Targeted Radionuclide Therapy Research Articles

287 (PB067) - Investigation of a novel radionuclide carrier for targeted radionuclide therapy

Background: In internal radiation therapy of cancer, optimal targeting ligand and type of therapeutic radionuclide must be considered carefully for effective treatment. In addition, optimal ligand and nuclide type may vary depending on diverse parameters characterizing the tumor. Thus, for use in various cancers, there is a need for the development of a carrier that can firmly bind to a variety of nuclides. Here we introduce a biocompatible iron oxide nano radionuclide carrier. By reacting nanoparticles and nuclides using our conjugate synthesizer, it is possible to bind near-permanently nuclides to our nanocarriers. Material and methods: To test the carrier’s biocompatibility, particles were labeled with a fluorescence dye and injected intravenously into female CD-1 mice. Mice were anesthetized and carrier biodistribution was recorded. In addition, to test the carrier’s radionuclide binding capabilities, carriers were radiolabeled with radioactive iodine and injected intravenously in CD-1 mice that were anesthetized and scanned using single-photon emission computed tomography (SPECT). Ligand-mediated cellular uptake of the carriers was demonstrated per iron content in human origin cancer cells qualitatively through Prussian blue staining and quantitatively by ICP-MS. Results: As a result of biodistribution studies, carriers circulated through the body during initial time points were rapidly excreted through the kidney and could be detected in the bladder at 3 hours post-injection. Rapid excretion of carriers allows for lowered whole-body radiation toxicity. SPECT data showed stable distribution of radioactive iodine throughout the whole body. Given that the normal distribution of free radioiodine is for it to accumulate in the thyroid, such a result is evidence of firm binding of nuclides to the carrier. Ligand-receptor-mediated cellular uptake of nanocarriers increased dose-dependently up to 24 hours post-treatment. Conclusions: Here we have introduced a biocompatible radionuclide carrier. Its biodistribution and near-permanent nuclide binding properties make it an admirable platform for targeted radionuclide therapy. Further in vivo studies have been carried out to test the carrier’s application for treating triple-negative breast cancers (TNBC) and platinum-resistant ovarian cancers using131I and folic acid targeted ligands. No conflict of interest.

Monte Carlo approach to comparison of parallel-hole collimators of clinical scintillation camera system for imaging astatine-211 (At-211)

Astatine-211 (At-211) is a promising alpha particle emitter for targeted radionuclide therapy. Since its daughter isotope (polonium-211(Po-211)) emits characteristic X-rays of about 80 keV, the distribution of At-211 in the body can be imaged by detecting the X-rays with a scintillation camera. However, the isotopes also emit high-energy gamma photons that are collimated with difficulty for a parallel-hole collimator of a clinical scintillation camera system, and thus the selection of a collimator is important. In this study, we compared the performances of low-energy high-resolution (LEHR), low-energy all-purpose (LEAP), medium-energy (ME), and high-energy (HE) parallel-hole collimators for At-211 using Monte Carlo simulation. We simulated a clinical scintillation camera system with the collimators using the Geant4 toolkit. The energy spectra, sensitivities, and spatial resolutions for the point source of At-211 were evaluated. Moreover, we simulated imaging of six sphere sources of At-211 in a 1-cm-thick cylindrical phantom filled with At-211 solution to evaluate image contrast. All of the results in this study are simulation data. The spatial resolution with LEHR was 7.6 mm full width at half maximum (FWHM) and the highest between collimators, while the sensitivity with LEAP was 85 cps/MBq and the highest. The image contrast acquired with the ME collimator was superior to those with the other collimators. We concluded that the LEHR, LEAP, and ME collimators had their advantages, so an optimum collimator should be selected depending on the purpose of imaging of At-211, although there was no advantage in using the HE collimator for the imaging of At-211.

A Review on Tumor Control Probability (TCP) and Preclinical Dosimetry in Targeted Radionuclide Therapy (TRT).

