Signal-transduction therapy. A novel approach to disease management

Novel Electrochemiluminescent Assays for Drug Discovery

IGEN's ORIGEN® technology, which is based on electrochemiluminescence, has been adopted by a number of research and bioanalytical laboratories who have recognized its exquisite sensitivity, high precision, wide dynamic range, and flexibility in formatting a wide variety of applications. IGEN's M-SERIES™ marks the introduction of the second generation of detection systems employing the ORIGEN technology specifically repackaged to address the needs of the high throughput laboratories involved in drug discovery. Assays are formatted without wash steps. Users realize the high performance of a heterogeneous technology with the convenience of a homogeneous format. The M-SERIES platform can address enzymatic assays (kinases, proteases, helicases, etc.), receptor-ligand or protein-protein assays, immunoassays, quantitation of nucleic acids, as well as other applications. Recent assay formats will be explored in detail.

Tyrosine kinase inhibitors: views of selectivity, sensitivity, and clinical performance

With the manufacture of imatinib, researchers introduced tyrosine kinase inhibitors (TKIs) into the clinical setting in 2000 to treat cancers; approximately fifteen other TKIs soon followed. Imatinib remains the most successful agent, whereas all the others have had modest effects on the cancers that they target. The current challenge is to identify the agents that need to be combined with TKIs to maximize their efficacy. One of the most promising approaches is to combine immune therapy with TKI treatment. In this review, the therapeutic potential of TKIs for treatment is discussed.

Synthesis of the cancer preventive peptide lunasin by lactic acid bacteria during sourdough fermentation

This study aimed to exploit the potential of sourdough lactic acid bacteria to release lunasin during fermentation of cereal and nonconventional flours. The peptidase activities of a large number of sourdough lactic acid bacteria were screened using synthetic substrates. Selected lactic acid bacteria were used as sourdough starters to ferment wholemeal wheat, soybean, barley, amaranth, and rye flours. Proteinase activity during fermentation was characterized by SDS-PAGE analysis of the water-soluble extracts. Albumins having molecular masses of 18 to 22 kDa, which included the size of lunasin precursors, were markedly affected by proteolysis of lactic acid bacteria. After fermentation, lunasin from the water-soluble extracts was quantified, purified, and identified through RP-HPLC and nano-LC-ESI-MS analyses. Compared to control doughs, the concentration of lunasin increased up to 2-4 times during fermentation. Lactobacillus curvatus SAL33 and Lactobacillus brevis AM7 synthesized the highest concentrations of lunasin in all the flours. Besides the presence of the entire lunasin sequence, fragments containing the immunoreactive epitope RGDDDDDDDDD were also found. This study shows that fermentation by lactic acid bacteria increased the concentration of lunasin to levels that would suggest new possibilities for the biological synthesis and for the formulation of functional foods.

Therapeutic prospect of Syk inhibitors

BACKGROUND

The non-receptor spleen tyrosine kinase (Syk; EC 2.7.10.2) is involved in signal transduction in a variety of cell types. In particular, it is a key mediator of immune receptors signaling in host inflammatory cells (B cells, mast cells, macrophages and neutrophils), important for both allergic and antibody-mediated autoimmune diseases. Deregulated Syk kinase activity also allows growth factor-independent proliferation and transforms bone marrow-derived pre-B cells that are able to induce leukemia. Consequently, the development of Syk kinase inhibitors could conceivably treat these disorders and so they have became a major focus in the pharmaceutical and biotech industry.

OBJECTIVE

In this review, we analyze the structure and role of Syk kinase, the use of small molecules, interacting with ATP-binding site, as inhibitors of kinase activity and finally the potential of using inhibitors of Syk kinase expression to attenuate pathological conditions.

CONCLUSION

Syk kinase inhibition is suggested as a powerful tool for the therapy of different pathologies.

Overproduction, purification and structure determination of human dual-specificity phosphatase 14

Dual-specificity phosphatases (DUSPs) are enzymes that participate in the regulation of biological processes such as cell growth, differentiation, transcription and metabolism. A number of DUSPs are able to dephosphorylate phosphorylated serine, threonine and tyrosine residues on mitogen-activated protein kinases (MAPKs) and thus are also classified as MAPK phosphatases (MKPs). As an increasing number of DUSPs are being identified and characterized, there is a growing need to understand their biological activities at the molecular level. There is also significant interest in identifying DUSPs that could be potential targets for drugs that modulate MAPK-dependent signaling and immune responses, which have been implicated in a variety of maladies including cancer, infectious diseases and inflammatory disorders. Here, the overproduction, purification and crystal structure at 1.88 A resolution of human dual-specificity phosphatase 14, DUSP14 (MKP6), are reported. This structural information should accelerate the study of DUSP14 at the molecular level and may also accelerate the discovery and development of novel therapeutic agents.

