Antibodies as delivery vehicles for radioimmunotherapy of infectious diseases

Evaluating the Targeting of a Staphylococcus-aureus-Infected Implant with a Radiolabeled Antibody In Vivo

Implant infections caused by Staphylococcus aureus are difficult to treat due to biofilm formation, which complicates surgical and antibiotic treatment. We introduce an alternative approach using monoclonal antibodies (mAbs) targeting S. aureus and provide evidence of the specificity and biodistribution of S.-aureus-targeting antibodies in a mouse implant infection model. The monoclonal antibody 4497-IgG1 targeting wall teichoic acid in S. aureus was labeled with indium-111 using CHX-A"-DTPA as a chelator. Single Photon Emission Computed Tomography/computed tomographyscans were performed at 24, 72 and 120 h after administration of the ¹¹¹In-4497 mAb in Balb/cAnNCrl mice with a subcutaneous implant that was pre-colonized with S. aureus biofilm. The biodistribution of this labelled antibody over various organs was visualized and quantified using SPECT/CT imaging, and was compared to the uptake at the target tissue with the implanted infection. Uptake of the ¹¹¹In-4497 mAbs at the infected implant gradually increased from 8.34 %ID/cm³ at 24 h to 9.22 %ID/cm³ at 120 h. Uptake at the heart/blood pool decreased over time from 11.60 to 7.58 %ID/cm³, whereas the uptake in the other organs decreased from 7.26 to less than 4.66 %ID/cm³ at 120 h. The effective half-life of ¹¹¹In-4497 mAbs was determined to be 59 h. In conclusion, ¹¹¹In-4497 mAbs were found to specifically detect S. aureus and its biofilm with excellent and prolonged accumulation at the site of the colonized implant. Therefore, it has the potential to serve as a drug delivery system for the diagnostic and bactericidal treatment of biofilm.

Virulence Characteristics and Emerging Therapies for Biofilm-Forming Acinetobacter baumannii: A Review

Simple Summary

Acinetobacter baumannii (A. baumannii) is one of the ESKAPE organisms and has the competency to build biofilms. These biofilms account for the most nosocomial infections all over the world. This review reflects on the various physicochemical and environmental factors such as adhesion, pili expression, growth surfaces, drug-resistant genes, and virulence factors that profoundly affect its resistant forte. Emerging drug-resistant issues and limitations to newer drugs are other factors affecting the hospital environment. Here, we discuss newer and alternative methods that can significantly enhance the susceptibility to Acinetobacter spp. Many new antibiotics are under trials, such as GSK-3342830, The Cefiderocol (S-649266), Fimsbactin, and similar. On the other hand, we can also see the impact of traditional medicine and the secondary metabolites of these natural products’ application in searching for new treatments. The field of nanoparticles has demonstrated effective antimicrobial actions and has exhibited encouraging results in the field of nanomedicine. The use of various phages such as vWUPSU and phage ISTD as an alternative treatment for its specificity and effectiveness is being investigated. Cathelicidins obtained synthetically or from natural sources can effectively produce antimicrobial activity in the micromolar range. Radioimmunotherapy and photodynamic therapy have boundless prospects if explored as a therapeutic antimicrobial strategy.

Abstract

Acinetobacter species is one of the most prevailing nosocomial pathogens with a potent ability to develop antimicrobial resistance. It commonly causes infections where there is a prolonged utilization of medical devices such as CSF shunts, catheters, endotracheal tubes, and similar. There are several strains of Acinetobacter (A) species (spp), among which the majority are pathogenic to humans, but A. baumannii are entirely resistant to several clinically available antibiotics. The crucial mechanism that renders them a multidrug-resistant strain is their potent ability to synthesize biofilms. Biofilms provide ample opportunity for the microorganisms to withstand the harsh environment and further cause chronic infections. Several studies have enumerated multiple physiological and virulence factors responsible for the production and maintenance of biofilms. To further enhance our understanding of this pathogen, in this review, we discuss its taxonomy, pathogenesis, current treatment options, global resistance rates, mechanisms of its resistance against various groups of antimicrobials, and future therapeutics.

