[Normal tissue tolerance to external beam radiation therapy: the stomach]

Effect of N-Terminal Peptide Modifications on In Vitro and In Vivo Properties of 177Lu-Labeled Peptide Analogs Targeting CCK2R

The therapeutic potential of minigastrin (MG) analogs for the treatment of cholecystokinin-2 receptor (CCK2R)-expressing cancers is limited by poor in vivo stability or unfavorable accumulation in non-target tissues. Increased stability against metabolic degradation was achieved by modifying the C-terminal receptor-specific region. This modification led to significantly improved tumor targeting properties. In this study, further N-terminal peptide modifications were investigated. Two novel MG analogs were designed starting from the amino acid sequence of DOTA-MGS5 (DOTA-DGlu-Ala-Tyr-Gly-Trp-(N-Me)Nle-Asp-1Nal-NH2). Introduction of a penta-DGlu moiety and replacement of the four N-terminal amino acids by a non-charged hydrophilic linker was investigated. Retained receptor binding was confirmed using two CCK2R-expressing cell lines. The effect on metabolic degradation of the new 177Lu-labeled peptides was studied in human serum in vitro, as well as in BALB/c mice in vivo. The tumor targeting properties of the radiolabeled peptides were assessed using BALB/c nude mice bearing receptor-positive and receptor-negative tumor xenografts. Both novel MG analogs were found to have strong receptor binding, enhanced stability, and high tumor uptake. Replacement of the four N-terminal amino acids by a non-charged hydrophilic linker lowered the absorption in the dose-limiting organs, whereas introduction of the penta-DGlu moiety increased uptake in renal tissue.

Organs at risk radiation dose constraints

Dose constraints are essential for performing dosimetry, especially for intensity modulation and for radiotherapy under stereotaxic conditions. We present the update of the recommendations of the French society of oncological radiotherapy for the use of these doses in classical current practice but also for reirradiation.

Radiopharmaceutical Formulation and Preclinical Testing of 68Ga-Labeled DOTA-MGS5 for the Regulatory Approval of a First Exploratory Clinical Trial

The new minigastrin analog DOTA-MGS5 is a promising new candidate for targeting cholecystokinin-2 receptor (CCK2R)-expressing tumors. To enable the clinical translation of PET/CT imaging using ⁶⁸Ga-labeled DOTA-MGS5, different quality and safety aspects need to be considered to comply with the regulatory framework for clinical trial application. The preparation of the radiopharmaceutical was established using a cassette-based automated synthesis unit. Product specifications, including analytical procedures and acceptance criteria, were adopted from Ph. Eur. monographs for other ⁶⁸Ga-labeled radiopharmaceuticals. Non-clinical studies included receptor affinity and cell uptake studies using two different CCK2R-expressing cell lines, as well as pharmacokinetic biodistribution studies in BALB/c mice for dosimetry calculations and toxicological studies in Wistar rats. The produced masterbatches fulfilled the defined acceptance criteria. DOTA-MGS5, with confirmed affinity to the CCK2R, showed a high specific cell uptake and no interaction with other receptors in vitro when radiolabeled with gallium-68. Favorable in vivo properties were observed in biodistribution and dosimetry studies. An effective dose of ~0.01 mSv/MBq was estimated for humans utilizing OLINDA/EXM software. A maximum peptide dose of 50 µg was established for the initial clinical dose based on the toxicity study in rats. The standardized production of [⁶⁸Ga]Ga-DOTA-MGS5 using an automated synthesis module and the performed non-clinical safety studies support a first exploratory clinical trial with this new PET imaging agent.

The INTER-ROMA Project - a Survey among Italian Radiation Oncologists on Their Approach to the Treatment of Bone Metastases

Aims and background

Radiotherapy has an established palliative role for bone metastases but despite the large number of patients treated there is still controversy surrounding the optimal radiotherapy schedule to prescribe. The aim of this survey was to determine the decision patterns of Italian radiation oncologists in four different clinical cases of patients with bone metastases.

Methods and study design

During the latest national meeting of the Italian Association of Radiation Oncology (AIRO), four clinical cases were presented to attending radiation oncologists. The cases were different with respect to the histology of the primary tumor, performance status, pain before and after analgesics, tumor site, and radiological characteristics of the metastatic lesions. For each clinical case the respondents were asked to give an indication for treatment; prescribe doses, volumes and treatment field arrangements; decide whether to prescribe prophylactic supportive therapy or not; and provide information about factors that particularly influenced prescription. Finally, a descriptive statistical analysis was performed.

