Dose escalation study with rhenium-188 hydroxyethylidene diphosphonate in prostate cancer patients with osseous metastases

Bisphosphonates as Radiopharmaceuticals: Spotlight on the Development and Clinical Use of DOTAZOL in Diagnostics and Palliative Radionuclide Therapy

Bisphosphonates are therapeutic agents that have been used for almost five decades in the treatment of various bone diseases, such as osteoporosis, Paget disease and prevention of osseous complications in cancer patients. In nuclear medicine, simple bisphosphonates such as 99mTc-radiolabelled oxidronate and medronate remain first-line bone scintigraphic imaging agents for both oncology and non-oncology indications. In line with the growing interest in theranostic molecules, bifunctional bisphosphonates bearing a chelating moiety capable of complexing a variety of radiometals were designed. Among them, DOTA-conjugated zoledronate (DOTAZOL) emerged as an ideal derivative for both PET imaging (when radiolabeled with 68Ga) and management of bone metastases from various types of cancer (when radiolabeled with 177Lu). In this context, this report provides an overview of the main medicinal chemistry aspects concerning bisphosphonates, discussing their roles in molecular oncology imaging and targeted radionuclide therapy with a particular focus on bifunctional bisphosphonates. Particular attention is also paid to the development of DOTAZOL, with emphasis on the radiochemistry and quality control aspects of its preparation, before outlining the preclinical and clinical data obtained so far with this radiopharmaceutical candidate.

Safety and Efficacy of 68 Ga- or 177 Lu-Labeled DOTA-IBA as a Novel Theranostic Radiopharmaceutical for Bone Metastases : A Phase 0/I Study

PURPOSE

We designed and synthesized a novel theranostic bisphosphonate radiopharmaceutical ( 68 Ga- or 177 Lu-labeled DOTA-ibandronic acid [ 68 Ga/ 177 Lu-DOTA-IBA]) for bone metastasis. In this study, the dosimetry, safety, and efficacy of 68 Ga/ 177 Lu-DOTA-IBA as a theranostic radiopharmaceutical for bone metastases were evaluated in patients with malignancy based on 68 Ga- and 177 Lu-DOTA-IBA images, blood samples, and dosimetric analysis.

PATIENTS AND METHODS

Eighteen patients with bone metastasis and progression under conventional therapies were included in this study. Baseline 99m Tc-MDP SPECT and 68 Ga-DOTA-IBA PET/CT were performed for comparative purposes within 3 days. After receiving 891.5 ± 301.3 MBq 177 Lu-DOTA-IBA, serial 177 Lu-DOTA-IBA SPECT bone scan was performed over 14 days. Dosimetric evaluation was performed for main organs and tumor lesions. Safety was assessed by blood biomarkers. Karnofsky Performance Status, pain score, and follow-up 68 Ga-DOTA-IBA PET/CT were performed for response evaluation.

RESULTS

Baseline 68 Ga-DOTA-IBA PET demonstrated a higher efficacy for detecting bone metastases compared with 99m Tc-MDP SPECT. The time-activity curves showed fast uptake and high retention of 177 Lu-DOTA-IBA in bone metastases (24 hours: 9.43 ± 2.75 %IA; 14 days: 5.45 ± 2.52 %IA). Liver, kidneys, and red marrow time-activity curves revealed a low uptake and fast clearance. The radiation-absorbed dose in bone metastasis lesions (6.40 ± 2.13 Gy/GBq) was significantly higher than that in red marrow (0.47 ± 0.19 Gy/GBq), kidneys (0.56 ± 0.19 Gy/GBq), or liver (0.28 ± 0.07 Gy/GBq), with all P 's < 0.001. Compared with baseline level, only one patient developed new grade 1 leukopenia (toxicity rate, 6%). The 177 Lu-DOTA-IBA therapy had no statistically significant effect on bone marrow hematopoietic function, liver function, and kidney function at any follow-up visit. Bone pain palliation was achieved in 82% (14/17) of patients. The 8-week follow-up 68 Ga-DOTA-IBA PET/CT demonstrated partial response in 3 patients, disease progression in 1 patient, and stable disease in 14 patients.

CONCLUSIONS

68 Ga/ 177 Lu-DOTA-IBA provides a set of potential theranostic radiopharmaceuticals and may have a good prospect for the management of bone metastasis.

Preparation, Characterization, and Preliminary Imaging Study of [188Re]Re-Ibandronate as a Novel Theranostic Radiopharmaceutical for Bone Metastasis

Background

Bone is a common site of metastasis from a malignant tumor. Several radiopharmaceuticals are available to relieve bone pain in patients with cancer. However, every radiopharmaceutical has its own disadvantages, and there is still a need to investigate easily accessible and high bone affinity radiopharmaceuticals. Ibandronate (IBA) and ¹⁸⁸Re were used for radiolabeling to develop and evaluate a novel type of bone-seeking radiopharmaceutical.

Methods

The preparation conditions of [¹⁸⁸Re]Re-IBA were investigated, and thin-layer chromatography was used to analyze radiochemical purity. The stability, plasma protein binding rate, lipid-water distribution coefficient, safety and biodistribution in normal mice, and bone imaging of [¹⁸⁸Re]Re-IBA in New Zealand rabbits were studied. In addition, the nude mice model of bone metastasis was established, and biodistribution and imaging characteristics of [¹⁸⁸Re]Re-IBA in these nude mice were studied.

Results

[¹⁸⁸Re]Re-IBA was successfully prepared with radiochemical purity >95%. The optimum preparation conditions were as follows: IBA, 0.8–1.4 mg; ascorbic acid, 0.2–0.5 mg; stannous chloride, 0.14–0.18 mg; potassium perrhenate, 0.005 mg; and [¹⁸⁸Re]ReO₄⁻ activity, 18.5–296 MBq, reacted for 30 min at 95°C with pH = 2. [¹⁸⁸Re]Re-IBA demonstrated good stability, high plasma protein binding rate, good hydrophilicity, and low toxicity. The biodistribution and bone imaging in normal animals showed rapid blood clearance, high bone uptake, low uptake in the solid organs and soft tissue, and high contrast during imaging. The biodistribution and imaging of bone metastasis in nude mice showed that [¹⁸⁸Re]Re-IBA has higher uptake in bone metastasis lesions than normal bone.

