Preclinical testing of radiopharmaceuticals for novel applications in HIV, bacterial and fungal infectious diseases.

Antibiotics, antifungal and antiviral medications have traditionally been used in the management of infections. Due to widespread emergence of resistance to antimicrobial medications, and their side effects, there is a growing need for alternative approaches for management of such conditions. Antibiotic resistant bacterial pathogens are on the rise. A cure has not been achieved for viral infections like AIDS, while fungal and parasitic infections are constant threats to the health of general public. The incidence of opportunistic infections in immunocompromised individuals like HIV patients, patients receiving high dose steroids, chemotherapy patients, and organ transplant recipients is on the rise. Radioimmunotherapy (RIT) has the potential to be a suitable and viable therapeutic modality in the arena of infection management. Provided the target-associated antigen is expressed by the target cells and minimally or not expressed by other tissues, selective targeting of radiation to target sites can be theoretically accomplished with relative sparing normal tissues from radiation exposure. In our laboratory we successfully demonstrated the effectiveness of RIT for treating infectious diseases. We targeted murine cryptococcosis with a mAb to the Cryptococcus neoformans capsular glucuronoxylomannan labeled with Bismuth-213 ((213)Bi) or Rhenium-188 ((188)Re). We subsequently extended the applicability of RIT for treating bacterial and viral infections. One of the advantages of using RIT to treat infections as opposed to cancer is that, in contrast to tumor cells, cells expressing microbial antigens are antigenically very different from host tissues and thus provide the potential for exquisite specificity and low cross-reactivity. Ever increasing incidence of infectious pathologies, exhaustion of antimicrobial possibilities and rising drug resistance calls for use of alternative and novel therapeutic options and we believe RIT is the need of the hour to combat these infections.

Treatment of early and established Cryptococcus neoformans infection with radiolabeled antibodies in immunocompetent mice.

We investigated the utility of radioimmunotherapy (RIT) in early and established cryptococcal infection in immunocompetent mice. RIT with (213)Bi-18B7 antibody completely eliminated fungus from mouse lungs and brains for early infection, while (188)Re-18B7 significantly reduced CFU in the lungs or both lungs and brains during early and established infection, respectively. The results point to the independence of RIT of the immune status of the host, which is encouraging for translation of this strategy into the clinic.

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.

The effect of radiation therapy on fungal growth: results of in vitro and in vivo studies.

OBJECTIVES: To investigate the effect of radiation therapy (XRT) on the growth of Candida and Cryptococcus. METHODS: (I) In vitro study: suspensions of Candida and Cryptococcus were irradiated by 0-20 Gy, and colony forming units (CFUs) were counted after 2 and 11 days. (II) In vivo study: (A) The XRT effect-Balb/c mice were injected with Candida or Cryptococcus and irradiated by 5 or 10 Gy. Homogenates of their kidneys or brains were cultured and CFUs were counted two days later. (B) Toxicity-Balb/c mice were injected with Candida and irradiated by 5 Gy. Control mice were either injected or irradiated. Overall survival was documented for all animals. RESULTS: (I) The CFU counts in the irradiated and non-irradiated mice were similar at days 2 and 11. (II) (A)-The CFUs were significantly low for both Candida and Cryptococcus injected and irradiated mice (p=0.02). (II) (B)-The overall survival of the injected mice was not affected by the additional irradiation and it was inferior to the irradiated mice only. CONCLUSIONS: XRT has a beneficial inhibitive effect on the in vivo but not the in vitro growth of fungi. It does not decrease the survival rate of injected mice. Clinical studies in selected patients with resistant invasive fungal infection are warranted.

Pitfalls in the computed tomographic diagnosis of toruloma.

A case of multiple intracerebral mass lesions is presented in which significant "improvement" in the computed tomographic appearance was noted following steroid and radiation therapies. Nonetheless, the patient's clinical course was one of rapid deterioration, and an autopsy revealed multiple torulomas. It seems that the computed tomographic appearance of torulomas can mimic those of other intracranial mass lesions and can be greatly altered by steroid and radiation therapies, either singly or in combination.

The spectrum of computerized tomography (CT) findings in central nervous system (CNS) infection due to Cryptococcus neoformans var. gattii in immunocompetent children.

Cranial CT scans of eleven immunocompetent children with central nervous system (CNS) infection due to Cryptococcus neoformans var. gattii were retrospectively reviewed. These children had an average age of 8.8 years and positive culture for C. n. var. gattii in cerebrospinal fluid. The most common signs and symptoms were headache, fever, nuchal rigidity, nausea and vomiting. No normal cranial CT was detected in any patient. Hypodense nodules were observed in all patients. The remaining scan abnormalities were as follows: nine had diffuse atrophy, six had hydrocephalus, and five had hydrocephalus coexistent with diffuse atrophy.

Cryptococcus gattii: in vitro susceptibility to photodynamic inactivation.

Cryptococus gattii is an emergent primary human pathogen that causes meningismus, papilledema, high intracranial pressure and focal involvement of the central nervous system in immunocompetent hosts. Prolonged antifungal therapy is the conventional treatment, but it is highly toxic, selects for resistant strains, contributes to therapy failure and has a poor prognosis. Photodynamic inactivation (PDI) offers a promising possibility for the alternative treatment of cryptococcosis. The aim of this study was to test the effectiveness of toluidine blue O (TBO) and light-emitting diode (LED) against C. gattii strains with distinct susceptibility profile to antifungal drugs (amphotericin B: 0.015-1.0 µg mL(-1); itraconazole: 0.015-2 µg mL(-1); fluconazole: 4-64 µg mL(-1)). Using 25 µM (6.76 µg mL(-1)) TBO and LED energy density of 54 J cm(-2) these fungal isolates presented variable susceptibility to PDI. The production of reactive oxygen species (ROS)/peroxynitrite was determined, and the catalase and peroxidase activities were measured. After PDI, high amounts of ROS/peroxynitrite are produced and higher catalase and peroxidase activities could be correlated with a lower susceptibility of C. gattii isolates to PDI. These results indicate that PDI could be an alternative to C. gattii growth inhibition, even of isolates less susceptible to classical antifungal drugs, also pointing to mechanisms related to their variable susceptibility behavior.

Evaluation of acute hematologic and long-term pulmonary toxicities of radioimmunotherapy of Cryptococcus neoformans infection in murine models.

We evaluated acute hematological and long-term pulmonary toxicity of radioimmunotherapy in murine models of Cryptococcus neoformans infection. Activities up to 250 microCi were well tolerated by healthy A/JCr mice for (213)Bi-18B7 and (188)Re-18B7 monoclonal antibodies. In infected mice, doses up to 150 microCi produced only transient toxicity. The lungs of treated mice had no evidence of radiation fibrosis.