The Use and Refinement of Rodent Models in Anti-cancer Drug Discovery: A Review

This review describes the changing use of tumour models in rodents (predominantly mice) as employed over the last four decades in anti-cancer drug discovery, and the refinements in the experimental methods used. Such models are required to examine the complexities of cancer biology (e.g. tumour angiogenesis, invasion and metastasis, host immunity factors) and the impact of potential therapies (e.g. drug pharmacokinetics, pharmacodynamics and therapeutic index), and they have produced efficacious human therapeutics. Animal welfare considerations have driven refinements to animal models of cancer over time, with the most dramatic refinements being facilitated by the move away from inherently cytotoxic therapeutic approaches toward targeted inhibitors of disease-related processes. Whereas, four decades ago, the impact of disease burden was used as an endpoint in the absence of defined mechanistic parameters, acute pharmacodynamic measures are now increasingly used to minimise the adverse effects of disease and experimental procedures in a given animal. The changes in the UK guidelines on the use of rodents in preclinical cancer testing are also used as an illustration of the progressive refinement in tumour models and drug testing.

Development of a HTRF kinase assay for determination of Syk activity

Regulation of protein phosphorylation is a primary cellular signaling mechanism. Many cellular responses to internal and external events are mitigated by protein kinase signaling cascades. Dysfunction of protein kinase activity has been linked to a variety of human pathologies, in the areas of cancer, inflammation, metabolism, cell cycle, apoptosis, as well as cardiovascular, neurodegenerative and autoimmune diseases [1-3]. As such, there is an important need for protein kinase activity detection methodologies for researchers engaged in Drug Discovery. A number of different technologies have been employed for the measurement of protein kinase activity, including radioactive methods, luminescent methods, and fluorescent methods. More recently, Homogeneous Time Resolved Fluorescence technology (HTRF^®), based on the principle of time-resolved fluorescent resonance energy transfer (TR-FRET), has been developed and applied for the measurement of protein kinase activity in vitro. This technology note describes the development of an HTRF^® assay for detection of Syk enzyme activity in a format consistent with the requirements of High-Throughput Screening (HTS) campaigns currently used in drug discovery.

Synthesis and biological evaluation of substituted 6-alkynyl-4-anilinoquinazoline derivatives as potent EGFR inhibitors

A series of C-6 or C-3' alkynyl-substituted 4-anilinoquinazoline derivatives was prepared straightforwardly by a Sonogashira reaction of the corresponding bromo-substituted 4-anilinoquinazolines. Bioactive assay of these compounds for in vitro EGFR kinase inhibition demonstrated that the novel 6-hydroxypropynyl-4-anilinoquinazoline 5e was a very potent EGFR kinase inhibitor with an IC(50) of 14 nM.

The cancer preventive peptide lunasin from wheat inhibits core histone acetylation

Lunasin is a unique 43-amino acid cancer preventive peptide initially reported in soybean and barley and has been shown to be chemopreventive in mammalian cells and in a skin cancer mouse model against oncogenes and chemical carcinogens. We report here the core histone H3- and H-acetylation inhibitory properties of lunasin from wheat, a new source of the peptide and from the livers of rats fed with lunasin-enriched wheat (LEW) to measure bioavailability. A non-radioactive histone acetyl transferase assay was used to measure inhibition of core histone acetylation. The presence of lunasin in wheat was established by Western blot and identified by liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS). Lunasin isolated from wheat seeds at different stages of development inhibited core histone H3 and H4 acetylation in a dose-dependent manner. Lunasin extracted from liver of rats fed with lunasin-enriched wheat (LEW) also inhibited histone acetylation confirming that the peptide is intact and bioactive. The amounts of lunasin in the developing seeds and in the rat liver correlated extremely well with the extent of inhibition of core histone acetylation.

Tyrphostins and other tyrosine kinase inhibitors

The development of tyrosine phosphorylation inhibitors has transformed the approach to cancer therapy and is likely to affect other fields of medicine. In spite of the conservation among protein tyrosine kinases (PTKs), one can develop small molecules that block the activity of a narrow spectrum of PTKs and that exhibit much less toxicity than the currently used chemotherapeutic agents. In this review, we discuss principles for inhibiting specific PTKs. We discuss (a) the birth of the concept of generating targeted, nontoxic signal transduction inhibitors, (b) the potential of substrate-competitive versus the more common ATP-competitive PTK inhibitors, (c) the combination of PTK inhibitors with other signal transduction inhibitors to induce apoptosis-the best way to induce the demise of the cancer cell, and (d) the potential to utilize PTK inhibitors/tyrphostins to attenuate nonmalignant pathological conditions, such as immune disorders, tissue rejection, and restenosis.

Design and Concise Synthesis of Fully Protected Analogues of l-γ-Carboxyglutamic Acid

The design and synthesis of four nonnaturally occurring amino acid analogues of l-gamma-carboxyglutamic acid (Gla), appropriately protected for Fmoc-based solid-phase peptide synthesis (SPPS), is described. These amino acids are Bu-Mal 2, BCAH 3, Pen-Mal 4, and Cm-Gla 5. These Gla analogues have been designed to replace the glutamic acid of position 1 in the cyclic decapeptide G1TE, which is a potent inhibitor of tyrosine kinase, to further enhance binding to the Grb2-SH2 domain of signal transduction receptors. In the new amino acids, the propionic acid side chain of Glu has been replaced by a malonyl or a carboxymethylmalonyl moiety located at different distances from the alpha-carbon to optimize interactions in the phosphotyrosine-binding cavity of the Grb2-SH2 domain. Additionally, a direct and efficient synthetic route for the preparation of Fmoc-protected l-gamma-carboxyglutamic acid, which is amenable to large-scale production, has been developed to provide this important and unique amino acid(1) in 55% overall yield.

