Laura Meléndez-Alafort

The management of rheumatoid arthritis and related inflammatory arthropathies is evolving from late structural assessment toward early molecular phenotyping of synovitis. Target-specific radiopharmaceuticals for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) now permit non-invasive detection of activated fibroblast-like synoviocytes, inflammatory macrophages, chemokine-driven immune-cell trafficking, angiogenesis, and mitochondrial stromal activation. This review analyzes the radiochemical basis of synovitis imaging, beginning with the radionuclide-dependent behavior of ¹¹C, ⁶⁸Ga, ⁶⁴Cu, [Al¹⁸F]²⁺, and ^99mTc, and then linking these properties to chelator selection, covalent radiolabeling, labeling conditions, and pharmacokinetics. The review further examines the development of radioligands targeting fibroblast activation protein (FAP), integrin α_vβ₃, folate receptor beta (β-FR), CXCR4, and the 18 kDa translocator protein (TSPO). It covers FAP-inhibitor scaffolds, RGD-based integrin probes, pteroyl-glutamate folate conjugates, CXCR4 antagonists, and TSPO heteroaromatic ligands. Clinical and translational datasets are discussed in relation to disease-activity evolution, treatment-response monitoring, and differentiation of stromal activation, macrophage infiltration, angiogenesis, and immune-cell recruitment. Finally, the review integrates kinetic modeling and dosimetric translation, emphasizing absorbed-dose estimation as a perspective on therapeutic optimization and safety constraints for emerging β-emitting and α-emitting synovial theranostics, ¹⁷⁷Lu and ²²⁵Ac. Collectively, these developments define a bench-to-bedside framework for rheumatology precision medicine, in which radiopharmaceutical chemistry, molecular imaging, clinical trial evidence, and patient-specific dosimetry converge to guide diagnosis, therapeutic selection, and future targeted synovial micro-radioresection.

Copper-64 is increasingly recognized for its advantages in positron emission tomography (PET) imaging and theranostic applications due to its favorable half-life, decay profile, and high spatial resolution. This research addresses the need for reliable, high-purity PET radiotracers by developing GMP-grade lyophilized kits for one-step preparation of ⁶⁴Cu-NOTA-peptides using gelatin as a chelating agent for metallic impurities and NOTA for selective copper binding. The approach was applied to five peptide analogs formulated for fast ⁶⁴Cu labeling: NOTA-iPSMA, NOTA-TOC, NOTA-iPD-L1, NOTA-iFAP, and NOTA-UBI 29–41, which were preclinically evaluated to enable the precise molecular imaging of cancer and infection. Each multidose kit included 0.5 μmol of the NOTA-peptide and 25 mg of gelatin, labeled with 925 MBq of ⁶⁴Cu. The radiochemical purity of the ⁶⁴Cu-NOTA-peptides exceeded 98% (mean 99.2% ± 0.3%) without the need for additional purification. The ⁶⁴Cu-radiotracers remained stable for at least 24 h at room temperature and showed high stability in human serum. In preclinical studies, saturation-binding assays demonstrated that affinity (Kd) was less than 10 nM in all ⁶⁴Cu-NOTA-peptides, with tumor-to-lung ratios ranging from 14 to 290 at 2 h post-injection and low liver uptake (2.95% ± 1.36% ID/g). The research demonstrated that these formulations, which include peptides specific to PSMA, SSTR2, PD-L1, FAP, and infection sites, offer excellent in vivo performance and high PET imaging quality in mice with induced tumors or infection sites. The findings support the use of gelatin-NOTA-peptide kits as a standardized and practical solution for producing ⁶⁴Cu-labeled peptides, facilitating routine clinical PET imaging, and advancing personalized molecular diagnostics.

