Determination of peptide content and purity of DOTA-peptides by metal ion titration and UPLC: an alternative method to monitor quality of DOTA-peptides

In vitro and in vivo analyses of eFAP: a novel FAP-targeting small molecule for radionuclide theranostics and other oncological interventions

BACKGROUND

Fibroblast activation protein (FAP), a transmembrane serine protease overexpressed by cancer-associated fibroblasts in the tumor stroma, is an interesting biomarker for targeted radionuclide theranostics. FAP-targeting radiotracers have demonstrated to be superior to [18F]FDG PET/CT in various solid cancers. However, these radiotracers have suboptimal tumor retention for targeted radionuclide therapy (TRT). We aimed to develop a novel FAP-targeting pharmacophore with improved pharmacokinetics by introducing a substitution at the 8-position of (4-quinolinoyl)-glycyl-2-cyanopyrrolidine, which allows for conjugation of a chelator, dye, or other payloads.

RESULTS

Here we showed the synthesis of DOTA-conjugated eFAP-6 and sulfo-Cyanine5-conjugated eFAP-7. After chemical characterization, the uptake and specificity of both tracers were determined on FAP-expressing cells. In vitro, [111In]In-eFAP-6 demonstrated a superior affinity and a more rapid, although slightly lower, peak uptake than gold standard [111In]In-FAPI-46. Confocal microscopy demonstrated a quick FAP-mediated internalization of eFAP-7. Studies with HT1080-huFAP xenografted mice confirmed a more rapid uptake of [177Lu]Lu-eFAP-6 vs. [177Lu]Lu-FAPI-46. However, tumor retention at 24 h post injection of [177Lu]Lu-eFAP-6 was lower than that of [177Lu]Lu-FAPI-46, hereby currently limiting its use for TRT.

CONCLUSION

The superior affinity and faster tumor accumulation of eFAP-6 over FAPI-46 makes it a suitable compound for radionuclide imaging. After further optimization, the eFAP series has great potential for various oncological interventions, including fluorescent-guided surgery and effective targeted radionuclide theranostics.

Implementing Ac-225 labelled radiopharmaceuticals: practical considerations and (pre-)clinical perspectives

BACKGROUND

In the past years, there has been a notable increase in interest regarding targeted alpha therapy using Ac-225, driven by the observed promising clinical anti-tumor effects. As the production and technology has advanced, the availability of Ac-225 is expected to increase in the near future, making the treatment available to patients worldwide.

MAIN BODY

Ac-225 can be labelled to different biological vectors, whereby the success of developing a radiopharmaceutical depends heavily on the labelling conditions, purity of the radionuclide source, chelator, and type of quenchers used to avoid radiolysis. Multiple (methodological) challenges need to be overcome when working with Ac-225; as alpha-emission detection is time consuming and highly geometry dependent, a gamma co-emission is used, but has to be in equilibrium with the mother-nuclide. Because of the high impact of alpha emitters in vivo it is highly recommended to cross-calibrate the Ac-225 measurements for used quality control (QC) techniques (radio-TLC, HPLC, HP-Ge detector, and gamma counter). More strict health physics regulations apply, as Ac-225 has a high toxicity, thereby limiting practical handling and quantities used for QC analysis.

CONCLUSION

This overview focuses specifically on the practical and methodological challenges when working with Ac-225 labelled radiopharmaceuticals, and underlines the required infrastructure and (detection) methods for the (pre-)clinical application.

Preclinical Evaluation of a PSMA-Targeting Homodimer with an Optimized Linker for Imaging of Prostate Cancer

Prostate-specific membrane antigen (PSMA) targeting radiopharmaceuticals have been successfully used for diagnosis and therapy of prostate cancer. Optimization of the available agents is desirable to improve tumor uptake and reduce side effects to non-target organs. This can be achieved, for instance, via linker modifications or multimerization approaches. In this study, we evaluated a small library of PSMA-targeting derivatives with modified linker residues, and selected the best candidate based on its binding affinity to PSMA. The lead compound was coupled to a chelator for radiolabeling, and subject to dimerization. The resulting molecules, 22 and 30, were highly PSMA specific (IC₅₀ = 1.0-1.6 nM) and stable when radiolabeled with indium-111 (>90% stable in PBS and mouse serum up to 24 h). Moreover, [¹¹¹In]In-30 presented a high uptake in PSMA expressing LS174T cells, with 92.6% internalization compared to 34.1% for PSMA-617. Biodistribution studies in LS174T mice xenograft models showed that [¹¹¹In]In-30 had a higher tumor and kidney uptake compared to [¹¹¹In]In-PSMA-617, but increasing T/K and T/M ratios at 24 h p.i. Tumors could be clearly visualized at 1 h p.i. by SPECT/CT after administration of [¹¹¹In]In-22 and [¹¹¹In]In-PSMA-617, while [¹¹¹In]In-30 showed a clear signal at later time-points (e.g., 24 h p.i.).

