Targeted Radionuclide Therapy Research Articles

Comparative study on application of 177Lu-labeled rituximab, tetulomab, cetuximab and huA33 monoclonal antibodies to targeted radionuclide therapy

Purpose Dose coefficients from rituximab, tetulomab, cetuximab, and huA33 monoclonal antibodies labelled with the radionuclide 177Lu were estimated for human organs and tumours via a theoretical simulation based on experimental results. Methods The real experimental results were obtained from radiopharmaceutical distribution in hairless mice. Using the Sparks and Aydogan method, the cumulated activity for humans was recalculated. The simulation was used to assess the behaviour of MAbs labelled with 177Lu after injection into the human body. The average absorbed doses were calculated for the most exposed organs and tissues. Results The huA33 monoclonal antibodies (MAbs) labelled with 177Lu (Lu-rituximab, Lu-tetulomab, Lu-cetuximab, and Lu-huA33), presented the maximum nuclear transformation per Bq intake for the main organs (blood, kidneys, liver, lung, and spleen, as well as for a tumour) The absorbed dose in the liver is three times lower for Lu-huA33 compared to the other drugs. In the case of cetuximab, the spleen received the lowest dose compared to the other drugs. The dependencies on absorbed dose for the alveolar, bronchioles, bone surface, heart wall, kidneys, liver, lung, lymphatic nodes, and spleen, are presented. For tumours, the absorbed dose for each drug is calculated separately for a sphere of unit volume by using the information on the injected dose. Conclusion, The ratios of the dose coefficient for the tumour to each organ, indicate that lutetium-177 can be recommended for targeted radionuclide therapy since the dose per tumour is much greater than the dose per organ.

Astatine-211 labelled a small molecule peptide: specific cell killing in vitro and targeted therapy in a nude-mouse model

Abstract Extensive interest in the development of α-emitting radionuclides astatine-211 (211At) stems from the potential superiority for the treatment of smaller tumors, disseminated disease, and metastatic disease. VP2, a small molecule fusion peptide, can specifically bind to the VPAC1 receptor which is over-expressed in malignant epithelial tumors. In our recent study, we performed the preparation of 211At labelled VP2 through a one-step method. In this work, we explored the targeted radionuclide therapy with [211At]At-SPC-VP2 in vitro and in vivo. The cytotoxicity and specific cell killing of [211At]At-SPC-VP2 were evaluated using the CCK-8 assay. Compared with the [211At]NaAt, the VPAC1-targeted radionuclide compound [211At]At-SPC-VP2 showed more effective cytotoxicity in vitro. Targeted radioactive therapy trial was carried out in non-small-cell lung cancer (NSCLC) xenograft mice. For the therapy experiment, 4 groups of mice were injected via the tail vein with 370 kBq, 550 kBq, 740 kBq, 3 × ∼246 kBq of [211At]At-SPC-VP2, of which the second and third injections were given 4 and 8 days after the first injection, respectively. As controls, animals were treated with saline or 550 kBq [211At]NaAt. The body weight and tumor size of mice were monitored before the administration and every 2 days thereafter. Cytotoxic radiation of partial tissue samples such as kidneys, liver and stomach of mice were assessed by immunohistochemical examination. The tumor growth was inhibited and significantly improved survival was achieved in mice treated with [211At]At-SPC-VP2, two-fold prolongation of survival compared with the control group, which received normal saline or 550 kBq [211At]NaAt. No renal or hepatic toxicity was observed in the mice receiving [211At]At-SPC-VP2, but gastric pathological sections showed 211At uptake in stomach resulting in later toxicity, highlighting the importance of further enhancing the stability of labelled compounds.

Estimating the Relative Biological Effectiveness of Auger Electron Emitter 123I in Human Lymphocytes

Auger electron emitters are considered to be a promising strategy for targeted radionuclide therapy of metastatic diseases, given their high linear energy transfer (LET) and short range in tissue which could potentially limit normal tissue toxicity. Particularly, Auger electron emitters that can be targeted into the DNA of tumor cells have been considered as an attractive cancer therapy in the past decade. In this study, the efficiency of induction of chromosomal damage by Auger electron emitter 123I (half-life 13.2 hours) was investigated by using the cytokinesis-block micronucleus assay. A stannylated deoxyuridine was synthesized and radiolabeled with 123I, resulting in 123IUdR that carried the Auger electron emitter across the nuclear membrane and allowed its incorporation into newly synthesized DNA. The DNA damage caused by the 123I Auger cascade was estimated by evaluating the induced micronuclei frequencies in human peripheral blood lymphocytes obtained from three different donors. The isolated lymphocytes were stimulated with phytohaemagglutinin (1 mg/mL) for 48 hours before pulse labelling with 123IUdR and the S-phase fraction was determined using flow cytometry. Geant4 Monte Carlo calculations were performed to determine the absorbed dose in cells by the Auger emitter. The relative biological effectiveness (RBE) was calculated by comparing the dose response curves for 123IUdR with the reference dose response curves, obtained by 60Co γ-ray irradiation, for lymphocytes of the same donors. This resulted in a range of individual RBE values from 3 up to 10, depending on the donor and the radiation dose. In addition, dose limiting RBE values (RBEMax) were calculated for each donor and ranged from 5 to 11, dependent on the inherent radiosensitivity of the donors. This study provides valuable information on the RBE of Auger electron emitter 123I, which is identified as a promising theranostic radionuclide for future targeted radionuclide therapy.

