5-amino-1-(chloromethyl)-1,2 dihydro-3H-benz [e]indoles:: Relationships between structure and cytotoxicity for analogues bearing different DNA minor groove binding subunits

A series of 5-amino-seco-CBI compounds, designed for use as effecters for prodrugs, were prepared to study structure-activity relationships for the cytotoxicity of side chain analogues. Compounds were prepared by coupling 1-(chloromethyl)-5-nitro-1,2-dihydro-3H-benz[e]indole to appropriate carboxylic acids, followed by nitro group reduction, or by coupling suitable 5-amino-protected indolines to alpha,beta-unsaturated acids, followed by deblocking. These AT-specific DNA alkylating agents were evaluated for cytotoxicity in a series of tumor cell lines (AA8, UV4, EMT6, SKOV3). For those analogues bearing an indolecarbonyl side chain, the 5'-methoxy derivative was the most cytotoxic (IC50 1.3 nM in AA8 cells, 4 h exposure), comparable to that of the parent CBI-TMI (5',6',7'-trimethoxyindole) derivative (IC50 0.46 nM in the above assay). A subset of solubilized derivatives bearing O(CH2)(2)NMe2 substituents were about 10-fold less potent. For compounds containing an acryloyl linker in the side chain, the 4'-methoxycinnamoyl derivative proved the most cytotoxic (IC50 0.09 nM in the above assay). A number of these 5-amino-seco-CBI-TMI analogues (including the solubilized compounds) are of interest both as cytotoxins and as components of amine-based prodrugs designed for tumor-specific activation.