Design, Synthesis and Molecular Modeling Study of Radiotracers Based on Tacrine and Its Derivatives for Study on Alzheimer’s Disease and Its Early Diagnosis

From 1993 to 2013, tacrine was an approved drug for Alzheimer’s disease. Due to its strong inhibitory properties towards cholinesterase, tacrine causes an increase in the level of the neurotransmitter acetylcholine in the cholinergic system of the central nervous system. This work presents a review of articles in which tacrine or its derivatives labeled with the radionuclides 3H, 11C, 14C, 123I, 99mTc and 68Ga were used as vectors in radiotracers dedicated to the diagnosis of Alzheimer’s disease. The possibility of clinical applications of the obtained radiopreparations was assessed by analyzing their physicochemical properties, ability to cross the blood–brain barrier and the level of uptake in the brain. Based on these data, it was shown that radiopreparations based on the tacrine molecule or its very close analogues retain the ability to cross the blood–brain barrier, while radiopreparations containing a more modified tacrine molecule (connected via a linker to a radionuclide chelator) lose this ability. This is probably the result of the addition of a chelator, which significantly increases the size of the radiopreparation and reduces its lipophilicity. Computer docking studies of tacrine derivatives and/or radiopreparations showed how these compounds bind to the active sites of acetyl- and butyrylcholinesterase

The Significance of NK1 Receptor Ligands and Their Application in Targeted Radionuclide Tumour Therapy

To date, our understanding of the Substance P (SP) and neurokinin 1 receptor (NK1R) system shows intricate relations between human physiology and disease occurrence or progression. Within the oncological field, overexpression of NK1R and this SP/NK1R system have been implicated in cancer cell progression and poor overall prognosis. This review focuses on providing an update on the current state of knowledge around the wide spectrum of NK1R ligands and applications of radioligands as radiopharmaceuticals. In this review, data concerning both the chemical and biological aspects of peptide and nonpeptide ligands as agonists or antagonists in classical and nuclear medicine, are presented and discussed. However, the research presented here is primarily focused on NK1R nonpeptide antagonistic ligands and the potential application of SP/NK1R system in targeted radionuclide tumour therapy

Common Shortcomings in Study on Radiopharmaceutical Design Research: A Case Study of 99mTc-Labelled Methotrexate

The aim of the work carried out was to draw attention to shortcomings that often appear at the stage of designing new radiopharmaceuticals. Based on a case study of 99mTc-labelled methotrexate, this article describes frequent mistakes or misconceptions present not only in the referenced studies, but also in numerous radiopharmaceutical studies. The recommendations provided in this article highlight fundamental aspects of the credibility of radiopharmaceutical scientific research leading to the reliable results

Synthesis, Physicochemical and Biological Study of Gallium-68- and Lutetium-177-Labeled VEGF-A₁₆₅/NRP-1 Complex Inhibitors Based on Peptide A7R and Branched Peptidomimetic

Neuropilin-1 (NRP-1) is a surface receptor found on many types of cancer cells. The overexpression of NRP-1 and its interaction with vascular endothelial growth factor-165 (VEGF165) are associated with tumor growth and metastasis. Therefore, compounds that block the VEGF165/NRP-1 interaction represent a promising strategy to image and treat NRP-1-related pathologies. The aim of the presented work was to design and synthesize radioconjugates of two known peptide-type inhibitors of the VEGF165/NRP-1 complex: A7R peptide and its shorter analog, the branched peptidomimetic Lys(hArg)-Dab-Pro-Arg. Both peptide-type inhibitors were coupled to a radionuclide chelator (DOTA) via a linker (Ahx) and so radiolabeled with Ga-68 and Lu-177 radionuclides, for diagnostic and therapeutic uses, respectively. The synthesized radioconjugates were tested for their possible use as theranostic-like radiopharmaceuticals for the imaging and therapy of cancers that overexpress NRP-1. The obtained results indicate good efficiency of the radiolabeling reaction and satisfactory stability, at least 3t1/2 for the 68Ga- and 1t1/2 for the 177Lu-radiocompounds, in solutions mimicking human body fluids. However, enzymatic degradation of both the studied inhibitors caused insufficient stability of the radiocompounds in human serum, indicating that further modifications are needed to sufficiently stabilize the peptidomimetics with inhibitory properties against VEGF165/NRP-1 complex formation

The Role of VEGF Receptors as Molecular Target in Nuclear Medicine for Cancer Diagnosis and Combination Therapy

One approach to anticancer treatment is targeted anti-angiogenic therapy (AAT) based on prevention of blood vessel formation around the developing cancer cells. It is known that vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptors (VEGFRs) play a pivotal role in angiogenesis process; hence, application of angiogenesis inhibitors can be an effective approach in anticancer combination therapeutic strategies. Currently, several types of molecules have been utilised in targeted VEGF/VEGFR anticancer therapy, including human VEGF ligands themselves and their derivatives, anti-VEGF or anti-VEGFR monoclonal antibodies, VEGF binding peptides and small molecular inhibitors of VEGFR tyrosine kinases. These molecules labelled with diagnostic or therapeutic radionuclides can become, respectively, diagnostic or therapeutic receptor radiopharmaceuticals. In targeted anti-angiogenic therapy, diagnostic radioagents play a unique role, allowing the determination of the emerging tumour, to monitor the course of treatment, to predict the treatment outcomes and, first of all, to refer patients for AAT. This review provides an overview of design, synthesis and study of radiolabelled VEGF/VEGFR targeting and imaging agents to date. Additionally, we will briefly discuss their physicochemical properties and possible application in combination targeted radionuclide tumour therapy

