A Novel N-Oxide Drug, AQ4N, Has In Vitro Activity in Lymphoma and Leukemia Cell Lines and Selectively Targets Lymphocytes and Lymphatic Tissues in Vivo.

An ideal treatment for lymphoma and leukemia is the use of highly selective compounds to eliminate diseased cells with minimal systemic toxicity to normal tissues (cf. imatinib mesylate; Gleevec). AQ4N (1,4 bis[[2-(dimethylamino)ethylamino}-5,8-hydroxyanthracene-9,10-dione bis N-oxide) is designed to have little or no toxicity until selectively activated by bioreduction in hypoxic cells to AQ4 (reduced AQ4N), a highly potent DNA topoisomerase II inhibitor. In a series of studies, AQ4 has been shown to have potent cytotoxicity on lymphoma and leukemia cell lines in vitro and AQ4N has selective activity in lymphatic tissues in vivo. The IC50 of AQ4, was 0.63, 12.0, 90.5 and 150 nM in Namalwa, Daudi, Ramos, and Raji human lymphoma cell lines and 1.0, 6.0, and 20 nM in HL-60, KG1a and K562 human leukemia cell lines. On several of the tumor lines the activity of AQ4 was more potent than doxorubicin (i.e. IC50 for Dox was 20.3 nM on Namalwa). AQ4N also had anti-proliferative activity at μM levels indicating a potential mechanism for activation by these cell lines. In repeat dose toxicology studies of AQ4N in pigmented rats and cynomolgus monkeys, the maximum tolerated doses (MTD; rats: 20 mg/kg/wk x 6; monkeys 6 mg/kg/wk x 6) resulted in lymphoid tissue atrophy. A decrease in lymphocyte levels and atrophy of the spleen, thymus, and mandibular and mesenteric lymph nodes were observed at terminal sacrifice of the animals. In contrast, there was an absence of myelosuppression and only mild neutropenia and minor bone marrow atrophy at the MTD. Administration of radiolabeled AQ4N (¹⁴C-benzene) to pigmented rats and cynomolgus monkeys indicated persistence of AQ4N radioactivity in lymphoid tissues for several weeks after a single dose (rats: 20 mg/kg (130–140 μCi/kg); monkeys: 10 mg/kg (135 μCi/kg)). For example, in rats the half-life of radioactive AQ4N in the spleen was 538 hrs with 0.9 μg AQ4N/g tissue (spleen) remaining one week after dosing. Monkeys demonstrated a similar effect with 76.5–86.8 μg AQ4N/g tissue observed in the spleen one week after treatment. Other tissues contained significantly less radioactive AQ4N with the exception of the liver (67.9–78.6 μg AQ4N/g tissue) and adrenal cortex (78.7–86.6 μg AQ4N/g tissue). While some hypertrophy and eosinophila was observed in the adrenal glands, liver toxicity was not observed at the MTD in the repeat dose cynomolgus monkey toxicology study. Overall, these initial findings indicate that AQ4N is active in vitro against human lymphoma and leukemia cell lines and selectively targets lymphoid tissues in vivo suggesting the potential benefit of AQ4N in the treatment of lymphoproliferative diseases.