177Lu-DOTA-HYNIC-Lys(Nal)-Urea-Glu: Biokinetics, Dosimetry, and Evaluation in Patients with Advanced Prostate Cancer

Real world experience with [99mTc]Tc-HYNIC-iPSMA SPECT prostate cancer detection: interim results from the global NOBLE registry

PURPOSE

[99mTc]Tc-HYNIC-iPSMA is a novel technetium-99m-labelled small molecule inhibitor of the prostate-specific membrane antigen (PSMA) for detecting prostate cancer (PC). The objective of this registry was to collect and evaluate [99mTc]Tc-HYNIC-iPSMA patient data and images to establish the safety and tolerability, and clinical utility of this agent in imaging at different stages of PC.

METHODS

Patients 18 to 80 years old with primary staging and metastatic PC were eligible. Patients unable to perform prescribed examinations, undergo a [99mTc]Tc-HYNIC-iPSMA planar and SPECT or SPECT/CT (when available), or sign a patient informed consent form were excluded from the registry. All eligible patients underwent a screening and baseline visit before imaging with [99mTc]Tc-HYNIC-iPSMA. The primary safety endpoint was assessed by collecting and grading all treatment-related adverse events using the Common Terminology Criteria for Adverse Events. Patients were followed until disease progression, death, serious or intolerable adverse events, registry termination by the sponsor, patient withdrawal, or lost to follow-up. Analysis was planned for when data was available from 40 enrolled patients.

RESULTS

40 patients enrolled in 6 countries and received [99mTc]Tc-HYNIC-iPSMA tracer administration followed by planar and SPECT imaging. Of the 40 patients included, investigators reported a change in management due to the [99mTc]Tc-HYNIC-iPSMA imaging in 17/40 of patients (42.5%). No adverse events were reported.

CONCLUSIONS

[99mTc]Tc-HYNIC-iPSMA is a promising option to identify PSMA-positive prostate cancer on SPECT and could improve patient access to PSMA imaging worldwide.

Synthesis and Preclinical Evaluation of a Bispecific PSMA-617/RM2 Heterodimer Targeting Prostate Cancer

Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) have been used for diagnostic molecular imaging/therapy of prostate cancer (PCa). To address tumor heterogeneity, we synthesized and evaluated a bispecific PSMA/GRPR ligand (3) combining PSMA-617 (1) and the GRPR antagonist RM2 (2) with the radiometal chelator DOTA. 3 was radiolabeled with 68Ga ([68Ga]Ga-3) and 177Lu ([177Lu]Lu-3). [68Ga]Ga-3 was tested in the following PCa cell lines for receptor affinity, time kinetic cell-binding/specificity, and cell-internalization: PC-3 and LNCaP. Compared to the monomers (1 and 2), ligand 3 showed specific cell binding, similar receptor affinities, and higher lipophilicity, while its internalization rates and cell-binding were superior. Docking calculations showed that 3 can have binding interactions of PSMA-617 (1) inside the PSMA receptor funnel and RM2 (2) inside the GRPR. In vivo biodistribution studies for [68Ga]Ga-3 showed dual targeting for PSMA(+) and GRPR(+) tumors and higher tumor uptake, faster pharmacokinetic, and lower kidney uptake compared to 1 and 2.

Estimation of the relative biological effectiveness (RBE) of the Lu-DOTA-iPSMA177<!--Q1:CorrectlyacknowledgingtheprimaryfundersandgrantIDsofyourresearchisimportanttoensurecompliancewithfunderpolicies.Pleasemakesurethatfundersarementionedaccordingly.--> radiopharmaceutical

