Antibody-guided alpha radiation effectively damages fungal biofilms

Assessing the In Vitro Potential of Glatiramer Acetate (Copaxone®) as a Chemotherapeutic Candidate for the Treatment of Cryptococcus neoformans Infection

Cryptococcosis is a systemic mycosis affecting immunosuppressed individuals, caused by various Cryptococcus species. The current treatment utilizes a combination of antifungal drugs, but issues such as nephrotoxicity, restricted or limited availability in certain countries, and resistance limit their effectiveness. Repurposing approved drugs presents a viable strategy for developing new antifungal options. This study investigates the potential of glatiramer acetate (Copaxone®) as a chemotherapy candidate for Cryptococcus neoformans infection. Various techniques are employed to evaluate the effects of glatiramer acetate on the fungus, including microdilution, XTT analysis, electron and light microscopy, and physicochemical measurements. The results demonstrate that glatiramer acetate exhibits antifungal properties, with an IC50 of 0.470 mg/mL and a minimum inhibitory concentration (MIC) of 2.5 mg/mL. Furthermore, it promotes enhanced cell aggregation, facilitates biofilm formation, and increases the secretion of fungal polysaccharides. These findings indicate that glatiramer acetate not only shows an antifungal effect but also modulates the key virulence factor-the polysaccharide capsule. In summary, repurposing glatiramer acetate as a potential chemotherapy option offers new prospects for combating C. neoformans infection. It addresses the limitations associated with current antifungal therapies by providing an alternative treatment approach.

Radioimmunotherapy for the treatment of infectious diseases: a comprehensive update

INTRODUCTION

Corona Virus Disease of 2019 (COVID-19) pandemic has renewed interest in monoclonal antibodies for treating infectious diseases. During last two decades experimental data has been accumulated showing the potential of radioimmunotherapy (RIT) of infectious diseases. In addition, COVID-19 pandemic has created a novel landscape for opportunistic fungal infections in post-COVID-19 patients resulting from severe immune suppression.

AREAS COVERED

We analyze recent results on targeting "pan-antigens" shared by fungal pathogens in mouse models and in healthy dogs; on developing RIT of prosthetic joint infections (PJI); examine RIT as potential human immunodeficiency virus (HIV) cure strategy and analyze its mechanisms and safety. Literature review was performed using PubMed and Google Scholar and includes relevant articles from 2000 to 2022.

EXPERT OPINION

Some of the RIT of infection applications can, hopefully, be moved into the clinic earlier than others after preclinical development: (1) RIT of opportunistic fungal infections might contribute to saving lives as current antifungal drugs do not work in severely immunocompromised patients; (2) RIT of patients with PJI. Success of RIT in these patients will allow to expand the application of RIT to other similarly vulnerable patients' populations such as cancer patients with weakened immune system and organ transplant recipients.

Treating infections with ionizing radiation: a historical perspective and emerging techniques

Background

Widespread use and misuse of antibiotics have led to a dramatic increase in the emergence of antibiotic resistant bacteria, while the discovery and development of new antibiotics is declining. This has made certain implant-associated infections such as periprosthetic joint infections, where a biofilm is formed, very difficult to treat. Alternative treatment modalities are needed to treat these types of infections in the future. One candidate that has been used extensively in the past, is the use of ionizing radiation. This review aims to provide a historical overview and future perspective of radiation therapy in infectious diseases with a focus on orthopedic infections.

Methods

A systematic search strategy was designed to select studies that used radiation as treatment for bacterial or fungal infections. A total of 216 potentially relevant full-text publications were independently reviewed, of which 182 focused on external radiation and 34 on internal radiation. Due to the large number of studies, several topics were chosen. The main advantages, disadvantages, limitations, and implications of radiation treatment for infections were discussed.

Results

In the pre-antibiotic era, high mortality rates were seen in different infections such as pneumonia, gas gangrene and otitis media. In some cases, external radiation therapy decreased the mortality significantly but long-term follow-up of the patients was often not performed so long term radiation effects, as well as potential increased risk of malignancies could not be investigated. Internal radiation using alpha and beta emitting radionuclides show great promise in treating fungal and bacterial infections when combined with selective targeting through antibodies, thus minimizing possible collateral damage to healthy tissue.

