99mTc-Doxycycline hyclate: a new radiolabeled antibiotic for bacterial infection imaging

Radiolabeling and preclinical animal model evaluation of DTPA coupled 99mTc-labelled flutamide complex ([99mTc]DTPA-FLUT) as a potential radiotracer for cancer imaging

BACKGROUND

Advances in molecular imaging strategies have had an effect on precise diagnosis and treatment. Research has been intensified to develop more effective and versatile radiopharmaceuticals to uplift diagnostic efficiency and, consequently, the treatment.

PURPOSE

To label the flutamide (FLUT) coupled with diethylenetriamine pentaacetate (DTPA) with technetium-99 m (99mTc) and to evaluate its binding efficiency with rhabdomyosarcoma (RMS) cancer cells.

MATERIAL AND METHODS

Radiolabeling of FLUT with 185 MBq freshly eluted 99mTcO4-1 was carried out via DTPA bifunctional chelating agent using stannous chloride reducing agent at pH 5. The labeled compound was assessed for its purity using chromatography analysis, stability in saline and blood serum, AND charge using paper electrophoresis. Normal biodistribution was studied using a mouse model, while binding affinity with RMS cancer cells was studied using an internalization assay. The in vivo accumulation of RMS cancer cells in a rabbit model was monitored using a SPECT gamma camera.

RESULTS

Radiolabeling reaction displayed a pharmaceutical yield of 97% and a stability assay showed >95% intact radiopharmaceutical up to 6 h in saline and blood serum. In vitro internalization studies showed the potential of [99mTc]DTPA-FLUT to enter into cancer cells. This biodistribution study showed rapid blood clearance and minimum uptake by body organs, and scintigraphy displayed the [99mTc]DTPA-FLUT uptake by lesion, induced by RMS cancer cell lines in rabbit.

CONCLUSION

Stable, newly developed [99mTc]DTPA-FLUT seeks its way to internalize into RMS cancer cells, indicating it could be a potential candidate for the diagnosis of RMS cancer.

Recent Advancements in Radiopharmaceuticals for Infection Imaging

COVID-19 pandemic has heightened the interest toward diagnosis and treatment of infectious diseases. Nuclear medicine, with its powerful scintigraphic, single photon emission computer tomography (SPECT), and positron emission tomography (PET) imaging modalities, has always played an important role in diagnosis of infections and distinguishing them from the sterile inflammation. In addition to the clinically available radiopharmaceuticals, there has been a decades-long effort to develop more specific imaging agents with some examples being radiolabeled antibiotics and antimicrobial peptides for bacterial imaging, radiolabeled antifungals for fungal infections imaging, radiolabeled pathogen-specific antibodies, and molecular engineered constructs. In this chapter, we discuss some examples of the work published in the last decade on developing nuclear imaging agents for bacterial, fungal, and viral infections to generate more interest among nuclear medicine community toward conducting clinical trials of these novel probes, as well as toward developing novel radiotracers for imaging infections.

Current Status of SPECT Radiopharmaceuticals for Specific Bacteria Imaging

Imaging infection still represents a challenge for researchers. Despite nuclear medicine (NM) offers valuable tools able to discriminate between infections and inflammation, there is an unmet clinical need to develop new strategies able to specifically target the causative pathogen, to select the best antimicrobial treatment for each patient and to accurately assess therapeutic efficacy. These aspects are commonly addressed by microbiology or histology but the diagnosis often relies on invasive procedures that are prone to contamination or sample bias and do not reflect the spatial heterogeneity of the infective process. Therefore, in the era of personalized medicine and treatment, a lot of efforts are in play to improve a personalized diagnosis. Molecular imaging is an ideal candidate for this purpose and, indeed, research is going fast to this direction aiming to find more selective and proper antimicrobial treatments and to overcome broad-spectrum antibiotic use, which still represents the major cause of bacterial drug-resistance. Several approaches for specifically image bacteria have been proposed and provided encouraging perspectives in preclinical studies. Nevertheless, the majority of these promising approaches are still confined in "bench stages" and crucial issues still need to be addressed before their translation in clinical practice. This review will focus on radiolabeled antibiotics for SPECT imaging of bacteria, their mechanisms of action, their potentiality and limitations for "bed-side" applications.

