Calibration-free reaction yield quantification by HPLC with a machine-learning model of extinction coefficients.

Reaction optimization and characterization depend on reliable measures of reaction yield, often measured by high-performance liquid chromatography (HPLC). Peak areas in HPLC chromatograms are correlated to analyte concentrations by way of calibration standards, typically pure samples of known concentration. Preparing the pure material required for calibration runs can be tedious for low-yielding reactions and technically challenging at small reaction scales. Herein, we present a method to quantify the yield of reactions by HPLC without needing to isolate the product(s) by combining a machine learning model for molar extinction coefficient estimation, and both UV-vis absorption and mass spectra. We demonstrate the method for a variety of reactions important in medicinal and process chemistry, including amide couplings, palladium catalyzed cross-couplings, nucleophilic aromatic substitutions, aminations, and heterocycle syntheses. The reactions were all performed using an automated synthesis and isolation platform. Calibration-free methods such as the presented approach are necessary for such automated platforms to be able to discover, characterize, and optimize reactions automatically.

Situational prevention: Pharmacotherapy during periods of increased risk for migraine attacks.

The small molecule calcitonin gene-related peptide receptor antagonists (gepants) are the only drug class with medicines indicated for both the acute and preventive treatment of migraine. Given this dual capacity to both treat and prevent, along with their favorable tolerability profiles and lack of an association with medication-overuse headache, headache specialists have begun to use gepants in ways that transcend the traditional categories of acute and preventive treatment. One approach, called situational prevention, directs patients to treat during the interictal phase, before symptoms develop, in situations of increased risk for migraine attacks. Herein, we present three patients to illustrate scenarios of gepant use for situational prevention. In each case, a gepant was started in anticipation of a period of increased headache probability (vulnerability) and continued for a duration of 1 day to 5 consecutive days. Although this approach may expose patients to medication when headache may not have developed, the tolerability and safety profile and preventive effect of gepants may represent a feasible approach for some patients. Situational prevention is an emerging strategy for managing migraine before symptoms develop in individuals who can identify periods when the probability of headache is high. This paper is intended to increase awareness of this strategy and stimulate future randomized, placebo-controlled trials to rigorously assess this strategy.

Ventrointermediate thalamic stimulation improves motor learning in humans.

Ventrointermediate thalamic stimulation (VIM-DBS) modulates oscillatory activity in a cortical network including primary motor cortex, premotor cortex, and parietal cortex. Here we show that, beyond the beneficial effects of VIM-DBS on motor execution, this form of invasive stimulation facilitates production of sequential finger movements that follow a repeated sequence. These results highlight the role of thalamo-cortical activity in motor learning.

Partitioning of an Enzyme-Polymer Surfactant Nanocomplex into Lipid-Rich Cellular Compartments Drives In Situ Hydrolysis of Organophosphates.

Most organophosphates (OPs) are hydrophobic, and after exposure, can sequester into lipophilic regions within the body, such as adipose tissue, resulting in long term chronic effects. Consequently, there is an urgent need for therapeutic agents that can decontaminate OPs in these hydrophobic regions. Accordingly, an enzyme-polymer surfactant nanocomplex is designed and tested comprising chemically supercharged phosphotriesterase (Agrobacterium radiobacter; arPTE) electrostatically conjugated to amphiphilic polymer surfactant chains ([cat.arPTE][S-]). Experimentally-derived structural data are combined with molecular dynamics (MD) simulations to provide atomic level detail on conformational ensembles of the nanocomplex using dielectric constants relevant to aqueous and lipidic microenvironments. These show the formation of a compact admicelle pseudophase surfactant corona under aqueous conditions, which reconfigures to yield an extended conformation at a low dielectric constant, providing insight into the mechanism underpinning cell membrane binding. Significantly, it demonstrated that [cat.arPTE][S-] spontaneously binds to human mesenchymal stem cell membranes (hMSCs), resulting in on-cell OP hydrolysis. Moreover, the nanoconstruct can endocytose and partition into the intracellular fatty vacuoles of adipocytes and hydrolyze sequestered OP.

