Bisimidazoacridones induce a potent cytostatic effect in colon tumor cells that sensitizes them to killing by UCN-01.

PURPOSE: To determine the ability of WMC26, a prototypic bisimidazoacridone (BIA), to induce apoptosis in sensitive colon adenocarcinoma cells and to advance the hypothesis that cancer cells that are growth-arrested by WMC26 are predisposed to undergo apoptotic death by abrogators of cell cycle checkpoints. METHODS: The antiproliferative activity of WMC26 was examined in detail by a 4-day MTT assay, cell counting, BrdU incorporation and a two-color LIVE/DEAD assay. To detect apoptosis a number of established techniques were used, including gel electrophoresis, flow cytometry, and confocal laser microscopy of treated cells. The activity of senescence-associated beta-galactosidase in treated cells was also analyzed. RESULTS: WMC26, at physiological concentrations, induced complete and longlasting growth arrest of HCT116 cells in culture but did not trigger cell death. The growth-arrested cells (blocked at G1 and G2/M cell cycle checkpoints) did not synthesize DNA but were metabolically active and had intact plasma membranes. Although they resembled the senescence-like phenotype reported to be induced by treatment with some antitumor agents, the cells did not express senescence-associated beta-galactosidase, an indicator of the senescence-like state. Treatment of WMC26 growth-arrested cells with 1 microM UCN-01, an abrogator of the G2/M checkpoint, caused a very rapid (1 h) change in morphology and cell death within 72 h. CONCLUSIONS: BIAs do not induce apoptosis in sensitive colon tumor cells. They are highly cytostatic but only marginally toxic to the cells even at concentrations 100-fold higher than those sufficient for complete growth arrest. In this respect WMC26 differs from some other DNA-interacting antitumor agents that produce cell growth arrest at low concentrations but are toxic at higher doses. The complete growth arrest induced by WMC26 in colon cancer cells sensitized them to apoptotic death induced by UCN-01. This finding suggests that a combination of WMC26 and cyclin-dependent kinase inhibitors may be an attractive treatment method for colon cancer that utilizes the highly tumor-selective activity of WMC26.

Bisimidazoacridones: effect of molecular environment on conformation and photophysical properties.

Bisimidazoacridones (BIA) are highly selective antineoplastic and antiviral agents. Ultraviolet-visible spectroscopy and steady-state and time-resolved fluorescence spectroscopy studies were carried out to probe the behavior of BIA in aqueous and nonaqueous (organic solvents, colloid micelles) solutions. Three ranges of fluorescence lifetimes were revealed: approximately 0.2-0.5 ns (presumably reflecting the chromophore-chromophore interaction), approximately 1-5 ns (interpreted as linker-perturbed chromophore decay) and approximately 6-12 ns (nonperturbed chromophore decay). The pre-exponential and steady-state contributions of these components to the decay signal as well as the data on steady-state fluorescence intensities, wavelength maxima and bandwidths showed that the BIA conformations in solution were sensitive to the environment and influenced strongly by their propensity to minimize hydrophobic interactions. In water, the molecules tend to adopt condensed conformations that bring the two imidazoacridone moieties into close proximity (resulting in intramolecular fluorescence energy transfer), while in nonaqueous systems the conformations become more relaxed. The transfer from a polar to more lipophilic environment of macromolecules is suggested to be the main driving force for binding of BIA to biomacromolecules, such as nucleic acids.

Inhibition of acute-, latent-, and chronic-phase human immunodeficiency virus type 1 (HIV-1) replication by a bistriazoloacridone analog that selectively inhibits HIV-1 transcription.

Nanomolar concentrations of temacrazine (1,4-bis[3-(6-oxo-6H-v-triazolo[4,5,1-de]acridin-5-yl)amino-propyl ]piperazine) were discovered to inhibit acute human immunodeficiency virus type 1 (HIV-1) infections and suppress the production of virus from chronically and latently infected cells containing integrated proviral DNA. This bistriazoloacridone derivative exerted its mechanism of antiviral action through selective inhibition of HIV-1 transcription during the postintegrative phase of virus replication. Mechanistic studies revealed that temacrazine blocked HIV-1 RNA formation without interference with the transcription of cellular genes or with events associated with the HIV-1 Tat and Rev regulatory proteins. Although temacrazine inhibited the in vitro 3' processing and strand transfer activities of HIV-1 integrase, with a 50% inhibitory concentration of approximately 50 nM, no evidence of an inhibitory effect on the intracellular integration of proviral DNA into the cellular genome during the early phase of infection could be detected. Furthermore, temacrazine did not interfere with virus attachment or fusion to host cells or the enzymatic activities of HIV-1 reverse transcriptase or protease, and the compound was not directly virucidal. Demonstration of in vivo anti-HIV-1 activity by temacrazine identifies bistriazoloacridones as a new class of pharmaceuticals that selectively blocks HIV-1 transcription.

Structure-activity relationship for antineoplastic imidazoacridinones: synthesis and antileukemic activity in vivo.

Synthesis of several new 5-amino-substituted derivatives of 5-amino-6H-imidazo[4,5,1-de]-acridin-6-one bearing in the benzene ring OH, OCH3, CH3, tert-butyl, or OCH2O groups is described. 8-OH-substituted compounds or double-substituted 7-OH-10-OCH3 compounds demonstrated potent in vivo activity against murine P388 leukemia. The highest activity was exhibited by 5-[[2-[[2-(diethylamino)ethyl]amino]ethyl]amino]-8-hydroxy-6H- imidazo[4,5,1-de]-acridin-6-one (4c).

