Side-Chain Modified [^99mTc]Tc-DT1 Mimics:A Comparative Study in NTS₁R-Positive Models

Radiolabeled neurotensin analogs have been developed as candidates for theranostic use against neurotensin subtype 1 receptor (NTS1R)-expressing cancer. However, their fast degradation by two major peptidases, neprilysin (NEP) and angiotensin-converting enzyme (ACE), has hitherto limited clinical success. We have recently shown that palmitoylation at the ε-amine of Lys7 in [99mTc]Tc-[Lys7]DT1 (DT1, N4-Gly-Arg-Arg-Pro-Tyr-Ile-Leu-OH, N4 = 6-(carboxy)-1,4,8,11-tetraazaundecane) led to the fully stabilized [99mTc]Tc-DT9 analog, displaying high uptake in human pancreatic cancer AsPC-1 xenografts but unfavorable pharmacokinetics in mice. Aiming to improve the in vivo stability of [99mTc]Tc-DT1 without compromising pharmacokinetics, we now introduce three new [99mTc]Tc-DT1 mimics, carrying different pendant groups at the ε-amine of Lys7: MPBA (4-(4-methylphenyl)butyric acid)—[99mTc]Tc-DT10; MPBA via a PEG4-linker—[99mTc]Tc-DT11; or a hydrophilic PEG6 chain—[99mTc]Tc-DT12. The impact of these modifications on receptor affinity and internalization was studied in NTS1R-positive cells. The effects on stability and AsPC-1 tumor uptake were assessed in mice without or during NEP/ACE inhibition. Unlike [99mTc]Tc-DT10, the longer-chain modified [99mTc]Tc-DT11 and [99mTc]Tc-DT12 were significantly stabilized in vivo, resulting in markedly improved tumor uptake compared to [99mTc]Tc-DT1. [99mTc]Tc-DT11 was found to achieve the highest AsPC-1 tumor values and good pharmacokinetics, either without or during NEP inhibition, qualifying for further validation in patients with NTS1R-positive tumors using SPECT/CT.</p

Optimizing the Profile of Tc-99m Tc-NT(7-13) Tracers in Pancreatic Cancer Models by Means of Protease Inhibitors

Background: The overexpression of neurotensin subtype 1 receptors (NTS1Rs) in human tumors may be elegantly exploited for directing neurotensin (NT)-based radionuclide carriers specifically to cancer sites for theranostic purposes. We have recently shown that [99mTc]Tc–DT1 ([99mTc]Tc–[N4–Gly7 ]NT(7–13)) and [99mTc]Tc–DT5 ([99mTc]Tc–[N4–βAla7 ,Dab9 ]NT(7–13)) show notably improved uptake in human colon adenocarcinoma WiDr xenografts in mice treated with neprilysin (NEP) inhibitors and/or angiotensin-converting enzyme (ACE) inhibitors compared with untreated controls. Aiming toward translation of this promising approach in NTS1R-positive pancreatic ductal adenocarcinoma (PDAC) patients, we now report on the impact of registered NEP/ACE inhibitors on the performance of [99mTc]Tc–DT1 and [99mTc]Tc–DT5 in pancreatic cancer models. Methods: The cellular uptake of [99mTc]Tc–DT1 and [99mTc]Tc–DT5 was tested in a panel of pancreatic cell lines, and their stability was assessed in mice treated or not treated with Entresto, lisinopril, or their combinations. Biodistribution was conducted in severe combined immunodeficiency (SCID) mice bearing pancreatic AsPC-1 xenografts. Results: The Entresto + lisinopril combination maximized the metabolic stability of the fast-internalizing [99mTc]Tc–DT1 in mice, resulting in notably enhanced tumor uptake (7.05 ± 0.80% injected activity (IA)/g vs. 1.25 ± 0.80% IA/g in non-treated controls at 4 h post-injection; p < 0.0001). Conclusions: This study has shown the feasibility of optimizing the uptake of [99mTc]Tc–DT1 in pancreatic cancer models with the aid of clinically established NEP/ACE inhibitors, in favor of clinical translation prospects

Key-protease inhibition regimens promote tumor targeting of neurotensin radioligands

