Ionizing radiation delivered by specific antibody is therapeutic against a fungal infection

Abstract

There is an urgent need for new antimicrobial therapies to combat drug resistance, new pathogens, and the relative inefficacy of current therapy in compromised hosts. Ionizing radiation can kill microorganisms quickly and efficiently, but this modality has not been exploited as a therapeutic antimicrobial strategy. We have developed methods to target ionizing radiation to a fungal cell by labeling a specific mAb with the therapeutic radioisotopes Rhenium-188 and Bismuth-213. Radiolabeled antibody killed cells of human pathogenic fungus Cryptococcus neoformans in vitro, thus converting an antibody with no inherent antifungal activity into a microbicidal molecule. Administration of radiolabeled antibody to mice with C. neoformans infection delivered 213 Bi and 188 Re to the sites of infection, reduced their organ fungal burden, and significantly prolonged their survival without apparent toxicity. This study establishes the principle that targeted radiation can be used for the therapy of an infectious disease, and suggests that it may have wide applicability as an antimicrobial strategy.

Comparative Evaluation of Capsular Polysaccharide-Specific IgM and IgG Antibodies and F(ab′)2 and Fab Fragments as Delivery Vehicles for Radioimmunotherapy of Fungal Infection

“…Isotype-matching control mAb MOPC21 (IgG1) and TEPC (IgM) were acquired from MP Biochemicals. F(ab ¶) 2 and Fab fragments of 18B7 mAb were obtained by digestion using immobilized ficin from a commercial kit [ImmunoPure IgG1 Fab and F(ab ¶) 2 preparation kit, Pierce]. Fab fragments were obtained by digestion of 18B7 for 3 h at 37jC on a ficin column in the presence of 20 mg/mL cysteine.…”

“…The molecular weight of the obtained fragments was analyzed by SDS-PAGE and fast protein liquid chromatography. The protein concentration was determined by the method of Lowry et al (12) Re ''directly '' as described (2). For radiolabeling of whole 18B7 and of its F(ab ¶) 2 and Fab fragments with 111 In, the antibodies were incubated overnight at room temperature in bicarbonate buffer at pH 8.5 with 1.5 molar excess of bifunctional chelating agent N-[2-amino-3-(p-isothiocyanatophenyl)propy1]-trans-cyclohexane-1,2-diamine-N,N ¶,N ¶ ¶,NØ,NØ-pentaacetic acid (CHXA").…”

“…Conclusions: Comparative evaluation of IgG and IgM and of F(ab ¶) 2 and Fab fragments as potential delivery vehicles for radioimmunotherapy of cryptococcal infection strongly suggests that affinity for the target antigen is an important prerequisite for successful targeting of infection in vivo and that in vitro affinity measurements may predict the in vivo efficacy of candidate monoclonal antibodies.…”

“…As a part of an on-going effort to translate the radioimmunotherapy of infection to the clinic, we have carried out a comparative evaluation of capsular polysaccharide-specific antibodies with IgG1 and IgM isotypes as well as of F(ab ¶) 2 and Fab fragments as potential delivery vehicles for radioimmunotherapy of the human pathogenic fungus CN.…”

Fungal Vaccines and Immunotherapeutics

“…The isotopes, 213 bismuth and 188 rhenium, which emit a and b particles, respectively, have been shown to significantly prolong survival of infected mice (Dadachova et al 2003). Additionally, 213 Bi-18B7 was shown to be superior to amphotericin in clearing disseminated C. neoformans (Bryan et al 2010).…”