Emerging Preclinical and Clinical Applications of Theranostics for Nononcological Disorders

Studies in nuclear medicine have shed light on molecular imaging and therapeutic approaches for oncological and nononcological conditions. Using the same radiopharmaceuticals for diagnosis and therapeutics of malignancies, the theranostics approach, has improved clinical management of patients. Theranostic approaches for nononcological conditions are recognized as emerging topics of research. This review focuses on preclinical and clinical studies of nononcological disorders that include theranostic strategies. Theranostic approaches are demonstrated as possible in the clinical management of infections and inflammations. There is an emerging need for randomized trials to specify the factors affecting validity and efficacy of theranostic approaches in nononcological diseases.

(68)Ga-labeled phage-display selected peptides as tracers for positron emission tomography imaging of Staphylococcus aureus biofilm-associated infections: Selection, radiolabelling and preliminary biological evaluation

INTRODUCTION

Staphylococcus aureus is a major cause of skin and deep-sited infections, often associated with the formation of biofilms. Early diagnosis and initiated therapy is essential to prevent disease progression and to reduce complications that can be serious. Imaging techniques are helpful combining anatomical with functional data in order to describe and characterize site, extent and activity of the disease. The purpose of the study was to identify and (68)Ga-label peptides with affinity for S. aureus biofilm and evaluate their potential as bacteria-specific positron emission tomography (PET) imaging agents.

METHODS

Phage-displayed dodecapeptides were selected using an in vitro grown S. aureus biofilm as target. One cyclic (A8) and two linear (A9, A11) dodecapeptides were custom synthesized with 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid (DOTA) conjugated via a lysine linker (K), and for A11 also a glycine-serine-glycine spacer (GSG). The (68)Ga-labeling of A8-K-DOTA, A9-K-DOTA, and A11-GSGK-DOTA were optimized and in vitro bacterial binding was evaluated for (68)Ga-A9-K-DOTA and (68)Ga-A11-GSGK-DOTA. Stability of (68)Ga-A9-K-DOTA was studied in vitro in human serum, while the in vivo plasma stability was analyzed in mice and pigs. Additionally, the whole-body distribution kinetics of (68)Ga-A9-K-DOTA was measured in vivo by PET imaging of pigs and ex vivo in excised mice tissues.

RESULTS

The (68)Ga-A9-K-DOTA and (68)Ga-A11-GSGK-DOTA remained stable in product formulation, whereas (68)Ga-A8-K-DOTA was unstable. The S. aureus binding of (68)Ga-A11-GSGK-DOTA and (68)Ga-A9-K-DOTA was observed in vitro, though blocking of the binding was not possible by excess of cold peptide. The (68)Ga-A9-K-DOTA was degraded slowly in vitro, while the combined in vivo evaluation in pigs and mice showed a rapid blood clearance and renal excretion of the (68)Ga-A9-K-DOTA.

CONCLUSION

The preliminary in vitro and in vivo studies of the phage-display S. aureus biofilm-selected (68)Ga-A9-K-DOTA showed desirable features for a novel bacteria-specific imaging agent, despite of relative fast blood degradation in vivo.

Antibodies as a source of anti-infective peptides: an update

This review focuses on antibodies (Abs) and their function in immune protection, with particular emphasis on microbicidal Abs. Some aspects of Abs and Ab-drug conjugates as targeting therapeutic agents are also discussed. The main aim, however, is devoted to Ab-derived peptides modulating functions of the immune system and to the latest experimental evidence of Abs as a source of anti-infective and antitumor peptides derived from their complementarity determining regions and constant regions.

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.

Immunodetection of fungal and oomycete pathogens: established and emerging threats to human health, animal welfare and global food security

Filamentous fungi (moulds), yeast-like fungi, and oomycetes cause life-threatening infections of humans and animals and are a major constraint to global food security, constituting a significant economic burden to both agriculture and medicine. As well as causing localized or systemic infections, certain species are potent producers of allergens and toxins that exacerbate respiratory diseases or cause cancer and organ damage. We review the pathogenic and toxigenic organisms that are etiologic agents of both animal and plant diseases or that have recently emerged as serious pathogens of immunocompromised individuals. The use of hybridoma and phage display technologies and their success in generating monoclonal antibodies for the detection and control of fungal and oomycete pathogens are explored. Monoclonal antibodies hold enormous potential for the development of rapid and specific tests for the diagnosis of human mycoses, however, unlike plant pathology, their use in medical mycology remains to be fully exploited.