Conclusions

Our study encompassed the successful preparation of [¹⁸⁸Re]Re-IBA, a novel bone-seeking radiopharmaceutical, and confirmed it has potential in the treatment of bone metastasis and monitoring through imaging.

Bifunctional chelators for radiorhenium: past, present and future outlook

Targeted radionuclide therapy (TRNT) is an ever-expanding field of nuclear medicine that provides a personalised approach to cancer treatment while limiting toxicity to normal tissues. It involves the radiolabelling of a biological targeting vector with an appropriate therapeutic radionuclide, often facilitated by the use of a bifunctional chelator (BFC) to stably link the two entities. The radioisotopes of rhenium, 186Re (t 1/2 = 90 h, 1.07 MeV β-, 137 keV γ (9%)) and 188Re (t 1/2 = 16.9 h, 2.12 MeV β-, 155 keV γ (15%)), are particularly attractive for radiotherapy because of their convenient and high-abundance β--particle emissions as well as their imageable γ-emissions and chemical similarity to technetium. As a transition metal element with multiple oxidation states and coordination numbers accessible for complexation, there is great opportunity available when it comes to developing novel BFCs for rhenium. The purpose of this review is to provide a recap on some of the past successes and failings, as well as show some more current efforts in the design of BFCs for 186/188Re. Future use of these radionuclides for radiotherapy depends on their cost-effective availability and this will also be discussed. Finally, bioconjugation strategies for radiolabelling biomolecules with 186/188Re will be touched upon.

Dosimetry of bone seeking beta emitters for bone pain palliation metastases

Amongst cancer patients, bone pain due to skeletal metastases is a major cause of morbidity. A number of beta-emitting radiopharmaceuticals have been used to provide internal radiotherapy of bone metastases and provide palliative pain relief. In this article we describe the different physical characteristics of the various beta emitting radionuclides which have been used in this clinical setting and the potential impact of differences in dose-rate on radiobiological outcomes. A detailed review of the biodistribution of these treatments, based on both in-vivo clinical investigations and post mortem autoradiography assessments is provided. These treatments result in physiological delivery of radiation doses to the target disease as well as to critical healthy organs. Particular attention is paid to the radiation doses received by normal bone tissue, bone marrow as well as metastatic bone disease. The underlying models of radiation transport within bone and bone marrow are reviewed alongside the practical steps that must be taken to acquire and analyse the information require for clinical dosimetry assessments. The role of whole body measurements, blood and faecal assays as well as both planar and tomographic gamma camera imaging are considered. In addition we review the rationale for allocating measured bone uptake between trabecular and cortical bone tissue. The difference between bone volume and bone surface seeking radiopharmaceuticals are also discussed. This review also extends to the development of preclinical models of bone metastases which may inform future dosimetric calculations. Finally, we also present a comprehensive review of the dosimetry of the established treatments ⁸⁹Strontium-chloride; ³²Phosphorus; ¹⁸⁸Rhenium-hydroxyethylidine disphosphonate; ¹⁸⁶Rhenium-1,1-hydroxyethylidene disphosphonate (¹⁸⁶Re-HEDP); ¹⁵³Samarium-ethylenediaminetetramethylene phosphonate; as well as the emerging treatments ¹⁸⁸Rhenium-zoledronic acid; ¹⁸⁸Rhenium-ibedronat; ¹⁷⁷Lutetium-zoledronic acid; and ¹⁷⁷Lutetium ethylenediaminetetramethylene phosphonate. This review highlights not only the inter treatment differences in the radiation absorbed doses delivered to metastatic disease by different radiopharmaceuticals but also the intra treatment differences which result in a large range of observed doses between patients.

Drug and molecular radiotherapy combinations for metastatic castration resistant prostate cancer

Metastatic castration resistant prostate cancer (mCRPC) is a highly lethal disease. Several novel therapies have been assessed in the past years. Targeting DNA damage response (DDR) pathways in prostate cancer became a promising treatment strategy and olaparib and rucaparib, Poly(ADP-ribose) polymerase (PARP) inhibitors, have been approved for patients carrying mutations in homologous recombination (HR) repair pathways. Other DDR inhibitor targets, such as ATM, ATR, CHK1, CHK2, and WEE1 are under extensive investigation. Additionally, molecular radiotherapy (MRT) including [¹⁷⁷Lu]Lu-PSMA, [²²⁵Ac]Ac-PSMA, [²²³Ra]Ra-dichloride, [¹⁵³Sm]-EDTMP, [¹⁸⁸Re]Re-HDMP and GRPR-targeted MRT treat cancer through internal ionizing radiation causing DNA damage and demonstrate promising efficacy in clinical trials. In the field of immunotherapy, checkpoint inhibition as well as sipuleucel-T and PROSTVAC demonstrated only limited efficacy in mCRPC when used as monotherapy. This review discusses recent therapeutic strategies for mCRPC highlighting the need for rational combination of treatment options.

Systemic Radiotherapy of Bone Metastases With Radionuclides

Treatments of bone metastases using radionuclides are now well established in oncology. It is also a field that continues to develop. This article reviews the evidence base that led to the approval of strontium-89 and samarium-153 ethylenediaminetetramethylene phophanate (EDTMP) for the palliation of pain from bone metastases, as well as the evidence for the use of radium-223 in metastatic castrate-resistant prostate cancer. Efforts to optimise treatments and improve response rates, either by safely increasing the radiation dose to bone metastases or by combining treatment with non-radiation-based therapies, are discussed. In addition, the development of both alpha- and beta-particle-emitting radiopharmaceuticals designed to target prostate-specific membrane antigen are reviewed.