Mechanisms and markers of carcinogenesis and neoplastic progression

Neoplastic transformation evolves over a period of time involving the progression of the cellular immunophenotype (IP) from normal to hyperplastic to dysplastic, and finally, to fully malignant IPs. Superimposed on these changes is the interaction of the initiated cell with its microenvironment, whereby the neoplastically transformed cells, through the regulation or dysregulation of cytoskeletal, integrin, protease and adhesion molecules, develop a novel manner of relation with their surrounding microenvironment. Studies of the neuroendocrine-immune network revealed that the hormonal and cytokine milieu plays an important role impacting the growth and dedifferentiation capabilities of neoplastic cells. This is further affected by the tumour cells themselves determining the constitution of this hormonal microenvironment, allowing the most aggressive and invasive of neoplastically transformed cell clones to promote their own growth and dissemination. The elucidation of the steps of the progression of cancer from premalignant to metastatic and invasive forms is of utmost importance in the differential diagnosis of neoplasms and in the establishment of more efficacious therapeutic regimens. These regimens will certainly begin to take on a more individualised form. The functional characterisation of various human malignancies as to the neoplastically transformed cells' IP, the bases of their interaction with tissue stromal elements, and the molecules involved in the humoral microenvironment of the particular stage of tumour will certainly allow for the better diagnosis, staging, prognostication and treatment of cancers in the future. This paper reviews carcinogenesis from nutritional, genetic and molecular, and humoral aspects, and discusses the importance of tumour markers in the diagnosis and therapeutic management of human cancer.

Drug Discovery in the Kinase Inhibitory Field Using the Nested Chemical Library™ Technology

Kinase inhibitors are at the forefront of modern drug research, where mostly three technologies are used for hit-and-lead finding: high throughput screening of random libraries, three-dimensional structure-based drug design based on X-ray data, and focused libraries around limited number of new cores. Our novel Nested Chemical Library (NCL) (Vichem Chemie Research Ltd., Budapest, Hungary) technology is based on a knowledge base approach, where focused libraries around selected cores are used to generate pharmacophore models. NCL was designed on the platform of a diverse kinase inhibitory library organized around 97 core structures. We have established a unique, proprietary kinase inhibitory chemistry around these core structures with small focused sublibraries around each core. All the compounds in our NCL library are stored in a big unified Structured Query Language database along with their measured and calculated physicochemical and ADME/toxicity (ADMET) properties, together with thousands of molecular descriptors calculated for each compound. Biochemical kinase inhibitory assays on selected, cloned kinase enzymes for a few hundred NCL compound sets can provide sufficient biological data for rational computerized design of new analogues, based on our pharmacophore model-generating 3DNET4W QSPAR (quantitative structure-property/activity relationships) approach. Using this pharmacophore modeling approach and the ADMET filters, we can preselect synthesizable compounds for hit-and-lead optimization. Starting from this point and integrating the information from QSPAR, high-quality leads can be generated within a small number of optimization cycles. Applying NCL technology we have developed lead compounds for several validated kinase targets.

Killing time for cancer cells

As the signalling pathways that control cellular proliferation and death are unravelled, a range of targets have emerged as candidates for molecular cancer therapy. For their survival, cancer cells depend on a few highly activated signalling pathways; inhibition of these pathways has a strong apoptotic effect and can lead to tumour regression. But drugs that exploit this weakness, such as imatinib, have not cured patients: withdrawal of the drug leads to disease recurrence, and sustained treatment leads to the emergence of drug-resistant clones. Can cancer be cured, or will it have to be controlled as a chronic disease?

Receptor-Targeted Cancer Therapy

Insight into the molecular mechanisms of malignant transformation is changing the way cancer is being treated. Conventional treatment strategies target the DNA of all dividing cells, resulting in a significantly increased risk of collateral toxicity. In addition, the accumulation of multiple mutations leads to drug resistance in many cancer cells. Targeted strategies have now been developed that specifically disrupt oncogenically active cell surface receptors and endogenous signaling molecules. These agents have a much greater selectivity for tumor tissue and decreased risk of side effects. Increased signaling through ErbB receptors via gene amplification, overexpression, and mutation has been implicated in many human cancers and associated with poor prognosis. Interruption of this process has been shown to cause antitumor effects. Downregulation of the ErbB receptors, HER-2/neu, and later EGFR, with monoclonal antibodies was the first demonstration of targeted therapy. Subsequently, the ErbB tyrosine kinase domain has been successfully targeted with small molecule inhibitors. The development of novel ErbB-directed entities is ongoing, with particular promise being shown by strategies targeting receptor interaction in oligomeric complexes.

