIL. When MN58b and TRAIL were combined, there was a marked 71% tumor growth inhibition, suggesting that MN58b is able to sensitize SW620 to TRAIL-induced apoptosis in vivo, and confirming all the in vitro observed effects. CONCLUSION: ChoKα inhibition can enhance TRAIL-induced apoptosis in DLD-1 cells and is able to abrogate TRAIL resistance in SW620 cells. Considering that MN58b when used alone exhibits anticancer activities in vitro and in vivo against a wide variety of tumor-derived cell lines, this study establishes its additional potential use in combination with TRAIL on tumors that develop TRAIL resistance.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1545.

Regulation of Akt(ser473) phosphorylation by choline kinase in breast carcinoma cells

BACKGROUND

The serine/threonine kinase PKB/Akt plays essential role in various cellular processes including cell growth and proliferation, metabolism and cell survival. The importance of the Akt pathway is highlighted by the mutation of various components of the pathway such as the PTEN and PI3-kinase (P110alpha) in human cancers. In this paper, we employed an RNA interference library targeting all human kinases to screen for kinases involved in the regulation of Akt activation, in particular serine 473 phosphorylation. Here, we transfected the MDA-MB 468 breast cell line with the human kinome siRNA library and measured Akt activation using an antibody specific for phosphoserine 473 of Akt.

RESULTS

The screen revealed that phosphorylation of Akt(ser473) can be regulated by more than 90 kinases. Interestingly, phosphorylation of Akt(ser473), but not thr308, can be severely reduced by inhibition of Choline kinase activity via siRNA or small molecule inhibitors. We show here that the regulation of Akt phosphorylation by Choline kinase is PI3K-independent. In addition, xenograft tumors treated with Choline kinase inhibitors demonstrated a statistically significant decrease in Akt(ser473) phosphorylation. Importantly, the reduction in phosphorylation correlates with regression of these xenograft tumors in the mouse model.

CONCLUSION

High Choline kinase expression and activity has previously been implicated in tumor development and metastasis. The mechanism by which Choline kinase is involved in tumor formation is still not fully resolved. From our data, we proposed that Choline kinase plays a key role in regulating Akt(ser473) phosphorylation, thereby promoting cell survival and proliferation.

Differential role of human choline kinase alpha and beta enzymes in lipid metabolism: implications in cancer onset and treatment

BACKGROUND

The Kennedy pathway generates phosphocoline and phosphoethanolamine through its two branches. Choline Kinase (ChoK) is the first enzyme of the Kennedy branch of synthesis of phosphocholine, the major component of the plasma membrane. ChoK family of proteins is composed by ChoKalpha and ChoKbeta isoforms, the first one with two different variants of splicing. Recently ChoKalpha has been implicated in the carcinogenic process, since it is over-expressed in a variety of human cancers. However, no evidence for a role of ChoKbeta in carcinogenesis has been reported.

METHODOLOGY/PRINCIPAL FINDINGS

Here we compare the in vitro and in vivo properties of ChoKalpha1 and ChoKbeta in lipid metabolism, and their potential role in carcinogenesis. Both ChoKalpha1 and ChoKbeta showed choline and ethanolamine kinase activities when assayed in cell extracts, though with different affinity for their substrates. However, they behave differentially when overexpressed in whole cells. Whereas ChoKbeta display an ethanolamine kinase role, ChoKalpha1 present a dual choline/ethanolamine kinase role, suggesting the involvement of each ChoK isoform in distinct biochemical pathways under in vivo conditions. In addition, while overexpression of ChoKalpha1 is oncogenic when overexpressed in HEK293T or MDCK cells, ChoKbeta overexpression is not sufficient to induce in vitro cell transformation nor in vivo tumor growth. Furthermore, a significant upregulation of ChoKalpha1 mRNA levels in a panel of breast and lung cancer cell lines was found, but no changes in ChoKbeta mRNA levels were observed. Finally, MN58b, a previously described potent inhibitor of ChoK with in vivo antitumoral activity, shows more than 20-fold higher efficiency towards ChoKalpha1 than ChoKbeta.

