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The synthesis of 8-hydroxy and 8-methoxy analogues of some substituted 5-aminoimidazoacridinones (4) is described. The synthesis was carried out by a three-step sequence from the corresponding 1-chloro-4-nitro-9(10H)-acridinone precursors (1). The annulation of the imidazolo ring onto the aminoacridinone chromophore was accomplished by heating the required aminoacridinone (3) with formic acid or, in the case of 1-methyl derivatives, with N,N-dimethylacetamide. Potent cytotoxic activity against L1210 leukemia, as well as antitumor activity against P388 leukemia in mice, was demonstrated for the 8-hydroxy analogues. The corresponding 8-methoxy derivatives were not cytotoxic. However, in some cases, they showed significant in vivo antileukemic activity.

A series of 8-substituted 5-[(aminoalkyl)amino]-6H-v-triazolo[4,5,1-de]acridin-6-ones (2), structurally related to the imidazoacridinones (1), was synthesized and tested for cytotoxic and antineoplastic activity. Preliminary biological results indicated that the 8-OH derivatives possess the highest antitumor activity. No relationship has been found between the nature of the C-8 substituent and antitumor activity.

A new class of antineoplastic agents, the 5-substituted imidazo[4,5,1-de]acridin-6-ones with an (aminoalkyl)amino group in the side chain, has been made. These compounds were synthesized by reduction of 1-substituted 4-nitroacridin-9(10H)-ones and subsequent reaction of the derived amines with carboxylic acids. Their cytotoxic activity against HeLaS3 cells in tissue culture and in vivo antitumor activity against P388 leukemia in mice was demonstrated. A strict relationship between the antineoplastic activity and the number of methylene spacers between proximal and distal nitrogens in the side chain was established.

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Imidazoacridinone C-1311 is a DNA-targeting antitumor intercalator/alkylator currently undergoing Phase II clinical trials. Here, we elucidated the sequence of death responses to C-1311 in human leukemia MOLT4 cells using drug concentration (30 nM) that causes near complete cell growth inhibition at 48 h. Early (6-12 h) responses included transient accumulation of cells at the G2/M border followed by also transient rise in several mitotic markers. Mitotic attempts were largely abnormal, resulting in numerous multinucleated cells (peaking at 24-39 h and declining markedly at later times). These events, indicative of mitotic catastrophe, were not associated with immediate cell death. The fraction of necrotic cells did not exceed 3%. Also, the classical manifestations of apoptosis were marginal at 24 h and their progression clearly followed the decline in the fraction of mitotic and multinucleated cells. Quantification of several apoptotic markers (including phosphatidylserine externalization, apoptotic DNA breaks, mitochondrial dysfunction, caspase activation, and cell membrane integrity) showed a considerable progression and the shift from early to late apoptosis at later times. At 72 h, >80% of cells were apoptotic. Collectively, these findings show that C-1311-induced mitotic catastrophe is not the ultimate death event but rather a step precipitating delayed, albeit massive, apoptotic responses.

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