An active site mutation induces oxygen reactivity in D-arginine dehydrogenase: A case of superoxide diverting protons †.

Enzymes are potent catalysts that increase biochemical reaction rates by several orders of magnitude. Flavoproteins are a class of enzymes whose classification relies on their ability to react with molecular oxygen (O2) during catalysis using ionizable active site residues. Pseudomonas aeruginosa D-arginine dehydrogenase (PaDADH) is a flavoprotein that oxidizes D-arginine for P. aeruginosa survival and biofilm formation. The crystal structure of PaDADH reveals the interaction of the glutamate 246 (E246) side chain with the substrate and at least three other active site residues, establishing a hydrogen bond network in the active site. Additionally, E246 likely ionizes to facilitate substrate binding during PaDADH catalysis. This study aimed to investigate how replacing the E246 residue with leucine affects PaDADH catalysis and its ability to react with O2 using steady-state kinetics coupled with pH profile studies. The data reveal a gain of O2 reactivity in the E246L variant, resulting in a reduced flavin semiquinone species and superoxide (O2•-) during substrate oxidation. The O2•- reacts with active site protons, resulting in an observed non-stoichiometric slope of 1.5 in the enzyme's log (kcat/Km) pH profile with D-arginine. Adding superoxide dismutase results in an observed correction of the slope to 1.0. This study demonstrates how O2•- can alter the slopes of limbs in the pH profiles of flavin-dependent enzymes and serves as a model for correcting non-stoichiometric slopes in elucidating reaction mechanisms of flavoproteins.

Sucralose (C12H19Cl3O8) impact on microbial activity in estuarine and freshwater marsh soils.

As the general population's diet has shifted to reflect current weight-loss trends, there has been an increase in zero-calorie artificial sweetener usage. Sucralose (C12H19Cl3O8), commonly known as Splenda® in the USA, is a primary example of these sweeteners. In recent years, sucralose has been identified as an environmental contaminant that cannot easily be broken down via bacterial decomposition. This study focuses on the impact of sucralose presence on microbial communities in brackish and freshwater systems. Microbial respiration and fluorescence were measured as indicators of microbial activity in sucralose-dosed samples taken from both freshwater and estuarine marsh environments. Results showed a significant difference between microbial concentration and respiration when dosed with varying levels of sucralose. Diatom respiration implied a negative correlation of community abundance with sucralose concentration. The freshwater cyanobacterial respiration increased in the presence of sucralose, implying a positive correlation of community abundance with sucralose concentration. This was in direct contrast to its brackish water counterpart. However, further investigation is necessary to confirm any potential utility of these communities in the breakdown of sucralose in the marsh environment.

Descemet Membrane Endothelial Keratoplasty as Treatment for Late-Onset Interface Fluid Syndrome After Laser In Situ Keratomileusis.

PURPOSE: We herein present Descemet membrane endothelial keratoplasty (DMEK) as an effective surgical means of treatment for the management of interface fluid syndrome (IFS) in a series of cases with distant history of laser in situ keratomileusis (LASIK). METHODS: Three cases from a single institution were included. All patients had documented IFS in the setting of history of LASIK. All 3 patients underwent DMEK for the treatment of IFS. Visual acuity, clinical findings, pachymetry, endothelial cell count, and anterior segment optical coherence tomography were recorded. RESULTS: We describe 3 cases of late-onset IFS that developed in eyes many years after LASIK (ranging from 15 to 31 years). All 3 patients had clinically significant corneal edema and evidence of poor endothelial function at the time of IFS diagnosis. DMEK was subsequently performed in each case. All 3 eyes showed resolution of corneal edema and improvement in best-corrected visual acuity after DMEK. CONCLUSIONS: DMEK can provide successful visual and anatomical recovery in patients who have had previous LASIK and experience late-onset IFS due to endothelial cell dysfunction.

Towards co-design of rehabilitation technologies: a collaborative approach to prioritize usability issues.