Conclusion

The novel prospects of radiation treatment strategies against planktonic and biofilm-related microbial infections seem feasible and are worth investigating further. However, potential risks involving radiation treatment must be considered in each individual patient.

Recent Research Trends on Bismuth Compounds in Cancer Chemoand Radiotherapy

Background:

Application of coordination chemistry in nanotechnology is a rapidly developing research field in medicine. Bismuth complexes have been widely used in biomedicine with satisfactory therapeutic effects, mostly in Helicobacter pylori eradication, but also as potential antimicrobial and anti-leishmanial agents. Additionally, in recent years, application of bismuth-based compounds as potent anticancer drugs has been studied extensively.

Methods:

Search for data connected with recent trends on bismuth compounds in cancer chemo- and radiotherapy was carried out using web-based literature searching tools such as ScienceDirect, Springer, Royal Society of Chemistry, American Chemical Society and Wiley. Pertinent literature is covered up to 2016.

Results:

In this review, based on 213 papers, we highlighted a number of current problems connected with: (i) characterization of bismuth complexes with selected thiosemicarbazone, hydrazone, and dithiocarbamate classes of ligands as potential chemotherapeutics. Literature results derived from 50 papers show that almost all bismuth compounds inhibit growth and proliferation of breast, colon, ovarian, lung, and other tumours; (ii) pioneering research on application of bismuth-based nanoparticles and nanodots for radiosensitization. Results show great promise for improvement in therapeutic efficacy of ionizing radiation in advanced radiotherapy (described in 36 papers); and (iii) research challenges in using bismuth radionuclides in targeted radioimmunotherapy, connected with choice of adequate radionuclide, targeting vector, proper bifunctional ligand and problems with 213Bi recoil daughters toxicity (derived from 92 papers).

Conclusion:

This review presents recent research trends on bismuth compounds in cancer chemo- and radiotherapy, suggesting directions for future research.

Biofilm Formation by Cryptococcus neoformans

The fungus Cryptococcus neoformans possesses a polysaccharide capsule and can form biofilms on medical devices. The increasing use of ventriculoperitoneal shunts to manage intracranial hypertension associated with cryptococcal meningoencephalitis highlights the importance of investigating the biofilm-forming properties of this organism. Like other microbe-forming biofilms, C. neoformans biofilms are resistant to antimicrobial agents and host defense mechanisms, causing significant morbidity and mortality. This chapter discusses the recent advances in the understanding of cryptococcal biofilms, including the role of its polysaccharide capsule in adherence, gene expression, and quorum sensing in biofilm formation. We describe novel strategies for the prevention or eradication of cryptococcal colonization of medical prosthetic devices. Finally, we provide fresh thoughts on the diverse but interesting directions of research in this field that may result in new insights into C. neoformans biology.

Virulence of Cryptococcus sp. Biofilms In Vitro and In Vivo using Galleria mellonella as an Alternative Model

Cryptococcus neoformans and C. gattii are fungal pathogens that are most commonly found in infections of the central nervous system, which cause life-threatening meningoencephalitis and can grow as a biofilm. Biofilms are structures conferring protection and resistance of microorganism to the antifungal drugs. This study compared the virulence of planktonic and biofilm cells of C. neoformans and C. gattii in Galleria mellonella model, as well as, the quantification of gene transcripts LAC1, URE1, and CAP59 by real time PCR. All three of the genes showed significantly increased expressions in the biofilm conditions for two species of Cryptococcus, when compared to planktonic cells. C. neoformans and C. gattii cells in the biofilm forms were more virulent than the planktonic cells in G. mellonella. This suggests that the biofilm conditions may contribute to the virulence profile. Our results contribute to a better understanding of the agents of cryptococcosis in the host-yeast aspects of the interaction.

