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Three kinds of para-phenylenediamine (PDA) derivatives bearing nitronyl nitroxide (NN) groups were prepared and characterized on the basis of the electrochemical, electron spin resonance (ESR) spectroscopic, absorption spectroscopic, and magnetic susceptibility measurements. It was clarified that the oxidation potential of the central PDA unit is strongly influenced by the numbers of substituted electron-withdrawing NN groups. In addition, the intervalence charge transfer in the central PDA unit was detected in the monocationic states of the PDAs with two NN groups, indicating the coexistence of the localized spins and the delocalized spin on theses molecules. Moreover, pulsed ESR measurements confirmed that the delocalized spin on the central PDA unit and the localized two spins on the NN groups were ferromagnetically coupled in the monocationic states.

A thermostable aspartase gene (aspB) from Bacillus sp. YM55-1 was cloned and the gene sequenced. The aspB gene (1407 bp ORF) encodes a protein with a molecular mass of 51 627 Da, consisting of 468 amino-acid residues. An amino-acid sequence comparison revealed that Bacillus YM55-1 aspartase shared 71% homology with Bacillus subtilis aspartase and 49% with Escherichia coli and Pseudomonas fluorescens aspartases. The E. coli TK237/pUCASPB strain, which was obtained by transforming E. coli TK237 (aspartase-null strain) with a vector plasmid (pUCASPB) containing the cloned aspB gene, produced a large amount of the enzyme corresponding to . 10% of the total soluble protein. The over-expressed recombinant enzyme (native molecular mass: 200 kDa) was purified effectively and rapidly using heat treatment and affinity chromatography. In order to probe the catalytic residues of this enzyme, two conserved amino-acid residues, Lys183 and His134, were individually mutated to alanine. Although the tertiary structure of each mutant was estimated to be the same as that of wild-type aspartase in CD and fluorescence measurements, the Lys183Ala mutant lost its activity completely, whereas His134Ala retained full activity. This finding suggests that Lys183 may be involved in the catalytic activity of this thermostable Bacillus YM55-1 aspartase.

Purpose: The purpose of the present study was to evaluate the antitumor activity and pharmacokinetic profile of MEN4901/T-0128 in nude mice bearing human tumor xenografts in comparison with irinotecan (CPT-11) and T-2513. Experimental Design: We have determined the antitumor activity of MEN4901/T-0128, CPT-11, and T-2513 in BALB/cA Jcl nude mice bearing human gastric (H-81), colon (H-110), lung (Mqnu-1, H-74), esophageal (H-204), liver (H-181), and pancreatic (H-48) cancer lines, which had been serially transplanted s.c. and maintained in nude mice, and characterized the pharmacokinetic profile of MEN4901/T-0128 in nude mice bearing human gastric carcinoma St-4. Results: MEN4901/T-0128 administered i.v. showed a marked antitumor activity in each of these tumor models, producing tumor shrinkage in the models of H-204 and H-181 carcinomas at its maximum tolerated dose of 80 mg/kg (expressed as T-2513) weekly for 4 weeks (q7d × 4) and tumor-shrinking or marked growth-inhibitory effects in the models of H-81, H-110, Mqnu-1, H-74, and H-48 carcinomas at 1/3 of its maximum tolerated dose (q7d × 4). Pharmacokinetic analysis showed that MEN4901/T-0128 had an extended plasma half-life with sustained tumor levels of T-2513, which may explain the superior activity of MEN4901/T-0128 in vivo. Conclusions: Because the efficacies of some drugs in this human cancer-nude mouse panel correlated well with their clinical outcomes in patients with the same type of cancers, the findings provide direct support that MEN4901/T-0128 is more efficacious than CPT-11 and is an excellent candidate for clinical trials for the treatment of solid tumors.

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