Propranolol Treatment Reduces A549-Derived Lung Cancer Spheroids via Intrinsic Apoptosis

Propranolol (PRO), a non-selective beta-adrenergic receptor inhibitor, has been recently discovered to possess anti-tumorigenic effects in cancer patients. Therefore, we aimed to investigate the in vitro effects of PRO in A549-derived lung cancer spheroids in terms of cell viability, spheroid formation, cell cycle regulation, cell differentiation, and apoptosis.

The effect of 24-hour PRO treatment on A549 cell viability was assessed using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. A sub-cytotoxic PRO concentration (125 μM) was employed to evaluate its impact on the clonogenicity of A549-derived cancer spheroids after seven days of incubation. Messenger Ribonucleic Acid (mRNA) levels of cell cycle regulators including cyclin-dependent kinase inhibitor 1A (p21) and G2 checkpoint kinase (WEE1), apoptotic markers such as caspases 3, 8, 9 (CASP3, CASP8, CASP9), and stem cell differentiation markers, namely POU class 5 homeobox 1 (octamer-binding transcription factor 4 (OCT4)), prominin 1 (CD133), and adenosine triphosphate (ATP) binding cassette subfamily G member 2 (ABCG2) were measured using reverse transcription quantitative polymerase chain reaction (RT-qPCR) after a 24-hour treatment of cancer spheroids with PRO.

PRO treatment reduced cell viability and inhibited the clonogenicity of cancer spheroids by activating intrinsic apoptotic markers CASP3 and CASP9, leading to cell cycle arrest via increased p21 expression. PRO did not significantly alter stem cell differentiation markers.

The proliferation and clonogenic activity of lung cancer spheroids can be effectively suppressed with PRO, primarily through inducing intrinsic apoptosis following p21-mediated cell cycle arrest. While short-term PRO exposure did not affect the gene expression levels of stem cell differentiation markers, the notable decrease in both cell viability and spheroid formation efficiency suggests the potential of PRO as a therapeutic drug in lung cancer treatment.