Yuka Matsushima

. Thioflavin T binding assays, nondenaturing gel electrophoresis, and morphological analyses revealed that SS-Aβ42 maintained oligomeric structure, whereas wild-type Aβ42 and the highly aggregative Aβ42 mutant with E22P substitution (E22P-Aβ42) formed Aβ fibrils. In agreement with these observations, SS-Aβ42 was more cytotoxic compared to the wild-type and E22P-Aβ42 in cell cultures. Furthermore, we developed a monoclonal antibody, designated TxCo-1, using the toxic conformation of SS-Aβ42 as immunogen. X-ray crystallography of the TxCo-1/SS-Aβ42 complex, enzyme immunoassay, and immunohistochemical studies confirmed the recognition site and specificity of TxCo-1 to SS-Aβ42. Immunohistochemistry with TxCo-1 antibody identified structures resembling senile plaques and vascular Aβ in brain samples of AD subjects. However, TxCo-1 immunoreactivity did not colocalize extensively with Aβ plaques identified with conventional Aβ antibodies. Together, these findings indicate that Aβ with a turn at positions 22 and 23, which is prone to form Aβ oligomers, could show strong cytotoxicity and accumulated in brains of AD subjects. The SS-Aβ42 and TxCo-1 antibody should facilitate understanding of the pathological role of Aβ with toxic conformation in AD.

We report a method to fix the conformation of Aβ42 to the toxic or non-toxic form by intramolecular disulfide bonds. We found that an Aβ42 analog crosslinked within the molecule at the 17th and 28th amino acid residues exhibited high aggregative ability and potent neurotoxicity comparable to those of E22P-Aβ42. This analog would be useful in the research of Aβ42 oligomers and to develop reliable antibodies for early diagnosis of Alzheimer's disease.

Quinocarmycin monocitrate is a novel antitumor antibiotic isolated from Streptomyces melanovinaceus. We have utilized a human tumor clonogenic assay to test the antitumor activity of this drug against carcinoma of the lung and to compare its activity with those of mitomycin C or cisplatin, which are components of the clinically effective regimens in therapy for this disease. The overall in vitro response rate (defined as less than 50% survival of tumor colony forming units) for quinocarmycin at 0.1 and 1.0 microgram/ml continuous exposure was 42% and 72%, respectively, which was superior to that of other drugs. Quinocarmycin and other antitumor drugs do not have identical spectra of antitumor activities in vitro, suggesting that this compound with good in vitro activity should be further developed for clinical trials.