Targeted radionuclide therapy (TRT) uses radiopharmaceuticals to specifically irradiate tumor cells while sparing healthy tissue. Response to this treatment highly depends on the absorbed dose. Tumor control probability (TCP) models aim to predict the tumor response based on the absorbed dose by taking into account the different characteristics of TRT. For instance, TRT employs radiation with a high linear energy transfer (LET), which results in an increased effectiveness. Furthermore, a heterogeneous radiopharmaceutical distribution could result in a heterogeneous dose distribution at a tissue, cellular as well as subcellular level, which will generally reduce the tumor response. Finally, the dose rate in TRT is protracted, relatively low, and variable over time. This allows cells to repair more DNA damage, which may reduce the effectiveness of TRT. Within this review, an overview is given on how these characteristics can be included in TCP models, while some experimental findings are also discussed. Many parameters in TCP models are preclinically determined and TCP models also play a role in the preclinical stage of radiopharmaceutical development; however, this all depends critically on the calculated absorbed dose. Accordingly, an overview of the existing preclinical dosimetry methods is given, together with their limitation and applications. It can be concluded that although the theoretical extension of TCP models from external beam radiotherapy towards TRT has been established quite well, the experimental confirmation is lacking. Thus, requiring additional comprehensive studies at the sub-cellular, cellular, and organ level, which should be provided with accurate preclinical dosimetry.

A Treatment Paradigm Shift: Targeted Radionuclide Therapies for Metastatic Castrate Resistant Prostate Cancer

Simple SummaryMetastatic prostate cancer has traditionally been treated with a combination of hormonal and chemotherapy regimens. With the recent FDA approval of targeted radionuclide therapeutics, there is now a new class of therapy that is routinely available to patients and clinicians. This review explores the most commonly studied therapeutic radiopharmaceuticals and their appropriate use and contraindications. Additionally, we detail how these therapeutic radiopharmaceuticals can fit into the common medical oncology practice and future directions of this field of medicine.The recent approval of 177Lu PSMA-617 (Pluvicto®) by the United States Food and Drug Administration (FDA) is the culmination of decades of work in advancing the field of targeted radionuclide therapy for metastatic prostate cancer. 177Lu PSMA-617, along with the bone specific radiotherapeutic agent, 223RaCl2 (Xofigo®), are now commonly used in routine clinical care as a tertiary line of therapy for men with metastatic castrate resistant prostate cancer and for osseus metastatic disease respectively. While these radiopharmaceuticals are changing how metastatic prostate cancer is classified and treated, there is relatively little guidance to the practitioner and patient as to how best utilize these therapies, especially in conjunction with other more well-established regimens including hormonal, immunologic, and chemotherapeutic agents. This review article will go into detail about the mechanism and effectiveness of these radiopharmaceuticals and less well-known classes of targeted radionuclide radiopharmaceuticals including alpha emitting prostate specific membrane antigen (PSMA)-, gastrin-releasing peptide receptor (GRPR)-, and somatostatin targeted radionuclide therapeutics. Additionally, a thorough discussion of the clinical approach of these agents is included and required futures studies.

Radionuclides for Targeted Therapy: Physical Properties.

A search in PubMed revealed that 72 radionuclides have been considered for molecular or functional targeted radionuclide therapy. As radionuclide therapies increase in number and variations, it is important to understand the role of the radionuclide and the various characteristics that can render it either useful or useless. This review focuses on the physical characteristics of radionuclides that are relevant for radionuclide therapy, such as linear energy transfer, relative biological effectiveness, range, half-life, imaging properties, and radiation protection considerations. All these properties vary considerably between radionuclides and can be optimised for specific targets. Properties that are advantageous for some applications can sometimes be drawbacks for others; for instance, radionuclides that enable easy imaging can introduce more radiation protection concerns than others. Similarly, a long radiation range is beneficial in targets with heterogeneous uptake, but it also increases the radiation dose to tissues surrounding the target, and, hence, a shorter range is likely more beneficial with homogeneous uptake. While one cannot select a collection of characteristics as each radionuclide comes with an unchangeable set, all the 72 radionuclides investigated for therapy—and many more that have not yet been investigated—provide numerous sets to choose between.

Antitumor efficacy of 90Y-NM600 targeted radionuclide therapy and PD-1 blockade is limited by regulatory T cells in murine prostate tumors

BackgroundSystemic radiation treatments that preferentially irradiate cancer cells over normal tissue, known as targeted radionuclide therapy (TRT), have shown significant potential for treating metastatic prostate cancer. Preclinical studies have demonstrated...

Radionuclide Delivery Strategies in Tumor Treatment: A Systematic Review.