Castration-resistant prostate cancer presents radiotherapeutic challenges, especially in optimizing the cytosolic internalization of therapeutic radiopharmaceuticals. This research aimed to design and evaluate in vitro, a new dimeric radiopharmaceutical, [¹⁷⁷Lu]Lu–iPSMA–iGRP78, which combines PSMA and GRP78 inhibitors in a heterodimeric radioligand to improve the radionuclide internalization and cytotoxicity efficacy. Molecular docking showed that the dimer iPSMA–iGRP78 presents a higher affinity for GRP78 (CNN-docking score: −14.0 kcal·mol⁻¹, pKi: 10) and for PSMA (CNN-docking score: −17.0 kcal·mol⁻¹, pKi: 11.5) compared to the monomers iGRP78 (CNN-docking score: −11.0 kcal·mol⁻¹, pKi: 9.4) and iPSMA (CNN-docking score: −13.9 kcal·mol⁻¹, pKi: 10.2). The saturation binding assay using LNCaP cells (PSMA+, CS-GRP78+) showed an affinity (K_d) of 1.883 nM for [¹⁷⁷Lu]Lu–iPSMA–iGRP78 and 2.245 nM for [¹⁷⁷Lu]Lu–iPSMA. The dimeric radiopharmaceutical achieved 10.44 ± 2.43% cytosolic internalization and 4.81 ± 0.94% nuclear internalization, while the [¹⁷⁷Lu]Lu–iPSMA monomer showed 6.45 ± 0.60% cytosolic internalization and no uptake in the cell nucleus. In PC3 cells (PSMA–, CS-GRP78–), [¹⁷⁷Lu]Lu–iPSMA–iGRP78 uptake was negligible, demonstrating specificity. Treatment with the dimeric radiopharmaceutical reduced cell viability (69.93 ± 4.85% of dead cells) significantly more than [¹⁷⁷Lu]Lu–iPSMA (38.63 ± 6.13% of dead cells). In conclusion, conjugation of a GRP78 inhibitor to [¹⁷⁷Lu]Lu–iPSMA improves the radionuclide internalization and cytotoxicity in prostate cancer cells, suggesting that the bispecific radiopharmaceutical is a promising strategy in prostate cancer treatment.

Objective. The aim of this study was to evaluate the impact of the nuclear properties of six β ⁻-emitting radionuclides (⁴⁷Sc, ⁶⁷Cu, ¹¹¹Ag, ¹⁶¹Tb, ¹⁷⁷Lu, and ¹⁸⁸Re) on the dosimetric outcomes of two tumour-targeting radiopharmaceuticals (RPs), with distinct pharmacokinetics: the peptide DOTA-folate conjugate cm09 and the monoclonal antibody HuM195. The study specifically focused on assessing the radiation-absorbed doses in organs and tumours, as well as comparing the efficacy and safety of the twelve RPs for targeted radionuclide therapy (TRT). Approach. Murine biodistribution data for both RPs were scaled to adult human models to determine biological residence times and the number of disintegrations in source organs and tumours. Dosimetric estimations were performed using OLINDA and MIRDCell software, considering different tumour sizes and organ-specific radiation exposure for both male and female phantoms. Main results. Significant differences in organ and tumour dosimetry were found across the considered radionuclides and tumour-targeting agents, attributable to the nuclear properties of the radionuclides and the RP pharmacokinetics. PFP-HuM195 labelled with ¹⁶¹Tb and ¹¹¹Ag demonstrated efficient dose delivery to tumour from 1–10 mm, but also higher organ-absorbed doses per unit of injected activity than other labelling radionuclides. Cm09 exhibited less variability in tumour absorbed dose as the labelling radionuclide varied, but also produced much higher kidney absorbed doses than PFP-HuM195. Normalising to the same tumour absorbed dose showed that ¹⁷⁷Lu and ¹⁶¹Tb are the safer options for treating small tumours (2.7–12.4 mm) with both RPs. These results demonstrate that the choice of radionuclide has a significant impact on both therapeutic efficacy and organ safety. Significance. This research demonstrates that selecting the appropriate radionuclide for TRT can optimise therapeutic outcomes while minimising radiation exposure to healthy tissues. The findings contribute to advancing personalised TRT approaches by considering RP-specific pharmacokinetics and radionuclide characteristics, paving the way for more effective cancer treatments.

Targeted radionuclide therapy (TRT) utilizes radiopharmaceuticals to deliver radiation directly to cancer cells while sparing healthy tissues. Beyond the absorbed dose of ablative radiation, TRT induces non-targeted effects (NTEs) that significantly enhance its therapeutic efficacy. These effects include radiation-induced bystander effects (RIBEs), abscopal effects (AEs), radiation-induced genomic instability (RIGI), and adaptive responses, which collectively influence the behavior of cancer cells and the tumor microenvironment (TME). TRT also modulates immune responses, promoting immune-mediated cell death and enhancing the efficacy of combination therapies, such as the use of immune checkpoint inhibitors. The molecular mechanisms underlying TRT involve DNA damage, oxidative stress, and apoptosis, with repair pathways like homologous recombination (HR) and non-homologous end joining (NHEJ) playing critical roles. However, challenges such as tumor heterogeneity, hypoxia, and radioresistance limit the effectiveness of this approach. Advances in theranostics, which integrate diagnostic imaging with TRT, have enabled personalized treatment approaches, while artificial intelligence and improved dosimetry offer potential for treatment optimization. Despite the significant survival benefits of TRT in prostate cancer and neuroendocrine tumors, 30–40% of patients remain unresponsive, which highlights the need for further research into molecular pathways, long-term effects, and combined therapies. This review outlines the dual mechanisms of TRT, direct toxicity and NTEs, and discusses strategies to enhance its efficacy and expand its use in oncology.

