Search Results (69)

Targeted radioligand therapy (RLT) is an emerging field in anticancer therapeutics with great potential across tumor types and stages of disease. While much progress has focused on agents targeting somatostatin receptors and prostate-specific membrane antigen (PSMA), the same advanced radioconjugation methods and molecular targeting have spurred the development of numerous theranostic combinations for other targets. A number of the most promising agents have progressed to clinical trials and are poised to change the landscape of positron emission tomography (PET) imaging. Here, we present recent data on some of the most important emerging molecular targeted agents with their exemplar clinical images, including agents targeting fibroblast activation protein (FAP), hypoxia markers, gastrin-releasing peptide receptors (GRPrs), and integrins. These radiopharmaceuticals share the promising characteristic of being able to image multiple types of cancer. Early clinical trials have already demonstrated superiority to ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) for some, suggesting the potential to supplant this longstanding PET radiotracer. Here, we provide a primer for practicing radiologists, particularly nuclear medicine clinicians, to understand novel PET imaging agents and their clinical applications, as well as the availability of companion targeted radiotherapeutics, the status of their regulatory approval, the potential challenges associated with their use, and the future opportunities and perspectives. Full article

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. Full article

Background/Objectives: Radiolabeled biomolecules specifically targeting overexpressed structures on tumor cells hold great potential for prostate cancer (PCa) imaging and therapy. Due to heterogeneous target expression, single radiopharmaceuticals may not detect or treat all lesions, while simultaneously applying two or more radiotracers potentially improves staging, stratification, and therapy of cancer patients. This study explores a dual-tracer SPECT approach using [¹¹¹In]In-RM2 (targeting the gastrin-releasing peptide receptor, GRPR) and [^99mTc]Tc-PSMA-I&S (targeting the prostate-specific membrane antigen, PSMA) as a proof of concept. To mimic heterogeneous tumor lesions in the same individual, we aimed to establish a dual xenograft mouse model for preclinical evaluation. Methods: CHO-K1 cells underwent lentiviral transduction for human GRPR or human PSMA overexpression. Six-to-eight-week-old female immunodeficient mice (NOD SCID) were subsequently inoculated with transduced CHO-K1 cells in both flanks, enabling a dual xenograft with similar target density and growth of both xenografts. Respective dual-isotope imaging and γ-counting protocols were established. Target expression was analyzed ex vivo by Western blotting. Results: In vitro studies showed similar target-specific binding and internalization of [¹¹¹In]In-RM2 and [^99mTc]Tc-PSMA-I&S in transduced CHO-K1 cells compared to reference lines PC-3 and LNCaP. However, in vivo imaging showed negligible tumor uptake in xenografts of the transduced cell lines. Ex vivo analysis indicated a loss of the respective biomarkers in the xenografts. Conclusions: Although the technical feasibility of a dual-tracer SPECT imaging approach using ¹¹¹In and ^99mTc has been demonstrated, the potential of [^99mTc]Tc-PSMA-I&S and [¹¹¹In]In-RM2 in a dual-tracer cocktail to improve PCa diagnosis could not be verified. The animal model, and in particular the transduced cell lines developed exclusively for this project, proved to be unsuitable for this purpose. The in/ex vivo experiments indicated that results from an in vitro model may not necessarily be successfully transferred to an in vivo setting. To assess the potential of this dual-tracer concept to improve PCa diagnosis, optimized in vivo models are needed. Nevertheless, our strategies address key challenges in dual-tracer applications, aiming to optimize future SPECT imaging approaches. Full article

Pediatric central nervous system (CNS) tumors, including gliomas, medulloblastomas, and diffuse midline gliomas (previously diffuse intrinsic pontine gliomas), remain a major clinical challenge due to their complex biology, limited treatment effectiveness, and generally poor prognosis. Standard treatments are often aggressive and associated with substantial toxicity, particularly in advanced stages. This review highlights recent developments in radiopharmaceuticals for molecular imaging and targeted radiotherapy. A comprehensive literature analysis was conducted, focusing on radiotracers with clinical relevance in pediatric neuro-oncology, including metabolic, peptide receptor-based, and antibody-based agents. Radiopharmaceuticals such as ¹⁸F-FLT, ⁶⁴CuCl₂, and 1-L-18F-FETrp have improved the ability to monitor tumor biology, proliferation, and treatment response, aiding in diagnosis at an early stage, assessment of tumor behavior, and detection of recurrence or progression. Additionally, peptide receptor-based radiotracers, such as ⁶⁸Ga-DOTATATE and ¹⁷⁷Lu-DOTATATE, are already used for both diagnostic purposes and targeted radiotherapy, particularly in neuroblastomas and gliomas. Antibody-based radiotracers like ¹³¹I-omburtamab, targeting B7-H3, are emerging as promising tools for addressing difficult-to-treat tumors such as diffuse midline glioma. Collectively, these advances provide new hope for children afflicted by these devastating malignancies, offering promising solutions for more specific and precise diagnosis and, additionally, for more effective, personalized, and less toxic tumor therapies. Full article

