The off‑target effect of loratadine triggers autophagy‑mediated apoptosis in lung adenocarcinoma cells by deactivating JNK, p38, and STAT3 signaling through both PP2A‑dependent and independent pathways

Lung adenocarcinoma (LUAD) is a typical inflammation‑associated cancer, and anti‑inflammatory medications can be valuable in cancer therapy. Loratadine, a histamine receptor H1 (HRH1) antagonist, shows both anti‑inflammatory and anticancer properties. The present study aimed to evaluate impacts of loratadine on LUAD cells as well as in a LUAD xenograft mouse model, and explore underlying mechanisms. Mechanistic investigations were conducted through using western blotting, flow cytometry, immunohistochemistry, acridine orange staining, TUNEL assays, and <i>in silico</i> analyses of loratadine‑modulated genes in LUAD specimens. It was observed that loratadine inhibited LUAD cell proliferation and colony formation by inducing autophagy‑mediated apoptotic cell death independently of HRH1. In a LUAD xenograft model, loratadine decreased tumor proliferation and angiogenesis while enhancing autophagy and apoptosis. Mechanistically, loratadine induced protein phosphatase 2A (PP2A) activation to deactivate c‑Jun N‑terminal kinase (JNK)1/2 and p38 in H23 and PC9 LUAD cells. Additionally, loratadine inhibited signal transducer and activator of transcription 3 (STAT3) activation via a PP2A‑independent pathway. Furthermore, the combination of loratadine with inhibitors for JNK, p38 and STAT3 all enhanced proliferation inhibition of loratadine alone in both cell lines. In the clinic, patients with LUAD expressing high PP2A had favorable prognoses. The present study suggests that loratadine can be used as a PP2A activator for LUAD treatment, and the combination of repurposing loratadine with inhibitors of STAT3, JNK and p38 would be an effectively strategy for inhibiting LUAD growth.