Doxycycline hyclate stimulates inducible nitric oxide synthase and arginase imbalance, potentiating inflammatory and oxidative lung damage in schistosomiasis

BACKGROUND

We investigated the relationship between inducible nitric oxide synthase (iNOS) and arginase pathways, cytokines, macrophages, oxidative damage and lung granulomatous inflammation in S. mansoni-infected and doxycycline-treated mice.

METHODS

Swiss mice were randomized in four groups: (i) uninfected, (ii) infected with S. mansoni, (iii) infected + 200 mg/kg praziquantel (Pzt), (iv) and (v) infected + 5 and 50 mg/kg doxycycline. Pzt (reference drug) was administered in a single dose and doxycycline for 60 days.

RESULTS

S. mansoni-infection determined extensive lung inflammation, marked recruitment of M2 macrophages, cytokines (IL-4, IL-5, IFN-γ, TNF-α) upregulation, intense eosinophil peroxidase (EPO) levels, arginase expression and activity, reduced iNOS expression and nitric oxide (NO) production. The higher dose of doxycycline aggravated lung granulomatous inflammation, downregulating IL-4 levels and M2 macrophages recruitment, and upregulating iNOS expression, EPO, NO, IFN-γ, TNF-α, M1 macrophages, protein carbonyl and malondialdehyde tissue levels. The number and size of granulomas in doxycycline-treated animals was higher than untreated and Pzt-treated mice. Exudative/productive granulomas were predominant in untreated and doxycycline-treated animals, while fibrotic/involutive granulomas were more frequent in Pzt-treated mice. The reference treatment with Pzt attenuated all these parameters.

CONCLUSION

Our findings indicated that doxycycline aggravated lung granulomatous inflammation in a dose-dependent way. Although Th1 effectors are protective against several intracellular pathogens, effective schistosomicidal responses are dependent of the Th2 phenotype. Thus, doxycycline contributes to the worsening of lung granulomatous inflammation by potentiating eosinophils influx and downregulating Th2 effectors, reinforcing lipid and protein oxidative damage in chronic S. mansoni infection.

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.

Highlights of the Latest Developments in Radiopharmaceuticals for Infection Imaging and Future Perspectives

COVID-19 pandemic has heightened the interest toward diagnosis and treatment of infectious diseases. Nuclear medicine with its powerful scintigraphic, single photon emission computer tomography (SPECT) and positron emission tomography (PET) imaging modalities has always played an important role in diagnosis of infections and distinguishing them from the sterile inflammation. In addition to the clinically available radiopharmaceuticals there has been a decades-long effort to develop more specific imaging agents with some examples being radiolabeled antibiotics and antimicrobial peptides for bacterial imaging, radiolabeled anti-fungals for fungal infections imaging, radiolabeled pathogen-specific antibodies and molecular engineered constructs. In this opinion piece, we would like to discuss some examples of the work published in the last decade on developing nuclear imaging agents for bacterial, fungal, and viral infections in order to generate more interest among nuclear medicine community toward conducting clinical trials of these novel probes, as well as toward developing novel radiotracers for imaging infections.

177Lu-doxycycline as potential radiopharmaceutical: electrochemical characterization, radiolabeling, and biodistribution in tumor-bearing mice

PURPOSE

Recent studies with doxycycline as adjuvant therapy to conventional chemotherapy have shown promising results in cancer therapy. The current study aimed to examine the capability of ¹⁷⁷Lu-labeled tetracycline ligand, doxycycline hyclate, to use as an anticancer agent.