Neutron-activated theranostic radionuclides for nuclear medicine

Theranostics in nuclear medicine refers to personalized patient management that involves targeted therapy and diagnostic imaging using a single or combination of radionuclide (s). The radionuclides emit both alpha (α) or beta (β^-) particles and gamma (γ) rays which possess therapeutic and diagnostic capabilities, respectively. However, the production of these radionuclides often faces difficulties due to high cost, complexity of preparation methods and that the products are often sourced far from the healthcare facilities, hence losing activity due to radioactive decay during transportation. Subject to the availability of a nuclear reactor within an accessible distance from healthcare facilities, neutron activation is the most practical and cost-effective route to produce radionuclides suitable for theranostic purposes. Holmium-166 (¹⁶⁶Ho), Lutetium-177 (¹⁷⁷Lu), Rhenium-186 (¹⁸⁶Re), Rhenium-188 (¹⁸⁸Re) and Samarium-153 (¹⁵³Sm) are some of the most promising neutron-activated radionuclides that are currently in clinical practice and undergoing clinical research for theranostic applications. The aim of this paper is to review the physical characteristics, current clinical applications and future prospects of these neutron activated radionuclides in theranostics. The production, physical properties, validated clinical applications and clinical studies for each neutron-activated radionuclide suitable for theranostic use in nuclear medicine are reviewed in this paper.

Targeted Palliative Radionuclide Therapy for Metastatic Bone Pain

Bone metastasis develops in multiple malignancies with a wide range of incidence. The presence of multiple bone metastases, leading to a multitude of complications and poorer prognosis. The corresponding refractory bone pain is still a challenging issue managed through multidisciplinary approaches to enhance the quality of life. Radiopharmaceuticals are mainly used in the latest courses of the disease. Bone-pain palliation with easy-to-administer radionuclides offers advantages, including simultaneous treatment of multiple metastatic foci, the repeatability and also the combination with other therapies. Several β¯- and α-emitters as well as pharmaceuticals, from the very first [⁸⁹Sr]strontium-dichloride to recently introduced [²²³Ra]radium-dichloride, are investigated to identify an optimum agent. In addition, the combination of bone-seeking radiopharmaceuticals with chemotherapy or radiotherapy has been employed to enhance the outcome. Radiopharmaceuticals demonstrate an acceptable response rate in pain relief. Nevertheless, survival benefits have been documented in only a limited number of studies. In this review, we provide an overview of bone-seeking radiopharmaceuticals used for bone-pain palliation, their effectiveness and toxicity, as well as the results of the combination with other therapies. Bone-pain palliation with radiopharmaceuticals has been employed for eight decades. However, there are still new aspects yet to be established.

Spine and Non-spine Bone Metastases - Current Controversies and Future Direction

Bone is a common site of metastases in advanced cancers. The main symptom is pain, which increases morbidity and reduces quality of life. The treatment of bone metastases needs a multidisciplinary approach, with the main aim of relieving pain and improving quality of life. Apart from systemic anticancer therapy (hormonal therapy, chemotherapy or immunotherapy), there are several therapeutic options available to achieve palliation, including analgesics, surgery, local radiotherapy, bone-seeking radioisotopes and bone-modifying agents. Long-term use of non-steroidal analgesics and opiates is associated with significant side-effects, and tachyphylaxis. Radiotherapy is effective mainly in localised disease sites. Bone-targeting radionuclides are useful in patients with multiple metastatic lesions. Bone-modifying agents are beneficial in reducing skeletal-related events. This overview focuses on the role of surgery, including minimally invasive treatments, conventional radiotherapy in spinal and non-spinal bone metastases, bone-targeting radionuclides and bone-modifying agents in achieving palliation. We present the clinical data and their associated toxicity. Recent advances are also discussed.

Rhenium-188 Labeled Radiopharmaceuticals: Current Clinical Applications in Oncology and Promising Perspectives

Rhenium-188 (¹⁸⁸Re) is a high energy beta-emitting radioisotope with a short 16.9 h physical half-life, which has been shown to be a very attractive candidate for use in therapeutic nuclear medicine. The high beta emission has an average energy of 784 keV and a maximum energy of 2.12 MeV, sufficient to penetrate and destroy targeted abnormal tissues. In addition, the low-abundant gamma emission of 155 keV (15%) is efficient for imaging and for dosimetric calculations. These key characteristics identify ¹⁸⁸Re as an important therapeutic radioisotope for routine clinical use. Moreover, the highly reproducible on-demand availability of ¹⁸⁸Re from the ¹⁸⁸W/¹⁸⁸Re generator system is an important feature and permits installation in hospital-based or central radiopharmacies for cost-effective availability of no-carrier-added (NCA) ¹⁸⁸Re. Rhenium-188 and technetium-99 m exhibit similar chemical properties and represent a “theranostic pair.” Thus, preparation and targeting of ¹⁸⁸Re agents for therapy is similar to imaging agents prepared with ^99mTc, the most commonly used diagnostic radionuclide. Over the last three decades, radiopharmaceuticals based on ¹⁸⁸Re-labeled small molecules, including peptides, antibodies, Lipiodol and particulates have been reported. The successful application of these ¹⁸⁸Re-labeled therapeutic radiopharmaceuticals has been reported in multiple early phase clinical trials for the management of various primary tumors, bone metastasis, rheumatoid arthritis, and endocoronary interventions. This article reviews the use of ¹⁸⁸Re-radiopharmaceuticals which have been investigated in patients for cancer treatment, demonstrating that ¹⁸⁸Re represents a cost effective alternative for routine clinical use in comparison to more expensive and/or less readily available therapeutic radioisotopes.

A phase 0 study of the pharmacokinetics, biodistribution, and dosimetry of 188Re-liposome in patients with metastatic tumors

BACKGROUND

Liposomes are drug nano-carriers that are capable of targeting therapeutics to tumor sites because of enhanced permeability retention (EPR). In several preclinical studies with various tumor-bearing mice models, ¹⁸⁸Re-liposome that has been developed by the Institute of Nuclear Energy Research (INER) demonstrates favorable in vivo tumor targeting, biodistribution, pharmacokinetics, and dosimetry. It inhibits the growth of tumors, increased survival, demonstrates good synergistic combination, and was safe to use. This study conducts a phase 0 low-radioactivity clinical trial of nano-targeted radiotherapeutics ¹⁸⁸Re-liposome to evaluate the effectiveness with which it targets tumors and the pharmacokinetics, biodistribution, dosimetry, and its safety in use. Twelve patients with metastatic cancers are studied in this trial. Serial whole-body scans and SPECT/CT are taken at 1, 4, 8, 24, 48, and 72 h after intravenous injection of 111 MBq of ¹⁸⁸Re-liposome. The effectiveness with which tumors are targeted, the pharmacokinetics, biodistribution, dosimetry, and safety are evaluated using the VelocityAI and OLINDA/EXM software. Blood samples are collected at different time points for a pharmacokinetics study and a safety evaluation that involves monitoring changes in liver, renal, and hematological functions.

