In-vivo inhibition of neutral endopeptidase 1 results in higher absorbed tumor doses of [177Lu]Lu-PP-F11N in humans: the lumed phase 0b study.

BACKGROUND: A new generation of radiolabeled minigastrin analogs delivers low radiation doses to kidneys and are considered relatively stable due to less enzymatic degradation. Nevertheless, relatively low tumor radiation doses in patients indicate limited stability in humans. We aimed at evaluating the effect of sacubitril, an inhibitor of the neutral endopeptidase 1, on the stability and absorbed doses to tumors and organs by the cholecystokinin-2 receptor agonist [177Lu]Lu-PP-F11N in patients. In this prospective phase 0 study eight consecutive patients with advanced medullary thyroid carcinoma and a current somatostatin receptor subtype 2 PET/CT scan were included. Patients received two short infusions of ~ 1 GBq [177Lu]Lu-PP-F11N in an interval of ~ 4 weeks with and without Entresto® pretreatment in an open-label, randomized cross-over order. Entresto® was given at a single oral dose, containing 48.6 mg sacubitril. Adverse events were graded and quantitative SPECT/CT and blood sampling were performed. Absorbed doses to tumors and relevant organs were calculated. RESULTS: Pretreatment with Entresto® showed no additional toxicity and increased the stability of [177Lu]Lu-PP-FF11N in blood significantly (p < 0.001). Median tumor-absorbed doses were 2.6-fold higher after Entresto® pretreatment (0.74 vs. 0.28 Gy/GBq, P = 0.03). At the same time, an increase of absorbed doses to stomach, kidneys and bone marrow was observed, resulting in a tumor-to-organ absorbed dose ratio not significantly different with and without Entresto®. CONCLUSIONS: Premedication with Entresto® results in a relevant stabilization of [177Lu]Lu-PP-FF11N and consecutively increases radiation doses in tumors and organs. Trial registration clinicaltrails.gov, NCT03647657. Registered 20 August 2018.

Radiolabeled Somatostatin Receptor Antagonist Versus Agonist for Peptide Receptor Radionuclide Therapy in Patients with Therapy-Resistant Meningioma: PROMENADE Phase 0 Study.

Our primary aim was to compare the therapeutic index (tumor-to-bone marrow and tumor-to-kidney absorbed-dose ratios) of the new radiolabeled somatostatin receptor antagonist [177Lu]Lu-DOTA-JR11 with the established radiolabeled somatostatin receptor agonist [177Lu]Lu-DOTATOC in the same patients with progressive, standard therapy-refractory meningioma. Methods: In this prospective, single-center, open-label phase 0 study (NCT04997317), 6 consecutive patients were included: 3 men and 3 women (mean age, 63.5 y). Patients received 6.9-7.3 GBq (standard injected radioactivity) of [177Lu]Lu-DOTATOC followed by 3.3-4.9 GBq (2 GBq/m2 × body surface area) of [177Lu]Lu-DOTA-JR11 at an interval of 10 ± 1 wk. In total, 1 [177Lu]Lu-DOTATOC and 2-3 [177Lu]Lu-DOTA-JR11 treatment cycles were performed. Quantitative SPECT/CT was done at approximately 24, 48, and 168 h after injection of both radiopharmaceuticals to calculate meningioma and organ absorbed doses as well as tumor-to-organ absorbed-dose ratios (3-dimensional segmentation approach for meningioma, kidneys, liver, bone marrow, and spleen). Results: The median of the meningioma absorbed dose of 1 treatment cycle was 3.4 Gy (range, 0.8-10.2 Gy) for [177Lu]Lu-DOTATOC and 11.5 Gy (range, 4.7-22.7 Gy) for [177Lu]Lu-DOTA-JR11. The median bone marrow and kidney absorbed doses after 1 treatment cycle were 0.11 Gy (range, 0.05-0.17 Gy) and 2.7 Gy (range, 1.3-5.3 Gy) for [177Lu]Lu-DOTATOC and 0.29 Gy (range, 0.16-0.39 Gy) and 3.3 Gy (range, 1.6-5.9 Gy) for [177Lu]Lu-DOTA-JR11, resulting in a 1.4 (range, 0.9-1.9) times higher median tumor-to-bone marrow absorbed-dose ratio and a 2.9 (range, 2.0-4.8) times higher median tumor-to-kidney absorbed-dose ratio with [177Lu]Lu-DOTA-JR11. According to the Common Terminology Criteria for Adverse Events version 5.0, 2 patients developed reversible grade 2 lymphopenia after 1 cycle of [177Lu]Lu-DOTATOC. Afterward, 2 patients developed reversible grade 3 lymphopenia and 1 patient developed reversible grade 3 lymphopenia and neutropenia after 2-3 cycles of [177Lu]Lu-DOTA-JR11. No grade 4 or 5 adverse events were observed at 15 mo or more after the start of therapy. The disease control rate was 83% (95% CI, 53%-100%) at 12 mo or more after inclusion. Conclusion: Treatment with 1 cycle of [177Lu]Lu-DOTA-JR11 showed 2.2-5.7 times higher meningioma absorbed doses and a favorable therapeutic index compared with [177Lu]Lu-DOTATOC after injection of 1.4-2.1 times lower activities. The first efficacy results demonstrated a high disease control rate with an acceptable safety profile in the standard therapy for refractory meningioma patients. Therefore, larger studies with [177Lu]Lu-DOTA-JR11 are warranted in meningioma patients.