Structural Characterization of the Solution Chemistry of Zirconium(IV) Desferrioxamine: A Coordination Sphere Completed by Hydroxides.

Positron emission tomography (PET) using radiolabeled, monoclonal antibodies has become an effective, noninvasive method for tumor detection and is a critical component of targeted radionuclide therapy. Metal ion chelator and bacterial siderophore desferrioxamine (DFO) is the gold standard compound for incorporation of zirconium-89 in radiotracers for PET imaging because it is thought to form a stable chelate with [89Zr]Zr4+. However, DFO may not bind zirconium-89 tightly in vivo, with free zirconium-89 reportedly liberated into the bones of experimental mouse models. Although high bone uptake has not been observed to date in humans, this potential instability has been proposed to be related to the unsaturated coordination sphere of [89Zr]Zr-DFO, which is thought to consist of the 3 hydroxamate groups of DFO and 1 or 2 water molecules. In this study, we have used a combination of X-ray absorption spectroscopy and density functional theory (DFT) geometry optimization calculations to further probe the coordination chemistry of this complex in solution. We find the extended X-ray absorption fine structure (EXAFS) curve fitting of an aqueous solution of Zr(IV)-DFO to be consistent with an 8-coordinate Zr with oxygen ligands. DFT calculations suggest that the most energetically favorable Zr(IV) coordination environment in DFO likely consists of the 3 hydroxamate ligands from DFO, each with bidentate coordination, and 2 hydroxide ligands. Further EXAFS curve fitting provides additional support for this model. Therefore, we propose that the coordination sphere of Zr(IV)-DFO is most likely completed by 2 hydroxide ligands rather than 2 water molecules, forming Zr(DFO)(OH)2.

Evaluation of Actinium-225 Labeled Minigastrin Analogue [225Ac]Ac-DOTA-PP-F11N for Targeted Alpha Particle Therapy.

The overexpression of cholecystokinin B receptor (CCKBR) in human cancers led to the development of radiolabeled minigastrin analogues for targeted radionuclide therapy, which aims to deliver cytotoxic radiation specifically to cancer cells. Alpha emitters (e.g., actinium-225) possess high potency in cancer cell-killing and hold promise for the treatment of malignant tumors. In these preclinical studies, we developed and evaluated CCKBR-targeted alpha particle therapy. The cellular uptake and cytotoxic effect of actinium-225 labeled and HPLC-purified minigastrin analogue [225Ac]Ac-PP-F11N were characterized in the human squamous cancer A431 cells transfected with CCKBR. Nude mice bearing A431/CCKBR tumors were used for biodistribution and therapy studies followed by histological analysis and SPECT/CT imaging. In vitro, [225Ac]Ac-PP-F11N showed CCKBR-specific and efficient internalization rate and potent cytotoxicity. The biodistribution studies of [225Ac]Ac-PP-F11N revealed CCKBR-specific uptake in tumors, whereas the therapeutic studies demonstrated dose-dependent inhibition of tumor growth and extended mean survival time, without apparent toxicity. The histological analysis of kidney and stomach indicated no severe adverse effects after [225Ac]Ac-PP-F11N administration. The post-therapy SPECT-CT images with [111In]In-PP-F11N confirmed no CCKBR-positive tumor left in the mice with complete remission. In conclusion, our study demonstrates therapeutic efficacy of [225Ac]Ac-PP-F11N without acute radiotoxicity in CCKBR-positive cancer model.