Breaking the mould - novel diagnostic and therapeutic strategies for invasive pulmonary aspergillosis in the immune deficient patient

Invasive pulmonary aspergillosis (IPA) caused by the ubiquitous environmental fungus Aspergillus is a frequently fatal lung disease of immunocompromised humans accounting for more than 200,000 infections each year, with an associated mortality rate of 30-90%. This review addresses the current status of IPA diagnosis and treatment and the urgent need to develop accurate, non-invasive strategies for identifying pulmonary infections in the ever-expanding population of immune deficient patients at risk of acquiring opportunistic fungal infections including hematological malignancy and hematopoetic stem cell transplant patients. Recent advances in the use of an Aspergillus-specific monoclonal antibody, JF5, for point-of-care diagnosis of IPA using lateral-flow technology is examined, as is its use in PET/MRI bioimaging and radio-immunotherapy using radionuclide-labeled single chain antibody fragments, Fab fragments, and a fully humanized JF5 derivative.

Radioimmunotherapy of Cryptococcus neoformans spares bystander mammalian cells

AIM

Previously, we showed that radioimmunotherapy (RIT) for cryptococcal infections using radioactively labeled antibodies recognizing the cryptococcal capsule reduced fungal burden and prolonged survival of mice infected with Cryptococcus neoformans. Here, we investigate the effects of RIT on bystander mammalian cells.

MATERIALS & METHODS

Heat-killed C. neoformans bound to anticapsular antibodies, unlabeled or labeled with the β-emitter rhenium-188 (16.9-h half-life) or the α-emitter bismuth-213 (46-min half-life), was incubated with macrophage-like J774.16 cells or epithelial-like Chinese hamster ovary cells. Lactate dehydrogenase activity, crystal violet uptake, reduction of tetrazolium dye (2,3)-bis-(2-methoxy-4-nitro-5-sulfenyl)-(2H)-terazolium-5-carboxanilide and nitric oxide production were measured.

RESULTS

The J774.16 and Chinese hamster ovary cells maintained membrane integrity, viability and metabolic activity following exposure to radiolabeled C. neoformans.

CONCLUSION

RIT of C. neoformans is a selective therapy with minimal effects on host cells and these results are consistent with observations that RIT-treated mice with cryptococcal infection lacked RIT-related pathological changes in lungs and brain tissues.

Radioimmunotherapy of fungal diseases: the therapeutic potential of cytocidal radiation delivered by antibody targeting fungal cell surface antigens

Radioimmunotherapy is the targeted delivery of cytocidal radiation to cells via specific antibody. Although mature for the treatment of cancer, RIT of infectious diseases is in pre-clinical development. However, as there is an obvious and urgent need for novel approaches to treat infectious diseases, RIT can provide us with a powerful approach to combat serious diseases, including invasive fungal infections. For example, RIT has proven more effective than standard amphotericin B for the treatment of experimental cryptococcosis. This review will discuss the concepts of RIT, its applications for infectious diseases, and the strides made to date to bring RIT of infectious diseases to fruition. Finally, we will discuss the potential of PAN-FUNGAL RIT, the targeting of conserved fungal cell surface antigens by RIT, as a treatment modality for fungi prior to the formal microbiological identification of the specific pathogen. In sum, RIT provides a mechanism for the targeted killing of drug susceptible or resistant fungi irrespective of the host immune status and may dramatically reduce the length of therapy currently required for many invasive fungal diseases.

Cryptococcus neoformans as a Model for Radioimmunotherapy of Infections

There is an obvious and urgent need for novel approaches to treat infectious diseases. The use of monoclonal antibodies in therapy of infectious diseases is now experiencing renewed interest. During the last 5 years radioimmunotherapy (RIT), a modality previously developed only for cancer treatment, has been successfully adapted for the treatment of experimental fungal, bacterial, and viral infections. As our model organism for studying the efficacy, mechanisms, potential toxicity, and radioresistance to RIT, as well as for comparison of RIT with the existing antimicrobial therapies we have chosen the encapsulated yeast Cryptococcus neoformans (CN). The success of RIT approach in laboratory studies provides encouragement for feasibility of therapeutically targeting microbes with labeled antibodies. In addition, the creation of “panantibodies” for RIT which would recognize antigens shared by the whole class of pathogens such as fungi, for example, would facilitate the introduction of RIT into the clinic.