Despite substantial improvement in the definitive management of primary prostate cancer, a significant number of patients experience biochemical recurrence—a clinical state in which serum prostate-specific antigen (PSA) levels rise prior to the development of physical signs or symptoms. The early detection and localization of biochemical recurrence may confer eligibility for salvage therapy; therefore, imaging techniques that provide accurate disease visualization are imperative. In this review, we discuss various imaging methods for localizing disease in the context of biochemical recurrence in prostate cancer. Particularly, we describe available or investigational positron emission tomography (PET) radiotracers, such as ¹⁸F-FDG, ¹⁸F-NaF, choline (both ¹⁸F and ¹¹C), the ¹⁸F-labeled amino acid derivative fluciclovine, prostate-specific membrane antigen (PSMA) radioligands, and the short peptide compound bombesin. Generally, PET radiotracers such as ¹⁸F-FDG, ¹⁸F-NaF, and ¹⁸F/¹¹C choline have fallen out of favor because of their inferior sensitivity and/or specificity in relation to more recently developed radiotracers. ¹⁸F-fluciclovine has addressed these shortcomings by exploiting the upregulation of amino acid transporters in tumors; however, PSMA-targeting agents have significantly advanced the management of biochemical recurrence of prostate cancer through their high sensitivity and specificity, enabling the identification of candidates for radionuclide therapy. Investigational agents, such as bombesin-based radiotracers, may address the shortcomings of treating prostate cancer with little to no PSMA expression. Full article

Background/Objectives: Prostate cancer (PC) represents the second most diagnosed form of cancer in men on a global scale. Despite the theranostic efficacy of prostate-specific membrane antigen (PSMA) radioligands, there is a spectrum of PC disease in which PSMA expression is low or absent. The gastrin-releasing peptide receptor (GRPR), also known as the bombesin type 2 receptor, has been identified as a target in both the early and advanced stages of PC. The objective of this study was to prepare and preclinically evaluate [^99mTc]Tc-iPSMA-Bombesin ([^99mTc]Tc-iPSMA-BN), estimate dosimetry in healthy subjects, and assess the diagnostic efficacy of the radiotracer in patients with metastatic PC, with the hypothesis of non-inferiority to one of the gold standards, [¹⁸F]-PSMA-1007. Moreover, the potential of [^99mTc]Tc-iPSMA-BN as a theranostic pair with [¹⁷⁷Lu]Lu-iPSMA-BN was investigated. Methods: [^99mTc]Tc-iPSMA-BN was prepared under GMP conditions with radiochemical purities > 95%, showing specific recognition by PSMA and GRP receptors in prostate cancer cells and mice bearing PC tumors. Six healthy volunteers were enrolled, and [^99mTc]Tc-iPSMA-BN SPECT/CT imaging (740 MBq) was performed to estimate the dosimetry. The pilot clinical study included seven mCRPC and four mCSPC patients with prior androgen deprivation therapy. All patients had a recent [¹⁸F]-PSMA-PET/CT scan and were enrolled in this prospective study on their own signed behalf. Volumetric lesion target-to-background ratios (TBRs) were obtained from PET/CT and SPECT/CT images. Results: [^99mTc]Tc-iPSMA-BN effective radiation dose was 1.94 ± 0.39 mSv/740 MBq. A total of 178 lesions were detected via CT, 162 via [¹⁸F]-PSMA-1007 PET, and 155 via [^99mTc]Tc-iPSMA-BN SPECT. Three patients with mCRPC had higher TBR values on SPECT than on PET. [^99mTc]Tc-iPSMA-BN appears to have better lesion detection in patients with aggressive histologic transformation. Two-way ANOVA analysis revealed a significant difference in TBR values between patients with mCRPC and mCSPC (p < 0.05) but no difference between [¹⁸F]-PSMA-1007 and [^99mTc]Tc-iPSMA-BN (p > 0.05). In one patient, [¹⁷⁷Lu]Lu-iPSMA-BN showed a high correlation with [^99mTc]Tc-iPSMA-BN for lesions that concentrated radioactivity. Conclusions: [^99mTc]Tc-iPSMA-BN SPECT/CT is a promising alternative not only for diagnostic purposes but also for broadening the spectrum of PC patients who may benefit from radionuclide theranostics. The results justify the development of a clinical trial involving a significant number of patients with PC. Full article

