Abstract
Morphine has been suggested to affect cancer cell dynamics and decrease survival rates in lung cancer patients at specific doses, but the precise mechanisms poorly understood. In this study, we aimed to investigate the molecular mechanisms by which morphine modulates the malignant characteristics of non-small cell lung cancer. Cell proliferation was assessed via the Cell Counting Kit-8 assay, and cell migration and invasion were examined via wound healing and Transwell assays. We employed immunofluorescence staining to evaluate E-cadherin expression in A549 and Lewis lung cancer (LLC) cell lines and immunohistochemistry to evaluate E-cadherin expression in nude mice tumours. Additionally, the in vivo effects of morphine on lung cancer progression were explored in a xenograft tumour experiments, in which naloxone was used as a morphine antagonist. Western blot analysis was performed to detect E-cadherin, phosphorylated mTOR (p-mTOR), mTOR, phosphorylated AKT (p-AKT), AKT, phosphorylated PI3K (p-PI3K), and PI3K protein levels in A549 and LLC cells as well as in tumour samples. Morphine (10 µM) significantly increased the proliferation of A549 and LLC cells in vitro (p < 0.05). It also enhanced the migratory and invasive capacities of these cell lines (p < 0.01). Mechanistically, morphine treatment (10 µM) led to a reduction in the expression of E-cadherin, and an increase in the phosphorylation of PI3K, AKT, and mTOR in A549 and LLC cells (p < 0.01). Morphine treatment (1.5 mg/kg) also reduced E-cadherin expression in xenograft tumours and promoted tumour growth in vivo (p < 0.05). This effect was reversed by naloxone (0.1 mg/kg). The results demonstrated that morphine stimulates the malignant proliferation of A549 and LLC cell lines and promotes xenograft tumour growth. Perhaps by specifically targeting MOR, morphine triggers a signalling cascade that activates the PI3K/AKT/mTOR pathway while inhibiting the EMT marker E-cadherin, which may consequently promote the progression of lung cancer.