Calcium Carbonate Microparticles as Carriers of 224Ra: Impact of Specific Activity in Mice with Intraperitoneal Ovarian Cancer

Eighteen-Months Safety and Efficacy Following Intraperitoneal Treatment With 224Radium-Labeled Microparticles After CRS-HIPEC in Patients With Peritoneal Metastasis From Colorectal Cancer

BACKGROUND AND OBJECTIVES

Peritoneal metastasis from colorectal cancer carries a high risk for relapse after cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC). A novel alpha-emitting radiopharmaceutical (Radspherin) has been designed to deliver short-range radiation to micrometastases and free-floating tumor cells.

METHODS

A Phase 1/2a study evaluated the safety, tolerability, and signal of efficacy of escalating doses of Radspherin injected intraperitoneally after CRS-HIPEC.

RESULTS

Eleven patients received 1-4 MBq (Group 1) whereas 12 patients received 7 MBq; nine patients single dose/three patients split-dose (Group 2). Median age was 66.5 and 61.5 years, and median peritoneal cancer index 6 and 7, respectively. One hundred and seventy-eight adverse events were reported, only seven were deemed related to Radspherin. Thirteen serious adverse events (SAEs) were reported in eight patients and no SAEs were related to Radspherin. At 18-months, none of the 12 patients receiving 7 MBq experienced peritoneal recurrences, however four had non-peritoneal recurrences. Across both groups (n = 22), 41% had recurrent disease, only 14% of them in the peritoneum.

CONCLUSIONS

Radspherin was well tolerated. At 18 months, median disease-free survival has not been reached, and none of the patients receiving the recommended dose (7 MBq) had peritoneal recurrences. The results are encouraging and warrant further clinical evaluation.

Functionalized Calcium Carbonate-Based Microparticles as a Versatile Tool for Targeted Drug Delivery and Cancer Treatment

Nano- and microparticles are increasingly widely used in biomedical research and applications, particularly as specific labels and targeted delivery vehicles. Silica has long been considered the best material for such vehicles, but it has some disadvantages limiting its potential, such as the proneness of silica-based carriers to spontaneous drug release. Calcium carbonate (CaCO3) is an emerging alternative, being an easily available, cost-effective, and biocompatible material with high porosity and surface reactivity, which makes it an attractive choice for targeted drug delivery. CaCO3 particles are used in this field in the form of either bare CaCO3 microbeads or core/shell microparticles representing polymer-coated CaCO3 cores. In addition, they serve as removable templates for obtaining hollow polymer microcapsules. Each of these types of particles has its specific advantages in terms of biomedical applications. CaCO3 microbeads are primarily used due to their capacity for carrying pharmaceutics, whereas core/shell systems ensure better protection of the drug-loaded core from the environment. Hollow polymer capsules are particularly attractive because they can encapsulate large amounts of pharmaceutical agents and can be so designed as to release their contents in the target site in response to specific stimuli. This review focuses first on the chemistry of the CaCO3 cores, core/shell microbeads, and polymer microcapsules. Then, systems using these structures for the delivery of therapeutic agents, including drugs, proteins, and DNA, are outlined. The results of the systematic analysis of available data are presented. They show that the encapsulation of various therapeutic agents in CaCO3-based microbeads or polymer microcapsules is a promising technique of drug delivery, especially in cancer therapy, enhancing drug bioavailability and specific targeting of cancer cells while reducing side effects. To date, research in CaCO3-based microparticles and polymer microcapsules assembled on CaCO3 templates has mainly dealt with their properties in vitro, whereas their in vivo behavior still remains poorly studied. However, the enormous potential of these highly biocompatible carriers for in vivo applications is undoubted. This last issue is addressed in depth in the Conclusions and Outlook sections of the review.

Size-dependent therapeutic efficiency of 223Ra-labeled calcium carbonate carriers for internal radionuclide therapy of breast cancer

The size of drug carriers strongly affects their biodistribution, tissue penetration, and cellular uptake in vivo. As a result, when such carriers are loaded with therapeutic compounds, their size can influence the treatment outcomes. For internal α-radionuclide therapy, the carrier size is particularly important, because short-range α-emitters should be delivered to tumor volumes at a high dose rate without any side effects, i.e. off-target irradiation and toxicity. In this work, we aim to evaluate and compare the therapeutic efficiency of calcium carbonate (CaCO3) microparticles (MPs, >2 μm) and nanoparticles (NPs, <100 nm) labeled with radium-223 (223Ra) for internal α-radionuclide therapy against 4T1 breast cancer. To do this, we comprehensively study the internalization and penetration efficiency of these MPs and NPs, using 2D and 3D cell cultures. For further therapeutic tests, we develop and modify a chelator-free method for radiolabeling of CaCO3 MPs and NPs with 223Ra, improving their radiolabeling efficiency (>97%) and radiochemical stability (>97%). After intratumoral injection of 223Ra-labeled MPs and NPs, we demonstrate their different therapeutic efficiencies against a 4T1 tumor. In particular, 223Ra-labeled NPs show a tumor inhibition of approximately 85%, which is higher compared to 60% for 223Ra-labeled MPs. As a result, we can conclude that 223Ra-labeled NPs have a more suitable biodistribution within 4T1 tumors compared to 223Ra-labeled MPs. Thus, our study reveals that 223Ra-labeled CaCO3 NPs are highly promising for internal α-radionuclide therapy.

