Evaluating radiation-induced bystander and abscopal effects conferred by novel gold nanoparticle formulations

Although clinically rare, abscopal responses have been enhanced by combining RT with immune checkpoint inhibitors.<br><br>Two novel AuNP platforms were developed and functionalised to improve stability and cellular uptake via surface conjugation with polyethylene glycol (PEG) and antagonistic chemokine receptor-targeting pepducins: AuX2R, targeting CXCR1/2 receptors, and AuXR4, targeting CXCR4. This thesis investigated the effects of AuX2R and AuXR4 on direct and indirect radiation responses in prostate (DU145) and head and neck (FaDu) cancer models.

Radiation-induced bystander signaling was assessed using irradiated cell conditioned media (ICCM) transferred from irradiated donor cells to unirradiated recipient cells. Both DU145 and FaDu cells could produce and respond to inhibitory bystander signals. However, these effects were observed only with ICCM collected 1 h post-irradiation, with the effect lost by 24 h post-IR.

The impact of pepducins alone was first examined and showed no effect on the direct radiation response. Notably, treatment with the CXCR1/2 pepducin prevented inhibitory RIBEs, whereas the CXCR4 pepducin had minimal direct effect on bystander signaling. <br><br>Both AuX2R and AuXR4 enhanced radiosensitivity in DU145 and FaDu cells and amplified inhibitory bystander effects. In addition, bystander signals generated from AuX2R or AuXR4 treated cells reduced stemness-associated features in FaDu cells, pointing to an impact on tumour cell plasticity.

The immunomodulatory potential of these nanoparticles was also explored. In vitro experiments indicated that both AuX2R and AuXR4 can influence immune responses. However, in vivo combination therapy with IR and an immune checkpoint inhibitor showed limited therapeutic benefit.

Surprisingly and in contrast to our existing data, in this tumour model AuX2R produced only a modest delay in primary tumour growth beyond IR alone and did not affect the growth of a secondary abscopal tumour. Despite this, flow cytometric analysis revealed evidence of immune activation within the primary tumour microenvironment, including increased cytotoxic T-cell populations.<br><br>Overall, AuX2R and AuXR4 effectively radiosensitised prostate and head-and-neck cancer cell models, triggering genotoxic stress in unirradiated bystander cells.

While preliminary findings indicate some capacity for immune modulation, systemic anti-tumour responses were not observed in vivo, highlighting the need for further optimisation and investigation.<br><br><i>Thesis is embargoed until 31 July 2031.</i><br>