RESULTS

The T_½z for ¹⁸⁸Re-liposome in blood and plasma are 36.73 ± 14.00 h and 52.02 ± 45.21 h, respectively. The doses of radiation that are absorbed to vital organs such as the liver, spleen, lung, kidney, and bone marrow are 0.92 ± 0.35, 1.38 ± 1.81, 0.58 ± 0.28, 0.32 ± 0.09, and 0.06 ± 0.01 mGy/MBq, respectively, which is far less than the reference maximum tolerance dose after injection of ¹⁸⁸Re-liposome. ¹⁸⁸Re-liposome is absorbed by metastatic tumor lesions and the normal reticuloendothelial (RES) system. Certain patients exhibit a therapeutic response.

CONCLUSION

This phase 0 exploratory IND study shows that nanocarrier ¹⁸⁸Re-liposome achieves favorable tumor accumulation and tumor to normal organ uptake ratios for a subset of cancer patients. The clinical pharmacokinetic, biodistribution, and dosimetry results justify a further dose-escalating phase 1 clinical trial.

TRIAL REGISTRATION

Taiwan FDA MA1101G0 (Jan 31, 2012).

Personalized Radiation Therapy in Cancer Pain Management

The majority of advanced cancer patients suffer from pain, which severely deteriorates their quality of life. Apart from analgesics, bisphosphonates, and invasive methods of analgesic treatment (e.g., intraspinal and epidural analgesics or neurolytic blockades), radiation therapy plays an important role in pain alleviation. It is delivered to a growing primary tumour, lymph nodes, or distant metastatic sites, producing pain of various intensity. Currently, different regiments of radiation therapy methods and techniques and various radiation dose fractionations are incorporated into the clinical practice. These include palliative radiation therapy, conventional external beam radiation therapy, as well as modern techniques of intensity modulated radiation therapy, volumetrically modulated arch therapy, stereotactic radiosurgery or stereotactic body radiation therapy, and brachytherapy or radionuclide treatment (e.g., radium-223, strontium-89 for multiple painful osseous metastases). The review describes the possibilities and effectiveness of individual patient-tailored conventional and innovative radiation therapy approaches aiming at pain relief in cancer patients.

Targeted Radionuclide Therapy of Painful Bone Metastases: Past Developments, Current Status, Recent Advances and Future Directions

Bone pain arising from secondary skeletal malignancy constitutes one of the most common types of chronic pain among patients with cancer which can lead to rapid deterioration of the quality of life. Radionuclide therapy using bone-seeking radiopharmaceuticals based on the concept of localization of the agent at bone metastases sites to deliver focal cytotoxic levels of radiation emerged as an effective treatment modality for the palliation of symptomatic bone metastases. Bone-seeking radiopharmaceuticals not only provide palliative benefit but also improve clinical outcomes in terms of overall and progression-free survival. There is a steadily expanding list of therapeutic radionuclides which are used or can potentially be used in either ionic form or in combination with carrier molecules for the management of bone metastases. This article offers a narrative review of the armamentarium of bone-targeting radiopharmaceuticals based on currently approved investigational and potentially useful radionuclides and examines their efficacy for the treatment of painful skeletal metastases. In addition, the article also highlights the processes, opportunities, and challenges involved in the development of bone-seeking radiopharmaceuticals. Radium-223 is the first agent in this class to show an overall survival advantage in Castration-Resistant Prostate Cancer (CRPC) patients with bone metastases. This review summarizes recent advances, current clinical practice using radiopharmaceuticals for bone pain palliation, and the expected future prospects in this field.

Metal-based antitumor compounds: beyond cisplatin

Despite improvements in the 5-year survival rate to over 80% in cancers, such as Hodgkin lymphoma and testicular cancer, more aggressive tumors including pancreatic and brain cancer still have extremely low survival rates. The establishment of chemoresistance, responsible for the reduction in treatment efficiency and cancer relapse, is one possible explanation for this setback. Metal-based compounds, a class of anticancer drugs, are largely used in the treatment of cancer. Herein, we will review the use of metal-based small molecules in chemotherapy, focusing on recent studies, and we will discuss how new nonplatinum-based agents are prompting scientists to increase drug specificity to overcome chemoresistance in cancer cells.

Rhenium-188 Hydroxyethane 1,1-Diphosphonic Acid (HEDP) for Bone Pain Palliation Using BARC-HEDP Kits versus Pars-HEDP Kits: A Comparison on Preparation and Performance Aspects at Hospital Radiopharmacy

Purpose of the Study:

Rhenium-188 hydroxyethane 1,1-diphosphonic acid (HEDP) is a clinically established radiopharmaceutical for palliation of bone pain due to osseous metastases. Recently, the Bhabha Atomic Research Centre (BARC) had developed a freeze-dried kit for the preparation of rhenium-188 HEDP. The present study compares the radiochemistry aspects of indigenous BARC-HEDP kits with commercially available HEDP kits from Pars Isotope Company, Iran.

Materials and Methods:

Freeze-dried HEDP kits were obtained from Radiopharmaceuticals Division, BARC, and Pars Isotope Company, Iran. Following recommended procedures, rhenium-188 HEDP was prepared using freeze-dried kits from both sources using freshly eluted rhenium-188 sodium perrhenate obtained from a commercial tungsten-188/rhenium-188 generator.

Results:

Both kits could be used for the preparation of rhenium-188 HEDP in >95% radiochemical purity (RCP). Rhenium-188 HEDP prepared from both kits showed comparable in vitro stability as well as pharmacokinetic properties. The normal bone-to-soft tissue ratio observed for rhenium-188 HEDP prepared using BARC-HEDP kit and Pars-HEDP kit was 1.993 and 1.416, respectively.

