Antitumor benzothiazoles. 14. Synthesis and in vitro biological properties of fluorinated 2-(4-aminophenyl)benzothiazoles

Synthetic routes to a series of mono- and difluorinated 2-(4-amino-3-substituted-phenyl)benzothiazoles have been devised. Whereas mixtures of regioisomeric 5- and 7-fluoro-benzothiazoles were formed from the established Jacobsen cyclization of precursor 3-fluoro-thiobenzanilides, two modifications to this general process have allowed the synthesis of pure samples of these target compounds. Fluorinated 2-(4-aminophenyl)benzothiazoles were potently cytotoxic (GI(50) < 1 nM) in vitro in sensitive human breast MCF-7 (ER+) and MDA 468 (ER-) cell lines but inactive (GI(50) > 10 microM) against PC 3 prostate, nonmalignant HBL 100 breast, and HCT 116 colon cells. The biphasic dose-response relationship characteristically shown by the benzothiazole series against sensitive cell lines was exhibited by the 4- and 6-fluoro-benzothiazoles (10b,d) but not by the 5- and 7-fluoro-benzothiazoles (10h,i). The most potent broad spectrum agent in the NCI cell panel was 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (10h) which, unlike the 6-fluoro isomer (10d), produces no exportable metabolites in the presence of sensitive MCF-7 cells. Induction of cytochrome P450 CYP1A1, a crucial event in determining the antitumor specificity of this series of benzothiazoles, was not compromised. 10h is currently the focus of pharmaceutical and preclinical development.

Antitumour benzothiazoles. Part 15: The synthesis and physico-chemical properties of 2-(4-aminophenyl)benzothiazole sulfamate salt derivatives

A series of sulfamate salt derivatives of the potent and selective 2-(4-aminophenyl)benzothiazole antitumour agents has been prepared and their evaluation as potential prodrugs for parenteral administration carried out. The salts were sparingly soluble under aqueous conditions (pH 4-9), and degradation to the active free amine was shown to occur under strongly acidic conditions. The salts were found to be markedly less active than their parent amines against sensitive human tumour cell lines in vitro.

Role of Cyp1A1 in modulation of antitumor properties of the novel agent 2-(4-amino-3-methylphenyl)benzothiazole (DF 203, NSC 674495) in human breast cancer cells

2-(4-Amino-3-methylphenyl)benzothiazole (DF 203, NSC 674495) is a candidate antitumor agent with potent and selective activity against human-derived tumor cell lines in vitro and in vivo. Only sensitive cell lines (e.g., MCF-7) were able to accumulate and metabolize DF 203, forming the main inactive metabolite, 2-(4-amino-3-methylphenyl)-6-hydroxybenzothiazole (6-OH 203). Selective metabolism may therefore underlie its antitumor profile. DF 203 6-hydroxylase activity by MCF-7 cells was not constitutive but induced only after pretreatment of cells with DF 203, 3-methylcholanthrene, or beta-naphthoflavone. 6-Hydroxylation was strongly inhibited by either goat antirat cytochrome P450 1A1 (CYP1A1) serum or alpha-naphthoflavone. Both alpha-naphthoflavone and 6-OH 203 abrogated DF 203-induced growth inhibition. Microsomes from genetically engineered human B-lymphoblastoid cells expressing CYP1A1, CYP1B1, or CYP2D6 metabolized DF 203 to 6-OH 203. Immunoblot analysis detected significantly enhanced CYP1A1 protein in a panel of sensitive breast cancer cell lines after exposure to DF 203. Neither constitutive expression nor induction of CYP1A1 protein was detected in nonresponsive breast (HBL 100, MDA-MB-435, and MCF-7/ADR) and prostate (PC 3 and DU 145) cancer cell lines. The expression of CYP1B1 was also modulated by DF 203 in the same sensitive cell lines. However, of the two isoforms, only CYP1A1 activity was irreversibly inhibited by DF 203 and significantly inhibited by 6-OH 203. In sensitive cell lines only, [14C]DF 203-derived radioactivity bound covalently to a Mr 50,000, protein which was immunoprecipitated by CYP1A1 antiserum. The covalent binding of [14C]DF 203 to recombinant CYP1A1 enzyme was NADPH-dependent and reduced by 6-OH 203 and glutathione. CYP1A1 appears essential for the metabolism of DF 203 and may have a pivotal, yet undefined, role in its antitumor activity.

