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Biomedical subjects

Shigeo Yagi

Publications and source records attributed to Shigeo Yagi.

25 records · Page 2Linked to original sources
PubMed2003

In vivo efficacy of recombinant methioninase is enhanced by the combination of polyethylene glycol conjugation and pyridoxal 5'-phosphate supplementation.

Recombinant methioninase (rMETase) is an enzyme active in preclinical mouse models of human cancer. The efficacy of rMETase is due to depletion of plasma methionine, an amino acid for which tumors generally have an abnormally high methionine requirement. Furthermore, transient methionine depletion results in a markedly increased sensitivity of the tumors to several chemotherapeutic agents. This study characterized methods to prolong the half-life of rMETase to extend the in vivo period of depletion of plasma and tumor methionine. In the present study, rMETase was coupled to methoxypolyethylene glycol succinimidyl glutarate-5000 in order to prolong the half-life of rMETase and thus extend the in vivo period of depletion of plasma and tumor methionine. Matrix-assisted laser desorption ionization mass spectrometry indicated that one sub-unit of rMETase was modified by approximately 4, 6 and 8 PEG molecules when rMETase was PEGylated at molar ratios of PEG/rMETase of 30/1, 60/1, and 120/1, respectively. PEG-rMETase (120/1) had a serum half-life increase of 20-fold, and methionine depletion time increased 12-fold compared to unmodified rMETase. The increase in in vivo half-life depended on the extent of PEGylation of rMETase. In addition, a remarkable prolongation of in vivo activity and effective methionine depletion by the PEG-rMETase was achieved by the simultaneous administration of pyridoxal 5'-phosphate. PEGylation also reduced the immunogenicity of rMETase. The extent of reduction in immunogenicity depended on the number of residues PEGylated. PEG-rMETase 30/1 had a 10-fold decrease in IgG titer while PEG-rMETase 120/1 had a 10(4)-fold decreased titer compared to naked rMETase. Thus, the molecular modification of PEGylation confers critical new properties to rMETase for development as a cancer therapeutic.

Animals↗
PubMed2003

Efficacy of camptothecin analog DX-8951f (Exatecan Mesylate) on human pancreatic cancer in an orthotopic metastatic model.

We determined the antitumor and antimetastatic efficacy of the camptothecin analogue DX-8951f in an orthotopic metastatic mouse model of pancreatic cancer. DX-8951f showed efficacy against two human pancreatic tumor cell lines in this model. These cell lines were transduced with the green fluorescent protein, enabling high-resolution visualization of tumor and metastatic growth in vivo. The DX-8951f studies included both an early and advanced cancer model. In the early model, using the human pancreatic cancer lines MIA-PaCa-2 and BxPC-3, treatment began when the orthotopic primary tumor was approximately 7 mm in diameter. DX-8951f was significantly effective against both MIA-PaCa-2 and BxPC-3. In contrast, 2', 2'-difluorodeoxycytidine (gemcitabine), the standard treatment for pancreatic cancer, did not have significant efficacy against MIA-PaCa-2. Although gemcitabine showed significant activity against BxPC-3 primary tumor growth, it was not effective on metastasis. In the model of advanced disease, using BxPC-3, treatment started when the orthotopic primary tumor was 13 mm in diameter. DX-8951f was significantly effective in a dose-response manner on the BxPC-3 primary tumor. DX-8951f also demonstrated antimetastatic activity in the late-stage model, significantly reducing the incidence of lymph node metastasis while eliminating lung metastasis. In contrast, gemcitabine was only moderately effective against the primary tumor and ineffective against metastasis at both sites in the late-stage model. Therefore, DX-8951f was highly effective against primary and metastatic growth in this very difficult-to-treat disease and showed significantly higher efficacy than gemcitabine, the standard treatment of pancreatic cancer. DX-8951f, therefore, has important clinical promise and has more positive features than the currently used camptothecin analogue CPT-11, which requires metabolic activation and is toxic.

Animals↗
PubMed2003

Environmental isolation of Balamuthia mandrillaris associated with a case of amebic encephalitis.