Introduction: Early stakeholder engagement is critical to the successful development and translation of rehabilitation technologies, a pivotal step of which is usability testing with intended end-users. To this end, several methods employ end-user feedback to identify usability and implementation issues. However, the process of prioritizing identified issues seldom leverages the knowledge and expertise of the range of stakeholders who will ultimately affect the demand and supply of a device. This paper describes a novel method to prioritize end-user feedback using transdisciplinary stakeholder consultation and address it in subsequent product development. The proposed approach was demonstrated using a case study relating to the development of a novel technology for neural recovery after spinal cord injury. Method: Feedback from five individuals with chronic spinal cord injury was collected during two-hour usability evaluation sessions with a fully functional high-fidelity system prototype. A think-aloud and semi-structured interview protocol was used with each participant to identify usability and acceptability issues relating to the system in a 3-phase approach. Phase 1 involved extracting usability issues from think-aloud and semi-structured interview data. Phase 2 involved rating the usability issues based on their significance, technical feasibility, and implementation priority by relevant internal and external stakeholders. Finally, Phase 3 involved aggregating the usability issues according to design and implementation elements to facilitate solution generation, and these solutions were then raised as action tasks for future design iterations. Results: Sixty usability issues representing nine facets of usability were rated. Eighty percent of issues were rated to be of moderate to high significance, 83% were rated as being feasible to address, and 75% were rated as addressable using existing project resources. Fifty percent of the issues were rated to be a high priority for implementation. Evaluation of the grouped issues identified 21 tasks which were mapped to the product roadmap for integration into future design iterations. Discussion: This paper presents a method for meaningful transdisciplinary stakeholder engagement in rehabilitation technology development that can extended to other projects. Alongside a worked example, we offer practical considerations for others seeking to co-develop rehabilitation technologies.

Water birth: a systematic review and meta-analysis of maternal and neonatal outcomes.

OBJECTIVE: This systematic review and meta-analysis aimed to conduct a thorough and contemporary assessment of maternal and neonatal outcomes associated with water birth in comparison with land-based birth. DATA SOURCES: We conducted a comprehensive search of PubMed, EMBASE, CINAHL, and gray literature sources, from inception to February 28, 2023. STUDY ELIGIBILITY CRITERIA: We included randomized and nonrandomized studies that assessed maternal and neonatal outcomes in patients who delivered either conventionally or while submerged in water. METHODS: Pooled unadjusted odds ratios with 95% confidence intervals were calculated using a random-effects model (restricted maximum likelihood method). We assessed the 95% prediction intervals to estimate the likely range of future study results. To evaluate the robustness of the results, we calculated fragility indices. Maternal infection was designated as the primary outcome, whereas postpartum hemorrhage, perineal lacerations, obstetrical anal sphincter injury, umbilical cord avulsion, low Apgar scores, neonatal aspiration requiring resuscitation, neonatal infection, neonatal mortality within 30 days of birth, and neonatal intensive care unit admission were considered secondary outcomes. RESULTS: Of the 20,642 articles identified, 52 were included in the meta-analyses. Based on data from observational studies, water birth was not associated with increased probability of maternal infection compared with land birth (10 articles, 113,395 pregnancies; odds ratio, 0.93; 95% confidence interval, 0.76-1.14). Patients undergoing water birth had decreased odds of postpartum hemorrhage (21 articles, 149,732 pregnancies; odds ratio, 0.80; 95% confidence interval, 0.68-0.94). Neonates delivered while submerged in water had increased odds of cord avulsion (10 articles, 91,504 pregnancies; odds ratio, 1.75; 95% confidence interval, 1.38-2.24) and decreased odds of low Apgar scores (21 articles, 165,917 pregnancies; odds ratio, 0.69; 95% confidence interval, 0.58-0.82), neonatal infection (15 articles, 53,635 pregnancies; odds ratio, 0.64; 95% confidence interval, 0.42-0.97), neonatal aspiration requiring resuscitation (19 articles, 181,001 pregnancies; odds ratio, 0.60; 95% confidence interval, 0.43-0.84), and neonatal intensive care unit admission (30 articles, 287,698 pregnancies; odds ratio, 0.56; 95% confidence interval, 0.45-0.70). CONCLUSION: When compared with land birth, water birth does not appear to increase the risk of most maternal and neonatal complications. Like any other delivery method, water birth has its unique considerations and potential risks, which health care providers and expectant parents should evaluate thoroughly. However, with proper precautions in place, water birth can be a reasonable choice for mothers and newborns, in facilities equipped to conduct water births safely.