Relative biological effectiveness is a radiobiological parameter relevant in radiotherapy planning and useful in evaluating the physiological impact of radiation in different tissues. Targeted radionuclide therapy allows the selective and specific deposition of higher radiation doses in a noninvasive way and without collateral effects through the administration of radiopharmaceuticals. Lu-DOTA-177(hydrazinylnicotinoyl-Lys-(Nal)-NH-CO-NH-Glu) also called Lu-iPSMA177 is a third generation radiopharmaceutical composed by a peptide that recognizes the prostate-specific membrane antigen (PSMA), a membrane protein overexpressed in several types of cancer and that mediates the radiopharmaceutical's recognition of cancer cells. The present study reports radiobiological parameters of Lu-iPSMA177 and demonstrates the superiority of targeted radiopharmaceuticals over external radiotherapy treatment options in terms of their relative biological effectiveness. The relative biological effectiveness value of 1.020±0.003 for the LINAC, estimated by fitting the linear-quadratic model equation to the resulting survival curves, was like those of 1.25±0.04,1.060±0.005and1.00±0.04 obtained by an alternative method in relation to the mean lethal doses at 90, 80 or 60 survival percent respectively. While the relative biological effectiveness values of 5.65±0.13,4.72±0.27and2.87±0.19 estimated for Lu-iPSMA177 were significantly higher than those for the LINAC. The results confirm that the biological effect produced by the deposition of a radiation absorbed dose delivered by the LINAC can be induced with a quarter of that dose using Lu-iPSMA177 due to the energy distribution, dose-rate and energy fluence.

The preparation, biodistribution, and human's absorbed dose evaluation of Radio-Scandium-HYNIC-TOC for somatostatin-receptor-positive neuroendocrine tumors therapy by animal study

BACKGROUND

Most of the neuroendocrine tumors (NETs) express Somatostatin receptors (SSTr), which are the main bases for the development of several radiopharmaceuticals for therapy and imaging of these types of tumors. In this study, 46 Scandium nuclide was used to label a peptide compound via hydrazinonicotinyl-Tyr3-Octreotide (HYNIC-TOC) and researched further for somatostatin-receptor NETs treatment.

METHODS AND MATERIALS

The labeling procedure was conducted at 95°C for 10 min. The compound stability was tested in the environment of human serum at 37°C. The biodistribution of compound was investigated in balb/c normal mice and mice bearing AR4-2J tumor. Absorbed Doses of Human Organs were estimated by extrapolation of the biokinetics data of compound in mice to human's organs and then the absorbed doses were estimated by application of MATLAB and MIRDOSE software.

RESULTS

Labeling yield was more than 90% with 555 MBq/mg specific activity. The radio-labeled compound expressed well consistency in human serum. The tumor uptake reached 3.831 ID/g% until 4 h post-injection and increased to 5.564%ID/g until 24 h post-injection.

CONCLUSION

The main achievement of this study was high tumor uptake of 46 Sc-HYNIC-TOC which may be therapeutically valuable for the therapy of NETs. The estimation of the absorbed dose of human from 47 Scandium-HYNIC-TOC showed low absorbed doses in critical organs and the elimination of the radiopharmaceutical was through the gastrointestinal tract.

Targeted Endoradiotherapy with Lu2O3-iPSMA/-iFAP Nanoparticles Activated by Neutron Irradiation: Preclinical Evaluation and First Patient Image

Prostate-specific membrane antigen (PSMA) is expressed in a variety of cancer cells, while the fibroblast activation protein (FAP) is expressed in the microenvironment of tumors. Previously, we reported the ability of iPSMA and iFAP ligands to specifically target PSMA and FAP proteins, as well as the preparation of stable 177Lu2O3 nanoparticles (<100 nm) functionalized with target-specific peptides. This research aimed to evaluate the dosimetry and therapeutic response of Lu2O3-iPSMA and Lu2O3-iFAP nanoparticles activated by neutron irradiation to demonstrate their potential for theranostic applications in nuclear medicine. The biokinetic behavior, radiation absorbed dose, and metabolic activity ([18F]FDG/micro-PET, SUV) in preclinical tumor tissues (athymic mice), following treatment with 177Lu2O3-iPSMA, 177Lu2O3-iFAP or 177Lu2O3 nanoparticles, were assessed. One patient with multiple colorectal liver metastases (PSMA-positive) received 177Lu2O3-iPSMA under a “compassionate use” protocol. Results indicated no significant difference (p < 0.05) between 177Lu2O3-iPSMA and 177Lu2O3-iFAP, regarding tumor radiation absorbed doses (105 ± 14 Gy, 99 ± 12 Gy and 58 ± 7 Gy for 177Lu2O3-iPSMA, 177Lu2O3-iFAP, and 177Lu2O3, respectively) and tumor metabolic activity (SUV of 0.421 ± 0.092, 0.375 ± 0.104 and 1.821 ± 0.891 for 177Lu2O3-iPSMA, 177Lu2O3-iFAP, and 177Lu2O3, respectively) in mice after treatment, which correlated with the observed therapeutic response. 177Lu2O3-iPSMA and 177Lu2O3-iFAP significantly inhibited tumor progression, due to the prolonged tumor retention and a combination of 177Lu radiotherapy and iPSMA or iFAP molecular recognition. There were negligible uptake values in non-target tissues and no evidence of liver and renal toxicity. The doses received by the patient’s liver metastases (42−210 Gy) demonstrated the potential of 177Lu2O3-iPSMA for treating colorectal liver metastases.

