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Volume 122 (2003)
- Issue 6 Pages 473-
- Issue 5 Pages 367-
- Issue 4 Pages 34A-
- Issue 3 Pages 192-
- Issue 2 Pages 111-
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Volume 122, Issue 6
Displaying 1-9 of 9 articles from this issue
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Reviews: Tyrosine Kinase as a Molecular Target for Drugs
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Yoshiro MARUArticle type: Reviews
2003 Volume 122 Issue 6 Pages 473-481
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSTyrosine kinase (TK) plays an important role in a variety of biological circumstances including growth, apoptosis, differentiation, immune system, angiogenesis, development, and so forth. Some inhibitors for TK have been successful in clinical applications in malignant disorders. Due to its physiological participation in cells exposed to many stimuli and to structural homology of high degree, true molecular targeting requires complete understanding of signal transduction pathways in all of the cells in which the targeted TK is involved.
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Motowo NAKAJIMA, Wakako TOGAArticle type: Reviews
2003 Volume 122 Issue 6 Pages 482-490
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSThe Philadelphia chromosome found in leukemia cells of chronic myelogenous leukemia (CML) patients is produced by translocation between chromosomes 9 and 22, resulting in expression of a chimera protein of Bcr and Abl kinase in the cytoplasm. Bcr-Abl kinase attracted oncology researchers as a molecular target for CML therapy, and a variety of small Abl kinase inhibitors were synthesized. STI571 (imatinib mesylate) was produced by modification of 2-phenylaminopyrimidine, a core structure of protein kinase C inhibitor, to improve selectivity, stability, solubility, and bioavailability. STI571 competitively binds to the ATP binding site of Bcr-Abl kinase and inhibits Abl tyrosine kinase activity. STI571 showed significant efficacy in the clinical study with CML patients at all stages: chronic phase, accelerated phase, and blast crisis. More than 90% of the patients showed good hematologic response to STI571. STI571 is also a potent inhibitor of a receptor-type c-Kit tyrosine kinase. Therefore, STI571 was examined for therapeutic efficacy against malignant Gastro-Intestinal Stromal Tumors (GIST), which are mainly caused by aberrant expression of a mutated c-Kit that is constitutively active without binding of a ligand, stem cell factor (SCF). More than a half of the metastatic GIST patients enrolled in the clinical study responded to STI571. Thus, STI571 is now used as a therapeutic drug for both CML and GIST in more than 80 countries worldwide. Certain point mutations in the ATP binding site were found to be a cause of resistance to STI571 in both Bcr-Abl and c-Kit kinases. Therefore, it would be better to make a precise therapeutic strategy with STI571 based on the gene analysis data. It is also expected that it will be possible to design an inhibitor to overcome such resistance by using the structural information on the mutants.
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Seiichi YANO, Motonori YAMAGUCHI, Rui-Ping DONGArticle type: Reviews
2003 Volume 122 Issue 6 Pages 491-497
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSMany malignant tumors including non-small cell lung cancer (NSCLC) express or over-express EGFR that have shown correlations with rapid growth, metastases, resistance to conventional chemotherapy or radiotherapy, and poor prognosis. Gefitinib is a potent and selective inhibitor of EGFR tyrosine kinase (EGFRTK). Gefitinib specifically inhibited EGF-stimulated cell proliferation in vitro and it also exhibited a broad anti-tumor spectrum against NSCLC, prostate, colorectal, and ovarian cancers in vivo. Gefitinib showed dose-dependent and reversible reduction of c-fos mRNA level and decreased Ki67 significantly in tumors in vivo. In in vitro studies, gefitinib arrested the cell cycle at G1 phase by inducing intrinsic cyclin-dependent kinase (cdk) inhibitors and following inhibition of cdk2. Apoptosis was also seen in gefitinib-treated tumor cells and skin biopsy samples from clinical study. Gefitinib inhibited VEGF production in tumor cells through inhibition of EGFR signaling, leading to suppression of angiogenesis. In clinical studies, gefitinib demonstrated therapeutic benefit in patients who failed conventional chemotherapy. No correlation has been established between the anti-tumor activity of gefitinib and EGFR expression level, whilst sensitivity factors to gefitinib are yet to be elucidated. Identification of sensitivity factors will be a key for effective use of EGFRTK inhibitors including gefitinib for cancer treatment.
