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Biomedical subjects

Y Takakura

Publications and source records attributed to Y Takakura.

226 records · Page 13Linked to original sources
PubMed1984

Antitumor activity of lipophilic prodrugs of mitomycin C entrapped in liposome or O/W emulsion.

Nine lipophilic la-N-substituted prodrugs of mitomycin C were formulated in lipid dispersion dosage forms and their fundamental antitumor activities were evaluated. The prodrugs were efficiently incorporated into liposome or O/W emulsion according to their increased lipophilicities , while mitomycin C was hardly entrapped into them. Almost complete incorporation was observed in nonyloxycarbonyl and cholesteryloxycarbonyl mitomycin C which showed partition coefficients over 8000 in chloroform/water system. The release rate from these dosage forms determined by a dynamic dialysis method decreased with an increase in the partition coefficients of the derivatives. All prodrugs entrapped in liposome or O/W emulsion showed significant antitumor activities against L1210 leukemia in i.p.-i.p. system except for cholesteryloxycarbonyl mitomycin C. In spite of considerable antitumor activities showen in the forms of liposome and emulsion, saline suspension of nonyloxycarbonyl mitomycin C failed to exhibit any activity because of its poor aqueous solubility. These results suggested the utility of the combining delivery system of lipophilic prodrug with physical device such as liposome and O/W emulsion.

Animals↗
PubMed1984

Enhanced lymphatic delivery of mitomycin C conjugated with dextran.

Absorption and lymphatic transfer of a polymeric prodrug of mitomycin C (MMC), mitomycin C-dextran conjugate (MMC-D), following i.m. injection were studied in rats in order to assess the feasibility of a macromolecular prodrug as a lymphotropic delivery system. Three types of MMC-D, conjugates with dextran with molecular weights of 10,000, 70,000 and 500,000, were synthesized, and the disposition of MMC was determined by bioassay. Following i.m. injection of MMC-D, MMC was retained at the injection site for a long period in a conjugated form while MMC administered as a free form disappeared rapidly. The disappearance was markedly influenced by the size of carrier dextran, because the remaining amount of MMC increased with an increase of molecular size. The lymphatic uptake of the drug was evaluated by determining the concentration in the regional lymph nodes and thoracic lymph fluid. In contrast to a slight lymphatic uptake following i.v. and i.m. injection of free MMC, MMC-D exhibited remarkable accumulation in the regional lymph nodes after i.m. injection which persisted up to 48 hr. MMC-D (Mr 10,000) appeared in the thoracic lymph as both the conjugated and the free form. Larger MMC-D gave a persistent supply of free MMC in thoracic lymph, suggesting that it was accumulated in the lymph node and supplying MMC continuously. These MMC-Ds suppressed the lymph node metastases introduced by a s.c. inoculation of L1210 leukemia cells. The usefulness of MMC-D as a lymphotropic delivery system for preventing lymphatic metastasis of cancer was suggested.

Animals↗
PubMed1983

Substrate specificity of tissue plasminogen activator and urokinase as determined with synthetic chromogenic substrates.

Three different synthetic chromogenic substrates )H-glutamylglycyl-L-arginine-p-nitroanilide (S-2227), pyro-glutamyl-glycyl-L-arginine-p-nitroanilide (S-2444), and H-D-isoleucyl-L-prolyl-L-arginine-p-nitroanilide (S-2288] were investigated for use in the measurement of plasminogen activator activity with high molecular weight urokinase (H-UK), low molecular weight urokinase (L-UK), and tissue plasminogen activator (TPA). The three substrates were hydrolyzed by both TPA-type and UK-type plasminogen activator. As regards the amidolytic activity of S-2227, TPA exhibited a weaker amidolytic activity, and L-UK a stronger activity. In the case of the amidolytic activity of S-2444, no great difference between the three activators was observed in terms of Vmax. As regards the amidolytic activity of S-2288, L-UK exhibited a stronger activity, and TPA a weaker activity. It is suggested that the molecular size of the synthetic chromogenic substrate was too small when compared to natural substrate (fibrin), and therefore that fibrin-binding sites around the catalytic site in TPA are not recognized.