Complete genome sequences of Gordonia rubripertincta phages OtterstedtS21 and Patos.

We report the genomes of two viruses with siphovirus morphology, OtterstedtS21 and Patos, from Albany, New York, using Gordonia rubripertincta. The genomes of OtterstedtS21 and Patos are ~68 kbp long with 58% GC content. Both phages group with cluster DV based on gene content similarity to phages in the Actinobacteriophage database.

Pharmacokinetics of mebendazole in plasma and cerebrospinal fluid following a single oral dose in healthy dogs.

Novel therapies are needed for treatment of gliomas. Mebendazole previously demonstrated anti-neoplastic effects on canine glioma cell lines at in vitro mean inhibitory concentrations (IC50) of 10 ng/mL. Our study aimed to titrate the oral dose of mebendazole necessary to achieve concentrations ≥10 ng/mL in cerebrospinal fluid (CSF) of healthy dogs. We hypothesized that an oral dose up to 200 mg/kg would be necessary. Phase one was a dose titration study using a total of 6 mixed breed dogs that described dose vs. plasma concentrations for 72 h after single oral dosing of either 50 mg/kg (n = 2), 100 mg/kg (n = 2), or 200 mg/kg (n = 2). Based on phase one, phase two dogs (total of 9) received 100 mg/kg (n = 4) or 200 mg/kg (n = 5) orally and blood samples were collected intermittently for 60 h with CSF samples collected intermittently for 24 h. Mebendazole was quantitated in plasma and CSF using high performance liquid chromatography. Median peak plasma concentrations (Cmax) were reached at 7 ± 2 h (100 mg/kg) of 220 ng/mL (81, 283) and at 15 ± 4 h (200 mg/kg) of 147 ng/ml (112, 298). The respective area under the curve (AUC: ng/ml/h) reported as a median was 2,119 (1,876, 3,288) vs. 3,115 (1,559, 4,972). Median plasma concentrations (ng/ml) for 100 vs. 200 mg/kg were 47 (32, 52) vs. 65 (35, 104), respectively. For CSF, the median value for Cmax (at 100 mg/kg vs. 200 mg/kg) was 8 (2, 28) vs. 21 (12, 27) and AUC was 87 (22, 157) vs. 345 (92, 372), respectively. Relative bioavailability in CSF vs. plasma was 4 to 10%. Although several animals demonstrated clinical signs indicative of gastrointestinal upset [i.e., vomiting (n = 2), diarrhea (n = 2), or both (n = 1)], these events were not considered serious. The in vitro IC50 for gliomas can be reached in CSF at 100 mg/kg (n = 1), however a 200 mg/kg dose yielded more consistent concentrations.

Separation of cyclotron-produced cobalt-55/58m from iron targets using cation exchange chromatography with non-aqueous solvents and extraction chromatography.

Cobalt-55 and -58m form a theranostic pair that has relevant properties for cancer research. We report a cation exchange chromatography/extraction chromatography method that separates cyclotron-produced 55/58mCo from 54/57Fe in <1.5 h, recovers >85% Co and achieves [55Co]Co-NOTA and -DOTA AMA 89 ± 48 and 35 ± 7 MBq/nmol (EOB), respectively. Cobalt-55 and -58m were quantitatively labeled to functionalized NOTA at 106 and 50 MBq/nmol (EOB), respectively, corroborating measured AMA. This method is faster than previously published methods and achieves better [55/58mCo]Co-NOTA and -DOTA AMA.

Recycling of 52Cr electroplated targets for 52gMn production.

