Therapeutic efficacy of an alpha-particle emitter labeled anti-GD2 humanized antibody against osteosarcoma-a proof of concept study

PURPOSE

Current treatments for osteosarcoma (OS) have a poor prognosis, particularly for patients with metastasis and recurrence, underscoring an urgent need for new targeted therapies to improve survival. Targeted alpha-particle therapy selectively delivers cytotoxic payloads to tumors with radiolabeled molecules that recognize tumor-associated antigens. We have recently demonstrated the potential of an FDA approved, humanized anti-GD2 antibody, hu3F8, as a targeted delivery vector for radiopharmaceutical imaging of OS. The current study aims to advance this system for alpha-particle therapy of OS.

METHODS

The hu3F8 antibody was radiolabeled with actinium-225, and the safety and therapeutic efficacy of the [225Ac]Ac-DOTA-hu3F8 were evaluated in both orthotopic murine xenografts of OS and spontaneously occurring OS in canines.

RESULTS

Significant antitumor activity was proven in both cases, leading to improved overall survival. In the murine xenograft's case, tumor growth was delayed by 16-18 days compared to the untreated cohort as demonstrated by bioluminescence imaging. The results were further validated with magnetic resonance imaging at 33 days after treatment, and microcomputed tomography and planar microradiography post-mortem. Histological evaluations revealed radiation-induced renal toxicity, manifested as epithelial cell karyomegaly and suggestive polyploidy in the kidneys, suggesting rapid recovery of renal function after radiation damage. Treatment of the two canine patients delayed the progression of metastatic spread, with an overall survival time of 211 and 437 days and survival beyond documented metastasis of 111 and 84 days, respectively.

CONCLUSION

This study highlights the potential of hu3F8-based alpha-particle therapy as a promising treatment strategy for OS.

Early Normal Tissue Effects and Bone Marrow Relative Biological Effectiveness for an Actinium 225-Labeled HER2/neu-Targeting Antibody

PURPOSE

In this study we determined the dose-independent relative biological effectiveness (RBE2) of bone marrow for an anti-HER2/neu antibody labeled with the alpha-particle emitter actinium 225 (225Ac). Hematologic toxicity is often a consequence of radiopharmaceutical therapy (RPT) administration, and dosimetric guidance to the bone marrow is required to limit toxicity.

METHODS AND MATERIALS

Female neu/N transgenic mice (MMTV-neu) were intravenously injected with 0 to 16.65 kBq of the alpha-particle emitter labeled antibody, 225Ac-DOTA-7.16.4, and euthanized at 1 to 9 days after treatment. Complete blood counts were performed. Femurs and tibias were collected, and bone marrow was isolated from 1 femur and tibia and counted for radioactivity. Contralateral intact femurs were fixed, decalcified, and assessed by histology. Marrow cellularity was the biologic endpoint selected for RBE2 determination. For the reference radiation, both femurs of the mice were photon irradiated with 0 to 5 Gy using a small animal radiation research platform.

RESULTS

Response as measured by cellularity for the alpha-particle emitter RPT (αRPT) RPT and the external beam radiation therapy were linear and linear quadratic, respectively, as a function of absorbed dose. The resulting dose-independent RBE2 for bone marrow was 6.

CONCLUSIONS

As αRPT gains prominence, preclinical studies evaluating RBE in vivo will be important in relating to human experience with beta-particle emitter RPT. Such normal tissue RBE evaluations will help mitigate unexpected toxicity in αRPT.

Gel-forming therapeutic peptide exhibits sustained delivery and efficacy in a mouse model of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a particularly aggressive and invasive subtype of breast cancer that represents a major cause of death of women worldwide. Here we describe the efficacy of an integrin-binding antiangiogenic peptide in a variety of delivery methods and dosing conditions. This peptide, AXT201, demonstrated consistent anti-tumor efficacy when administered intraperitoneally, subcutaneously, and intratumorally, and retained this activity even when dosing frequency was reduced to once every two weeks. Finally, in vivo imaging and biodistribution studies of AXT201 showed a long-term persistence of at least 10 days at the site of injection and a stable detectable signal in the blood over 48 h, indicating a sustained release profile. Taken together, these findings indicate AXT201 exhibits favorable pharmacokinetic properties for a 20-mer peptide.

