Medicinal (Radio) Chemistry: Building Radiopharmaceuticals for the Future

Radiopharmaceuticals are increasingly playing a leading role in diagnosing, monitoring, and treating disease. In comparison with conventional pharmaceuticals, the development of radiopharmaceuticals does follow the principles of medicinal chemistry in the context of imaging-altered physiological processes. The design of a novel radiopharmaceutical has several steps similar to conventional drug discovery and some particularity. In the present work, we revisited the insights of medicinal chemistry in the current radiopharmaceutical development giving examples in oncology, neurology, and cardiology. In this regard, we overviewed the literature on radiopharmaceutical development to study overexpressed targets such as prostate-specific membrane antigen and fibroblast activation protein in cancer; β-amyloid plaques and tau protein in brain disorders; and angiotensin II type 1 receptor in cardiac disease. The work addresses concepts in the field of radiopharmacy with a special focus on the potential use of radiopharmaceuticals for nuclear imaging and theranostics.

In vivo behavior of technetium-99m labeled ibuprofen in infection and inflamation animal models

OBJECTIVE

The objective of this study was to develop radiolabeled ibuprofen (99mTc-ibu) for imaging and discrimination of inflammation and infection and compare its biodistribution in two different animal models.

SIGNIFICANCE

The development of radiolabeled ibuprofen as an imaging agent for inflammation and infection may have significant clinical implications for the diagnosis and management of various inflammatory and infectious diseases. This study provides a promising approach to the detection of sterile infections.

METHODS

Ibuprofen was radiolabeled with 99mTc using the stannous chloride method with a yield of 99.05 ± 0.83% (n = 5). The in vivo biological behavior of radiolabeled ibuprofen was determined in Wistar albino rat models of sterile inflammation and bacterial infection with Staphylococcus aureus gram-positive bacteria. Biodistribution studies were carried out at different time points, and the results were compared between the two animal models.

RESULTS

The uptake of 99mTc-ibu in sterile inflammation sites at all time points was higher than that in the infection sites. This suggests that 99mTc-ibu can be used to discriminate between sterile inflammation and bacterial infection.

CONCLUSIONS

The results of this study suggest that the detection of sterile infections with 99mTc-ibu is possible and highly encouraging.

Preparation, biological evaluation and radiolabeling of [99mTc]-technetium tricarbonyl procainamide as a tracer for heart imaging in mice

This study focuses on the synthesis and preliminary bio-evaluation of [99mTc]-technetium tricarbonyl procainamide ([99mTc]-technetium tricarbony PA) as a viable cardiac imaging agent. The compound, [99mTc]-technetium tricarbony PA, was synthesized by labelling procainamide with a [99mTc]-technetium tricarbonyl core, yielding a high radiochemical yield and radiochemical purity of 98%. Under optimal circumstances, high radiochemical yield and purity were obtained utilizing [99mTc]-technetium tricarbonyl core within 30 min of incubation at pH 9, 200 µg substrate concentration, and 100 °C reaction temperature. The heart showed a high absorption of 32.39 ± 0.88% of the injected dose/g organ (ID/g), confirming the suitability of [99mTc]-technetium tricarbonyl PA as a viable complex for heart imaging.

Enhancement of the thermal and physicochemical properties of styrene butadiene rubber composite foam using nanoparticle fillers and electron beam radiation

This study investigates the physicochemical and thermal properties of styrene–butadiene rubber (SBR) nanocomposite foam. Nano-calcium carbonate (CaCO3) was prepared from eggshells (ESs) waste. Sponge rubber nanocomposites were prepared and were irradiated by electron beam (EB) radiation at 25, 75, and 150 kGy. Their physicochemical properties, including foam density, compression set (CS), hardness, abrasion loss, and expansion ratio, and their thermal stability were investigated. The physicochemical properties were enhanced by adding 2.5 phr of a foaming agent. Among the composites examined, the foam composites containing nano-CaCO3 had the lowest CS, abrasion loss, and expansion ratio and the highest hardness and foam density. The results confirmed that the thermal stability was improved by incorporating nano-CaCO3 into the SBR foam and as the radiation dose increased. The sponge containing nanoclay demonstrated an intermediate behavior, whereas that with CaCO3 nanoparticles showed low average cell diameter and size and high cell wall thickness. The radiation process enhanced the foam density, CS, abrasion loss, hardness, and thermal property of the developed nanocomposites by inducing the formation of intermolecular crosslinks within the composite matrix. The results showed that physicochemical properties improved by increasing the radiation dose at 25 kGy.

