Diaza- and Triazachrysenes: Potent Topoisomerase-Targeting Agents with Exceptional Antitumor Activity against the Human Tumor Xenograft, MDA-MB-435 Alexander L. Ruchelman, a Sudhir K. Singh, a Xiaohua Wu, a,b Abhijit Ray, a Jin-Ming Yang, b,c Tsai-Kun Li, c Angela Liu, c Leroy F. Liu b,c and Edmond J. LaVoie a,b, * a Department of Pharmaceutical Chemistry, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8020, USA b The Cancer Institute of New Jersey, New Brunswick, NJ 08901, USA c Department of Pharmacology, The University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA Received 26 June 2002; accepted 9 August 2002 Abstract—Several 5,12-diazachrysen-6-ones and 5,6,11-triazachrysen-12-ones were synthesized with varied substituents at the 5- or 11-position, respectively. Each compound was evaluated for its potential to stabilize the cleavable complex formed with TOP1 and DNA. Two analogues with very potent TOP1-targeting activity, 3a and 4a, exhibited cytotoxic activity with IC 50 values at or below 2nM against RPMI8402. Compound 3a was active in vivo by either ip or po administration in the human tumor xenograft athymic nude mice model. # 2002 Elsevier Science Ltd. All rights reserved. DNA topology is regulated by DNA topoisomerases that catalyze the breaking and rejoining of DNA strands. 1 3 Topoisomerases are critical to both replica- tion and transcription. There are two major types of topoisomerases, type I [e.g., topoisomerase I (TOP1)] and type II [e.g., topoisomerase II (TOP2)], based upon differences in their initial mechanisms wherein a single- or double-stranded DNA break is implicated. 1 3 Topoisomerase-targeting agents that can stabilize the cleavable complex formed between the enzyme and DNA have proved to be effective in the treatment of cancer. This drug-induced stabilization of the enzyme– DNA cleavable complex effectively converts these nuclear enzymes into cellular poisons. Camptothecin was the first agent identified as a TOP1- targeting agent. 4 The extensive studies on camptothecin and its structurally related analogues have resulted in the clinical development of two TOP1-targeting drugs, topotecan (Hycamptin 1 ) and irinotecan (CPT-11/ Camptosar 1 ). Both of these drugs have incorporated within their structure the camptothecin-ring system, which includes the presence of a g-lactone. Hydrolysis of this lactone moiety results in an inactive derivative that possesses high affinity for human serum albumin. 5 7 The metabolic instability of this lactone and the observation that both topotecan and irinotecan are substrates for efflux transporters associated with resis- tance have prompted further studies on the development of novel TOP1-targeting agents. 8 10 Recently, bi- and terbenzimidazoles, 11,12 benz[a]anthracenes, 13 certain benzo[c]phenanthridine and protoberberine alkaloids and their synthetic analogues, 14,15 indolocarbazoles, 16 the fungal metabolites bulgarein, 17 and saintopin, 18 sev- eral indenoisoquinolines 19 and benzophenazines 20 have been identified as TOP1-targeting agents. Studies in our laboratory originating with proto- berberine analogues and more recently with non- charged heterocyclic analogues have revealed that appropriately substituted benzo[i]phenanthridines and 0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(02)00737-0 Bioorganic & Medicinal Chemistry Letters 12 (2002) 3333–3336 *Correspondingauthorat:ErnestMarioSchoolofPharmacy,Rutgers University, 160 Frelinghuysen Road, Piscataway, NJ 08854, USA. Tel.: +1-732-445-2674; fax: +1-732-445-6312; e-mail: elavoie@rci. rutgers.edu Website: http://www.rci.rutgers.edu/  layla/Faculty/LaVoie.htm