RADIOIMMUNOTHERAPY COMBATING METHICILLIN-RESISTANT <i>STAPHYLOCOCCUS AUREUS</i> AND ITS BIOFILM IN VITRO

Aim Prosthetic joint infections (PJI) remain a great challenge in orthopedic surgery with a high mortality rate. It is particularly complicated by biofilms and infections caused by Methicillin-resistant Staphylococcus aureus (MRSA). It concurrently shields bacteria from host immune responses and confers resistance to antibiotics. This study aims to investigate the efficacy of radioimmunotherapy as an innovative therapeutic modality to address the challenges posed by MRSA and its biofilm. Method We induced specific monoclonal antibodies 4497-IgG1 as carriers, which target wall teichoic acids (WTA) existing on MRSA and its biofilm. Radionuclides actiniumr-225 ( 225 Ac, α-emitter) and lutetium-177 ( 177 Lu, β-emitter) were conjugated with mAbs using DOTA as chelator. Quality control was assessed using thin layer chromatography and immunoreactivity assays. 225 Ac- and 177 Lu-labelled 4497-IgG1 were employed to evaluate the susceptibility of MRSA and its biofilm to the radioimmunotherapy in vitro. Planktonic MRSA and biofilms, at concentrations of 10 8 and 10 7 CFU/mL, were incubated at 37°C for 60 minutes in PBS containing either 225 Ac-mAb (0 - 14.8 kBq) or 177 Lu-mAb (0 - 14.8 MBq). Radiolabelled dunituximab and free radionuclides serve as isotype-matched negative control. The bacterial viability and metabolic activity were subsequently quantified using CFU and XTT assays. Results The radiochemical purity of the 225 Ac-mAbs and 177 Lu-mAbs complex were determined to be 95.4% and 96.16%. Immunoreactivity fractions of them were measured at 81.8% and 80.8%. 225 Ac-mAbs and 177 Lu-mAbs exhibited significant and dose-dependent antimicrobial effects on both planktonic MRSA and biofilm. 225 Ac- and 177 Lu-4497IgG1 at doses of 7.4 kBq and 7.4 MBq resulted in more than 4-log reduction in bacterial counts. In biofilms, 2-log reduction at the highest 225 Ac radioactivity of 14,8kBq. The 177 Lu complex showed a strong dose-dependent effect, with a reduction of up to 4-log. The XTT assay confirmed these findings, showing a decrease in metabolic activity corresponding to a decrease in bacterial counts, and a slight increase in metabolic activity at the lower dose. Conclusions Our study demonstrates the efficacy of 225 Ac and 177 Lu-labelled 4497-IgG1 antibodies in mediating dose-dependent bactericidal effects against planktonic MRSA and biofilms in vitro. This indicates that radioimmunotherapy could be a potential targeted therapeutic strategy against MRSA and its biofilm. Further research in preclinical and clinical settings is warranted to validate and refine these findings on biofilm-associated implant infections.