11‐Cl‐BBQ, a select modulator of AhR‐regulated transcription, suppresses lung cancer cell growth via activation of p53 and p27^Kip1

Abstract

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor and functions as a tumour suppressor in different cancer models. In the present study, we report detailed characterization of 11-chloro-7Hbenzimidazo[2,1-a]benzo[de]iso-quinolin-7-one (11-Cl-BBQ) as a select modulator of AhR-regulated transcription (SMAhRT) with anti-cancer actions. Treatment of lung cancer cells with 11-Cl-BBQ induced potent and sustained AhR-dependent anti-proliferative effects by promoting G1 phase cell cycle arrest. Investigation of 11-Cl-BBQ-induced transcription in H460 cells with or without the AhR expression by RNA-sequencing revealed activation of p53 signalling. In addition, 11-Cl-BBQ suppressed multiple pathways involved in DNA replication and increased expression of cyclindependent kinase inhibitors, including p27 Kip1 , in an AhR-dependent manner. CRISPR/Cas9 knockout of individual genes revealed the requirement for both p53 and p27 Kip1 for the AhR-mediated anti-proliferative effects. Our results identify 11-Cl-BBQ as a potential lung cancer therapeutic, highlight the feasibility of targeting AhR and provide important mechanistic insights into AhR-mediated-anticancer actions.

Tumor-Suppressive Functions of the Aryl Hydrocarbon Receptor (AhR) and AhR as a Therapeutic Target in Cancer

“…Examples include Wnt/β-catenin signaling [ 83 , 84 ], TGFβ and SHH signaling [ 85 , 86 ], pluripotency factors [ 87 , 88 , 89 ], epigenetic regulators such as BET proteins [ 90 ], and estrogen receptor α (ERα) [ 91 , 92 ]. AhR can also regulate the progression of the cell cycle through interactions with checkpoint regulators such as Rb [ 72 , 93 ] and activating the expression of cell cycle inhibitors such as cyclin G2 [ 77 ] and the cyclin-dependent kinase inhibitors p27 Kip1 [ 69 , 78 , 94 ] and p21 Cip1 [ 79 ].…”

“…We identified benzimidazoisoquinolines (BBQs) as a class of high-affinity, rapidly metabolized AhR ligands that do not exhibit in vivo toxicity and drive AhR-dependent immunomodulation [ 8 , 110 , 111 , 112 ]. In NSCLC, we recently discovered 11-chloro-7H-benzimidazo[2,1-a]benzo[de]iso-quinolin-7-one (11-Cl-BBQ) as a ligand that exhibited AhR-dependent antiproliferative effects [ 94 ]. The activation of AhR by 11-Cl-BBQ induced the expression of the cell cycle inhibitors p21 Cip1 , p27 Kip1 , and CABLES1 (a newly identified cyclin-dependent kinase inhibitor) [ 113 , 114 ] and activated p53 signaling [ 94 ].…”

“…In NSCLC, we recently discovered 11-chloro-7H-benzimidazo[2,1-a]benzo[de]iso-quinolin-7-one (11-Cl-BBQ) as a ligand that exhibited AhR-dependent antiproliferative effects [ 94 ]. The activation of AhR by 11-Cl-BBQ induced the expression of the cell cycle inhibitors p21 Cip1 , p27 Kip1 , and CABLES1 (a newly identified cyclin-dependent kinase inhibitor) [ 113 , 114 ] and activated p53 signaling [ 94 ]. Importantly AhR, p27 Kip1 , and p53 were found to be required for the G1 phase cell cycle arrest downstream of 11-Cl-BBQ [ 94 ].…”

“…The activation of AhR by 11-Cl-BBQ induced the expression of the cell cycle inhibitors p21 Cip1 , p27 Kip1 , and CABLES1 (a newly identified cyclin-dependent kinase inhibitor) [ 113 , 114 ] and activated p53 signaling [ 94 ]. Importantly AhR, p27 Kip1 , and p53 were found to be required for the G1 phase cell cycle arrest downstream of 11-Cl-BBQ [ 94 ].…”

“…This phenomenon is supported by a recent study indicating that AhR is a key negative regulator of proliferation and tumorigenesis in p53 knockout cancer cells, which was identified by an unbiased genome-wide knockdown approach [ 158 ]. Both AhR and p53 can transcriptionally regulate the tumor suppressor p21 Cip1 [ 28 , 79 , 94 , 159 ], pro-apoptotic factors such as Bcl-2 associated X-protein (Bax) [ 160 , 161 ], and insulin-like growth factor binding protein (IGFBP3) [ 162 ]. It is possible that AhR and p53 cooperate to co-regulate common tumor suppressor gene programs downstream of cellular stress events.…”