Biscatecholate-monohydroxamate mixed ligand siderophore-carbacephalosporin conjugates are selective sideromycin antibiotics that target Acinetobacter baumannii

Chemical syntheses and biological evaluation of biscatecholate-monohydroxamate mixed ligand sideromycins utilizing the carbacephalosporin β-lactam antibiotic loracarbef and the fluoroquinolone antibiotic ciprofloxacin are described. The mixed ligand β-lactam sideromycin (1b) had remarkably selective and extremely potent antibacterial activity against the Gram-negative pathogen Acinetobacter baumannii ATCC 17961 (MIC = 0.0078 μM). The antibacterial activity of the β-lactam sideromycin was inversely related to the iron(III) concentration in the testing media and was antagonized by the presence of the competing parent siderophore. These data suggested that active transport of the mixed ligand β-lactam sideromycin across the outer cell membrane of A. baumannii via siderophore-uptake pathways was responsible for the selective and potent antibacterial activity.

Methodology for labeling proteins and peptides with lead-212 (212Pb)

INTRODUCTION

Alpha particles possess an exquisite degree of cytotoxicity when employed for targeted α-particle therapy (TAT) or radioimmunotherapy (RIT). (212)Pb, which acts as an in vivo generator of the α-emitting nuclide (212)Bi has shown great promise in pre-clinical studies when used to label the HER2 binding antibody, trastuzumab. Currently, the first RIT clinical trial employing (212)Pb radiolabeled trastuzumab is in progress. This report provides detailed current protocol operations and steps that were generated for use in the clinical trial as well as the relevant pre-clinical experimentation, and describes in detail the labeling of proteins or peptides with (212)Pb as provided via a (224)Ra based generator system.

METHODS

(212)Pb was eluted from the (224)Ra/(212)Pb generator using hydrochloric acid (2M). The generator eluate was evaporated and digested with nitric acid (8M) followed by extraction of the (212)Pb with dilute nitric acid (0.1M). The dilute nitric acid solution of (212)Pb was used to label the immunoconjugate Trastuzumab-TCMC (2-(4-isothiocyanatobenzyl-1,4,7,10-tetraaza-1,4,7,10,tetra-(2-carbamonylmethyl)-cyclododecane) at pH5.5.

RESULTS

Elution of (212)Pb from the generator was efficient yielding>90% of available (212)Pb. Trastuzumab-TCMC was efficiently labeled with a radiochemical yield of 94% ± 4% (n=7) by ITLC and an isolated yield of 73% ± 3% (n=7).

CONCLUSIONS

The results show the feasibility of generating radioimmunoconjugates and peptide conjugates for use as in vivo α generator systems in the clinic. The technology holds promise in applications involving the treatment of minimal disease such as micrometastases and residual tumor after surgical debulking, hematological cancers, infections, and compartmental cancers, such as ovarian cancer.

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.

Neutralizing monoclonal antibody to edema toxin and its effect on murine anthrax

Edema factor (EF) is a component of an anthrax toxin that functions as an adenylate cyclase. Numerous monoclonal antibodies (MAbs) have been reported for the other Bacillus anthracis toxin components, but relatively few to EF have been studied. We report the generation of six murine hybridoma lines producing two IgM and four IgG1 MAbs to EF. Of the six MAbs, only one IgM neutralized EF, as assayed by an increase in cyclic AMP (cAMP) production by Chinese hamster ovary (CHO) cells. Analysis of the variable gene elements revealed that the single neutralizing MAb had a different binding site than the others. There was no competition between the neutralizing IgM and the nonneutralizing IgG MAbs indicative of different specificity. MAb-based capture enzyme-linked immunosorbent assay (ELISA) detected EF in liver lysates from mice infected with B. anthracis Sterne 34F2. Administration of the neutralizing IgM MAb to A/JCr mice lethally infected with B. anthracis strain Sterne had no significant effect on median time to death, but mice treated with the MAb were more likely to survive infection. Combining the neutralizing IgM to EF with a subprotective dose of a neutralizing MAb to protective antigen (PA) prolonged mean time to death of infected mice, suggesting that neutralization of EF and PA could produce synergistic beneficial effects. In summary, the results from our study and literature observations suggest that the majority of Abs to EF are nonneutralizing, but the toxin has some epitopes that can be targeted by the humoral response to generate useful Abs that may contribute to defense against anthrax.