Neurotensin subtype 1 receptors (NTS1R) represent attractive molecular targets for directing radiolabeled neurotensin (NT) analogs to tumor lesions for diagnostic and therapeutic purposes. This approach has been largely undermined by the rapid in vivo degradation of linear NT-based radioligands. Herein, we aim to increase the tumor targeting of three99mTc-labeled NT analogs by the in-situ inhibition of two key proteases involved in their catabolism. DT1 ([N4- Gly7]NT(7-13)), DT5 ([N4-βAla7,Dab9]NT(7-13)), and DT6 ([N4-βAla7,Dab9,Tle12]]NT(7-13)) were labeled with99mTc. Their profiles were investigated in NTS1R-positive colon adenocarcinoma WiDr cells and mice treated or not with the neprilysin (NEP)-inhibitor phosphoramidon (PA) and/or the angiotensin converting enzyme (ACE)-inhibitor lisinopril (Lis). Structural modifications led to the partial stabilization of99mTc-DT6 in peripheral mice blood (55.1 ± 3.9% intact), whereas99mTc-D

Bis(Disulfide)-Bridged Somatostatin-14 Analogs and Their [¹¹¹In]In-Radioligands:Synthesis and Preclinical Profile

The overexpression of one or more somatostatin receptors (SST1–5R) in human tumors has provided an opportunity for diagnosis and therapy with somatostatin-like radionuclide carriers. The application of “pansomatostatin” analogs is expected to broaden the clinical indications and upgrade the diagnostic/therapeutic efficacy of currently applied SST2R-prefering radioligands. In pursuit of this goal, we now introduce two bicyclic somatostatin-14 (SS14) analogs, AT5S (DOTA-Ala1-Gly2-c[Cys3-Lys4-Asn5-c[Cys6-Phe7-DTrp8-Lys9-Thr10-Cys11]-Thr12-Ser13-Cys14]) and AT6S (DOTA-Ala1-Gly2-c[Cys3-Lys4-c[Cys5-Phe6-Phe7-DTrp8-Lys9-Thr10-Phe11-Cys12]-Ser13-Cys14]), suitable for labeling with trivalent radiometals and designed to sustain in vivo degradation. Both AT5S and AT6S and the respective [111In]In-AT5S and [111In]In-AT6S were evaluated in a series of in vitro assays, while radioligand stability and biodistribution were studied in mice. The 8/12-mer bicyclic AT6S showed expanded affinity for all SST1–5R and agonistic properties at the SST2R, whereas AT5S lost all affinity to SST1–5R. Both [111In]In-AT5S and [111In]In-AT6S remained stable in the peripheral blood of mice, while [111In]In-AT6S displayed low, but specific uptake in AR4-2J tumors and higher uptake in HEK293-SST3R tumors in mice. In summary, high radioligand stability was acquired by the two disulfide bridges introduced into the SS14 motif, but only the 8/12-mer ring AT6S retained a pansomatostatin profile. In consequence, [111In]In-AT6S targeted SST2R-/SST3R-positive xenografts in mice. These results call for further research on pansomatostatin-like radioligands for cancer theranostics.</p

Bis(Disulfide)-Bridged Somatostatin-14 Analogs and Their [¹¹¹In]In-Radioligands:Synthesis and Preclinical Profile

The overexpression of one or more somatostatin receptors (SST1–5R) in human tumors has provided an opportunity for diagnosis and therapy with somatostatin-like radionuclide carriers. The application of “pansomatostatin” analogs is expected to broaden the clinical indications and upgrade the diagnostic/therapeutic efficacy of currently applied SST2R-prefering radioligands. In pursuit of this goal, we now introduce two bicyclic somatostatin-14 (SS14) analogs, AT5S (DOTA-Ala1-Gly2-c[Cys3-Lys4-Asn5-c[Cys6-Phe7-DTrp8-Lys9-Thr10-Cys11]-Thr12-Ser13-Cys14]) and AT6S (DOTA-Ala1-Gly2-c[Cys3-Lys4-c[Cys5-Phe6-Phe7-DTrp8-Lys9-Thr10-Phe11-Cys12]-Ser13-Cys14]), suitable for labeling with trivalent radiometals and designed to sustain in vivo degradation. Both AT5S and AT6S and the respective [111In]In-AT5S and [111In]In-AT6S were evaluated in a series of in vitro assays, while radioligand stability and biodistribution were studied in mice. The 8/12-mer bicyclic AT6S showed expanded affinity for all SST1–5R and agonistic properties at the SST2R, whereas AT5S lost all affinity to SST1–5R. Both [111In]In-AT5S and [111In]In-AT6S remained stable in the peripheral blood of mice, while [111In]In-AT6S displayed low, but specific uptake in AR4-2J tumors and higher uptake in HEK293-SST3R tumors in mice. In summary, high radioligand stability was acquired by the two disulfide bridges introduced into the SS14 motif, but only the 8/12-mer ring AT6S retained a pansomatostatin profile. In consequence, [111In]In-AT6S targeted SST2R-/SST3R-positive xenografts in mice. These results call for further research on pansomatostatin-like radioligands for cancer theranostics.</p