Background/Objective: Programmed cell death ligand-1 (PD-L1), which is overexpressed in certain tumors, inhibits the body’s natural immune response by providing an “off” signal that enables cancer cells to evade the immune system. It has been demonstrated that [¹⁷⁷Lu]Lu-DOTA-iPD-L1 (PD-L1 inhibitor cyclic peptide) promotes immune responses. This study aimed to synthesize and evaluate [¹⁸F]AlF-NOTA-iPD-L1 as a novel radiotracer for PD-L1 positron emission tomography (PET) imaging and as a potential theranostic pair for [¹⁷⁷Lu]Lu-DOTA-iPD-L1. Methods: The NOTA-iPD-L1 peptide conjugate was synthesized and characterized by U.V.-vis, I.R.-FT, and UPLC-mass spectroscopies. Radiolabeling was performed using [¹⁸F]AlF as the precursor, and the radiochemical purity (HPLC), partition coefficient, and serum stability were assessed. Cellular uptake and internalization (in 4T1 triple-negative breast cancer cells), binding competition, immunofluorescence, and Western blot assays were applied for the radiotracer in vitro characterization. Biodistribution in mice bearing 4T1 tumors was performed, and molecular imaging (Cerenkov images) of [¹⁸F]AlF-NOTA-iPD-L1 and [¹⁷⁷Lu]Lu-DOTA-iPD-L1 in the same mouse was obtained. Results: [¹⁸F]AlF-NOTA-iPD-L1 was prepared with a radiochemical purity greater than 97%, and it demonstrated high in vitro and in vivo stability, as well as specific recognition by the PD-L1 protein (IC₅₀ = 9.27 ± 2.69 nM). Biodistribution studies indicated a tumor uptake of 6.4% ± 0.9% ID/g at 1-hour post-administration, and Cerenkov images showed a high tumor uptake of both [¹⁸F]AlF-NOTA-iPD-L1 and ¹⁷⁷Lu-iPD-L1 in the same mouse. Conclusions: These results warrant further studies to evaluate the clinical usefulness of [¹⁸F]AlF-NOTA-iPD-L1/[¹⁷⁷Lu]Lu-DOTA-iPD-L1 as a radiotheranostic pair in combination with anti-PD-L1/PD1 immunotherapy.

[This corrects the article DOI: 10.1021/acsomega.4c09450.].

Cancer immunotherapy is a relatively new approach to cancer treatment. Peptides that target specific pathways and cells involved in immunomodulation can potentially improve the efficacy of cancer therapy. Recently, we reported iPD-L1 as a novel inhibitor peptide that specifically targets the cancer cell ligand PD-L1 (programmed death ligand 1). PD-L1 is responsible for inhibiting the immune checkpoint protein PD-1 expressed by regulatory T cells. On the other hand, anti-PD-L1 immunotherapy in combination with external beam radiotherapy has shown improved outcomes in the treatment of breast and lung cancer. The aim of this research was to prepare 177Lu-labeled iPD-L1 and to preclinically evaluate its radiotherapeutic potential and role as a tumor immunomodulator by measuring macrophage activation, IL-10, TGFβ, and PD-L1 expression in 4T1 triple-negative breast cancer cells and murine 4T1 tumors after treatment with 177Lu-iPD-L1. The iPD-L1 ligand, characterized by UPLC mass, UV-Vis, and FT-IR spectroscopies, showed a chemical purity of 99%. The 177Lu-iPD-L1 radiochemical purity was 98.9 ± 1.1%. In vitro and in vivo studies demonstrated radiotracer stability in human serum (> 97% after 24 h evaluated by radio-HPLC), adequate affinity by the PDL1 protein (IC50 = 4.21 nM), and specific detection for PD-L1 assessed in 4T1, HCT116, and AR42J cancer cells, in which PD-L1 expression was verified by immunofluorescence and Western Blot assays. After treatment with 177Lu-iPD-L1 (0.4 Bq/cell), flow cytometry results showed a significant decrease in cell viability of 4T1 cells (dead 56.2%) compared to 177LuCl3 (dead 34.2%) and untreated cells (dead 9.4%). With high tumor uptake (6.97 ± 1.04%ID) and hepatobiliary and renal clearance, lutetium-177-labeled iPD-L1 delivered a tumor dose of 27 Gy/37 MBq and less than 0.36 Gy/37 MBq to non-source organs. PD-L1 positive tumors showed a significant increase in activated macrophages, PD-L1, IL-10, and TGFβ expression levels after 177Lu-iPD-L1 treatment as evaluated by ELISA assay and immunohistochemistry. Therefore, this study warrants further dosimetric and clinical studies to determine the immunomodulatory effect and therapeutic efficacy of 177Lu-iPD-L1 in treating PD-L1-positive tumors in combination with anti-PD-1/PD-L1 immunotherapy protocols.