Large-scale in vitro microdosimetry via live cell microscopy imaging: implications for radiosensitivity and RBE evaluations in alpha-emitter radiopharmaceutical therapy

BACKGROUND

Alpha-emitter radiopharmaceutical therapy (αRPT) has shown promising outcomes in metastatic disease. However, the short range of the alpha particles necessitates dosimetry on a near-cellular spatial scale. Current knowledge on cellular dosimetry is primarily based on in vitro experiments using cell monolayers. The goal of such experiments is to establish cell sensitivity to absorbed dose (AD). However, AD cannot be measured directly and needs to be modeled. Current models, often idealize cells as spheroids in a regular grid (geometric model), simplify binding kinetics and ignore the stochastic nature of radioactive decay. It is unclear what the impact of such simplifications is, but oversimplification results in inaccurate and non-generalizable results, which hampers the rigorous study of the underlying radiobiology.

METHODS

We systematically mapped out 3D cell geometries, clustering behavior, agent binding, internalization, and subcellular trafficking kinetics for a large cohort of live cells under representative experimental conditions using confocal microscopy. This allowed for realistic Monte Carlo-based (micro)dosimetry. Experimentally established surviving fractions of the HER2 + breast cancer cell line treated with a ²¹²Pb-labelled anti-HER2 conjugate or external beam radiotherapy, anchored a rigorous statistical approach to cell sensitivity and relative biological effectiveness (RBE) estimation. All outcomes were compared to a reference geometric model, which allowed us to determine which aspects are crucial model components for the proper study of the underlying radiobiology.

RESULTS

In total, 567 cells were measured up to 26 h post-incubation. Realistic cell clustering had a large (2x), and cell geometry a small (16.4% difference) impact on AD, compared to the geometric model. Microdosimetry revealed that more than half of the cells do not receive any dose for most of the tested conditions, greatly impacting cell sensitivity estimates. Including these stochastic effects in the model, resulted in significantly more accurate predictions of surviving fraction and RBE (permutation test; p < .01).

CONCLUSIONS

This comprehensive integration of the biological and physical aspects resulted in a more accurate method of cell survival modelling in αRPT experiments. Specifically, including realistic stochastic radiation effects and cell clustering behavior is crucial to obtaining generalizable radiobiological parameters.

Bone Marrow Relative Biological Effectiveness for a 212Pb-labeled Anti-HER2/neu Antibody

PURPOSE

We have determined the in vivo relative biological effectiveness (RBE) of an alpha-particle-emitting radiopharmaceutical therapeutic agent (²¹²Pb-labeled anti-HER2/neu antibody) for the bone marrow, a potentially dose-limiting normal tissue.

METHODS AND MATERIALS

The RBE was measured in mice using femur marrow cellularity as the biological endpoint. External beam radiation therapy (EBRT), delivered by a small-animal radiation research platform was used as the reference radiation. Alpha-particle emissions were delivered by ²¹²Bi after the decay of its parent nuclide ²¹²Pb, which was conjugated onto an anti-HER2/neu antibody. The alpha-particle absorbed dose to the marrow after an intravenous administration (tail vein) of 122.1 to 921.3 kBq ²¹²Pb-TCMC-7.16.4 was calculated. The mice were sacrificed at 0 to 7 days after treatment and the radioactivity from the femur bone marrow was measured. Changes in marrow cellularity were assessed by histopathology.

RESULTS

The dose response for EBRT and ²¹²Pb-anti-HER2/neu antibody were linear-quadratic and linear, respectively. On transforming the EBRT dose-response relationship into a linear relationship using the equivalent dose in 2-Gy fractions of external beam radiation formalism, we obtained an RBE (denoted RBE2) of 6.4, which is independent of cellularity and absorbed dose.