Conclusions:

Both HEDP kits provided a user-friendly solution for the preparation of rhenium-188 HEDP. While Pars-HEDP-kit permits the addition of only 2 mL of rhenium-188 perrhenate solution per kit vial, BARC-HEDP-kit allows up to 5 mL. This feature permits the preparation of patient dose of rhenium-188 HEDP even with older generators providing rhenium-188 perrhenate having a low radioactive concentration (activity/mL). In addition, availability of an indigenous product is always preferable over imported options.

PEGylated liposome-encapsulated rhenium-188 radiopharmaceutical inhibits proliferation and epithelial-mesenchymal transition of human head and neck cancer cells in vivo with repeated therapy

Human head and neck squamous cell carcinoma (HNSCC) is usually treated with chemoradiotherapy, but the therapeutic efficacy could be hampered by intrinsic radioresistance and early relapse. Repeated administrations of rhenium-188 (¹⁸⁸Re)-conjugated radiopharmaceutical has been reported to escalate the radiation doses for better control of advanced human cancers. Here we found that high dosage of ¹⁸⁸Re-liposome, the liposome-encapsulated ¹⁸⁸Re nanoparticles exhibited significant killing effects on HNSCC FaDu cells and SAS cells but not on OECM-1 cells. To investigate the biological and pharmaceutical responses of high ¹⁸⁸Re-liposomal dosage in vivo, repeated doses of ¹⁸⁸Re-liposome was injected into the orthotopic tumor model. FaDu cells harboring luciferase reporter genes were implanted in the buccal positions of nude mice followed by intravenous injection of ¹⁸⁸Re-liposome. The Cerenkov luminescence imaging (CLI) was performed to demonstrate an increased accumulation of ¹⁸⁸Re-liposome in the tumor lesion of nude mice with repeated doses compared to a single dose. Repeated doses also enhanced tumor growth delay and elongated the survival of tumor-bearing mice. These observations were associated with significant loss of Ki-67 proliferative marker and epithelial–mesenchymal transition (EMT) markers in excised tumor cells. The body weights of mice were not significantly changed using different doses of ¹⁸⁸Re-liposome, yet repeated doses led to lower blood counts than a single dose. Furthermore, the pharmacokinetic analysis showed that the internal circulation of repeated ¹⁸⁸Re-liposomal therapy was elongated. The biodistribution analysis also demonstrated that accumulations of ¹⁸⁸Re-liposome in tumor lesions and bone marrow were increased using repeated doses. The absorbed dose of repeated doses over a single dose was about twofold estimated for a 1 g tumor. Together, these data suggest that the radiopharmacotherapy of ¹⁸⁸Re-liposome can enhance tumor suppression, survival extension, and internal circulation without acute toxicity using repeated administrations.

Radionuclide Therapy for Bone Metastases: Utility of Scintigraphy and PET Imaging for Treatment Planning

The skeleton is a common site for cancer metastases. Bone metastases are a major cause of morbidity and mortality and associated with pain, pathologic fractures, spinal cord compression, and decreased survival. Various radionuclides have been used for pain therapy. Recently, an α-emitter has been shown to improve overall survival of patients with bone metastases from castration-resistant prostate cancer and was approved as a therapeutic agent. The aim of this article is to provide an overview regarding state of the art radionuclide therapy options for bone metastases, with focus on the role of PET imaging in therapy planning.

188Re-HEDP therapy in the therapy of painful bone metastases

For bone-targeted radionuclide therapy (BTRT), different commercial radiopharmaceuticals are available such as strontium-89, 186Rhenium-hydroxyethylidene diphosphonate (186Re-HEDP), Samarium-153-ethylenediamine tetramethylene phosphonic acid, and radium-223. Unfortunately, the commercial available radiopharmaceuticals are very expensive (from 1,200 to 36,000€ per patient in Europe). The 188W/188Re generator is an ideal source for the long-term (4-6 months) continuous availability of 188Re suitable for the preparation of radiopharmaceuticals for different radionuclide therapies. Labeling at HEDP, it can use cost-effective for BTRT, if enough patients are available for therapy. And so, 188Re-HEDP is the ideal candidate in developing countries which high population to replace the other agents. Two German groups documented a response rate of 80% without any severe side effects and similar bone marrow toxicity compared to the other compounds for 188Re-HEDP. Using 188Re-HEDP in repeated treatments, a prolonged overall survival of repeated to single application was observed (from 4.5 months for single to 15.7 months using ≥≥3 applications).

Bone lesion absorbed dose profiles in patients with metastatic prostate cancer treated with molecular radiotherapy

OBJECTIVE

The aim of this study was to calculate the range of absorbed doses that could potentially be delivered by a variety of radiopharmaceuticals and typical fixed administered activities used for bone pain palliation in a cohort of patients with metastatic castration-resistant prostate cancer (mCRPC). The methodology for the extrapolation of the biodistribution, pharmacokinetics and absorbed doses from a given to an alternative radiopharmaceutical is presented.

METHODS

Sequential single photon emission CT images from 22 patients treated with 5 GBq of 186Re-HEDP were used to extrapolate the time-activity curves for various radiopharmaceuticals. Cumulated activity distributions for the delivered and extrapolated treatment plans were converted into absorbed dose distributions using the convolution dosimetry method. The lesion absorbed doses obtained for the different treatments were compared using the patient population distributions and cumulative dose-volume histograms.

RESULTS

The median lesion absorbed doses across the patient cohort ranged from 2.7 Gy (range: 0.6-11.8 Gy) for 1100 MBq of 166Ho-DOTMP to 21.8 Gy (range: 4.5-117.6 Gy) for 150 MBq of 89Sr-dichloride. 32P-Na3PO4, 153Sm-EDTMP, 166Ho-DOTMP, 177Lu-EDTMP and 188Re-HEDP would have delivered 41, 32, 85, 20 and 64% lower absorbed doses, for the typical administered activities as compared to 186Re-HEDP, respectively, whilst 89Sr-dichloride would have delivered 25% higher absorbed doses.

CONCLUSION

For the patient cohort studied, a wide range of absorbed doses would have been delivered for typical administration protocols in mCRPC. The methodology presented has potential use for emerging theragnostic agents. Advances in knowledge: The same patient cohort can receive a range of lesion absorbed doses from typical molecular radiotherapy treatments for patients with metastatic prostate cancer, highlighting the need to establish absorbed dose response relationships and to treat patients according to absorbed dose instead of using fixed administered activities.