CONCLUSION/SIGNIFICANCE

This study represents the first evidence of the distinct metabolic role of ChoKalpha and ChoKbeta isoforms, suggesting different physiological roles and implications in human carcinogenesis. These findings constitute a step forward in the design of an antitumoral strategy based on ChoK inhibition.

A critical role for choline kinase-alpha in the aggressiveness of bladder carcinomas

Bladder cancer is one of the most common causes of death in industrialized countries. New tumor markers and therapeutic approaches are still needed to improve the management of bladder cancer patients. Choline kinase-alpha (ChoKalpha) is a metabolic enzyme that has a role in cell proliferation and transformation. Inhibitors of ChoKalpha show antitumoral activity and are expected to be introduced soon in clinical trials. This study aims to assess whether ChoKalpha plays a role in the aggressiveness of bladder tumors and constitutes a new approach for bladder cancer treatment. We show here that ChoKalpha is constitutively altered in human bladder tumor cells. Furthermore, in vivo murine models, including an orthotopic model to mimic as much as possible the physiological conditions, revealed that increased levels of ChoKalpha potentiate both tumor formation (P< or =0.0001) and aggressiveness of the disease on different end points (P=0.011). Accordingly, increased levels of ChoKalpha significantly reduce survival of mice with bladder cancer (P=0.05). Finally, treatment with a ChoKalpha-specific inhibitor resulted in a significant inhibition of tumor growth (P=0.02) and in a relevant increase in survival (P=0.03).

Choline kinase alpha depletion selectively kills tumoral cells

Choline Kinase (ChoK) comprises a family of cytosolic enzymes involved in the synthesis of phosphatidylcholine (PC), the most abundant phospholipid in eukaryotic cell membranes. One of the ChoK isoforms, Choline Kinase alpha (ChoKalpha), is found over expressed in human tumours. Chemical inhibitors able to interfere with ChoK activity have proven to be effective antitumoral drugs in vitro and in vivo. To validate the use of selective ChoKalpha inhibitors in cancer therapy, we have developed a genetic strategy to interfere specifically with ChoKalpha activity based on the generation of a shRNA against the alpha isoform of ChoK. Here we demonstrate that specific inhibition of ChoKalpha by shRNA has antitumor activity. The specific depletion of ChoKalpha induces apoptosis in several tumor-derived cell lines from breast, bladder, lung and cervix carcinoma tumors, while the viability of normal primary cells is not affected. Furthermore, this selective antiproliferative effect is achieved both under in vitro and in vivo conditions, as demonstrated by an inducible ChoKalpha suppression system in human tumour xenografts. These results demonstrate that ChoKalpha inhibition is a useful antitumoral strategy per se, and provides definitive and non-ambiguous evidence that ChoKalpha can be used as an efficient and selective drug target for cancer therapy.

TWIST1 overexpression is associated with nodal invasion and male sex in primary colorectal cancer

BACKGROUND

TWIST1 is a basic helix-loop-helix (bHLH) transcription factor that has been involved in tumor progression and metastasis in several cancer types, although no evidence has been provided yet on its implication in colorectal carcinogenesis.

METHODS

We examined the expression pattern of TWIST1 messenger RNA (mRNA) in 54 colorectal cancer biopsies compared with each respective adjacent normal mucosa by real-time reverse-transcriptase polymerase chain reaction (RT-PCR) methodology.

RESULTS

TWIST1 mRNA was found significantly overexpressed in colorectal cancer samples compared to nontumorous colon mucosa (P < 0.0001). Receiver operating characteristic (ROC) curve analysis demonstrated that TWIST1 mRNA levels are significantly increased in patients with nodal invasion and, interestingly, a significant correlation with patient sex was also found.