SPECT Imaging of SST2-Expressing Tumors with 99mTc-Based Somatostatin Receptor Antagonists: The Role of Tetraamine, HYNIC, and Spacers.

[99mTc]Tc-HYNIC-TOC is the most widely used 99mTc-labeled somatostatin receptor (SST) agonist for the SPECT imaging of SST-expressing tumors, such as neuroendocrine tumors. Recently, radiolabeled SST antagonists have shown improved diagnostic efficacy over agonists. 99mTc-labeled SST antagonists are lacking in clinical practice. Surprisingly, when [99mTc]Tc-HYNIC was conjugated to the SST2 antagonist SS01, SST2 imaging was not feasible. This was not the case when [99mTc]Tc-N4 was conjugated to SS01. Here, we assessed the introduction of different spacers (X: ß-Ala, Ahx, Aun and PEG4) among HYNIC and SS01 with the aim of restoring the affinity of HYNIC conjugates. In addition, we used the alternative antagonist JR11 for determining the suitability of HYNIC with 99mTc-labeled SST2 antagonists. We performed a head-to-head comparison of the N4 conjugates of SS01 and JR11. [99mTc]Tc-HYNIC-TOC was used as a reference, and HEK-SST2 cells were used for in vitro and in vivo evaluation. EDDA was used as a co-ligand for all [99mTc]Tc-HYNIC conjugates. The introduction of Ahx restored, to a great extent, the SST2-mediated cellular uptake of the [99mTc]Tc-HYNIC-X conjugates (X: spacer), albeit lower than the corresponding [99mTc]Tc-N4-conjugates. SPECT/CT images showed that all 99mTc-labeled conjugates accumulated in the tumor and kidneys with [99mTc]Tc-HYNIC-PEG4-SS01, [99mTc]Tc-N4-SS01 and [99mTc]Tc-N4-JR11 having notably higher kidney uptake. Biodistribution studies showed similar or better tumor-to-non-tumor ratios for the [99mTc]Tc-HYNIC-Ahx conjugates, compared to the [99mTc]Tc-N4 counterparts. The [99mTc]Tc-HYNIC-Ahx conjugates of SS01 and JR11 were comparable to [99mTc]Tc-HYNIC-TOC as imaging agents. HYNIC is a suitable chelator for the development of 99mTc-labeled SST2 antagonists when a spacer of appropriate length, such as Ahx, is used.

Cholecystokinin 2 Receptor Agonist 177Lu-PP-F11N for Radionuclide Therapy of Medullary Thyroid Carcinoma: Results of the Lumed Phase 0a Study.

