Current Drug Targets, Volume 4, No. 4, 2003
Contents
Inwardly Rectifying Potassium Channels in the
Regulation of Vascular Tone
Pp.281-289
Sophocles
Chrissobolis and Christopher G. Sobey
Endoglin (CD105): A Target for Anti-angiogenetic
Cancer Therapy Pp.291-296
E.
Fonsatti , M. Altomonte, P. Arslan and M. Maio
Vascular and Parenchymal Mechanisms in
Multiple Drug Resistance: a Lesson from Human Epilepsy
Pp.297-304
Matteo
Marroni , Nicola Marchi , Luca Cucullo , N. Joan Abbott , Kathy Signorelli and Damir Janigro
The Molecular Targets of Antitumor
2’-deoxycytidine Analogues
Pp.305-313
Tohru
Obata , Yoshio Endo, Daigo Murata, Kazuki Sakamoto and Takuma Sasaki
Anticoagulant Therapy for Acute Lung Injury
or Pneumonia Pp.315-321
Marcus
J. Schultz , Marcel Levi , and Tom van der Poll
Zinc Homeostasis-regulating Proteins: New
Drug Targets for Triggering Cell Fate Pp.323-338
F.
Chimienti , M. Aouffen , A. Favier
and M. Seve
Gene Therapy with Transcription Factor Decoy
Oligonucleotides as a Potential Treatment for Cardiovascular Diseases Pp.339-346
Naruya Tomita , Haruhito Azuma , Yasufumi Kaneda , Toshio Ogihara and Ryuichi Morishita
Update on Tandem Pore (2P) Domain K+
Channels Pp.347-351
C. Spencer Yost
Abstracts
[Back to top] Inwardly Rectifying Potassium Channels in the
Regulation of Vascular Tone
Sophocles
Chrissobolis and Christopher G. Sobey
Potassium ion (K+) channel activity is one of the major determinants of vascular muscle
cell membrane potential and thus vascular tone. Four types of K+ channels are functionally important in the vasculature - Ca2+-activated K+ (KCa) channels, voltage-dependent
K+ (KV) channels, ATP-sensitive K+ (K ATP) channels, and inwardly rectifying K+ (KIR) channels, and the latter type will be the subject of
this review. Recent advances in vascular KIR channel research indicate that
this channel: 1) is present in vascular muscle; 2) modulates basal arterial
tone; 3) mediates powerful hyperpolarization and vasodilator responses to small
but physiological increases in extracellular K+; 4) may contribute to vasodilatation in response to flow-induced shear
stress; 5) may be inhibited by protein kinase C activity; 6) may be involved in
vasorelaxation mediated by endothelium-derived hyperpolarizing factor; and 7)
may be functionally altered in cardiovascular diseases. Vascular effects of KIR
channels have so far been most extensively studied in the cerebral circulation
where KIR function may be important in coupling cerebral metabolism
and blood flow.
[Back to top] Endoglin (CD105): A Target for
Anti-angiogenetic Cancer Therapy
E.
Fonsatti , M. Altomonte, P. Arslan and M. Maio
Targeting of tumor
vasculature is a promising strategy for cancer treatment. Among endothelial
cell markers, Endoglin, a cell membrane glycoprotein, is emerging as an
attractive therapeutic target on angiogenetic blood vessels, and it currently
represents a powerful marker to quantify tumor angiogenesis. In normal human
tissues, Endoglin is weakly expressed on erytroid precursors, stromal cells and
activated monocytes, whereas it is strongly expressed on proliferating
endothelial cells. In human neoplasias of different histotype, Endoglin is
mainly present on endothelial cells of both periand intra-tumoral blood
vessels, while it is weakly expressed or absent on neoplastic cells. Endoglin
is an accessory component of the receptor complex of Transforming Growth Factor
(TGF)-b, a pleiotropic cytokine that modulates
angiogenesis by the regulation of different cellular functions including
proliferation, differentiation and migration. Interestingly, the
over-expression of Endoglin antagonizes several cellular responses to TGF- b1, while its down-regulation potentiates cellular responses to TGF- b1. In animal models, administration of radiolabeled anti-Endoglin
monoclonal antibodies (mAb) efficiently images primary tumors, and naked or
conjugated anti-Endoglin mAb suppress angiogenesis and tumor growth. In this
review we will summarize the complex of experimental evidences pointing to
Endoglin as a vascular target to design innovative bioimmunotherapeutic
strategies in human neoplasias.