Background: The concept of radiotheranostics relies on the overexpression of a biomolecular target on malignant cells to direct diagnostic/therapeutic radionuclide-carriers specifically to cancer lesions. The concomitant expression of more than one target in pathological lesions may be elegantly exploited to improve diagnostic sensitivity and therapeutic efficacy. Toward this goal, we explored a first example of a combined application of [^99mTc]Tc-DT11 (DT11, N₄-Lys(MPBA-PEG4)-Arg-Arg-Pro-Tyr-Ile-Leu-OH; NTS₁R-specific) and [^99mTc]Tc-DB7(DB7, N₄-PEG2-DPhe-Gln-Trp-Ala-Val-Gly-His-Leu-NHEt; GRPR-specific) in prostate cancer models. Methods: Accordingly, the behavior of [^99mTc]Tc-DT11 was compared with that of the [^99mTc]Tc-DT11+[^99mTc]Tc-DB7 mixture in prostate adenocarcinoma PC-3 cells and xenografts in mice. The impact of stabilizing both radiotracers by Entresto^®, as a source of the potent neprilysin inhibitor sacubitrilat, was also investigated. Results: The PC-3 cell binding of the [^99mTc]Tc-DT11+[^99mTc]Tc-DB7 mixture surpassed that of [^99mTc]Tc-DT11. Likewise, the PC-3 tumor uptake of the [^99mTc]Tc-DT11+[^99mTc]Tc-DB7 mixture at 4 h post-injection was superior (7.70 ± 0.89%IA/g) compared with [^99mTc]Tc-DT11 (4.23 ± 0.58%IA/g; p < 0.0001). Treatment with Entresto^® led to further enhancement of the tumor uptake (to 11.57 ± 1.92%IA/g; p < 0.0001). Conclusions: In conclusion, this first preclinical study on prostate cancer models revealed clear advantages of dual NTS₁R/GRPR targeting, justifying further assessment of this promising concept in other cancer models. Full article

Multimodality reporter gene imaging combines the sensitivity, resolution and translational potential of two or more signals. The approach has not been widely adopted by the animal imaging community, mainly because its utility in this area is unproven. We developed a new complementation-based reporter gene system where the large component of split NanoLuc luciferase (LgBiT) presented on the surface of cells (TM-LgBiT) interacts with a radiotracer consisting of the high-affinity complementary HiBiT peptide labeled with a radionuclide. Radiotracer uptake could be imaged in mice using SPECT/CT and bioluminescence within two hours of implanting reporter-gene-expressing cells. Imaging data were validated by ex vivo biodistribution studies. Following the demonstration of complementation between the TM-LgBiT protein and HiBiT radiotracer, we validated the use of the technology in the highly specific in vivo multimodal imaging of cells. These findings highlight the potential of this new approach to facilitate the advancement of cell and gene therapies from bench to clinic. Full article

The use of metabolically stabilized, radiolabeled somatostatin (SST) analogs ([⁶⁸Ga]Ga/[¹⁷⁷Lu]Lu-DOTA-TATE/TOC/NOC) is well established in nuclear medicine. Despite the pivotal role of these radioligands in the diagnosis and therapy of neuroendocrine tumors (NETs), their inability to interact with all five somatostatin receptors (SST_1–5R) limits their clinical potential. [¹¹¹In]In-AT2S is a radiolabeled DOTA-conjugate derived from the parent peptide SST-14 that exhibits high binding affinity to all SSTR subtypes, but its poor metabolic stability represents a serious disadvantage for clinical use. In order to address this issue, we have replaced strategic trans-amide bonds of [¹¹¹In]In-AT2S with metabolically stable 1,4-disubstituted 1,2,3-triazole bioisosteres. From the five cyclic triazolo-peptidomimetics investigated, only [¹¹¹In]In-XG1 combined a preserved nanomolar affinity for the SST_1,2,3,5R subtypes in vitro and an improved stability in vivo (up to 17% of intact peptide 5 min postinjection (pi) versus 6% for [¹¹¹In]In-AT2S). The involvement of neprilysin (NEP) in the metabolism of [¹¹¹In]In-XG1 was confirmed by coadministration of Entresto^®, a registered antihypertensive drug, in vivo releasing the selective and potent NEP-inhibitor sacubitrilat. A pilot SPECT/CT imaging study conducted in mice bearing hSST₂R-positive xenografts failed to visualize the xenografts due to the pronounced kidney uptake (>200% injected activity (IA)/g at 4 h pi), likely the result of the formation of cationic metabolites. To corroborate the imaging data, the tumors and the kidneys were excised and analyzed with a γ-counter. Even if receptor-specific tumor uptake for [¹¹¹In]In-XG1 could be confirmed (1.61% IA/g), further optimization is required to improve its pharmacokinetic properties for radiotracer development. Full article