Treatment of patients with advanced medullary thyroid carcinoma (MTC) is still a challenge. For more than 2 decades, it has been known that the cholecystokinin 2 receptor is a promising target for the treatment of MTC with radiolabeled minigastrin analogs. Unfortunately, kidney toxicity has precluded their therapeutic application so far. In 6 consecutive patients, we evaluated with advanced 3-dimensional dosimetry whether improved minigastrin analog 177Lu-DOTA-(d-Glu)6-Ala-Tyr-Gly-Trp-Nle-Asp-PheNH2 (177Lu-PP-F11N) is a suitable agent for the treatment of MTC. Methods: Patients received 2 injections of about 1 GBq (∼80 µg) of 177Lu-PP-F11N with and without a solution of succinylated gelatin (SG, a plasma expander used for nephroprotection) in a random crossover sequence to evaluate biodistribution, pharmacokinetics, and tumor and organ dosimetry. An electrocardiogram was obtained and blood count and blood chemistry were measured up to 12 wk after the administration of 177Lu-PP-F11N to assess safety. Results: In all patients, 177Lu-PP-F11N accumulation was visible in tumor tissue, stomach, and kidneys. Altogether, 13 tumors were eligible for dosimetry. The median absorbed doses for tumors, stomach, kidneys, and bone marrow were 0.88 (interquartile range [IQR]: 0.85-1.04), 0.42 (IQR: 0.25-1.01), 0.11 (IQR: 0.07-0.13), and 0.028 (IQR: 0.026-0.034) Gy/GBq, respectively. These doses resulted in median tumor-to-kidney dose ratios of 11.6 (IQR: 8.11-14.4) without SG and 13.0 (IQR: 10.2-18.6) with SG; these values were not significantly different (P = 1.0). The median tumor-to-stomach dose ratio was 3.34 (IQR: 1.14-4.70). Adverse reactions (mainly hypotension, flushing, and hypokalemia) were self-limiting and not higher than grade 1. Conclusion:177Lu-PP-F11N accumulates specifically in MTC at a dose that is sufficient for a therapeutic approach. With a low kidney and bone marrow radiation dose, 177Lu-PP-F11N shows a promising biodistribution. The dose-limiting organ is most likely the stomach. Further clinical studies are necessary to evaluate the maximum tolerated dose and the efficacy of 177Lu-PP-F11N.

Biodistribution, Pharmacokinetics, and Dosimetry of 177Lu-, 90Y-, and 111In-Labeled Somatostatin Receptor Antagonist OPS201 in Comparison to the Agonist 177Lu-DOTATATE: The Mass Effect.

Radiolabeled somatostatin receptor (SSTR) antagonists have shown in vivo higher uptake in SSTR-expressing tumors than agonists. In this preclinical study, the SSTR2 antagonist OPS201 (DOTA-JR11; DOTA-[Cpa-c(DCys-Aph(Hor)-DAph(Cbm)-Lys-Thr-Cys)-DTyr-NH2]) labeled with 177Lu, 90Y, and 111In was compared with the SSTR2 agonist 177Lu-DOTATATE. Methods: Biodistribution, pharmacokinetics, SPECT/CT, and dosimetry studies were performed to assess the bioequivalence of all radiotracers. Use of escalated peptide mass and nephroprotective agents were systematically investigated. Results: The tumor residence time was 15.6 h (13.4-17.7) for 177Lu-OPS201 (10 pmol) and 6.4 h (5.4-7.3) for 177Lu-DOTATATE, resulting in a 2.5-times-higher tumor dose for the antagonist than for the agonist (0.854 vs. 0.333 mGy/MBq for a 4-cm tumor). The overall tumor-to-kidney dose ratio was approximately 24% and 32% higher for 177Lu-OPS201 than for 90Y-OPS201 and 177Lu-DOTATATE, respectively. 111In-OPS201 had a biodistribution significantly different from 90Y-OPS201 and is therefore not a surrogate for 90Y-OPS201 dosimetry studies. Importantly, and in contrast to 177Lu-DOTATATE, injection of 10, 200, and 2,000 pmol of 177Lu-OPS201 did not cause any relevant tumor saturation, with tumor uptake 4 h after injection: 23.9, 24.9, and 18.8 percentage of injected activity per gram of tissue (%IA/g), respectively, for the antagonist (P > 0.05), as compared with 17.8, 12.0, and 9.9 %IA/g for the agonist (P < 0.05). Increasing the peptide mass of 177Lu-OPS201 from 10 to 200 pmol drastically decreased the effective dose from 0.0908 to 0.0184 mSv/MBq and decreased the uptake in the liver, bone marrow, and all SSTR2-expressing organs; thus, the therapeutic index improved considerably. Lysine and succinylated gelatine, alone or in combination, significantly reduced the renal dose of 177Lu-OPS201 compared with the control group, by 45%, 25%, and 40%, respectively (P < 0.05). The reduction was similar for 10 and 200 pmol, whereas lysine performed better than succinylated gelatine. Conclusion:177Lu-OPS201 exhibits higher tumor uptake, longer tumor residence time, and improved tumor-to-kidney dose ratio compared with 177Lu-DOTATATE and 90Y-OPS201. Importantly, the mass-escalation study indicates that an optimized antagonist mass might further improve the safety window of peptide receptor radionuclide therapy by reducing the liver and bone marrow doses as well as the effective dose. Clinical studies are warranted to confirm the efficacy and advantageous toxicity profile of 177Lu-OPS201.

Uterine glycogen metabolism in mink during estrus, embryonic diapause and pregnancy.

