Cardioprotective effects of the novel anthracycline antitumor agent N-benzyladriamycin-14-valerate (AD 198)
Authors: Len Lothstein, Polly A. Hofmann, Trevor W. Sweatman, Jennifer D. Bilyeu, Ganesh R. Panta, Mervyn Israel, Judith E. Soberman, Marcello Arsura
Journal: Cancer Research (2004)

1134   The antitumor efficacy of nuclear-targeted anthracyclines, such as doxorubicin (DOX) is often limited by dose-dependent cardiomyopathies occurring in up to 25% of all treated patients at doses as low as 600 mg/sq m and as early as 6 months after DOX-based therapy. Anthracyclines generate reactive oxygen species (ROS) through an iron-dependent redox reactions on the quinone ring of the chromophore. ROS induce cardiomyocyte apoptosis and impede myocardial contractility. Lower doses of DOX reduce the frequency of cardiomyopathies, but produce sub-clinical damage leading to reduced cardiac functional reserve and rendering the patient more sensitive to superimposed cardiac stress. In an effort to eliminate DOX cardiotoxicity while retaining potent antitumor efficacy, we have developed a novel class of extranuclear-targeted anthracyclines, represented by N-benzyladriamycin-14-valerate (AD 198), that retains antitumor potency through a mechanism that is distinct from DOX. AD 198 binds to the C1b regulatory domain of protein kinase C (PKC). The resulting stimulation of kinase activity leads to rapid apoptosis in proliferating cells and is unimpeded by Bcl-2/Bcl-XL, Bcr-Abl, P-gp or p53 dysfunction. AD 198 demonstrates no organ toxicity in vivo and myelosuppression only at higher doses than DOX. Remarkably, AD 198 is chronically non-cardiotoxic in mice despite the presence of a quinone ring capable of generating ROS. To characterize the underlying basis of non-cardiotoxicity, we sought to determine the effect of AD 198 treatment on PKC-e, an important signaling nexus in the preconditioning pathway involved in cardiomyocyte survival. AD 198 induces rapid and specific PKC-e translocation to membrane in isolated rat and mouse cardiomyocytes. PKC-e activation also induces NF-kB activity and phosphorylation of p38-MAPK. Since NF-kB and p38 are two downstream target of PKC involved in myocardial early- and late-phase preconditioning, we tested the ability of AD 198 to induce cardiac preconditioning ex vivo. For this purpose, isolated rat hearts were perfused with oxygenated Krebs-Henseleit buffer containing either DMSO (vehicle control), DOX or AD 198 for 15 min, then subjected to global ischemia by arterial occlusion, followed by reperfusion with drug-free buffer for 1 hr. Left ventricular developed pressure (LVDP) was used as a measure of functional recovery from ischemia. In the presence of DMSO alone, LVDP exhibits a 22.5% recovery during reperfusion compared with pre-ischemic pressure. Perfusion with 1 uM DOX decreases post-ischemic LVDP recovery to just 7.5%. Perfusion with AD 198 as low as 0.1 uM produces up to 82.4% recovery of LVDP. Studies in PKC-e knockout mice reveal reduced cardioprotection by AD 198. These results suggest that AD 198 non-cardiotoxicity in vivo correlates with induction of cardioprotective signaling in myocytes through PKC-e activation.