GRT-X Stimulates Dorsal Root Ganglia Axonal Growth in Culture via TSPO and Kv7.2/3 Potassium Channel Activation.

GRT-X, which targets both the mitochondrial translocator protein (TSPO) and the Kv7.2/3 (KCNQ2/3) potassium channels, has been shown to efficiently promote recovery from cervical spine injury. In the present work, we investigate the role of GRT-X and its two targets in the axonal growth of dorsal root ganglion (DRG) neurons. Neurite outgrowth was quantified in DRG explant cultures prepared from wild-type C57BL6/J and TSPO-KO mice. TSPO was pharmacologically targeted with the agonist XBD173 and the Kv7 channels with the activator ICA-27243 and the inhibitor XE991. GRT-X efficiently stimulated DRG axonal growth at 4 and 8 days after its single administration. XBD173 also promoted axonal elongation, but only after 8 days and its repeated administration. In contrast, both ICA27243 and XE991 tended to decrease axonal elongation. In dissociated DRG neuron/Schwann cell co-cultures, GRT-X upregulated the expression of genes associated with axonal growth and myelination. In the TSPO-KO DRG cultures, the stimulatory effect of GRT-X on axonal growth was completely lost. However, GRT-X and XBD173 activated neuronal and Schwann cell gene expression after TSPO knockout, indicating the presence of additional targets warranting further investigation. These findings uncover a key role of the dual mode of action of GRT-X in the axonal elongation of DRG neurons.

Chemical Standardization of Milk Thistle (Silybum marianum L.) Extract Using UHPLC-MS/MS and the Method of Standard Addition.

Extracts prepared from the seeds of the medicinal plant milk thistle [Silybum marianum (L.) Gaertn. (Asteraceae)] are widely used as dietary supplements due to anti-inflammatory, antitumor, and hepatoprotective effects. Called silymarin, the main components of lipophilic extracts of milk thistle seeds are flavonoids and flavonolignans including silybin A, silybin B, isosilybin A, isosilybin B, silydianin, silychristin, taxifolin, and 2,3-dehydrosilybins. The aim of this study was to develop a method based on UHPLC-MS/MS for the chemical authentication and standardization of milk thistle silymarin. Validation included the method of standard addition to account for the lack of a blank matrix. Potential matrix effects were investigated by analyzing silymarin standards dissolved only in the initial UHPLC mobile phase. Measurements of six flavonolignans and taxifolin in the milk thistle extract using UHPLC-MS/MS with standard addition or external standard calibration produced similar results for all analytes except silydianin and 2,3-dehydrosilybin B, which showed significant peak enhancement during negative ion electrospray due to botanical matrix effects. The UHPLC-MS/MS-based method of standard addition requires <10 min per injection and is suitable for the standardization of silymarin from milk thistle in support of preclinical and clinical studies of safety and efficacy.

Preoperative Crohn's Disease Exclusion Diet and Exclusive Enteral Nutrition in Adults with Crohn's Disease: A Feasibility Randomised Controlled Trial.

Preoperative exclusive enteral nutrition (EEN) improves nutritional status, reduces intestinal inflammation, and likely improves surgical outcomes. Crohn's disease exclusion diet with partial enteral nutrition (CDED) also reduces intestinal inflammation but its safety preoperatively is unknown. This single-blinded, multicentre, randomised controlled trial of three preoperative nutritional therapies aimed to assess the feasibility of recruiting and retaining patients and collecting primary and secondary effectiveness outcomes. Adults undergoing elective Crohn's disease surgery with a body mass index (BMI) > 18.5 kg/m2 and without significant weight loss were eligible to participate. Patients were randomly assigned to six weeks of preoperative EEN, CDED, or standard care. Feasibility, nutritional, radiological, and surgical outcomes were recorded. Over 18 months, 48 patients were screened, 17 (35%) were randomised, and 13/17 (76%) patients were retained in the intervention phase. It was feasible to collect primary and secondary effectiveness data; at day 30, three patients had Clavien Dindo Grade 2 complications, and 10 had no complications. Nutritional therapy adherence of patients retained in the study was high. Recruitment and retention of patients who need elective Crohn's disease surgery for preoperative nutritional therapy is possible, although a shorter duration may improve EEN completion. The impact on surgical outcomes should be assessed in a larger study.