Application of Neurokinin-1 Receptor in Targeted Strategies for Glioma Treatment. Part I: Synthesis and Evaluation of Substance P Fragments Labeled with 99mTc and 177Lu as Potential Receptor Radiopharmaceuticals

Gliomas, particularly WHO grade IV glioblastoma multiforme, are one of the most common and aggressive primary tumors of the central nervous system. The neuropeptide, substance P (SP), is the physiological ligand of the neurokinin-1 (NK-1) receptor that is consistently overexpressed in glioblastoma cells. The aim of this work was to study physico-chemical and biological properties of different SP analogues labeled with technetium-99m and lutetium-177 radionuclides. The synthesized compounds were characterized in vitro by partition coefficients (logP) and their stability was investigated in various physiological solutions. Biological properties (Kd, Bmax) were characterized using the U373 MG cell line. The obtained lipophilicity values of the [99mTc]NS3/CN-SP and [177Lu]DOTA-SP radiobioconjugates were in the range of −0.3 to +0.6 and −2.5 to −5.0, respectively. The studied radiobioconjugates were stable in PBS buffer and CSF, as well as in 10 mM histidine and/or cysteine solutions whereas in human serum showed enzymatic biodegradation. [177Lu]DOTA-[Thi8,Met(O2)11]SP(1–11), [177Lu]DOTA-SP(4–11) and [177Lu]DOTA-[Thi8,Met(O2)11]SP(5–11) radiobioconjugates bound specifically to NK-1 receptors expressed on glioblastoma cells with affinity in the nanomolar range. To conclude, the shorter analogues of SP can be used as vectors, nevertheless they still do not fulfil all requirements for preparations in nuclear medicine

Scandium-44 Radiolabeled Peptide and Peptidomimetic Conjugates Targeting Neuropilin-1 Co-Receptor as Potential Tools for Cancer Diagnosis and Anti-Angiogenic Therapy

Pathological angiogenesis, resulting from an imbalance between anti- and pro-angiogenic factors, plays a pivotal role in tumor growth, development and metastasis. The inhibition of the angiogenesis process by the VEGF/VEGFR-2/NRP-1 pathway raises interest in the search for such interaction inhibitors for the purpose of the early diagnosis and treatment of angiogenesis-dependent diseases. In this work we designed and tested peptide-based radiocompounds that selectively bind to the neuropilin-1 co-receptor and prevent the formation of the pro-angiogenic VEGF-A165/NRP-1 complex. Three biomolecules, A7R and retro-inverso DR7A peptides, and the branched peptidomimetic Lys(hArg)-Dab-Pro-Arg (K4R), conjugated with macrocyclic chelator through two linkers’ types, were labeled with theranostic scandium-44 radionuclide, and studied in vitro as potential targeted radiopharmaceuticals. ELISA (enzyme-linked immunosorbent assay) studies showed no negative effect of the introduced biomolecules’ changes and high NRP-1 affinity in the case of A7R- and K4R-radiocompounds and a lack affinity for DR7A-radiocompounds. All radiopeptides showed a hydrophilic nature as well as high stability against ligand exchange reactions in cysteine/histidine solutions. Unfortunately, all radiocompounds showed unsatisfactory nano-scale stability in human serum, especially for use as therapeutic radioagents. Further work is ongoing and focused on the search for angiogenesis inhibitors that are more human serum stable

Novel NK1R-Targeted ⁶⁸Ga-/¹⁷⁷Lu-Radioconjugates with Potential Application against Glioblastoma Multiforme: Preliminary Exploration of Structure–Activity Relationships

Locoregionally administered, NK1 receptor (NK1R) targeted radionuclide therapy is a promising strategy for the treatment of glioblastoma multiforme. So far, the radiopharmaceuticals used in this approach have been based on the endogenous agonist of NK1R, Substance P or on its close analogues. Herein, we used a well-known, small molecular NK1R antagonist, L732,138, as the basis for the radiopharmaceutical vector. First, 14 analogues of this compound were evaluated to check whether extending the parent structure with linkers of different lengths would not deteriorate the NK1R binding. The tested analogues had affinity similar to or better than the parent compound, and none of the linkers had a negative impact on the binding. Next, five DOTA conjugates were synthesized and used for labelling with 68Ga and 177Lu. The obtained radioconjugates turned out to be fairly lipophilic but showed rather limited stability in human plasma. Evaluation of the receptor affinity of the (radio)conjugates showed that neither the chelator nor the metal negatively impacts the NK1R binding. The 177Lu-radioconjugates exhibited the binding characteristics towards NK1R similar or better than that of the 177Lu-labelled derivative of Substance P, which is in current clinical use. The experimental results presented herein, along with their structural rationalization provided by modelling, give insight for the further molecular design of small molecular NK1R-targeting vectors

Physicochemical and Biological Study of 99mTc and 68Ga Radiolabelled Ciprofloxacin and Evaluation of [99mTc]Tc-CIP as Potential Diagnostic Radiopharmaceutical for Diabetic Foot Syndrome Imaging

This paper presents the application of ciprofloxacin as a biologically active molecule (vector) for delivering diagnostic radiopharmaceuticals to the sites of bacterial infection. Ciprofloxacin-based radioconjugates containing technetium-99m or gallium-68 radionuclides were synthesised, and their physicochemical (stability, lipophilicity) and biological (binding study to Staphylococcus aureus and Pseudomonas aeruginosa) properties were investigated. Both the tested radiopreparations met the requirements for radiopharmaceuticals, and technetium-99m-labelled ciprofloxacin turned out to be a good radiotracer for the tomography of diabetic foot syndrome using SPECT