Purification and biochemical properties of glutathione S-transferase from Lactuca sativa

A glutathione S-transferase (GST) from Lactuca sativa was purified to electrophoretic homogeneity approximately 403-fold with a 9.6% activity yield by DEAE-Sephacel and glutathione (GSH)-Sepharose column chromatography. The molecular weight of the enzyme was determined to be approximately 23,000 by SDS-polyacrylamide gel electrophoresis and 48,000 by gel chromatography, indicating a homodimeric structure. The activity of the enzyme was significantly inhibited by ShexylGSH and S-(2,4-dinitrophenyl) glutathione. The enzyme displayed activity towards 1-chloro-2,4-dinitrobenzene, a general GST substrate and high activities towards ethacrynic acid. It also exhibited glutathione peroxidase activity toward cumene hydroperoxide.

Grb2 SH2 domain-binding peptide analogs as potential anticancer agents

The growth factor receptor-bound protein 2 (Grb2) plays an important role in the Ras signaling pathway. Several proteins were found to be overexpressed by oncogenes in the Ras signaling pathway, rendering Grb2 a potential target for the design of antitumor agents. Blocking the interaction between the phosphotyrosine-containing activated receptor and the Src-homology 2 (SH2) domain of Grb2 thus constitutes an important strategy for the development of potential anticancer agents. X-ray, NMR structural investigations, and molecular modeling studies have provided the target structure of Grb2 SH2 domain-alone or complexed with a phosphotyrosine-containing peptide-which is useful for the structure-based design of peptides or peptidomimetics with high affinity for the Grb2 SH2 domain. We review here the variety of approaches to Grb2 SH2 pepide inhibitors developed with the aim of interrupting Grb2 recognition. Inhibitory effects of peptide analogs on the Grb2 SH2 domain and their binding affinities for Grb2 SH2 were determined by ELISA, cell-based assays, or Surface Plasman Resonance (SPR) technology. Results of theses studies provide important information for further modifications of lead peptides, and should lead to the discovery of potent peptides as anticancer agents.

Neurofibromatosis type 1 tumour suppressor gene expression is deficient in psoriatic skin in vivo and in vitro: a potential link to increased Ras activity

BACKGROUND

Neurofibromatosis type 1 (NF1) protein (neurofibromin) accelerates the inactivation of Ras-GTP in various cell types. Somatic mutations of the NF1 gene may lead to malignant transformation and uncontrolled proliferation. We have previously shown that NF1 protein expression is downregulated in psoriasis in vivo.

OBJECTIVES

To study the functional expression and distribution of NF1 mRNA and protein in vivo and in psoriatic and normal keratinocyte cultures.

METHODS

Immunohistochemistry and in situ hybridization were used to study NF1 gene and protein expression in psoriasis in vivo. Furthermore, Northern and in situ hybridizations, immunoblot and localization analyses were utilized to study NF1 mRNA and protein in vitro in keratinocyte cultures.

RESULTS

NF1 tumour suppressor gene expression was reduced in lesional psoriatic skin compared with perilesional and normal skin in vivo. The in vitro results showed that the levels of NF1 mRNA and protein were reduced in cultured psoriatic keratinocytes during cellular differentiation even after multiple passaging of the cells. Moreover, cultured nonlesional psoriatic keratinocytes were almost equally defective as lesional cells with respect to NF1 expression.

CONCLUSIONS

Our findings demonstrate that psoriatic keratinocytes maintain an altered phenotype and gene expression profile even when isolated from interaction with lymphocytes and fibroblasts, which are known to increase proliferation of keratinocytes. As NF1 protein is regarded as a Ras proto-oncogene regulator, the aberrant expression and distribution of NF1 protein and mRNA found in the present study may be causative to the previously described increased activation of Ras in psoriatic lesions, and relate to altered cellular behaviour.

Tyrosine kinase receptors as attractive targets of cancer therapy

Receptor tyrosine kinases (RTKs) are the main mediators of the signaling network that transmit extracellular signals into the cell, and control cellular differentiation and proliferation. Recent and rapid advances in our understanding of cellular signaling by receptor tyrosine kinases, in normal and malignant cells, have brought to light the potential of RTKs as selective anti-cancer targets. Their activity is normally tightly controlled and regulated. Overexpression of RTK proteins or functional alterations caused by mutations in the corresponding genes or abnormal stimulation by autocrine growth factor loops contribute to constitutive RTK signaling, resulting in dysregulated cell growth and cancer. The mechanisms of uncontrolled RTK signaling that leads to cancer has provided the rationale for anti-RTK drug development. Herceptin, Gleevec, and Iressa are the first examples of drugs which have successfully translated basic research on oncogenes into cancer therapeutics. RTKs can be viewed as multifunctional targets, and strategies towards the prevention and inhibition of RTK signaling include antibodies, antagonist ligands, small molecule inhibitors of protein kinase activity, and inhibitors of protein-protein interactions. Progresses in the field of rational drug design and computational chemistry will vastly benefit from the availability of increasing structural knowledge of both the kinase domains and the ligand-binding sites of these receptors.

