Intraperitoneal alpha therapy with 224Ra-labeled microparticles combined with chemotherapy in an ovarian cancer mouse model

A novel alpha-therapy consisting of ²²⁴Ra-labeled calcium carbonate microparticles (²²⁴Ra-CaCO₃-MP) has been designed to treat micrometastatic peritoneal disease via intraperitoneal (IP) administration. This preclinical study aimed to evaluate its efficacy and tolerability when given as a single treatment or in combination with standard of care chemotherapy regimens, in a syngeneic model of ovarian cancer in immune competent mice. Female C57BL/6 mice bearing ID8-fLuc ovarian cancer were treated with ²²⁴Ra-CaCO₃-MP 1 day after IP tumor cell inoculation. The activity dosages of ²²⁴Ra ranged from 14 to 39 kBq/mouse. Additionally, ²²⁴Ra-CaCO₃-MP treatment was followed by either carboplatin (80 mg/kg)-pegylated liposomal doxorubicin (PLD, 1.6 mg/kg) or carboplatin (60 mg/kg)-paclitaxel (10 mg/kg) on day 14 post tumor cell inoculation. All treatments were administered via IP injections. Readouts included survival, clinical signs, and body weight development over time. There was a slight therapeutic benefit after single treatment with ²²⁴Ra-CaCO₃-MP compared to the vehicle control, with median survival ratios (MSRs) ranging between 1.1 and 1.3. The sequential administration of ²²⁴Ra-CaCO₃-MP with either carboplatin-paclitaxel or carboplatin-PLD indicated a synergistic effect on overall survival at certain ²²⁴Ra activities. Moreover, the combinations tested appeared well tolerated in terms of weight assessment in the first 4 weeks after treatment. Overall, this research supports the further evaluation of ²²⁴Ra-CaCO₃-MP in patients with ovarian cancer. However, the most optimal chemotherapy regimen to combine with ²²⁴Ra-CaCO₃-MP should be identified to fully exploit its therapeutic potential.

Effect of Particle Carriers for Intraperitoneal Drug Delivery on the Course of Ovarian Cancer and Its Immune Microenvironment in a Mouse Model

Novel treatment strategies are needed to provide a better prognosis for ovarian cancer. For this purpose, the current study was designed to evaluate the effects of different types of particle drug carriers on tumor response and on the tumor immune microenvironment (TME) after intraperitoneal (IP) administration in a murine tumor model. Mice with ID8-fLuc ovarian cancer were injected IP with pegylated liposomes, hydroxyapatite, polystyrene, poly(lactic-co-glycolic acid) (PLGA) and calcium carbonate (CaCO₃) microparticles to evaluate the effect of the candidate carriers without drugs. Our results show that several types of microparticle drug carriers caused hyperproliferation of the tumor when injected IP, as reflected in a reduced survival or an accelerated onset of ascites. Alterations of the product formulation of CaCO₃ microparticles could result in less hyperproliferation. The hyperproliferation caused by CaCO₃ and PLGA was largely driven by a strong innate immune suppression. A combination with chemotherapy was not able to sufficiently counteract the tumor progression caused by the drug carriers. This research points towards the importance of evaluating a drug carrier before using it in a therapeutic setting, since drug carriers themselves can detrimentally influence tumor progression and immune status of the TME. However, it remains to be determined whether the hyperproliferation in this model will be of relevance in other cancer models or in humans.