52gMn is a promising radionuclide for positron emission tomography (PET). Enriched 52Cr targets are required to minimize formation of 54Mn radioisotopic impurities during production with proton beams. The need for radioisotopically pure 52gMn, accessibility and cost of 52Cr, sustainability of the radiochemical process, and potential for iterative purification of target materials motivate this development of recyclable, electroplated 52Cr metal targets and radiochemical isolation and labeling with resulting >99.89% radionuclidically pure 52gMn. The run-to-run replating efficiency is 60 ± 20%, and unplated chromium from this method is recovered with 94% efficiency as 52CrCl3 hexahydrate. The decay-corrected molar activity of chemically isolated 52gMn for common chelating ligands was 376 MBq/µmol.

Work Intensity of Postoperative Care Following Implantation of Presbyopia-Correcting versus Monofocal Intraocular Lenses.

Purpose: To compare the work intensity of postoperative care following implantation of presbyopia-correcting intraocular lenses (IOLs) to that of standard monofocal IOLs. Patients and Methods: This open-label, multicenter, comparative study retrospectively reviewed the case records of cataract surgery patients who underwent bilateral implantation of either presbyopia-correcting IOLs (presby-IOL group; N=177) or standard monofocal IOLs (monofocal group; N=177). Outcome measures included the total time the patient spent in the office, number of visits, mean duration of visits, and the number of procedures and diagnostic tests during the first postoperative year. Outcome measures were compared between the first 90 days and days 91-365 after surgery. Results: Mean (±SD) time spent in the office during the first postoperative year was 5:50 ± 3:35 hours (H:MM) over 6.6 ± 2.9 visits in the presby-IOL group, compared to 3:38 ± 1:36 hours over 4.9 ± 1.6 visits in the monofocal IOL group (p <0.001). During the first 90 days, a presby-IOL patient spent 40 minutes longer in the office than a monofocal IOL patient (3:39 ± 1:38 hours vs 2.59 ± 1:13 hours) (p <0.001). During days 91-365, time in the office was 1:32 hours longer (p <0.001), and the mean visit duration was 8 minutes longer for the presby-IOL patients (p=0.002) than those with monofocal IOL. In addition, the presby-IOL patients underwent more procedures and diagnostic tests (p ≤0.001) as compared with standard monofocal cataract surgery patients. Conclusion: Patients implanted with presbyopia-correcting IOLs require significantly more clinic time, diagnostic testing, and procedures postoperatively as compared with standard monofocal cataract surgery patients.

Nipple properties affect sensorimotor integration during bottle feeding in an infant pig model.

Infant feeding is a critical neurological milestone in development defined by the coordination of muscles, peripheral nerves, and brainstem nuclei. In infants, milk flow rate is often limited to improve feeding performance without treating the underlying deficiencies in the sucking and swallowing processes. Modification of the neuromotor response via sensory information from the nipple during bottle feeding is an unexplored avenue for physiology-based interventions. In this study, we assessed how differences in nipple hole size and nipple stiffness affect sucking muscle activation and subsequent movement. We fabricated four bottle nipples of varying hole size and stiffness to determine how variation in nipple properties affects the sucking behavior of infant pigs. Our results demonstrate that sensory information from the nipple affects sucking motor output. Nipple hole sizes and stiffnesses with a larger milk flow rate resulted in greater muscle activity and kinematic movement. Additionally, our results suggest that sensorimotor interventions are better directed toward modulating tongue function rather than the mandible movements due to a greater response to sensory information. Understanding how sensory information influences infant feeding is instrumental in promoting effective infant feeding.

Achilles Tendon Injuries in the Pediatric Population.

