Stereoselective synthesis of chiral pinene[5,6]bipyridine ligands and their coordination chemistry.

The C(2)-symmetric chiral pinene[5,6]bipyridine V (Chart 1) was synthesized according to a procedure published by our group recently (Kolp, B.; Abeln, D.; Stoeckli-Evans, H.; Zelewsky, A. v. Eur. J. Inorg. Chem. 2001, 1207). A series of stereoselectively alkylated derivatives (Va-Vo) (Table 1) was prepared. The solid-state structures of the compounds Vc and Vk were determined by single-crystal X-ray diffraction, where both compounds show a transoid conformation of the bipyridine unit and proved to be alkylated stereoselectively from the sterically less hindered side of the pinene moiety. The X-ray structure of the cobalt complex 4 shows the metal ion to be tetrahedrally coordinated by one chiral bipyridine V and two chloride ligands. If 2 equiv of ligand V was used, 2:1 complexes were obtained with Cu(I), Ag(I), and Co(II) ions.

Pi* level tuning in a series of diimine ligands based on density functional theory: application to photonic devices.

Energy- and electron-transfer processes are very important for artificial photosynthesis and a variety of other applications. [(bpy)2Ru(PAP)Os(bpy)2]4+ and its oxidized form [(bpy)2Ru(PAP)Os(bpy)2]5+ perform efficient photoinduced energy- and electron-transfer processes, respectively (k(en) = 5.2 x 10(7) s(-1), k(el) = 7.2 x 10(6) s(-1)). The introduction of appropriate donor and acceptor units on the Ru2+ center can improve the lifetime of the excited state, resulting in a much longer and efficient storage of energy. Nonempirical (density functional) calculations and experimental data are used to predict the best donor and acceptor ligands for improving electron- and energy-transfer processes. Such a result can be extended to all polynuclear complexes where electronic coupling between the metal centers is very weak.

Novel metal-organic ruthenium(II) diimin complexes for use as longwave excitable luminescent oxygen probes.

New ruthenium(II) diimine complexes are presented which are useful as luminescent oxygen probes. Because their luminescence excitation maxima are between 535 and 570 nm, they can be photo-excited by green LEDs which are much brighter than the blue LEDs used so far for existing Ru diimines. The spectral and photophysical properties as well as the solubility properties of the new probes are investigated and discussed in terms of quenching, photostability, and lifetimes. The probes were incorporated into organic polymers by three different methods, to obtain oxygen-sensitive materials for use in optical oxygen sensing. The membranes were characterized with respect to oxygen sensitivity, luminescence intensity, response times, and stability. Notwithstanding the poor luminescence of the new ruthenium(II) probes, their stability, LED compatibility and efficient quenching by oxygen makes them an interesting alternative to existing luminescent oxygen probes.

Enhancement of epidermal growth factor receptor expression on glioma cells by recombinant tumor necrosis factor alpha.

Recombinant tumor necrosis factor alpha (rTNF alpha; optimal dose 1000 U/ml) significantly increased the density of epidermal growth factor receptor (EGF-R) in three of four glioma cell lines in culture as determined by binding analysis of anti-EGF-R monoclonal antibody (mAb) 425. Since enhancement of EGF-R expression by rTNF-alpha was inhibited when cells were treated with the protein synthesis inhibitor cycloheximide, the effects of rTNF alpha may be protein-synthesis-dependent. The dose of rTNF alpha that was optimal for up-regulation of EGF-R on glioma cells did not inhibit the growth of these cells. 125I-labeled mAb 425 lysed glioma cells in culture following its internalization into the cells. After glioma cells had been treated with rTNF alpha, the growth-inhibitory effects of the mAb were significantly enhanced, probably a reflection of the increase in EGF-R density on the tumor cell surfaces. The rTNF alpha effects were specific to the EGF-R and did not affect unrelated glioma-associated antigens. In our previous clinical trials, 125I-labeled mAb 425 showed immunotherapeutic effects in glioma patients. The present study provides the basis for considerations of combined immunotherapy of glioma patients with 125I-labeled mAb 425 and rTNF alpha.

Immunotherapy of human glioma xenografts with unlabeled, 131I-, or 125I-labeled monoclonal antibody 425 to epidermal growth factor receptor.