Modulation of autonomic balance by tumors and viruses

Autonomic balance, a function generally under host control, is subject to modulation by other signalers. In some cases, modulation of host autonomic function through behavioral and physical stressors exerted by another individual may have negative consequences for the stress recipient by inducing sympathetic bias. Modulation of autonomic function may sometimes benefit one party at the expense of another. Tumors and HIV are examples of illegitimate signalers who may induce host sympathetic bias to promote their own growth and evade host immune surveillance. Paraneoplastic and paraviral syndromes such as hypertrophic osteoarthopathy, QTc prolongation, insomnia, and cachexia could be viewed as epiphenomena related to the tumoral and viral manipulation of host autonomic balance. In a more general framework, other paraneoplastic and paraviral syndromes may represent epiphenomena related to modulation of endocrine, cytokine, and autonomic functions by tumors and viruses to promote their own survival. Spatial distribution of cancers and viruses within the host may reflect affinity for strategic locations that facilitate manipulation of a variety of host functions including autonomic, endocrine, and cytokine regulation. A more general for understanding spatial distribution of diseases based on gradients of autonomic balance in the body are explored. Darwinian perspectives are discussed.

Structural basis for a non-phosphorus-containing cyclic peptide binding to Grb2-SH2 domain with high affinity

Blocking the interaction between phosphotyrosine (pTyr)-containing activated receptors and the Src homology 2 (SH2) domain of the growth factor receptor bound protein 2 (Grb2) is considered to be an effective and non-cytotoxic strategy to develop new anti-proliferative agents due to its potential to shut down the Ras activation pathway. Generally, the pTyr-X-Asn minimal binding motif is required for a high-affinity ligand binding to the Grb2-SH2 domain. Using phage-display techniques, we discovered a non-pTyr-containing cyclic peptide G1 with moderate binding affinity from 10(7) different sequences. To understand the structural basis for the high-affinity binding of these novel non-phosphorus-containing inhibitors to the Grb2-SH2 domain, we extensively studied herein the unique functional requirements of the acidic side chain in Tyr-2 position due to the absence of the phosphate group in these non-phosphorylated peptides. A comprehensive SAR study was also carried out to develop potent Grb2-SH2 domain antagonists based upon this novel template. With both the peptidomimetic optimization of the amino acid side-chains and the constraint of the backbone conformation guided by molecular modeling, we developed several potent antagonists with low nanomolar range binding affinity, such as cyclic peptide 20 with an IC(50)=0.026 microM, which is one of the most potent non-phosphorus-containing Grb2-SH2 antagonists reported to date. Whole cell assays indicate that peptide 20 can penetrate the cell membranes and inhibit the association of Grb2 with p185(erbB2) in erbB2-overexpressing MDA-MA-453 cancer cells at low micromolar concentrations.

Solid-phase synthesis of a pepticinnamin E library

Pepticinnamin E is a naturally occurring bisubstrate inhibitor of farnesyltransferase. Based on the structure of the natural product, a compound library was synthesized by variation of eight structural parameters. Following three different routes, a total of 51 analogues was synthesized on the polymeric support in 6-11-step parallel syntheses. Overall yields ranged from 3 to 63%, and the compounds were obtained with >90% purity.

Identification of mono- and bisubstrate inhibitors of protein farnesyltransferase and inducers of apoptosis from a pepticinnamin E library

A library of 51 analogues of the naturally occurring protein farnesyltransferase inhibitor pepticinnamin E was investigated biologically. Several compounds with pronounced inhibitory activity were discovered with the lowest IC(50) value reaching 1 microM. The library contains inhibitors which are competitive to either farnesylpyrophosphate or the peptide substrate and a bisubstrate inhibitor. This activity is supported and rationalized by molecular modelling experiments and different binding modes of the inhibitors deduced from them. Several compounds induced apoptosis in a Ras-transformed tumour cell line, and in one case this correlated with farnesyltransferase-inhibiting activity.

Cytokines and signal transduction pathways mediated by anthralin in alopecia areata-affected Dundee experimental balding rats

Although many therapeutic modalities have been tested on alopecia areata, patient outcomes have been disappointing. Use of animal models would help to develop more efficient therapies as well as understanding therapeutic mechanisms. We have demonstrated that 0.1% topical anthralin ointment is 100% effective in restoring follicular activity in Dundee experimental balding rats. This is the most promising topical treatment for Dundee experimental balding rats among the therapeutic agents tested on this model. Various cytokines have been shown to be associated with the pathogenesis of alopecia areata. To test whether any of these cytokines might be modulated by anthralin, an RNase protection assay and the real-time polymerase chain reaction were performed to compare their expression between anthralin-treated and control skins. These experiments showed that expression of tumor necrosis factor-alpha and interferon-gamma was inhibited by anthralin, whereas expression of interleukin-1alpha/beta and their receptor antagonist, interleukin-1Ra, and interleukin-10 was stimulated by anthralin. In addition, using an antibody-based multi-immunoblotting technique, we found that certain signaling regulatory proteins were modulated by anthralin. Their potential roles in reversing the autoimmune-arrested follicular activity in Dundee experimental balding rats are discussed.