Radon-220 diffusion from 224Ra-labeled calcium carbonate microparticles: Some implications for radiotherapeutic use

Alpha-particle emitting radionuclides continue to be the subject of medical research because of their high energy and short range of action that facilitate effective cancer therapies. Radium-224 (²²⁴Ra) is one such candidate that has been considered for use in combating micrometastatic disease. In our prior studies, a suspension of ²²⁴Ra-labeled calcium carbonate (CaCO₃) microparticles was designed as a local therapy for disseminated cancers in the peritoneal cavity. The progenies of ²²⁴Ra, of which radon-220 (²²⁰Rn) is the first, together contribute three of the four alpha particles in the decay chain. The proximity of the progenies to the delivery site at the time of decay of the ²²⁴Ra-CaCO₃ microparticles can impact its therapeutic efficacy. In this study, we show that the diffusion of ²²⁰Rn was reduced in labeled CaCO₃ suspensions as compared with cationic ²²⁴Ra solutions, both in air and liquid volumes. Furthermore, free-floating lead-212 (²¹²Pb), which is generated from released ²²⁰Rn, had the potential to be re-adsorbed onto CaCO₃ microparticles. Under conditions mimicking an in vivo environment, more than 70% of the ²¹²Pb was adsorbed onto the CaCO₃ at microparticle concentrations above 1 mg/mL. Further, the diffusion of ²²⁰Rn seemed to occur whether the microparticles were labeled by the surface adsorption of ²²⁴Ra or if the ²²⁴Ra was incorporated into the bulk of the microparticles. The therapeutic benefit of differently labeled ²²⁴Ra-CaCO₃ microparticles after intraperitoneal administration was similar when examined in mice bearing intraperitoneal ovarian cancer xenografts. In conclusion, both the release of ²²⁰Rn and re-adsorption of ²¹²Pb are features that have implications for the radiotherapeutic use of ²²⁴Ra-labeled CaCO₃ microparticles. The release of ²²⁰Rn through diffusion may extend the effective range of alpha-particle dose deposition, and the re-adsorption of the longer lived ²¹²Pb onto the CaCO₃ microparticles may enhance the retention of this nuclide in the peritoneal cavity.

Abstract 3922: Biodistribution of Ra-224 and its daughter Pb-212 after intraperitoneal infusion of Ra-224 labeled microparticles in rats

Introduction: Radium-224 (Ra-224) labeled calcium carbonate (CaCO3) microparticles were developed with the intent to treat micrometastases located in the abdominal cavity. The slowly degradable microparticles act as carriers for the α-emitter Ra-224 and ensure high intraperitoneal (IP) retention of the radioactivity without cellular targeting. This novel α-therapy has a short action range in tissue and is designed to confine the radiation exposure to the IP cavity, treating both linings of the peritoneal surfaces and liquid volumes. The distribution of the Ra-224 labeled microparticles was examined by planar gamma imaging, SPECT and CT. The ex vivo biodistribution of Ra-224 and its progeny Pb-212 was also determined.

Experimental procedures: Fifteen female Wistar rats were infused IP with Ra-224-labeled microparticles (200-400 kBq, 100 mg CaCO3). The injections were performed by use of a perforated catheter (pigtail catheter), followed by a Plasmalyte flush to mimic the planned clinical administration. The Ra-224 labeled microparticles were imaged using both planar gamma imaging, SPECT and CT to evaluate the distribution over time in the abdominal region. Ex vivo biodistribution was performed 2, 24, 96, 168 and 336 hours after particle infusion and organs were harvested for activity measurements. The activity was determined at 2 hours and 48 hours after harvesting for all samples. This allowed differentiation between the biodistribution of Ra-224 and the biodistribution of its progeny Pb-212. Furthermore, 4 rats were injected IP with free Ra-224 and 2 rats were injected intravenously with free Ra-224 to achieve a baseline for the biodistribution. These control animals were euthanized at 24 and 168 hours, and 168 hours, respectively.

Results: Based on both CT and SPECT images, the particles distributed to the entire peritoneum, albeit with local areas of high microparticle concentration. Over the course of the experiment there was, as expected, a modest but evident systemic leakage of Ra-224 from the particles in the peritoneal cavity. The amount was estimated by the bone uptake of radioisotopes Pb-212 and Ra-224, using IP administered free Ra-224 as reference. The retention of Ra-224 in the peritoneal cavity was found to be > 87% at 24 hours and > 77% at 168 hours. Redistribution of the progeny Pb-212 was observed as modest uptake in the kidneys.

