Radioimmunotherapy combating biofilm-associated infection in vitro

Abstract

Background: Addressing prosthetic joint infections poses a significant challenge within orthopedic surgery, marked by elevated morbidity and mortality rates. The presence of biofilms and infections attributed to Staphylococcus aureus (S. aureus) further complicates the scenario.

Objective: To investigate the potential of radioimmunotherapy as an innovative intervention to tackle biofilm-associated infections.

Methods: Our methodology involved employing specific monoclonal antibodies 4497-IgG1, designed for targeting wall teichoic acids found on S. aureus and its biofilm. These antibodies were linked with radionuclides actinium-225 (²²⁵Ac) and lutetium-177 (¹⁷⁷Lu) using DOTA as a chelator. Following this, we evaluated the susceptibility of S. aureus and its biofilm to radioimmunotherapy in vitro, assessing bacterial viability and metabolic activity via colony-forming unit enumeration and xylenol tetrazolium assays.

Results: Both [²²⁵Ac]4497-IgG1 and [¹⁷⁷Lu]4497-IgG1 exhibited a noteworthy dose-dependent reduction in S. aureus in planktonic cultures and biofilms over a 96-h exposure period, compared to non-specific antibody control groups. Specifically, doses of 7.4 kBq and 7.4 MBq of [²²⁵Ac]4497-IgG1 and [¹⁷⁷Lu]4497-IgG1 resulted in a four-log reduction in planktonic bacterial counts. Within biofilms, 14.8 kBq of [²²⁵Ac]4497-IgG1 and 14.8 Mbq [¹⁷⁷Lu]4497-IgG1 led to reductions of two and four logs, respectively.

Conclusion: Our findings underscore the effectiveness of [²²⁵Ac]4497-IgG1 and [¹⁷⁷Lu]4497-IgG1 antibodies in exerting dose-dependent bactericidal effects against planktonic S. aureus and biofilms in vitro. This suggests that radioimmunotherapy might serve as a promising targeted treatment approach for combating S. aureus and its biofilm.

Keywords: Staphylococcus aureus; actinium-225; antibodies; biofilm; infection; lutetium-177; radioimmunotherapy; wall teichoic acids.

FIGURE 1

Binding plot (A) of the ratio of specifically bound radiolabeled antibody to the total applied radioactivity as a function of cell concentration (X-axis). The cell concentration is expressed as cells (million/ml). Lindmo plot (B) showing total/bound activity as a function of inverse cell concentration expressed as 1/cells (ml/million).

FIGURE 2

Susceptibility of S. aureus and its biofilm to ²²⁵Ac and ¹⁷⁷Lu. (A) Susceptibility of planktonic S. aureus to ²²⁵Ac. (B) Susceptibility of planktonic S. aureus to ¹⁷⁷Lu. (C) Susceptibility of S. aureus in biofilm state to ²²⁵Ac. (D) Susceptibility of S. aureus in biofilm state to ¹⁷⁷Lu.

FIGURE 3

Antibacterial efficacy of RIT against S. aureus and its biofilm. (A) [²²⁵Ac]mAb treating planktonic S. aureus. (B) [¹⁷⁷Lu]mAb treating planktonic S. aureus. (C) [²²⁵Ac]mAb treating S. aureus biofilm. (D) [¹⁷⁷Lu]mAb treating S. aureus biofilm.

FIGURE 4

XTT assay results showing the metabolic activity of S. aureus and its biofilm after treatment with RIT. (A) Metabolic activity of planktonic S. aureus treated with [²²⁵Ac]mAb. (B) Metabolic activity of planktonic S. aureus treated with [¹⁷⁷Lu]mAb. (C) Metabolic activity of S. aureus biofilm treated with [²²⁵Ac]mAb. (D) Metabolic activity of S. aureus biofilm treated with [¹⁷⁷Lu]mAb.