Antitumor Benzothiazoles. 8. Synthesis, Metabolic Formation, and Biological Properties of the C- and N-Oxidation Products of Antitumor 2-(4-Aminophenyl)benzothiazoles

Abstract

2-(4-Aminophenyl)benzothiazoles 1 and their N-acetylated forms have been converted to C- and N-hydroxylated derivatives to investigate the role of metabolic oxidation in the mode of action of this series of compounds. 2-(4-Amino-3-methylphenyl)benzothiazole (1a, DF 203, NSC 674495) is a novel and potent antitumor agent with selective growth inhibitory properties against human cancer cell lines. Very low IC(50) values (<0.1 microM) were encountered in the most sensitive breast cancer cell lines, MCF-7 and T-47D, whereas renal cell line TK-10 was weakly inhibited by 1a. Cell lines from the same tissue origin, MDA-MB-435 (breast), CAKI-1 (renal), and A498 (renal), were insensitive to 1a. Accumulation and metabolism of 1a were observed in sensitive cell lines only, with the highest rate of metabolism occurring in the most sensitive MCF-7 and T-47D cells. Thus, differential uptake and metabolism of 1a by cancer cell lines may underlie its selective profile of anticancer activity. A major metabolite in these sensitive cell lines has been identified as 2-(4-amino-3-methylphenyl)-6-hydroxybenzothiazole (6c). Hydroxylation of 1a was not detected in the homogenate of previously untreated MCF-7, T-47D, and TK-10 cells but was readily observed in homogenates of sensitive cells that were pretreated with 1a. Accumulation and covalent binding of [(14)C]1a derived radioactivity was observed in the sensitive MCF-7 cell line but not in the insensitive MDA-MB-435 cell line. The mechanism of growth inhibition by 1a, which is unknown, may be dependent on the differential metabolism of the drug to an activated form by sensitive cell lines only and its covalent binding to an intracellular protein. However, the 6-hydroxy derivative 6c is not the 'active' metabolite since, like all other C- and N-hydroxylated benzothiazoles examined in this study, it is devoid of antitumor properties in vitro.

DNA damage and cell cycle arrest induced by 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203, NSC 703786) is attenuated in aryl hydrocarbon receptor deficient MCF-7 cells

“…Previous observations have shown that cytotoxicity of benzothiazoles is mediated via activation of the AhR signalling pathway (Kashiyama et al, 1999;Chua et al, 2000;Loaiza-Pérez et al, 2002). In addition, cytotoxicity across a large panel of human tumour cell lines correlates with CYP1A1 inducibility .…”

“…2-(4-Amino-3-methylphenyl)benzothiazoles are novel compounds with potent and unique antitumour properties (Shi et al, 1996;Bradshaw et al, 1998a, b;Kashiyama et al, 1999). It was demonstrated that selective metabolism in vitro of the parent agent DF 203 (NSC 674495) correlated very highly with its antiproliferative activity, with uptake and biotransformation observed only in those cell lines that are sensitive to the compound, such as MCF-7 and T47D breast carcinoma cells (Kashiyama et al, 1999).…”

“…It was demonstrated that selective metabolism in vitro of the parent agent DF 203 (NSC 674495) correlated very highly with its antiproliferative activity, with uptake and biotransformation observed only in those cell lines that are sensitive to the compound, such as MCF-7 and T47D breast carcinoma cells (Kashiyama et al, 1999). CYP1A1, whose expression and activity are induced only in sensitive cells, appears to be responsible for the metabolic hydroxylation of DF 203 in position 6, which produces an inactive and antagonistic molecule .…”

Benzothiazole derivatives substituted in position 2 as biologically active substances with plant growth regulation activity

“…Benzothiazole derivatives represent an extensive group of heterocyclic compounds, several of which have already found application in the medical sphere as medicines (Kashiyama et al 1999) as well as in agriculture (Pulkrábek et al 1999, Henselová et al 2001). 3-R-substituted benzothiazole derivatives induced dedifferentiation and morphogenesis of plants in vitro (Sekerka et al 1989), influenced growth in Triticum aestivum (Sutoris et al 1993) and stimulated plant regeneration and peroxidase activity in Brassica oleraceae (Havel et al 1994).…”

Mechanisms of acquired resistance to 2-(4-aminophenyl)benzothiazole (CJM 126, NSC 34445)

“…We have shown that cells lines inherently sensitive to this class of agent rapidly sequester and metabolize 2-(4-aminophenyl)benzothiazoles, whereas no net uptake was detected by intrinsically resistant cell lines Kashiyama et al 1999). Compared with MCF-7 wt and MCF-7 10 µM 126 , MCF-7 10 nM 126 cells, selected in the presence of the more cytotoxic concentration of 10 nM CJM 126, demonstrated dramatically impaired depletion of CJM 126 from media ( Figure 3A) with predominantly cytoplasmic intracellular drug localization (Figure 4).…”