Detection of experimental infections with 99mTc-labeled monoclonal antibodies against TNF-alpha and interleukin-8

Facile One-Pot Strategy for Radiosynthesis of 99mTc-Doxycycline to Diagnose Staphylococcus aureus in Infectious Animal Models

The accurate and early diagnosis of infection is an important feature in the biomedical sciences for better treatment and to decrease the rate of morbidity associated with diseases. Doxycycline (DC) is a semisynthetic antibiotic that belongs to tetracycline family and usually prescribed to treat a variety of infections. The objective of the present research work was to develop a new radiopharmaceutical ^99mTc-Doxycycline (^99mTc-DC), by using SnCl₂·2H₂O as a reducing agent for diagnostic applications. It was confirmed through this study that ^99mTc-DC possessed high radiolabeling yield (95%). In vitro studies were performed by incubating ^99mTc-DC in human serum at 37 °C. The in vitro binding interaction of the labeled antibiotic was analyzed with bacterial strain (live Staphylococcus aureus cells), and its stability was further determined. Moreover, for in vivo infection imaging study, the infection was induced with S. aureus (gram positive) cells intramuscularly injected in mice models followed by biodistribution studies for ^99mTc-DC that were performed. Biodistribution studies of ^99mTc-DC showed that the radiotracer was significantly accumulated at the site of infection and indicated the renal route of excretion. Scintigraphic images obtained as a result of in vivo study showed good uptake of prepared radiotracer (^99mTc-DC) in the infectious lesions at 1-, 4-, and 24-h post-injection. Target-to-non-target ratios for ^99mTc-DC were significantly different for the infectious lesions and non-infected tissues and remained 2.13 ± 0.3 up to 24-h post-injection of ^99mTc-DC. ^99mTc-DC showed preferential binding to living bacterial infected sites as compared to other parts of the body, and thus it can be inferred that ^99mTc-DC might be a potential candidate to diagnose the infection.

Technetium-99m labeled Ibuprofen: Development and biological evaluation using sterile inflammation induced animal models

In this study we are presenting the development of technetium-99m (^99mTc) labeled ibuprofen for the imaging of aseptic inflammation. ^99mTc-Ibuprofen complex was developed by optimizing the radiolabeling conditions such as reaction time, ligand and reducing agent concentration, pH, reaction time and temperature. Following the addition of 600 µg of ibuprofen, 4 µg of stannous chloride as reducing agent and 300 MBq ^99mTc radioactivity; the pH of reaction mixture was adjusted to 11 and allowed to react for 15 min at room temperature. Chromatography analysis revealed > 94% ^99mTc-ibuprofen complex formation with promising stability in saline and blood serum up to 6 h. Biodistribution study using normal and sterile inflammation induced mice indicated low accumulation of labeled compound in key body organs; however, kidneys (14.76 ± 0.87% ID/g organ) and bladder (31.6 ± 3.0% ID/g organ) showed comparatively higher radioactivity due to main excretory path. Inflamed to normal tissues ratio (T/NT), at 1 h post-injection, showed promising value (4.57 ± 0.56). The SPECT imaging of artificially inflammation induced rabbit model also verified the biodistribution results. In conclusion, radiochemical purity and biological evaluation of ^99mTc-ibuprofen complex indicates the agent can be utilized for imaging of deep seated aseptic inflammation.

Translation of ceragenin affinity for bacteria to an imaging reagent for infection

Responses to bacterial infections may be manifest systemically without evidence of the location of the infection site. A rapid means of pinpointing infection sites would be useful in providing effective and possibly localized treatment. Successful means of identifying infection sites would require two components: (1) a molecule capable of recognizing bacteria and (2) a means of communicating recognition. For the recognition element, we used a ceragenin, a small molecule with affinity for bacterial membranes that was designed as a mimic of endogenous antimicrobial peptides. For the communication element, we used ⁶⁴Cu, which is a positron emitter. By conjugating a copper chelating group to the ceragenin, the two elements were combined. Chelation of ⁶⁴Cu by the conjugate was effective and provided a stable complex that allowed in vivo imaging. When administered to mice in a thigh infection model, the ⁶⁴Cu-labeled conjugate accumulated at the site of infection (right thigh) without accumulation at the complementary site (left thigh). This conjugate may provide a means of identifying infection sites in patients presenting general signs of infection without localized symptoms.