Monoclonal antibody (mAb) 425 (IgG2a) binds to the external domain of the epidermal growth factor receptor. This determinant is highly expressed by human glioma tissues but rarely by normal brain tissues, and is absent on peripheral blood lymphocytes and bone marrow cells. The mAb exerts variable cytotoxic effects against cultured human glioma cells in conjunction with human and murine effector cells. Inhibition of growth of s.c. glioma xenografts in nude mice by the mAb may be mediated by murine macrophages or may be related to the capacity of the mAb to antagonize growth stimulation of glioma cells by epidermal growth factor. In approaches to radioimmunotherapy of human glioma with mAb 425, the 125I-labeled mAb 425 exhibited more significant antitumor effects than the 131I-labeled mAb both in vitro and in vivo in xenotransplanted nude mice. These differences may be due to enhanced nuclear damage caused by 125I-labeled versus 131I-labeled fragments following their internalization into the glioma cells. Our studies provide the rationale for immunotherapy of glioma patients with either unlabeled or 125I-labeled anti-epidermal growth factor receptor mAb 425.

Regulation of angiogenesis in vitro by collagen metabolism.

The role of collagen in microvascular growth was investigated using the aortic ring model of angiogenesis. Collagen production by vasoformative outgrowths in plasma clot culture of rat aorta was either stimulated with ascorbic acid or inhibited with the proline analogue cis-hydroxyproline. Microvessels proliferating in the absence of ascorbic acid supplements became ecstatic and developed large lumina. In contrast, newly formed microvessels in the presence of ascorbic acid remained small and maintained thin lumina throughout the angiogenic process. Biochemical studies demonstrated enhanced collagen production and deposition in cultures treated with ascorbic acid. Ultrastructural studies of these cultures showed a marked increase in newly formed interstitial collagen in the perivascular matrix and in regions of the plasma clot containing nonendothelial mesenchymal cells. Small microvessels with thin lumina similar to the ones observed in ascorbic acid-treated plasma clot cultures were obtained by growing aortic explants in gels of interstitial collagen in the absence of ascorbic acid. Inhibition of collagen production with the proline analogue cis-hydroxyproline had a marked anti-angiogenic effect in both plasma clot and collagen gel cultures. The anti-angiogenic effect of cis-hydroxyproline was abolished by adding L-proline to the culture medium, thereby restoring normal metabolism. These results support the hypothesis that angiogenesis is regulated by collagen production and suggest that the size of newly formed microvessels is influenced by the degree of collagenization of the extracellular matrix.

Monoclonal antibody-dependent, cell-mediated cytotoxicity against human malignant gliomas.

Two monoclonal antibodies (MAbs), IgG2a MAb ASHG4 and IgG2b MAb ASHE2, were produced in mice immunized with cultured human malignant glioma cells. Both MAbs bound strongly to the surfaces of long-term cultured glioma cells, and MAb ASHE2 also bound strongly to short-term cultured glioma cells. Sections of frozen glioma tissues bound both MAbs strongly, whereas normal brain tissues showed weaker reactivities, and tissues derived from carcinomas of various histological types were completely unreactive. Furthermore, the MAbs did not bind to peripheral blood cells or bone marrow cells. Although both MAbs bound to the same Mr 27,000-29,000 protein, they may detect different or overlapping epitopes on this antigen. Because MAbs ASHE2 and ASHG4 lysed cultured glioma cells with human peripheral blood lymphocytes as effector cells, they are promising reagents for approaches to immunotherapy of human malignant gliomas.

Monoclonal antibodies with cytotoxic reactivities against human gliomas.

Monoclonal antibodies (MAb's) reactive with human malignant glioma cells were derived from mice inoculated with cells from fresh glioma tissue. Seven MAb's were selected for study based on their high-level binding in immunoperoxidase and immunofluorescence assay to most of the glioma tissues derived from various patients and based on the absence of binding to normal bone marrow cells. Four of the seven MAb's did not bind to any of the four normal brain tissues tested, whereas three MAb's bound to one or two of these tissues. Two MAb's bound to the surfaces of cultured glioma cells in radioimmunoassay. One of these MAb's (AS-AY1, immunoglobulin (Ig)(G1) lysed cultured glioma cells with human lymphocytes or murine macrophages as effector cells; the other MAb (AS-AY2, IgM) was reactive in complement-dependent cytotoxicity assay. These two MAb's therefore seem especially promising reagents in approaches to immunotherapy of human malignant glioma.