CONCLUSIONS

Evidence for upregulation of TWIST1 mRNA in colorectal cancer is provided, suggesting its implication in the onset of malignant progression of this disease. In addition, significant higher levels of TWIST1 mRNA were found in men than in women, suggesting a possible transcriptional regulation of TWIST1 by sexual hormones. The use of TWIST1 as a new prognostic marker of advanced malignancy, and as a potential therapeutic target in colorectal cancer, is proposed.

Cdc42 is highly expressed in colorectal adenocarcinoma and downregulates ID4 through an epigenetic mechanism

Cdc42, a member of Rho GTPases family, is involved in the regulation of several cellular functions, such as rearrangement of actin cytoskeleton, membrane trafficking, cell-cycle progression, and transcriptional regulation. Aberrant expression or activity of Cdc42 has been reported in several tumours. Here, the specific role of Cdc42 in development and progression of colorectal cancer was analyzed through microarrays technology. A comparative analysis of Cdc42 overexpressing cells versus cells with decreased Cdc42 levels through siRNA revealed that Cdc42 overexpression down-regulated the potential tumour suppressor gene ID4. Results were validated by quantitative RT-PCR and the methylation status of the specific promoter, analyzed. Methylation-specific PCR and bisulfite sequencing PCR analysis revealed that Cdc42 induced the methylation of the CpG island of the ID4 promoter. Colorectal adenocarcinoma samples were compared with the corresponding adjacent normal tissue of the same patient in order to determine specific gene expression levels. The downregulation of ID4 by Cdc42 was also found of relevance in colorectal adenocarcinoma biopsies. Cdc42 was found to be overexpressed with high incidence (60%) in colorectal cancer samples, and this expression was associated with silencing of ID4 with statistical significance (p<0.05). Cdc42 may have a role in the development of colon cancer. Furthermore, inhibition of Cdc42 activity may have a direct impact in the management of colorectal cancer.

A critical role for Rac1 in tumor progression of human colorectal adenocarcinoma cells

Colorectal adenocarcinoma is the second cause of cancer mortality in developed countries. Rac1 is a member of the family of Rho GTPases that regulates many intracellular signaling pathways, including those involved in tumorigenesis, invasion, and metastasis. We have investigated the role of Rac1 in colorectal tumor progression by genetic modification of the human colorectal adenocarcinoma cell line SW620 to either overexpress Rac1 or lack Rac1 expression. Tumor behavior was studied by orthotopic injection of stably modified cell lines into the cecal wall of athymic nude mice, a model that replicates the histopathological appearance and clinical behavior of human colorectal adenocarcinoma in humans. While overexpression of Rac1 resulted in an accelerated tumorigenic process, inducing a faster mortality rate, inhibition of Rac1 completely suppressed tumor formation. These results suggest that Rac1 plays a major role in colorectal adenocarcinoma progression. Finally, interference with Rac1 function may provide an important tool to block the malignant phenotype of colorectal adenocarcinoma cells.

Expression of choline kinase alpha to predict outcome in patients with early-stage non-small-cell lung cancer: a retrospective study

BACKGROUND

Adequate prognostic markers to predict outcome of patients with lung cancer are still needed. The aim of this study was to assess whether choline kinase alpha (ChoKalpha) gene expression could identify patients with different prognoses. ChoKalpha is an enzyme involved in cell metabolism and proliferation and has a role in oncogene-mediated transformation in several human tumours, including lung cancer.

METHODS

60 patients with non-small-cell lung cancer (NSCLC) who had undergone surgical resection in a single centre were enrolled into the study as the training group. We used real-time reverse-transcriptase PCR (RT-PCR) to measure ChoKalpha gene expression and analyse the association between ChoKalpha expression and survival in evaluable patients. Additionally, a second group of 120 patients with NSCLC from a different hospital were enrolled into the study as the validation group. We did an overall analysis of all 167 patients who had available tissue to confirm the cut-off point for future studies. The primary endpoints were lung-cancer-specific survival and relapse-free survival.

