Tretazicar (CB 1954), an antitumor prodrug, is highly selective against the Walker 256 rat tumour line. Tretazicar is enzymatically activated to generate a bifunctional agent, which can form DNA-DNA interstrand cross-links. Tretazicar in rat cells involves the reduction of its 4-nitro group to a 4-hydroxylamine by the enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1)^[1][2]. In Vitro: Tretazicar (CB 1954) (0.1-1000 μM; 3 days) has sensitivity for retrovirally transduced AB22 (AB22-nr) cells with an IC₅₀ of 3 μM^[3].
DNA cross-link formation in affected cells is a result of the bioactivation of the drug by the enzyme DT diaphorase (NAD(P)H dehydro-genase (quinone)) in the Walker cells which reduces the 4-nitro group of Tretazicar. The product of this reaction is a difunctional alkylating agent, 5-aziridin-1-yl-4-hydroxylamino-2-nitrobenzamide^[4]. In Vivo: Tretazicar (CB 1954) (80 mg/kg; i.p. on days 2 and 9) results in a significant increase in survival^[3].