MATERIALS AND METHODS

Doxycycline was radiolabeled with beta-emitting radioisotope ¹⁷⁷Lu. Complex formation and its interaction with DNA were investigated electrochemically. Binding of ¹⁷⁷Lu-doxycycline to CT 26 cell line was done. Biodistribution of ¹⁷⁷Lu-doxycycline was examined in healthy Wistar rats and CT26 colon carcinoma tumor-bearing mice by i.v. and i.p. administration, respectively.

RESULTS

Doxycycline hyclate was successfully radiolabeled with ¹⁷⁷Lu in high radiolabeling yield (>99%). The radiolabeled complex was stable in vitro in saline and human serum over 72 h. Non-radioactive Lu-doxycycline complex formation was demonstrated electrochemically as well. Intercalative interactions of the doxycycline and Lu-doxycycline with DNA were proved using simultaneously spectrophotometric and electrochemical methods. The binding of the radiolabeled complex with plasma proteins was 4.0 ± 0.4%. The partition coefficient showed the lipophilic nature of the complex similar to the free ligand. The binding curve demonstrates binding from 0.1 nM concentrations of ¹⁷⁷Lu-doxycycline, with half-binding estimated ∼100 nM. Biodistribution studies of ¹⁷⁷Lu-doxycycline in CT26 colon tumor-bearing mice showed a satisfactory accumulation rate in the tumor (2.88 ± 0.85% ID/g) 3 h after intraperitoneal injection. Both the hepatobiliary system and the urinary system were prominent as excretory routes of the radiolabeled complex.

CONCLUSION

Considering obtained results, ¹⁷⁷Lu-doxycycline complex, due to its excellent electrochemical and biological characteristics, with emphasis on the binding ability to DNA via intercalative interaction as well as significant accumulation in the tumor, is suitable for further in vivo studies to investigate its potential use in cancer treatment.

99m Tc-labeled antibiotics for infection diagnosis: Mechanism, action, and progress

Discovery of penicillin marked a turning point in the history of infection therapy which also led to the emergence of bacterial resistance. It is now 100 years to fight with ever-muted variants of pathogens by developing more and more antibiotics. Since 1987 to todate, no successful class of antibiotic was introduced; this three decade period is known as "the discovery void" period. While, the clinically approved antibiotics are gradually dying in front of bacterial resistance due to which bacterial infections are appearing leading cause of death and disability. Nuclear medicine imaging technique is the strongest modality to diagnose and follow-up of deep-seated and complicated infections. However, the selection of radiolabeled antimicrobial agents plays critical role in gaining sensitivity and specificity of the imaging results. This review comprises of two main sections; first section explains antibiotic targets, and second section explains the imaging efficacy of ^99m Tc-labeled antimicrobial agents against bacterial infection along with the emphasis on progress and update of ^99m Tc-labeled antibiotics as infection imaging probes. The review, in conclusion, could be an acceleration for radiopharmaceutical chemists for designing and developing ^99m Tc-labeled antimicrobial agents to improve infection imaging quality.

Targeted nanomedicines for the treatment of bone disease and regeneration

Targeted delivery by either passive or active targeting of therapeutics to the bone is an attractive treatment for various bone related diseases such as osteoporosis, osteosarcoma, multiple myeloma, and metastatic bone tumors. Engineering novel drug delivery carriers can increase therapeutic efficacy and minimize the risk of side effects. Developmnet of nanocarrier delivery systems is an interesting field of ongoing studies with opportunities to provide more effective therapies. In addition, preclinical nanomedicine research can open new opportunities for preclinical bone-targeted drug delivery; nevertheless, further research is needed to progress these therapies towards clinical applications. In the present review, the latest advancements in targeting moieties and nanocarrier drug delivery systems for the treatment of bone diseases are summarized. We also review the regeneration capability and effective delivery of nanomedicines for orthopedic applications.