CONCLUSIONS

Because hematologic toxicity is dose limiting in almost all antibody-based RPT, in vivo measurements of RBE are important in helping identify an initial administered activity in phase 1 escalation trials. Applying the RBE2 and assuming typical antibody clearance kinetics (biological half-life of 48 hours), using a modified blood-based dosimetry method, an average administered activity of approximately 185.5 MBq (5.0 mCi) per patient could be administered before hematologic toxicity is anticipated.

Anti-GD2 antibody for radiopharmaceutical imaging of osteosarcoma

PURPOSE

Osteosarcoma (OS) is the most frequently diagnosed bone cancer in children with little improvement in overall survival in the past decades. The high surface expression of disialoganglioside GD2 on OS tumors and restricted expression in normal tissues makes it an ideal target for anti-OS radiopharmaceuticals. Since human and canine OS share many biological and molecular features, spontaneously occurring OS in canines has been an ideal model for testing new imaging and treatment modalities for human translation. In this study, we evaluated a humanized anti-GD2 antibody, hu3F8, as a potential delivery vector for targeted radiopharmaceutical imaging of human and canine OS.

METHODS

The cross-reactivity of hu3F8 with human and canine OS cells and tumors was examined by immunohistochemistry and flow cytometry. The hu3F8 was radiolabeled with indium-111, and the biodistribution of [¹¹¹In]In-hu3F8 was assessed in tumor xenograft-bearing mice. The targeting ability of [¹¹¹In]In-hu3F8 to metastatic OS was tested in spontaneous OS canines.

RESULTS

The hu3F8 cross reacts with human and canine OS cells and canine OS tumors with high binding affinity. Biodistribution studies revealed selective uptake of [¹¹¹In]In-hu3F8 in tumor tissue. SPECT/CT imaging of spontaneous OS canines demonstrated avid uptake of [¹¹¹In]In-hu3F8 in all metastatic lesions. Immunohistochemistry confirmed the extensive binding of radiolabeled hu3F8 within both osseous and soft lesions.

CONCLUSION

This study demonstrates the feasibility of targeting GD2 on OS cells and spontaneous OS canine tumors using hu3F8-based radiopharmaceutical imaging. Its ability to deliver an imaging payload in a targeted manner supports the utility of hu3F8 for precision imaging of OS and potential future use in radiopharmaceutical therapy.

Abstract 3313: Single-cell level absorbed dose assessment and radiosensitivity modeling for alpha-emitter radiopharmaceutical therapy

The radiobiological response to alpha-emitter radiopharmaceutical therapy (αRPT) is often studied in cell monolayers. In these experiments, the goal is to establish the relationship between absorbed dose and cell survival probability. However, absorbed dose is not readily known and needs to be estimated. Current models to estimate this commonly idealize cells as biologically inert spheres (geometric model). This results in inaccurate and non-generalizable results, which could hamper the rigorous study of the underlying radiobiology. The purpose of this study was to estimate the variability in absorbed dose on a single-cell level by combining 3D measurements of cell geometries, as well as the dynamics of carrier molecule binding and trafficking in individual cells with full physics simulations of the alpha emissions. This comprehensive integration of the biological and physical aspects allows for a more accurate way to model cell survival in these αRPT experiments. Live cells were imaged on a confocal microscope. Experimental conditions of previous cell survival experiments with 212Pb on NT2.5 HER2+ breast cancer cells were replicated. A relevant antibody was tagged with AF488. 3D time lapses of membrane binding kinetics and internalization were recorded. All cells were segmented into nuclei, membrane and cytosol compartments using a purpose-build algorithm. Pharmacokinetic models were fit to the temporal antibody signals, which enabled validation with experimental binding assays. Monte Carlo simulations using the exact antibody locations in each time frame allowed for the precise estimation of dose rate over time. Single-cell absorbed dose estimates were used to model previously obtained cell survival curves. Over 300 cells were measured between 0 and 26 hours post incubation. A large range in absorbed doses was observed (coefficient of variation 0.74). The median contribution of membrane-bound activity to absorbed dose was in agreement with geometric models (error less than 6%). However the contribution of antibody internalization and perinuclear trafficking to absorbed dose varied widely between cells and over time. Cell clustering contributed 46% of the total dose, and was 6x higher than in the geometric model. Applying this to previous cell survival data yielded an estimated radiosensitivity kappa of 7.1 (geometric model: 2.8). Cell clustering has a larger, and cell geometry has a smaller impact than is assumed in current models. Perinuclear trafficking of internalized Ab positively impacts cell nucleus absorbed dose, which is typically ignored. Dose variability should be included in radiosensitivity modeling. More accurate absorbed dose estimations which result from a better understanding of the different contributing factors, will improve generalizability of the radiobiological models established in these cell monolayer experiments to more complex models.

