The synthesis of pteroyl-lys conjugates and its application as Technetium-99m labeled radiotracer for folate receptor-positive tumor targeting

New Bioconjugated Technetium and Rhenium Folates Synthesized by Transmetallation Reaction with Zinc Derivatives

The zinc dithiocarbamates functionalized with folic acid 2_Zn and 3_Zn were synthesized with a simple straightforward method, using an appropriated folic acid derivative and a functionalized zinc dithiocarbamate (1_Zn). Zinc complexes 2_Zn and 3_Zn show very low solubilities in water, making them useful for preparing Tc-99m radiopharmaceuticals with a potentially high molar activity. Thus, the transmetallation reaction in water medium between the zinc complexes 2_Zn or 3_Zn and the cation fac-[^99mTc(H₂O)₃(CO)₃]⁺, in the presence of the monodentate ligand TPPTS, leads to the formation of the 2 + 1 complexes fac-[^99mTc(CO)₃(SS)(P)] bioconjugated to folic acid (2_Tc and 3_Tc). In spite of the low solubility of 2_Zn and 3_Zn in water, the reaction yield is higher than 95%, and the excess zinc reagent is easily removed by centrifugation. The Tc-99m complexes were characterized by comparing their HPLC with those of the homologous rhenium complexes (2_Re and 3_Re) previously synthesized and characterized by standard methods. Preliminary in vivo studies with 2_Tc and 3_Tc indicate low specific binding to folate receptors. In summary, Tc-99m folates 2_Tc and 3_Tc were prepared in high yields, using a one-pot transmetallation reaction with low soluble zinc dithiocarbamates (>1 ppm), at moderate temperature, without needing a subsequent purification step.

Bioconjugated technetium carbonyls by transmetalation reaction with zinc derivatives

The transmetalation reaction between zinc dithiocarbamates functionalized with organic groups and the cation fac-[^99mTc(H₂O)₃(CO)₃]⁺ has been studied as a new strategy to bind biomolecules to this radionuclide for preparing radiopharmaceuticals with high molar activity. All complexes were obtained in high yields by heating at moderate temperatures and without subsequent purification. The chemical identity was ascertained by HPLC comparison with the homologous rhenium complexes. Stability studies in cysteine solution and serum have shown a good stability of the coordination set fac-[^99mTc(CO)₃(SS)(P)]. Preliminary biological studies of the radiocomplex functionalized with D-(+)-glucosamine with carcinoma cells have been performed.

Development of Folate Receptor-Targeted PET Radiopharmaceuticals for Tumor Imaging-A Bench-to-Bedside Journey

The folate receptor-α (FR-α) is overexpressed in many epithelial cancers, including ovary, uterus, kidneys, breast, lung, colon and prostate carcinomas, but shows limited expression in normal tissues such as kidneys, salivary glands, choroid plexus and placenta. FR-α has therefore emerged as a promising target for the delivery of therapeutic and imaging agents to FR-positive tumors. A series of folate-based PET (positron emission tomography) radiopharmaceuticals have been developed for the selective targeting of FR-positive malignancies. This review provides an overview on the research progress made so far regarding the design, radiosynthesis and the utility of the folate-derived PET radioconjugates for targeting FR-positive tumors. For the most part, results from folate radioconjugates labeled with fluorine-18 (t_1/2 = 109.8 min) and gallium-68 (t_1/2 = 67.7 min) have been presented but folates labeled with "exotic" and new PET radionuclides such as copper-64 (t_1/2 = 12.7 h), terbium-152 (t_1/2 = 17.5 h), scandium-44 (t_1/2 = 3.97 h), cobalt-55 (t_1/2 = 17.5 h) and zirconium-89 (t_1/2 = 78.4 h) are also discussed. For tumor imaging, none of the reported PET radiolabeled folates reported to date has made the complete bench-to-bedside journey except [¹⁸F]AzaFol, which made it to patients with metastatic ovarian and lung cancers in a multicenter first-in-human trial. In the near future, however, we expect more clinical trials with folate-based PET radiopharmaceuticals given the increasing clinical interest in imaging and the treatment of FR-related malignancies.