Infection imaged via autoradiography with ceragenin conjugated to a copper radiolabel.

18F-FDG-PET/CT in Initiation and Progression of Inflammation and Infection

Objective:

Detection/localization of infection and inflammation is important for the initiation of correct treatment as well as its maintenance. Nuclear medicine imaging methods play an important role in determining infection and inflammation. ¹⁸F-2’-deoxy-2-fluoro-d-glucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) is highly sensitive in such cases when used with tomographic cross-sections. In this study, the development and progression of infection and inflammation were monitored on rats by using ¹⁸F-FDG via PET/CT.

Methods:

Sterile and infected abscesses were formed on rats using turpentine and S. aureus, respectively. For evaluation of the formation and progression of the abscess, ¹⁸F-FDG was injected into the rats and they were imaged by PET/CT at intervals of twenty-four hours for five days. Maximum standard uptake value (SUV_max) of ¹⁸F-FDG was calculated.

Results:

The highest activity involvement was seen on the first day of abscess formation. On the first day, SUV_max of the S. aureus abscess was 3.9±0.9 while in the sterile abscess SUV_max in the first day was 2.2±0.8. ¹⁸F-FDG uptake decreased day by day and it reached the background level on the fourth and fifth days. There were statistically significant differences between S. aureus and sterile abscess, and between sterile abscess and background activity in terms of SUV_max values during the first three days (p<0.05). On the fourth and fifth days, there was no statistically significant difference between S. aureus and sterile abscess, and between sterile abscess and background activity (p>0.05).

Conclusion:

The results demonstrated that the SUV_max value for ¹⁸F-FDG can be useful in the early differentiation of sterile and infected abscess. In addition, ¹⁸F-FDG-PET imaging has the advantage of local availability of equipment and labeled agents leading rapid diagnosis of differentiation of infection and inflammation.

Molecular probing of TNF: From identification of therapeutic target to guidance of therapy in inflammatory diseases

Therapy by blocking tumor necrosis factor (TNF) activity is highly efficacious and profoundly changed the paradigm of several inflammatory diseases. However, a significant proportion of patients with inflammatory diseases do not respond to TNF inhibitors (TNFi). Prediction of therapeutic response is required for TNFi therapy. Isotope labeled anti-TNF antibodies or TNF receptor have been investigated to localize TNF production at inflammatory tissue in animal models and in patients with inflammatory diseases. The in vivo detection of TNF has been associated with treatment response. Recently, fluorophore labeled anti-TNF antibody in combination with confocal laser endomicroscopy in patients with Crohn's disease yielded more accurate and quantitative in vivo detection of TNF in the diseased mucosa. More importantly, this method demonstrated high therapeutic predication value. Fluorophore labeled TNF binding aptamers in combination with modern imaging technology offers additional tools for in vivo TNF probing.

Noninvasive allograft imaging of acute rejection: evaluation of (131)I-anti-CXCL10 mAb

The purpose of this study was to investigate the use of iodine-131-labeled anti-CXCL10 mAb as tracer targeted at CXCL10 to detect acute rejection (AR) with mice model. Expression of CXCL10 was proved by RT-PCR, ELISA, and immunochemistry staining. All groups were submitted to whole-body autoradioimaging and ex vivo biodistribution studies after tail vein injection of (131)I-anti-CXCL10 mAb. The highest concentration/expression of CXCL10 was detected in allograft tissue compared with allograft treated with tacrolimus and isograft control. Tacrolimus could obviously inhibit the rejection of allograft. Allograft could be obviously imaged at all checking points, much clearer than the other two groups. The biodistribution results showed the highest uptake of radiotracer in allograft. T/NT (target/nontarget) ratio was 4.15 ± 0.25 at 72 h, apparently different from allograft treated with tacrolimus (2.29 ± 0.10), P < 0.05. These data suggest that CXCL10 is a promising target for early stage AR imaging and (131)I-CXCL10 mAb can successfully image AR and monitor the effect of immunosuppressant.