Comparison between 177Lu-iPSMA and 225Ac-iPSMA dosimetry at a cellular level in an animal bone metastasis model

The recent use of prostate-specific membrane antigen as a biological target have improved the theragnostic approach to prostate and other types of cancer. Radiopharmaceuticals based on PSMA inhibitors radiolabeled with beta emitters as Lutetium-177 have demonstrated remarkable efficacy and safety, however, their clinical evaluation have also shown that therapeutic response of bone located metastases is poorer than that presented by soft tissue lesions. These observations conducted to the development and study at different levels of PSMA-targeting alpha-particle therapy exhibiting effective and promising antitumor activity. However, some aspects of the use of alpha emitters such as cellular dosimetry should be considered before applying them safely. The aim of the present work was to compare and calculate the absorbed dose of 177Lu-iPSMA and 225Ac-iPSMA using an animal bone metastasis model and experimental data obtained from cellular fractionation. The number of disintegrations and the dose factors for the theragnostic iPSMA pair, molecule that can be radiolabeled with 177Lu or 225Ac, were determined based on MIRD methodology, and used to calculate the absorbed dose to cell nucleus. A five times difference between 225Ac-iPSMA and 177Lu-iPSMA average dose rate to the tumor was calculated, being 2.3 ± 0.037 for the first and 0.5 ± 0.018 Gy for the second, both for each activity unit (MBq) administered.

A Systematic Review and Meta-analysis of the Effectiveness and Toxicities of Lutetium-177-labeled Prostate-specific Membrane Antigen-targeted Radioligand Therapy in Metastatic Castration-Resistant Prostate Cancer

CONTEXT

Castration-resistant prostate cancer (CRPC) treatment is an evolving challenge. Prostate-specific membrane antigen (PSMA)-targeted endoradiotherapy/radioligand therapy (PRLT) with small-molecule, urea-based agents labeled with the β-particle-emitting radionuclide lutetium-177 (177Lu) is a promising new approach.

OBJECTIVE

In this systematic review and meta-analysis, we evaluated the efficacy and toxicity of PRLT.

EVIDENCE ACQUISITION

A systematic search was performed in PubMed/Medline (last updated February 18, 2019). A total of 250 studies were reviewed, and 24 studies with 1192 patients were included in the analysis. Proportions of patients with ≥50% serum prostate-specific antigen (PSA) decrease, any PSA decrease, and any PSA increase were extracted. Proportions of patients showing any grade toxicity and those with grade 3/4 toxicities based on Common Terminology Criteria for Adverse Events (CTCAE) grading were extracted from manuscripts. Overall survival and progression-free survival were evaluated. A meta-analysis of single proportions was carried out. Furthermore, we compared the two most common PRLT agents, 177Lu-PSMA with 177Lu-PSMA-I&T, for effectiveness and toxicity.

