A high level of EpCAM overexpression in lung cancer makes this protein a promising target for targeted therapy. Radionuclide visualization of EpCAM expression would facilitate the selection of patients potentially benefiting from such treatment. Single-photon computed tomography (SPECT) using ^99mTc-labeled engineered scaffold protein DARPin Ec1 has shown its effectiveness in imaging tumors with overexpression of EpCAM in preclinical studies, providing high contrast just a few hours after injection. This first-in-human study aimed to evaluate the safety and distribution of [^99mTc]Tc(CO)₃-(HE)₃-Ec1 in patients with primary lung cancer. Twelve lung cancer patients were injected with 300.7 ± 103.2 MBq of [^99mTc]Tc(CO)₃-(HE)₃-Ec1. Whole-body planar imaging (at 2, 4, 6 and 24 h after injection) and SPECT/CT of the lung (at 2, 4, and 6 h) were performed. The patients’ vital signs and possible side effects were monitored up to 7 days after injection. The patients tolerated the injection of [^99mTc]Tc(CO)₃-(HE)₃-Ec1 well, and their somatic condition remained normal during the entire follow-up period. There were no abnormalities in blood and urine tests after injection of [^99mTc]Tc(CO)₃-(HE)₃-Ec1. The highest absorbed doses were in the kidneys, liver, pancreas, thyroid, gallbladder wall, and adrenals. There was also a relatively high accumulation of [^99mTc]Tc(CO)₃-(HE)₃-Ec1 in the small and large intestines, pancreas and thyroid. According to the SPECT/CT, accumulation of [^99mTc]Tc(CO)₃-(HE)₃-Ec1 in the lung tumor was found in all patients included in the study. Intensive accumulation of [^99mTc]Tc(CO)₃-(HE)₃-Ec1 was also noted in regional metastases. [^99mTc]Tc(CO)₃-(HE)₃-Ec1 can potentially be considered a diagnostic tracer for imaging EpCAM expression in lung cancer patients and other tumors with overexpression of EpCAM.

The use of radiopharmaceuticals for diagnostics in oncology allows for the detection of the disease at an early stage. Among diagnostic radionuclides, ^99mTc is a promising isotope that has been used to create several drugs for clinical use. One of the most effective ^99mTc chelators is 6-hydrazinylnicotinic acid (HYNIC), which, when combined with various vector molecules, can be used for targeted delivery of radionuclides to tumor tissues. At the same time, it is known that tetrapyrrole macrocycles are capable of selective accumulation in tumors, and thus can be used to target radiopharmaceuticals with ^99mTc. In this work, the conjugate of natural chlorin and HYNIC was obtained, and preliminary preclinical studies were carried out on its radiocomplex with ^99mTc.

Radionuclide molecular imaging of epidermal growth factor receptor (EGFR) expression might permit the selection of patients for EGFR-targeting therapies. Designed ankyrin repeat protein (DARPin) E01 with a high affinity to the ectodomain III of the EGFR is a possible EGFR imaging probe. The goal of this study was to evaluate the potential of radiolabeled DARPin E01 for in vivo imaging of EGFR. DARPin E01 containing the (HE)₃-tag was site-specifically labeled with a residualizing ^99mTc (using ^99mTc]Tc(CO)₃). Two methods providing non-residualizing ¹²³I labels, direct electrophilic radioiodination and indirect radioiodination using [¹²³I]I-para-iodobenzoate (PIB), were tested. [^99mTc]Tc-(HE)₃-E01 and [¹²³I]I-(HE)₃-E01-PIB preserved specific binding to EGFR-expressing cells and affinity in the single-digit nanomolar range. Direct labeling with ¹²³I resulted in a substantial loss of binding. In vitro cellular processing studies showed that both [^99mTc]Tc-(HE)₃-E01 and [¹²³I]I-(HE)₃-E01-PIB had rapid binding and relatively slow internalization. Evaluation of [^99mTc]Tc-(HE)₃-E01 biodistribution in normal CD1 mice showed that its hepatic uptake was non-saturable, suggesting that this tracer does not bind to murine EGFR. A side-by-side comparison of biodistribution and tumor targeting of [^99mTc]Tc-(HE)₃-E01 and [¹²³I]I-(HE)₃-E01-PIB was performed in Nu/j mice bearing EGFR-positive A-431 and EGFR-negative Ramos human cancer xenografts. Both radiolabeled DARPins demonstrated EGFR-specific tumor uptake. However, [¹²³I]I-(HE)₃-E01-PIB had appreciably lower uptake in normal organs compared to [^99mTc]Tc-(HE)₃-E01, which provided significantly (p < 0.05) higher tumor-to-organ ratios. Gamma-camera imaging confirmed that [¹²³I]I-(HE)₃-E01-PIB demonstrated a higher imaging contrast in preclinical models than [^99mTc]Tc-(HE)₃-E01. In conclusion, DARPin (HE)₃-E01 labeled using a non-residualizing [¹²³I]I-para-iodobenzoate (PIB) label is the preferred radiotracer for in vivo imaging of EGFR expression in cancer.