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.

Radiolabeled antibodies to Bacillus anthracis toxins are bactericidal and partially therapeutic in experimental murine anthrax

Bacillus anthracis is a powerful agent for use in biological warfare, and infection with the organism is associated with a high rate of mortality, underscoring the need for additional effective therapies for anthrax. Radioimmunotherapy (RIT) takes advantage of the specificity and affinity of the antigen-antibody interaction to deliver a microbicidal radioactive nuclide to a site of infection. RIT has proven therapeutic in experimental models of viral, bacterial, and fungal infections; but it is not known whether this approach can successfully employ toxin binding monoclonal antibodies (MAbs) for diseases caused by toxigenic bacteria. Indirect immunofluorescence studies with MAbs to protective antigen (MAbs 7.5G gamma2b and 10F4 gamma1) and lethal factor (MAb 14FA gamma2b) revealed the surface expression of toxins on bacterial cells. Scatchard analysis of MAbs revealed high binding constants and numerous binding sites on the bacterial surface. To investigate the microbicidal properties of these MAbs, our group radiolabeled MAbs with either (188)Re or (213)Bi. In vitro, (213)Bi was more efficient than (188)Re in mediating microbicidal activity against B. anthracis. The administration of MAbs [(213)Bi]10F4 gamma1 and [(213)Bi]14FA gamma2b prolonged the survival of A/JCr mice infected with B. anthracis Sterne bacterial cells but not B. anthracis Sterne spores. These results indicate that RIT with MAbs that target B. anthracis toxin components can be used to treat experimental anthrax infection and suggest that toxigenic bacteria may be targeted with radiolabeled MAbs.

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.

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.

Targeted alpha-therapy: past, present, future?

Monoclonal antibodies have become a viable strategy for the delivery of therapeutic, particle emitting radionuclides specifically to tumor cells to either augment anti-tumor action of the native antibodies or to solely take advantage of their action as targeting vectors. Proper and rational selection of radionuclide and antibody combinations is critical to making radioimmunotherapy (RIT) a standard therapeutic modality due to the fundamental and significant differences in the emission of either alpha- and beta-particles. The alpha-particle has a short path length (50-80 microm) that is characterized by high linear energy transfer (100 keV microm(-1)). Actively targeted alpha-therapy potentially offers a more specific tumor cell killing action with less collateral damage to the surrounding normal tissues than beta-emitters. These properties make targeted alpha-therapy an appropriate therapy to eliminate minimal residual or micrometastatic disease. RIT using alpha-emitters such as (213)Bi, (211)At, (225)Ac, and others has demonstrated significant activity in both in vitro and in vivo model systems. Limited numbers of clinical trials have progressed to demonstrate safety, feasibility, and therapeutic activity of targeted alpha-therapy, despite having to traverse complex obstacles. Further advances may require more potent isotopes, additional sources and more efficient means of isotope production. Refinements in chelation and/or radiolabeling chemistry combined with rational improvements of isotope delivery, targeting vectors, molecular targets, and identification of appropriate clinical applications remain as active areas of research. Ultimately, randomized trials comparing targeted alpha-therapy combined with integration into existing standards of care treatment regimens will determine the clinical utility of this modality.

