68Ga and 188Re Starch-Based Microparticles as Theranostic Tool for the Hepatocellular Carcinoma: Radiolabeling and Preliminary In Vivo Rat Studies

Microfluidic Fabrication of Silica Microspheres Infused with Positron Emission Tomography Imaging Agents

Selective internal radiation therapy (SIRT) is a treatment which delivers radioactive therapeutic microspheres via the hepatic artery to destroy tumorigenic tissue of the liver. However, the dose required varies significantly from patient to patient due to nuances in individual biology. Therefore, a positron emission tomography (PET) imaging surrogate, or radiotracer, is used to predict in vivo behavior of therapeutic Y-90 spheres. The ideal surrogate should closely resemble Y-90 microspheres in morphology for highest predictive accuracy. This work presents the fabrication of positron-emitting silica microspheres infused with PET radiotracers copper, fluorine, and gallium. A quick one-pot synthesis is used to create precursor sol, followed by droplet formation with flow-focusing microfluidics, and finally thermal treatment to yield 10-50 μm microspheres with narrow size distribution. Loading of the infused element is controllable in the sol synthesis, while the final sphere size is tunable based on microfluidic flow rates and device channel width. The system is then employed to make radioactive Ga-68 microspheres, which are tested for radioactivity and stability. The fabrication method can be completed within a few hours, depending on the desired microsphere quantity. A microfluidic system is applied to fabricate silica particles loaded with diverse elemental infusions, including radioactive Ga-68.

Microspheres as a Carrier System for Therapeutic Embolization Procedures: Achievements and Advances

The targeted delivery of anti-cancer drugs and isotopes is one of the most pursued goals in anti-cancer therapy. One of the prime examples of such an application is the intra-arterial injection of microspheres containing cytostatic drugs or radioisotopes during hepatic embolization procedures. Therapy based on the application of microspheres revolves around vascular occlusion, complemented with local therapy in the form of trans-arterial chemoembolization (TACE) or radioembolization (TARE). The broadest implementation of these embolization strategies currently lies within the treatment of untreatable hepatocellular cancer (HCC) and metastatic colorectal cancer. This review aims to describe the state-of-the-art TACE and TARE technologies investigated in the clinical setting for HCC and addresses current trials and new developments. In addition, chemical properties and advancements in microsphere carrier systems are evaluated, and possible improvements in embolization therapy based on the modification of and functionalization with therapeutical loads are explored.

Cold Kit Labeling: The Future of 68Ga Radiopharmaceuticals?

Over the last couple of decades, gallium-68 (68Ga) has gained a formidable interest for PET molecular imaging of various conditions, from cancer to infection, through cardiac pathologies or neuropathies. It has gained routine use, with successful radiopharmaceuticals such as somatostatin analogs ([68Ga]Ga-DOTATOC and [68Ga]GaDOTATATE) for neuroendocrine tumors, and PSMA ligands for prostate cancer. It represents a major clinical impact, particularly in the context of theranostics, coupled with their 177Lu-labeled counterparts. Beside those, a bunch of new 68Ga-labeled molecules are in the preclinical and clinical pipelines, with some of them showing great promise for patient care. Increasing clinical demand and regulatory issues have led to the development of automated procedures for the production of 68Ga radiopharmaceuticals. However, the widespread use of these radiopharmaceuticals may rely on simple and efficient radiolabeling methods, undemanding in terms of equipment and infrastructure. To make them technically and economically accessible to the medical community and its patients, it appears mandatory to develop a procedure similar to the well-established kit-based 99mTc chemistry. Already available commercial kits for the production of 68Ga radiopharmaceuticals have demonstrated the feasibility of using such an approach, thus paving the way for more kit-based 68Ga radiopharmaceuticals to be developed. This article discusses the development of 68Ga cold kit radiopharmacy, including technical issues, and regulatory aspects.

