O-P04 Sonodynamic Therapy Complements PD-L1 Immune Checkpoint Inhibition in a Murine Model of Pancreatic Cancer

Background The emergence of immune checkpoint inhibitors (ICI’s) in the past decade has proven transformative in the area of immuno-oncology. The PD-1 / PD-L1 axis has been particularly well studied and monoclonal antibodies developed to block either the receptor (anti PD-1) or its associated ligand (anti PD-L1) can generate potent anti-tumour immunity in certain tumour models. However, many “immune cold” tumours remain unresponsive to ICI’s. Sonodynamic therapy (SDT) is a targeted anti-cancer treatment that uses ultrasound to activate a sensitiser with the resulting generation of reactive oxygen species (ROS) causing direct cell death. SDT has also been shown to stimulate the adaptive immune system in a pre-clinical cancer model. We investigate the ability of combining ICI and microbubble mediated SDT at controlling tumour growth in a bilateral pancreatic cancer model. Methods Preparation of O2MB-RB are shown below (scheme 1). Cytotoxicity of SDT and immunotherapy in-vivo are illustrated below (Figure 1). Figure 1 highlights that T110299 cells were subcutaneously implanted in the right and left dorsum of C57 mice. Group 1 received an IP injection of anti-mouse PD-L1 antibody (10mg/kg). After 2 hours, mice in this group received an IV injection of O2MB-RB suspension while receiving ultrasound applied to the right-hand-side (target) tumour. Group 2 received the same as Group 1 but no anti PD-L1 antibody; Group 3 received anti-PD-L1 antibody alone and Group 4 remained untreated. Flow cytometry analysis were carried out to investigate tumour infiltrating CD4+ and CD8+ T-lymphocytes. Results The results demonstrated a significant 287% decrease in tumour volume when compared to untreated animals 11 days following the initial treatment with SDT, which reduced further to 369% when SDT was combined with anti-PD-L1 ICI treatment. Analysis of residual tumour tissues remaining after treatment revealed increased levels of infiltrating CD4+ and CD8+ T-lymphocytes (respectively 4.65 and 3.16-fold more) in the off-target tumours of animals where the target tumour was treated with SDT and anti-PD-L1, when compared to untreated tumours. These results suggest that SDT treatment elicits an adaptive immune response that is potentiated by the anti-PD-L1 ICI in this particular model of pancreatic cancer. Conclusions In conclusion, microbubble mediated SDT treatment of a target tumour in a bilateral tumour model of pancreatic cancer, enables growth control at both the target and off-target tumours which is further enhanced when combined with anti-PD-L1 ICI treatment. Combining SDT with anti-PD-L1 ICI treatment, which is also well tolerated, could provide an attractive treatment option for pancreatic cancer, particularly for patients with advanced disease who may not be physically capable of undertaking a toxic chemotherapy regimen.