Radioimmunotherapy is effective against high-inoculum Cryptococcus neoformans infection in mice and does not select for radiation-resistant cryptococcal cells.

We investigated the utility of radioimmunotherapy (RIT) in the treatment of experimental cryptococcal infection with high-inoculum and the possibility of RIT treatment selecting for fungal cells with radiation-resistant phenotypes. RIT reduced mortality in high-burden infections, and we found no evidence for the development of radiation-resistant cells.

Radiofungicidal effects of external gamma radiation and antibody-targeted beta and alpha radiation on Cryptococcus neoformans.

We evaluated the clonogenic survival, membrane permeability, metabolic activity (XTT reduction), and apoptosis (FLICA binding) of Cryptococcus neoformans cells subjected to gamma rays from an external source, and beta and alpha particles delivered to fungal cells by capsule-specific antibody. We found that gamma, beta, and alpha radiation affected cells through different pathways.

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.

PURPOSE: The applicability of radioimmunotherapy with organism-specific monoclonal antibodies to treatment of infectious disease in experimental models has been recently shown for fungal, bacterial, and viral infections. To identify the best delivery vehicle for radioimmunotherapy of human pathogenic fungus Cryptococcus neoformans (CN), we have done comparative evaluation of capsular polysaccharide-specific antibodies with IgG1 and IgM isotypes and F(ab')2 and Fab fragments. EXPERIMENTAL DESIGN: 18B7 IgG1 and 13F1 IgM and their isotype-matching controls were radiolabeled with 188Re, and their binding to 24067 and H99 CN strains was evaluated by doing Scatchard and kinetics analyses. The doses delivered during in vitro radioimmunotherapy were estimated using a cellular dosimetry algorithm. The biodistribution of 188Re-labeled 18B7 and 13F1 and of 111In-labeled 18B7 and its F(ab')2 and Fab fragments was done in A/JCr mice systemically infected with 24067 CN strain. RESULTS: 18B7 IgG1 showed superior to 13F1 IgM binding to 24067 CN (Ka=1.7x10(9) mol/L(-1) and 5.4x10(7) mol/L(-1), respectively). Substantial killing of 24067 and H99 CN cells was achieved with 1 microCi 188Re-18B7 (55 cGy dose), whereas no killing was observed for 1 microCi 188Re-13F1 (2 cGy dose). In vivo 188Re-18B7 localized specifically in the lungs of CN-infected mice, whereas uptake of 188Re-13F1 was nonspecific. 111In-F(ab')2 fragments showed higher uptake in the lungs and lower in the liver at the 48-h time point in comparison with intact 111In-18B7. 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.

Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi.

BACKGROUND: Melanin pigments are ubiquitous in nature. Melanized microorganisms are often the dominating species in certain extreme environments, such as soils contaminated with radionuclides, suggesting that the presence of melanin is beneficial in their life cycle. We hypothesized that ionizing radiation could change the electronic properties of melanin and might enhance the growth of melanized microorganisms. METHODOLOGY/PRINCIPAL FINDINGS: Ionizing irradiation changed the electron spin resonance (ESR) signal of melanin, consistent with changes in electronic structure. Irradiated melanin manifested a 4-fold increase in its capacity to reduce NADH relative to non-irradiated melanin. HPLC analysis of melanin from fungi grown on different substrates revealed chemical complexity, dependence of melanin composition on the growth substrate and possible influence of melanin composition on its interaction with ionizing radiation. XTT/MTT assays showed increased metabolic activity of melanized C. neoformans cells relative to non-melanized cells, and exposure to ionizing radiation enhanced the electron-transfer properties of melanin in melanized cells. Melanized Wangiella dermatitidis and Cryptococcus neoformans cells exposed to ionizing radiation approximately 500 times higher than background grew significantly faster as indicated by higher CFUs, more dry weight biomass and 3-fold greater incorporation of (14)C-acetate than non-irradiated melanized cells or irradiated albino mutants. In addition, radiation enhanced the growth of melanized Cladosporium sphaerospermum cells under limited nutrients conditions. CONCLUSIONS/SIGNIFICANCE: Exposure of melanin to ionizing radiation, and possibly other forms of electromagnetic radiation, changes its electronic properties. Melanized fungal cells manifested increased growth relative to non-melanized cells after exposure to ionizing radiation, raising intriguing questions about a potential role for melanin in energy capture and utilization.

Interaction of radiolabeled antibodies with fungal cells and components of the immune system in vitro and during radioimmunotherapy for experimental fungal infection.

BACKGROUND: The usefulness of radioimmunotherapy (RIT) for infectious diseases was recently demonstrated for several fungal and bacterial infections, but the mechanisms by which RIT is effective against microbes are uncertain. METHODS: We investigated the interaction between polysaccharide capsule-binding 18B7 monoclonal antibodies (MAbs) labeled with alpha-emitter 213Bi and Cryptococcus neoformans cells as well as between 213Bi-18B7 and components of immune system, both in vitro and in vivo. RESULTS: For 213Bi-18B7, the microbicidal effect was predominantly due to "direct-hit" killing, with some contribution from the "crossfire" effect. The efficacy of cell killing correlated with the binding capacity of the MAb to the capsule and was dependent on the MAb isotype. RIT also promoted the apoptosis-like death of fungal cells. Cooperation was observed in vitro between the antifungal activity of macrophages and RIT, suggesting the potential for synergistic action in vivo. RIT was associated with changes in concentration of the cytokines interleukin (IL)-2, IL-4, IL-10, tumor necrosis factor-alpha, and interferon-gamma, suggesting that the therapeutic effects of RIT may result from changes in the inflammatory response. CONCLUSIONS: The present results suggest that the antimicrobial efficacy of RIT involves killing through promotion of fungal cell apoptosis-like death, reduction in yeast capsule size, cooperation with macrophages, and modulation of the inflammatory response.