Cellular S-value evaluation based on real human cell models using the GATE MC package

Exploring the spatial distribution of the energy loss of ionising radiation at the subcellular level is indispensable for evaluating the radiobiological effects of targeted radionuclide therapy accurately. Believing that S-values are important for obtaining the target dose, the Committee on Medical Internal Radiation Dose (MIRD) proposed a method to obtain the cellular dosimetric parameter. However, most available data on cellular S-values were calculated based on simple geometric models, such as ellipsoids or spheres, which do not accurately reflect biological reality. To investigate the influence of the cellular model on S-values, calculations were performed for two kinds of polygon-surface phantom models of realistic, individual human cells, the lung epithelial cell model (the B2B Phantom model) and the hepatocyte model (the Liver Phantom model), using the Monte Carlo (MC) software package GATE. To analyse the influence of cell geometry on the final S-value, the differences in the S-values between the realistic cell models and simple geometric sphere and ellipsoid models with similar volumes were calculated and compared for six different combinations of source and target regions. The irradiation conditions were 0.01–1.10 MeV monoenergetic electron sources and the Auger electronic therapy nuclides Ga-67, Tc-99m, In-111, I-125 and Tl-201, which are commonly used in nuclear medicine. The S-values calculated in this study are different from the results of the simple geometry models proposed by previous researchers. Two more precise polygon-surface phantom models of realistic, individual human cells were used, which provided more accurate information about the cell dose and will be very useful for the diagnostic application of radiotherapy in the future.

New Bifunctional Chelator 3p-C-NEPA for Potential Applications in Lu(III) and Y(III) Radionuclide Therapy and Imaging.

We have developed structurally unique bifunctional chelators in the NETA, NE3TA, and DEPA series for potential radiopharmaceutical applications. As part of our continued research efforts to generate efficient bifunctional chelators for targeted radionuclide therapy and imaging of various diseases, we designed a scorpion-like chelator that is proposed to completely saturate the coordination spheres of Y(III) and Lu(III). We herein report the synthesis and evaluation of a new chelator (3p-C-NEPA) with 10 donor groups for complexation with β-emitting radionuclides 90Y(III), 86Y(III), and 177Lu(III). The chelator was synthesized and evaluated for radiolabeling kinetics with the readily available radioisotopes 90Y and 177Lu, and the corresponding 90Y or 177Lu-radiolabeled complexes were evaluated for in vitro stability in human serum and in vivo complex stability in mice. The new chelator rapidly bound 90Y or 177Lu and formed a stable complex with the radionuclides. The new chelator 3p-C-NEPA radiolabeled with either 90Y or 177Lu remains stable in human serum without dissociation for 10 days. 177Lu-labeled 3p-C-NEPA produced a favorable in vivo biodistribution profile in normal mice.

Combination Strategies to Improve Targeted Radionuclide Therapy.

In recent years, targeted radionuclide therapy (TRT) has emerged as a promising strategy for cancer treatment. In contrast to conventional radiotherapy, TRT delivers ionizing radiation to tumors in a targeted manner, reducing the dose that healthy tissues are exposed to. Existing TRT strategies include the use of 177Lu-DOTATATE, 131I-metaiodobenzylguanidine, Bexxar, and Zevalin, clinically approved agents for the treatment of neuroendocrine tumors, neuroblastoma, and non-Hodgkin lymphoma, respectively. Although promising results have been obtained with these agents, clinical evidence acquired to date suggests that only a small percentage of patients achieves complete response. Consequently, there have been attempts to improve TRT outcomes through combinations with other therapeutic agents; such strategies include administering concurrent TRT and chemotherapy, and the use of TRT with known or putative radiosensitizers such as poly(adenosine diphosphate ribose) polymerase and mammalian-target-of-rapamycin inhibitors. In addition to potentially achieving greater therapeutic effects than the respective monotherapies, these strategies may lead to lower dosages or numbers of cycles required and, in turn, reduce unwanted toxicities. As of now, several clinical trials have been conducted to assess the benefits of TRT-based combination therapies, sometimes despite limited preclinical evidence being available in the public domain to support their use. Although some clinical trials have yielded promising results, others have shown no clear survival benefit from particular combination treatments. Here, we present a comprehensive review of combination strategies with TRT reported in the literature to date and evaluate their therapeutic potential.

Targeted Radionuclide Therapy in Patient-Derived Xenografts Using 177Lu-EB-RGD.