Targeted Radium Alpha Therapy in the Era of Nanomedicine: In Vivo Results

Targeted alpha-particle therapy using radionuclides with alpha emission is a rapidly developing area in modern cancer treatment. To selectively deliver alpha-emitting isotopes to tumors, targeting vectors, including monoclonal antibodies, peptides, small molecule inhibitors, or other biomolecules, are attached to them, which ensures specific binding to tumor-related antigens and cell surface receptors. Although earlier studies have already demonstrated the anti-tumor potential of alpha-emitting radium (Ra) isotopes-Radium-223 and Radium-224 (223/224Ra)-in the treatment of skeletal metastases, their inability to complex with target-specific moieties hindered application beyond bone targeting. To exploit the therapeutic gains of Ra across a wider spectrum of cancers, nanoparticles have recently been embraced as carriers to ensure the linkage of 223/224Ra to target-affine vectors. Exemplified by prior findings, Ra was successfully bound to several nano/microparticles, including lanthanum phosphate, nanozeolites, barium sulfate, hydroxyapatite, calcium carbonate, gypsum, celestine, or liposomes. Despite the lengthened tumor retention and the related improvement in the radiotherapeutic effect of 223/224Ra coupled to nanoparticles, the in vivo assessment of the radiolabeled nanoprobes is a prerequisite prior to clinical usage. For this purpose, experimental xenotransplant models of different cancers provide a well-suited scenario. Herein, we summarize the latest achievements with 223/224Ra-doped nanoparticles and related advances in targeted alpha radiotherapy.

Biocompatible conjugated polymer nanoparticles labeled with 225Ac for tumor endoradiotherapy

Recently, endoradiotherapy based on actinium-225 (225Ac) has attracted increasing attention, which is due to its α particles can generate maximal damage to cancer cells while minimizing unnecessary radiation effects on healthy tissues. Herein, 111In/225Ac-radiolabeled conjugated polymer nanoparticles (CPNs) coated with amphiphilic polymer DSPE-PEG-DOTA have been developed as a new injectable nano-radiopharmaceuticals for cancer endoradiotherapy under the guidance of nuclear imaging. Single photon emission computed tomography/computed tomography (SPECT/CT) using 111In-DOTA-PEG-CPNs as nano probe indicates a prolonged retention of radiolabeled nanocarriers, which was consistent with the in vivo biodistribution examined by direct radiometry analysis. Significant inhibition of tumor growth has been observed in murine 4T1 models treated with 225Ac-DOTA-PEG-CPNs when compared to mice treated with PBS or DOTA-PEG-CPNs. The 225Ac-DOTA-PEG-CPNs group experienced no single death within 24 days with the median survival considerably extended to 35 days, while all the mice treated with PBS or DOTA-PEG-CPNs died at 20 days post injection. Additionally, the histopathology studies demonstrated no obvious side effects on healthy tissues after treatment with 225Ac-DOTA-PEG-CPNs. All these results reveal that the new 225Ac-labeled DOTA-PEG-CPNs is promising as paradigm for endoradiotherapy.

Gadolinium-Based Nanoparticles Sensitize Ovarian Peritoneal Carcinomatosis to Targeted Radionuclide Therapy

Ovarian cancer (OC) is the most lethal gynecologic malignancy (5-y overall survival rate, 46%). OC is generally detected when it has already spread to the peritoneal cavity (peritoneal carcinomatosis). This study investigated whether gadolinium-based nanoparticles (Gd-NPs) increase the efficacy of targeted radionuclide therapy using [177Lu]Lu-DOTA-trastuzumab (an antibody against human epidermal growth factor receptor 2). Gd-NPs have radiosensitizing effects in conventional external-beam radiotherapy and have been tested in clinical phase II trials. Methods: First, the optimal activity of [177Lu]Lu-DOTA-trastuzumab (10, 5, or 2.5 MBq) combined or not with 10 mg of Gd-NPs (single injection) was investigated in athymic mice bearing intraperitoneal OC cell (human epidermal growth factor receptor 2-positive) tumor xenografts. Next, the therapeutic efficacy and toxicity of 5 MBq of [177Lu]Lu-DOTA-trastuzumab with Gd-NPs (3 administration regimens) were evaluated. NaCl, trastuzumab plus Gd-NPs, and [177Lu]Lu-DOTA-trastuzumab alone were used as controls. Biodistribution and dosimetry were determined, and Monte Carlo simulation of energy deposits was performed. Lastly, Gd-NPs' subcellular localization and uptake, and the cytotoxic effects of the combination, were investigated in 3 cancer cell lines to obtain insights into the involved mechanisms. Results: The optimal [177Lu]Lu-DOTA-trastuzumab activity when combined with Gd-NPs was 5 MBq. Moreover, compared with [177Lu]Lu-DOTA-trastuzumab alone, the strongest therapeutic efficacy (tumor mass reduction) was obtained with 2 injections of 5 mg of Gd-NPs/d (separated by 6 h) at 24 and 72 h after injection of 5 MBq of [177Lu]Lu-DOTA-trastuzumab. In vitro experiments showed that Gd-NPs colocalized with lysosomes and that their radiosensitizing effect was mediated by oxidative stress and inhibited by deferiprone, an iron chelator. Exposure of Gd-NPs to 177Lu increased the Auger electron yield but not the absorbed dose. Conclusion: Targeted radionuclide therapy can be combined with Gd-NPs to increase the therapeutic effect and reduce the injected activities. As Gd-NPs are already used in the clinic, this combination could be a new therapeutic approach for patients with ovarian peritoneal carcinomatosis.