Cannabinoid residuals in tissues of lambs fed spent hemp biomass and consumer's exposure assessment.

Spent hemp biomass (SHB) contains trace amounts of cannabinoids, including Δ9-tetrahydrocannabinol (Δ9-THC), that may accumulate in the tissues of animals consuming SHB. We measured cannabinoid residues in the liver, adipose tissue, and muscle of finishing lambs fed either 10% or 20% SHB for 8 weeks, or 4 weeks followed by 4 weeks SHB withdrawal. We detected multiple cannabinoids in the liver at a similar proportion to the SHB. However, CBD and Δ9-THC were enriched >20-fold in the adipose and muscle, compared to their proportion in SHB. The highest concentration of Δ9-THC was detected in adipose tissue and was 7.4-times higher than in muscle. Most cannabinoids were undetectable in tissues after 4 weeks of clearance. The consumers' exposure assessment on Δ9-THC revealed tissue levels of total THC (THCA+Δ9-THC) that exceed the acute reference dose of 1 µg/kg BW across population groups. When consuming meat from the lambs fed 10% and 20% SHB, the maximum total THC exposure was 2.03 and 7.32 µg/kg BW, respectively, equal to or below the Lowest Observed Adverse Effect Level of 36 µg/kg BW, the No Observed Adverse Effect Level of 12 µg/kg BW or a tolerable dose intake of 7 µg/kg BW.

Preclinical studies of RA475, a guanidine-substituted spirocyclic candidate RPN13/ADRM1 inhibitor for treatment of ovarian cancer.

There is an urgent unmet need for more targeted and effective treatments for advanced epithelial ovarian cancer (EOC). The emergence of drug resistance is a particular challenge, but small molecule covalent inhibitors have promise for difficult targets and appear less prone to resistance. Michael acceptors are covalent inhibitors that form bonds with cysteines or other nucleophilic residues in the target protein. However, many are categorized as pan-assay interference compounds (PAINS) and considered unsuitable as drugs due to their tendency to react non-specifically. Targeting RPN13/ADRM1-mediated substrate recognition and deubiquitination by the proteasome 19S Regulatory Particle (RP) is a promising treatment strategy. Early candidate RPN13 inhibitors (iRPN13) produced a toxic accumulation of very high molecular weight polyubiquitinated substrates, resulting in therapeutic activity in mice bearing liquid or solid tumor models, including ovarian cancer; however, they were not drug-like (PAINS) because of their central piperidone core. Up284 instead has a central spiro-carbon ring. We hypothesized that adding a guanidine moiety to the central ring nitrogen of Up284 would produce a compound, RA475, with improved drug-like properties and therapeutic activity in murine models of ovarian cancer. RA475 produced a rapid accumulation of high molecular polyubiquitinated proteins in cancer cell lines associated with apoptosis, similar to Up284 although it was 3-fold less cytotoxic. RA475 competed binding of biotinylated Up284 to RPN13. RA475 shows improved solubility and distinct pharmacodynamic properties compared to Up284. Specifically, tetraubiquitin firefly luciferase expressed in leg muscle was stabilized in mice more effectively upon IP treatment with RA475 than with Up284. However, pharmacologic analysis showed that RA475 was more rapidly cleared from the circulation, and less orally available than Up284. RA475 shows reduced ability to cross the blood-brain barrier and in vitro inhibition of HERG. Treatment of mice with RA475 profoundly inhibited the intraperitoneal growth of the ID8-luciferase ovarian tumor model. Likewise, RA475 treatment of immunocompetent mice inhibited the growth of spontaneous genetically-engineered peritoneal tumor, as did weekly cisplatin dosing. The combination of RA475 and cisplatin significantly extended survival compared to individual treatments, consistent with synergistic cytotoxicity in vitro. In sum, RA475 is a promising candidate covalent RPN13i with potential utility for treatment of patients with advanced EOC in combination with cisplatin.