Currently, most patients with non-small cell lung cancer (NSCLC) are diagnosed in advanced stages with a poor five-year survival rate. Therefore, intensive research aimed at finding novel therapeutic strategies has been ongoing; experimental models that reliably emulate NSCLC disease are greatly needed to predict responses to novel therapeutics. Therefore, we developed patient-derived xenograft (PDX) models of NSCLC, which we then used to evaluate the therapeutic efficacy of 177Lu-EB-RGD, a peptide-based radiopharmaceutical with improved pharmacokinetics that targets integrin αvβ3 In this study, three different groups of NSCLC-PDXs were successfully established, all of which maintained the same IHC and genetic characteristics of the human primary tumor. The two NSCLC-PDX groups with intense and low expression of integrin αvβ3 (denoted as PDXαvβ3+ and PDXαvβ3-) were chosen as the experimental models to evaluate the in vivo biological behavior of 177Lu-EB-RGD. In SPECT imaging and biodistribution studies, 177Lu-EB-RGD showed significantly higher accumulation in PDXαvβ3+ and PDXαvβ3- models than its corresponding monomer 177Lu-RGD. A single dose of 18.5 MBq 177Lu-EB-RGD was enough to completely eradicate the tumors in PDXαvβ3+, with no sign of tumor recurrence during the observation period. Such treatment was also efficacious in PDXαvβ3-: a single dose of 29.6 MBq 177Lu-EB-RGD led to a significant delay in tumor growth as compared with that in the control or 177Lu-RGD group. The preclinical data from the use of this model suggest that 177Lu-EB-RGD may be an effective treatment option for NSCLC and should be further evaluated in human trials.

Investigation of a Pharmacological Approach for Reduction of Renal Uptake of Radiolabeled ADAPT Scaffold Protein.

Albumin binding domain-Derived Affinity ProTeins (ADAPTs) are small (5 kDa) engineered scaffold proteins that are promising targeting agents for radionuclide-based imaging. A recent clinical study has demonstrated that radiolabeled ADAPTs can efficiently visualize human epidermal growth factor receptor 2 (HER2) expression in breast cancer using SPECT imaging. However, the use of ADAPTs directly labeled with radiometals for targeted radionuclide therapy is limited by their high reabsorption and prolonged retention of activity in kidneys. In this study, we investigated whether a co-injection of lysine or gelofusin, commonly used for reduction of renal uptake of radiolabeled peptides in clinics, would reduce the renal uptake of [99mTc]Tc(CO)3-ADAPT6 in NMRI mice. In order to better understand the mechanism behind the reabsorption of [99mTc]Tc(CO)3-ADAPT6, we included several compounds that act on various parts of the reabsorption system in kidneys. Administration of gelofusine, lysine, probenecid, furosemide, mannitol, or colchicine did not change the uptake of [99mTc]Tc(CO)3-ADAPT6 in kidneys. Sodium maleate reduced the uptake of [99mTc]Tc(CO)3-ADAPT6 to ca. 25% of the uptake in the control, a high dose of fructose (50 mmol/kg) reduced the uptake by ca. two-fold. However, a lower dose (20 mmol/kg) had no effect. These results indicate that common clinical strategies are not effective for reduction of kidney uptake of [99mTc]Tc(CO)3-ADAPT6 and that other strategies for reduction of activity uptake or retention in kidneys should be investigated for ADAPT6.

Production of Copper Radionuclides in Compact Medical Cyclotrons using Solid Targets.

Over the last several years there has been a growing interest in the use of radiopharmaceuticals labeled with metallic radionuclides, especially isotopes of copper (Cu). Cu has a unique set of radionuclides with a potential application not only for diagnostic imaging but also for applications in targeted radionuclide therapy. To review the methods and routes used for the production of Cu radionuclides in compact medical cyclotrons (Ep<20 MeV) using solid targets. The cyclotron production of Cu radionuclides using solid targets has proven to be very efficient. The large number of compact medical cyclotrons distributed worldwide, and the high target yields in the production of Cu radionuclides achieved at these energies, form a potential network of distribution to satisfy the growing demand for these radionuclides, especially 64Cu.

Human dosimetry of free 211At and meta-[211At]astatobenzylguanidine (211At-MABG) estimated using preclinical biodistribution from normal mice

Background211At is one of the ideal nuclides for targeted radionuclide therapies (TRTs). Meta-[211At]astatobenzylguanidine (211At-MABG) has been proposed for the treatment of pheochromocytoma. To effectively use these radiopharmaceuticals, dosimetry must be performed. It is important to determine the absorbed doses of free 211At and 211At-MABG to determine the organs that may be at risk when using TRTs. The aim of this study was to estimate human dosimetry from preclinical biodistribution of free 211At and 211At-MABG in various organs in normal mice.MethodsMale C57BL/6 N mice were administered 0.13 MBq of free 211At or 0.20 MBq of 211At-MABG by tail-vein injection. The mice were sacrificed at 5 min, and at 1, 3, 6, and 24 h after the injection (n = 5 for each group). The percentage of injected activity per mass in organs and blood (%IA/g) was determined. The human absorbed doses of free 211At and 211At-MABG were calculated using the Organ Level INternal Dose Assessment/EXponential Modeling (OLINDA/EXM) version 2.0 and IDAC-Dose 2.1.ResultsHigh uptake of free 211At was observed in the lungs, spleen, salivary glands, stomach, and thyroid. The absorbed doses of free 211At in the thyroid and several tissues were higher than those of 211At-MABG. The absorbed doses of 211At-MABG in the adrenal glands, heart wall, and liver were higher than those of free 211At.ConclusionsThe absorbed doses of 211At-MABG in organs expressing the norepinephrine transporter were higher than those of free 211At. In addition, the biodistribution of free 211At was different from that of 211At-MABG. The absorbed dose of free 211At may help predict the organs potentially at risk during TRTs using 211At-MABG due to deastatination.