Background/Objectives: Gastrin-releasing peptide receptor (GRPR) is overexpressed in breast cancer and might be used as a theranostics target. The expression of GRPR strongly correlates with estrogen receptor (ER) expression. Visualization of GRPR-expressing breast tumors might help to select the optimal treatment. Developing GRPR-specific probes for SPECT would permit imaging-guided therapy in regions with restricted access to PET facilities. In this first-in-human study, we evaluated the safety, biodistribution, and dosimetry of the [^99mTc]Tc-DB8 GRPR-antagonistic peptide. We also addressed the important issue of finding the optimal injected peptide mass. Methods: Fifteen female patients with ER-positive primary breast cancer were enrolled and divided into three cohorts receiving [^99mTc]Tc-DB8 (corresponding to three distinct doses of 40, 80, or 120 µg DB8) comprising five patients each. Additionally, four patients with ER-negative primary tumors were injected with 80 µg [^99mTc]Tc-DB8. The injected activity was 360 ± 70 MBq. Planar scintigraphy was performed after 2, 4, 6, and 24 h, and SPECT/CT scans followed planar imaging 2, 4, and 6 h after injection. Results: No adverse events were associated with [^99mTc]Tc-DB8 injections. The effective dose was 0.009–0.014 mSv/MBq. Primary tumors and all known lymph node metastases were visualized irrespective of injected peptide mass. The highest uptake in the ER-positive tumors was 2 h after injection of [^99mTc]Tc-DB8 at a 80 µg DB8 dose (SUV_max 5.3 ± 1.2). Injection of [^99mTc]Tc-DB8 with 80 µg DB8 provided significantly (p < 0.01) higher uptake in primary ER-positive breast cancer lesions than injection with 40 µg DB8 (SUV_max 2.0 ± 0.3) or 120 µg (SUV_max 3.2 ± 1.4). Tumor-to-contralateral breast ratio after injection of 80 μg was also significantly (p < 0.01, ANOVA test) higher than ratios after injection of other peptide masses. The uptake in ER-negative lesions was significantly lower (SUV_max 2.0 ± 0.3) than in ER-positive tumors. Conclusions: Imaging using [^99mTc]Tc-DB8 is safe, tolerable, and associated with low absorbed doses. The tumor uptake is dependent on the injected peptide mass. The injection of an optimal mass (80 µg) provides the highest uptake in ER-positive tumors. At optimal dosing, the uptake was significantly higher in ER-positive than in ER-negative lesions.