FINDINGS

Seven of the 60 patients in the training group were not evaluable due to insufficient tissue. In the 53 evaluable patients, the cut-off for those with ChoKalpha overexpression was defined by receiver operator under the curve (ROC) methodology. 4-year lung-cancer-specific survival was 54.43% (95% CI 28.24-80.61) for 25 patients with ChoKalpha expression above the ROC-defined cut-off compared with 88.27% (75.79-100) for 28 patients with concentrations of the enzyme below this cut-off (hazard ratio [HR] 3.14 [0.83-11.88], p=0.07). In the validation group, six of the 120 enrolled patients were not evaluable due to insufficient tissue. For the other 114 patients, 4-year lung-cancer-specific survival was 46.66% (32.67-59.65) for those with ChoKalpha expression above the ROC-defined cut-off compared with 67.01% (50.92-81.11) for patients with concentrations of ChoKalpha below the cut-off (HR 1.87 [1.01-3.46], p=0.04). A global analysis of all 167 patients further confirmed the association between ChoKalpha overexpression and worse clinical outcome of patients with NSCLC: 4-year lung-cancer-specific survival for ChoKalpha expression above the ROC-defined cut-off was 49.00% (36.61-60.38) compared with 70.52% (59.80-76.75) for those with concentrations of ChoKalpha below the cut-off (HR 1.98 [1.14-3.45], p=0.01). The overall analysis confirmed the cut-off for ChoKalpha expression should be 1.91-times higher than concentrations noted in healthy tissues when ChoKalpha is used as an independent predictive factor of relapse-free and lung-cancer-specific survival in patients with early-stage NSCLC.

INTERPRETATION

ChoKalpha expression is a new prognostic factor that could be used to help identify patients with early-stage NSCLC who might be at high risk of recurrence, and to identify patients with favourable prognosis who could receive less aggressive treatment options or avoid adjuvant systemic treatment. New treatments that inhibit ChoKalpha expression or activity in patients with lung cancer should be studied further.

Orthotopic microinjection of human colon cancer cells in nude mice induces tumor foci in all clinically relevant metastatic sites

Despite metastasis as an important cause of death in colorectal cancer patients, current animal models of this disease are scarcely metastatic. We evaluated whether direct orthotopic cell microinjection, between the mucosa and the muscularis layers of the cecal wall of nude mice, drives tumor foci to the most relevant metastatic sites observed in humans and/or improves its yield as compared with previous methods. We injected eight animals each tested human colorectal cancer cell line (HCT-116, SW-620, and DLD-1), using a especially designed micropipette under binocular guidance, and evaluated the take rate, local growth, pattern and rate of dissemination, and survival time. Take rates were in the 75 to 88% range. Tumors showed varying degrees of mesenteric and retroperitoneal lymphatic foci (57 to 100%), hematogenous dissemination to liver (29 to 67%) and lung (29 to 100%), and peritoneal carcinomatosis (29 to 100%). Tumor staging closely correlated with animal survival. Therefore, the orthotopic cell microinjection procedure induces tumor foci in the most clinically relevant metastatic sites: colon-draining lymphatics, liver, lung, and peritoneum. The replication of the clinical pattern of dissemination makes it a good model for advanced colorectal cancer. Moreover, this procedure also enhances the rates of hematogenous and lymphatic dissemination at relevant sites, as compared with previously described methods that only partially reproduce this pattern.

Differential expression of Rac1 identifies its target genes and its contribution to progression of colorectal cancer

The small GTPase Rac1 is involved in the regulation of critical cellular functions, such as transcription control, cell cycle, and organization of actin cytoskeleton. Rac1 signalling modulates cancer progression since its overexpression leads to an increased tumour growth of xenografts of human colorectal tumour cells, while a drastic reduction of Rac1 expression by siRNA interferes with cancer progression (Espina et al., unpublished results). We aimed to study the molecular basis for the specific contribution of Rac1 in the progression of colorectal cancer. Comparative microarray analysis of a human colorectal carcinoma cell line genetically engineered to display different levels of Rac1 identified novel target genes for this GTPase. These results suggest that Rac1 plays a critical role in signalling transduction pathways relevant to human colorectal tumour progression, such as activation of Wnt signalling, inhibition of TGF-beta signalling, and enhancement of metastasis-inducing genes.