Protein kinase inhibitors as a therapeutic modality

Most of the signal transduction pathways are mediated by protein kinases regulating every aspect of cell function. Mutations which deregulate their expression or their function or both result in cancers. Therefore, protein kinase inhibitors has become the focus of development of new therapies for cancer. Almost all 120 protein tyrosine kinases are involved in signaling, whereas only a handful of Ser/Thr kinases are involved. Thus, most of the effort is directed toward the development of tyrosine phosphorylation inhibitors. The success of Gleevec in the treatment of chronic myeloid leukemia and of Iressa for lung cancer validates the approach.

Anticancer bisquaternary heterocyclic compounds: a ras-ional design

A new family of symmetrical bisquaternary compounds with semirigid linkers have shown to be highly specific for Choline Kinase (ChoK) inhibition and to exert antitumoural activity in cell lines and in mice. A three-parameter regression equation has been derived which satisfactorily describes the ex vivo inhibitory potency of ChoK of the title compounds. The electronic effect of the group at position 4 of the cationic head plays a critical role although the hydrophobic contribution, especially that of the linker, favors the ChoK inhibitory activity. The antiproliferative activity (in vitro assay) is correlated with the ChoK inhibition (ex vivo assay) through the electronic effect and a squared term of the overall lipophilicity of the molecules. We also provide in vivo evidence that ChoK is a novel target for the design of antitumoural drugs. All these results suggest that ChoK plays a crucial role in the onset of carcinogenesis.

Chronic administration of a tyrosine kinase inhibitor restores functional and morphological changes of the basilar artery during chronic hypertension

OBJECTIVE

Activation of tyrosine kinase appears to play an important role in pathogenesis of cardiovascular disease during chronic hypertension. In the present study, we tested the hypothesis that long-term treatment with an inhibitor of tyrosine kinase would have beneficial effects on hypertension-induced morphological and functional changes of the cerebral artery.

METHODS

Male spontaneously hypertensive rats (SHR; 4 months old) were fed normal rat chow, or that containing an inhibitor of tyrosine kinase, genistein (1 mg/kg chow). Normotensive Wistar-Kyoto (WKY) rats were also fed either of the chows. After feeding the rats for 2 months, we measured wall thickness, diameter of the basilar artery and its dilator responses to acetylcholine (ACh); Y-26763, an opener of ATP-sensitive potassium channels; and Y-27632, an inhibitor of Rho-associated kinase.

RESULTS

Treatment with genistein did not cause significant changes in physiological variables, including mean arterial pressure in either strain. In control SHR, the wall thickness of the basilar artery was greater than that of WKY rats. Genistein treatment reduced the wall thickness significantly in SHR. Vasodilator responses induced by ACh and Y-26763 were markedly attenuated in SHR compared to WKY rats, and treatment of SHR with genistein significantly improved the vasodilatation. Dilatation of the artery in response to Y-27632 was enhanced in SHR compared to WKY rats and treatment of SHR with genistein did not affect the enhanced vasodilator responses to Y-27632.

CONCLUSIONS

Chronic treatment with genistein may be a novel approach to prevent cerebrovascular disorders.

Inhibitors of the ras oncogene as therapeutic targets

Advances in our understanding of the molecular pathways and genetic mutations that control tumor cell proliferation and metastasis present an opportunity to develop novel, mechanism-based therapeutic strategies. Ras mutations are the most frequently activated oncogenes in human tumors, with over 30% expressing ras mutations. Molecular dissection of the signaling pathway and the mechanisms of ras anchorage, post-translational modification, and downstream effector signaling of ras now under intensive investigation will help us to design additional methods for ras-directed therapy in an effort to reach an optimal treatment for human tumors that will most likely comprise a combination of modalities targeted at the different underlying genetic defects. The successes and limitations of ras-targeted therapies must be viewed in light of the increasing understanding of the complexity of the ras-signaling pathway. Only now are we beginning to discover the many functions of this integrated pathway, such as the differences between the actions of various ras isoforms that may affect our choice of therapeutic approach. Many of these Ras therapeutic targets have shown success in preclinical studies, and some have shown efficacy in clinical trials with minimal toxicities. Compounds that block ras-transforming activity without affecting normal ras function seem more attractive for the future development of ras-targeted therapy. FTIs may partially fulfill such requirements. Based on their specific, novel, and mechanism-based action; minimal toxicity; and encouraging responses in clinical trials, the development of Ras therapeutic targets as single agents or in combination with conventional chemotherapy and radiotherapy should be pursued.

Tyrosine kinases as targets for cancer therapy

Enhanced protein tyrosine kinase (PTK) activity correlates with the development of cancer and other proliferative diseases. The hypothesis that PTK inhibitors may be of value in the treatment of cancer led to the systematic synthesis of selective tyrosine phosphorylation inhibitors (tyrphostins) that show in vitro and in vivo anticancer activity. This review will provide an overview of research efforts in the development of tyrphostins such as AG 957, AG 1112, and AG 1318. Other tyrphostins discussed are AG 1478 and RG 13022, which are both epidermal growth factor receptor kinase inhibitors; AG 490, a Jak-2 kinase inhibitor; AG 1296, a PDGFR kinase inhibitor; and STI 571 (imatinib, Glivec/Gleevec; Novartis Pharma AG, Basel, Switzerland). STI 571 is now approved for the treatment of chronic myeloid leukemia and shows activity against gastrointestinal stromal tumors. The chemistry, kinetics, biological activity, and clinical potential of these compounds will be discussed.