The aim of this review was to assess recent progress in targeted radionuclide tumor therapy, focusing on the best delivery strategies. A literature search was conducted in PubMed, Web of Science, and Scopus using the terms “radionuclides”, “liposomes”, “avidin–biotin interaction”, “theranostic”, and “molecular docking”. The 10 year filter was applied, except for the avidin–biotin interaction. Data were retrieved from both preclinical and clinical settings. Three targeting strategies were considered: pretargeting, liposomes, and ligands. Pretargeting can be achieved by exploiting the avidin–biotin interaction. This strategy seems very promising, although it has been investigated mainly in resectable tumors. Radiolabeled liposomes have attracted new interest as probes to identify the most suitable patients for treatment with liposomal formulations of common chemotherapeutics. The use of ligands for the delivery of radiotherapeutics to a specific target is still the most appealing strategy for treating tumors. The most appropriate ligand can be identified by virtually simulating its interaction with the receptor. All strategies showed great potential for use in targeted radionuclide therapy, but they also have numerous drawbacks. The most promising option is probably the one based on the use of new ligands.

Preclinical Assessment of the Combination of PSMA-Targeting Radionuclide Therapy with PARP Inhibitors for Prostate Cancer Treatment.

Prostate specific membrane antigen targeted radionuclide therapy (PSMA-TRT) is a promising novel treatment for prostate cancer (PCa) patients. However, PSMA-TRT cannot be used for curative intent yet, thus additional research on how to improve the therapeutic efficacy is warranted. A potential way of achieving this, is combining TRT with poly ADP-ribosylation inhibitors (PARPi), which has shown promising results for TRT of neuroendocrine tumor cells. Currently, several clinical trials have been initiated for this combination for PCa, however so far, no evidence of synergism is available for PCa. Therefore, we evaluated the combination of PSMA-TRT with three classes of PARPi in preclinical PCa models. In vitro viability and survival assays were performed using PSMA-expressing PCa cell lines PC3-PIP and LNCaP to assess the effect of increasing concentrations of PARPi veliparib, olaparib or talazoparib in combination with PSMA-TRT compared to single PARPi treatment. Next, DNA damage analyses were performed by quantifying the number of DNA breaks by immunofluorescent stainings. Lastly, the potential of the combination treatments was studied in vivo in mice bearing PC3-PIP xenografts. Our results show that combining PSMA-TRT with PARPi did not synergistically affect the in vitro clonogenic survival or cell viability. DNA-damage analysis revealed only a significant increase in DNA breaks when combining PSMA-TRT with veliparib and not in the other combination treatments. Moreover, PSMA-TRT with PARPi treatment did not improve tumor control compared to PSMA-TRT monotherapy. Overall, the data presented do not support the assumption that combining PSMA-TRT with PARPi leads to a synergistic antitumor effect in PCa. These results underline that extensive preclinical research using various PCa models is imperative to validate the applicability of the combination strategy for PCa, as it is for other cancer types.

Fast beta-emitter Monte Carlo simulations and full patient dose calculations of targeted radionuclide therapy: introducing egs_mird.

Targeted radionuclide therapy (TRT) is a fast-growing field garnering much interest, with several clinical trials currently underway, that has a steady increase in development of treatment techniques. Unfortunately, within the field and many clinical trials, the dosimetry calculation techniques used remain relatively simple, often using a mix of S-value calculations and kernelconvolutions. The common TRT calculation techniques, although very quick, can often ignore important aspects of patient anatomy and radionuclide distribution, as well as the interplay there-in. This paper introduces egs_mird, a new Monte Carlo (MC) application built in EGSnrc which allows users to model full patient tissue and density (using clinical CT images) and radionuclide distribution (using clinical PET images) for fast and detailed dose TRT calculation. The novel application egs_mird is introduced along with a general outline of the structure of egs_mird simulations. The general structure of the code, and the track-length (TL) estimator scoring implementation for variance reduction, is described. A new egs++ source class egs_internal_source, created to allow detailed patient-wide source distribution, and a modified version of egs_radionuclide_source, changed to be able to work with egs_internal_source, are also described. The new code is compared to other MC calculations of S-values kernels of 131 I, 90 Y, and 177 Lu in the literature, along with further self-validation using a histogram variant of the electron Fano test. Several full patient prostate 177 Lu TRT prostate cancer treatment simulations are performed using a single set of patient DICOM CT and [18 F]-DCFPyL PETdata. Good agreement is found between S-value kernels calculated using egs_mird with egs_internal_source and those found in the literature. Calculating 1000 doses (individual voxel uncertainties of ∼0.05%) in a voxel grid Fano test for monoenergetic 500keV electrons and 177 Lu electrons results in 94% and 99% of the doses being within 0.1% of the expected dose, respectively. For a hypothetical 177 Lu treatment, patient prostate, rectum, bone marrow, and bladder dose volume histograms (DVHs) results did not vary significantly when using the TL estimator and not modeling electron transport, modeling bone marrow explicitly (rather than using generic tissue compositions), and reducing activity to voxels containing partial or full calcifications to half or none, respectively. Dose profiles through different regions demonstrate there are some differences with model choices not seen in the DVH. Simulations using the TL estimator can be completed in under 15 min (∼30 min when using standard interaction scoring). This work shows egs_mird to be a reliable MC code for computing TRT doses as realistically as the patient Computed Tomography (CT) and Positron Emission Tomography (PET) data allow. Furthermore, the code can compute doses to sub-1% uncertainty within 15 min, with little to no optimization. Thus, this work supports the use of egs_mird for dose calculations inTRT.

