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Research Articles: Therapeutics, Targets, and Development

DNA sequence–selective adenine alkylation, mechanism of adduct repair, and in vivo antitumor activity of the novel achiral seco-amino-cyclopropylbenz[e]indolone analogue of duocarmycin AS-I-145

¹ Cancer Research Drug-DNA Interactions Research Group, Department of Oncology, University College London, London, United Kingdom; ² Taiho Pharmaceutical Co., Ltd., 1-27, Misugidai Hanno-City, Saitama, Japan; ³ Division of Natural Sciences and Department of Chemistry, Hope College, Holland, Michigan

Requests for reprints: John A. Hartley, Department of Oncology, University College London, 91 Riding House Street, London W1W 7BS, United Kingdom. Phone: 440-20-7679-9299; Fax: 440-20-7436-2956. E-mail: john.hartley{at}ucl.ac.uk

Abstract

AS-I-145 is a novel achiral seco-amino-cyclopropylbenz[e]indolone (seco-amino-CBI) analogue of duocarmycin that has evolved from an alternative strategy of designing CC-1065/duocarmycin agents lacking the characteristic chiral center of the natural agents. The sequence specificity of this compound was assessed by a Taq polymerase stop assay, identifying the sites of covalent modification on plasmid DNA. The adenine-N3 adducts were confirmed at AT-rich sequences using a thermally induced strand cleavage assay. These studies reveal that this compound retains the inherent sequence selectivity of the related natural compounds. The AS-I-145 sensitivity of yeast mutants deficient in excision and post-replication repair (PRR) pathways was assessed. The sensitivity profile suggests that the sequence-specific adenine-N3 adducts are substrates for nucleotide excision repair (NER) but not base excision repair (BER). Single-strand ligation PCR was employed to follow the induction and repair of the lesions at nucleotide resolution in yeast cells. Sequence specificity was preserved in intact cells, and adduct elimination occurred in a transcription-coupled manner and was dependent on a functional NER pathway and Rad18. The involvement of NER as the predominant excision pathway was confirmed in mammalian DNA repair mutant cells. AS-I-145 showed good in vivo antitumor activity in the National Cancer Institute standard hollow fiber assay and was active against the human breast MDA-MD-435 xenograft when administered i.v. or p.o. Its novel structure and in vivo activity renders AS-I-145 a new paradigm in the design of novel achiral analogues of CC-1065 and the duocarmycins. [Mol Cancer Ther 2007;6(10):2708–18]

Grant support: J.A. Hartley acknowledges program grant support from Cancer Research (C2259/A3083).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Note: Present address for Peter J. McHugh: Cancer Research Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.

Received 4/25/07; revised 8/ 3/07; accepted 8/31/07.