Targeting the Virus with Radioimmunotherapy in Virus-Associated Cancers

"Virus-associated cancer" (VAC) refers to a cancer where viral infection results in the malignant transformation of the host's infected cells. Examples of viruses linked to cancers are the Epstein-Barr virus (EBV), which is associated with lymphomas, as well as nasopharyngeal and breast cancer; hepatitis B virus (HBV) and hepatitis C virus (HCV), which are both associated with hepatocellular carcinoma; and human papilloma viruses (HPVs), which are associated with cancer of the cervix. We have recently demonstrated that HIV-1-infected cells can be eliminated in vitro and in vivo by targeting viral glycoproteins expressed on the surface of infected cells with radiolabeled viral protein-specific monoclonal antibodies and proposed that this approach can be applicable to the broad range of viral infectious diseases. In VAC, the tumor cells can exhibit viral antigens both internally or on their surfaces. As a result, viral antigens in tumors represent a potential antigenic target that is clearly different from normal tissues. In principle, these proteins could be targeted by radioimmunotherapy (RIT). In this paper, we describe the potential of this approach and review some of the issues involved in the development of this approach. RIT of VAC is fundamentally different from the previously described uses of RIT, which have targeted tumor-associated antigens that are "self" proteins.

Targeted killing of virally infected cells by radiolabeled antibodies to viral proteins

BACKGROUND

The HIV epidemic is a major threat to health in the developing and western worlds. A modality that targets and kills HIV-1-infected cells could have a major impact on the treatment of acute exposure and the elimination of persistent reservoirs of infected cells. The aim of this proof-of-principle study was to demonstrate the efficacy of a therapeutic strategy of targeting and eliminating HIV-1-infected cells with radiolabeled antibodies specific to viral proteins in vitro and in vivo.

METHODS AND FINDINGS

Antibodies to HIV-1 envelope glycoproteins gp120 and gp41 labeled with radioisotopes bismuth 213 ((213)Bi) and rhenium 188 ((188)Re) selectively killed chronically HIV-1-infected human T cells and acutely HIV-1-infected human peripheral blood mononuclear cells (hPBMCs) in vitro. Treatment of severe combined immunodeficiency (SCID) mice harboring HIV-1-infected hPBMCs in their spleens with a (213)Bi- or (188)Re-labeled monoclonal antibody (mAb) to gp41 resulted in a 57% injected dose per gram uptake of radiolabeled mAb in the infected spleens and in a greater than 99% elimination of HIV-1-infected cells in a dose-dependent manner. The number of HIV-1-infected thymocytes decreased 2.5-fold in the human thymic implant grafts of SCID mice treated with the (188)Re-labeled antibody to gp41 compared with those treated with the (188)Re-control mAb. The treatment did not cause acute hematologic toxicity in the treated mice.

CONCLUSIONS

The current study demonstrates the effectiveness of HIV-targeted radioimmunotherapy and may provide a novel treatment option in combination with highly active antiretroviral therapy for the eradication of HIV.

Antibody-guided alpha radiation effectively damages fungal biofilms

The use of indwelling medical devices--pacemakers, prosthetic joints, catheters--is rapidly growing and is often complicated by infections with biofilm-forming microbes that are resistant to antimicrobial agents and host defense mechanisms. We investigated for the first time the use of microbe-specific monoclonal antibodies (MAbs) as delivery vehicles for targeting biofilms with cytocidal radiation. MAb 18B7 (immunoglobulin G1 [IgG1]), which binds to capsular polysaccharides of the human pathogenic fungus Cryptococcus neoformans, penetrated cryptococcal biofilms, as shown by confocal microscopy. When the alpha radiation-emitter 213-Bismuth ((213)Bi) was attached to MAb 18B7 and the radiolabeled MAb was added to C. neoformans biofilms, there was a 50% reduction in biofilm metabolic activity. In contrast, when the IgM MAb 13F1 labeled with (213)Bi was used there was no penetration of the fungal biofilm and no damage. Unlabeled 18B7, (213)Bi-labeled nonspecific MAbs, and gamma and beta types of radiation did not have an effect on biofilms. The lack of efficacy of gamma and beta radiation probably reflects the radioprotective properties of polysaccharide biofilm matrix. Our results indicate that C. neoformans biofilms are susceptible to treatment with antibody-targeted alpha radiation, suggesting a novel option for the prevention or treatment of microbial biofilms on indwelling medical devices.