Identification and antitumor activity of a reduction product in the murine metabolism of pyrazoloacridine (NSC-366140)

Abstract

Purpose. Pyrazoloacridine (PZA) is a newly developed anticancer agent currently undergoing clinical trials. Its mode of action has not been elucidated but the presence in its chemical structure of a 5-nitro functional group and its activity against oxygen-deficient cancerous cells argue in favor of enzymatic nitro reduction as a possible pathway for its antitumor activity. In order to assess the involvement of the nitro functiona lity in PZA activity, as well as to determine other metabolic products, a pharmacological and chemical study of PZA was designed. Methods. Urine and stool samples were collected from mice before and after treatment with PZA. Samples were fractionated using chromatographic methods and then evaluated using mass spectrometry (MS). One of the characterized metabolites was synthesized and tested in vitro and in vivo for anticancer activity. Results. One major fraction from mouse stool was initially characterized by MS as the 5-aminopyrazoloacridine (5-APZ). This compound was chemically synthesized by catalytic hydrogenation of PZA and stabilized as the hydrochloride salt. 5-APZ was marginally cytotoxic in vitro and was inactive in vivo against a tumor cured by PZA (Panc 03). Conclusions. Bioreduction of the nitro group to an amine compound from PZA represents a pathway in the metabolic sequence of PZA. The inactivity of the chemically generated amine product does not provide conclusive evidence that this pathway is not involved in the cytotoxicity of PZA because other intermediates in the nitro reduction pathway may have a role in the activity of PZA. In particular, the hydroxylamine derivative of PZA could give answers to the involvement of this pathway in PZA cytotoxicity.