A prospective observational cohort study comparing the treatment effectiveness and safety of ciclosporin, dupilumab and methotrexate in adult and paediatric patients with atopic dermatitis: results from the UK-Irish A-STAR register.

BACKGROUND: The main conventional systemic atopic dermatitis (AD) treatments are methotrexate (MTX) and ciclosporin (CyA). Dupilumab was the first novel systemic agent to enter routine clinical practice. There are no head-to-head randomised controlled trials or real-world studies comparing these agents directly. Network meta-analyses provide indirect comparative efficacy and safety data and have shown strong evidence for dupilumab and CyA. OBJECTIVES: The aim of this study was to compare the real-world clinical effectiveness and safety of CyA, dupilumab and MTX in AD. METHODS: We compared the effectiveness and safety of these systemic agents in a prospective observational cohort study of adult and paediatric patients recruited into the UK-Irish Atopic eczema Systemic TherApy Register (A-STAR). Treatment effectiveness measures included Eczema Area and Severity Index (EASI), Patient-Oriented Eczema Measure (POEM), Peak Pruritus Numerical Rating Scale (PP-NRS), Dermatology Life Quality Index (DLQI) and children's DLQI (cDLQI). Minimum duration of treatment was 28 days and follow-up was 12 months. Adjusted Cox-regression was used to compare the hazards of achieving EASI-50, EASI-75 and EASI-90 over time, and linear mixed-effects models were used to estimate changes in efficacy scores. Treatment safety was assessed by examining adverse events (AEs) at follow-up visits. RESULTS: 488 patients (n=311 adults and n=177 children/adolescents) on dupilumab (n=282), methotrexate (n=149), or CyA (n=57) were included. CyA and MTX were primarily used first line, while dupilumab was mainly a second line systemic as per UK National Institute of Clinical and Care Excellence (NICE) recommendations. EASI-50, EASI-75 and EASI-90 were achieved more rapidly in the dupilumab and CyA groups compared to MTX. After adjustment for previous severity, the reduction in EASI, POEM, PP-NRS and DLQI was greater for patients treated with dupilumab compared to MTX. In severe patients the reduction in EASI, POEM, and PP-NRS was even greater with CyA. The incidence of AEs was similar across groups (734, 654 and 594 per 10,000 person-month on CyA, dupilumab and MTX respectively). CONCLUSIONS: This real-world comparison of CyA, dupilumab and MTX in AD suggests that dupilumab is consistently more effective than MTX and that CyA is most effective in very severe disease within one follow-up year.

Norepinephrine Neurons in the Nucleus of the Solitary Tract Suppress Luteinizing Hormone Secretion in Female Mice.

Stress impairs fertility, at least in part, via inhibition of gonadotropin secretion. Luteinizing hormone (LH) is an important gonadotropin that is released in a pulsatile pattern in males and in females throughout the majority of the ovarian cycle. Several models of stress, including acute metabolic stress, suppress LH pulses via inhibition of neurons in the arcuate nucleus of the hypothalamus that co-express kisspeptin, neurokinin B, and dynorphin (termed KNDy cells) which form the pulse generator. The mechanism for inhibition of KNDy neurons during stress, however, remains a significant outstanding question. Here, we investigated a population of catecholamine neurons in the nucleus of the solitary tract (NTS), marked by expression of the enzyme dopamine beta-hydroxylase (DBH), in female mice. First, we found that a subpopulation of DBH neurons in the NTS are activated (express c-Fos) during metabolic stress. Then, using chemogenetics we determined that activation of these cells is sufficient to suppress LH pulses, augment corticosterone secretion, and induce sickness-like behavior. In subsequent studies, we identified evidence for suppression of KNDy cells (rather than downstream signaling pathways) and determined that the suppression of LH pulses was not dependent on the acute rise in glucocorticoids. Together these data support the hypothesis that DBH cells in the NTS are important for regulation of neuroendocrine and behavioral responses to stress.Significance Statement Stress impairs fertility, at least in part, via inhibition of gonadotropin secretion. The gonadotropin luteinizing hormone (LH) is secreted in a pulsatile pattern in males and females throughout most of the ovarian cycle to support gamete development and sex steroid production in both sexes. Here, we investigated a population of catecholamine neurons in the nucleus of the solitary tract (NTS) for their role in regulation of pulsatile LH secretion. We demonstrate that these neurons are sufficient to suppress pulsatile LH secretion via inhibition of kisspeptin neurons in ovariectomized mice. Moreover, these NTS neurons are also sufficient to augment corticosterone concentrations and induce sickness-like behavior, which raises the possibility that these neurons are important for neuroendocrine and behavioral responses during stress.