(99m)Tc-labeling of ciprofloxacin and nitrofuryl thiosemicarbazone using fac-[(99m)Tc(CO)3(H2O)3] core: evaluation of their efficacy as infection imaging agents

The aim of this study was to radiolabel ciprofloxacin (Cip) and nitrofuryl thiosemicarbazone (NFT) with the fac-[(99m)Tc(CO)(3)(H(2)O)(3)](+) core and to evaluate the ability of the radiopharmaceuticals as tracers in detecting sites of infection. Cip and NFT were radiolabeled with the fac-[(99m)Tc(CO)(3)(H(2)O)(3)](+) core and characterized by RHPLC. The stabilities of the preparations were evaluated in saline and rat serum. In vitro binding studies of the radiopharmaceuticals with S. aureus were performed. Biodistribution studies were conducted at different time points after injecting (i.v.) the radiopharmaceuticals in rats (intramuscularly infected with S. aureus) as well as in rats with sterile inflammation. To assess the infection targeting capacity of (99m)Tc-tricarbonyl ciprofloxacin and nitrofuryl thiosemicarbazone, (99m)Tc(v)O-Cip and (99m)Tc(v)O-NFT were used as control. Scintigraphic imaging studies of tricarbonyl compounds and (99m)Tc(v)O-Cip were performed at 4 h after injection. The radiochemical purities of (99m)Tc(CO)(3)-Cip and (99m)Tc(CO)(3)-NFT were between 97-98% as determined by thin layer chromatography (TLRC) and RHPLC; no further purification is necessary before injection. The radiopharmaceuticals exhibited substantial stability when incubated in isotonic saline and serum up to 24 h. Biodistribution studies showed maximum uptake in the infected rat thigh muscle at 4 h post injection and washing out at slower rate from the infected site than the oxo technetium chelate. The mean ratios of uptake in infected/non-infected thighs were 3.87:1, 3.41:1 and 3.17:1 for (99m)Tc(CO)(3)-Cip, (99m)Tc(CO)(3)-NFT and (99m)Tc(v)O-Cip respectively. During scintigraphic studies, infection sites appeared quite distinctly with (99m)Tc(CO)(3)-Cip and (99m)Tc(CO)(3)-NFT, comparable to the behaviour with (99m)Tc(v)O-Cip. These results encouraged us for further development of infection imaging radiopharmaceuticals based on the (99m)Tc-tricarbonyl core.

Various routes of administration of (99m)Tc-labeled synthetic lactoferrin antimicrobial peptide hLF 1-11 enables monitoring and effective killing of multidrug-resistant Staphylococcus aureus infections in mice

The synthetic antimicrobial peptide representative of the first 11 N-terminal amino acids of human lactoferrin (hLF 1-11) kills multidrug-resistant Staphylococcus aureus (MRSA). This study displays antimicrobial activity of hLF 1-11, via various routes of administration, against MRSA infections in mice. Radiolabeling hLF 1-11 with technetium-99m ((99m)Tc-hLF 1-11) enables scintigraphic monitoring directly after administration. (99m)Tc-hLF 1-11 was taken up by the gall bladder, intestines, and kidneys. Most of the radioactivity was captured in the urinary bladder and about 1% of the injected dose accumulated into infected thigh muscles. At 2 or 24h after either intravenously, subcutaneously, intraperitoneally, or orally injected a single dose of 0.04 mg/kg hLF 1-11 in mice significantly reduced (20-60 times) the number of viable MRSA. In a dose-response setting in immunocompetent mice maximum bactericidal effects (10,000 times reduction) of intravenously injected (99m)Tc-hLF 1-11 was seen with 40 mg/kg whereas the same dose of orally administered (99m)Tc-hLF 1-11 induced about approximately 100 times reduction. In conclusion, intravenously and orally administrated (99m)Tc-hLF 1-11 accumulates in infected tissues and is highly effective against experimental infections with MRSA. Moreover, scintigraphy is an excellent tool to study the pharmacology of experimental compounds and to determine the uptake in infected tissues.