Conclusions: High peritoneal retention of both Ra-224 and its progeny Pb-212 after IP injection of Ra-224 labeled CaCO3 microparticles, was found in rats with high translational value to the clinical setting. SPECT imaging supported distribution of the Ra-224 labeled microparticles to the entire peritoneal lumen in the animals. SPECT and CT revealed some clusters of labeled microparticles. Due to the short range of the therapeutic relevant α-particles, the clusters are not expected to have an impact on therapeutic or safety aspects.

Citation Format: Jesper Fonslet, Carsten H. Nielsen, Lotte K. Kristensen, Ida S. Jorstad, Kim Lindland, Roy H. Larsen, Øyvind S. Bruland, Andreas Kjaer, Tina B. Bønsdorff. Biodistribution of Ra-224 and its daughter Pb-212 after intraperitoneal infusion of Ra-224 labeled microparticles in rats [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3922.

Ra-224 labeling of calcium carbonate microparticles for internal α-therapy: Preparation, stability, and biodistribution in mice

Internal therapy with α‐emitters should be well suited for micrometastatic disease. Radium‐224 emits multiple α‐particles through its decay and has a convenient 3.6 days of half‐life. Despite its attractive properties, the use of ²²⁴Ra has been limited to bone‐seeking applications because it cannot be stably bound to a targeting molecule. Alternative delivery systems for ²²⁴Ra are therefore of considerable interest. In this study, calcium carbonate microparticles are proposed as carriers for ²²⁴Ra, designed for local therapy of disseminated cancers in cavitary regions, such as peritoneal carcinomatosis. Calcium carbonate microparticles were radiolabeled by precipitation of ²²⁴Ra on the particle surface, resulting in high labeling efficiencies for both ²²⁴Ra and daughter ²¹²Pb and retention of more than 95% of these nuclides for up to 1 week in vitro. The biodistribution after intraperitoneal administration of the ²²⁴Ra‐labeled CaCO₃ microparticles in immunodeficient mice revealed that the radioactivity mainly remained in the peritoneal cavity. In addition, the systemic distribution of ²²⁴Ra was found to be strongly dependent on the amount of administered microparticles, with a reduced skeletal uptake of ²²⁴Ra with increasing dose. The results altogether suggest that the ²²⁴Ra‐labeled CaCO₃ microparticles have promising properties for use as a localized internal α‐therapy of cavitary cancers.

Therapeutic Effect of α-Emitting 224Ra-Labeled Calcium Carbonate Microparticles in Mice with Intraperitoneal Ovarian Cancer

BACKGROUND: Ovarian cancer patients with chemotherapy-resistant residual microscopic disease in the peritoneal cavity have a considerable need for new treatment options. Alpha-emitting radionuclides injected intraperitoneally may be an attractive therapeutic option in this situation as they are highly cytotoxic, while their short range in tissues can spare surrounding radiosensitive organs in the abdomen. Herein we evaluate the therapeutic efficacy of a novel α-emitting compound specifically designed for intracavitary radiation therapy. METHODS: The α-emitter ²²⁴Ra was absorbed on calcium carbonate microparticles. Immunodeficient, athymic nude mice with human ovarian cancer cells growing intraperitoneally were treated with different activity levels of ²²⁴Ra-microparticles. Tumor growth, survival, and tolerance of the treatment were assessed. Two tumor models based on the cell lines, ES-2 and SKOV3-luc, with different growth patterns were studied. RESULTS: In both models, intraperitoneal treatment with ²²⁴Ra-microparticles gave significant antitumor effect with either considerably reduced tumor volume or a survival benefit. An advantageous discovery was that only a few kilobecquerels per mouse were needed to yield therapeutic effects. The treatment was well tolerated up to a dose of 1000 kBq/kg with no signs of acute or subacute toxicity observed. CONCLUSIONS: Intraperitoneal α-therapy with ²²⁴Ra-microparticles demonstrated a significant potential for treatment of peritoneal micrometastases in ovarian carcinoma.