Citation Format: Remco Bastiaannet, Ioanna Liatsou, Robert Hobbs, George Sgouros. Single-cell level absorbed dose assessment and radiosensitivity modeling for alpha-emitter radiopharmaceutical 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 3313.

Abstract 213: Assessing the role of X-ray radiation in combination with a DNA-PK inhibitor on cellular activity and adhesion using an in vitro HER2-positive breast cancer model

Introduction: Breast cancer (BC) is the most common cancer for women regardless of ethnicity, and the leading cause of cancer-related deaths in women. Radiation therapy (XRT) plays a vital role in multidisciplinary treatment approaches. Although XRT has been found to reduce breast cancer recurrence and mortality rate, like all other therapeutics, XRT contains some risks. Radiation can increase the mortality rate due to the risk of ischemic heart diseases. As part of an overall effort to understand the interaction between different types of radiations (e.g., radiopharmaceutical therapy (RPT) with β or α-particle emitters) and DNA double-strand break repair (DSB) repair pathways, we observed that impairment of DNA DSB by DNA-PKcs inhibitor (NU7441) fragmented HER2-positive BC spheroids in the presence of XRT. This could be possibly due to the modulation of cellular adhesion protein mediated by DNA-PK inhibition. In this study, we aim to assess the spheroids fragmentations and also measure the cell viability and levels of a cell adhesion protein, β1-integrin in irradiated HER2-positive monolayer cells, to get a mechanistic view for XRT and NU7441 combinatorial action so as to compare with β- or α-emitter RPT.

Methods: In brief, NT2.5 BC spheroids were formed in agarose-coated 96-well plates. For both spheroids and monolayer cells, half of the media was replaced with fresh media containing 1 nM-5μM of NU7441 every other day. A colorimetric cell viability kit was used to measure cell viability and western blot analysis was performed to measure the β1-integrin level, which was normalized against β-actin.

Results: Microscopic analysis suggested that XRT increased spheroid fragmentations in the presence of NU7441 compared to the XRT alone. Interaction between XRT and NU7441 (6.68% of the total variation, P&lt;0.0001) was found for the cell viability data, where XRT (74.07% of the total variation, P&lt;0.0001) and NU7441 (5.07% of the total variation, P&lt;0.0001) both regulated cell viability on their own. Western blot data suggest that β1-integrin level was reduced for 8 Gy XRT and 5 μM NU7441 combination compared to the no XRT and vehicle combination. Moreover, 2-way ANOVA analysis revealed that XRT plays a role to regulate the β1-integrin level in NT2.5 monolayer cells (57.61% of the total variation, P&lt;0.0001).

Conclusion: XRT increased BC spheroids fragmentations when DNA damage was inhibited by a small molecule inhibitor. XRT and NU7441 both regulated NT2.5 cell viability with an interaction between them. Furthermore, XRT reduced β1-integrin level in monolayer NT2.5 cells. The XRT and NU7441 combination may induce fragmentations by decreasing cell viability and adhesion proteins. Future studies assessing the mechanisms of XRT and DNA PK inhibitor in BC spheroids and in vivo are warranted to confirm these results.