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

2-(4-aminophenyl)benzothiazole (CJM 126) elicits potent growth inhibition in human-derived breast carcinoma cell lines, including oestrogen receptor-positive (ER+) MCF-7wt cells. Analogues substituted in the 3' position with I (DF 129), CH3 (DF 203), or Cl (DF 229) possess an extended profile of antitumour activity with remarkable selective activity in cell lines derived from solid tumours associated with poor prognosis, e.g. breast, ovarian, renal and colon. Growth inhibition occurs via unknown, possibly novel mechanism(s) of action. Two cell lines have been derived from sensitive MCF-7wt breast cancer cells (IC50 value < 0.001 microM) following long-term exposure to 10 nM or 10 microM CJM 126, MCF-7(10 nM 126) and MCF-7(10 microM 126) respectively, which demonstrate acquired resistance to this agent (IC50 > 30 microM) and cross-resistance to DF 129, DF 203 and DF 229. Sensitivity to tamoxifen, benzo[a]pyrene (BP), mitomyin C, doxorubicin and actinomycin D is retained. Resistance may, in part, be conferred by the constitutively increased expression of bcl-2 and p53 proteins detected in MCF-7(10 nM 126) and MCF-7(10 microM 126 lysates. Significantly decreased depletion of CJM 126 (30 microM) from nutrient medium of MCF-7(10 microM 126) cells was observed with predominantly cytoplasmic drug localization and negligible DNA strand breaks. N-acetyl transferase (NAT)1 and NAT2 proteins were expressed by all three MCF-7 sub-lines, but significantly higher expression of NAT2 was accompanied by enhanced acetylation efficacy in MCF-7(10 nM 126) cells. In contrast, CJM 126 (30 microM) was rapidly depleted from nutrient medium of MCF-7(10 microM 126) culture and accessed nuclei of these cells exerting damage to DNA. The major biotransformation product of CJM 126 in MCF-7(10 microM 126) cells was 2-(4-aminophenyl)-6-hydroxybenzothiazole (6-OH 126). This metabolite possessed no antitumour activity. Accordingly, in this sub-line, low constitutive expression and activity of cytochrome P450 (CYP) 1A1 was detected.

Antitumor benzothiazoles. 8. Synthesis, metabolic formation, and biological properties of the C- and N-oxidation products of antitumor 2-(4-aminophenyl)benzothiazoles

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.

Antitumor benzothiazoles. 7. Synthesis of 2-(4-acylaminophenyl)benzothiazoles and investigations into the role of acetylation in the antitumor activities of the parent amines

2-(4-Aminophenyl)benzothiazoles display potent and selective antitumor activity against inter alia breast, ovarian, colon, and renal cell lines, but their mechanism of action, though yet to be defined, may be novel. Metabolism is suspected to play a central role in the mode of action of these benzothiazoles since drug uptake and biotransformation were observed in sensitive cell lines (e.g., breast MCF-7 and MDA 468 cells) in vitro, whereas insensitive cell lines (e.g., prostate PC 3 cells) showed negligible uptake and biotransformation. N-Acyl derivatives of the arylamines have been synthesized, and in vitro studies confirm N-acetylation and oxidation as the main metabolic transformations of 2-(4-aminophenyl)benzothiazoles, with the predominant process being dictated by the nature of the 3'-substituent. The prototype amine 3 underwent mainly N-acetylation in vitro, while 3'-substituted analogues 4 and 5 were primarily oxidized. N-Acetylation of 4 to 11 exerts a drastic dyschemotherapeutic effect in vitro, but acetylation of the halogeno congeners 5-7 gave acetylamines 12-14 which substantially retain selective antitumor activity. In vivo pharmacokinetic studies in rats confirmed rapid and exclusive N-acetylation of the 3'-methyl analogue 4, but less acetylation with the 3'-chloro analogue 5. Distinct expression patterns of N-acetyltransferase NAT1 and NAT2 have been demonstrated in our panel of cell lines.

Properties and purification of a glucose-inducible human fatty acid synthase mRNA-binding protein

Glucose stabilizes the mRNA for human fatty acid synthase (FAS), an enzyme relevant to diverse human disorders, including hyperlipidemia, obesity, and malignancy. To determine the underlying mechanisms, RNA gel mobility shift assays were used to demonstrate that human Hep G2 cells contain a cytoplasmic factor that binds specifically to the 3'-terminus of the human FAS mRNA. D-Glucose increased RNA-binding activity by 2.02-fold (P = 0.0033), with activity peaking 3 h after glucose feeding. Boiling or treatment of extracts with proteinase K abolished binding. Ultraviolet cross-linking of the FAS mRNA-binding factor followed by SDS-PAGE resolved a proteinase K-sensitive band with an apparent molecular mass of 178 +/- 7 kDa. The protein was purified to homogeneity using nondenaturing polyacrylamide gels as an affinity matrix. Acid phosphatase treatment of the protein prevented binding to the FAS mRNA, but binding activity was unaffected by modification of sulfhydryl groups and was not Mg2+ or Ca2+ dependent. Deletion and RNase T1 mapping localized the binding site of the protein to 37 nucleotides characterized by the repetitive motif ACCCC and found within the first 65 bases of the 3'-UTR. Hybridization of the FAS transcript with an oligonucleotide antisense to this sequence abolished binding. These findings indicate that a 178-kDa glucose-inducible phosphoprotein binds to an (ACCCC)n-containing sequence in the 3'-UTR of the FAS mRNA within the same time frame that glucose stabilizes the FAS message. This protein may participate in the posttranscriptional control of FAS gene expression.