γ-Tocotrienol-Loaded Liposomes for Radioprotection from Hematopoietic Side Effects Caused by Radiotherapeutic Drugs.

With the successful development and increased use of targeted radionuclide therapy for treating cancer comes the increased risk of radiation injury to bone marrow-both direct suppression and stochastic effects, leading to neoplasia. Herein, we report a novel radioprotector drug, a liposomal formulation of γ-tocotrienol (GT3), or GT3-Nano for short, to mitigate bone marrow radiation damage during targeted radionuclide therapy. Methods: GT3 was loaded into liposomes using passive loading. 64Cu-GT3-Nano and 3H-GT3-Nano were synthesized to study the in vivo biodistribution profile of the liposome and GT3 individually. The radioprotection efficacy of GT3-Nano was assessed after acute 137Cs whole-body irradiation at a sublethal (4 Gy), a lethal (9 Gy), or a single high-dose administration of 153Sm-ethylenediamine-N,N,N',N'-tetrakis(methylene phosphonic acid) (EDTMP). Flow cytometry and fluorescence microscopy were used to analyze hematopoietic cell population dynamics and the cellular site of GT3-Nano localization in the spleen and bone marrow, respectively. Results: Bone marrow uptake and retention (percentage injected dose per gram of tissue) at 24 h was 6.98 ± 2.34 for 64Cu-GT3-Nano and 7.44 ± 2.52 for 3H-GT3-Nano. GT3-Nano administered 24 h before or after 4 Gy of total-body irradiation (TBI) promoted rapid and complete hematopoietic recovery, whereas recovery of controls stalled at 60%. GT3-Nano demonstrated dose-dependent radioprotection, achieving 90% survival at 50 mg/kg against lethal 9-Gy TBI. Flow cytometry of the bone marrow indicated that progenitor bone marrow cells MPP2 and CMP were upregulated in GT3-Nano-treated mice. Immunohistochemistry showed that GT3-Nano accumulates in CD105-positive sinusoid epithelial cells. Conclusion: GT3-Nano is highly effective in mitigating the marrow-suppressive effects of sublethal and lethal TBI in mice. GT3-Nano can facilitate rapid recovery of hematopoietic components in mice treated with the endoradiotherapeutic agent 153Sm-EDTMP.

Monte Carlo dosimetry of a realistic multicellular model of follicular lymphoma in a context of radioimmunotherapy.

Small-scale dosimetry studies generally consider an artificial environment where the tumors are spherical and the radionuclides are homogeneously biodistributed. However, tumor shapes are irregular and radiopharmaceutical biodistributions are heterogeneous, impacting the energy deposition in targeted radionuclide therapy. To bring realism, we developed a dosimetric methodology based on a three-dimensional in vitro model of follicular lymphoma incubated with rituximab, an anti-CD20 monoclonal antibody used in the treatment of non-Hodgkin lymphomas, which might be combined with a radionuclide. The effects of the realistic geometry and biodistribution on the absorbed dose were highlighted by comparison with literature data. Additionally, to illustrate the possibilities of this methodology, the effect of different radionuclides on the absorbed dose distribution delivered to the in vitro tumor were compared. The starting point was a model named multicellular aggregates of lymphoma cells (MALC). Three MALCs of different dimensions and their rituximab biodistribution were considered. Geometry, antibody location and concentration were extracted from selective plane illumination microscopy. Assuming antibody radiolabeling with Auger electron (125 I and 111 In) and β- particle emitters (177 Lu, 131 I and 90 Y), we simulated energy deposition in MALCs using two Monte Carlo codes: Geant4-DNA with "CPA100" physics models for Auger electron emitters and Geant4 with "Livermore" physics models for β- particle emitters. MALCs had ellipsoid-like shapes with major radii, r, of ~0.25, ~0.5 and ~1.3mm. Rituximab was concentrated in the periphery of the MALCs. The absorbed doses delivered by 177 Lu, 131 I and 90 Y in MALCs were compared with literature data for spheres with two types of homogeneous biodistributions (on the surface or throughout the volume). Compared to the MALCs, the mean absorbed doses delivered in spheres with surface biodistributions were between 18% and 38% lower, while with volume biodistribution they were between 15% and 29% higher. Regarding the radionuclides comparison, the relationship between MALC dimensions, rituximab biodistribution and energy released per decay impacted the absorbed doses. Despite releasing less energy, 125 I delivered a greater absorbed dose per decay than 111 In in the r~0.25mm MALC (6.78·10-2 vs 6.26·10-2 µGy·Bq-1 ·s-1 ). Similarly, the absorbed doses per decay in the r~0.5mm MALC for 177 Lu (2.41·10-2 µGy·Bq-1 ·s-1 ) and 131 I (2.46·10-2 µGy·Bq-1 ·s-1 ) are higher than for 90 Y (1.98·10-2 µGy·Bq-1 ·s-1 ). Furthermore, radionuclides releasing more energy per decay delivered absorbed dose more uniformly through the MALCs. Finally, when considering the radiopharmaceutical effective half-life, due to the biological half-life of rituximab being best matched by the physical half-life of 177 Lu and 131 I compared to 90 Y, the first two radionuclides delivered higher absorbed doses. In the simulated configurations, β- emitters delivered higher and more uniform absorbed dose than Auger electron emitters. When considering radiopharmaceutical half-lives, 177 Lu and 131 I delivered absorbed doses higher than 90 Y. In view of real irradiation of MALCs, such a work may be useful to select suited radionuclides and to help explain the biological effects.