[Back to top] Vascular and Parenchymal Mechanisms in
Multiple Drug Resistance: a Lesson from Human Epilepsy
Matteo
Marroni , Nicola Marchi , Luca Cucullo , N. Joan Abbott , Kathy Signorelli and Damir Janigro
Long term treatment
with antiepileptic drugs (AEDs) is the standard therapeutic approach to
eradicate seizures. However, a small but significant number of patients fail
AED treatment. Intrinsic drug resistance may depend on two main and not
necessarily mutually exclusive mechanisms: 1) Loss of pharmacological target
(e.g., GABAA receptors); 2) poor penetration of the drug into the
central nervous system (CNS). The latter is due to the action of multiple drug
resistance proteins capable of active CNS extrusion of drugs. These include
MDR1 ((P-glycoprotein, PgP), the multidrug resistance related proteins MRP1-5,
and lung-resistance protein (LRP). Overexpression of MDR1 occurs in human
epileptic brain. It has therefore been proposed that MDR1/PgP may contribute to
multiple drug resistance in epilepsy. In addition to MDR1/PgP, other genes such
as MRP2, MRP5, and human cisplatin resistance–associated protein are also
overexpressed in drug-resistant epilepsy. In normal brain tissue MDR1/PgP is
expressed almost exclusively by endothelial cells (EC), while in epileptic
cortex both EC and perivascular astrocytes express MDR1/PgP. The underlying
causes for tissue differences may be genomic (i.e., at the DNA level), or
MDR1/PgP could be induced by seizures, previous drug treatment, or a
combination of the above. We will present evidence showing that expression of
multiple drug resistance genes in epilepsy is a complex phenomenon and that
glial cells are involved. This second line of defense for xenobiotics may have
profound implications for the pharmacokinetic properties of antiepileptic drugs
and their capacity to reach neuronal targets.
[Back to top] The Molecular Targets of Antitumor
2’-deoxycytidine Analogues
Tohru
Obata , Yoshio Endo, Daigo Murata, Kazuki Sakamoto and Takuma Sasaki
Most antitumor
2’-deoxycytidine (dCyd) analogues, such as Ara-C (1-ß-arabinofuranosylcytosine)
and gemcitabine (2’-deoxy-2’,2’-difluolo-cytidine), have common antitumor
mechanisms and metabolic pathways. These nucleosides are transported into tumor
cells via specific nucleoside transporters (NT), and then phosphorylated toward
each monophosphate form by dCyd kinase. Finally, tri-phosphate forms are
enzymatically produced and efficiently inhibit DNA synthesis. It is believed
that dCyd kinase is a very important activator of antitumor 2’-dCyd analogues
and an attractive molecular target for biochemical modulation. Resistant cells
established by continuous exposure to 2’-dCyd analogues in vitro have extremely
high resistance as compared with parental cells, and their resistance indexes
are sometimes increased between several hundred to thousand times. Such high
resistance is generally attributed to deficiency of dCyd kinase activity, but
the clinical resistance index of Ara-C-resistant patients is estimated to be
increased a maximum of 20 times compared with non-treated patients. The
differences between experimental and clinical resistances may be caused by
different mechanisms of resistance. To clarify such resistance mechanisms, we
carried out research focused on NT and dCyd kinase. Our results show that
earlier resistant cells, that exhibited a 20 times lower resistance index, had
a reduced NT activity but retained dCyd kinase activity. In contrast, dCyd
kinase activity was deficient in later resistant cells that showed maximum
resistance. Both NT and dCyd kinase activities are important for the
acquisition of resistance and are useful as molecular targets for biochemical
modulation or the development of novel antitumor 2’-dCyd analogues. These
results suggest that NT activity is likely to be responsible for clinical
resistance.
[Back to top] Anticoagulant Therapy for Acute Lung Injury or Pneumonia
Marcus
J. Schultz , Marcel Levi , and Tom van der Poll
Pulmonary changes
in thrombin formation in patients with acute lung injury or pneumonia are
remarkably similar to systemic changes in coagulation observed in septic
patients. Since anticoagulant therapy has proven to be successful in the treatment
of patients with sepsis, the same therapeutic strategy may benefit patients
with acute lung injury or pneumonia. Based on the fact that inflammation not
only leads to dysregulation of the coagulation system, but vice versa,
activation of coagulation amplifies inflammatory processes as well, it can be
questioned whether the advantage of anticoagulant therapy is solely related to
its influence on disturbed thrombin formation. In this paper we will discuss
local changes in the haemostatic balance during acute lung injury, both in
pre-clinical and clinical studies. Until now, pre-clinical studies have
demonstrated that interventions aimed at correction of coagulation
abnormalities may form an important strategy in patients with acute lung injury
in the future. Pre-clinical studies on use of anticoagulants during pneumonia
are presently performed and data are underway.
[Back to top] Zinc Homeostasis-regulating Proteins: New
Drug Targets for Triggering Cell Fate
F.