Discovery of rhenium and masurium (technetium) by Ida Noddack-Tacke and Walter Noddack

The history of the early identification of elements and their designation to the Mendeleev Table of the Elements was an important chapter in German science in which Ida (1896-1978) and Walter (1893-1960) Noddack played an important role in the first identification of rhenium (element 75, 1925) and technetium (element 43, 1933). In 1934 Ida Noddack was also the first to predict fission of uranium into smaller atoms. Although the Noddacks did not for some time later receive the recognition for the first identification of technetium-99m, their efforts have appropriately more recently been recognized. The discoveries of these early pioneers are even more astounding in light of the limited technologies and resources which were available during this period. The Noddack discoveries of elements 43 and 75 are related to the sub sequent use of rhenium-188 (beta/ gamma emitter) and technetium-99m (gamma emitter) in nuclear medicine. In particular, the theranostic relationship between these two generator-derived radioisotopes has been demonstrated and offers new opportunities in the current era of personalized medicine.

Clinical utility of 188Rhenium-hydroxyethylidene-1,1-diphosphonate as a bone pain palliative in multiple malignancies

¹⁸⁸Rhenium-hydroxyethylidene-1,1-diphosphonate (¹⁸⁸Re-HEDP) is a clinically established radiopharmaceutical for bone pain palliation of patients with metastatic bone cancer. Herein, the effectiveness of ¹⁸⁸Re-HEDP for the palliation of painful bone metastases was investigated in an uncontrolled initial trial in 48 patients with different types of advanced cancers. A group of 48 patients with painful bone metastases of lung, prostate, breast, renal, and bladder cancer was treated with 2.96–4.44 GBq of ¹⁸⁸Re-HEDP. The overall response rate in this group of patients was 89.5%, and their mean visual analog scale score showed a reduction from 9.1 to 5.3 (P < 0.003) after 1 week posttherapy. The patients did not report serious adverse effects either during intravenous administration or within 24 h postadministration of ¹⁸⁸Re-HEDP. Flare reaction was observed in 54.2% of patients between day 1 and day 3. There was no correlation between flare reaction and response to therapy (P < 0.05). Although bone marrow suppression was observed in patients receiving higher doses of ¹⁸⁸Re-HEDP, it did not result in any significant clinical problems. The present study confirmed the clinical utility and cost-effectiveness of ¹⁸⁸Re-HEDP for palliation of painful bone metastases from various types of cancer in developing countries.

Theranostics in nuclear medicine practice

The importance of personalized medicine has been growing, mainly due to a more urgent need to avoid unnecessary and expensive treatments. In nuclear medicine, the theranostic approach is an established tool for specific molecular targeting, both for diagnostics and therapy. The visualization of potential targets can help predict if a patient will benefit from a particular treatment. Thanks to the quick development of radiopharmaceuticals and diagnostic techniques, the use of theranostic agents has been continually increasing. In this article, important milestones of nuclear therapies and diagnostics in the context of theranostics are highlighted. It begins with a well-known radioiodine therapy in patients with thyroid cancer and then progresses through various approaches for the treatment of advanced cancer with targeted therapies. The aim of this review was to provide a summary of background knowledge and current applications, and to identify the advantages of targeted therapies and imaging in nuclear medicine practices.

Novel small peptides derived from VEGF125-136: potential drugs for radioactive diagnosis and therapy in A549 tumor-bearing nude mice

Vascular endothelial growth factor receptor (VEGFR) is a critical factor in tumor angiogenesis and has been considered a potential target for receptor-mediated radionuclide imaging and therapy. In this study, we identified two peptides (QKRKRKKSRKKH and RKRKRKKSRYIVLS) derived from VEGF125-136 that displayed high binding affinities to VEGFR and strong inhibition of A549 cell growth. 99mTc- and 188Re-labeled peptides displayed high labeling efficiency and favorable stability in saline and human plasma. At the cellular level, the radiolabeled peptides could bind with A549 cells and be internalized via the VEGFR-1-mediated pathway. 99mTc/188Re-labeled peptide was significantly accumulated at xenograft tumors, as observed with single-photon emission computed tomography (SPECT) planar imaging. Moreover, 188Re-labeled peptides significantly inhibited tumor growth, prolonged the survival time of the tumor-bearing nude mice and resulted in much more necrotic regions and apoptotic cells in the A549 xenograft tumors. These results demonstrated that these two peptides as candidate drugs for radionuclide imaging and tumor therapy.

In Vitro Evaluation of 188Re-HEDP: A Mechanistic View of Bone Pain Palliations

Skeletal metastasis is common in advanced stages of various cancers, particularly of the prostate and breast carcinoma. ¹⁸⁸Re-HEDP (1-hydroxyethane 1, 1-diphosphonic acid) is a clinically established radiopharmaceutical for bone pain palliation of osseous metastasis, and it takes advantage of high bone affinity. The present work aims at elucidating the possible mechanisms of cell killing by ¹⁸⁸Re-HEDP in osteosarcoma cells and biodistribution studies in mice.¹⁸⁸Re-HEDP complex was prepared by using lyophilized HEDP kits prepared in-house. In vitro cellular uptake in mineralized bone matrix was found to be 13.41% ± 0.46% (at 2 hours), which was reduced to 2.44% ± 0.12% in the presence of excess amounts of unlabeled HEDP ligand. Uptake of ¹⁸⁸Re-HEDP in bones of normal Swiss mice in vivo and mineralized bone in vitro indicated its affinity toward the bone matrix. The study also revealed that cellular toxicity and G2/M cell cycle arrest were dose dependent. At higher doses, G2/M cell cycle arrest was observed, which might be the major cause of cell death and a possible mechanism of bone pain relief.