Interaction of tyrosine kinase inhibitors with the human multidrug transporter proteins, MDR1 and MRP1

Specific tyrosine kinase inhibitors (TKIs) are rapidly developing clinical tools applied for the inhibition of malignant cell growth and metastasis formation. Most of these newly developed TKI molecules are hydrophobic, thus rapidly penetrate the cell membranes to reach intracellular targets. However, a large number of tumor cells overexpress multidrug transporter membrane proteins, which efficiently extrude hydrophobic drugs and thus may prevent the therapeutic action of TKIs. In the present work, we demonstrate that the most abundant and effective cancer multidrug transporters, MDR1 and MRP1, directly interact with several TKIs under drug development or already in clinical trials. This interaction with the transporters does not directly correlate with the hydrophobicity or molecular structure of TKIs, and shows a large variability in transporter selectivity and affinity. We suggest that performing enzyme- and cell-based multidrug transporter interaction tests for TKIs may greatly facilitate drug development, and allow the prediction of clinical TKI resistance based on this mechanism. Moreover, diagnostics for the expression of specific multidrug transporters in the malignant cells, combined with information on the interactions of the drug transporter proteins with TKIs, should allow a highly effective, individualized clinical treatment for cancer patients.

Phase I and pharmacokinetic study of BIBX 1382 BS, an epidermal growth factor receptor (EGFR) inhibitor, given in a continuous daily oral administration

The pyrimido-pyrimidine BIBX 1382 BS inhibits the intracellular tyrosine kinase domain of the epidermal growth factor receptor (EGFR), thus specifically reverting the aberrant enzymatic activity from overexpressed and constitutively activated EGFR. A phase I and pharmacokinetic study of this new specific molecule was carried out. After initially performing an accelerated titration design from the first toxicities onwards, a modified Fibonacci scheme was used to escalate the daily oral dose. The following dosages and cycles (defined as treatment during 28 days) were applied: 25 mg: 6; 50 mg: 3; 100 mg: 6; 200 mg: 7; 150 mg: 3. Over a 10 months accrual phase, 11 patients (pts) (7 females, 4 males) with a median age of 63 years (range 50-73 years), World Health Organization Performance Status (WHO PS) 0:5 pts, 1:6 pts and miscellaneous solid tumours were entered. The median number of cycles applied per pt was 2 (range 1-7). Reversible, dose-dependent increase of liver enzymes (maximal Common Toxicity Criteria (CTC) grades: gamma-glutamyl transferase (GGT): 4, aspartate aminotransferase (GOT): 3, alanine aminotransferase (GPT): 3, alkaline phosphatase (AP): 3, bilirubin: 3) occurred. Oral medication yielded plasma levels far below those expected to be efficacious. In conclusion, target plasma levels could not be reached via the oral route at a reasonable dosage. Meanwhile, a preclinically unknown metabolite was identified from the urine of one patient. Subsequently, this metabolite was found to be abundant in patient plasma. The metabolite was demonstrated to be pharmacologically inactive. Due to a dose-limiting increase of liver enzymes, low bioavailability of BIBX 1382 BS and the detection of a pharmacologically inactive metabolite, this trial was discontinued.

Relationship between lipophilicity and antitumor activity of molecule library of Mannich ketones determined by high-performance liquid chromatography, clogP calculation and cytotoxicity test

A series of Mannich ketones were synthesized in order to study the relative importance of structure and specific substitutions in relation to their lipophilicity and antitumor activity. Substitutions were carried out with morpholinyl, pirrolidinyl, piperidyl and tetrahydro-isoquinolyl groups in various positions on three different skeletons. Lipophilicity of Mannich ketones was characterised by chromatography data (log k') and by software calculated parameters (clogP). Compounds were tested on their ability to inhibit the proliferation of the A431 human adenocarcinoma cell line evaluated by MTT and apoptosis assays. The results suggest that the higher the lipophilicity values (log k' and clogP), the higher the antitumor and apoptotic activity of Mannich ketones. Determination of lipophilicity by measuring the log k' or by calculating the clogP values of the compounds may help to predict their biological activities.

NF-kappaB in transplantation: friend or foe?

NF-kappaB is an inducible nuclear transcription factor regulating the expression of many genes. NF-kappaB activation may function as a master switch in a variety of immune and inflammatory processes, including sepsis and transplant tolerance. In this review, we summarize features of NF-kappaB regulation, as well as describe its role in intracellular signal transduction pathways. Subsequently, we concentrate on the role of NF-kappaB in the field of organ transplantation and the role of NF-kappaB in organ ischemia/reperfusion injury and graft rejection. Finally, potential therapeutic strategies are discussed to modify NF-kappaB activity with certain immunosuppression medications, including cyclosporine, tacrolimus, and glucocorticoids.