Bisimidazoacridones and related compounds: new antineoplastic agents with high selectivity against colon tumors.

A new class of potent and highly selective antitumor agents has been synthesized. Bisimidazoacridones, where the tetracyclic ring systems are held together by either a N2-methyldiethylenetriamine or 3,3'-diamino-N-methyldipropylamine linker, and related asymmetrical compounds, where one of the imidazoacridone ring system was replaced by a triazoloacridone ring system, were found to be cytostatic and cytotoxic in vitro. Some of these compounds, such as 5,5'-[(methylimino)bis(3,1-propanediylimino)]bis[6H-imidazo[ 4,5,1-de]acridin-6-one] (4b) showed remarkably high activity and selectivity for colon cancer in the National Cancer Institute screen. This antitumor effect was also apparent in colony survival assays utilizing the colon cancer line, HCT-116, and in in vivo assays involving xenografts of tumor derived from HCT-116 in nude mice. The tested compounds exhibited relatively low acute toxicity and were well-tolerated by the treated animals. The bisimidazoacridones interact with nucleic acids in vitro but preliminary experimental and modeling data indicate that in spite of their structure, they may not be bis-intercalators. While the precise mode of action of these compounds is not yet understood, they appear to be excellent candidates for clinical development.

Mechanism of action of bisimidazoacridones, new drugs with potent, selective activity against colon cancer.

Antitumor bisimidazoacridones are bifunctional DNA binders which have recently been shown to selectively target human colon carcinoma cells in vitro and in vivo and appear to be excellent candidates for clinical development. We have studied the mechanism of action of one bisimidazoacridone, WMC26, which is 1,000-10,000 times more toxic to human colon carcinoma cells (HCT116) than to melanoma cells (SKMEL2) in vitro. Plasmid DNA exposed to WMC26 showed enhanced digestion by DNase I at A-T-rich sites, suggesting alterations in DNA conformation upon drug binding. These results led us to investigate whether WMC26 was selectively toxic due to a specific recognition of DNA bends by repair excinucleases, as has been demonstrated with the DNA bisintercalator, ditercalinium. Both prokaryotic and eukaryotic cells with intact repair capacity were shown to be selectively sensitive to WMC26, strongly indicating that excision repair plays a role in its toxicity. Confocal microscopy studies utilizing fluorescence of the WMC26 chromophore showed compound localization in the perinuclear cytoplasmic area, as had been previously noted for ditercalinium, indicating that cytoplasmic DNA could be the target. This irreversible accumulation of compound was gradually followed by vacuolization of the cytoplasm and cell death. Cell cycle analysis of both lines treated with WMC26 or with ditercalinium showed that, while the latter induced HCT116 growth arrest at G1-G0, WMC26 also blocked the cell cycle at G2-M; SKMEL2 cells did not undergo any changes in cell cycle as a result of either treatment. Our data show that WMC26 is 10-100 times more cytotoxic than ditercalinium in vitro. Like ditercalinium, WMC26 appears to exert its toxicity via cytoplasmic elements, through a mechanism involving excision repair processes. However, its highly selective cytotoxicity may stem from additional undefined targets in sensitive colon cancer cells.

Experimental antitumor activity and toxicity of the selected triazolo- and imidazoacridinones.

Toxicity and antitumor effects of four compounds from the groups of triazoloacridinones and imidazoacridinones were evaluated in transplantable tumor systems in mice, including P388 leukemia, B16 melanoma and 2 colon adenocarcinomas C26 and C38. Tested compounds had moderate antileukemic activity but were active against B16 melanoma and 3 of them were very efficacious against colon tumors, providing high percentages of "cures". Toxicity for healthy mice, as well as antitumor activity, were found to depend on a treatment protocol. The compounds were better tolerated and gave higher antitumor effects when given as fractionated treatment. They displayed also sex-dependent toxicity and activity.

Pyrimidoacridine derivatives as potential antitumor agents.

A series of some N-alkylaminoalkyl derivatives of pyrimido[5,6,1-d,e]acridine-1,3,7-trione (3) was synthesized as new potential antitumor drugs, starting from the suitable 9,10-dihydro-9-oxo-4-acridinecarboxamides and using phosgene as cyclizing agent. 1-(9,10-dihydro-9-oxo-4-acridinecarbonyl)-3-alkyl-2-imidazolido nes were also obtained as side products. The final products 3 and some carboxamides were tested "in vitro" against L 1210 leukemia and "in vivo" against P388 leukemia. Of the tested compounds, one is active "in vivo", another shows significant cytotoxic activity "in vitro", but is inactive or toxic "in vivo".

Chromophore-modified antineoplastic imidazoacridinones. Synthesis and activity against murine leukemias.

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.

8-Substituted 5-[(aminoalkyl)amino]-6H-v-triazolo[4,5,1-de]acridin-6-ones as potential antineoplastic agents. Synthesis and biological 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.

5-[(Aminoalkyl)amino]imidazo[4,5,1-de]acridin-6-ones as a novel class of antineoplastic agents. Synthesis and biological 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.