BACKGROUND: Achilles tendon injuries are common in adults, and there is extensive literature describing the injury characteristics and treatment of these adult injuries. However, Achilles injuries are rare in the pediatric population and as a result, there is limited research reported on this age group. We therefore sought to characterize the injury presentation, treatment and outcomes for pediatric patients with partial and complete Achilles injuries. METHODS: A retrospective chart review was conducted of patients aged 0-18 treated for Achilles tendon injuries at 2 geographically distinct tertiary institutions between 2008 and 2021. Data collected included demographics, injury characteristics, and treatment course. Injury types were separated into 2 cohorts: traumatic Achilles injuries and ruptures due to muscular contraction. Traumatic injuries were further delineated into 2 injury mechanisms: open injuries related to penetrating trauma and closed injuries related to blunt trauma. Standard descriptive analyses were utilized to summarize findings. RESULTS: Thirty-nine patients (43.6% female, median age 15 years) were identified, 29 (74.4%) of whom had complete tears. Twenty-five patients (64.1%) presented with traumatic injuries; among these, 48.0% (n=12/25) were ≤12 years. All patients ≤12 years sustained a traumatic injury. The most common traumatic mechanism was an open laceration due to penetrating trauma (68.0%), followed by closed ruptures associated with blunt trauma (32.0%). Fourteen patients (35.9%) presented with closed ruptures due to muscular contraction. Four patients (10.2%) had a prior history of clubfoot treated with Achilles tenotomy. Thirty-five patients (89.7%) were surgically treated with an open repair. The median immobilization period across all patients was 11 weeks (interquartile range: 10-12), starting most commonly with a posterior splint (46.2%) and concluding with a CAM boot (94.9%). Of patients with full follow-up data (n=22/39), all resumed normal activities, with a median clearance time of 6 months (interquartile range: 5-7.9). CONCLUSIONS: We found that older adolescents (≥14 y) were more likely to rupture their Achilles tendon through a forceful muscular contraction, whereas younger patients (≤12 y) were more likely to injure their Achilles via a traumatic mechanism. Most patients were treated operatively and returned to sports at a median time of 6 months. A further prospective study is warranted to better characterize treatment protocols and patient outcomes in this population. LEVEL OF EVIDENCE: Level-IV.

Nr2f1a maintains atrial nkx2.5 expression to repress pacemaker identity within venous atrial cardiomyocytes of zebrafish.

Maintenance of cardiomyocyte identity is vital for normal heart development and function. However, our understanding of cardiomyocyte plasticity remains incomplete. Here, we show that sustained expression of the zebrafish transcription factor Nr2f1a prevents the progressive acquisition of ventricular cardiomyocyte (VC) and pacemaker cardiomyocyte (PC) identities within distinct regions of the atrium. Transcriptomic analysis of flow-sorted atrial cardiomyocytes (ACs) from nr2f1a mutant zebrafish embryos showed increased VC marker gene expression and altered expression of core PC regulatory genes, including decreased expression of nkx2.5, a critical repressor of PC differentiation. At the arterial (outflow) pole of the atrium in nr2f1a mutants, cardiomyocytes resolve to VC identity within the expanded atrioventricular canal. However, at the venous (inflow) pole of the atrium, there is a progressive wave of AC transdifferentiation into PCs across the atrium toward the arterial pole. Restoring Nkx2.5 is sufficient to repress PC marker identity in nr2f1a mutant atria and analysis of chromatin accessibility identified an Nr2f1a-dependent nkx2.5 enhancer expressed in the atrial myocardium directly adjacent to PCs. CRISPR/Cas9-mediated deletion of the putative nkx2.5 enhancer leads to a loss of Nkx2.5-expressing ACs and expansion of a PC reporter, supporting that Nr2f1a limits PC differentiation within venous ACs via maintaining nkx2.5 expression. The Nr2f-dependent maintenance of AC identity within discrete atrial compartments may provide insights into the molecular etiology of concurrent structural congenital heart defects and associated arrhythmias.

Interface fluid syndrome after LASIK surgery: retrospective pooled analysis and systematic review.

Interface fluid syndrome (IFS) is a complication associated with laser in situ keratomileusis (LASIK) surgery where a fluid pocket in the corneal stroma decreases visual acuity. A systematic review of IFS cases using PRISMA guidelines was performed yielding a total of 33 patients. 2 outcomes were selected for logistic regression analysis: final corrected distance visual acuity (CDVA) and need for surgical management. Results showed 33.3% of patients required surgery, 51.5% had their IFS resolve within 1 month or sooner, and 51.5% had final CDVA 20/25 or better. Higher presenting intraocular pressure (IOP) and duration of IFS ≤1 month was associated with higher odds of final CDVA 20/25 or better (adjusted odds ratio [aOR] 1.12, P = .04; aOR 7.71, P = .02, respectively). Endothelial cell dysfunction led to 17.55 greater odds for requiring surgical compared to medical management (aOR 0.36, P = .04). Presenting IOP and duration of IFS predicted final CDVA, while prior endothelial cell dysfunction predicted need for surgery.