Ciprofloxacin: from infection therapy to molecular imaging

Diagnosis of deep-seated bacterial infection remains a serious medical challenge. The situation is becoming more severe with the increasing prevalence of bacteria that are resistant to multiple antibiotic classes. Early efforts to develop imaging agents for infection, such as technetium-99m (^99mTc) labeled leukocytes, were encouraging, but they failed to differentiate between bacterial infection and sterile inflammation. Other diagnostic techniques, such as ultrasonography, magnetic resonance imaging, and computed tomography, also fail to distinguish between bacterial infection and sterile inflammation. In an attempt to bypass these problems, the potent, broad-spectrum antibiotic ciprofloxacin was labeled with ^99mTc to image bacterial infection. Initial results were encouraging, but excitement declined when controversial results were reported. Subsequent radiolabeling of ciprofloxacin with ^99mTc using tricarbonyl and nitrido core, fluorine and rhenium couldn't produce robust infection imaging agent and remained in discussion. The issue of developing a robust probe can be approached by reviewing the broad-spectrum activity of ciprofloxacin, labeling strategies, potential for imaging infection, and structure-activity (specificity) relationships. In this review we discuss ways to accelerate efforts to improve the specificity of ciprofloxacin-based imaging.

Development of Nanoemulsion Based Gel Loaded with Phytoconstituents for the Treatment of Urinary Tract Infection and in Vivo Biodistribution Studies

Purpose: A nanoemulsion based gel containing Polyphenon 60 (P60) and cranberry (CRB) has been developed to deliver via intravaginal route for the treatment of urinary tract infection.

Methods: Polyphenon 60 and cranberry were loaded in a single nanoemulsion gel (NBG) by ultra-sonication method and characterized for particle size, rheological properties, in vitro release and growth curve analysis. P60+CRB NBG were radiolabelled using technetium pertechnetate (^99mTc) to perform in vivo pharmacokinetic studies in animals.

Results: The finalized NE had a droplet size of 58±1 nm. In vitro release of 90.92 ± 0.6% in 8 hr for P60 and 99.39 ± 0.5% in 6 hr for CRB was observed in simulated vaginal fluid. Growth curve of E. coli indicated the inhibitory action of nanoemulsion based gel at the fifth hour of inoculation. Gamma scintigraphy studies on female Sprague-Dawley rats showed transport of nanoemulsion based gel from the vaginal cavity into the systemic circulation. Further, biodistribution studies with radiolabelled P60+CRB NBG showed significant higher uptake of radiolabelled actives by kidney (3.20±0.16) and urinary bladder (3.64±0.29), when administered intravaginally.

Conclusion: The findings suggested ^99mTc-P60+CRB NBG can potentially be transported through vaginal cavity and reach the target organs and showed effective distribution in organs affected in urinary tract infection

Technetium-99m based small molecule radiopharmaceuticals and radiotracers targeting inflammation and infection

^99mTc-labeled antibiotics, antifungal drugs, antimicrobial peptides and COX-2 inhibitors are comprehensively reviewed.

Imaging bacteria with radiolabelled quinolones, cephalosporins and siderophores for imaging infection: a systematic review

Bacterial infections are still one of the main causes of patient morbidity and mortality worldwide. Nowadays, many imaging techniques, like computed tomography or magnetic resonance imaging, are used to identify inflammatory processes, but, although they recognize anatomical modifications, they cannot easily distinguish bacterial infective foci from non bacterial infections. In nuclear medicine, many efforts have been made to develop specific radiopharmaceuticals to discriminate infection from sterile inflammation. Several compounds (antimicrobial peptides, leukocytes, cytokines, antibiotics…) have been radiolabelled and tested in vitro and in vivo, but none proved to be highly specific for bacteria. Indeed factors, including the number and strain of bacteria, the infection site, and the host condition may affect the specificity of tested radiopharmaceuticals. Ciprofloxacin has been proposed and intensively studied because of its easy radiolabelling method, broad spectrum, and low cost, but at the same time it presents some problems such as low stability or the risk of antibiotic resistance. Therefore, in the present review studies with ciprofloxacin and other radiolabelled antibiotics as possible substitutes of ciprofloxacin are reported. Among them we can distinguish different classes, such as cephalosporins, fluoroquinolones, inhibitors of nucleic acid synthesis, inhibitors of bacterial cell wall synthesis and inhibitors of protein synthesis; then also others, like siderophores or maltodextrin-based probes, have been discussed as bacterial infection imaging agents. A systematic analysis was performed to report the main characteristics and differences of each antibiotic to provide an overview about the state of the art of imaging infection with radiolabelled antibiotics.