Fungal Biofilms: Relevance in the Setting of Human Disease

The use of indwelling medical devices is rapidly growing and is often complicated by infections with biofilm-forming microbes that are resistant to antimicrobial agents and host defense mechanisms. Fungal biofilms have emerged as a clinical problem associated with these medical device infections, causing significant morbidity and mortality. This review discusses the recent advances in the understanding of fungal biofilms, including the role of fungal surface components in adherence, gene expression, and quorum sensing in biofilm formation. We propose novel strategies for the prevention or eradication of microbial colonization of medical prosthetic devices.

Monoclonal antibody-based therapies for microbial diseases

The monoclonal antibody (mAb) revolution that currently provides many new options for the treatment of neoplastic and inflammatory diseases has largely bypassed the field of infectious diseases. Only one mAb is licensed for use against an infectious disease, although there are many in various stages of development. This situation is peculiar given that serum therapy was one of the first effective treatments for microbial diseases and that specific antibodies have numerous antimicrobial properties. The underdevelopment and underutilization of mAb therapies for microbial diseases has various complex explanations that include the current availability of antimicrobial drugs, small markets, high costs and microbial antigenic variation. However, there are signs that the climate for mAb therapeutics in infectious diseases is changing given increasing antibiotic drug resistance, the emergence of new pathogenic microbes for which no therapy is available, and development of mAb cocktail formulations. Currently, the major hurdle for the widespread introduction of mAb therapies for microbial diseases is economic, given the high costs of immunoglobulin preparations and relatively small markets. Despite these obstacles there are numerous opportunities for mAb development against microbial diseases and the development of radioimmunotherapy provides new options for enhancing the magic bullet. Hence, there is cautious optimism that the years ahead will see more mAbs in clinical use against microbial diseases.

Our current understanding of fungal biofilms

Fungal biofilms are an escalating clinical problem associated with significant rates of mortality. Candida albicans is the most notorious of all fungal biofilm formers. However, non-Candida species, yeasts such as Cryptococcus neoformans, and filamentous moulds such as Aspergillus fumigatus, have been shown to be implicated in biofilm-associated infections. Fungal biofilms have distinct developmental phases, including adhesion, colonisation, maturation and dispersal, which are governed by complex molecular events. Recalcitrance to antifungal therapy remains the greatest threat to patients with fungal biofilms. This review discusses our current understanding of the basic biology and clinical implications associated with fungal biofilms.

The capsule of the fungal pathogen Cryptococcus neoformans

The capsule of the fungal pathogen Cryptococcus neoformans has been studied extensively in recent decades and a large body of information is now available to the scientific community. Well-known aspects of the capsule include its structure, antigenic properties and its function as a virulence factor. The capsule is composed primarily of two polysaccharides, glucuronoxylomannan (GXM) and galactoxylomannan (GalXM), in addition to a smaller proportion of mannoproteins (MPs). Most of the studies on the composition of the capsule have focused on GXM, which comprises more than 90% of the capsule's polysaccharide mass. It is GalXM, however, that is of particular scientific interest because of its immunological properties. The molecular structure of these polysaccharides is very complex and has not yet been fully elucidated. Both GXM and GalXM are high molecular mass polymers with the mass of GXM equaling roughly 10 times that of GalXM. Recent findings suggest, however, that the actual molecular weight might be different to what it has traditionally been thought to be. In addition to their structural roles in the polysaccharide capsule, these molecules have been associated with many deleterious effects on the immune response. Capsular components are therefore considered key virulence determinants in C. neoformans, which has motivated their use in vaccines and made them targets for monoclonal antibody treatments. In this review, we will provide an update on the current knowledge of the C. neoformans capsule, covering aspects related to its structure, synthesis and particularly, its role as a virulence factor.