Generation and characterization of monoclonal antibodies against choline kinase alpha and their potential use as diagnostic tools in cancer

Choline kinase alpha (ChoKalpha) is a metabolic enzyme involved in the synthesis of phosphatidylcholine, recently implicated in cancer onset since it is overexpressed in a variety of human cancers such as mammary, lung, colorectal and prostate adenocarcinomas. Furthermore, overexpression of ChoKalpha in human HEK293T cells confers them oncogenic properties with the induction of tumors after subcutaneous injection in nude mice. ChoKalpha levels in tumor samples have been analyzed using polyclonal antibodies and Western blotting. These techniques have considerable limitations and do not allow for a precise and efficient evaluation of the real significance of ChoK overexpression in human carcinogenesis. We developed a set of monoclonal antibodies with high specificity and sensitivity against ChoKalpha, and characterized their properties. We provide evidence that the newly generated MoAbs against ChoKalpha have potential use in cancer diagnosis by conventional immunohistochemistry techniques.

18F-choline images murine atherosclerotic plaques ex vivo

OBJECTIVE

Current imaging modalities of atherosclerosis mainly visualize plaque morphology. Valuable insight into plaque biology was achieved by visualizing enhanced metabolism in plaque-derived macrophages using 18F-fluorodeoxyglucose (18F-FDG). Similarly, enhanced uptake of 18F-fluorocholine (18F-FCH) was associated with macrophages surrounding an abscess. As macrophages are important determinants of plaque vulnerability, we tested 18F-FCH for plaque imaging.

METHODS AND RESULTS

We injected 18F-FCH (n=5) or 18F-FDG (n=5) intravenously into atherosclerotic apolipoprotein E-deficient mice. En face measurements of aortae isolated 20 minutes after 18F-FCH injections demonstrated an excellent correlation between fat stainings and autoradiographies (r=0.842, P<0.0001), achieving a sensitivity of 84% to detect plaques by 18F-FCH. In contrast, radiotracer uptake 20 minutes after 18F-FDG injections correlated less with en face fat stainings (r=0.261, P<0.05), reaching a sensitivity of 64%. Histological analyses of cross-sections 20 minutes after coinjections of 18F-FCH and 14C-FDG (n=3) showed that 18F-FCH uptake correlated better with fat staining (r=0.740, P<0.0001) and macrophage-positive areas (r=0.740, P<0.0001) than 14C-FDG (fat: r=0.236, P=0.29 and CD68 staining: r=0.352, P=0.11), respectively.

CONCLUSIONS

18F-FCH identifies murine plaques better than 18F-FDG using ex vivo imaging. Enhanced 18F-FCH uptake into macrophages may render this tracer a promising candidate for imaging plaques in patients.

Rho GTPase expression in tumourigenesis: evidence for a significant link

Rho proteins belong to the small GTPases superfamily. They function as molecular switches that, in response to diverse stimuli, control key signaling and structural aspects of the cell. Although early studies proposed a role for Rho GTPases in cellular transformation, this effect was underestimated due to the fact that no genetic mutations affecting Rho-encoding genes were found in tumors. Recently, it has become evident that Rho GTPases participate in the carcinogenic process by either overexpression of some of the members of the family with oncogenic activity, downmodulation of other members with suggested tumor suppressor activity, or by alteration of upstream modulators or downstream effectors. Thus, alteration of the levels of expression of different members of the family of Rho GTPases has been detected in many types of human tumors leading to a great interest in the cellular effects elicited by these oncoproteins. This essay reviews the current evidence of dysregulation of Rho signaling by overexpression in human tumors.

