Viskochil, David

Abstract BACKGROUND Mirdametinib, a MEK1/2 inhibitor, is the first FDA-approved medicine for both adults and children (≥2y) with NF1-PN not amenable to complete resection. In the phase 2b ReNeu trial (NCT03962543), confirmed objective response rate (ORR) was 41% in adults and 52% in children. This analysis explored relationships between baseline characteristics and mirdametinib responses in ReNeu. METHODS Confirmed ORR was the proportion of patients with ≥20% reduction from baseline in target PN volume by magnetic resonance imaging on consecutive scans during the 24-cycle treatment phase (“responders”) as assessed by blinded independent central review. Characteristics included age, body surface area (BSA), sex, race, ethnicity, target PN location, PN type (typical, nodular, or solitary nodular), target PN volume, and progression status. Rates of dose reductions and treatment-related adverse events (TRAEs) were evaluated. These factors were descriptively analyzed for potential relationships with confirmed objective response (data cutoff: 20September2023). RESULTS With mirdametinib, there was no clear difference between responders (n=53) and non-responders (n=61) in age (mean, 22.89 and 22.67y), BSA (mean, 1.42 and 1.51 m2), sex (60.4% and 57.4% female), race (83.0% and 68.9% White), or ethnicity (83.0% and 85.2% non-Hispanic/Latino). The majority of responders and non-responders had head/neck for target PN location (50.9% and 47.5%), typical PN type (81.1% and 63.9%), and baseline progression status (60.4% and 55.7%). Mean (95% CI) target PN volume was 283.43 (155.19, 411.66) and 415.74 (211.71, 619.77) mL, respectively. Dose reduction (11.3%; 18.0%) and TRAE rates (96.2%; 96.7%) were comparable. CONCLUSIONS This analysis suggests mirdametinib provides clinical benefit across a broad range of patient and NF1-PN tumor characteristics; a relationship between analyzed baseline characteristics and confirmed objective response was not established. Mean PN volume was higher in non-responders, though CIs overlapped. Dose reductions and emergence of TRAEs did not appear to impact response to mirdametinib. SUPPORT SpringWorks Therapeutics, Inc.

Abstract BACKGROUND Mirdametinib is the first FDA-approved MEK1/2 inhibitor for both adults and children ≥2 years with NF1 who have symptomatic PN not amenable to complete resection. We report results from the phase 2b ReNeu trial (NCT03962543), including the LTFU. METHODS In ReNeu, mirdametinib was administered in 3-weeks-on/1-week-off 28-day cycles. Following the 24-cycle treatment phase, patients could continue mirdametinib in an optional LTFU. We report results through June 12, 2024, approximately 9 months from the previous data cutoff. RESULTS Fifty-eight adults and 56 children received mirdametinib. Median (range) duration of treatment was 21.8 (0.4, 54.4) months in adults and 25.4 (1.6, 48.5) months in children. Among LTFU-eligible patients, 26/31 (84%) adults and 32/37 (86%) children entered LTFU. Confirmed objective response rate (ORR, treatment+LTFU phases) was 47% (27/58; 95%CI, 33%, 60%) in adults and 55% (31/56; 95%CI, 42%, 69%) in children. Among confirmed responders, 18 adults and 19 children achieved a deep response (best target PN volume reduction from baseline of >50%). Median (range) best percentage change from baseline in target PN volume was –41% (–90%, 13%) in adults and –43% (–98%, 48%) in children. Median duration of response (DoR) was not reached for either age cohort. Treatment-related adverse events (TRAEs) in ≥25% of patients were dermatitis acneiform, diarrhea, nausea, and vomiting in adults; and diarrhea, dermatitis acneiform, and paronychia in children. Grade ≥3 TRAEs occurred in 17% of adults and 25% of children. Dose interruptions, dose reductions, and discontinuations due to TRAEs occurred in 9%, 17%, and 22%, respectively, of adults, and 14%, 14%, and 9%, respectively, of children. CONCLUSIONS Improved confirmed ORR was observed with longer duration of mirdametinib, with additional deep responses achieved in both adults and children. Mirdametinib continued to be well tolerated with a manageable safety profile and no new safety signals in the LTFU.