Somatostatin receptor imaging: The presence of somatostatin receptors in rheumatoid arthritis

Objective. To investigate the in vivo and in vitro expression of somatostatin receptors (SS-R) on synovial membranes of patients with rheumatoid arthritis (RA). Methods. The joints of 14 consecutive patients with active RA, 4 patients with severe osteoarthritis (OA), and 30 control patients were studied. The somatostatin analog [111In-DTPA-D-Phe1]-octreotide was used for in vivo SS-R scintigraphy, and the somatostatin analog [125I-Tyr3]-octreotide for in vitro SS-R autoradiography. Results. Seventy-six percent (220 of 290) of the painful joints and 76% (207 of 274) of the swollen joints of the patients with RA were visualized by SS-R scintigraphy. The degree of pain and swelling correlated well with positive scintigraphy findings in the joints (P < 0.0001). In 2 of the RA patients who underwent scintigraphy, as well as in 4 of 5 other patients, in vitro studies of the synovial membranes showed the presence of specific SS-R. In patients with OA, uptake of radioactivity in the affected joints was significantly lower than that in patients with RA. None of the joints of the control patients demonstrated uptake of radioactivity. Conclusion. SS-R are present in the synovial tissue of p

Somatostatin receptor scintigraphy in cutaneous malignant lymphomas

Background: Lymphoid cells may express somatostatin receptors (SS-Rs) on their cell surface. Therefore radiolabeled somatostalin analogues may be used to visualize SS-R-positive lymphoid neoplasms in vivo. Exact staging is the basis for treatment decisions in cutaneous malignant lymphoma. We considered the possibility that SS-R scintigraphy might offer a clinically useful method of diagnostic imaging in patients with cutaneous malignant lymphoma. Objective: We evaluated SS-R scintigraphy in comparison with conventional staging methods in the staging of cutaneous malignant lymphoma. Methods: We conducted a prospective study in 14 consecutive patients with histologically proven cutaneous malignant lymphoma. SS-R scintigraphy was compared with physical, radiologic, and bone marrow examinations. Lymph node excisions were performed in patients with palpable lymph nodes. Results: SS-R scintigraphy was positive in the lymph nodes in all four patients with malignant lymph node infiltration and negative in the three patients with dermatopathic lymphadenopathy. In two patients, previously unsuspected lymphoma localizations were visualized by SS-R scintigraphy. In only three patients all skin lesions were visualized by SS-R scintigraphy; these three patients had not been treated with topical corticosteroids. SS-R scintigraphy failed to detect an adrenal mass in one patient and bone marrow infiltration in two patients. Conclusion: SS-R scintigraphy may help distinguish dermatopathic lymphadenopathy from malignant lymph node infiltration in patients with cutaneous malignant lymphoma

An unusual case of multiple endocrine neoplasia type 1 and the role of 111In-pentetreotide scintigraphy

A 50-year-old woman is described with a very unusual combination of MEN-1 syndrome with a negative family history. At first she had been treated because of a clinically non-functioning pituitary adenoma in the maxillary sinus. Six years later a carcinoid tumour was discovered by means of 111In-pentreotide scintigraphy

Peptide receptor radionuclide therapy

Peptide receptor radionuclide therapy is a new treatment modality for patients with inoperable or metastasised neuroendocrine gastroenteropancreatic tumours. After the successful implementation of somatostatin receptor scintigraphy in daily clinical practice, the next logical step was to increase the radiation dose of the administered radiolabelled somatostatin analogue in an attempt to induce tumour shrinkage. Since then, an increasing number of patients has been successfully treated with this approach, resulting in a substantial numbers of patient with objective tumour shrinkage. Serious side-effects have been rare. This article reviews the effectiveness of the different radiolabelled somatostatin analogues used, the currently known side-effects and the survival data available. Furthermore, clinical issues, including indication and timing of therapy, are discussed. Finally, important directions for future research are briefly mentioned to illustrate that, although the currently available results already suggest a favourable outcome compared with other systemic therapies, new strategies are being developed to increase efficacy