Abstract 2262: Low-dose targeted radionuclide therapy has favorable local and systemic effects on immune populations in a murine prostate cancer model

Abstract Introduction: Prostate cancer remains the second leading cause of cancer-related death in American men because of its metastatic, incurable form. Prostate cancer responds poorly to checkpoint blockade likely due to its immunosuppressive microenvironment with relatively few infiltrating CD8+ T cells, limited mutational burden, and activity of myeloid-derived suppressor cells (MDSCs). External beam radiotherapy (EBRT) has been shown to help overcome this suppressive state, but EBRT is infeasible for patients with widely metastatic disease. Our group has developed a compound called NM600 that can be used to deliver radiation to all sites of disease simultaneously in an approach called Targeted radionuclide therapy (TRT). However, the effects of TRT on immune populations within prostate tumors are not yet well described. In this study, we examined the effects of TRT in the form of 90Y-NM600 on mice bearing Myc-CaP prostate tumors. Methods: 6-week old male FVB mice were implanted subcutaneously with Myc-CaP cells, then given a single intravenous injection of either 50 (“low-dose”) or 250 (“high-dose”) μCi of 90Y-NM600, estimated to deliver 3.1 Gy or 15.5 Gy to 300 mm3 tumors, respectively. Groups of mice (n=3) were then euthanized at several timepoints following TRT administration. Their tumors and spleens were collected for analysis by flow cytometry and Luminex cytokine analysis. A separate group (n=5) were followed for survival to 2000 mm3. Results: Flow cytometry of splenocytes revealed that high-dose, but not low-dose TRT caused a 6-fold increase in numbers of MDSCs (p = 0.002) at Day 21 compared to baseline. Additionally, low-dose TRT caused a 2-fold (p = 0.005) increase in CD8+ T cells at Day 21 compared to baseline, unlike in the high-dose condition. These CD8+ T cells in the low-dose TRT condition were predominantly proliferating naïve T cells. Flow cytometry of tumor infiltrating lymphocytes showed a 13% increase in CD8+ T cells in both dose conditions at Day 14 (p = 0.03). Returning CD8+ T cells displayed high expression of PD-1, CTLA-4, and LAG-3. Within the tumor, there was an 8-fold increase in chemokines including CXCL1, Rantes, and MIP2 at Day 21, suggesting that there may be further recruitment of tumor infiltrating cells even three weeks following treatment. Mice treated with high-dose TRT (median survival 37 days, p = .029) had significantly improved median survival compared to control (median survival 23 days), unlike low-dose treated mice (median survival 29 days, p =.250). Conclusions: These data suggest that low-dose TRT is superior for immunomodulation because, although it has little effect on tumor growth, it increases intratumoral CD8+ T cell infiltration while avoiding deleterious systemic immune effects. We hypothesize that immunomodulatory TRT combined with checkpoint blockade will improve anti-tumor efficacy compared to high-dose TRT. Citation Format: Hemanth Kumar Potluri, Reinier Hernandez, Christopher D. Zahm, Joseph Grudzinski, Christopher Massey, Jamey Weichert, Douglas G. McNeel. Low-dose targeted radionuclide therapy has favorable local and systemic effects on immune populations in a murine prostate cancer model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2262.