Development of an electrochemical 188W/188Re generator as a technique for separation and purification of 188Re in radiopharmaceutical applications

In this study, a simple electrochemical procedure adaptable for using low specific activity ¹⁸⁸W for separation and purification of ¹⁸⁸Re from ¹⁸⁸W to obtain no carrier added (NCA) ¹⁸⁸Re is developed. The electrochemical parameters were optimized to maximize the ¹⁸⁸Re electrodeposition yield with minimal ¹⁸⁸W contamination. Two cycle electrolysis procedure was developed. The first electrochemical cell was used for separation of ¹⁸⁸Re and in the second electrochemical cell, separation and purification of ¹⁸⁸Re with >90% deposition yield of ¹⁸⁸Re and minimal contamination of ¹⁸⁸W (<10^-4%) was achieved. The overall electrodeposition yield of ¹⁸⁸Re was >90% with >99% radionuclidic purity and >99% radiochemical purity suitable for radiopharmaceutical applications. Furthermore, the performance of the generator remained consistent during a period of 69 days, one half-life of ¹⁸⁸W, when the electrochemical separation procedure was performed frequently, at least once in 5 days.

Pharmaceutical and clinical development of phosphonate-based radiopharmaceuticals for the targeted treatment of bone metastases

Therapeutic phosphonate-based radiopharmaceuticals radiolabeled with beta, alpha and conversion electron emitting radioisotopes have been investigated for the targeted treatment of painful bone metastases for >35years. We performed a systematic literature search and focused on the pharmaceutical development, preclinical research and early human studies of these radiopharmaceuticals. The characteristics of an ideal bone-targeting therapeutic radiopharmaceutical are presented and compliance with these criteria by the compounds discussed is verified. The importance of both composition and preparation conditions for the stability and biodistribution of several agents is discussed. Very few studies have described the characterization of these products, although knowledge on the molecular structure is important with respect to in vivo behavior. This review discusses a total of 91 phosphonate-based therapeutic radiopharmaceuticals, of which only six agents have progressed to clinical use. Extensive clinical studies have only been described for (186)Re-HEDP, (188)Re-HEDP and (153)Sm-EDTMP. Of these, (153)Sm-EDTMP represents the only compound with worldwide marketing authorization. (177)Lu-EDTMP has recently received approval for clinical use in India. This review illustrates that a thorough understanding of the radiochemistry of these agents is required to design simple and robust preparation and quality control methods, which are needed to fully exploit the potential benefits of these theranostic radiopharmaceuticals. Extensive biodistribution and dosimetry studies are indispensable to provide the portfolios that are required for assessment before human administration is possible. Use of the existing knowledge collected in this review should guide future research efforts and may lead to the approval of new promising agents.

Treatment of painful bone metastases in prostate and breast cancer patients with the therapeutic radiopharmaceutical rhenium-188-HEDP. Clinical benefit in a real-world study

AIM

Rhenium-188-HEDP ((188)Re-HEDP) is an effective radiopharmaceutical for the palliative treatment of osteoblastic bone metastases. However, only limited data on its routine use are available and its effect on quality of life (QoL) has not been studied. Therefore, we evaluated the clinical benefit of (188)Re-HEDP in routine clinical care.

PATIENTS AND METHODS

Prostate or breast cancer patients with painful bone metastases receiving (188)Re-HEDP as a routine clinical procedure were eligible for evaluation. Clinical benefit was assessed in terms of efficacy and toxicity. Pain palliation and QoL were monitored using the visual analogue scale (VAS), corrected for opioid intake, and the EORTC QLQ-C30 Global health status/QoL-scale. Thrombocyte and leukocyte nadirs were used to assess haematological toxicity.

RESULTS

45 and 47 patients were evaluable for pain palliation and QoL, respectively. After a single injection of (188)Re-HEDP, the overall pain response rate was 69% and mean VAS-scores decreased relevantly and significantly (p < 0.05). Repeated treatment resulted in similar pain response. The overall QoL response rate was 68% and mean Global health status/QoL-scores increased relevantly and significantly. Haematological side effects were mild and transient.

CONCLUSION

The clinically relevant response on pain and quality of life and the limited adverse events prove clinical benefit of treatment with (188)Re-HEDP and support its use in routine clinical care. Its effectiveness appears comparable to that of external beam radiotherapy.

Drug composition matters: the influence of carrier concentration on the radiochemical purity, hydroxyapatite affinity and in-vivo bone accumulation of the therapeutic radiopharmaceutical 188Rhenium-HEDP

INTRODUCTION

(188)Rhenium-HEDP is an effective bone-targeting therapeutic radiopharmaceutical, for treatment of osteoblastic bone metastases. It is known that the presence of carrier (non-radioactive rhenium as ammonium perrhenate) in the reaction mixture during labeling is a prerequisite for adequate bone affinity, but little is known about the optimal carrier concentration.

METHODS

We investigated the influence of carrier concentration in the formulation on the radiochemical purity, in-vitro hydroxyapatite affinity and the in-vivo bone accumulation of (188)Rhenium-HEDP in mice.

RESULTS

The carrier concentration influenced hydroxyapatite binding in-vitro as well as bone accumulation in-vivo. Variation in hydroxyapatite binding with various carrier concentrations seemed to be mainly driven by variation in radiochemical purity. The in-vivo bone accumulation appeared to be more complex: satisfactory radiochemical purity and hydroxyapatite affinity did not necessarily predict acceptable bio-distribution of (188)Rhenium-HEDP.

CONCLUSIONS

For development of new bisphosphonate-based radiopharmaceuticals for clinical use, human administration should not be performed without previous animal bio-distribution experiments. Furthermore, our clinical formulation of (188)Rhenium-HEDP, containing 10 μmol carrier, showed excellent bone accumulation that was comparable to other bisphosphonate-based radiopharmaceuticals, with no apparent uptake in other organs.

ADVANCES IN KNOWLEDGE

Radiochemical purity and in-vitro hydroxyapatite binding are not necessarily predictive of bone accumulation of (188)Rhenium-HEDP in-vivo.

IMPLICATIONS FOR PATIENT CARE

The formulation for (188)Rhenium-HEDP as developed by us for clinical use exhibits excellent bone uptake and variation in carrier concentration during preparation of this radiopharmaceutical should be avoided.