Background: Treatment of metastatic neuroendocrine tumors (NET) with ¹⁷⁷Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) results in favorable response only in a subset of patients. We investigated the prognostic value of quantitative pre-treatment semi-automatic ⁶⁸Ga-DOTATATE PET/CT analysis in NET patients treated with PRRT. Methods: The medical records of 94 NET patients who received at least one cycle of PRRT at a single institution were retrospectively reviewed. On each pre-treatment ⁶⁸Ga-DOTATATE PET/CT, the total tumor volume (TTV), maximum tumor standardized uptake value for the patient (SUVmax), and average uptake in the lesion with the lowest radiotracer uptake (SUVmin) were determined with a semi-automatic tumor delineation method. Progression-free survival (PFS) and overall survival (OS) among the patients were compared based on optimal cutoff values for the imaging parameters. Results: On Kaplan–Meier analysis and univariate Cox regression, significantly shorter PFS was observed in patients with lower SUVmax, lower SUVmin, and higher TTV. On multivariate Cox regression, lower SUVmin and higher TTV remained predictive of shorter PFS. Only higher TTV was found to be predictive of shorter OS on Kaplan–Meier and Cox regression analyses. In a post hoc Kaplan–Meier analysis, patients with at least one high-risk feature (low SUVmin or high TTV) showed shorter PFS and OS, which may be the most convenient parameter to measure in clinical practice. Conclusions: The tumor volume and lowest lesion uptake on ⁶⁸Ga-DOTATATE PET/CT can predict disease progression following PRRT in NET patients, with the former also predictive of overall survival. NET patients at risk for poor outcomes following PRRT can be identified with semi-automated quantitative analysis of ⁶⁸Ga-DOTATATE PET/CT. Full article

Previously, we demonstrated that the ¹⁷⁷Lu-labeled single-chain variable fragment of an anti-prostate-specific membrane antigen (PSMA) IgG D2B antibody (scFvD2B) showed higher prostate cancer (PCa) cell uptake and tumor radiation doses compared to ¹⁷⁷Lu-labeled Glu-ureide-based PSMA inhibitory peptides. To obtain a ^99mTc-/¹⁷⁷Lu-scFvD2B theranostic pair, this research aimed to synthesize and biochemically characterize a novel ^99mTc-scFvD2B radiotracer. The scFvD2B-Tag and scFvD2B antibody fragments were produced and purified. Then, two HYNIC derivatives, HYNIC-Gly-Gly-Cys-NH₂ (HYNIC-GGC) and succinimidyl-HYNIC (S-HYNIC), were used to conjugate the scFvD2B-Tag and scFvD2B isoforms, respectively. Subsequently, chemical characterization, immunoreactivity tests (affinity and specificity), radiochemical purity tests, stability tests in human serum, cellular uptake and internalization in LNCaP(+), PC3-PIP(++) or PC3(−) PCa cells of the resulting unlabeled HYNIC-scFvD2B conjugates (HscFv) and ^99mTc-HscFv agents were performed. The results showed that incorporating HYNIC as a chelator did not affect the affinity, specificity or stability of scFvD2B. After purification, the radiochemical purity of ^99mTc-HscFv radiotracers was greater than 95%. A two-sample t-test of ^99mTc-HscFv1 and ^99mTc-HscFv1 uptake in PC3-PIP vs. PC3 showed a p-value < 0.001, indicating that the PSMA receptor interaction of ^99mTc-HscFv agents was statistically significantly higher in PSMA-positive cells than in the negative controls. In conclusion, the results of this research warrant further preclinical studies to determine whether the in vivo pharmacokinetics and tumor uptake of ^99mTc-HscFv still offer sufficient advantages over HYNIC-conjugated peptides to be considered for SPECT/PSMA imaging. Full article