Breast Tumor Targeting with PAMAM-PEG-5FU-99mTc As a New Therapeutic Nanocomplex: In In-vitro and In-vivo studies

Dendrimer-based targeted drug delivery, as an innovative polymeric drug-delivery system, is promising for cancer therapy. Folate receptors (FR) are overexpressed in many types of tumor cells, such as breast cell carcinomas, which allow folate-targeted delivery. Therefor polyethylene glycol (PEG) modified-PAMAM G4 dendrimers were functionalized with folic acid (FA), as targeting agent. Then, 5-FU (5-fluorouracil) and ^99mTc (technetium-99 m) as therapeutic agents were respectively loaded and conjugated to previous nano-complex (PEG-PAMAM G4-FA-5FU-^99mTc). The value of drug loading was calculated by TGA analysis (16.97%). Drug release profiles of PEG-PAMAM G4-FA-5FU-^99mTc and PEG-PAMAM G4-FA-5FU were evaluated. The radiochemical purity of PEG-PAMAM G4-FA-5FU-^99mTc and PEG-PAMAM G4-FA-^99mTc was obtained at >95% with excellent in-vitro and in-vivo stabilities. PEG-PAMAM G4-FA-5FU-^99mTc was synthesized and the stability studies were carried out by the ITLC methods in serum (86.67% and 83.75%) and PBS. Combinational therapy effects of 5-FU and ^99mTc containing nano-complexes were evaluated on 4 T1 (mouse breast cancer) and MDA-MB-231 (human breast adenocarcinoma) cancer cell lines. Excellent uptake values were obtained for FA-decorated nano-complexes on 4 T1 and MDA-MB-231 cell lines. Subsequently, tumor inhibition effects of PEG-PAMAM G4-FA-5FU-^99mTc and PEG-PAMAM G4-FA-5FU were evaluated using the breast tumor-bearing BALB/C mice. Graphical abstract Breast Tumor Targeting with PAMAM-PEG-5FU- ^99mTc As a New Therapeutic Nanocomplex: in In-vitro and In-vivo Studies was presented. This targeted drug delivery system can significantly increase the efficiency of cancer therapy, and reduce the treatment cost and time.

Antimicrobial activity of some novel 2-(2-iodophenylimino)-5-arylidenethiazolidin-4-one derivatives

Background

Infectious diseases, especially those caused by multidrug-resistant bacteria, are becoming a serious problem worldwide because of the lack of effective therapeutic agents. Moreover, most antifungal drugs exhibit low efficacy and high toxicity because of the similarity between fungal and human cells. These issues warrant the search for potential new agents.

Objectives

To synthesize potent 2-(2-iodophenylimino)-5-arylidenethiazolidin-4-one derivatives, improve the synthetic process, elucidate their structures, and determine their antimicrobial activity.

Methods

2-Iodoaniline was used as an initial reactant in a 3-step process for the synthesis of 2-(2-iodophenylimino)-5-arylidenethiazolidin-4-one derivatives, including an acylation reaction, a cyclization reaction, and aldol condensation reactions. The structures of the obtained derivatives were investigated and elucidated using spectral methods. Antimicrobial activity toward 5 bacterial strains and 2 fungal strains was determined using Kirby–Bauer and agar dilution methods.

Results

We successfully synthesized 12 novel compounds and elucidated their structures. The derivatives had no antifungal activities. By contrast, they showed remarkable antibacterial activities. Some of them with minimum inhibitory concentrations (MICs) ≤8 μg/mL in both Staphylococcus aureus and methicillin-resistant S. aureus.

Conclusions

A simple and flexible way to synthesize new compounds with a thiazolidin-4-one ring was determined. Some of these new compounds have outstanding effects with low MICs for bacteria. Their further investigation as therapeutic agents is warranted.