Immune Checkpoint Inhibitor-Mediated Cancer Theranostics with Radiolabeled Anti-Granzyme B Peptide.

Although immune checkpoint inhibitors (ICI) have revolutionized cancer management, patient response can be heterogeneous, and the development of ICI resistance is increasingly reported. Novel treatment strategies are necessary not only to expand the use of ICI to previously unresponsive tumor types but also to overcome resistance. Targeted radionuclide therapy may synergize well with ICIs since it can promote a pro-inflammatory tumor microenvironment. We investigated the use of a granzyme B targeted peptide (GZP) as a cancer theranostic agent, radiolabeled with 68Ga (68Ga-GZP) as a PET imaging agent and radiolabeled with 90Y (90Y-GZP) as a targeted radionuclide therapy agent for combinational therapy with ICI in murine models of colon cancer. Our results demonstrate that GZP increasingly accumulates in tumor tissue after ICI and that the combination of ICI with 90Y-GZP promotes a dose-dependent response, achieving curative response in some settings and increased overall survival.

Searching for a Paradigm Shift in Auger-Electron Cancer Therapy with Tumor-Specific Radiopeptides Targeting the Mitochondria and/or the Cell Nucleus.

Although 99mTc is not an ideal Auger electron (AE) emitter for Targeted Radionuclide Therapy (TRT) due to its relatively low Auger electron yield, it can be considered a readily available “model” radionuclide useful to validate the design of new classes of AE-emitting radioconjugates. With this in mind, we performed a detailed study of the radiobiological effects and mechanisms of cell death induced by the dual-targeted radioconjugates 99mTc-TPP-BBN and 99mTc-AO-BBN (TPP = triphenylphosphonium; AO = acridine orange; BBN = bombesin derivative) in human prostate cancer PC3 cells. 99mTc-TPP-BBN and 99mTc-AO-BBN caused a remarkably high reduction of the survival of PC3 cells when compared with the single-targeted congener 99mTc-BBN, leading to an augmented formation of γH2AX foci and micronuclei. 99mTc-TPP-BBN also caused a reduction of the mtDNA copy number, although it enhanced the ATP production by PC3 cells. These differences can be attributed to the augmented uptake of 99mTc-TPP-BBN in the mitochondria and enhanced uptake of 99mTc-AO-BBN in the nucleus, allowing the irradiation of these radiosensitive organelles with the short path-length AEs emitted by 99mTc. In particular, the results obtained for 99mTc-TPP-BBN reinforce the relevance of targeting the mitochondria to promote stronger radiobiological effects by AE-emitting radioconjugates.

Theranostics: an integrated imaging and therapies for personalized nuclear medicine

Synopsis: Theranostics, a pairing of diagnostic biomarkers with therapeutic agents, was first introduced into nuclear medicine in 1940’s to identify the relevant molecular targets in cancer for the treatment and imaging on thyroid cancer patients with radioactive iodide-131 or RAI. Among several radionuclides used for theranostics, Lutetium-177 (177Lu), the beta-emitter, has been recognized as a radioisotope that widely used for therapeutic agent in targeted radionuclide therapy. This talk aims to review and explore the emerging radionuclides that widely used for theranostics in nuclear medicine. Radiopharmaceutical dosimetry and personalized treatment planning will also be provided in this presentation.