Results

Three hundred questionnaires were distributed to radiation oncologists attending the congress. One hundred twenty-five questionnaires were returned but only 122 (40.6%) were adequately completed and considered for the analysis. Considerable differences were observed among radiation oncologists in prescribing and delivering radiotherapy for bone metastases. There was also a notable divergence from international guidelines, which will be discussed in this report.

Conclusions

Despite the results of clinical trials, Italian radiation oncologists differ considerably in their decisions on treatment doses and volumes. National guidelines are needed in order that patients can be treated uniformly and better data will become available for evidence-based palliative radiotherapy.

177Lu Labeled Cyclic Minigastrin Analogues with Therapeutic Activity in CCK2R Expressing Tumors: Preclinical Evaluation of a Kit Formulation

Minigastrin (MG) analogues specifically target cholecystokinin-2 receptors (CCK2R) expressed in different tumors and enable targeted radiotherapy of advanced and disseminated disease when radiolabeled with a beta emitter such as ¹⁷⁷Lu. Especially truncated MG analogues missing the penta-Glu sequence are associated with low kidney retention and seem therefore most promising for therapeutic use. Based on [d-Glu¹,desGlu^2-6]MG (MG11) we have designed the two cyclic MG analogues cyclo^1,9[γ-d-Glu¹,desGlu^2-6,d-Lys⁹]MG (cyclo-MG1) and cyclo^1,9[γ-d-Glu¹,desGlu^2-6,d-Lys⁹,Nle¹¹]MG (cyclo-MG2). In the present work we have developed and preclinically evaluated a pharmaceutical kit formulation for the labeling with ¹⁷⁷Lu of the two DOTA-conjugated cyclic MG analogues. The stability of the kits during storage as well as the stability of the radiolabeled peptides was investigated. A cell line stably transfected with human CCK2R and a control cell line without receptor expression were used for in vitro and in vivo studies with the radioligands prepared from kit formulations. In terms of stability ¹⁷⁷Lu-DOTA-cyclo-MG2 showed advantages over ¹⁷⁷Lu-DOTA-cyclo-MG1. Still, for both radioligands a high receptor-mediated cell uptake and favorable pharmacokinetic profile combining receptor-specific tumor uptake with low unspecific tissue uptake and low kidney retention were confirmed. Investigating the therapy efficacy and treatment toxicity in xenografted BALB/c nude mice a receptor-specific and comparable therapeutic effect could be demonstrated for both radioligands. A 1.7- to 2.6-fold increase in tumor volume doubling time was observed for receptor-positive tumors in treated versus untreated animals, which was 39-73% higher when compared to receptor-negative tumors. The treatment was connected with transient bone marrow toxicity and minor signs of kidney toxicity. All together the obtained results support further studies for the clinical translation of this new therapeutic approach.

[Radiotherapy for retroperitoneal sarcomas]

The management of retroperitoneal sarcoma can be very challenging, and the quality of initial treatment strategy appears to be a crucial prognostic factor. En bloc surgery is currently the standard of care for these rare tumours and perioperative treatments such as chemotherapy or radiotherapy have not been validated yet. However, local-regional relapse constitutes the most common disease course. While adjuvant radiotherapy is less and less common due to gastrointestinal toxicities, preoperative radiation therapy offers numerous advantages and is being evaluated as part of a national multicentre phase II study (TOMOREP trial) and is the subject of a European randomized phase III study (STRASS trial). The objective of this article is to present data on preoperative irradiation in terms of dose, volumes and optimal radiotherapy techniques for the treatment of this rare disease.

Overview of whole body gamma knife for locally advanced pancreatic cancer

Pancreatic cancer is a disease that seriously threatens the health of human beings. The treatment options currently available for pancreatic cancer are still limited. In this article, we describe the principle of whole body gamma knife and SBRT (a treatment similar to whole body gamma knife) for the treatment of advanced pancreatic cancer. By improving the absorbed dose in the lesion, whole body gamma knife can control tumor progression and improve survival in patients with pancreatic cancer with low side effects. Despite that controversy still exists, the advantages of SBRT in the treatment of pancreatic cancer have been gradually recognized in foreign countries.