EVIDENCE SYNTHESIS

Among the 24 included studies, 20 included data on 177Lu-PSMA-617, three included data on 177Lu-PSMA-I&T, and one study had aggregated data for 177Lu-PSMA-617 and 177Lu-PSMA-I&T. The estimated proportion of 177Lu-PSMA-617-treated patients who showed a serum PSA decrease of ≥50% with at least an 8-wk interval between therapy and PSA measurement was 0.44 (0.39; 0.50). Therapy with 177Lu-PSMA-I&T demonstrated an estimated proportion of patients with ≥50% PSA reduction to be 0.36 (0.26; 0.47). The aggregate results for men treated with more than one cycle of any kind of PRLT showed an estimated proportion of 0.46 (0.41; 0.51) for PSA response ≥50%. Regarding aggregate data from all of the PRLT agents, we found that grade 3 and 4 toxicities were uncommon, with estimated proportions from 0.01 (0.00;0.04) for nausea, fatigue, diarrhea, and elevated aspartate transaminase up to 0.08 (0.05; 0.12) for anemia. There was considerable heterogeneity among the studies in the "any-grade toxicity" groups. Meta-regression showed that more than one cycle of PRLT is associated with a greater proportion of patients with ≥50% PSA reduction. Overall survival according to pooled hazard ratios (HRs) for any PSA decline was 0.29 (0.18; 0.46), and for >50% PSA reduction was 0.67 (0.43; 1.07). Progression-free survival according to a pooled HR of >50% PSA reduction was 0.53 (0.32; 0.86).

CONCLUSIONS

The relatively high number of PSA responders alongside the low rate of severe toxicity reflects the potentially promising role of PRLT in treating CRPC. The ultimate utility of this treatment modality will become clearer as multiple prospective studies continue to accrue. In the interim, this systematic review and meta-analysis can serve as a compendium of effectiveness and adverse events associated with PRLT for treating clinicians.

PATIENT SUMMARY

Prostate-specific membrane antigen-targeted endoradiotherapy/radioligand therapy (PRLT) is associated with ≥50% reduction in prostate-specific antigen level in a large number of patients and a low rate of toxicity, reflecting its potential in treating castration-resistant prostate cancer. This systematic review and meta-analysis presents as a compendium of the effectiveness and adverse events related to PRLT for treating clinicians.

Preclinical dosimetric studies of 177 Lu-scFvD2B and comparison with 177 Lu-PSMA-617 and 177 Lu-iPSMA endoradiotherapeutic agents

PURPOSE

Internal dosimetry has become a very important tool to evaluate the risks and benefits of new endoradiotherapeutic agents. Nowadays, some of the most successful targeted radionuclide therapy (TRT) agents are ¹⁷⁷ Lu-DOTA conjugates based on low molecular weight (LMW) Glu-ureido PSMA inhibitors. It has, however, been demonstrated that the DOTA chelating moiety reduces the internalization of the LMW-PSMA agent and its radiation dose to the tumor. Previously, we reported that ¹⁷⁷ Lu-scFvD2B, an antibody-based construct, demonstrated statistically significant higher cell uptake and internalization in LNCaP prostate cancer (PCa) cells (PSMA-positive) when compared to the LMW-PSMA agents, ¹⁷⁷ Lu-PSMA-617 and ¹⁷⁷ Lu-iPSMA, two of the endoradiotherapeutic agents which currently are the most used in PCa therapy. The aim of this study is to estimate the preclinical ¹⁷⁷ Lu-scFvD2B organ and tumor-absorbed doses, and to compare the values with those of ¹⁷⁷ Lu-PSMA-617 and ¹⁷⁷ Lu-iPSMA.

METHODS

¹⁷⁷ Lu-scFvD2B, ¹⁷⁷ Lu-PSMA-617, and ¹⁷⁷ Lu-iPSMA were prepared and their radiochemical purity determined. Biodistribution studies of each radiopharmaceutical were then carried out in healthy mice to define the main source organs (SO) and to calculate the number of disintegrations in each source organs per unit of administered activity (N_SO ). Absorbed dose in the main organs were then calculated for each ¹⁷⁷ Lu-conjugate by means of OLINDA/EXM 2.1.1 software, using the calculated N_SO for both the adult male and the mouse phantoms as program inputs. Images of mice bearing micropulmonary tumors injected with ¹⁷⁷ Lu-conjugates were also obtained. Tumor standardized uptake values (SUV) for the different conjugates, obtained from the 3D SPECT image reconstruction of these mice, were used as the number of disintegrations in a tumor site per unit of administered activity (N_T ). The tumor-absorbed dose was calculated using the published electron dose S-values for sphere models with diameters ranging from 10 µm to 10 mm and considering a uniform activity distribution and tumor density equivalent to water density.