Prostate-Specific Membrane Antigen-Targeted Radiopharmaceuticals in Diagnosis and Therapy of Prostate Cancer: Current Status and Future Perspectives

Prostate cancer is the most common cancer to affect men in the United States and the second most common cancer in men worldwide. Prostate-specific membrane antigen (PSMA)-based positron emission tomography (PET) imaging has become increasingly popular as a novel molecular imaging technique capable of improving the clinical management of patients with prostate cancer. To date, several ⁶⁸Ga and ¹⁸F-labeled PSMA-targeted molecules have shown promising results in imaging patients with recurrent prostate cancer using PET/computed tomography (PET/CT). Studies of involving PSMA-targeted radiopharmaceuticals also suggest a higher sensitivity and specificity, along with an improved detection rate over conventional imaging (CT scan and methylene diphosphonate bone scintigraphy) and ¹¹C/¹⁸F-choline PET/CT. In addition, PSMA-617 and PSMA I&T ligands can be labeled with α- and β-emitters (e.g., ²²⁵Ac, ⁹⁰Y, and ¹⁷⁷Lu) and serve as a theranostic tool for patients with metastatic prostate cancer. While the clinical impact of such concept remains to be verified, the preliminary results of PSMA molecular radiotherapy are very encouraging. Herein, we highlighted the current status of development and future perspectives of PSMA-targeted radiopharmaceuticals and their clinical applications.

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.

Theranostics in Interventional Oncology: Versatile Carriers for Diagnosis and Targeted Image-Guided Minimally Invasive Procedures

We are continuously progressing in our understanding of cancer and other diseases and learned how they can be heterogeneous among patients. Therefore, there is an increasing need for accurate characterization of diseases at the molecular level. In parallel, medical imaging and image-guided therapies are rapidly developing fields with new interventions and procedures entering constantly in clinical practice. Theranostics, a relatively new branch of medicine, refers to procedures combining diagnosis and treatment, often based on patient and disease-specific features or molecular markers. Interventional oncology which is at the convergence point of diagnosis and treatment employs several methods related to theranostics to provide minimally invasive procedures tailored to the patient characteristics. The aim is to develop more personalized procedures able to identify cancer cells, selectively reach and treat them, and to assess drug delivery and uptake in real-time in order to perform adjustments in the treatment being delivered based on obtained procedure feedback and ultimately predict response. Here, we review several interventional oncology procedures referring to the field of theranostics, and describe innovative methods that are under development as well as future directions in the field.

Transarterial Radioembolization (TARE) Agents beyond 90Y-Microspheres

Liver malignancies, either primary tumours (mainly hepatocellular carcinoma and cholangiocarcinoma) or secondary hepatic metastases, are a major cause of death, with an increasing incidence. Among them, hepatocellular carcinoma (HCC) presents with a dark prognosis because of underlying liver diseases and an often late diagnosis. A curative surgical treatment can therefore only be proposed in 20 to 30% of the patients. However, new treatment options for intermediate to advanced stages, such as internal radionuclide therapy, seem particularly attractive. Transarterial radioembolization (TARE), which consists in the use of intra-arterial injection of a radiolabelled embolising agent, has led to very promising results. TARE with 90Y-loaded microspheres is now becoming an established procedure to treat liver tumours, with two commercially available products (namely, SIR-Sphere® and TheraSphere®). However, this technology remains expensive and is thus not available everywhere. The aim of this review is to describe TARE alternative technologies currently developed and investigated in clinical trials, with special emphasis on HCC.

Biodistribution, pharmacokinetics, and organ-level dosimetry for 188Re-AHDD-Lipiodol radioembolization based on quantitative post-treatment SPECT/CT scans

Background

Rhenium-188-labelled-Lipiodol radioembolization is a safe and cost-effective treatment for primary liver cancer. In order to determine correlations between treatment doses and patient response to therapy, accurate patient-specific dosimetry is required. Up to date, the reported dosimetry of ¹⁸⁸Re-Lipiodol has been based on whole-body (WB) planar imaging only, which has limited quantitative accuracy. The aim of the present study is to determine the in vivo pharmacokinetics, bio-distribution, and organ-level dosimetry of ¹⁸⁸Re-AHDD-Lipiodol radioembolization using a combination of post-treatment planar and quantitative SPECT/CT images. Furthermore, based on the analysis of the pharmacokinetic data, a practical and relatively simple imaging and dosimetry method that could be implemented in clinics for ¹⁸⁸Re-AHDD-Lipiodol radioembolization is proposed.