Background: The gastrin-releasing peptide receptor (GRPr) is highly overexpressed in several solid tumors, including treatment-naïve and recurrent prostate cancer. [⁶⁸Ga]Ga-RM2 is a well-established radiotracer for PET imaging of GRPr, and [¹⁷⁷Lu]Lu-RM2 has been proposed as a therapeutic alternative for patients with heterogeneous and/or low expression of PSMA. In this study, we aimed to evaluate the expression of GRPr and PSMA in a group of patients diagnosed with castration-resistant prostate cancer (mCRPC) by means of PET imaging. Methods: Seventeen mCRPC patients referred for radio-ligand therapy (RLT) were enrolled and underwent [⁶⁸Ga]Ga-PSMA-11 and [⁶⁸Ga]Ga-RM2 PET/CT imaging, 8.8 ± 8.6 days apart, to compare the biodistribution of each tracer. Uptake in healthy organs and tumor lesions was assessed by SUV values, and tumor-to-background ratios were analyzed. Results: [⁶⁸Ga]Ga-PSMA-11 showed significantly higher uptake in tumor lesions in bone, lymph nodes, prostate, and soft tissues and detected 23% more lesions compared to [⁶⁸Ga]Ga-RM2. In 4/17 patients (23.5%), the biodistribution of both tracers was comparable. Conclusions: Our results show that in our cohort of mCRPC patients, PSMA expression was higher compared to GRPr. Nevertheless, RLT with [¹⁷⁷Lu]Lu-RM2 may be an alternative treatment option for selected patients or patients in earlier disease stages, such as biochemical recurrence. Full article

Kisspeptins (KPs, KISS1) and their receptor (KISS1R) play a pivotal role as metastasis suppressor for many cancers. Low or lost KP expression is associated with higher tumor grade, increased metastatic potential, and poor prognosis. Therefore, KP expression has prognostic relevance and correlates with invasiveness in cancers. Furthermore, KISS1R represents a very promising target for molecular imaging and therapy for KISS1R-expressing tumors. The goal of this study was to evaluate the developed KISS1-54 derivative, [⁶⁸Ga]KISS1-54, as a PET-imaging probe for KISS1R-expressing tumors. The NODAGA-KISS1-54 peptide was labeled by Gallium-68, and the stability of the resulting [⁶⁸Ga]KISS1-54 evaluated in injection solution and human serum, followed by an examination in different KISS1R-expressing tumor cell lines, including HepG2, HeLa, MDA-MB-231, MCF7, LNCap, SK-BR-3, and HCT116. Finally, [⁶⁸Ga]KISS1-54 was tested in LNCap- and MDA-MB-231-bearing mice, using µ-PET, assessing its potential as an imaging probe for PET. [⁶⁸Ga]KISS1-54 was obtained in a 77 ± 7% radiochemical yield and at a >99% purity. The [⁶⁸Ga]KISS1-54 cell uptake amounted to 0.6–4.4% per 100,000 cells. Moreover, the accumulation of [⁶⁸Ga]KISS1-54 was effectively inhibited by nonradioactive KISS1-54. In [⁶⁸Ga]KISS1-54-PET, KISS1R-positive LNCap-tumors were clearly visualized as compared to MDA-MB-231-tumor implant with predominantly intracellular KISS1R expression. Our first results suggest that [⁶⁸Ga]KISS1-54 is a promising candidate for a radiotracer for targeting KISS1R-expressing tumors via PET. Full article