RESULTS

All ¹⁷⁷ Lu-labeled agents were obtained in high yield (98%). Dosimetric studies carried out using mouse phantoms demonstrated that organ absorbed doses of ¹⁷⁷ Lu-scFvD2B were from 1.4 to 2.3 times higher than those for ¹⁷⁷ Lu-iPSMA and from 1.5 to 2.6 times higher than those for ¹⁷⁷ Lu-PSMA-617. However, the ¹⁷⁷ Lu-scFvD2B values of tumor-absorbed doses for all investigated tumor sizes were from 2.8 to 3.0 times greater than those calculated for ¹⁷⁷ Lu-iPSMA and ¹⁷⁷ Lu-PSMA-617, respectively. Moreover, ¹⁷⁷ Lu-scFvD2B showed the highest tumor/kidney ratio when compared to those reported for ¹⁷⁷ Lu-albumin conjugates.

CONCLUSIONS

In this preclinical study, we demonstrated the potential of ¹⁷⁷ Lu-scFvD2B as a therapeutic agent for PSMA-expressing tumors, due to its higher tumor-absorbed dose when compared with ¹⁷⁷ Lu-LMW agents.

[99mTc]Tc-iPSMA SPECT brain imaging as a potential specific diagnosis of metastatic brain tumors and high-grade gliomas

BACKGROUND

PSMA (prostate-specific membrane antigen) protein is heavily expressed in the proliferating microvasculature of high-grade gliomas (HGG) and brain metastases (BM). This research aimed to assess [99mTc]Tc-iPSMA SPECT brain imaging as a potential specific diagnosis of HGG and BM by PSMA-targeting in their proliferating vasculature.

METHODS

Forty-one patients, with suspected brain tumors, as detected by enhanced MRI scanning, were enrolled to undergo preoperative [99mTc]Tc-iPSMA SPECT brain imaging. Semiquantitative image analyses, to evaluate the maximum target-to-background ratio (TBRmax), were performed. All diagnoses were histopathologically confirmed. PSMA expression was evaluated by immunohistochemistry (IHC) in 11 brain tumor tissues. TBRmax values were correlated with IHC results and tumor WHO grade (HGG vs LGG).

RESULTS

[99mTc]Tc-iPSMA images showed increased uptake in BM, HGG, and recurrent gliomas (TBRmax of 25.1 ± 7.1, 18.5 ± 9.0, 15.0 ± 9.9, respectively), and was negative in treatment-naive patients with LGG and reactive gliosis. PSMA was highly expressed in the vascular endothelium of grade IV gliomas and BM, while its expression was extremely low in LGG and completely absent in gliosis. By using 2.8 as a threshold value for TBRmax, the specificity, sensitivity, PPV, NPV and accuracy were 100%, 94%, 100%, 77% and 95%, respectively.

CONCLUSIONS

The results of this pilot study show that [99mTc]Tc-iPSMA SPECT brain imaging is a specific and potentially useful neuroimaging tool for assessing tumoral neovasculature formation in gliomas and brain metastases.

Preliminary dosimetric analysis of DOTA-folate radiopharmaceutical radiolabelled with 47Sc produced through natV(p,x)47Sc cyclotron irradiation

⁴⁷Sc is one of the most promising theranostic radionuclides, thanks to its low energy γ-ray emission (159 keV), suitable for single photon emission computed tomography imaging and its intense β ^- emission, useful for tumour treatment. Despite promising preclinical results, the translation of ⁴⁷Sc-therapeutic agents to the clinic is hampered by its limited availability. Among different ⁴⁷Sc-production routes currently being investigated, the ^natV(p,x)⁴⁷Sc reaction has proved to be of particular interest, thanks to the low-cost and easy availability on the market of ^natV material and the diffusion of medium energy proton cyclotrons. However, the cross section of this specific nuclear reaction is quite low and small amounts of Sc-contaminants are co-produced at energies E _P ≤ 45 MeV, namely ⁴⁸Sc and ⁴⁶Sc. The main concern with these Sc-contaminants is their contribution to the patient absorbed dose. For such a reason, the absorbed dose contributions to healthy organs and the effective dose contributions by the three radioisotopes, ⁴⁸Sc, ⁴⁷Sc and ⁴⁶Sc, were evaluated using DOTA-folate conjugate (cm10) as an example of radiopharmaceutical product. Considering as acceptable the limits of 99% for the radionuclidic purity and 10% for the contribution of radioactive Sc-contaminants to the total effective dose after ⁴⁷Sc-cm10 injection, it was obtained that proton beam energies below 35 MeV must be used to produce ⁴⁷Sc through irradiation of a ^natV target.