Radiotheranostics in oncology: current challenges and emerging opportunities.

Structural imaging remains an essential component of diagnosis, staging and response assessment in patients with cancer; however, as clinicians increasingly seek to noninvasively investigate tumour phenotypes and evaluate functional and molecular responses to therapy, theranostics - the combination of diagnostic imaging with targeted therapy - is becoming more widely implemented. The field of radiotheranostics, which is the focus of this Review, combines molecular imaging (primarily PET and SPECT) with targeted radionuclide therapy, which involves the use of small molecules, peptides and/or antibodies as carriers for therapeutic radionuclides, typically those emitting α-, β- or auger-radiation. The exponential, global expansion of radiotheranostics in oncology stems from its potential to target and eliminate tumour cells with minimal adverse effects, owing to a mechanism of action that differs distinctly from that of most other systemic therapies. Currently, an enormous opportunity exists to expand the number of patients who can benefit from this technology, to address the urgent needs of many thousands of patients across the world. In this Review, we describe the clinical experience with established radiotheranostics as well as novel areas of research and various barriers to progress.

Combination of [177Lu]Lu-DOTA-TATE Targeted Radionuclide Therapy and Photothermal Therapy as a Promising Approach for Cancer Treatment: In Vivo Studies in a Human Xenograft Mouse Model.

Peptide receptor radionuclide therapy (PRRT) relies on α- and β-emitting radionuclides bound to a peptide that commonly targets somatostatin receptors (SSTRs) for the localized killing of tumors through ionizing radiation. A Lutetium-177 (177Lu)-based probe linked to the somatostatin analog octreotate ([177Lu]Lu-DOTA-TATE) is approved for the treatment of certain SSTR-expressing tumors and has been shown to improve survival. However, a limiting factor of PRRT is the potential toxicity derived from the high doses needed to kill the tumor. This could be circumvented by combining PRRT with other treatments for an enhanced anti-tumor effect. Photothermal therapy (PTT) relies on nanoparticle-induced hyperthermia for cancer treatment and could be a useful add-on to PRRT. Here, we investigate a strategy combining [177Lu]Lu-DOTA-TATE PRRT and nanoshell (NS)-based PTT for the treatment of SSTR-expressing small-cell lung tumors in mice. Our results showed that the combination treatment improved survival compared to PRRT alone, but only when PTT was performed one day after [177Lu]Lu-DOTA-TATE injection (one of the timepoints examined), showcasing the effect of treatment timing in relation to outcome. Furthermore, the combination treatment was well-tolerated in the mice. This indicates that strategies involving NS-based PTT as an add-on to PRRT could be promising and should be investigated further.

Abstract 2732: A mathematical model for optimization of combination therapy involving targeted radionuclide and CAR-T cell therapy

Abstract Background: Immunotherapy with chimeric antigen receptor - T (CAR-T) cells and targeted radionuclide therapy (TRT) are two highly promising therapies in cancer treatment. Often, these therapies show limited efficacy in complete eradication of cancer cells making the combination of these two therapies an attractive cancer treatment option. The complications involved in dosing and scheduling of these therapies make mathematical modeling an appropriate method for analyzing and predicting disease response to these therapies. Here we propose a mathematical model evaluating disease response to the combination of these two therapies and explore the optimization of their dosing and scheduling. Methods: An ordinary differential equation-based formalism is proposed for simulation of tumor response to CAR-T cell therapy as well as TRT. CAR-T cell dose and injected radioactivity was input to the model. Among others, key model parameters included tumor proliferation rate, tumor cell and CAR-T cell radiosensitivity, CAR-T cell killing rate, CAR-T cell decay rate indicating persistence. Preclinical experiments involving CS1- CAR-T cell therapy and 225Ac-DOTA-Daratumumab TRT in a multiple myeloma mice model were used to parameterize the model. Sensitivity study of the model parameters using overall survival (OS) and progression-free survival (PFS) as evaluation metrics, was performed to elucidate the parameters with highest impact. Results: OS and PFS were 97 and 55 days when CAR-T cell therapy was given prior to TRT as compared to OS of 43 days for untreated control mice. Sensitivity study of model parameters showed that tumor proliferation has the highest impact on survival metrics. For a ±50% change in tumor proliferation rate, OS changed by -41%/+111% and PFS changed by -62%/+147%. Similar changes in TRT injected activity and CAR-T cell dose changed OS by ± 15% and ±21% respectively. Accordingly, PFS changed by roughly ±32% and ±45% respectively. A variation of the interval between the therapies showed that faster growing tumors required a shorter interval between the two therapies. The sequence of therapies was also changed and TRT prior to CAR-T cell therapy demonstrated shorter PFS (43 days) due to the adverse effects of radiation on CAR-T cells. Conclusion: For a fixed dose of TRT and CAR-T cells, tumor proliferation rate was found to be the prime factor impacting therapy interval. The presented work shows the key parameters required for planning and optimizing preclinical experiments and clinical trials. Using disease, CAR-T cell and radionuclide-specific parameters as shown in this work as well as incorporating immune stimulating effects of radiation would make it an extremely potent tool for optimizing combination therapies. Citation Format: Vikram Adhikarla, Dennis Awuah, Alexander B. Brummer, Enrico Caserta, Amrita Krishnan, Flavia Pichiorri, Megan M. Minnix, John E. Shively, Jeffrey Y.C. Wong, Xiuli Wang, Russell C. Rockne. A mathematical model for optimization of combination therapy involving targeted radionuclide and CAR-T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2732.

