PTTG1 knockdown enhances radiation-induced antitumour immunity in lung adenocarcinoma

Aim: Ionizing radiation (IR) can induce local and systemic antitumour immune responses to some degree and augment immunotherapeutic efficacy. IR may also increase residual tumour cell invasion and elicit immuno-suppression in the tumour microenvironment (TME). It remains poorly understand, whether IR leads to immune negative response or invasive capacity increases in lung adenocarcinoma (LAC). Materials and methods: RNA interference (RNAi) was used to silence pituitary tumour-transforming gene-1 (PTTG1) and SMAD3 expression in LAC cells. A coculture system of tumour cells and PBMCs was constructed. Cells were exposed to different doses (0, 4 and 8 Gy) of X-ray irradiation. Flow cytometric analysis and Transwell assays were applied. An orthotopic Lewis lung cancer (LLC) mouse tumour model was established. Biolumi-nescence imaging (BLI) was used. LLC tumours were exposed to a single 15 Gy dose of X-ray irradiation. Key findings: PTTG1 knockdown reinforced the inhibitory effect of IR on the invasive ability of A549 cells and enhanced the antitumour T cell immunity induced by IR via the transforming growth factor-beta 1 (TGF-beta 1)/SMAD3 pathway. Positive antitumour immune response and immunosuppression were simultaneously triggered by a single 15 Gy dose of local tumour irradiation. PTTG1 knockdown weakened invasive capacity and promoted the immune response balance induced by IR to tilt towards active immunity, which contributed to reduce metastasis and prolonged overall survival (OS) in orthotopic LLC tumour-bearing mouse. Significance: Targeted blockade of PTTG1 and the TGF-beta 1/SMAD3 pathway may ameliorate the immunosup-pressive TME and enhance the systemic antitumour immune response induced by a single high-dose IR treatment.