Novel inhibitors of carboxypeptidase G2 (CPG2): potential use in antibody-directed enzyme prodrug therapy.

The design and synthesis of potent thiocarbamate inhibitors for carboxypeptidase G2 are described. The best thiocarbamate inhibitor N-(p-methoxybenzenethiocarbonyl)amino-L-glutamic acid 6d, chosen for preliminary investigations of in vitro antibody-directed enzyme prodrug therapy (ADEPT), abrogated the cytotoxicity of a combination of A5B7-carboxypeptidase G2 conjugate and prodrug PGP (N-p-{N,N-bis (2-chloroethyl)amino}phenoxycarbonyl-L-glutamate) toward LS174T cells. This is the first report of a small-molecule enzyme inhibitor proposed for use in conjunction with the ADEPT approach.

Regioselective C-3-O-acylation and O-methylation of 4,6-O-benzylidene-beta-D-gluco- and galactopyranosides displaying a range of anomeric substituents.

The regioselective C-3-O-acylation and O-methylation of a range of 4,6-O-benzylidene-beta-D-gluco- and galactopyranosides has been studied. Regioselectivity is achieved by forming the copper chelate of the 2,3-diol using either sodium hydride and copper(II) chloride, or copper(II) acetylacetanoate, or copper(II) acetate, prior to introduction of the acylating or methylating agent.

High temperature reduction of metmyoglobin in aqueous muscle extracts.

Oxymyoglobin in aqueous extracts of fresh beef longissimus dorsi muscles was initially oxidised to metmyoglobin during heat treatments at temperatures in the range 50-70 °C. The metmyoglobin then underwent reduction to a red pigment that was shown spectrally to be identical to oxymyoglobin. The formation of oxymyoglobin involved a heat induced precipitate that when removed from the solution, allowed oxidation to metmyoglobin to occur. However, on re-addition of the precipitate further reduction to oxymyoglobin took place. Dialysis of the muscle extract prior to heating markedly inhibited the reduction but addition of NADH to the dialysate permitted further reduction. The precipitate plus NADH caused oxymyoglobin formation in the presence of metmyoglobin but neither the precipitate nor NADH alone induced this formation. It is concluded that the initial conversion of oxymyoglobin to metmyoglobin on heating fresh beef muscle extracts was reversible and that the reverse reaction depended on the presence of both NADH and a muscle protein.

Melanocyte-directed enzyme prodrug therapy (MDEPT): development of a targeted treatment for malignant melanoma.

A novel prodrug rationally designed to function as a tyrosinase substrate has been synthesised to allow targeted treatment of malignant melanoma. This agent has been evaluated for tyrosinase-mediated drug release, and has been shown to act in the desired manner. Furthermore, differential cytotoxicity has been demonstrated in cell lines which express tyrosinase and those which do not.

Melanocyte-Directed enzyme prodrug therapy (MDEPT): development of second generation prodrugs for targeted treatment of malignant melanoma.

Evaluation of second generation prodrugs for MDEPT, by oximetry, has highlighted structural properties that are advantageous and disadvantageous for efficient oxidation using mushroom tyrosinase. In particular, a sterically undemanding prodrug bis-(2-chloroethyl)amino-4-hydroxyphenylaminomethanone 28 was synthesised and found to be oxidised by mushroom tyrosinase at a superior rate to tyrosine methyl ester, the carboxylic acid of which is the natural substrate for tyrosinase. The more sterically demanding phenyl mustard prodrugs 9 and 10 were oxidised by mushroom tyrosinase at a similar rate to tyrosine methyl ester. In contrast, tyramine chain elongation via heteroatom insertion was detrimental and the rate of mushroom tyrosinase oxidation of phenyl mustard prodrugs 21 and 22 decreased by 10 nanomol/min.

Novel monosaccharides as potent inhibitors of cell proliferation.

The effects of several novel monosaccharides upon thymidine incorporation into both normal and tumour cells were investigated. The monosaccharide 2-deoxy-3-[1-(R)-(ethoxycarbonyl)ethyl]- alpha-D-allo-pyranose had the most inhibitory effect on proliferation, with the (S)-enantiomer having less inhibitory effects. The chiral centre at carbon-7 was found to be an important part of the molecule, as 2-deoxy-3-[methoxycarbonyl methyl]-alpha-D-allo-pyranose had greatly decreased anti-proliferative properties in comparison with the parent compound. In addition, the 2-deoxy structure at carbon-2 was also found to be important, as 3-[1-(S)-(ethoxycarbonyl)ethyl]-alpha-D-allo-hexopyranose had greatly decreased inhibitory properties in comparison with the parent compound. The results indicate that these novel monosaccharides possess potent anti-proliferative properties, related to their chiral carbon-7 and 2-deoxy carbon-2 structure and suggest that further substitutions of the functional group at carbon-7 may improve these properties and possibly produce inhibitor selectivity for tumour cells in preference to normal cells.