Chromogenic Compounds↗
PubMedDate not supplied

Age-dependent changes of mineral contents in men and women's calcanei.

To elucidate age-related change of mineral contents in human bones, the mineral content and density of human calcanei were determined by inductively coupled plasma atomic emission spectrometry and dual-energy X-ray absorptiometry. Calcanei were removed from 27 subjects (17 men and 10 women) who died in the age range from 40-98 yr old. Both the inductively coupled plasma emission spectrometry and dual-energy X-ray absorptiometry indicated that there were age-dependent decreases of the mineral contents and density in the men's calcaneus in the age range from 40-98 yr, but not in the women's calcaneus in the age range from 42-87 yr. It was also found that the calcanean masses of the men and women remained constant within the same age range until 98 yr.

Absorptiometry, Photon↗
PubMedDate not supplied

Preparation and properties of the immunoconjugate composed of anti-human colon cancer monoclonal antibody and mitomycin C-dextran conjugate.

Monoclonal antibody (mAb) A7, produced against human colon cancer, was conjugated with a polymeric prodrug of mitomycin C (MMC), the MMC-dextran conjugate with an anionic charge (MMCDan) and a molecular weight of 70,000. The amino groups were introduced into the MMCDan by reacting ethylenediamine with the carboxyl group in the spacer arm of the dextran bridge by a carbodiimide-catalyzed reaction. The coupling to mAb A7 was performed using SPDP. A 15 M excess of ethylenediamine produced an optimal MMCDan with amino groups, which resulted in a homogenous conjugate (A7-MMCD) with minimal formation of high-molecular-weight aggregates in about a 30% yield of both IgG and MMC. The molar binding ratio of IgG:dextran:MMC in A7-MMCD was estimated to be 1:1.2:40. A7-MMCD, having MMC prodrug properties, released active MMC with a half-life of 29.1 h and had an almost neutral electric charge under physiological conditions. A competitive binding assay using 125I-labeled A7 revealed that the A7-MMCD almost fully retained its antibody-binding activity. The cytotoxicity of A7-MMCD was assayed by determining the degree of inhibition of [3H]-thymidine in corporation in two different ways using the human colon cancer cell line SW1116. A 48-h continuous exposure test revealed that the pharmacological activity of MMC in A7-MMCD was completely preserved. In addition, A7-MMCD exhibited about a 14-fold greater cytotoxicity than MMCDan when the IC50 values determined using a 2-h pretreatment exposure system were compared. These results suggest that A7-MMCD could be useful in immunotargeting chemotherapy for colorectal cancer.

Antibodies, Monoclonal↗
PubMedDate not supplied

Disposition and pharmacokinetics of a polymeric prodrug of mitomycin C, mitomycin C-dextran conjugate, in the rat.

The disposition and pharmacokinetics of a polymeric prodrug of mitomycin C (MMC), mitomycin C-dextran conjugate (MMCD), following iv bolus administration was studied in rats. Three types of MMCD, conjugates with dextran of molecular weights of 10,000, 70,000, and 500,000, were tested and disposition of carrier dextran and MMC was determined by 14C radioactivity counting and bioassay, respectively. Radioactivity was accumulated in the reticuloendothelial system such as the liver, spleen, and lymph nodes after injection of all three types of 14C-MMCD, but not in the lung, heart, and muscle. Renal distribution of 14C-MMCD varied with the molecular size of the carrier. After injection of cold MMCD, plasma concentrations of MMC in the free and conjugated forms were determined separately on the bases of bioassay. Similar sustained plasma levels of MMC were detected regardless of the carrier size although the concentration-time profiles of MMCD varied with the size of dextran. These plasma concentration data were fitted to a compartment model including a first order conversion process from MMCD to MMC in the central and peripheral compartments of MMCD. Kinetical analysis revealed that MMCD acts as a reservoir of MMC which behaves characteristically as a macromolecule while supplying active MMC in the body.

Animals↗