Preparation of 212Pb-labeled monoclonal antibody using a novel 224Ra-based generator solution

INTRODUCTION

Alpha-emitting radionuclides have gained considerable attention as payloads for cancer targeting molecules due to their high cytotoxicity. One attractive radionuclide for this purpose is ²¹²Pb, which by itself is a β-emitter, but acts as an in vivo generator for its short-lived α-emitting daughters. The standard method of preparing ²¹²Pb-labeled antibodies requires handling and evaporation of strong acids containing high radioactivity levels by the end user. An operationally easier and more rapid process could be useful since the 10.6h half-life of ²¹²Pb puts time constraints on the preparation protocol. In this study, an in situ procedure for antibody labeling with ²¹²Pb, using a solution of the generator nuclide ²²⁴Ra, is proposed as an alternative protocol for preparing ²¹²Pb-radioimmunoconjugates.

METHODS

Radium-224, the generator radionuclide of ²¹²Pb, was extracted from its parent nuclide, ²²⁸Th. Lead-212-labeling of the TCMC-chelator conjugated monoclonal antibody trastuzumab was carried out in a solution containing ²²⁴Ra in equilibrium with progeny. Subsequently, the efficiency of separating the ²¹²Pb-radioimmunoconjugate from ²²⁴Ra and other unconjugated daughter nuclides in the solution using either centrifugal separation or a PD-10 desalting size exclusion column was evaluated and compared.

RESULTS

Radiolabeling with ²¹²Pb in ²²⁴Ra-solutions was more than 90% efficient after only 30min reaction time at TCMC-trastuzumab concentrations from 0.15mg/mL and higher. Separation of ²¹²Pb-labeled trastuzumab from ²²⁴Ra using a PD-10 column was clearly superior to centrifugal separation. This method allowed recovery of approximately 75% of the ²¹²Pb-antibody-conjugate in the eluate, and the remaining amount of ²²⁴Ra was only 0.9±0.8% (n=7).

CONCLUSIONS

The current work demonstrates a novel method of producing ²¹²Pb-based radioimmunoconjugates from a ²²⁴Ra-solution, which may be simpler and less time-consuming for the end user compared with the method established for use in clinical trials of ²¹²Pb-TCMC-trastuzumab.

Evaluation of CD146 as Target for Radioimmunotherapy against Osteosarcoma

BACKGROUND

Osteosarcoma is a rare form of cancer but with a substantial need for new active drugs. There is a particular need for targeted therapies to combat metastatic disease. One possible approach is to use an antibody drug conjugate or an antibody radionuclide conjugate to target the osteosarcoma metastases and circulating tumor cells. Herein we have evaluated a radiolabeled monoclonal antibody targeting CD146 both in vitro and in vivo.

METHODS AND RESULTS

A murine monoclonal anti-CD146 IgG1 isotype antibody, named OI-3, was developed along with recombinant chimeric versions with human IgG1 or human IgG3 Fc sequences. Using flow cytometry, selective binding of OI-3 to human osteosarcoma cell lines OHS, KPDX and Saos-2 was confirmed. The results confirm a higher expression level of CD146 on human osteosarcoma cells than HER2 and EGFR; antigens targeted by commercially available therapeutic antibodies. The biodistribution of 125I-labeled OI-3 antibody variants was compared with 125I-labeled chimeric anti-EGFR antibody cetuximab in nude mice with subcutaneous OHS osteosarcoma xenografts. OI-3 was able to target CD146 expressing tumors in vivo and showed improved tumor to tissue targeting ratios compared with cetuximab. Subsequently, the three OI-3 variants were conjugated with p-SCN-Bn-DOTA and labeled with a more therapeutically relevant radionuclide, 177Lu, and their biodistributions were studied in the nude mouse model. The 177Lu-labeled OI-3 variants were stable and had therapeutically relevant biodistribution profiles. Dosimetry estimates showed higher absorbed radiation dose to tumor than all other tissues after administration of the chimeric IgG1 OI-3 variant.