Radiolabeled nanomaterials for biomedical applications: radiopharmacy in the era of nanotechnology

BACKGROUND

Recent advances in nanotechnology have offered new hope for cancer detection, prevention, and treatment. Nanomedicine, a term for the application of nanotechnology in medical and health fields, uses nanoparticles for several applications such as imaging, diagnostic, targeted cancer therapy, drug and gene delivery, tissue engineering, and theranostics.

RESULTS

Here, we overview the current state-of-the-art of radiolabeled nanoparticles for molecular imaging and radionuclide therapy. Nanostructured radiopharmaceuticals of technetium-99m, copper-64, lutetium-177, and radium-223 are discussed within the scope of this review article.

CONCLUSION

Nanoradiopharmaceuticals may lead to better development of theranostics inspired by ingenious delivery and imaging systems. Cancer nano-theranostics have the potential to lead the way to more specific and individualized cancer treatment.

The aqueous chemistry of radium

Available literature data on the aqueous chemistry of radium are compiled. There are limited available experimental data and a significant portion of the data has been estimated using electrostatic techniques, typically based on the corresponding data of barium. The available data are compared with the corresponding data of barium (and strontium) and a methodology for estimating additional radium thermochemical data is described.

A Novel Single-Step-Labeled 212Pb-CaCO3 Microparticle for Internal Alpha Therapy: Preparation, Stability, and Preclinical Data from Mice

Lead-212 is recognized as a promising radionuclide for targeted alpha therapy for tumors. Many studies of ²¹²Pb-labeling of various biomolecules through bifunctional chelators have been conducted. Another approach to exploiting the cytotoxic effect is coupling the radionuclide to a microparticle acting as a carrier vehicle, which could be used for treating disseminated cancers in body cavities. Calcium carbonate may represent a suitable material, as it is biocompatible, biodegradable, and easy to synthesize. In this work, we explored ²¹²Pb-labeling of various CaCO₃ microparticles and developed a protocol that can be straightforwardly implemented by clinicians. Vaterite microparticles stabilized by pamidronate were effective as ²¹²Pb carriers; labeling yields of ≥98% were achieved, and ²¹²Pb was strongly retained by the particles in an in vitro stability assessment. Moreover, the amounts of ²¹²Pb reaching the kidneys, liver, spleen, and skeleton of mice following intraperitoneal (i.p.) administration were very low compared to i.p. injection of unbound ²¹²Pb²⁺, indicating that CaCO₃-bound ²¹²Pb exhibited stability when administered intraperitoneally. Therapeutic efficacy was observed in a model of i.p. ovarian cancer for all the tested doses, ranging from 63 to 430 kBq per mouse. Lead-212-labeled CaCO₃ microparticles represent a promising candidate for treating intracavitary cancers.

Improved Formulation of 224Ra-Labeled Calcium Carbonate Microparticles by Surface Layer Encapsulation and Addition of EDTMP

Radium-224-labeled CaCO₃ microparticles have been developed to treat peritoneal carcinomatosis. The microparticles function as carriers of ²²⁴Ra, facilitating intraperitoneal retention of the alpha-emitting radionuclide. It was necessary to control the size of microparticles in suspension over time and introduce a sterilization process for the clinical use of the radiopharmaceutical. Ethylenediamine tetra(methylene phosphonic acid) (EDTMP) was investigated as a stabilizing additive. The possibility of encapsulating the radiolabeled microparticles with an outer surface layer of CaCO₃ for the improved retention of radioactivity by the carrier was studied. This work evaluated these steps of optimization and their effect on radiochemical purity, the biodistribution of radionuclides, and therapeutic efficacy. An EDTMP concentration of >1% (w/w) relative to CaCO₃ stabilized the particle size for at least one week. Without EDTMP, the median particle size increased from ~5 µm to ~25 µm immediately after sterilization by autoclaving, and the larger microparticles sedimented rapidly in suspension. The percentage of adsorbed ²²⁴Ra progeny ²¹²Pb increased from 56% to 94% at 2.4-2.5% (w/w) EDTMP when the ²²⁴Ra-labeled microparticles were layer-encapsulated. The improved formulation also resulted in a suitable biodistribution of radionuclides in mice, as well as a survival benefit for mice with intraperitoneal ovarian or colorectal tumors.

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.