Development of 177Lu-scFvD2B as a Potential Immunotheranostic Agent for Tumors Overexpressing the Prostate Specific Membrane Antigen

The clinical translation of theranostic ¹⁷⁷Lu-radiopharmaceuticals based on inhibitors of the prostate-specific membrane antigen (PSMA) has demonstrated positive clinical responses in patients with advanced prostate cancer (PCa). However, challenges still remain, particularly regarding their pharmacokinetic and dosimetric properties. We developed a potential PSMA-immunotheranostic agent by conjugation of a single-chain variable fragment of the IgGD2B antibody (scFvD2B) to DOTA, to obtain a ¹⁷⁷Lu-labelled agent with a better pharmacokinetic profile than those previously reported. The labelled conjugated ¹⁷⁷Lu-scFvD2B was obtained in high yield and stability. In vitro, ¹⁷⁷Lu-scFvD2B disclosed a higher binding and internalization in LNCaP (PSMA-positive) compared to PC3 (negative control) human PCa cells. In vivo studies in healthy nude mice revealed that ¹⁷⁷Lu-scFvD2B present a favorable biokinetic profile, characterized by a rapid clearance from non-target tissues and minimal liver accumulation, but a slow wash-out from kidneys. Micro-SPECT/CT imaging of mice bearing pulmonary microtumors evidenced a slow uptake by LNCaP tumors, which steadily rose up to a maximum value of 3.6 SUV at 192 h. This high and prolonged tumor uptake suggests that ¹⁷⁷Lu-scFvD2B has great potential in delivering ablative radiation doses to PSMA-expressing tumors, and warrants further studies to evaluate its preclinical therapeutic efficacy.

Hybrid (2D/3D) Dosimetry of Radiolabeled Gold Nanoparticles for Sentinel Lymph Node Detection in Patients with Breast Cancer

Previously, we reported the preparation and preclinical studies of ^99mTc-labeled gold nanoparticles-mannose (^99mTc-AuNP-mannose) with potential for sentinel lymph node (SLN) detection by using nuclear medicine procedures. This study aimed to evaluate the biokinetics and hybrid (2D/3D) dosimetry of ^99mTc-AuNP-mannose in five patients with breast cancer under a sentinel lymph node detection protocol. Anterior and posterior whole-body planar images (2D, at 0.5, 2, 6, and 24 h) and single-photon emission computed tomography (3D at 6.5 h)/computed tomography (SPECT/CT) images were acquired after ^99mTc-AuNP-mannose administration (37 MBq). Through a hybrid quantification method, activity in tissues of interest at the different acquisition times was determined and integrated over time to obtain the total nuclear transformations (N), as well as the mean residence time, in each tissue. N values and the OLINDA code were used for estimating the internal radiation absorbed doses. Results demonstrated that ^99mTc-AuNP-mannose successfully accumulates and remains up to 24 h in the sentinel lymph node without detectable migration to other lymph nodes and no side effects on patients. Negligible absorption of the radiolabeled nanoparticles into the circulatory system was observed, from which the radio-nanosystem is rapidly eliminated by kidneys. Hybrid (2D/3D) dosimetry evaluations showed equivalent doses to SLN, breast, and kidneys of 172.34, 5.32, and 0.08 mSv/37 MBq, respectively, with an effective dose of 2.05E - 03 mSv/MBq. The mean effective residence time in SLN was 0.92 h. This preliminary study indicates that the use of ^99mTc-AuNP-mannose for successful SLN detection in patients is safe, producing an effective dose at the level recommended for diagnostic studies (<10 mSv).