Citation Format: Mahmud Hasan, Ioanna Liatsou, George Sgouros. Assessing the role of X-ray radiation in combination with a DNA-PK inhibitor on cellular activity and adhesion using an in vitro HER2-positive breast cancer model [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 213.

212Pb-conjugated anti-rat HER2/neu antibody against a neu-N derived murine mammary carcinoma cell line: cell kill and RBE in vitro

PURPOSE

In the current work, the RBE of a ²¹²Pb-conjugated anti-HER2/neu antibody construct has been evaluated, in vitro, by colony formation assay. The RBE was estimated by comparing two absorbed dose-survival curves: the first obtained from the conjugated ²¹²Pb experiments (test radiation), the second obtained by parallel experiments of single bolus irradiation of external beam (reference radiation).

MATERIALS AND METHODS

Mammary carcinoma NT2.5 cells were treated with (0-3.70) kBq/ml of radiolabeled antibody. Nonspecific binding was assessed with addition of excess amount of unlabeled antibody. The colony formation curves were converted from activity concentration to cell nucleus absorbed dose by simulating the decay and transport of all daughter and secondary particles of ²¹²Pb, using the Monte Carlo code GEANT 4.

RESULTS

The radiolabeled antibody yielded an RBE of 8.3 at 37% survival and a survival independent RBE (i.e. RBE2) of 9.9. Unbound/untargeted ²¹²Pb-labeled antibody, as obtained in blocking experiments yielded minimal alpha-particle radiation to cells. Conclusions: These results further highlight the importance of specific targeting toward achieving tumor cell kill and low toxicity to normal tissue.

Abstract P169: Dynamic cell-level modeling of antibody binding and internalization for radiosensitivity assessements in alpha-emitter radiopharmaceutical therapy

The radiobiological response to alpha-emitter radiopharmaceutical therapy (αRPT) is often studied in cell monolayers. The geometric models which are currently used to estimate the relationship between isotope activity concentration and cell survival probability typically idealize cells as spheres without considering cellular biological processes. This results in inaccurate and non-generalizable results, which could hamper the rigorous study of the underlying radiobiology. The purpose of this study was to create accurate absorbed dose models by combining Monte Carlo simulations with 3D measurements of cell clustering and geometries, as well as dynamic carrier molecule binding and trafficking in individual cells of cell monolayers. This allows for a more accurate way to model cell survival in these αRPT experiments. Experimental conditions of previous cell survival experiments with 212Pb on NT2.5 HER2+ breast cancer cells were replicated. Live cells were imaged on a confocal microscope. Nuclei were stained with Hoechst and the media was stained with labelled dextran, creating a negative template of the cells. A relevant antibody (Ab) was tagged with AF488. 3D time lapses of membrane binding kinetics and internalization were recorded. Photobleaching was modelled and corrected for. All cells were segmented into nuclei, membrane and cytosol compartments using a purpose-build algorithm. The temporal antibody signals were used to fit pharmacokinetic models, which enabled interpolation and validation with experimental binding assays. The segmentations were used in a Monte Carlo code. S-values for every compartment and time frame were calculated using the Ab distribution directly, capturing the effect of Ab trafficking. Absorbed doses were calculated for each cell and were used to model previously obtained cell survival curves. Statistics were calculated for &gt;100 cells. We observed a large range in absorbed doses (coefficient of variation 0.74). Absorbed doses to the nucleus per unit decay on the membrane, which are mainly determined by cellular geometries, agreed with the geometric model (error &lt;6%). S-values for intercellular decays increased &gt;50% over time, which corresponds to perinuclear trafficking of Abs. The dose contribution of neighboring cells was high (46% of total dose; 6x geometric model), highlighting the importance of cell clustering. Applying this to previous cell survival data yielded an estimated radiosensitivity kappa of 7.1 (geometric model: 2.8). Cell clustering has a larger, and cell geometry has a smaller impact than is assumed in current models. Perinuclear trafficking of internalized Ab positively impacts cell nucleus absorbed dose, which is typically ignored. Dose variability should be included in radiosensitivity modeling. We intend to use such rigorous and highly detailed, cell-level analyses to arrive at simplifications that are generalizable and whose accuracy is better understood. For example, based on our findings a better accounting of cell clustering would substantially improve geometric model calculations.