Thirteen patients with histologically proven hepatocellular carcinoma underwent ¹⁸⁸Re-AHDD-Lipiodol radioembolization. A series of 2–3 WB planar images and one SPECT/CT scan were acquired over 48 h after the treatment. The time-integrated activity coefficients (TIACs, also known as residence-times) and absorbed doses of tumors and organs at risk (OARs) were determined using a hybrid WB/SPECT imaging method.

Results

Whole-body imaging showed that ¹⁸⁸Re-AHDD-Lipiodol accumulated mostly in the tumor and liver tissue but a non-negligible amount of the pharmaceutical was also observed in the stomach, lungs, salivary glands, spleen, kidneys, and urinary bladder. On average, the measured effective half-life of ¹⁸⁸Re-AHDD-Lipiodol was 12.5 ± 1.9 h in tumor. The effective half-life in the liver and lungs (the two organs at risk) was 12.6 ± 1.7 h and 12.0 ± 1.9 h, respectively. The presence of ¹⁸⁸Re in other organs was probably due to the chemical separation and subsequent release of the free radionuclide from Lipiodol.

The average doses per injected activity in the tumor, liver, and lungs were 23.5 ± 40.8 mGy/MBq, 2.12 ± 1.78 mGy/MBq, and 0.11 ± 0.05 mGy/MBq, respectively. The proposed imaging and dosimetry method, consisting of a single SPECT/CT for activity determination followed by ¹⁸⁸Re-AHDD-Lipiodol clearance with the liver effective half-life of 12.6 h, resulted in TIACs estimates (and hence, doses) mostly within ± 20% from the reference TIACs (estimated using three WB images and one SPECT/CT).

Conclusions

The large inter-patient variability of the absorbed doses in tumors and normal tissue in ¹⁸⁸Re-HDD-Lipiodol radioembolization patients emphasizes the importance of patient-specific dosimetry calculations based on quantitative post-treatment SPECT/CT imaging.

Electronic supplementary material

The online version of this article (10.1186/s40658-018-0227-6) contains supplementary material, which is available to authorized users.

Tracking Tumor Colonization in Xenograft Mouse Models Using Accelerator Mass Spectrometry

Here we introduce an Accelerator Mass Spectrometry (AMS)-based high precision method for quantifying the number of cancer cells that initiate metastatic tumors, in xenograft mice. Quantification of ¹⁴C per cell prior to injection into animals, and quantification of ¹⁴C in whole organs allows us to extrapolate the number of cancer cells available to initiate metastatic tumors. The ¹⁴C labeling was optimized such that 1 cancer cell was detected among 1 million normal cells. We show that ~1–5% of human cancer cells injected into immunodeficient mice form subcutaneous tumors, and even fewer cells initiate metastatic tumors. Comparisons of metastatic site colonization between a highly metastatic (PC3) and a non-metastatic (LnCap) cell line showed that PC3 cells colonize target tissues in greater quantities at 2 weeks post-delivery, and by 12 weeks post-delivery no ¹⁴C was detected in LnCap xenografts, suggesting that all metastatic cells were cleared. The ¹⁴C-signal correlated with the presence and the severity of metastatic tumors. AMS measurements of ¹⁴C-labeled cells provides a highly-sensitive, quantitative assay to experimentally evaluate metastasis and colonization of target tissues in xenograft mouse models. This approach can potentially be used to evaluate tumor aggressiveness and assist in making informed decisions regarding treatment.