Solanidine Metabolites as Diet-Derived Biomarkers of CYP2D6-Mediated Tamoxifen Metabolism in Breast Cancer Patients.

Tamoxifen is an important antiestrogen for the treatment of hormone receptor-positive breast cancer and undergoes bioactivation by CYP2D6 to its active metabolite endoxifen. Genetic variation in CYP2D6 has been linked to endoxifen levels during tamoxifen therapy. Recent studies have suggested solanidine, a glycoalkaloid phytochemical in potatoes, undergoes CYP2D6-mediated metabolism to 4-OH-solanidine (m/z 414) and 3,4-seco-solanidine-3,4-dioic acid (SSDA; m/z 444). Using a retrospective cohort of 1,032 breast cancer patients on tamoxifen therapy, we examined the association of solanidine metabolites with CYP2D6 activity and its correlation with tamoxifen metabolism. Solanidine, 4-OH-solanidine, or SSDA was detected in 99.7% (N = 1,029) of plasma samples. Decreased solanidine metabolite ratios were found in CYP2D6 intermediate and poor metabolizers (P < 0.0001). Patients on CYP2D6 strong inhibitors had a 77.6% and 94.2% decrease in 4-OH-solandine/solanidine (P < 0.0001) and SSDA/solanidine (P < 0.0001), respectively. The ratio of endoxifen to tamoxifen was highly correlated with both 4-OH-solandine/solanidine (ρ = 0.3207, P < 0.0001) and SSDA/solanidine (ρ = 0.5022, P < 0.0001) ratios. Logistic regression modeling was used to determine that 4-OH-solanidine/solanidine and SSDA/solanidine ratios below 2.1 and 0.8, respectively, predicted endoxifen concentrations of <16 nM. In conclusion, solanidine, 4-OH-solanidine, and SSDA are diet-derived biomarkers of CYP2D6 activity. Moreover, in patients on tamoxifen therapy, 4-OH-solanidine/solanidine and SSDA/solanidine predicted endoxifen levels including the inhibitory effects of concomitantly prescribed CYP2D6-interacting medications. Accordingly, 4-OH-solanidine/solanidine or SSDA/solanidine ratio has the potential to be particularly useful prior to initiation of tamoxifen or for determining the impact of CYP2D6 drug interactions, as well as prior to switching from an aromatase inhibitor to tamoxifen.

Efficacy and safety of delgocitinib cream in adults with moderate to severe chronic hand eczema (DELTA 1 and DELTA 2): results from multicentre, randomised, controlled, double-blind, phase 3 trials.