Abstract BACKGROUND Mirdametinib is the first FDA-approved MEK1/2 inhibitor for both adults and children (≥2 years) with NF1 who have symptomatic PN not amenable to complete resection. We report updated results from the LTFU phase of the pivotal, phase 2b ReNeu trial (NCT03962543) evaluating the efficacy and safety of mirdametinib. MATERIALS AND METHODS In ReNeu, mirdametinib capsules or tablets for oral suspension (2 mg/m2 BID, max 4 mg BID) are administered in 3-weeks-on/1-week-off 28-day cycles. Following the 24-cycle (~2 years) treatment phase, patients could continue mirdametinib in an optional LTFU phase. These analyses are inclusive of the treatment and LTFU phases (data cutoff: June 12, 2024; an additional 9 months of cumulative data following the primary analysis). Exploratory analyses reported here included confirmed objective response rate (ORR; proportion of patients with ≥20% reduction of target PN volume from baseline on consecutive MRI scans within 2 to 6 months, assessed by blinded independent central review), duration of response (DoR), change from baseline in target PN volume, and safety. RESULTS Fifty-eight adults and 56 children were dosed with mirdametinib. Median (range) duration of mirdametinib treatment was 21.8 (0.4, 54.4) months in adults and 25.4 (1.6, 48.5) months in children. Among LTFU-eligible patients, 26/31 (84%) adults and 32/37 (86%) children entered the LTFU. Confirmed ORR was 47% (27/58; 95% CI, 33%, 60%) in adults and 55% (31/56; 95% CI, 42%, 69%) in children. Of patients with a confirmed objective response, 18 adults and 19 children achieved a deep response (best target PN volume reduction from baseline of >50%). Median (range) best percentage change from baseline in target PN volume was -41% (-90%, 13%) in adults and -43% (-98%, 48%) in children. Median DoR was not reached. Treatment-related adverse events (TRAEs) in ≥25% of patients were dermatitis acneiform, diarrhoea, nausea, and vomiting in adults, and diarrhoea, dermatitis acneiform, and paronychia in children. Grade ≥3 TRAEs occurred in 17% of adults and 25% of children. Dose interruptions, dose reductions, and discontinuations due to TRAEs occurred in 9%, 17%, and 22%, respectively, of adults, and in 14%, 14%, and 9%, respectively, of children. CONCLUSIONS An increase in confirmed ORR was observed with longer duration of mirdametinib treatment, with additional deep responses achieved in both adults and children with NF1-PN. Mirdametinib continued to be well tolerated with a manageable safety profile and no new safety signals identified in the LTFU phase. SUPPORTED BY SpringWorks Therapeutics, Inc.

Abstract Patients with NF1-PN experience pain and other symptoms that negatively impact functioning and quality-of-life. We present patient- and parent proxy-reported HRQoL outcomes from ReNeu (NCT03962543), a pivotal, phase 2b trial of mirdametinib, an investigational MEK1/2 inhibitor, in adults and children (≥2 y) with NF1-PN causing morbidities. Fifty-eight adults and 56 children received mirdametinib (2 mg/m2 BID; 3-weeks-on/1-week-off, 28-d cycles). Change in HRQoL was assessed by Pediatric QoL Inventory (PedsQL) 4.0 Generic Core Scales from baseline across the 24-cycle treatment phase; change from baseline at Cycle 13 (C13) was a prespecified secondary endpoint. PedsQL is a HRQoL measure for adults and children with a Total Score (TS) and 4 subscales: physical, emotional, social, and school/work. Items are reported on a 0-100 scale (higher scores=better HRQoL). Clinically meaningful improvement was defined as change from baseline >9.7 points for adults, >8.5 points for child self-report, and >9.0 points for parent proxy-report. PedsQL-TS improvement (least-squares mean, LSM [SE] change) from baseline at C13 was 3.9 (1.6; P=.018; n=34) for adults, 4.0 (2.4; P=.096; n=38) for children by self-report, and 5.6 (1.9; P=.005; n=43) by parent proxy-report. PedsQL-TS improvements for adults and children by parent proxy-report (not by children self-report) were observed early (at C5 and C3, respectively) and sustained through C24. Clinically meaningful improvement in PedsQL-TS from baseline at C13 was achieved by 37% (10/27) adults, 45% (13/29) children by self-report, and 47% (15/32) children by parent proxy-report (among patients who could have achieved a clinically meaningful change from baseline). Significant (P<.05) improvement from baseline to C13 was reported for physical (adults, children, and parent proxy-report), school/work (adults), and emotional and social (parent proxy-report) subscales. Adults and children (by parent proxy-report) with NF1-PN had clinically meaningful, early, and sustained improvement in HRQoL over the course of mirdametinib treatment.

