Biomedical subjects

Kazumi Sano

Publications and source records attributed to Kazumi Sano.

8 recordsLinked to original sources

PubMed2006

Rapid evolution of major histocompatibility complex class I genes in primates generates new disease alleles in humans via hitchhiking diversity.

A plausible explanation for many MHC-linked diseases is lacking. Sequencing of the MHC class I region (coding units or full contigs) in several human and nonhuman primate haplotypes allowed an analysis of single nucleotide variations (SNV) across this entire segment. This diversity was not evenly distributed. It was rather concentrated within two gene-rich clusters. These were each centered, but importantly not limited to, the antigen-presenting HLA-A and HLA-B/-C loci. Rapid evolution of MHC-I alleles, as evidenced by an unusually high number of haplotype-specific (hs) and hypervariable (hv) (which could not be traced to a single species or haplotype) SNVs within the classical MHC-I, seems to have not only hitchhiked alleles within nearby genes, but also hitchhiked deleterious mutations in these same unrelated loci. The overrepresentation of a fraction of these hvSNV (hv1SNV) along with hsSNV, as compared to those that appear to have been maintained throughout primate evolution (trans-species diversity; tsSNV; included within hv2SNV) tends to establish that the majority of the MHC polymorphism is de novo (species specific). This is most likely reminiscent of the fact that these hsSNV and hv1SNV have been selected in adaptation to the constantly evolving microbial antigenic repertoire.

Alleles↗

PubMed2006

Transport mechanism-based drug molecular design: novel camptothecin analogues to circumvent ABCG2-associated drug resistance of human tumor cells.

Acquired and intrinsic drug resistance in cancer is the major obstacle to long-term, sustained patient response to chemotherapy. Irinotecan (CPT-11) is a widely-used potent antitumor drug that inhibits mammalian DNA topoisomerase I (Topo I). However, overexpression of ABCG2 (BCRP/MXR/ABCP) reportedly confers cancer cells resistance to SN-38, the active form of CPT-11. To circumvent the ABCG2-associated drug resistance, we have synthesized and characterized a total of fourteen new camptothecin (CPT) analogues with respect to both the inhibition of Topo I and the substrate specificity of ABCG2. While the lactone E ring is a prerequisite for anticancer activity, modifications of the A or B rings do not significantly affect Topo I inhibition activity. In this context, we have synthesized new CPT analogues with different substitutions at positions 10 or 11 of the A ring. All of the tested CPT analogues strongly inhibited the Topo I activity in a cell-free system. Accordingly, we have examined ATP-dependent transport of those CPT analogues by using plasma membrane vesicles prepared from ABCG2-overexpressing cells. Based on the substrate specificity of ABCG2 thus evaluated, it is strongly suggested that CPT analogues with a hydroxyl group at position 10 or 11 of the A ring are good substrates for ABCG2 and therefore effectively extruded from cancer cells. Thus, hydrogen bond formation is considered to be involved in substrate recognition and/or transport processes of ABCG2. The present study provides a practical approach to discover new CPT-based drugs for the chemotherapy of drug-resistant human cancer.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2005

Genomic evolution of MHC class I region in primates.

To elucidate the origins of the MHC-B-MHC-C pair and the MHC class I chain-related molecule (MIC)A-MICB pair, we sequenced an MHC class I genomic region of humans, chimpanzees, and rhesus monkeys and analyzed the regions from an evolutionary stand-point, focusing first on LINE sequences that are paralogous within each of the first two species and orthologous between them. Because all the long interspersed nuclear element (LINE) sequences were fragmented and nonfunctional, they were suitable for conducting phylogenetic study and, in particular, for estimating evolutionary time. Our study has revealed that MHC-B and MHC-C duplicated 22.3 million years (Myr) ago, and the ape MICA and MICB duplicated 14.1 Myr ago. We then estimated the divergence time of the rhesus monkey by using other orthologous LINE sequences in the class I regions of the three primate species. The result indicates that rhesus monkeys, and possibly the Old World monkeys in general, diverged from humans 27-30 Myr ago. Interestingly, rhesus monkeys were found to have not the pair of MHC-B and MHC-C but many repeated genes similar to MHC-B. These results support our inference that MHC-B and MHC-C duplicated after the divergence between apes and Old World monkeys.

Animals↗

PubMed2004

Novel camptothecin analogues that circumvent ABCG2-associated drug resistance in human tumor cells.

Irinotecan (7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxycamptothecin; CPT-11) is a widely used potent antitumor drug that inhibits mammalian DNA topoisomerase I (Topo I); however, overexpression of ABCG2 (BCRP/MXR/ABCP) can confer cancer cell resistance to SN-38, the active form of CPT-11. We have recently demonstrated that plasma membrane vesicles prepared from ABCG2-overexpressing PC-6/SN2-5H cells transported SN-38 and its glucuronide conjugate in an ATP-dependent manner (Nakatomi et al., Biochem Biophys Res Commun 2001;288:827-32). In the present study, we have characterized a total of 14 new camptothecin (CPT) analogues with respect to both the inhibition of Topo I and the substrate specificity of ABCG2. All of the tested CPT analogues, which have different substitutions at positions 10 and 11, strongly inhibited the Topo I activity in a cell-free system, as did SN-38. Their antitumor activities in the SN-38-resistant PC-6/SN2-5H2 cell line greatly varied, however, being correlated with intracellular accumulation levels. We have examined ATP-dependent transport of those CPT analogues by using plasma membrane vesicles prepared from both PC-6/SN2-5H2 cells and ABCG2-transfected HEK-293 cells. Based on the substrate specificity of ABCG2 thus evaluated, it is strongly suggested that CPT analogues with high polarity are good substrates for ABCG2 and are therefore effectively extruded from cancer cells. In this context, to circumvent ABCG2-associated drug resistance, low-polarity CPT analogues are considered to be potent lead compounds. The present study provides a practical approach to discover new CPT-based drugs for the chemotherapy of drug-resistant human cancer.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2004

Beta-adrenergic blocking agents and intermittent claudication: systematic review.

