Abstract 2527: Amonafide and its metabolite N-acetyl amonafide are Top2 poisons with differing biochemical properties

Abstract

Abstract Naphthalimides derivatives have been extensively studied as anti-cancer agents. Amonafide (5-amino-2-[2-(dimethylamino)ethyl]-1H-benzo[de]isoquinoline-1,3(2H)-dione) showed clinical activity especially in some groups of AML patients. Amonafide has been shown to target topoisomerase II (Top2), and to stabilize Top2 covalent complexes. Therefore, the agent is a Top2 poison, however, the compound shows some unusual properties. Unlike most Top2 poisons, the action of amonafide against Top2 is largely ATP independent; In addition, amonafide leads to cleavage of DNA at a very restricted set of sites compared to other Top2 poisons such as mitoxantrone or etoposide. These findings have led to suggestions that amonafide may target Top2 in an unconventional way. Another obstacle to the clinical use of amonafide is variable drug metabolism. Felder and colleagues showed that amonafide is metabolized by N-acetyl transferase 2 (NAT2) to form N-acetyl amonafide (NAA). Toxicity of amonafide regimens is associated with higher levels of NAT2 activity 2. The mechanism of NAA toxicity has not been reported. We have used the ICE assay developed by Muller and colleagues to assess Top2 covalent complex levels in cells treated with either amonafide or NAA. We found that amonafide induces Top2 mediated DNA cleavage, and that covalent complexes formed by both Top2 alpha and Top2 beta were seen. Interestingly, NAA induced higher levels of Top2 covalent complexes than the parent compound. In addition, the level of Top2 covalent complexes increased with increasing NAA dose, whereas a plateau in the level of Top2 covalent complexes was seen with amonafide at relatively low doses. We are currently comparing the action of amonafide and NAA against purified human topoisomerases. We suggest that NAA is a Top2 poison, and a plausible hypothesis is that NAA may act more like a conventional Top2 poison, while amonafide may show a better therapeutic index because it has more limited potential for forming Top2 covalent complexes. These results may be useful in the further development of amonafide derivatives with a favorable therapeutic profile. (1) Felder, T. B.; McLean, M. A.; Vestal, M. L.; Lu, K.; Farquhar, D.; Legha, S. S.; Shah, R.; Newman, R. A. Drug Metab Dispos 1987, 15, 773. (2) Ratain, M. J.; Rosner, G.; Allen, S. L.; Costanza, M.; Van Echo, D. A.; Henderson, I. C.; Schilsky, R. L. J Clin Oncol 1995, 13, 741. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2527. doi:10.1158/1538-7445.AM2011-2527