CONCLUSION

Our results indicate that CD146 can be targeted in vivo by the radiolabeled OI-3 antibodies.

HES1, a target of Notch signaling, is elevated in canine osteosarcoma, but reduced in the most aggressive tumors

BACKGROUND

Hairy and enhancer of split 1 (HES1), a basic helix-loop-helix transcriptional repressor, is a downstream target of Notch signaling. Notch signaling and HES1 expression have been linked to growth and survival in a variety of human cancer types and have been associated with increased metastasis and invasiveness in human osteosarcoma cell lines. Osteosarcoma (OSA) is an aggressive cancer demonstrating both high metastatic rate and chemotherapeutic resistance. The current study examined expression of Notch signaling mediators in primary canine OSA tumors and canine and human osteosarcoma cell lines to assess their role in OSA development and progression.

RESULTS

Reverse transcriptase - quantitative PCR (RT-qPCR) was utilized to quantify HES1, HEY1, NOTCH1 and NOTCH2 gene expression in matched tumor and normal metaphyseal bone samples taken from dogs treated for appendicular OSA at the Colorado State University Veterinary Teaching Hospital. Gene expression was also assessed in tumors from dogs with a disease free interval (DFI) of <100 days compared to those with a DFI > 300 days following treatment with surgical amputation followed by standard chemotherapy. Immunohistochemistry was performed to confirm expression of HES1. Data from RT-qPCR and immunohistochemical (IHC) experiments were analyzed using REST2009 software and survival analysis based on IHC expression employed the Kaplan-Meier method and log rank analysis. Unbiased clustered images were generated from gene array analysis data for Notch/HES1 associated genes. Gene array analysis of Notch/HES1 associated genes suggested alterations in the Notch signaling pathway may contribute to the development of canine OSA. HES1 mRNA expression was elevated in tumor samples relative to normal bone, but decreased in tumor samples from dogs with a DFI < 100 days relative to those with a DFI > 300 days. NOTCH2 and HEY1 mRNA expression was also elevated in tumors relative to normal bone, but was not differentially expressed between the DFI tumor groups. Survival analysis confirmed an association between decreased HES1 immunosignal and shorter DFI.

CONCLUSIONS

Our findings suggest that activation of Notch signaling occurs and may contribute to the development of canine OSA. However, association of low HES1 expression and shorter DFI suggests that mechanisms that do not alter HES1 expression may drive the most aggressive tumors.

Differential gene expression in brain tissues of aggressive and non-aggressive dogs

BACKGROUND

Canine behavioural problems, in particular aggression, are important reasons for euthanasia of otherwise healthy dogs. Aggressive behaviour in dogs also represents an animal welfare problem and a public threat. Elucidating the genetic background of adverse behaviour can provide valuable information to breeding programs and aid the development of drugs aimed at treating undesirable behaviour. With the intentions of identifying gene-specific expression in particular brain parts and comparing brains of aggressive and non-aggressive dogs, we studied amygdala, frontal cortex, hypothalamus and parietal cortex, as these tissues are reported to be involved in emotional reactions, including aggression. Based on quantitative real-time PCR (qRT-PCR) in 20 brains, obtained from 11 dogs euthanised because of aggressive behaviour and nine non-aggressive dogs, we studied expression of nine genes identified in an initial screening by subtraction hybridisation.

RESULTS

This study describes differential expression of the UBE2V2 and ZNF227 genes in brains of aggressive and non-aggressive dogs. It also reports differential expression for eight of the studied genes across four different brain tissues (amygdala, frontal cortex, hypothalamus, and parietal cortex). Sex differences in transcription levels were detected for five of the nine studied genes.

CONCLUSIONS

The study showed significant differences in gene expression between brain compartments for most of the investigated genes. Increased expression of two genes was associated with the aggression phenotype. Although the UBE2V2 and ZNF227 genes have no known function in regulation of aggressive behaviour, this study contributes to preliminary data of differential gene expression in the canine brain and provides new information to be further explored.