Radioimmunotherapy of infectious diseases

The need for novel approaches to treat infectious diseases is obvious and urgent. This situation has renewed interest in the use of monoclonal antibodies (mAbs) to treat infectious diseases. During the last 5 years, radioimmunotherapy (RIT), a modality developed for cancer treatment, has been successfully adapted for the treatment of experimental fungal (C. neoformans and H. capsulatum), bacterial (S. pneumoniae and B. anthracis), and viral (HIV-1) infections. RIT produced none or only transient hematological toxicity in experimental animals. Investigation of radiobiological mechanisms of RIT of infections showed that microbial cells are killed by both "direct-hit" and "cross-fire" radiation. mAbs radiolabeled with either alpha- or beta-emitters stimulated apoptosis-like cell death, whereas only mAbs radiolabeled with alpha-emitter (213)Bi also decreased the metabolic activity of microbial cells. The success of this approach in laboratory studies, combined with earlier nuclear medicine experience in preclinical and clinical studies using radiolabeled organism-specific antibodies for imaging of infections, provides encouragement for the feasibility of therapeutically targeting microbes with labeled antibodies. We envision that first the organism-specific mAbs will be radiolabeled with imaging radionuclides such as (99m)Tc or (111)In to localize the sites of infection with single-photon emission computed tomography, followed by RIT with (188)Re- or (90)Y-labeled mAb, respectively. Also, immuno-position emission tomogrpahy might be used to image infection before treatment if such positron-emitting radionuclides as (86)Y (matching pair for (90)Y) or (124)I (matching pair for (131)I) are available. It might be possible to create a so-called "pan-antibody" that would recognize an antigen shared by a particular class of human pathogens such as fungi, for example. The availability of such antibodies would eliminate the necessity of having antibodies specific for each particular microorganism and would enormously enhance the development of RIT of infectious diseases.

Radioimmunotherapy of infection with Bi-labeled antibodies

Bismuth-213 ((213)Bi) (physical half-life 46 min) is a beta-emitter (97%) and an alpha-emitter (3%) which decays to short lived alpha-emitter Polonium-213 and could therefore be used as an in vivo generator of alpha particles with the energy of around 8 MeV. (213)Bi has been successfully used during the last decade in both clinical and pre-clinical work for radioimmunotherapy (RIT) of cancer with (213)Bi-labeled monoclonal antibodies (mAbs). RIT has been proposed as a novel techonology for treatment of infectious diseases. (213)Bi-labeled mAbs have been successfully used for treatment of experimental fungal, bacterial and viral infections with transient or none hematologic toxicity. The mechanisms of RIT of infection with (213)Bi-labeled mAbs include "direct" killing of cells and induction of apoptosis. In vivo RIT results in decrease of inflammation in infected organs. Among the delivery vehicles for RIT of infection whole IgG1 mAbs seem to be the most suitable in terms of the highest uptake in the target organs and the lowest - in normal tissues. RIT with alpha-emitter (213)Bi involves the application of established technology developed for the treatment of malignancies to infectious diseases. The development of RIT for infectious diseases is potentially easier than its application to tumor therapy given antigenic and tissue perfusion differences between sites of microbial infection and tumor infiltration. Nevertheless, considerable pre-clinical and clinical development work is likely to be required to learn how to use RIT for infection optimally.

Pathogenesis of mucosal biofilm infections: challenges and progress

Living-tissue biofilms remained unrecognized until very recently, mainly as a result of traditional microbial sampling techniques or histologic processing, which disrupt the spatial organization of the tissue microorganisms. Thus, the biofilm nature of certain mucosal infections was frequently unintentionally missed or disregarded. To a large extent, the study of human tissue biofilms is still in its infancy. However, with the advent of newer methodologies, such as fluorescent in situ hybridization and endoscopic confocal laser scanning microscopy, which combine the identification of microbes with in situ, direct visualization of their relationships with each other and with their substratum, mucosal tissue biofilms are becoming easier to study and, thus, their role in human infections is becoming more apparent. This review summarizes the challenges in the study of tissue biofilms, proposes two inflammation-centered - albeit opposite - pathogenetic models of mucosal tissue biofilm infections and suggests directions for future research and novel therapeutic approaches.

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.