PURPOSE Pharmacologic therapies for neurofibromatosis type 1-associated plexiform neurofibromas (NF1-PNs) are limited; currently, none are US Food and Drug Administration–approved for adults. METHODS ReNeu is an open-label, multicenter, pivotal, phase IIb trial of mirdametinib in 58 adults (≥18 years of age) and 56 children (2 to 17 years of age) with NF1-PN causing significant morbidities. Patients received mirdametinib capsules or tablets for oral suspension (2 mg/m 2 twice daily, maximum 4 mg twice daily), regardless of food intake, in 3 weeks on/1 week off 28-day cycles. The primary end point was confirmed objective response rate (ORR; proportion of patients with a ≥20% reduction of target PN volume from baseline on consecutive scans during the 24-cycle treatment phase) assessed by blinded independent central review (BICR) of volumetric magnetic resonance imaging. RESULTS Twenty-four of 58 adults (41%) and 29 of 56 children (52%) had a BICR-confirmed objective response during the 24-cycle treatment phase; in addition, two adults and one child had confirmed responses during long-term follow-up. Median (range) target PN volumetric best response was –41% (−90 to 13) in adults and –42% (−91 to 48) in children. Both cohorts reported significant and clinically meaningful improvement in patient- or parent proxy-reported outcome measures of worst tumor pain severity, pain interference, and health-related quality of life (HRQOL) that began early and were sustained during treatment. The most commonly reported treatment-related adverse events were dermatitis acneiform, diarrhea, and nausea in adults and dermatitis acneiform, diarrhea, and paronychia in children. CONCLUSION In ReNeu, the largest multicenter NF1-PN trial reported to date, mirdametinib treatment demonstrated significant confirmed ORRs by BICR, deep and durable PN volume reductions, and early, sustained, and clinically meaningful improvement in pain and HRQOL. Mirdametinib was well-tolerated in adults and children.

Abstract BACKGROUND PN in patients (pts) with NF1 can cause pain, disfigurement, impaired quality of life (QoL), and it can undergo malignant transformation. ReNeu (NCT03962543), a multicenter, open-label, phase 2b study, evaluated efficacy and safety of the highly selective, oral, investigational MEK1/2 inhibitor mirdametinib in adults (≥18 y) and children (2-17 y) with inoperable NF1 PN causing significant morbidities. MATERIAL AND METHODS Mirdametinib was administered as a capsule or dispersible tablet (2 mg/m2 BID, max 4 mg BID) without regard to food in 3 wk on/1 wk off 28-d cycles. The primary endpoint was confirmed objective response rate (ORR; percentage of pts with confirmed MRI-assessed ≥20% reduction of target PN volume by blinded independent central review [BICR] within the 24-cycle treatment phase). The minimum clinically relevant ORR (null) was defined as 23% for adults and 20% for children. Pts could continue treatment in an optional long-term follow-up (LTFU) phase. Additional key endpoints were duration of response (DoR), time to response (TTR), change from baseline in target PN volume, worst pain severity (Numerical Rating Scale-11 [NRS-11]), pain interference (Pain Interference Index [PII]), health-related (HR) QoL (PedsQL), and safety. RESULTS All 114 pts (58 adult, 56 children) received mirdametinib. As of the 20 Sept 2023 data cutoff (DCO), BICR-confirmed ORR during the treatment phase was 41% (95% CI, 29-55; P<.001 vs null) in adults and 52% (95% CI, 38-65; P<.001 vs null) in children. Two adults and 1 child had a confirmed response in the ongoing LTFU. Median (range) target PN volumetric best response from baseline was -41% (-90, 13) and -42% (-91, 48) in adult and children, respectively. As of the DCO, median treatment duration was 22 mo for each cohort, and median DoR was not reached. Median (range) TTR was 7.8 (4-19) mo in adults and 7.9 (4-19) mo in children. Adults and children had statistically significant improvements from baseline to Cycle 13 in NRS-11, PII, and key PedsQL measures. Most frequent (≥35% pts) treatment-emergent adverse events (TEAEs) were dermatitis acneiform, diarrhea, nausea, and vomiting in adults and diarrhea, dermatitis acneiform, and vomiting in children. 16% and 25% of adults and children, respectively, had grade ≥3 treatment-related AEs, and 22% and 9%, respectively, discontinued due to TEAEs. CONCLUSIONS In ReNeu, the largest multicenter NF1 PN trial reported to date, mirdametinib demonstrated a statistically significant ORR by BICR, with deep and durable PN volume reductions, significant improvements in pain severity, pain interference, and HRQoL, and a manageable safety profile in both adults and children. Together with a dispersible tablet formulation, these results underscore the potential of mirdametinib to become an important new treatment option for NF1 PN pts across all ages.