Abstract 1306: Radionuclide-specific effects of 90Y-, 177Lu-, or 225Ac-NM600 targeted radionuclide therapy on tumor immunomodulation and enhancing immunotherapy response in murine tumor models

Abstract Purpose: In preclinical studies, we have demonstrated that delivering low dose radiation to all tumor sites utilizing 90Y-NM600 improves the response to immune checkpoint inhibitors (ICIs). NM600 is an alkylphosphocholine analog that is selectively taken up and retained in murine and human tumors. In this study, the immunomodulatory capacities of three distinct radionuclides (90Y, 177Lu, 225Ac) were compared using immunologically cold syngeneic murine tumor models: MOC2 head and neck squamous cell carcinoma (HNSCC) and B78 melanoma. We hypothesized that physical properties of radionuclides (e.g. emission type, linear energy transfer (LET), half-life, dose rate) would differentially impact immunomodulation by TRT and ICI treatment response. Methods: Dosimetry performed using the Monte Carlo-based RAPID platform utilizing serial 86Y-NM600 PET/CT imaging determined that 100 μCi 90Y-NM600 or 200 μCi 177Lu-NM600 delivered ~12Gy to the MOC2 tumor and ~4Gy to the B78 tumor. 225Ac-NM600 was dosed at activities ≤0.5 μCi, as determined to be safe and effective previously. Mice bearing two MOC2, B78 WT, or Tmem173 -/- CRISPR deletion B78 (STING KO) tumors were randomized to receive external beam radiation therapy (EBRT), an equivalent tumor dose of 90Y- or 177Lu-NM600, 0.25 μCi 225Ac-NM600, or no radiation +/- dual ICI (anti-CTLA4 and anti-PDL1). Tumors, blood, bone marrow, and spleen were harvested at days 4, 7, 14, and 21 post-treatment for flow cytometry and RT-qPCR. Additional mice were monitored for tumor growth and survival following these treatments. Results: TRT and EBRT induced favorable tumor-specific immune cell infiltration (increased CD8/Treg ratio) at day 7. 225Ac-NM600 additionally induced similar changes at day 21, consistent with the longer half-life radioisotope (90Y: 65h; 177Lu: 161h; 225Ac: 240h). Expression of immune susceptibility markers (Mhc1, Pdl1) and type I interferon (IFN1) response-associated genes (Ifnβ1, Mx1) was upregulated following 12 Gy EBRT or TRT both in vitro and in vivo compared to non-irradiated controls in MOC2 cells and tumors. The timing and magnitude of these effects correlated with radionuclide half-life and LET. 225Ac-NM600 + ICI improved overall survival in B78 WT mice over 90Y- or 177Lu-NM600 + ICI, 225Ac-NM600 or ICI monotherapy, and non-irradiated controls. In the B78 STING KO melanoma cell line, this 225Ac-NM600 + ICI survival benefit was decreased. Conclusions: These studies demonstrate the capacity to deliver immunomodulatory radiation to tumors using gamma-, beta- or alpha-emitting TRT. The physical properties of the delivered radionuclide dictate timing and magnitude of the IFN1 response stimulated by TRT. Understanding these effects may be critical to safely and effectively integrating TRT and immunotherapies to enhance anti-tumor immunity in cancer patients. Citation Format: Caroline P. Kerr, Amber M. Bates, Joseph J. Grudzinski, Carolina A. Ferreira, Julia Sheehan-Klenk, David Adam, Maria Powers, Wonjong Jin, Justin C. Jagodinsky, Raghava N. Sriramaneni, Paul A. Clark, Luke Zangl, Anatoly N. Pinchuk, Alejandro J. Onate, Ria Kumari, Cynthia Choi, Christopher F. Massey, Bryan Bednarz, Reinier Hernandez, Jamey P. Weichert, Zachary S. Morris. Radionuclide-specific effects of 90Y-, 177Lu-, or 225Ac-NM600 targeted radionuclide therapy on tumor immunomodulation and enhancing immunotherapy response in murine tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1306.