To clarify contradictions in past reports and the package inserts for beta-adrenergic blocking agents (beta-blockers) for patients with intermittent claudication (IC), we investigated the effects of beta-blockers in patients with IC using the systematic review technique. Data sources were randomized, controlled trials that investigated the effects of beta-blockers compared with the placebo or untreated group (controls) in patients with IC. Primary endpoints were walking distance and walking time, and secondary endpoints were ankle-brachial index (ABI) and calf blood flow. Nine trials were included in the analysis. Meta-analysis showed that there was a significant worsening in maximal walking distance and initial claudication distance in patients receiving beta-blockers, with standardized mean differences of -0.31 and -0.39 (95% confidence interval -0.58 to -0.04 and -0.73 to -0.06, P=0.03 and 0.02, respectively) compared with controls. There were no significant differences in maximal walking time (0.07, -0.24 to 0.37), time to onset of claudication (0.12, -0.23 to 0.47), ABI at rest (0.24, -0.30 to 0.78), calf blood flow at rest (0.00, -0.26 to 0.25), and calf blood flow after exercise (-0.23, -0.69 to 0.22). However, only one trial evaluated ABI, and the number of cases is increasing, suggesting that beta-blockers do not worsen ABI. There was no evidence that beta-blockers prescribed for patients with IC have unsuitable "precautions" in the package inserts. However, reluctance to administer beta-blockers to patients because they have IC is not appropriate.

Adrenergic beta-Antagonists↗

PubMed2004

Transport of SN-38 by the wild type of human ABC transporter ABCG2 and its inhibition by quercetin, a natural flavonoid.

Irinotecan (CPT-11) is a widely-used potent anticancer drug that inhibits mammalian DNA topoisomerase I, however overexpression of the ATP-binding cassette transporter ABCG2 can confer cancer cells resistance to SN-38, the active form of CPT-11. In the present study, we have examined the contribution of three variant forms of ABCG2 to SN-38 resistance. Exogenous expression of the Arg482 (wild type), Gly482, and Thr482 variants of ABCG2 conferred HEK293 cells resistance to SN-38 by 15.0-, 5.0-, and 5.3-fold, respectively. In plasma membrane vesicles prepared from the ABCG2 variant cDNA-transfected HEK293 cells, [Arg482]ABCG2 transported SN-38 and its glucuronide conjugate in an ATP-dependent manner; however, only minimal transport activities were observed with the other variants (Gly482 and Thr482). In addition, we have screened natural flavonoids to find potent inhibitors of [Arg482]ABCG2. Quercetin was found to be the strongest inhibitor (Ki = 0.28 microM) among natural flavonoids tested in the plasma membrane system in this study. When [Arg482]ABCG2-transfected HEK293 cells were incubated with SN-38 in the presence of 20 microM quercetin, cellular resistance to SN-38 was partly reversed. In this context, certain flavonoid derivatives are considered to be good candidates for development of ABCG2 inhibitors.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2003

Simple non-ion-paired high-performance liquid chromatographic method for simultaneous quantitation of carboxylate and lactone forms of 14 new camptothecin derivatives.

SN-38 (7-ethyl-10-hydroxycamptothecin) is an active metabolite derived from the semi-synthetic compound camptothecin (CPT) named Irinotecan (CPT-11). The antitumor activity of SN-38 is 1000-fold more potent than the parent CPT-11. Fourteen new derivatives of camptothecin have recently been developed by Yakult Honsha (Tokyo, Japan). Here we describe a simple and cost-effective high-performance liquid chromatography (HPLC) method without an ion-pairing agent, which allows the simultaneous determination of both lactone and carboxylate forms of SN-38 and other camptothecin derivatives. A weak linear relationship between the HPLC retention factors (ln k') and the cellular concentrations of these compounds was observed. These results suggest that low-polarity compounds easily accumulate in cancer cells and may circumvent drug resistance. The HPLC analysis herein described is expected to greatly assist in derivative synthesis and chemical modification of camptothecin-based antitumor drugs.

Camptothecin↗

PubMed2002

Metabolism of sulphobromophthalein II. Species differences between rats, guinea-pigs and rabbits.

Interesting species differences in the metabolism of sulphobromophthalein sodium have been observed between rats, guinea-pigs and rabbits. The species difference was measured in terms of sulphobromophthalein monoglutathione conjugate (mGSH) positional isomer formation. After an intravenous injection of sulphobromophthalein to rats, 92% of sulphobromophthalein-mGSH excreted into bile was the alpha-isomer. In contrast, in guinea-pigs the three isomers alpha, beta and delta were excreted in equivalent amounts. In rabbits, the majority of sulphobromophthalein-mGSH was excreted as the beta-isomer. The formation ratio of glutathione (GSH) conjugates in-vitro using cytosolic glutathione S-transferases (GSTs) prepared from livers generally accounted for the biliary excretion ratio of alpha-, beta- and delta-monomercaptide isomers in-vivo. GSTs from the livers of rat, guinea-pig, and rabbit were purified and characterized. Although their main GSTs produced different isomers, their 20 amino acid residues showed that they belonged to the same class mu of GSTs. The results suggested differences of the three-dimensional structure of GSTs that formed sulphobromophthalein-mGSH isomers between the three animal species.

Animals↗