Radioiodination of balsalazide, bioevaluation, and characterization as a highly selective radiotracer for imaging of ulcerative colitis in mice

This work focuses on tracking ulcerative colitis in mice. High labeling yield and radiochemical purity were achieved for the formation of a [^125/131 I]balsalazide radiotracer at optimum conditions of oxidizing agent content (chloramines-T [Ch-T], 75 μg), substrate amount (100 μg), pH of reaction mixture (6), reaction time (30 min), and temperature (37°C), using radioactive iodine-125 (200-450 MBq). The radiolabeled compound, [^125/131 I]balsalazide, was stable in serum and saline solution during 24 h. Balsalazide is acting as a peroxisome proliferator-activated receptor (PPARγ). Biodistribution studies were carried in normal and ulcerated colon mice. High uptake of 75 ± 1.90% injected dose/g organ (ID/g) observed in ulcerated mice confirmed the suitability of [¹³¹ I]balsalazide as a novel radiotracer for ulcerative colitis imaging in mice.

Preparation, characterization, and bioevaluation of 99mTc-famotidine as a selective radiotracer for peptic ulcer disorder detection in mice

This work focuses on tracking peptic ulcer localized in mice. The formation of a [99mTc]dithiocarbamate of famotidine complex at optimum conditions of reaction temperature (37 °C), reaction time (30 min), pH of the reaction mixture (5), amount of substrate (100 µg), amount of reducing agent (tin (II) content, 50 µg), was achieved using radioactive Tc-99m (250–400 MBq), with labelling yield of 98% and high radiochemical purity. The in-vitro stability of [99mTc]dithiocarbamate of famotidine complex was shown to be high in rat serum for up to 8 h. Normal and ulcerated mice were used in biodistribution studies. Famotidine works by blocking histamine-2-receptor antagonists (H2RAs). The high absorption of [99mTc]dithiocarbamate of famotidine complex in stomach in amount of 27.15% injected dose/g organ (ID/g) observed in ulcerated mice for up to 24 h demonstrated its usefulness as a novel radiotracer for stomach imaging.

Radioiodinated esomeprazole as a model for peptic ulcer localization

This work focuses on tracking stomach ulcer localized in mice. High labeling yield and radiochemical purity were achieved for the formation of a [125I]esomeprazole radiotracer at optimum conditions of oxidizing agent content (chloramines-T (Ch-T), 100 μg), substrate amount (Esom, 100 μg), pH of reaction mixture (6), reaction time (30 min) and temperature (37 °C), using radioactive iodine-125 (200–450 MBq). The radiolabeled compound, [125I]esom, was stable in serum and saline solution during 24 h. Esom is acting as a histamine-2-receptor antagonist (H2RA). Biodistribution studies were carried in normal and ulcerated mice. High uptake of 78.12 ± 0.80% injected dose/g organ (ID/g) observed in ulcerated mice confirmed the suitability of [125I]esomeprazole as a novel radiotracer for stomach imaging.

Radioiodination and biological evaluation of irbesartan as a tracer for cardiac imaging

Irbesartan was labeled using 125I or 131I with N-bromosuccinimide (NBS) as an oxidizing agent. A lot of operators such as, quantity of substrate, the quantity of oxidizing agent, reaction temperature, reaction time, and pH of reaction medium were studied to optimize high radiochemical yield of [125I]IodoIrbesartan ([125I]Irb.). The preclinical evaluation of IodoIrbesartan in experimental mice indicated high accumulation in target organ of heart with a high heart/blood ratio of 12.85 at 30 min post-injection. This study indicates the suitability of [125I]IodoIrbesartan ([125I]Irb.) for cardiac imaging.