Development of a New FR-Targeting Agent 99mTc-HYNFA with Improved Imaging Contrast and Comparison of Multimerization and/or PEGylation Strategies for Radio-Folate Modification

This study aims to develop a new folate receptor (FR)-targeting agent for SPECT imaging with improved contrast and evaluate the modification strategies of multimerization and/or PEGylation in the development of new radio-folates. A series of novel folate derivatives have been synthesized and radiolabeled with ^99mTc using tricine and TPPTS as coligands. To better investigate their pharmacokinetics, cell uptake, biodistribution, and microSPECT/CT imaging were evaluated. Four radioligands displayed high KB cell uptake after incubation for 2 and 4 h. Presaturated with excess folic acid (FA) resulted in a significant blocking effect in KB cells, indicating specificity of these radioligands toward FR. Biodistribution and microSPECT imaging studies in KB tumor-bearing mice showed that the folate conjugate ^99mTc-HYNFA with poly(ethylene glycol) (PEG) and triazole linkage displayed the highest tumor uptake (16.30 ± 2.01 %ID/g at 2 h p.i. and 14.9 ± 0.62 %ID/g at 4 h p.i. in mice biodistribution) and best imaging contrast, indicating promising application prospect. More interestingly, the in vivo performance of this monomeric ^99mTc-HYNFA was much better than that of FA multimers and non-PEGylated monomers, suggesting that multimerization may not be a feasible method for the design of radio-folates. PEG linkage rather than FA multimerization should be taken into consideration in the development of folate-based radiopharmaceuticals in the future.

Synthesis and Evaluation of (99m)Tc-Labeled Dimeric Folic Acid for FR-Targeting

The folate receptor (FR) is overexpressed in a wide variety of human tumors. In our study, the multimeric concept was used to synthesize a dimeric folate derivative via a click reaction. The novel folate derivative (HYNIC-D₁-FA₂) was radiolabeled with ^99mTc using tricine and trisodium triphenylphosphine-3,3′,3″-trisulfonate (TPPTS) as coligands (^99mTc-HYNIC-D₁-FA₂) and its in vitro physicochemical properties, ex vivo biodistribution and in vivo micro-SPECT/CT imaging as a potential FR targeted agent were evaluated. It is a hydrophilic compound (log P = −2.52 ± 0.13) with high binding affinity (IC₅₀ = 19.06 nM). Biodistribution in KB tumor-bearing mice showed that ^99mTc-HYNIC-D₁-FA₂ had high uptake in FR overexpressed tumor and kidney at all time-points, and both of them could obviously be inhibited when blocking with free FA in the blocking studies. From the in vivo micro-SPECT/CT imaging results, good tumor uptake of ^99mTc-HYNIC-D₁-FA₂ was observed in KB tumor-bearing mice and it could be blocked obviously. Based on the results, this new radiolabeled dimeric FA tracer might be a promising candidate for FR-targeting imaging with high affinity and selectivity.

Synthesis and biological evaluation of (68) Ga-labeled Pteroyl-Lys conjugates for folate receptor-targeted tumor imaging

In order to develop novel (68) Ga-labeled PET tracers for folate receptor imaging, two DOTA-conjugated Pteroyl-Lys derivatives, Pteroyl-Lys-DOTA and Pteroyl-Lys-DAV-DOTA, were designed, synthesized and radiolabeled with (68) Ga. Biological evaluations of the two radiotracers were performed with FR-positive KB cell line and athymic nude mice bearing KB tumors. Both (68) Ga-DOTA-Lys-Pteroyl and (68) Ga-DOTA-DAV-Lys-Pteroyl exhibited receptor specific binding in KB cells in vitro. The tumor uptake values of (68) Ga-DOTA-Lys-Pteroyl and (68) Ga-DOTA-DAV-Lys-Pteroy were 10.06 ± 0.59%ID/g and 11.05 ± 0.60%ID/g at 2 h post-injection, respectively. Flank KB tumor was clearly visualized with (68) Ga-DOTA-DAV-Lys-Pteroyl by Micro-PET imaging at 2 h post-injection, suggesting the feasibility of using (68) Ga-labeled Pteroyl-Lys conjugates as a novel class of FR targeted probes.