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Masabumi SHIBUYAArticle type: Reviews
2003 Volume 122 Issue 6 Pages 498-503
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSAngiogenesis is deeply involved in the progression of major diseases such as cancer, diabetes, and rheumatoid arthritis. Molecular mechanism on angiogenesis was extensively studied, and several signaling systems including VEGF (VEGF-A), angiopoietin, PDGF, and ephrin were shown to be crucial for physiological angiogenesis. Interestingly, among these factors, VEGF appears to play key roles in most of the pathological angiogenesis, and other factors are considered to have additional effects on its development depending on the situation. VEGF binds and activates two tyrosine kinase receptors, VEGFR-1 (Flt-1) and VEGFR-2 (KDR/Flk-1), and stimulates endothelial cell growth, survival, and vascular permeability. VEGF induces not only tumor angiogenesis but also blood-vessel-dependent metastasis. Based on the importance of VEGF in diseases, many companies and institutes are now trying to generate appropriate small molecules as well as proteins that strongly antagonize the VEGF-VEGFR system. Several molecules quite effective for suppression of tumorigenesis and pathological angiogenesis in animal models are under clinical trials.
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Shin-ichi NIHIRAArticle type: Reviews
2003 Volume 122 Issue 6 Pages 504-514
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSHER2 is a member of the human epidermal growth factor receptor family, possessing protein kinase activity in its cytoplasmic domain. There were evidences indicating that (1) amplification of HER2/neu gene and HER2 protein over-expression in tumor cells was observed in 25-30% of human breast cancer and (2) amplification of HER2/neu correlated with poor prognosis, including shorter disease-free and overall survival. These evidences suggested HER2 was a promising candidate for novel molecular targets of breast cancer therapy. Herceptin is a recombinant humanized monoclonal antibody generated by Genentech, Inc. for the treatment of HER2 over-expressed/HER2 gene amplified metastatic breast cancer (MBC). Preclinical studies demonstrated that the antibody had anti-tumor activity in vivo and in vitro, and additive or synergistic enhancement of anti-tumor activity of the antibody was observed in combination with various anti-tumor agents in mouse models. In clinical studies, apparent extension of overall survival was observed in HER2 overexpressing MBC patients. Herceptin is the first anticancer drug whose use as a treatment for MBC patients is decided based on the status of the HER2 gene amplification/HER2 protein over-expression. The development and standardization of HER2 test were a key strategy in clinical development of this drug, since appropriate selection of patients with HER2 over-expression was the essential point for success.
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Review
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Takeshi SUZUKI, Keisuke TSUZUKI, Kimihiko KAMEYAMA, Shin KWAKArticle type: Review
2003 Volume 122 Issue 6 Pages 515-526
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSAs glutamate is a dominant excitatory neurotransmitter in the central nervous system, glutamate receptors, and especially AMPA receptors, are located ubiquitously in all brain areas. In this paper, we reviewed recent advances of studies on AMPA receptor functions. AMPA receptors are cation-conducting complexes composed of various combinations of four subunits (GluR1 to GluR4). The glutamine residue located in the pore-forming segment of GluR2 subunit (Q/R site) is changed to arginine by RNA editing at the pre mRNA stage in normal adult mammalian animal. The edited GluR2 subunit is a major determination of Ca2+ permeability of the AMPA receptor; only edited GluR2-lacking receptor shows high-Ca2+ permeability. The assembly of glutamate AMPA receptor subunit is not completely according to the stochastic theory. The heteromeric subunits assembly is more rapid than the homomeric assembly is. The transfer of AMPA receptor subunit to the plasma membrane is conducted in multiple ways. Many molecules that interact with the intracellular domain of AMPA receptor subunits are reported as the modulators of AMPA receptor subunit transfer. In the motoneuron of sporadic amyotrophic lateral sclerosis (ALS) patients, the efficiency of RNA editing at the GluR2 Q/R site is significantly decreased. Relative low level of edited GluR2 subunit expression is likely responsible for motoneuronal death in ALS. Recently, AMPA receptors in glial cells have been studied. Bergmann glial cells in cerebellum express Ca2+-permeable AMPA receptors. Conversion of these AMPA receptors to Ca2+-impermeable type receptors induces morphological and functional changes. Glioblastoma cells also express Ca2+-permeable AMPA receptors, and their conversion to Ca2+-impermeable receptors inhibits cell locomotion and induces apoptosis.
