Metabolism-Dependent Mutagenicity of a Compound Containing a Piperazinyl Indazole Motif: Role of a Novel P450-Mediated Metabolic Reaction Involving a Putative Oxaziridine Intermediate
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- 作者：Hao Chen ; Joel Murray ; Brian Kornberg ; Lloyd Dethloff ; David Rock ; Sham Nikam ; Abdul E. Mutlib
- 刊名：Chemical Research in Toxicology
- 出版年：2006
- 出版时间：October 2006
- 年：2006
- 卷：19
- 期：10
- 页码：1341 - 1350
- 全文大小：335K
- 年卷期：v.19,no.10(October 2006)
- ISSN：1520-5010
文摘
Compound 1a (6-chloro-5-{3-[4-(1H-indazol-3-yl)-piperazin-1-yl]-propyl}-3,3-dimethyl-1,3-dihydro-indol-2-one) was mutagenic to Salmonella typhimurium TA98 in the presence of rat liver S9 subcellularfraction. The metabolism of 1a in rat liver S9 or microsomes demonstrated that it underwent a P450-mediated N-deindazolation (loss of indazole ring) as a predominant metabolic pathway. To investigatea possible link between metabolism and mutagenicity, a structural analogue 1b (6-chloro-5-{3-[4-(1H-indazol-3-yl)-piperidin-1-yl]-propyl}-3,3-dimethyl-1,3-dihydro-indol-2-one), the cleaved product 2a (6-chloro-3,3-dimethyl-5-(3-piperazin-1-yl-propyl)-1,3-dihydro-indol-2-one), and the core motif 3a (3-piperazinyl indazole) were evaluated in the Ames assay. It was found that 1b was not mutagenic toSalmonella typhimurium TA98 in the absence or presence of a metabolic activating system. In contrastto 1a, 1b did not undergo the metabolic cleavage (loss of indazole ring). Marginal mutagenicity of 2a toTA98 was observed with rat liver S9, whereas 3a was shown to be a promutagen. It was furtherdemonstrated that 1a inactivated P450 3A, the principle enzyme catalyzing the N-deindazolation reaction,in an NADPH-, time-, and concentration-dependent manner. The kinetics of inactivation was characterizedby a KI of 8.1 
M and kinact of 0.114 min-1. The differences in mutagenicity between 1a and 1b suggestthat a chemical bond extending from the 3-position of the indazole to a heteroatom (as part of anothercyclic ring) is a prerequisite for the toxicity. The metabolic process leading to the elimination of theindazole from the rest of the molecule apparently plays a key role in causing mutagenicity. It is postulatedthat the N-deindazolation of 1a proceeds via an oxaziridine intermediate, the formation of which isindirectly inferred from the presence of benzoic acid in microsomal incubations. Benzoic acid is thoughtto be derived from the hydrolysis of 3-indazolone, an unstable product generated from the oxaziridine.Evidence suggests that the electrophilic oxaziridine intermediate may be responsible for the mutagenicityand inactivation of P450 3A.
M and kinact of 0.114 min-1. The differences in mutagenicity between 1a and 1b suggestthat a chemical bond extending from the 3-position of the indazole to a heteroatom (as part of anothercyclic ring) is a prerequisite for the toxicity. The metabolic process leading to the elimination of theindazole from the rest of the molecule apparently plays a key role in causing mutagenicity. It is postulatedthat the N-deindazolation of 1a proceeds via an oxaziridine intermediate, the formation of which isindirectly inferred from the presence of benzoic acid in microsomal incubations. Benzoic acid is thoughtto be derived from the hydrolysis of 3-indazolone, an unstable product generated from the oxaziridine.Evidence suggests that the electrophilic oxaziridine intermediate may be responsible for the mutagenicityand inactivation of P450 3A.