Citation Format: Remco Bastiaannet, Ioanna Liatsou, Robert Hobbs, George Sgouros. Dynamic cell-level modeling of antibody binding and internalization for radiosensitivity assessements in alpha-emitter radiopharmaceutical therapy [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P169.

Abstract 1395: Humanized GD2 antibody for targeted radiopharmaceutical therapy of human and canine osteosarcoma

Osteosarcoma (OS) is the most frequently diagnosed bone tumor in children in the United States. The prognosis for metastatic or recurrent OS has remained poor (5-year survival&lt;30%) with no new effective therapies developed during the past 30 years. The high expression of tumor antigen, ganglioside GD2, on a variety of tumors, including OS, with its restricted expression on normal tissue makes GD2 an ideal target for anti-OS radiopharmaceutical therapy. Since human and canine OS shares many biological and molecular features and the prevalence of OS in dogs is 27 times higher than that in humans, spontaneously occurring OS in dogs has been shown to be an ideal model for testing new treatments for human translation. In this study, we evaluated a humanized GD2 antibody, hu3F8, that was developed for neuroblastoma therapy, as a potential delivery vector for targeted radiopharmaceutical therapy of human and canine OS.The cross immunoreactivity of hu3F8 with canine OS cells (OSCA78) and tissue, and human OS cells was confirmed by immunohistochemistry staining and flow cytometry. The binding affinity of hu3F8 to GD2 was assessed in vitro in OSCA78 and IMR32 (a human neuroblastoma cell line known expressing GD2) cell lines using 111In-DTPA-hu3F8. The dissociation constant Kd was 7.4 ± 1.0 nM for OSCA78, and 6.2 ± 1.9 nM for IMR32. Biodistribution study was performed in Nu/Nu mice bearing either OSCA78 tumor or IMR32 tumor. At 24 h after 111In-DTPA-hu3F8 injection, the highest uptake was observed in the tumor, followed by the blood, spleen, lung, and kidneys. The mean tumor uptake was 12.0% ID/g for OSCA78 tumors and 15.0% ID/g for IMR32 tumors, with a tumor-to-muscle ratio of 10.6 and 21.1, and a tumor-to-blood ratio of 1.1 and 2.4, for OSCA78 and IMR32 tumors, respectively. The 72 h biodistribution study revealed the highest uptake of 111In-DTPA-hu3F8 in both OSCA78 (28.0% ID/g) and IMR32 (51.6% ID/g ) tumors, with a tumor-to-muscle ratio of 93.3 and 206.6, and a tumor-to-blood ratio of 6.7 and 8.4, for OSCA78 tumors and IMR32 tumors, respectively. The improved uptake of 111In-DTPA-hu3F8 in tumors at 72 h was indicative of selective binding of 111In-DTPA-hu3F8 to GD2 expressing tumors. SPECT imaging showed that both OSCA78 and IMR32 tumors with 111In-DTPA-hu3F8 had superior contrast to the background, while 111In-DTPA-Rituximab (an irrelevant antibody) injected OSCA78-bearing mouse only showed moderate contrast to the background in the kidney.The cross immunoreactivity and high binding affinity of hu3F8 to canine OS cells/tissue and its ability to deliver an imaging payload (111In) suggest that conjugating hu3F8 with a radionuclide, such as alpha-emitter, 225Ac, may provide a potent radiopharmaceutical therapy for human and canine OS.

Citation Format: Yingli Fu, Jing Yu, Ioanna Liatsou, Anders Josefsson, Yong Du, Jeffrey Bryan, Dara L. Kraitchman, George Sgouros. Humanized GD2 antibody for targeted radiopharmaceutical therapy of human and canine osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1395.