Radiolabeled Protein-inhibitor Peptides with Rapid Clinical Translation towards Imaging and Therapy

Protein interactions are the basis for the biological functioning of human beings. However, many of these interactions are also responsible for diseases, including cancer. Synthetic inhibitors of protein interactions based on small molecules are widely investigated in medicinal chemistry. The development of radiolabeled protein-inhibitor peptides for molecular imaging and targeted therapy with quickstep towards clinical translation is an interesting and active research field in the radiopharmaceutical sciences. In this article, recent achievements concerning the design, translational research and theranostic applications of structurally-modified small radiopeptides, such as prostate-specific membrane antigen (PSMA) inhibitors, fibroblast activation protein (FAP) inhibitors and antagonists of chemokine-4 receptor ligands (CXCR-4-L), with high affinity for cancer-associated target proteins, are reviewed and discussed.

Theoretical and experimental characterization of emission and transmission spectra of Cerenkov radiation generated by 177Lu in tissue

Cerenkov radiation (CR) is the emission of UV-vis light generated by the de-excitation of the molecules in the medium, after being polarized by an excited particle traveling faster than the speed of light. When β particles travel through tissue with energies greater than 219 keV, CR occurs. Tissues possess a spectral optical window of 600 to 1100 nm. The CR within this range can be useful for quantitative preclinical studies using optical imaging and for the in-vivo evaluation of Lu177-radiopharmaceuticals (β-particle emitters). The objective of our research was to determine the experimental emission light spectrum of Lu177-CR and evaluate its transmission properties in tissue as well as the feasibility to applying CR imaging in the preclinical studies of Lu177-radiopharmaceuticals. The theoretical and experimental characterizations of the emission and transmission spectra of Lu177-CR in tissue, in the vis-NIR region (350 to 900 nm), were performed using Monte Carlo simulation and UV-vis spectroscopy. Mice Lu177-CR images were acquired using a charge-coupled detector camera and were quantitatively analyzed. The results demonstrated good agreement between the theoretical and the experimental Lu177-CR emission spectra. Preclinical CR imaging demonstrated that the biokinetics of Lu177-radiopharmaceuticals in the main organs of mice can be acquired.

Assessment of the radiation absorbed dose produced by 177Lu-iPSMA, 225Ac-iPSMA and 223RaCl2 to prostate cancer cell nuclei in a bone microenvironment model

This research aimed to assess the radiation absorbed dose produced by ¹⁷⁷Lu-iPSMA (¹⁷⁷Lu-prostate specific membrane antigen inhibitor), ²²⁵Ac-iPSMA and ²²³RaCl₂ to prostate cancer cell nuclei in a simplified model of bone by using an experimental in-vitro prostate cancer LNCaP cell biokinetic study and Monte Carlo simulation with the MCNPX code. Results showed that ²²⁵Ac-iPSMA releases a nine hundred-fold radiation dose greater than ¹⁷⁷Lu-iPSMA and 14 times more than ²²³RaCl₂ per unit of activity retained in bone. ²²⁵Ac-iPSMA could be the best option for treatment of bone metastases in prostate cancer.

Less Exploited GPCRs in Precision Medicine: Targets for Molecular Imaging and Theranostics

Precision medicine relies on individually tailored therapeutic intervention taking into account individual variability. It is strongly dependent on the availability of target-specific drugs and/or imaging agents that recognize molecular targets and patient-specific disease mechanisms. The most sensitive molecular imaging modalities, Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET), rely on the interaction between an imaging radioprobe and a target. Moreover, the use of target-specific molecular tools for both diagnostics and therapy, theranostic agents, represent an established methodology in nuclear medicine that is assuming an increasingly important role in precision medicine. The design of innovative imaging and/or theranostic agents is key for further accomplishments in the field. G-protein-coupled receptors (GPCRs), apart from being highly relevant drug targets, have also been largely exploited as molecular targets for non-invasive imaging and/or systemic radiotherapy of various diseases. Herein, we will discuss recent efforts towards the development of innovative imaging and/or theranostic agents targeting selected emergent GPCRs, namely the Frizzled receptor (FZD), Ghrelin receptor (GHSR-1a), G protein-coupled estrogen receptor (GPER), and Sphingosine-1-phosphate receptor (S1PR). The pharmacological and clinical relevance will be highlighted, giving particular attention to the studies on the synthesis and characterization of targeted molecular imaging agents, biological evaluation, and potential clinical applications in oncology and non-oncology diseases. Whenever relevant, supporting computational studies will be also discussed.