Novel 2-(4-aminophenyl)benzothiazoles (e.g., compounds 1 and 2) possess highly selective, potent antitumor properties in vitro and in vivo. Elucidation of the mechanism of action of this structurally simple class of compounds has occurred in parallel with selection of a candidate clinical agent. Antitumor
benzothiazoles induce and are biotransformed by
cytochrome P 450 1A1 to putative active, as well as inactive metabolites. Metabolic inactivation of the molecule has been thwarted by isosteric replacement of
hydrogen with
fluorine atoms at positions around the
benzothiazole nucleus.
Amino acid conjugation to the exocyclic primary
amine function of 2-(4-aminophenyl)benzothiazoles has been used to overcome limitations posed by
drug lipophilicity. Water soluble, chemically stable
prodrugs rapidly and quantitatively revert to their parent
amine in mice, rats, and dogs in vivo. Plasma concentrations of
2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (2) regenerated from the lysylamide
prodrug (2b), sufficient to elicit cytocidal activity against ZR-75-1 and T47D
human mammary carcinoma cell lines persist > 6 h. The growth of breast (MCF-7) and ovarian (IGROV-1) xenograft
tumors is significantly retarded by 2b. Manageable toxic side effects are reported from preclinically efficacious doses of 2b.
Cytochrome P 450 1A1
protein expression, selectively induced in sensitive
carcinoma cells, was detected in MCF-7 and IGROV-1
tumors 24 h
after treatment of mice with 2b (20 mg/kg). The lysyl
amide prodrug of
2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole is potentially suitable for clinical evaluation.