3016 Background: PN in patients (pts) with NF1 can cause pain, disfigurement, impaired quality of life (QoL), and can undergo malignant transformation. ReNeu (NCT03962543), a multicenter, open-label, Phase 2b study, evaluated efficacy and safety of the highly selective, oral, investigational MEK1/2 inhibitor mirdametinib in adult (≥18 y) and pediatric (2-17 y) pts with inoperable NF1 PN causing significant morbidities. Methods: Mirdametinib was administered as a capsule or dispersible tablet (2 mg/m 2 BID, max 4 mg BID) without regard to food in 3 wk on/1 wk off 28-d cycles. The primary endpoint was confirmed objective response rate (ORR; percentage of pts with MRI-assessed ≥20% reduction of target PN volume by blinded independent central review [BICR] within the 24-cycle treatment phase). The minimum clinically relevant ORR (null) was defined as 23% for adults and 20% for pediatrics. Ptscould continue treatment in an optional long-term follow-up (LTFU) phase. Additional key endpoints were duration of response (DoR), time to response (TTR), change from baseline (BL) in target PN volume, pain severity (Numerical Rating Scale-11 [NRS-11]), pain interference (Pain Interference Index [PII]), health-related (HR) QoL (PedsQL), and safety. Results: All114 pts (58 adult, 56 pediatric) received mirdametinib. As of the 20 Sept 2023 data cutoff (DCO), BICR-confirmed ORR during the treatment phase was 41% (95% CI, 29-55; P<.001 vs null) in adults and 52% (95% CI, 38-65; P<.001 vs null) in pediatric pts. Two adult pts and 1 pediatric pt also had a confirmed response in the ongoing LTFU. Median (min, max) target PN volumetric best response from BL was -41% (-90, 13) and -42% (-91, 48) in adult and pediatric pts, respectively. As of the DCO, median treatment duration was 22 mo for each cohort and median DoR was not reached. Median (range) TTR was 7.8 (4-19) mo in adult pts and 7.9 (4-19) mo in pediatric pts. Adult and pediatric pts had statistically significant improvements from BL to cycle 13 in NRS-11, PII, and key PedsQL measures. Most frequent (≥35% pts) treatment-emergent adverse events (TEAEs) were dermatitis acneiform, diarrhea, nausea, and vomiting in adults and diarrhea, dermatitis acneiform, and vomiting in pediatric pts. 16% and 25% of adult and pediatric pts, respectively, had grade ≥3 treatment-related AEs, and 22% and 9%, respectively, discontinued due to TEAEs. Conclusions: In ReNeu, the largest multicenter NF1 PN trial reported to date, mirdametinib demonstrated a statistically significant ORR by BICR, with deep and durable PN volume reductions, significant improvements in pain severity, pain interference, and HRQoL, and a manageable safety profile in both adults and children. Together with a dispersible tablet formulation, these results underscore mirdametinib’s potential to become an important new treatment option for NF1 PN pts across all ages. Clinical trial information: NCT03962543 .

Pathogenic variants in KMT5B , a lysine methyltransferase, are associated with global developmental delay, macrocephaly, autism, and congenital anomalies (OMIM # 617788). Given the relatively recent discovery of this disorder, it has not been fully characterized. Deep phenotyping of the largest ( n = 43) patient cohort to date identified that hypotonia and congenital heart defects are prominent features that were previously not associated with this syndrome. Both missense variants and putative loss-of-function variants resulted in slow growth in patient-derived cell lines. KMT5B homozygous knockout mice were smaller in size than their wild-type littermates but did not have significantly smaller brains, suggesting relative macrocephaly, also noted as a prominent clinical feature. RNA sequencing of patient lymphoblasts and Kmt5b haploinsufficient mouse brains identified differentially expressed pathways associated with nervous system development and function including axon guidance signaling. Overall, we identified additional pathogenic variants and clinical features in KMT5B -related neurodevelopmental disorder and provide insights into the molecular mechanisms of the disorder using multiple model systems.