BACKGROUND: Chronic hand eczema is a fluctuating, inflammatory, pruritic, often painful disease of hands and wrists that strongly impacts quality of life and occupational capabilities of patients. The aim of phase 3 DELTA 1 and DELTA 2 was to assess the efficacy and safety of twice-daily applications of the topical pan-Janus kinase inhibitor delgocitinib cream 20 mg/g versus cream vehicle in adults with moderate to severe chronic hand eczema. METHODS: Both trials were randomised, double-blinded, and vehicle-controlled, with DELTA 1 being conducted at 53 trial centres in Canada, France, Germany, Italy, Poland, and the UK and DELTA 2 at 50 trial centres in Belgium, Canada, Denmark, Germany, the Netherlands, Poland, and Spain. Adults (aged ≥18 years) with moderate to severe chronic hand eczema were randomly assigned 2:1 to twice-daily delgocitinib cream 20 mg/g or cream vehicle for 16 weeks. The primary endpoint was Investigator's Global Assessment for Chronic Hand Eczema (IGA-CHE) treatment success at week 16, defined as IGA-CHE score of 0 (clear) or 1 (almost clear, defined as only barely perceptible erythema). Efficacy and safety were assessed in all patients who were exposed to trial treatment. These trials are registered with ClinicalTrials.gov, NCT04871711 and NCT04872101. FINDINGS: Between May 10, 2021, and Oct 31, 2022, 487 patients (181 male and 306 female) were enrolled in DELTA 1; between May 25, 2021, and Jan 6, 2023, 473 patients (161 male and 312 female) were enrolled in DELTA 2. 325 patients in DELTA 1 and 314 in DELTA 2 were assigned to delgocitinib cream; 162 patients in DELTA 1 and 159 in DELTA 2 were assigned to cream vehicle. At week 16, a greater proportion of delgocitinib-treated patients versus cream vehicle patients had IGA-CHE treatment success (64 [20%] of 325 vs 16 [10%] of 162 in DELTA 1 and 91 [29%] of 313 vs 11 [7%] of 159 in DELTA 2; both trials p≤0·0055). The proportion of patients who reported adverse events was similar with delgocitinib (147 [45%] of 325 in DELTA 1 and 143 [46%] of 313 in DELTA 2) and the cream vehicle (82 [51%] of 162 in DELTA 1 and 71 [45%] of 159 in DELTA 2). Most frequent adverse events occurring in at least 2% of patients were similar in both treatment groups and included COVID-19 and nasopharyngitis. INTERPRETATION: Overall, delgocitinib cream showed superior efficacy versus cream vehicle and was well tolerated over 16 weeks. These results support the clinical benefit of delgocitinib cream as a potential treatment option for patients with moderate to severe chronic hand eczema, who are unable to adequately control their disease with basic skin care practices and topical corticosteroids. FUNDING: LEO Pharma.

Prevalence of Late-Stage Parkinson's Disease in the US Healthcare System: Insights from TriNetX.

BACKGROUND: Patients in late-stage Parkinson's disease (PDLS) are caregiver-dependent, have low quality of life, and higher healthcare costs. OBJECTIVE: To estimate the prevalence of PDLS patients in the current US healthcare system. METHODS: We downloaded the 2010-2022 data from the TriNetX Diamond claims network that consists of 92 US healthcare sites. PD was identified using standard diagnosis codes, and PDLS was identified by the usage of wheelchair dependence, personal care assistance, and/or presence of diagnoses of dementia. Age of PDLS identification and survival information were obtained and stratified by demographic and the disability subgroups. RESULTS: We identified 1,031,377 PD patients in the TriNetX database. Of these, 18.8% fitted our definition of PDLS (n = 194,297), and 10.2% met two or more late-stage criteria. Among all PDLS, the mean age of PDLS identification was 78.1 (±7.7) years, and 49% were already reported as deceased. PDLS patients were predominantly male (58.5%) with similar distribution across PDLS subgroups. The majority did not have race (71%) or ethnicity (69%) information, but for the available information >90% (n = 53,162) were White, 8.2% (n = 5121) Hispanic/Latino, 7.8% (n = 4557) Black, and <0.01% (n = 408) Asian. Of the PDLS cohort, 71.6% identified with dementia, 12.9% had personal care assistance, and 4.8% were wheelchair-bound. CONCLUSIONS: Late-stage patients are a significant part of the PD landscape in the current US healthcare system, and largely missed by traditional motor-based disability staging. It is imperative to include this population as a clinical, social, and research priority. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Selective recruitment of the cerebellum evidenced by task-dependent gating of inputs.