Abstract 5350: RBE, in vivo, for a 212Pb-conjugated anti-HER2/neu antibody

The relative biological effectiveness is defined as the absorbed dose ratio (Dref(x)/Dtest(x)) of a reference radiation, Dref, to a test radiation, Dtest, that leads to a particular biological end-point, x. The majority of reported RBE values are obtained from in vitro irradiation of cells in monolayer culture wherein clonogenic survival is the end-point. As alpha-particle emitter radiopharmaceutical therapy (RPT) becomes a viable cancer therapy modality, RBE determinations, in vivo, are essential to assessing the potential efficacy and toxicity of alpha-emitter RPT. The aim of the study was to obtain the relative biological effectiveness, RBE, for alpha-particle emissions delivered by Bi-212, following the decay of Pb-212, conjugated onto an anti-HER2/neu antibody. Photon irradiation (200 kVp, 13 mA, 4 Gy/min, 10 × 10 mm2 collimator), delivered by a small animal radiation research platform (SARRP) was used as the reference radiation to irradiate the femurs of 6-8 weeks old female, neu/N transgenic mice (MMTV-neu). The biological endpoint was the reduction in hematopoietic cells in the region of the femur used for the RBE calculation. Alpha-particle emissions were delivered to this region by administering 325 kBq (8.8 μCi) of 212Pb-TCMC-7.16.4 intravenously (tail vein). Mice were sacrificed (n=3) at 1-7 days post-212Pb-TCMC-7.16.4 antibody administration. The long bones (femurs) were harvested, fixed with formalin and counted for radioactivity. The samples were also examined for histopathologic changes to assess the marrow cellularity. Clinical chemistry and hematological analysis were also performed on blood collected by cardiac puncture. The nadir in blood counts was observed 5 days after radiolabeled antibody injection. An absorbed dose to the marrow from the 212Bi alpha-particle emissions of 1.6 Gy yielded a marrow cellularity reduction of 50 %. The absorbed dose from XRT to achieve the same reduction in marrow cellularity was 5.7 Gy. This gives an RBE of 3.6 for a 212Pb-anti-HER2/neu antibody. Since hematologic toxicity is dose-limiting in almost all antibody-based RPT, in vivo measurements of RBE are critical to avoiding it. 2 Gy to the red marrow of low LET radiation is a threshold between low platelet toxicity grades (1 and 2) vs high (3 and 4) grade toxicity. These results suggest that the toxicity threshold for a 212Pb-antibody would be less than 1 Gy.

Citation Format: Ioanna Liatsou, Anders Josefsson, Angel Cortez, Robert F. Hobbs, Cory Brayton, Julien Torgue, George Sgouros. RBE, in vivo, for a 212Pb-conjugated anti-HER2/neu antibody [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 5350.

Cu(II) adsorption on 2-thiouracil-modified Luffa cylindrica biochar fibres from artificial and real samples, and competition reactions with U(VI)

The adsorption of Cu(II) ions by biochar fibres prior and after modification with 2-thiouracil on real and artificial samples has been studied by batch-type adsorption experiments, FTIR and XPS spectroscopy and competition reactions using U(VI) ions as competitor cations. The experimental data of the artificial samples clearly show that the modified material presents extraordinary higher affinity for Cu(II) ions even in the acidic pH range, the spectroscopic data indicate the formation of inner-sphere complexes and the competition reactions significantly higher selectivity of the 2-thiouracil modified biochar fibres for Cu(II). The 2-thiouracil-modified biochar fibres have been successfully applied to acid mine drainage (AMD) samples regarding the selective separation of Cu(II) ions from "real" samples. Regarding the desorption of copper from the biochar surface, although 100% copper recovery was achieved by eluting the metal ion using 1 M HNO3, the deterioration of the modified biochar fibers due to extensive 2-thiouracil release from the biochar surface limits the applicability of the present adsorbent in routine and large-scale applications.