Chimienti , M. Aouffen , A. Favier
and M. Seve
Zinc is an
essential trace element for life. Zinc is not only an important nutrient,
cofactor of numerous enzymes and transcription factors, but also it acts as an
intracellular mediator, similarly to calcium. The recent discovery of its
intracellular molecular pathways opens the door to new fields of drug design.
Zinc homeostasis results from a coordinated regulation by different proteins
involved in uptake, excretion and intracellular storage/trafficking of zinc. These
proteins are membranous transporters, belonging to the ZIP and ZnT families,
and metallothioneins. Their principal function is to provide zinc to new
synthesized proteins, important for several functions such as gene expression,
immunity, reproduction or protection against free radicals damage. Zinc
intracellular concentration is correlated to cell fate, ie proliferation,
differentiation or apoptosis, and modifications of zinc homeostasis are
observed in several pathologies affecting humans at any stage of life. Two
zinc-related diseases, acrodermatitis enteropathica and the lethal milk
syndrome, have been recently related to mutations in zinc transporters, SLC39A4
and ZnT-4, respectively. Zinc acts as an inhibitor of apoptosis, while its
depletion induces programmed cell death in many cell lines. However, excess
zinc can also be cytotoxic, and zinc transporters as well as metallothioneins
serve as zinc detoxificating systems. Several zinc channels, controlling the
intracellular zinc movements and the free form of the metal, maintain the
intracellular zinc homeostasis, and thus the balance between life and cell
death. Apart from these general activities, zinc has particular biological
roles in some specialized cells. It acts as a paracrine regulator in pancreatic
cell, neuron or neutrophil activity by a mechanism of vesicles-mediated metal
excretion and uptake. A well knowledge on zinc transporters will be useful to
develop new molecular targets to act on these zinc-regulated biological
functions.
[Back to top] Gene Therapy with Transcription Factor Decoy
Oligonucleotides as a Potential Treatment for Cardiovascular Diseases
Naruya Tomita , Haruhito Azuma , Yasufumi Kaneda , Toshio Ogihara and Ryuichi Morishita
Cardiovascular
diseases including renal diseases are the leading causes of mortality and
morbidity in developed countries. Most conventional therapy is inefficient and
tends to treat the symptoms rather than the underlying causes of the disorder.
Gene therapy based on oligonucleotides (ODN) offers a novel approach for the
prevention and treatment of cardiovascular diseases. Gene transfer into somatic
cells to interfere with the pathogenesis contributing to cardiovascular disease
may provide such a novel approach for better prevention and treatment of
cardiovascular disorders. The major development of gene transfer has
importantly contributed to intense investigation of the potential of gene
therapy in cardiovascular including renal medicine. The amazing advances in
molecular biology have provided a dramatic improvement of the technology that
is necessary to transfer target genes into somatic cells. Gene transfer methods
have been surprisingly improved. In fact, some of them (retroviral vectors,
adenoviral vectors or liposome based vectors, etc) have been used in the
clinical trials already. Recent progress in molecular biology has provided new
techniques to inhibit target gene expression. Especially, application of DNA
technology such as an antisense strategy to regulate the transcription of
diseaserelated genes in vivo has important therapeutic potential. Recently,
transfection of cis-element double-stranded ODN (= decoy) has been reported as
a new powerful tool in a new class of anti-gene strategies for gene therapy.
Transfection of double-stranded ODN corresponding to the cis sequence will
result in attenuation of the authentic cis-trans interaction, leading to
removal of trans-factors from the endogenous cis-elements with subsequent
modulation of gene expression.
[Back to top] Update on Tandem Pore (2P) Domain K+
Channels
C. Spencer Yost
The volatile
anesthetics are widely used in clinical practice today to produce a state of general
anesthesia. But despite more than 150 years of use and substantial scientific
investigation, the mechanism by which they produce central nervous system
depression remains elusive. Complete understanding of the cellular and
molecular basis of the anesthetized state produced by volatile anesthetics most
likely involves modulation of the activity of ion channel proteins; these
macromolecules provide the most likely molecular targets for these agents. Many
studies suggest the involvement of GABAergic and glutamatergic receptor systems
in mediating the action of volatile anesthetics. Another ionic current found
ubiquitously in neuronal tissues, background potassium currents (also known as
resting or leak K+ currents), have recently emerged as plausible targets
for volatile anesthetics. A unique structural class of K+ channels
with two pore-forming sequences in tandem (2P K+ channels)
contributes significantly to background K+ currents. The complete
identification of all the 2P K+ channel family members has likely
been accomplished. Within intact neuronal systems, background K+
channels are responsible for essential inhibition; these actions are enhanced
by volatile anesthetics. Thus, members of this family have emerged as strong
candidates for the molecular site of volatile anesthetic action.