Synthesis and radiolabelling of PSMA-targeted derivatives containing GYK/MVK cleavable linkers

Targeted radionuclide therapy (TRT) is a promising strategy to treat different types of cancer. TRT relies on a targeting vector used to deliver a therapeutic radionuclide specifically to the tumour site. Several low molecular weight ligands targeting the prostate-specific membrane antigen (PSMA) have been synthesized, but their pharmacokinetic properties still need to be optimized. Hereby, we describe the synthesis of new conjugates, featuring the cleavable linkers Gly-Tyr-Lys (GYK) and Met-Val-Lys (MVK), to reduce the dose delivered to the kidneys. Compounds were synthesized by solid-phase peptide synthesis (SPPS) and obtained in greater than 95% chemical purity. Radiolabelling was performed with both In-111 and Lu-177 to validate potential use of the compounds as both imaging and therapeutic agents. Radiochemical purity greater than 80% was obtained for both nuclides, but significant radiolysis was observed for the methionine-containing analogue. The results obtained thus far with the GYK-PSMA conjugate could warrant further biological investigations.

Improved Multimodal Tumor Necrosis Imaging with IRDye800CW-DOTA Conjugated to an Albumin-Binding Domain

Simple Summary

Anti-tumor treatment efficacy is determined by tumor shrinkage, which takes valuable time to become apparent and poses a risk of unnecessary treatment with severe side effects. Therefore, there is an unmet need for more reliable and specific methods to monitor treatment efficacy. We explore radiolabeled cyanines for imaging tumor necrosis as a unique marker for therapy efficacy. Moreover, spontaneous tumor necrosis is a hallmark for aggressively growing tumor types with poor prognosis. We improved the binding properties of a previously reported necrosis-avid contrast agent (NACA) and successfully detected spontaneous and therapy-induced tumor necrosis in mice using radioactivity and fluorescence imaging modalities. This NACA may pave the way to in vivo detection of tumor necrosis for early-stage determination of tumor aggressiveness and therapy efficacy.

Abstract

Purpose: To assess our improved NACA for the detection of tumor necrosis. Methods: We increased the blood circulation time of our NACA by adding an albumin-binding domain to the molecular structure. We tested the necrosis avidity on dead or alive cultured cells and performed SPECT and fluorescence imaging of both spontaneous and treatment-induced necrosis in murine breast cancer models. We simultaneously recorded [¹⁸F]FDG-PET and bioluminescence images for complementary detection of tumor viability. Results: We generated two albumin-binding IRDye800CW derivatives which were labeled with indium-111 with high radiochemical purity. Surprisingly, both albumin-binding NACAs had >10x higher in vitro binding towards dead cells. We selected [¹¹¹In]3 for in vivo experiments which showed higher dead cell binding in vitro and in vivo stability. The doxorubicin-treated tumors showed increased [¹¹¹In]3-uptake (1.74 ± 0.08%ID/g after saline treatment, 2.25 ± 0.16%ID/g after doxorubicin treatment, p = 0.044) and decreased [¹⁸F]FDG-uptake (3.02 ± 0.51%ID/g after saline treatment, 1.79 ± 0.11%ID/g after doxorubicin treatment, p = 0.040), indicating therapy efficacy. Moreover, we detected increased [¹¹¹In]3-uptake and tumor necrosis in more rapidly growing EMT6 tumors. Conclusions: Our albumin-binding NACA based on IRDye800CW facilitates tumor-necrosis imaging for assessment of therapy efficacy and aggressiveness in solid tumors using both fluorescence and SPECT imaging.

Measurement of reaction kinetics of [177Lu]Lu-DOTA-TATE using a microfluidic system

Design and evaluation of a microfluidic system that allowed the determination of Arrhenius parameters for the formation of [¹⁷⁷Lu]Lu-DOTA-TATE using clinical radiolabeling conditions.