Cyclotron production of 43Sc and 44gSc from enriched 42CaO, 43CaO, and 44CaO targets.

Introduction: 43Sc and 44gSc are both positron-emitting radioisotopes of scandium with suitable half-lives and favorable positron energies for clinical positron emission tomography (PET) imaging. Irradiation of isotopically enriched calcium targets has higher cross sections compared to titanium targets and higher radionuclidic purity and cross sections than natural calcium targets for reaction routes possible on small cyclotrons capable of accelerating protons and deuterons. Methods: In this work, we investigate the following production routes via proton and deuteron bombardment on CaCO3 and CaO target materials: 42Ca(d,n)43Sc, 43Ca(p,n)43Sc, 43Ca(d,n)44gSc, 44Ca(p,n)44gSc, and 44Ca(p,2n)43Sc. Radiochemical isolation of the produced radioscandium was performed with extraction chromatography using branched DGA resin and apparent molar activity was measured with the chelator DOTA. The imaging performance of 43Sc and 44gSc was compared with 18F, 68Ga, and 64Cu on two clinical PET/CT scanners. Discussion: The results of this work demonstrate that proton and deuteron bombardment of isotopically enriched CaO targets produce high yield and high radionuclidic purity 43Sc and 44gSc. Laboratory capabilities, circumstances, and budgets are likely to dictate which reaction route and radioisotope of scandium is chosen.

Cost to perform door-to-door universal sputum screening for TB in a high-burden community.

BACKGROUND: Population-based active case-finding (ACF) identifies people with TB in communities but can be costly. METHODS: We conducted an empiric costing study within a door-to-door household ACF campaign in an urban community in Uganda, where all adults, regardless of symptoms, were screened by sputum Xpert Ultra testing. We used a combination of direct observation and self-reported logs to estimate staffing requirements. Study budgets were reviewed to collect costs of overheads, equipment, and consumables. Our primary outcome was the cost per person diagnosed with TB. RESULTS: Over a 28-week period, three teams of two people collected sputum from 11,341 adults, of whom 48 (0.4%) tested positive for TB. Screening 1,000 adults required 258 person-hours of effort at a cost of US$35,000, 70% of which was for GeneXpert cartridges. The estimated cost per person screened was $36 (95% uncertainty range [95% UR] 34­38), and the cost per person diagnosed with Xpert-positive TB was $8,400 (95% UR 8,000­8,900). The prevalence of TB in the underlying community was the primary modifiable determinant of the cost per person diagnosed. CONCLUSION: Door-to-door screening can be feasibly performed at scale, but will require effective triage and identification of high-prevalence populations to be affordable and cost-effective.

Usage of Children's Makeup and Body Products in the United States and Implications for Childhood Environmental Exposures.

There is growing evidence of toxicity associated with ingredients found in cosmetics and personal care products. Children's makeup and body products (CMBPs) are widely marketed to children throughout the US; however, little is known about how and why children use them. We administered a survey to parents/guardians of children aged ≤12 years about the use of CMBPs. Among all the children (n = 312) of survey respondents (n = 207), 219 (70%) have used CMBPs in their lifetime. Older children used CMBPs at higher rates than younger children, and female children used CMBPs at higher rates than male children. Children of Hispanic/Latinx parents/guardians used CMBPs more often and for shorter durations and a greater proportion used lip, hair, and fragrance products than children of non-Hispanic parents/guardians. Approximately half the children that use CMBPs were reported to use them with play intentions. Compared to children of non-Hispanic parents/guardians, children of Hispanic/Latinx parents/guardians reported more play motivations for CMBP use. Using qualitative analysis approaches, responses suggest CMBPs are commonly used for fun or play activities. This mixed methods analysis serves as an introduction to understanding early life exposures to this unique and understudied class of products.