[131I]FIAU labeling of genetically transduced, tumor-reactive lymphocytes: cell-level dosimetry and dose-dependent toxicity

PURPOSE

Donor T cells have been shown to be reactive against and effective in adoptive immunotherapy of Epstein-Barr virus (EBV) lymphomas which develop in some leukemia patients post marrow transplantation. These T cells may be genetically modified by incorporation of a replication-incompetent viral vector (NIT) encoding both an inactive mutant nerve growth factor receptor (LNGFR), as an immunoselectable surface marker, and a herpes simplex virus thymidine kinase (HSV-TK), rendering the cells sensitive to ganciclovir. The current studies are based on the selective HSV-TK-catalyzed trapping (phosphorylation) of the thymidine analog [(131)I]-2'-fluoro-2'-deoxy-1-beta-D-arabinofuransyl-5-iodo-uracil (FIAU) as a means of stably labeling such T cells for in vivo trafficking (including tumor targeting) studies. Because of the radiosensitivity of lymphocytes and the potentially high absorbed dose to the nucleus from intracellular (131)I (even at tracer levels), the nucleus absorbed dose (D ( n )) and dose-dependent immune functionality were evaluated for NIT(+) T cells labeled ex vivo in [(131)I]FIAU-containing medium.

METHODS

Based on in vitro kinetic studies of [(131)I]FIAU uptake by NIT(+) T cells, D ( n ) was calculated using an adaptation of the MIRD formalism and the recently published MIRD cellular S factors. Immune cytotoxicity of [(131)I]FIAU-labeled cells was assayed against (51)Cr-labeled target cells [B-lymphoblastoid cells (BLCLs)] in a standard 4-h release assay.

RESULTS AND CONCLUSION

At median nuclear absorbed doses up to 830 cGy, a (51)Cr-release assay against BLCLs showed no loss of immune cytotoxicity, thus demonstrating the functional integrity of genetically transduced, tumor-reactive T cells labeled at this dose level for in vivo cell trafficking and tumor targeting studies.

Radiochemical and biological characteristics of 99mTc-UBI 29-41 for imaging of bacterial infections

A technetium-99m-labeled peptide derived from ubiquicidine, further referred to as 99mTc-UBI 29-41, targets bacterial and fungal infections, but not sterile inflammatory processes, in experimental animals. This paper reports on the radiochemical and biological features of this radioactive agent and the importance of the amino acid sequence of UBI 29-41 for imaging of infections. Radiochemical analyses of 99mTc-UBI 29-41 and a radiolabeled scrambled version of this peptide, i.e. 99mTc-Sc-UBI 29-41, revealed that both peptides were labeled rapidly (within 10 min) and effectively with little colloid formation (less than 5% of the total radioactivity) and very little free pertechnetate (or radioactive intermediates) in the preparations containing radiolabeled peptide. Furthermore, association of the peptides with bacteria could be competed with excess unlabeled peptide and this association proved to be temperature-dependent. Based on this in vitro data we concluded that labeling of peptides with 99mTc by this direct method is rapid, efficient, and safe. Scintigraphy demonstrated that radioactivity is rapidly removed from the circulation (half-lifes of UBI 29-41 and Sc-UBI 29-41 were 16 and 21 min, respectively) mainly by renal clearance. Analysis of murine blood revealed that only a small proportion of the intravenously injected 99mTc-peptides is associated with blood cells. Although both radiolabeled peptides accumulated rapidly at sites of infection, the values for 99mTc-UBI 29-41 were higher (P < 0.05) than for 99mTc-Sc-UBI 29-41. Moreover, injection of excess unlabeled UBI 29-41, but not Sc-UBI 29-41, into Staphylococcus aureus-infected mice prior to injection of 99mTc-UBI 29-41 significantly (P < 0.05) reduced the accumulation of this radiopharmaceutical at the site of infection. In addition, we observed significantly (P < 0.01) higher amounts of 99mTc-UBI 29-41 at the site of infection in mice using a carrier-free radiolabeled UBI 29-41 as compared with unpurified preparations containing radiolabeled UBI 29-41. This in vivo data indicates that the amino acid sequence of 99mTc-UBI 29-41 contributes to its accumulation at the site of infection.

Iodine-123 labelled radiopharmaceuticals and single-photon emission tomography: a natural liaison

Most nuclear medicine departments possess one or more imaging apparatuses for single-photon emission tomography (SPET). Molecules of biological interest to assess metabolism and receptor function are often labelled with 123I, which allows proper SPET imaging. The various methods for radiolabelling are reviewed. As the biological integrity of these agents has been demonstrated for numerous radiopharmaceuticals, the purpose of this review is to summarize the efficacy in various fields of medicine, including the imaging of tumours, infection, myocardium and cerebrum.