Acquired resistance to gemcitabine and cross-resistance in human pancreatic cancer clones.

The efficacy of gemcitabine (GEM), a standard treatment agent for pancreatic cancer, is insufficient because of primary or acquired resistance to this drug. Patients with tumors intrinsically sensitive to GEM gradually acquire resistance and require a shift to second agents, which are associated with the risk of cross-resistance. However, whether cross-resistance is actually present has long been disputed. Using six GEM-resistant and four highly GEM-resistant clones derived from the pancreatic cancer cell line BxPC-3, we determined the resistance of each clone and parent cell line to GEM and four anticancer agents (5-FU, CDDP, CPT-11, and DTX). The GEM-resistant clones had different resistances to GEM and other agents, and did not develop a specific pattern of cross-resistance. This result shows that tumor cells are heterogeneous. However, all highly GEM-resistant clones presented overexpression of ribonucleotide reductase subunit M1 (RRM1), a target enzyme for metabolized GEM, and showed cross-resistance with 5-FU. The expression level of RRM1 was high; therefore, resistance to GEM was high. We showed that a tumor cell acquired resistance to GEM, and cross-resistance developed in one clone. These results suggest that only cells with certain mechanisms for high-level resistance to GEM survive against selective pressure applied by highly concentrated GEM. RRM1 may be one of the few factors that can induce high resistance to GEM and a suitable therapeutic target for GEM-resistant pancreatic cancer.

Identification of amino acid residues of influenza A virus H3 HA contributing to the recognition of molecular species of sialic acid.

To identify a determinant of human H3 hemagglutinin (HA) amino acid residues linked to the recognition of molecular species of sialic acid, we generated six mutant viruses possessing either the wild-type HA gene from A/Memphis/1/71 (H3N2) or a genetically single-mutated HA gene at position 137, 144, 155, 158 or 193 from a genetic backbone of A/WSN/33 (H1N1) by reverse genetics. We evaluated the binding ability with four types of synthetic sialylglycolipids. The results indicate that the amino acid substitutions Thr155 to Tyr and Glu158 to Gly in H3 HA facilitate virus binding to N-glycolylneuraminic acid.

Involvement of the virulence gene products of Yersinia enterocolitica in the immune response of infected mice.

The virulence of Yersinia enterocolitica is known to be highly dependent on its virulence plasmid. However, it remains unclear whether the virulence plasmid is engaged also in the induction of cell-mediated immunity that is essential for protective immunity in the host. In this study, we have compared the induction of type 1 helper T cell immunity against Y. enterocolitica using a virulent strain (P+) harboring the pYV plasmid and an avirulent strain (P-) harboring no pYV. Spleen cells from both groups of mice immunized with 1/10 LD50 of P+ strain and those with 1/10 LD50 of P- strain produced a high level of gamma interferon (IFN-gamma) upon stimulation with heat-killed bacteria, and CD4+ T cells were exclusively responsible for IFN-gamma production. When crude Yersinia outer proteins (Yops) were used for antigenic stimulation, IFN-gamma response of immune spleen cells against crude Yops was observed only in mice immunized with P+ strain. Flowcytometric analysis revealed a significant level of increase in IFN-gamma-producing CD8+ T cells as well as the increase in IFN-gamma-producing CD4+ T cells against crude Yops. These results suggest that the virulence plasmid of Y. enterocolitica is involved in the induction of Th1-type of possibly protective T cells in infected mice.

Magnetism of [Ni(dmit)2] salts with [meso- and (1S, 2S)-diphenyl-1,2-ethanediammonium]([18]crown-6)2 supramolecular cations.

Meso- and (1S, 2S)-diphenyl-1,2-ethanediammonium (DPEDA2+) complexed with [18]crown-6 were introduced into [Ni(dmit)2]-based magnetic salts as countercations. The configurational difference of DPEDA2+ modulated the crystal structure and magnetic behavior of the salts. A two-dimensional (2D) Heisenberg antiferromagnetic square lattice was observed in (meso-diphenyl-1,2-ethane diammonium2+)([18]crown-6)2[Ni(dmit)2](-)2, which was the first example of a 2D magnetic lattice in [Ni(dmit)2]- salts.

Crystal structures and structural stabilities of the disulfide bond-deficient soybean proglycinin mutants C12G and C88S.

The constituent subunits of seed storage protein 11S globulin have two disulfide bonds that are common among 11S globulins from legume and nonlegume seeds. In the case of the A1aB1b subunit of soybean 11S globulin, glycinin, Cys12-Cys45 and Cys88-Cys298 are observed by X-ray crystallography. The significance of these two disulfide bonds for structural stability was investigated by mutagenesis of Cys12 to Gly and of Cys88 to Ser. The disulfide bond-deficient mutants C12G and C88S could form the correct conformations identical to that of the wild-type proglycinin except in the vicinities of the mutation sites C12 and C88 as shown by their crystal structures. Thermal stability monitored by differential scanning calorimetry of the mutants indicated that the contribution of these disulfide bonds to the thermal stability of proglycinin A1aB1b is low, although there is a small difference in the extent of the contribution between the two disulfide bonds (Cys12-Cys45 > Cys88-Cys298). The contribution of Cys88-Cys298 to the resistance of proglycinin A1aB1b to proteinase digestion is higher than that of Cys12-Cys45. Possible effects of structure on the different properties of C12G and C88S are discussed.