Choline Kinase Is a Novel Oncogene that Potentiates RhoA-Induced Carcinogenesis

Choline kinase is overexpressed in human breast, lung, colorectal, and prostate tumors, a finding that suggests the involvement of this enzyme in carcinogenesis. Here we show that overexpression of choline kinase induce oncogenic transformation of human embryo kidney fibroblasts and canine epithelial Madin-Darby canine kidney cells. Choline kinase lays downstream of RhoA signaling and is activated through ROCK kinase, one of the best-characterized RhoA effectors. In keeping with this, coexpression of RhoA and choline kinase potentiates both anchorage independent growth and tumorigenesis. Finally, choline kinase-mediated transformation is sensitive to MN58b, a well-characterized specific choline kinase inhibitor. These results provide the definitive evidence that choline kinase has oncogenic properties and that choline kinase inhibition constitutes a novel valid antitumor strategy.

Inhibition of choline kinase renders a highly selective cytotoxic effect in tumour cells through a mitochondrial independent mechanism

Tumour cells are frequently altered in their phospholipid metabolism. Choline kinase (ChoK, E.C. 2.7.1.32) activity, the first enzyme involved in the synthesis of phosphatidylcholine, is increased in a large number of human tumours and tumour-derived cell lines. We have previously reported that MN58b, a specific inhibitor of ChoK, has anti-tumoral activity. Here we show the high specificity of MN58b as a cytotoxic drug towards tumour cells, and explore further the basis of its mechanism of action in order to provide a rational understanding for its antitumoral activity. A dramatic difference in the response to the treatment of primary, normal and non-tumorigenic human cells when compared to tumour-derived cell lines was observed. In normal cells, blockage of de novo PCho synthesis by MN58b results in a reversible cell cycle arrest at G0/G1 phase. In contrast, ChoK inhibition in tumour cells promotes the induction of apoptosis. This effect depends on the cell cycle phase, being G1 the critical phase. Regarding the mechanism of apoptosis engagement, a loss of mitochondrial potential was observed 10-20 min after cytochrome c release, but caspase 3 activation preceded the loss of mitochondrial potential, indicating that activation of caspase 3 is independent of cytochrome c release. Our results are consistent with a non-intrinsic process as the mechanism underlying the induction of apoptosis by ChoK inhibition in tumoral cells.

Rho GTPases in human cancer: an unresolved link to upstream and downstream transcriptional regulation

The high incidence of overexpression of some members of the Rho family of GTPases in human tumors suggests that (1) these proteins are involved in cancer onset, and (2) they are potential candidates for a therapeutic intervention. In recent years, the characterization of downstream effectors to Rho GTPases has provided crucial clues on the general cellular effects that permit aberrant proliferation and adhesiveness of tumor cells. The activation of many of these effector proteins in turn results in the modulation of the activity of several transcription factors that play an important role at various levels of Rho signaling. The precise mechanisms by which Rho GTPases participate in carcinogenesis are still not fully understood. However, it is becoming more evident that the specific role of Rho overexpression in tumor initiation, progression and metastasis, as well as the nature and cause of such overexpression in specific human tumors (i.e., transient or stable; tumor environment-regulated; genetic or epigenetic) may be linked to the activation of specific signaling pathways that result in transcriptional regulation. In this review, we summarize the functions of Rho proteins in the regulation of several transcription factors and their relationship to tumor biology.

Influence of the linker in bispyridium compounds on the inhibition of human choline kinase

Studies have been aimed to establish the structure-activity relationship that define choline kinase (ChoK) inhibitory potency and antiproliferative activity of a set of 25 bispyridinium compounds with electron-releasing groups at position 4. Here we report that, according to their inhibitory activities against human ChoK, the enzymatic inhibitory potency is closely related to the size of the linker, the 3,3'-biphenyl moiety being the most suitable. The N-methylanilino and its derivatives, 4-chloro-N-methylanilino and 3,5-dichloro-N-methylanilino, render higher ChoK inhibitory and antiproliferative activities against the HT-29 human colon cancer cell line.