Bench to bedside development of GMP grade Rhenium-188-HEDP, a radiopharmaceutical for targeted treatment of painful bone metastases

Bone-targeting therapeutic radiopharmaceuticals are effective agents for treatment of painful bone metastases. Rhenium-188-HEDP is such a therapeutic radiopharmaceutical and has advantages over commercially available alternatives in terms of efficacy, safety and the ability to be produced on-site, allowing rapid treatment upon presentation of patients with pain. Unlike many other radiopharmaceuticals, there are no standardized preparation methods for Rhenium-188-HEDP. It is known, however, that drug composition may not only affect stability of the final drug product, but it may also influence bone affinity and, thus, efficacy. Furthermore, for support of clinical studies with Rhenium-188-HEDP as an investigational medicinal product, preparation of this radiopharmaceutical has to be performed under GMP conditions. To our knowledge, no group has reported on the preparation of Rhenium-188-HEDP under GMP conditions or on stock production of sterile non-radioactive starting materials. We present the production of GMP grade Rhenium-188-HEDP for application of this therapeutic radiopharmaceutical in routine clinical practice and for support of clinical studies. In addition, bio-distribution data of Rhenium-188-HEDP in mice and in patients with bone metastases originating from prostate cancer are presented.

Radiopharmaceuticals for bone metastasis therapy and beyond: a voyage from the past to the present and a look to the future

Bone cancer can be divided into primary and secondary (metastatic) bone cancer. Osteosarcoma is the most common type of primary bone cancer, but still is a rare cancer. The development of bone metastases is a common event for the cancer patient and the main cause of treatment failure and death, being chronic pain syndrome the most important complication. There are currently several therapeutic modalities for the treatment of metastatic bone disease, including radiation therapy. Treatment with radionuclides (β- and α-particle emitters and Auger electron cascades) is a safe and effective tool of medicine. There is a great deal of interest in diphosphonic acids in nuclear medicine as ligands for radiometals in bone-seeking diagnostic and therapeutic agents. Several radiopharmaceuticals have been designed with the phosphonates as ligands. A recent approach to develop an effective radiopharmaceutical for therapy of bone cancer was the design of a water-soluble polymer that would exploit the disrupted vasculature in tumors according to the enhanced permeability and retention effect. To enhance the effect of radionuclide therapy on the cancer cells, new strategies have recently been investigated, such as the combined radionuclide and chemotherapy, high-dose radionuclide therapy, and repeated radionuclide therapy.

The Role of Bone-Seeking Radionuclides in the Palliative Treatment of Patients with Painful Osteoblastic Skeletal Metastases

Background

Pain from skeletal metastases represents a major burden of advanced disease from solid tumors. Analgesic medications, bisphosphonates, hormonal agents, cytotoxic chemotherapy, and external beam radiotherapy are all effective treatments. However, patients often suffer from diffuse painful metastases and respond poorly to these standard therapies. Bone-seeking radionuclides can specifically target osteoblastic lesions to offer palliation of pain.

Methods

This article offers a narrative review of bone-seeking radionuclides, examines the evidence of safety and efficacy for the treatment of painful skeletal metastases, and presents guidelines for their appropriate use in this patient population.

Results

Seven bone-seeking radionuclides have shown evidence of both safety and efficacy in reducing pain from diffuse skeletal metastases. 153Sm-EDTMP and 89Sr are most commonly used in the United States and have been safely utilized for both repeat dosing as well as concurrent dosing with cytotoxic chemotherapy.

Conclusions

Targeted bone-seeking radionuclides are underutilized in the treatment of painful diffuse osteoblastic metastases. Several new agents are in active clinical investigation, and the pending approval of the first alpha-emitting radionuclide (223Ra) may offer a new class of agents that provide greater efficacy and less toxicity than those currently available for routine clinical use.

Palliation and survival after repeated (188)Re-HEDP therapy of hormone-refractory bone metastases of prostate cancer: a retrospective analysis

This retrospective study compared the effects of single and multiple administrations of (186)Re-hydroxyethylidenediphosphonate ((186)Re-HEDP) on palliation and survival of prostate cancer patients presenting with more than 5 skeletal metastases.

METHODS

A total of 60 patients were divided into 3 groups. Group A (n = 19) consisted of patients who had received a single injection; group B (n = 19), patients who had 2 injections; and group C (n = 22), patients who had 3 or more successive injections. The (188)Re-HEDP was prepared using non-carrier-added (188)Re obtained from an in-house (188)W/(188)Re generator after dilution with carrier perrhenate. Patients' data available from the referring physicians-including prostate-specific antigen levels-were entered into a Windows-based matrix and analyzed using a statistical program. The Gleason scores were similar for all 3 groups.

RESULTS

Mean survival from the start of treatment was 4.50 ± 0.81 mo (95% confidence interval [CI], 2.92-6.08) for group A, 9.98 ± 2.21 mo (95% CI, 5.65-14.31) for group B, and 15.66 ± 3.23 (95% CI, 9.33-22.0) for group C. Although the 3 groups did not differ in Gleason score, the number of lost life-years was significantly lower in group C than in groups A and B. Pain palliation was achieved in 89.5% of group A, 94.7% of group B, and 90.9% of group C.

CONCLUSION

Posttreatment overall survival could be improved from 4.50 to 15.66 mo by multiple-injection bone-targeted therapy with (188)Re-HEDP, when compared with a single injection. Significant pain palliation was common and independent of administration frequency.

Bisphosphonates as radionuclide carriers for imaging or systemic therapy

Bisphosphonates (BP's), biologically stable analogs of naturally occurring pyrophosphates, became the treatment of choice for pathologic conditions characterized by increased osteoclast-mediated bone resorption, namely Paget's disease, osteoporosis and tumor bone disease. Moreover, the clinical success of BP's is also associated with their use in (99m)Tc-based radiopharmaceuticals for bone imaging. In addition to the successful delivery of (99m)Tc (γ-emitter) to bone, BP's have also been used to deliver β(-)-particle emitting radiometals (e.g.(153)Sm, (186/188)Re) for bone-pain palliation. The main goal of this Review is to update the most recent research efforts toward the synthesis, characterization and biological evaluation of novel BP-containing radiometal complexes and radiohalogenated compounds for diagnostic or therapeutic purposes. The structure and in vivo properties of those compounds will be discussed and compared to the clinically available ones, namely in terms of image quality and therapeutic effect. We will also mention briefly the use of BP's as carriers of multimodal nuclear and optical imaging probes.