IgG-Binding Nanobody Capable of Prolonging Nanobody-Based Radiotracer Plasma Half-Life and Enhancing the Efficacy of Tumor-Targeted Radionuclide Therapy.

Nanobodies have been developed rapidly as targeted probes for molecular imaging owing to their high affinity, outstanding tissue penetration, and rapid blood clearance. However, the short retention time at the tumor site limits their application in targeted radionuclide therapy. In this study, we designed a dual-targeting nanobody referred to as MIRC213-709, which can specifically bind to the HER2 receptor in tumor cell lines with high affinity (by nanobody MIRC213) and endogenous IgG in plasma to prolong the half-life by the MIRC213 C-terminal fusion nanobody, MIRC709. The nanobodies were site-specifically radiolabeled with 99mTc and 177Lu, and radiochemical purity was >95% after purification. The long blood circulation time and tumor retention property of 99mTc/177Lu-MIRC213-709 were confirmed by a blood clearance assay, single-photon emission computed tomography (SPECT), and a biodistribution study. The blood clearance assay showed that the distribution phase half-life (T1/2α) and elimination phase half-life (T1/2β) of 99mTc-MIRC213-709 were 6.74- and 19.04-fold longer than those of 99mTc-MIRC213, respectively. The SPECT/CT and biodistribution results showed that the highest uptake of 177Lu-MIRC213 in the NCI-N87 model was 5.24 ± 0.95% ID/g at 6 h p.i., while the highest uptake of 177Lu-MIRC213-709 in the NCI-N87 model was 30.82 ± 7.29% ID/g at 48 h p.i. Compared with 177Lu-MIRC213, 177Lu-MIRC213-709 had a 16.9-fold increased tumor cumulative uptake (2606 ± 195.1 vs 153.9 ± 22.37% ID/g·h). The targeted radionuclide therapy assay was performed in the NCI-N87 tumor model, and treatment monitoring ended on day 32. The post-treatment/pretreatment tumor volumes were 12.99 ± 1.66, 3.58 ± 0.96, 1.26 ± 0.17, and 1.54 ± 0.50 in the 0, 9, and 18 MBq single-dose groups and the two 9 MBq divided dose group (14 days apart), respectively. All treatment groups showed significant therapeutic effects (P < 0.0001). Thus, fusion with the IgG-binding nanobody MIRC709 provides MIRC213 derivatives with improved metabolic properties for targeted radionuclide therapy.

Copper-67-Labeled Bombesin Peptide for Targeted Radionuclide Therapy of Prostate Cancer.

The gastrin-releasing peptide receptor (GRPR) is a promising molecular target for imaging and therapy of prostate cancer using bombesin peptides that bind to the receptor with high affinity. Targeted copper theranostics (TCTs) using copper radionuclides, 64Cu for imaging and 67Cu for therapy, offer significant advantages in the development of next-generation theranostics. [64Cu]Cu-SAR-BBN is in clinical development for PET imaging of GRPR-expressing cancers. This study explores the therapeutic efficacy of [67Cu]Cu-SAR-BBN in a pre-clinical mouse model. The peptide was radiolabeled with 67Cu, and specific binding of the radiolabeled peptide towards GRPR-positive PC-3 prostate cancer cells was confirmed with 52.2 ± 1.4% total bound compared to 5.8 ± 0.1% with blocking. A therapy study with [67Cu]Cu-SAR-BBN was conducted in mice bearing PC-3 tumors by injecting 24 MBq doses a total of six times. Tumor growth was inhibited by 93.3% compared to the control group on day 19, and median survival increased from 34.5 days for the control group to greater than 54 days for the treatment group. The ease and stability of the radiochemistry, favorable biodistribution, and the positive tumor inhibition demonstrate the suitability of this copper-based theranostic agent for clinical assessment in the treatment of cancers expressing GRPR.