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Review on New Drug
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Takanori IKEDAArticle type: Review on New Drug
2003 Volume 122 Issue 6 Pages 527-538
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSIvermectin is an oral semi-synthetic lactone anthelmintic agent derived from avermectins isolated from fermentation products of Streptomyces avermitilis. Ivermectin showed a concentration-dependent inhibitory effect on motility of a free-living nematode, Caenorhabditis elegans (C. elegans). There exist specific binding sites having a high affinity for ivermectin in the membrane fraction of C. elegans, and a strong positive correlation was detected between the affinity for these binding sites and the suppressive effect on motility of C. elegans in several ivermectin-related substances. These results suggested that the binding to these binding sites is important for the nematocidal activity of ivermectin. In oocytes of Xenopus laevis injected with the Poly (A)+ RNA of C. elegans, expression of a chloride channel, which is irreversibly activated by ivermectin, was recognized. The pharmacological properties of this channel suggest that the ivermectin-sensitive channel is a glutamate-activated chloride channel. As to the glutamate-activated chloride channel, two subtypes (GluCl-α and GluCl-β) were cloned, suggesting these subtypes constitute the glutamate-activated chloride channel. These findings suggest that ivermectin binds to glutamate-activated chloride channels existing in nerve or muscle cells of nematode with a specific and high affinity, causing hyperpolarization of nerve or muscle cells by increasing permeability of chloride ion through the cell membrane, and as a result, the parasites are paralyzed to death. In experimental infections in sheep and cattle, ivermectin exhibited potent dose-dependent anthelmintic effects on Haemonchus, Ostertagia, Trichostrongylus, Cooperia, Oesphagostomum, and Dictyocaulus. Anthelmintic effects were reported also in dogs, horses, and humans infected with Strongyloides. In the clinical Phase III trial in Japan, 50 patients infected with Strongyloides stercoralis were administered approx. 200 µg/kg of ivermectin to be given orally twice at an interval of 2 weeks. As a result, the Strongyloides stercoralis-eradicating rate was 98.0% (49/50).
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Pharmacological profiles and clinical effects of azelnidipine, a long-acting calcium channel blockerToshio SADA, Hironobu SAITOArticle type: Review on New Drug
2003 Volume 122 Issue 6 Pages 539-547
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSAzelnidipine (Calblock®) is a newly developed dihydropyridine-type calcium antagonist for the treatment of hypertension. In hypertensive animals, a single oral administration of azelnidipine caused a slowly developed and long-lasting hypotensive effect with a little reflex tachycardia. The extent of tachycardia was less with azelnidipine than with other agents of the same class. Long-term administrations of azelnidipine produced a stable antihypertensive effect with a slight decrease in heart rate. The hypotensive effect was preceded by an increase in plasma drug concentration and it persisted even after plasma drug concentration declined to very low levels. In the isolated arteries, the calcium blocking action developed gradually after treatment with azelnidipine and survived for a long period of time after the drug was removed from the bathing solution. These data suggest that the high affinity to vascular tissue contributes to the long-lasting hypotensive effects of this agent. The results from clinical studies in hypertensive patients indicated that once daily administration of azelnidipine achieved stable, 24-h control of blood pressure with no change or a slight decrease in heart rate. Clinical studies also showed a low incidence of adverse events such as headache, facial flush, dizziness, and palpitations. These characteristics make azelnidipine a new generation calcium antagonist that can be used for the treatment of hypertension.
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Masanori NISHIDAArticle type: Review on New Drug
2003 Volume 122 Issue 6 Pages 549-553
Published: 2003
Released on J-STAGE: November 20, 2003
JOURNAL FREE ACCESSXeloda (Capecitabine) is a fluorocytidine derivative that is selectively tumor-activated to its cytotoxic moiety, fluorouracil. Capecitabine is readily absorbed from the gastrointestinal tract. In the liver, a 60-kDa carboxylesterase(CE) hydrolyzes much of the compound to 5'-deoxy-5-fluorocytidine (5'-DFCR). Cytidine deaminase(CD), an enzyme found in most tissues, including tumors, subsequently converts 5'-DFCR to 5'-deoxy-5-fluorouridine (5'-DFUR). The enzyme thymidine phosphorylase (TP) then hydrolyzes 5'-DFUR to the active drug 5-FU. It is proved that some human carcinomas express TP in higher concentrations than surrounding normal tissues. In Japan, one of the phase 2 clinical trials tested the efficacy of twice daily oral Capecitabine at 1,657 mg/m2/d given for 3 weeks followed by a 1-week rest period and repeated in 4-week cycles in advanced/metastatic breast cancer patients resistant to or recurring during or after docetaxel therapy. The response rate was 20.0% (1 CR, 10 PRs). The median time to progression was 84 days and the median survival time was 452 days. The most common treatment-related adverse events throughout the phase 1 to 2 trials of capecitabine were hand-foot syndrome (50.7%), erythropenia (37.9%), lympopenia (31.0%), hyperbilirubinemia (33.0%) and so on. Capecitabine is expected to provide a new alternative for the treatment of advanced/metastatic breast cancer.
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