The impact of time at home on potential yield of home-based TB contact investigation.

BACKGROUND: The yield of TB contact tracing is often limited by challenges in reaching individuals during the screening process. We investigated the times at which index patients and household contacts were typically at home and the potential effects of expanding the timing of home-based contact investigation.METHODS: Index patients and household contacts in Kampala, Uganda, were asked about their likely availability at different day/time combinations. We calculated the "participant identification gap" (defined as the proportion of participants who reported being home <50% of the time) during business hours only. We then estimated the incremental reduction in the participant identification gap if hours were expanded to include weekday evenings, Saturdays, and Sundays. Statistical significance was assessed using McNemar´s tests.RESULTS: Nearly half of eligible individuals (42% of index patients and 52% of contacts) were not likely to be home during contact investigation conducted only during business hours. Expanding to weekday evenings, Saturdays, and Sundays would reduce this participant identification gap to 15% among index patients and 18% among contacts - while also reducing differences by sex and employment.CONCLUSIONS: Expanding hours for conducting contact investigation or other home-based health interventions could substantially reduce the number of individuals missed and address disparities in access to care.

Theranostic cobalt-55/58m for neurotensin receptor-mediated radiotherapy in vivo: A pilot study with dosimetry.

Neurotensin receptor 1 (NTSR1) can stimulate tumor proliferation through neurotensin (NTS) activation and are overexpressed by a variety of cancers. The high binding affinity of NTS/NTSR1 makes radiolabeled NTS derivatives interesting for cancer diagnosis and staging. Internalization of NTS/NTSR1 also suggests therapeutic application with high LET alpha particles and low energy electrons. We investigated the therapeutic efficacy of [58mCo]Co-NOTA-NT-20.3 in vivo using murine models xenografted with NTSR1-positive HT29 human colorectal adenocarcinoma cells, and utilized [55Co]Co-NOTA-NT-20.3 for dosimetry. METHODS: Targeting properties and cytotoxicity of [55/58mCo]Co-NOTA-NT-20.3 were assessed with HT29 cells. Female nude mice were xenografted with HT29 tumors and administered [55Co or 58mCo]Co-NOTA-NT-20.3 to evaluate pharmacokinetics or for therapy, respectively. Dosimetry calculations followed the Medical Internal Radiation Dose (MIRD) formalism and human absorbed dose rate per unit activity were obtained from OpenDose. The pilot therapy study consisted of two groups (each N = 3) receiving 110 ± 15 MBq and 26 ± 6 MBq [58mCo]Co-NOTA-NT-20.3 one week after tumor inoculation, and control (N = 3). Tumor sizes and masses were measured twice a week after therapy. Complete blood count and kidney histology were also performed to assess toxicity. RESULTS: HPLC measured radiochemical purity of [55,58mCo]Co-NOTA-NT-20.3 > 99 %. Labeled compounds retained NTS targeting properties. [58mCo]Co-NOTA-NT-20.3 exhibited cytotoxicity for HT29 cells and was >15× more potent than [58mCo]CoCl2. Xenografted tumors responded modestly to administered doses, but mice showed no signs of radiotoxicity. Absorbed dose to tumor and kidney with 110 MBq [58mCo]Co-NOTA-NT-20.3 were 0.6 Gy and 0.8 Gy, respectively, and other organs received less than half of the absorbed dose to tumor. Off-target radiation dose from cobalt-58g was small but reduces the therapeutic window. CONCLUSION: The enhanced in vitro cytotoxicity and high tumor-to-background led us to investigate the therapeutic efficacy of [58mCo]Co-NOTA-NT-20.3 in vivo. Although we were unable to induce tumor response commensurate with [177Lu]Lu-NT127 (NLys-Lys-Pro-Tyr-Tle-Leu) studies involving similar time-integrated activity, the absence of observed toxicity may constitute an opportunity for targeting vectors with improved uptake and/or retention to avoid the aftereffects of other high-LET radioactive emissions. Future studies with higher uptake, activity and/or multiple dosing regimens are warranted. The theranostic approach employed in this work was crucial for dosimetry analysis.