Marion C. Kirk

Identification of metabolites of 9-β-d-arabinofuranosyl-2-fluoroadenine, an antitumor and antiviral agent

Analysis of blood from a dog given a 400 mg/m2 dose of 9-beta-D-arabinofuranosyl-2-fluoroadenine (2-F-araA) led to the identification of parent drug and a major metabolite, 9-beta-D-arabinofuranosyl-2-fluorohypoxanthine. 2-Fluoroadenine, a toxic derivative of 2-F-araA, was not detected in blood within the limits of detection, suggesting that parent drug was absorbed and distributed without systemic exposure to this toxic derivative. Parent drug, 2-fluoroadenine, and 9-beta-D-arabinofuranosyl-2-fluorohypoxanthine were identified in urine of dog, monkey, and mouse.

Molecular pharmacology of the haloethyl nitrosoureas: Formation of 6-hydroxyethylguanine in DNA treated with BCNU (N,N1-bis[2-chloroethyl]-N-nitrosourea)

Summary The substituted base, 6-(β-hydroxyethyl)guanine, has been identified in DNA which has been treated with the antitumor agent, N,N 1 -bis(2-chloroethyl)-N-nitrosourea (BCNU). This finding provides support for the suggestion that interstrand crosslinks may involve substitution at this position. The presence of 6-hydroxyethylguanine in DNA could also explain the carcinogenic potential of the haloethyl nitrosoureas since this DNA modification is considered mutagenic.

Reaction of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) with guanosine: Evidence for a new mechanism of DNA modification

When guanosine reacts with 1,3-bis(2-chloro-2,2-dideuteroethyl)-1-nitrosourea in a mixture of pH 7.1 buffer and DMSO, the 7-chloroethylguanosine which is isolated contains two deuterium atoms located next to the guanine ring and beta to the chlorine atom as shown by electron impact mass spectrometry. It is proposed that initial attack by DNA bases occurs on the number 2 carbon of the haloethylnitrosourea with displacement of the chloride ion. In accordance with this proposed mechanism, 7-bromoethylguanosine is isolated as a major product when BCNU is reacted with guanosine in the presence of high concentrations of KBr. These results suggest that the antitumor activity of various haloethylating antitumor agents may be determined by structural changes which affect their mechanisms of reaction with DNA.

Mechanism of action of the nitrosoureas—IV: Synthesis of the 2-haloethylnitrosourea-induced DNA cross-link 1-(3-cytosinyl),2-(1-guanyl)ethane

The 2-haloethylnitrosoureas have been shown to form the cross-linked structure 1-(3-cytosinyl),2-(1-guanyl)ethane in DNA. This cross-link has now been synthesized by the reaction of O6-(2-fluoroethyl)guanosine with deoxycytidine in dimethyl sulfoxide followed by removal of the sugars by acid hydrolysis. This synthetic route supports the mechanism for cross-link formation in DNA that involves an initial attack on the O6-position of guanine, followed by a rearrangement and subsequent reaction with cytosine. It also provides a practical route to the synthesis of 1-(3-cytosinyl),2-(1-guanyl)ethane for studies involving formation of this cross-link in DNA.

Synthesis and characterization of 06-(2-chloroethyl)guanine: A putative intermediate in the cytotoxic reaction of chloroethylnitrosoureas with DNA

The chloroethylnitrosoureas are useful antitumor agents which evidently exert a significant part of their cytotoxic action through the formation of a unique 1-(3-deoxycytidyl), 2-(1-deoxyguanosinyl)ethane cross-link in DNA. It has been suggested that this cross-link is formed from O6-(2-chloro-ethyl)guanine, an initial product of DNA alkylation by the chloroethylnitrosoureas; however, O6-(2-chloroethyl)guanine has never been described. We have synthesized this derivative from the reaction of thionyl chloride with O6-(2-hydroxyethyl)guanine, and have found that it decomposes to 1-(2-hydroxyethyl)guanine through an intermediate, presumably 1,O6-ethanoguanine. Its half life at 37 degrees and pH 7.4 is 17.8 min.