This report describes the first isolation of the ameba Balamuthia mandrillaris from an environmental soil sample associated with a fatal case of amebic encephalitis in a northern California child. Isolation of the ameba into culture from autopsied brain tissue confirmed the presence of Balamuthia: In trying to locate a possible source of infection, soil and water samples from the child's home and play areas were examined for the presence of Balamuthia: The environmental samples (plated onto nonnutrient agar with Escherichia coli as a food source) contained, in addition to the ameba, a variety of soil organisms, including other amebas, ciliates, fungi, and nematodes, as contaminants. Presumptive Balamuthia amebas were recognized only after cultures had been kept for several weeks, after they had burrowed into the agar. These were transferred through a succession of nonnutrient agar plates to eliminate fungal and other contaminants. In subsequent transfers, axenic Naegleria amebas and, later, tissue cultures (monkey kidney cells) served as the food source. Finally, the amebas were transferred to cell-free axenic medium. In vitro, the Balamuthia isolate is a slow-growing organism with a generation time of approximately 30 h and produces populations of approximately 2 x 10(5) amebas per ml. It was confirmed as Balamuthia by indirect immunofluorescence staining with rabbit anti-Balamuthia serum and human anti-Balamuthia antibody-containing serum from the amebic encephalitis patient. The environmental isolate is similar in its antimicrobial sensitivities and identical in its 16S ribosomal DNA sequences to the Balamuthia isolate from the deceased patient.

Amebiasis↗
PubMedDate not supplied

Antimetastatic efficacy of oral 5-FU imaged by green fluorescent protein in real time.

The effectiveness of oral 5-FU in suppressing liver metastasis was assessed in a highly-metastatic mouse model. Doses of 20 and 25 mg/kg oral 5-FU significantly suppressed primary and metastatic tumor growth (p = 0.012). These inhibitory effects were more dramatic in suppressing liver metastasis (p = 0.0). The efficacy of 5-FU was visualized by whole-body fluorescence imaging of the green fluorescent protein-expressing tumor and its subsequent metastases. Toxicity was observed only in the 30 mg/kg dose. Furthermore, we showed that the non-toxic doses of 5-FU significantly prolonged survival in these animals. These data suggest the important clinical potential of oral 5-FU.

Administration, Oral↗
PubMedDate not supplied

Oral 5-FU is a more effective antimetastatic agent than UFT.

5-Fluorouracil (5-FU), a pyrimidine analog, is widely used to treat gastrointestinal and other cancers. In the present study, we compared the efficacy of oral 5-FU and the 5-FU prodrug, uracil plus tegafur (UFT), on liver metastasis in a highly metastatic mouse model. Genetic labeling of the tumor with green fluorescent protein (GFP) along with inexpensive video detectors, positioned external to the mouse, allowed the real-time monitoring of details of tumor growth, metastatic spread and drug response in this mouse model. 5-FU at 10 and 20 mg/kg significantly prolonged the survival time of treated animals compared with untreated controls (p=0.003 for 5-FU, 10 mg/kg; p=0.016 for 5-FU, 20 mg/kg). In contrast, UFT only showed a trend to increase survival (p=0.078). 5-FU at 10 mg/kg substantially prolonged the survival time compared to UFT (p=0.012). 5-FU (10 mg/kg) was also more effective in prolonging survival than Furtulon (5'-deoxy-5-fluorouridine, another 5-FU prodrug) (p=0.042). All control and UFT-treated animals died by day 45. In contrast, at 45 days, 5 out of 8 animals were alive in the 5-FU 10 mg/kg group, which was found to be the best treatment regimen in this study. 5-FU (10 mg/kg)-treated animals had a median survival time of 53 days compared to 26.5 in controls and 33.5 days for UFT. These results suggest the potential clinical superiority of oral 5-FU compared to UFT as an anti-metastatic agent. The data also suggest the lack of clinical need for complex and expensive prodrugs of 5-FU such as UFT.

Animals↗