Labeling and Selective Inactivation of Gram-Positive Bacteria Employing Bimodal Photoprobes with Dual Readouts

Carbohydrate-conjugated silicon(IV) phthalocyanines with bimodal photoactivity were developed as probes with both fluorescent labeling and photosensitizing capabilities, and the concomitant fluorescent labeling and photoinduced inactivation of Gram-positive and Gram-negative models was explored. The maltohexaose-conjugated photoprobe provides a dual readout to distinguish between both groups of pathogens, as only the Gram-positive species was inactivated, even though both appeared labeled with near-infrared luminescence. Antibiotic resistance did not hinder the phototoxic effect, as even the methicillin-resistant pathogen Staphylococcus aureus (MRSA) was completely photoinactivated. Time-resolved confocal fluorescence microscopy analysis suggests that the photoprobe sticks onto the outer rim of the microorganisms, explaining the resistance of Gram-negative species on the basis of their membrane constitution. The mannose-conjugated photoprobe yields a different readout because it is able to label and to inactivate only the Gram-positive strain.

Gamma scintigraphy and biodistribution of (99m)Tc-cefotaxime sodium in preclinical models of bacterial infection and sterile inflammation

(99m)Tc-cefotaxime sodium ((99m)Tc-CEF) was developed and standardized under varying conditions of reducing and antioxidant agent concentration, pH, radioactivity dose, and reducing agent type. Labeling studies were performed by changing the selected parameters one by one, and optimum labeling conditions were determined. After observing the conditions for maximum labeling efficiency and stability, lyophilized freeze dry kits were prepared accordingly. Simple method for radiolabeling of CEF with (99m)Tc has been developed and standardized. Labeling efficiency of (99m)Tc-CEF was assessed by both radio thin-layer chromatography and radio high-performance liquid chromatography and found higher than 90%. The labeled compound was found to be stable in saline and human serum up to 24 h. Two different freeze dry kits were developed and evaluated. Based on the data obtained from this study, both products were stable for 6 months with high labeling efficiency. The prepared cold kit was found sterile and pyrogen free. The bacterial infection and sterile inflammation imaging capacity of (99m)Tc-CEF was evaluated. Based on the in vivo studies, (99m)Tc-CEF has higher uptake in infected and inflamed thigh muscle than healthy thigh muscle.

Metal complexes containing natural and and artificial radioactive elements and their applications

Recent advances (during the 2007–2014 period) in the coordination and organometallic chemistry of compounds containing natural and artificially prepared radionuclides (actinides and technetium), are reviewed. Radioactive isotopes of naturally stable elements are not included for discussion in this work. Actinide and technetium complexes with O-, N-, N,O, N,S-, P-containing ligands, as well π-organometallics are discussed from the view point of their synthesis, properties, and main applications. On the basis of their properties, several mono-, bi-, tri-, tetra- or polydentate ligands have been designed for specific recognition of some particular radionuclides, and can be used in the processes of nuclear waste remediation, i.e., recycling of nuclear fuel and the separation of actinides and fission products from waste solutions or for analytical determination of actinides in solutions; actinide metal complexes are also usefulas catalysts forcoupling gaseous carbon monoxide, as well as antimicrobial and anti-fungi agents due to their biological activity. Radioactive labeling based on the short-lived metastable nuclide technetium-99m (^99mTc) for biomedical use as heart, lung, kidney, bone, brain, liver or cancer imaging agents is also discussed. Finally, the promising applications of technetium labeling of nanomaterials, with potential applications as drug transport and delivery vehicles, radiotherapeutic agents or radiotracers for monitoring metabolic pathways, are also described.