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.

Novel 99mTc radiolabeled folate complexes with PEG linkers for FR-positive tumor imaging: synthesis and biological evaluation

The novel complex ^99mTc(FA-PEG2-HYNIC)(tricine/TPPTS) was clearly visualized at 120 min p.i. at the FR-positive tumor, highlighting its potential as an effective folate receptor tumor imaging agent.

Preparation and biological evaluation of (99m) TcN-labeled pteroyl-lys derivative as a potential folate receptor imaging agent

In order to develop a novel (99m) Tc-labeled folate receptor (FR) imaging agent, a dithiocarbamate derivative, pteroyl-lys-DTC, was synthesized and radiolabeled with (99m) Tc through the [(99m) TcN](2+) intermediate. The radiochemical purity of the corresponding (99m) Tc-complex, (99m) TcN-pteroyl-lys-DTC, was over 95% as measured by reversed-phase HPLC. The (99m) TcN complex was stable under physiological conditions. (99m) TcN-pteroyl-lys-DTC exhibited specific FR binding in FR-positive KB cells in vitro. The biodistribution in tumor-bearing mice showed that the (99m) TcN-labeled radiotracer had good uptake (3.56 ± 0.09%ID/g at 2 h postinjection) in FR-positive KB tumors, as well as in the kidneys (30.34 ± 3.53%ID/g at 2 h postinjection). After coinjection with excess folic acid, the uptake in tumor and kidneys was significantly blocked. The results indicated that (99m) TcN-pteroyl-lys-DTC was able to target the FR-positive tumor cells and tissues specifically both in vitro and in vivo.

A novel (68)Ga-labeled pteroic acid-based pet tracer for tumor imaging via the folate receptor

The folate receptor (FR) is a very attractive target in oncological imaging as it is overexpressed by a variety of cancer types, whereas the expression in healthy tissue is very limited. The synthesis of regioisomeric pure folic acid derivatives normally requires a regioselective approach and does not allow the use of native folic acid (FA). As the pharmacophore of FA is assumed to be pteroic acid, its use without the glutamic acid moiety may enable the possibility to considerably simplify the synthesis of a positron emission tomography (PET) tracer for FR imaging. In this work, DO3A-EA-Pte was successfully synthesized and labeled with (68)Ga. It is stable for up to 3 h in PBS and against transchelation by transferrin. It also displays a lipophilicity that allows the assumption that it will show favorable in vivo characteristics for FR imaging via PET.

Folate-based radiotracers for PET imaging--update and perspectives

The folate receptor (FR) is expressed in many tumor types, among those ovarian and lung cancer. Due to the high FR affinity of folic acid, it has been used for targeting of FR-positive tumors, allowing specific delivery of attached probes to the malignant tissue. Therefore, nuclear imaging of FR-positive cancer is of clinical interest for selecting patients who could benefit from innovative therapy concepts based on FR-targeting. Positron emission computed tomography (PET) has become an established technique in clinical routine because it provides an increased spatial resolution and higher sensitivity compared to single photon emission computed tomography (SPECT). Therefore, it is of critical importance to develop folate radiotracers suitable for PET imaging. This review article updates on the design, preparation and pre-clinical investigation of folate derivatives for radiolabeling with radioisotopes for PET. Among those the most relevant radionuclides so far are fluorine-18 (t_1/2: 110 min, E_avβ⁺: 250 keV) and gallium-68 (t_1/2: 68 min, E_av β⁺: 830 keV). Recent results obtained with new PET isotopes such as terbium-152 (t_1/2: 17.5 h, Eβ⁺: 470 keV) or scandium-44 (t_1/2: 3.97 h, E_av β⁺: 632 keV) are also presented and discussed. Current endeavors for clinical implementation of PET agents open new perspectives for identification of FR-positive malignancies in patients.