Abstract 903: In vivo efficacy of bempegaldesleukin, immune checkpoint inhibition, and targeted radionuclide therapy in immunocompetent murine model of head and neck cancer

Abstract In preclinical studies, we have demonstrated that delivering low dose radiation therapy to all sites of metastatic cancer using targeted radionuclide therapy (TRT) can improve the response to immune checkpoint blockade. NM600 is a tumor-targeting alkylphosphocholine radiolabeled with 90Y. Following intravenous administration, NM600 is selectively taken up and retained in most murine and human cancer cells. Bempegaldesleukin (NKTR-214) is a first in class, CD122-preferential interleukin-2 (IL2) pathway agonist being studied for its ability to influence the IL2 pathway and selectively stimulate an immune response. The primary objective of this study was to test the hypothesis that NKTR-214 and 90Y-NM600 would increase the response to immune checkpoint blockade in the immunologically “cold” MOC2 syngeneic mouse model of head and neck squamous cell carcinoma (HNSCC). C57BL/6 female mice were engrafted with MOC2, a murine HNSCC cell line, in the right flank. When mean tumor volume reached ~100mm3, mice were randomized into eight treatment groups using a 2 × 2 × 2 study design for combinations of NKTR-214, 90Y-NM600, and anti-CTLA4. 100 µCi 90Y-NM600 was administered intravenously (IV, treatment day 1). Prior in vivo dosimetry performed using the Monte Carlo based RAPID platform following serial 86Y-NM600 PET/CT imaging demonstrated that this activity delivered ~8Gy to the MOC2 tumor. 200 µg anti-CTLA4 was delivered by intraperitoneal injection on days 4, 7, and 10. 16 µg NKTR-214 was given IV on days 6, 15, and 24. Tumor growth was monitored. In a parallel study, cohorts of mice were treated with PBS (control), NKTR-214, 90Y-NM600, or NKTR-214 + 90Y-NM600, and tumors were collected at day 14 for flow cytometry analysis. In the spontaneously metastatic, immunologically “cold” MOC2 HNSCC tumor model, 62.5% of mice treated with the combination of 90Y-NM600, NKTR-214, and anti-CTLA4 experienced complete tumor response, and these mice showed no observable primary or metastatic disease 60 days after treatment initiation. No mice receiving single or dual therapy combinations exhibited complete tumor response (p = &amp;lt;0.01). Treatment with NKTR-214 + 90Y-NM600 resulted in increased tumor infiltration by CD8+ T cells. Intriguingly, 90Y-NM600 triggered increased expression of the IL-2β receptor, CD122, on the surface of tumor infiltrating CD8+ T cells, suggesting a novel mechanism of synergy with NKTR-214. Combination therapy with NKTR-214, 90Y-NM600, and anti-CTLA4 resulted in complete and durable tumor response in a difficult to treat murine model of HNSCC. Therapeutic interaction between TRT and NKTR-214 may be a result from low dose radiation increasing the expression of CD122 on tumor infiltrating lymphocytes. Further preclinical and early phase clinical investigations are warranted to evaluate the therapeutic potential of such combinations. Citation Format: Gustavo A. Sosa, Amber M. Bates, Ravi Patel, Reinier Hernandez, Joseph J. Grudzinski, Ian Marsh, Bryan Bednarz, Alexander Pieper, Erin Nystuen, Sarah Emma, Elizabeth G. Sumiec, Jamey P. Weichert, Zachary S. Morris. In vivo efficacy of bempegaldesleukin, immune checkpoint inhibition, and targeted radionuclide therapy in immunocompetent murine model of head and neck cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 903.

Abstract 6511: Androgen receptor (AR) genomic alterations and clinical outcome with prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy

Abstract Background: Prostate-specific membrane antigen is a cell-surface glycoprotein commonly expressed on prostatic adenocarcinomas (PC). PSMA expression is related to AR signaling, generally with increased PSMA expression with dysregulation of the AR pathway. Targeted radionuclide therapies (TRT) involving radionuclides (177Lu, 225Ac, 90Y) conjugated to PSMA-specific antibodies (e.g. J591) or small molecule ligands (e.g. PSMA-617) are being developed and utilized in clinical trials. Genetic profiling of PC may predict responsiveness to PSMA-based therapies. Because of the relationship of AR and PSMA expression, we sought to assess the association between AR genomic aberrations and outcome following PSMA-TRT. Methods: Eligible subjects with progressive metastatic castration-resistant PC were enrolled in prospective PSMA-TRT clinical trials. Those who underwent targeted or whole-exome sequencing of their tumors were analyzed. Pre-treatment baseline clinical data were collected; outcome measures included PSA decline and overall survival (OS) post-therapy. Chi-square test was used to assess the association of AR alterations and PSA decline with multivariable logistic regression to control for known factors associated with response. The Kaplan-Meier method was used to assess OS with multivariable cox proportional hazards regression analysis to evaluate the independent effect of AR alterations on OS after controlling for prognostic variables. Results: 66 men with median age 69.6 years were enrolled. 38 (57%) received 177Lu-PSMA-617, 16 (24%) 177Lu-J591, 7 (11%) 225Ac-J591, and 5 (8%) both 177Lu-PSMA-617 and 177Lu-J591. The majority (59%) were poor-risk CALGB (Halabi) prognostic group. 31 patients (47%) had AR amplifications or resistance mutations. Patients with AR alterations were less likely to experience ≥30% PSA decline (32.3% vs. 62.9%, p=0.025) compared to wild-type, though this association was less significant after controlling for radionuclide dose and PSMA imaging intensity. AR alterations were associated with shortened OS (12.43 vs. 21.07 months, p=0.043). After controlling for radionuclide dose, Halabi group, PSMA imaging intensity, and receipt of subsequent FDA-approved life-prolonging therapies, AR alterations still were associated with shortened OS (HR 2.07 [1.02-4.2], p=0.04). Conclusion: AR resistance mutations and amplifications appear to result in poorer outcome following PSMA-TRT both in terms of PSA decline and overall survival. Genetic sequencing may inform responses to PSMA-based therapies, and prospective genomic panel testing is ongoing. Supported by: Weill Cornell Medicine, Prostate Cancer Foundation, Department of Defense, NIH Citation Format: Michael Sun, Muhammad Niaz, Charlene Thomas, Ariel Schaap, Kristine Lacuna, Panagiotis Vlachostergios, Paul Christos, Ana M. Molina, David M. Nanus, Cora N. Sternberg, Joseph Osborne, Neil H. Bander, Scott T. Tagawa. Androgen receptor (AR) genomic alterations and clinical outcome with prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6511.

A theranostic approach of [68Ga]Ga-DOTA.SA.FAPi PET/CT-guided [177Lu]Lu-DOTA.SA.FAPi radionuclide therapy in an end-stage breast cancer patient: new frontier in targeted radionuclide therapy.

A theranostic approach of [68Ga]Ga-DOTA.SA.FAPi PET/CT-guided [177Lu]Lu-DOTA.SA.FAPi radionuclide therapy in an end-stage breast cancer patient: new frontier in targeted radionuclide therapy.

A Genomic Profile of Local Immunity in the Melanoma Microenvironment Following Treatment with α Particle-Emitting Ultrasmall Silica Nanoparticles.

An α particle-emitting nanodrug that is a potent and specific antitumor agent and also prompts significant remodeling of local immunity in the tumor microenvironment (TME) has been developed and may impact the treatment of melanoma. Biocompatible ultrasmall fluorescent core–shell silica nanoparticles (C′ dots, diameter ∼6.0 nm) have been engineered to target the melanocortin-1 receptor expressed on melanoma through α melanocyte-stimulating hormone peptides attached to the C′ dot surface. Actinium-225 is also bound to the nanoparticle to deliver a densely ionizing dose of high-energy α particles to cancer. Nanodrug pharmacokinetic properties are optimal for targeted radionuclide therapy as they exhibit rapid blood clearance, tumor-specific accumulation, minimal off-target localization, and renal elimination. Potent and specific tumor control, arising from the α particles, was observed in a syngeneic animal model of melanoma. Surprisingly, the C′ dot component of this drug initiates a favorable pseudopathogenic response in the TME generating distinct changes in the fractions of naive and activated CD8 T cells, Th1 and regulatory T cells, immature dendritic cells, monocytes, MΦ and M1 macrophages, and activated natural killer cells. Concomitant upregulation of the inflammatory cytokine genome and adaptive immune pathways each describes a macrophage-initiated pseudoresponse to a viral-shaped pathogen. This study suggests that therapeutic α-particle irradiation of melanoma using ultrasmall functionalized core–shell silica nanoparticles potently kills tumor cells, and at the same time initiates a distinct immune response in the TME.

The electron affinity of astatine

One of the most important properties influencing the chemical behavior of an element is the electron affinity (EA). Among the remaining elements with unknown EA is astatine, where one of its isotopes, 211At, is remarkably well suited for targeted radionuclide therapy of cancer. With the At− anion being involved in many aspects of current astatine labeling protocols, the knowledge of the electron affinity of this element is of prime importance. Here we report the measured value of the EA of astatine to be 2.41578(7) eV. This result is compared to state-of-the-art relativistic quantum mechanical calculations that incorporate both the Breit and the quantum electrodynamics (QED) corrections and the electron–electron correlation effects on the highest level that can be currently achieved for many-electron systems. The developed technique of laser-photodetachment spectroscopy of radioisotopes opens the path for future EA measurements of other radioelements such as polonium, and eventually super-heavy elements.