Discovery of Antitumor Indolocarbazoles: Rebeccamycin, NSC 655649, and Fluoroindolocarbazoles

Byron   H.   Long; William   C.   Rose; Dolatrai   M.   Vyas; James   A.   Matson; Salvatore      Forenza

doi:10.2174/1568011023354218

Abstract

A fermentation directed product search for potential anticancer drugs conducted by Bristol-Myers in the 1970s and early 1980s resulted in the identification of a novel indolocarbazole (IC) rebeccamycin (RBM) as a potential drug development candidate. Subsequently, an analog program designed to impart distal site in vivo antitumor activity resulted in the discovery of diethylaminoethyl analog of RBM (DEAE-RBM), which is presently undergoing clinical evaluation as NSC 655649 and BMY-27557. Strong DNA intercalation is the primary mechanism of action of DEAE-RBM resulting in the potent catalytic inhibition of both topoisomerases I and II. Precursor feeding fermentation experiments with fluorine-substituted tryptophans yielded novel fluoroindolocarbazoles (FICs). These FICs were identified as targeting topoisomerase (topo) I in a mechanism-based screen and their action on topo I was confirmed by production of topo I-mediated single-strand breaks in DNA at sites essentially identical to those induced by ca mptothecin. Topo I dependent cytotoxicity was demonstrated for specific FICs using a P388 and camptothecin-resistant P388 / CPT45 pair of cell lines, the latter expresses little or no functional topo I. For example, topo I selectivity was greatest with 3,9-difluoro substituted FIC and was least significant and least cytotoxic with 4,8-difluoro substituted FIC. The review focuses on the discovery of the rebeccamycin class of compounds and their structure-activity relationships leading to the development of the clinical candidate BMY-27557 (NSC 655649), as well as the lead identification of the fluoroindolocarbazole class of compounds.

Keywords: Antitumor Indolocarbazoles, Fluoroindolocarbazoles, fluoroindolocarbazoles (FICs), Rebeccamycin (RBM), Fluorotryptophan, 7-oxostaurosporine, 1,11-dideschloro-6-N-hydroxy RBM

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