Genotoxic effects of MeCCNU on human peripheral blood lymphocytes.

MeCCNU (semustine, 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea, NSC 95441) is successfully used in the treatment of various human malignancies. The drug was tested for its in vitro genotoxic effects on human peripheral blood lymphocytes. Several drug concentrations were studied considering mean plasma level achieved in patients after the receipt of MeCCNU therapy. Induction of chromosome aberrations and sister chromatid exchange frequency had shown dose-effect relationship. Reduced mitotic activity and prolonged average generation time was observed in MeCCNU treated cultures. The results suggest that 'therapeutic' MeCCNU concentrations have genotoxic effects on human peripheral blood lymphocytes.

Nitroimidazoles as modifiers of nitrosourea pharmacokinetics.

We have studied the effect of a number of nitroimidazole sensitizers of varying lipophilicity on the pharmacokinetics of CCNU in mice. It was found that the effectiveness of these compounds in producing pharmacokinetic effects correlated directly with their lipophilicity, viz. in the order: benznidazole (Benzo) greater than Ro07-1902 misonidazole greater than (MISO) greater than Ro05-9963. The effects of MISO on the pharmacokinetics of 4 nitrosoureas of differing lipophilicity were also investigated. The plasma clearances of CCNU, BCNU and MeCCNU (high lipophilicity) were slowed by MISO whereas that of chlorozotocin (Chlz) (low lipophilicity) was unaffected. Thus, it seems that for a pharmacokinetic interaction to occur between a nitroimidazole and a nitrosourea, both the modifier and the cytotoxic agent must have a requisite degree of lipophilicity. As the same requirement appears to hold for enhancement of tumor response, these data provide further evidence that pharmacokinetic modification plays a major role in chemosensitization.

A high pressure liquid chromatographic procedure for monitoring 1-(2-chloroethyl)-3-(4-trans-methylcyclohexyl)-1-nitrosourea levels in body fluids.

A reverse phase high pressure liquid chromatographic method has been developed for the analysis of 1-(2-chloroethyl)-3-(4-trans-methylcyclohexyl)-1-nitrosourea (methyl-CCNU) levels present in body fluids. A value obtained for the plasma half-life for a single patient indicates that this may be larger than hitherto expected.

Lipophilic drugs and lipoproteins: partitioning effects on chloroethylnitrosourea reaction rates in serum.

Chloroethylnitrosoureas are anticancer agents that undergo chemical reactions in vitro and in vivo to form active alkylating agents. The rate at which lipophilic chloroethylnitrosourease decompose in serum is faster than in aqueous solution and comparable to in vivo clearance rates. The increase in reaction rate is known to be caused by a reaction catalyzed by protein. Addition of lipoproteins to serum stabilizes chloroethylnitrosoureas to degradation. A model is presented that correlates serum decomposition rates to lipoprotein concentrations. This model involves partitioning of lipophilic chloroethylnitrosoureas into the hydrophobic core region of the lipoproteins where the chloroethylnitrosourea is chemically stable and is not free to undergo protein binding nor aqueous chemical degradation reactions. Normal interindividual variations of serum lipoprotein concentrations and hence partitioning may be a significant factor affecting the tissue distribution and pharmacokinetics of lipophilic drugs.