Rational Design and Pharmacomodulation of Protein-Binding Theranostic Radioligands for Targeting the Fibroblast Activation Protein.

The fibroblast activation protein (FAP), overexpressed on cancer-associated fibroblasts (CAFs), has become a valuable target for tumor diagnosis and therapy. However, most FAP-based radioligands show insufficient tumor uptake and retention. In this study, three novel albumin-binding FAP ligands (denoted as FSDD0I, FSDD1I, and FSDD3I) were labeled with 68Ga and 177Lu to overcome these limitations. Cell-based studies and molecular docking assays were performed to identify the specificity and protein-binding properties for FAP. Positron emission tomography (PET) scans in human hepatocellular carcinoma patient-derived xenografts (HCC-PDXs) animal models revealed longer blood retention of 68Ga-FSDD0I than 68Ga-FAPI-04, 68Ga-FSDD1I, and 68Ga-FSDD3I. Remarkably, 68Ga-FSDD3I had prominent tumor-to-nontarget (T/NT) ratios. The prominent tumor retention properties of 177Lu-FSDD0I in single photon emission computed tomography (SPECT) imaging and biodistribution studies were demonstrated. In summary, this study reports a proof-of-concept study of albumin-binding radioligands for FAP-targeted imaging and targeted radionuclide therapy (TRT).

Development of a multi faceted platform containing a tetrazine, fluorophore and chelator: synthesis, characterization, radiolabeling, and immuno-SPECT imaging

BackgroundCombining optical (fluorescence) imaging with nuclear imaging has the potential to offer a powerful tool in personal health care, where nuclear imaging offers in vivo functional whole-body visualization, and the fluorescence modality may be used for image-guided tumor resection. Varying chemical strategies have been exploited to fuse both modalities into one molecular entity. When radiometals are employed in nuclear imaging, a chelator is typically inserted into the molecule to facilitate radiolabeling; the availability of the chelator further expands the potential use of these platforms for targeted radionuclide therapy if a therapeutic radiometal is employed. Herein, a novel mixed modality scaffold which contains a tetrazine (Tz)––for biomolecule conjugation, fluorophore—for optical imaging, and chelator—for radiometal incorporation, in one construct is presented. The novel platform was characterized for its fluorescence properties, radiolabeled with single-photon emission computed tomography (SPECT) isotope indium-111 (111In3+) and therapeutic alpha emitter actinium-225 (225Ac3+). Both radiolabels were conjugated in vitro to trans-cyclooctene (TCO)-modified trastuzumab; biodistribution and immuno-SPECT imaging of the former conjugate was assessed.ResultsKey to the success of the platform synthesis was incorporation of a 4,4′-dicyano-BODIPY fluorophore. The route gives access to an advanced intermediate where final chelator-incorporated compounds can be easily accessed in one step prior to radiolabeling or biomolecule conjugation. The DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) conjugate was prepared, displayed good fluorescence properties, and was successfully radiolabeled with 111In & 225Ac in high radiochemical yield. Both complexes were then separately conjugated in vitro to TCO modified trastuzumab through an inverse electron demand Diels–Alder (IEDDA) reaction with the Tz. Pilot small animal in vivo immuno-SPECT imaging with [111In]In-DO3A-BODIPY-Tz-TCO-trastuzumab was also conducted and exhibited high tumor uptake (21.2 ± 5.6%ID/g 6 days post-injection) with low uptake in non-target tissues.ConclusionsThe novel platform shows promise as a multi-modal probe for theranostic applications. In particular, access to an advanced synthetic intermediate where tailored chelators can be incorporated in the last step of synthesis expands the potential use of the scaffold to other radiometals. Future studies including validation of ex vivo fluorescence imaging and exploiting the pre-targeting approach available through the IEDDA reaction are warranted.