Aim: Angiotensin II (AngII) is known to play a significant part in the development of breast cancer by triggering cell propagation of breast cancer, tumor angiogenesis, and regulating tumor invasion and cell migration. AngII arbitrates its action via two G-protein-coupled receptors, AngII type 1 receptor (AT1) and AngII type 2 receptor (AT2). Overexpression of the AT1 receptor in breast cancer cells seems to promote tumor growth and angiogenesis, thus targeting the AT1 receptor using AngII peptide would facilitate the detection of breast carcinoma. We developed an AngII peptide intending to assess whether the peptide of the renin–angiotensin system holds the ability to target AT1 receptor-overexpressing breast cancer in vivo. Methods: DOTA-coupled AngII peptide was synthesized by conventional solid-phase peptide synthesis according to Fmoc/HATU chemistry. ⁶⁸Ga/¹⁷⁷Lu labeled AngII peptide was evaluated for its binding with TNBC MDA-MB-231 and ER+ MCF7 cell lines. Pharmacokinetics was studied in healthy balb/c mice and in vivo tumor targeting in nude mice with MDA-MB-231 tumors xenografts. Results: DOTA-AngII peptide was labeled efficiently with ⁶⁸Ga/¹⁷⁷Lu with high labeling efficiency (≥90%). The stability of the radiopeptide in human plasma was found to be high. The AngII peptide analog showed nanomolar (<40 nM) AT1 receptor-specific binding affinity. The radioactivity internalized into MDA-MBA-231 and MCF7 cells were 14.97% and 11.75%, respectively. In vivo, biodistribution in balb/c mice exhibited efficient clearance of ⁶⁸Ga/¹⁷⁷Lu-DOTA-AngII peptide from the blood and elimination predominantly by the renal system due to its hydrophilic nature. A low amount of radioactivity was seen in the major organs including lungs, liver, stomach, spleen, and intestines (<3% ID/g) except the kidneys. A high renal-urinary excretion was observed for the radiotracer. In the TNBC MDA-MB-231 xenografts model, radiolabeled AngII peptide exhibited specific and effective AT1-based targeting in vivo. A rapid and efficient tumor targeting (2.18% ID/g at 45 min p.i.) together with fast renal excretion (~67% ID) highlights the tumor-targeting potential of the radiotracer. The AT1 receptor specificity of the radiotracer was validated by blocking assays. Furthermore, PET imaging provided sufficient visualization of MDA-MB-231 tumors in nude mice. Conclusion: Our findings suggest that ⁶⁸Ga/¹⁷⁷Lu-DOTA-AngII peptide can be useful for the theranostic application of breast carcinomas. This study suggests the potential of this innovative class of peptides for rapid and efficient targeting of tumors and warrants further evaluation. Full article

Current cancer therapies focus on reducing immunosuppression and remodeling the tumor microenvironment to inhibit metastasis, cancer progression, and therapeutic resistance. Programmed death receptor 1 (PD-1) is expressed on immune T cells and is one of the so-called checkpoint proteins that can suppress or stop the immune response. To evade the immune system, cancer cells overexpress a PD-1 inhibitor protein (PD-L1), which binds to the surface of T cells to activate signaling pathways that induce immune suppression. This research aimed to synthesize PD-L1 inhibitory peptides (PD-L1-i) labeled with lutetium-177 (¹⁷⁷Lu-DOTA-PD-L1-i) and actinium-225 (²²⁵Ac-HEHA-PD-L1-i) and to preclinically evaluate their potential as radiopharmaceuticals for targeted radiotherapy at the tumor microenvironment level. Using PD-L1-i peptide as starting material, conjugation with HEHA-benzene-SCN and DOTA-benzene-SCN was performed to yield DOTA-PD-L1-i and HEHA-PD-L1-I, which were characterized by FT-IR, UV-vis spectroscopy, and HPLC. After labeling the conjugates with ²²⁵Ac and ¹⁷⁷Lu, cellular uptake in HCC827 cancer cells (PD-L1 positive), conjugate specificity evaluation by immunofluorescence, radiotracer effect on cell viability, biodistribution, biokinetics, and assessment of radiation absorbed dose in mice with in duced lung micrometastases were performed. ²²⁵Ac-HEHA-PD-L1-i and ¹⁷⁷Lu-DOTA-PD-L1-i, obtained with radiochemical purities of 95 ± 3% and 98.5 ± 0.5%, respectively, showed in vitro and in vivo specific recognition for the PD-L1 protein in lung cancer cells and high uptake in HCC287 lung micrometastases (>30% ID). The biokinetic profiles of ¹⁷⁷Lu-DOTA-PD-L1-i and ²²⁵Ac-DOTA-PD-L1-i showed rapid blood clearance with renal and hepatobiliary elimination and no accumulation in normal tissues. ²²⁵Ac-DOTA-PD-L1-i produced a radiation dose of 5.15 mGy/MBq to lung micrometastases. In the case of ¹⁷⁷Lu-DOTA-PD-L1-i, the radiation dose delivered to the lung micrometastases was ten times (43 mGy/MBq) that delivered to the kidneys (4.20 mGy/MBq) and fifty times that delivered to the liver (0.85 mGy/MBq). Therefore, the radiotherapeutic PD-L1-i ligands of ²²⁵Ac and ¹⁷⁷Lu developed in this research could be combined with immunotherapy to enhance the therapeutic effect in various types of cancer. Full article