The antitumour activity of 2‐(4‐amino‐3‐methylphenyl)‐5‐fluorobenzothiazole in human gastric cancer models is mediated by AhR signalling

Stomach cancer is the fourth most common cancer worldwide. Identification of novel molecular therapeutic targets and development of novel treatments are critical. Against a panel of gastric carcinoma cell lines, the activity of 2‐(4‐amino‐3‐methylphenyl)‐5‐fluorobenzothiazole (5F 203) was investigated. Adopting RT‐PCR, Western blot and immunohistochemical techniques, we sought to determine molecular pharmacodynamic (PD) markers of sensitivity and investigate arylhydrocarbon (AhR) receptor‐mediated signal transduction activation by 5F 203. Potent (IC(50) ≤ 0.09 μmol/L), selective (>250‐fold) in vitro antitumour activity was observed in MKN‐45 and AGS carcinoma cells. Exposure of MKN‐45 cells to 5F 203 triggered cytosolic AhR translocation to nuclei, inducing CYP1A1 (>50‐fold) and CYP2W1 (~20‐fold) transcription and protein (CYP1A1 and CYP2W1) expression. G2/M arrest and γH2AX expression preceded apoptosis, evidenced by PARP cleavage. In vivo, significant (P < .01) 5F 203 efficacy was observed against MKN‐45 and AGS xenografts. In mice‐bearing 5F 203‐sensitive MKN‐45 and 5F 203‐insensitive BGC‐823 tumours in opposite flanks, CYP1A1, CYP2W1 and γH2AX protein in MKN‐45 tumours only following treatment of mice with 5F 203 (5 mg/kg) revealed PD biomarkers of sensitivity. 5F 203 evokes potent, selective antitumour activity in vitro and in vivo in human gastric cancer models. It triggers AhR signal transduction, CYP‐catalysed bioactivation to electrophilic species causing lethal DNA double‐strand breaks exclusively in sensitive cells. 5F 203 represents a novel therapeutic agent with a mechanism of action distinct from current clinical drugs, exploiting novel molecular targets pertinent to gastric tumourigenesis: AhR, CYP1A1 and CYP2W1. PD markers of 5F 203 sensitivity that could guide patient selection have been identified.