We have determined uterine glycogen content, metabolizing enzyme expression and activity in the mink, a species that exhibits obligatory embryonic diapause, resulting in delayed implantation. Gross uterine glycogen concentrations were highest in estrus, decreased 50% by diapause and 90% in pregnancy (P ≤ 0.05). Endometrial glycogen deposits, which localized primarily to glandular and luminal epithelia, decreased 99% between estrus and diapause (P ≤ 0.05) and were nearly undetectable in pregnancy. Glycogen synthase and phosphorylase proteins were most abundant in the glandular epithelia. Glycogen phosphorylase activity (total) in uterine homogenates was higher during estrus and diapause, than pregnancy. While glycogen phosphorylase protein was detected during estrus and diapause, glycogen synthase was almost undetectable after estrus, which probably contributed to a higher glycogenolysis/glycogenesis ratio during diapause. Uterine glucose-6-phosphatase 3 gene expression was greater during diapause, when compared to estrus (P ≤ 0.05) and supports the hypothesis that glucose-6-phosphate resulting from phosphorylase activity was dephosphorylated in preparation for export into the uterine lumen. The relatively high amount of hexokinase-1 protein detected in the luminal epithelia during estrus and diapause may have contributed to glucose trapping after endometrial glycogen reserves were depleted. Collectively, our findings suggest to us that endometrial glycogen reserves may be an important source of energy, supporting uterine and conceptus metabolism up to the diapausing blastocyst stage. As a result, the size of uterine glycogen reserves accumulated prior to mating may in part, determine the number of embryos that survive to the blastocyst stage, and ultimately litter size.

An olfactory subsystem that detects carbon disulfide and mediates food-related social learning.

Olfactory signals influence social interactions in a variety of species. In mammals, pheromones and other social cues can promote mating or aggression behaviors; can communicate information about social hierarchies, genetic identity and health status; and can contribute to associative learning. However, the molecular, cellular, and neural mechanisms underlying many olfactory-mediated social interactions remain poorly understood. Here, we report that a specialized olfactory subsystem that includes olfactory sensory neurons (OSNs) expressing the receptor guanylyl cyclase GC-D, the cyclic nucleotide-gated channel subunit CNGA3, and the carbonic anhydrase isoform CAII (GC-D(+) OSNs) is required for the acquisition of socially transmitted food preferences (STFPs) in mice. Using electrophysiological recordings from gene-targeted mice, we show that GC-D(+) OSNs are highly sensitive to the volatile semiochemical carbon disulfide (CS(2)), a component of rodent breath and a known social signal mediating the acquisition of STFPs. Olfactory responses to CS(2) are drastically reduced in mice lacking GC-D, CNGA3, or CAII. Disruption of this sensory transduction cascade also results in a failure to acquire STFPs from either live or surrogate demonstrator mice or to exhibit hippocampal correlates of STFP retrieval. Our findings indicate that GC-D(+) OSNs detect chemosignals that facilitate food-related social interactions.

Preliminary evidence of attenuation of the disruptive effects of the NMDA glutamate receptor antagonist, ketamine, on working memory by pretreatment with the group II metabotropic glutamate receptor agonist, LY354740, in healthy human subjects.

RATIONALE: Some of the behavioral consequences of deficits in N-methyl-D-aspartate (NMDA) glutamate receptor function are thought to arise from the disinhibition of cortical glutamatergic circuitry. OBJECTIVE: This study evaluated whether pretreatment with a drug that reduces glutamatergic activation, the group II metabotropic glutamate receptor (mGluR) agonist, LY354740, reduced the cognitive effects of the NMDA glutamate receptor antagonist, ketamine, in healthy human subjects. METHODS: Nineteen healthy human subjects completed 3 test days during which LY354740 (matched placebo, 100 mg, 400 mg) was administered under double-blind conditions 4 h prior to the single-blind intravenous administration of saline and 5.7 h prior to ketamine administration (bolus of 0.26 mg/kg over 1 min, infusion of 0.65 mg/kg per hour for 100 min). Thus on each test day each subject received a single dose of LY354740 (or its matched placebo) and both saline and ketamine infusions. RESULTS: Ketamine impaired attention, working memory, and delayed recall. It also produced positive and negative symptoms, perceptual changes, and dysphoric mood. LY354740 did not have a significant effect on working memory on the placebo day; however, it produced a significant dose-related improvement in working memory during ketamine infusion. CONCLUSIONS: These data provide preliminary and suggestive evidence that LY354740 or other group II mGluR agonists might play a role in treating working memory impairment related to deficits in NMDA receptor function.