Functional magnetic resonance imaging (fMRI) studies have documented cerebellar activity across a wide array of tasks. However, the functional contribution of the cerebellum within these task domains remains unclear because cerebellar activity is often studied in isolation. This is problematic, as cerebellar fMRI activity may simply reflect the transmission of neocortical activity through fixed connections. Here, we present a new approach that addresses this problem. Rather than focus on task-dependent activity changes in the cerebellum alone, we ask if neocortical inputs to the cerebellum are gated in a task-dependent manner. We hypothesize that input is upregulated when the cerebellum functionally contributes to a task. We first validated this approach using a finger movement task, where the integrity of the cerebellum has been shown to be essential for the coordination of rapid alternating movements but not for force generation. While both neocortical and cerebellar activity increased with increasing speed and force, the speed-related changes in the cerebellum were larger than predicted by an optimized cortico-cerebellar connectivity model. We then applied the same approach in a cognitive domain, assessing how the cerebellum supports working memory. Enhanced gating was associated with the encoding of items in working memory, but not with the manipulation or retrieval of the items. Focusing on task-dependent gating of neocortical inputs to the cerebellum offers a promising approach for using fMRI to understand the specific contributions of the cerebellum to cognitive function.

Sustained benefits of onabotulinumtoxinA treatment in chronic migraine: An analysis of the pooled Phase 3 REsearch Evaluating Migraine Prophylaxis Therapy (PREEMPT) randomized controlled trials.

OBJECTIVE: To characterize the long-term (56-week) benefits of continuous onabotulinumtoxinA treatment response in individuals with chronic migraine (CM) who achieved reduction to <15 headache days/month with treatment. BACKGROUND: There are limited data exploring reductions in monthly headache days to levels consistent with episodic migraine among those experiencing CM. Understanding the impact of sustained preventive treatment response in CM can provide important information about the impact of successful therapy. METHODS: The two Phase 3 REsearch Evaluating Migraine Prophylaxis Therapy trials of onabotulinumtoxinA in adults included a 24-week, randomized, double-blind, placebo-controlled phase and a 32-week open-label phase. Data were pooled to determine proportions of individuals with <15 headache days/month while on treatment during several time periods in the double-blind phase (Weeks 21-24; any 12 consecutive weeks; Weeks 13-24) and the entire study (Weeks 53-56; any 12 consecutive weeks; any 4-week period). We assessed the long-term impact on mean monthly headache days and changes from baseline on the six-item Headache Impact Test (HIT-6) and Migraine-Specific Quality of Life questionnaire version 2.1 (MSQv2.1). RESULTS: We analyzed 1384 participants with chronic migraine (double-blind: onabotulinumtoxinA, n = 688; placebo, n = 696; open-label: n = 688 [onabotulinumtoxinA]). The discontinuation rates prior to the completion of the full 56-week treatment period for onabotulinumtoxinA and placebo were 25.4% (n = 175) and 29.3% (n = 204), respectively. During Weeks 13-24 of the double-blind phase, significantly more onabotulinumtoxinA-treated (386/688 [56.1%]) than placebo-treated (342/696 [49.1%]) individuals had <15 headache days/month (p = 0.010), with fewer monthly headache days for onabotulinumtoxinA versus placebo responders. The proportions of participants achieving <15 monthly headache days with onabotulinumtoxinA were 60.9% (419/688) at Weeks 25-56, 81.1% (558/688) at Weeks 53-56, and 79.4% (546/688) during any consecutive 12-week period. Mean changes from baseline on the HIT-6 and MSQv2.1 questionnaire surpassed within-group minimal important difference thresholds in all periods. At Week 24, onabotulinumtoxinA-treated participants who achieved <15 monthly headache days during Weeks 21-24 had a greater mean HIT-6 score reduction (-6.5 vs. -1.4) and greater mean MSQv2.1 Role-Function Restrictive score improvements (21.3 vs. 6.4) than those who did not achieve <15 monthly headache days during the same period. CONCLUSIONS: Participants who achieved <15 monthly headache days with onabotulinumtoxinA treatment achieved meaningful benefits in headache-related disability and migraine-specific quality of life compared with those who remained at or above the 15-monthly headache days threshold. Sustained benefits observed over 56 weeks support long-term onabotulinumtoxinA use for the prevention of CM.