Ras biochemistry and farnesyl transferase inhibitors: a literature survey

Over the last decades, knowledge on the genetic defects involved in tumor formation and growth has increased rapidly. This has launched the development of novel anticancer agents, interfering with the proteins encoded by the identified mutated genes. One gene of particular interest is ras, which is found mutated at high frequency in a number of malignancies. The Ras protein is involved in signal transduction: it passes on stimuli from extracellular factors to the cell nucleus, thereby changing the expression of a number of growth regulating genes. Mutated Ras proteins remain longer in their active form than normal Ras proteins, resulting in an overstimulation of the proliferative pathway. In order to function, Ras proteins must undergo a series of post-translational modifications, the most important of which is farnesylation. Inhibition of Ras can be accomplished through inhibition of farnesyl transferase, the enzyme responsible for this modification. With this aim, a number of agents, designated farnesyl transferase inhibitors (FTIs), have been developed that possess antineoplastic activity. Several of them have recently entered clinical trials. Even though clinical testing is still at an early stage, antitumor activity has been observed. At the same time, knowledge on the biochemical mechanisms through which these drugs exert their activity is expanding. Apart from Ras, they also target other cellular proteins that require farnesylation to become activated, e.g. RhoB. Inhibition of the farnesylation of RhoB results in growth blockade of the exposed tumor cells as well as an increase in the rate of apoptosis. In conclusion, FTIs present a promising class of anticancer agents, acting through biochemical modulation of the tumor cells.

Molecular approaches to receptors as targets for drug discovery

Many receptors have been selected as viable drug discovery targets. One particular class of receptors that have received much interest and so far relatively good success are the receptor protein tyrosine kinases (RPTKs). Typically, RPTKs are activated following the binding of the peptide growth factor ligand to its receptor. The RPTKs play crucial roles in signal transduction pathways that regulate a number of cellular functions, such as cell differentiation and proliferation, both under normal physiological conditions as well as in a variety of pathological disorders. A variety of different tumour types have been shown to have dysfunctional RPTKs, either as a result of excess production of the growth factor, the receptor or both, or via mutations in the RPTKs structure. Irrespective of the cause, this leads to the over-activity of the particular RPTK system and in turn to the aberrant and inappropriate cellular signalling within the tumour cell. RPTKs are attractive targets in the search for therapeutic agents, not only against cancers but also against many other disease indications. Although an ever-increasing number of RPTKs have been selected as viable molecular targets for drug discovery programmes, four examples will be covered in this article. These are the epidermal growth factor receptor (EGF-R), platelet-derived growth factor receptor (PDGF-R), fibroblast growth factor receptor (FGR-R) and vascular endothelial growth factor receptor (VEGF-R), with the main emphasis of interest being on their role in oncology.

Synthesis of functional Ras lipoproteins and fluorescent derivatives

For the study of biological signal transduction, access to correctly lipidated proteins is of utmost importance. Furthermore, access to bioconjugates that embody the correct structure of the protein but that may additionally carry different lipid groups or labels (i.e., fluorescent tags) by which the protein can be traced in biological systems, could provide invaluable reagents. We report here of the development of techniques for the synthesis of a series of modified Ras proteins. These modified Ras proteins carry a number of different, natural and non-natural lipid residues, and the process was extended to also provide access to a number of fluorescently labeled derivatives. The maleimide group provided the key to link chemically synthesized lipopeptide molecules in a specific and efficient manner to a truncated form of the H-Ras protein. Furthermore, a preliminary study on the biological activity of the natural Ras protein derivative (containing the normal farnesyl and palmitoyl lipid residues) has shown full biological activity. This result highlights the usefulness of these compounds as invaluable tools for the study of Ras signal transduction processes and the plasma membrane localization of the Ras proteins.

Fluorescence intensity multiple distributions analysis: concurrent determination of diffusion times and molecular brightness

Fluorescence correlation spectroscopy (FCS) has proven to be a powerful technique with single-molecule sensitivity. Recently, it has found a complement in the form of fluorescence intensity distribution analysis (FIDA). Here we introduce a fluorescence fluctuation method that combines the features of both techniques. It is based on the global analysis of a set of photon count number histograms, recorded with multiple widths of counting time intervals simultaneously. This fluorescence intensity multiple distributions analysis (FIMDA) distinguishes fluorescent species on the basis of both the specific molecular brightness and the translational diffusion time. The combined information, extracted from a single measurement, increases the readout effectively by one dimension and thus breaks the individual limits of FCS and FIDA. In this paper a theory is introduced that describes the dependence of photon count number distributions on diffusion coefficients. The theory is applied to a series of photon count number histograms corresponding to different widths of counting time intervals. Although the ability of the method to determine specific brightness values, diffusion times, and concentrations from mixtures is demonstrated on simulated data, its experimental utilization is shown by the determination of the binding constant of a protein-ligand interaction exemplifying its broad applicability in the life sciences.