Combi-molecules are agents designed to block receptors on their own and to further degrade to bioactive agents. Here we studied the fate of a novel combi-molecule of triazene class termed "ZRS1" in
biological medium using multilayer aggregates and mouse tumour models. ZRS1 is a second generation derivative of RB107, a
prodrug designed to release an EGFR inhibitor FD105 plus a methyl diazonium species. RB107 contains an acetoxymethyl function that is hydrolyzed too rapidly to generate
BJ2000, a monoalkyltriazene that further degrades to FD105 and
DNA alkylating methyldiazonium species. Recently, in order to prevent rapid hydrolysis of the acetoxymethylene function in the absence of cells and to delay the release of
BJ2000, we designed ZRS1 that contains a more stable acetoxymethyl
carbamate function. The results showed that ZRS1 was more stable than RB107 in cell culture medium supplemented with serum, with a rather long half life (>2 h). However, in an experiment where it was allowed to degrade in multilayer aggregates of
ovarian cancer cells OV90, it rapidly released
BJ2000 and its corresponding metabolite FD105, both in the medium and the multilayer aggregates. Interestingly, the intact ZRS1 could be detected in the multilayer aggregates with a T(max) around 10 min. Studies in vivo, in human DU145
prostate cancer xenograft model, revealed that ZRS1 blocked tumour growth and released FD105 and its acetylated metabolite FD105Ac, the latter being the major metabolite. Likewise, time course analysis in 4T1 mouse syngeneic
breast cancer model showed a rapid release of FD105 and FD105Ac in the plasma and in the tumours. In summary, ZRS1 appeared as a good
prodrug of the stable EGFR inhibitory metabolites FD105 and FD105Ac. Its ability to generate high concentrations of FD105Ac, a more potent EGFR inhibitor as is its major metabolite, is significant over previous methylating combi-molecules. Furthermore, this study showed that multilayer OV90 aggregates could be developed as an effective model to predict the stability and degradation of ZRS1 in vivo.