Abstract 3665: The novel DNA intercalator amonafide (AS1413), disrupts the cell cycle by mechanisms distinct from those of Topo II inhibitors daunorubicin and etoposide
Authors: Senderovich Shai , Jones David , Ajami Alfred , McLaughlin Fiona 
Published: February 2011

Amonafide-L-malate (amonafide, AS1413) is a novel DNA intercalator that induces apoptosis through mechanisms involving Topoisomerase II. Previous studies have indicated that amonafide has a number of important properties that differ from those of classical TopoII poisons: 1. Amonafide is not a substrate for Pgp, MRP-1 or BCRP, resistance mechanisms that may contribute to treatment failure with classical TopoII inhibitors. 2. Amonafide is a non-quinodal napthylamide derivative, which is structurally unrelated to anthracycline or anthracenedione classes of antileukemic agents. It therefore lacks the redox and free radical reactive pharmacophores associated with the cardiotoxicity of the anthracyclines. 3. While amonafide exerts cell killing by acting on the Topoisomerase II cycle, it does not form cleavable complexes. Further work on elucidating the action of amonafide on the Topoisomerase II cell cycle is outlined here.

Cell cycle analysis was performed on the AML cell lines Thp1 and KG1. Cells were exposed to AS1413, etoposide or daunorubicin at IC50 doses for 24 hours (etoposide and daunorubicin) or 48 hours (amonafide). Amonafide exposure resulted in a G2/M cell cycle arrest. Further analysis of the G2/M checkpoint by microscopic analysis of metaphase spreads from cells exposed to IC50 levels of amonafide showed that approximately 10% of the cells were arrested in metaphase (with chromosomes clearly visible), a higher proportion than seen in untreated cells. Furthermore, there was evidence for DNA bridge formation between cells which were not fully divided, indicating inhibition in metaphase. In contrast, etoposide treatment resulted in a G2/M arrest, with no cells visible in metaphase. Daunorubicin exhibited a G1/S arrest; while this was unexpected, the mechanism of action of daunorubicin has been shown to be less cell cycle specific, so this effect may be specific for the cell lines tested here. Again, no cells were arrested in metaphase. Cell cycle regulators such as p21 were up-regulated to a greater extent after exposure to amonafide than after etoposide or daunorubicin treatment. Further investigation of pharmacodynamic markers indicative of AS1413 clinical activity will be carried out.

Amonafide has shown activity in AML, a setting where anthracyclines are currently used. The findings outlined here and the other distinctive properties of amonafide, notably evasion of multi-drug resistance mechanisms, suggest that amonafide could offer a clinical profile distinct from that of classical TopoII poisons. The value of replacing an anthracycline with amonafide is currently being tested in a large randomised phase III trial comparing amonafide plus cytarabine with daunorubicin plus cytarabine in patients with secondary AML.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3665.