Aim. To study in vitro and in vivo the functional suitability of ^99mTc-labeled lyophilized formulation containing designed ankyrin repeat protein (DARPin) G3-(GGGS)₃Cys for radionuclide imaging of HER2/neu overexpression in malignant tumors.Materials and methods. To create a targeted protein, a modified genetic construct with the sequence encoding DARPin G3-(GGGS)₃Cys was used. To generate the experimental probe, we used a lyophilized formulation containing DARPin G3-(GGGS)₃Cys with auxiliary substances and ^99mTc sodium pertechnetate (500 MBq) incubated at 60 °C for 30 min. Radiochemical purity of ^99mTc-G3-(GGGS)₃Cys was analyzed by thin-layer radiochromatography. SKOV-3, BT-474, and DU-145 cell lines were used to test binding specificity in vitro. The dissociation constant was determined via a saturation binding assay on SKOV-3 cells with a range of protein concentrations from 0.2 to 40 nM. Nu/j mice bearing HER2-positive SKOV-3 xenografts and HER2-negative Ramos xenografts were used to evaluate the targeting properties and biodistribution.Results. A radiocomplex based on ^99mTc and a lyophilized formulation with DARPin G3-(GGGS)₃Cys was obtained with the radiochemical purity of more than 96%. Binding of ^99mTc-G3-(GGGS)₃Cys to the cells was specific (K_D 3.9 ± 0.5 nM) and proportional to the level of HER2/neu expression in the cells. The uptake of ^99mTc-G3-(GGGS)₃Cys in SKOV-3 xenografts was significantly higher than in Ramos xenografts. ^99mTc-G3-(GGGS)₃Cys demonstrated rapid blood and renal clearance and had low activity in the salivary glands and stomach. Liver uptake was about 5–7%ID/g. In addition, ^99mTc-G3-(GGGS)₃Cys exhibited very low uptakes in the lungs, muscles, small intestine, and bones.Conclusion. The ^99mTc-labeled lyophilized formulation with DARPin G3-(GGGS)₃Cys is functionally suitable for imaging HER2/neu overexpression in tumors, as it binds specifically to the receptor, is stable in vivo, and has favorable biodistribution in organs and tissues. The radiocomplex based on ^99mTc-G3-(GGGS)₃Cys was obtained by a simple method with high radiochemical purity.

Background/Objectives: The gastrin-releasing peptide receptor (GRPR) shows high-density expression in prostate cancer (PCa), especially in the early stages of the disease. The introduction of a safe radiotracer for assessing GRPR-expression in PCa may serve as an alternative or complementary tracer to PSMA-directed probes for patients with insufficient PSMA expression. In the present study, the tolerability and safety, biodistribution, and dosimetry of the new GRPR-targeting radiopeptide [^99mTc]Tc-DB8 were investigated for the first time in male PCa patients. A mass escalation study was performed, aiming to improve tumor-to-background contrast and, thereby, to enhance diagnostic accuracy. Methods: Sixteen male patients were enrolled in a single-center diagnostic open-label exploratory Phase I clinical trial. Patients were administered a single intravenous injection of 40, 80, or 120 µg of [^99mTc]Tc-DB8 peptide (n = 5–6) and underwent whole-body planar imaging (anterior and posterior) 2, 4, 6, and 24 h post-injection (pi) and SPECT-CT acquisition 2, 4, and 6 h pi. Results: Administration of [^99mTc]Tc-DB8 was well tolerated at all tested peptide masses. The effective dose did not differ significantly between the injected peptide mass and was 0.005 ± 0.003 mSv/MBq. High activity uptake was observed in the pancreas and kidneys, which 3-fold decreased with an increasing injected peptide mass from 40 to 120 µg. The activity uptake in primary tumors did not differ significantly between cohorts injected with different peptide masses [SUV_max 1.65–9.96]. The tumor-to-muscle ratios increased with time and were the highest for the cohort injected with 120 µg of peptide, 7.2 ± 3.1 (4.64-11-25) at 4 h pi. Conclusions: Single intravenous administration of [^99mTc]Tc-DB8, for visualization of GRPR expression in PCa using SPECT imaging was well tolerated in a peptide mass range of 40–120 µg. An injected peptide mass of 80–120 µg/patient and SPECT acquisition 2–4 h pi were found to be optimal for further clinical studies due to the significantly lower activity accumulation in the pancreas and kidneys.