DNL343

DNL343 is a first-in-class, orally bioavailable, brain-penetrant small molecule activator of eukaryotic initiation factor 2B (eIF2B), the guanine nucleotide exchange factor that governs the rate-limiting step in translation initiation and serves as the principal regulatory node of the integrated stress response (ISR). The compound was designed at Denali Therapeutics as an improvement over the prototype tool compound ISRIB, which despite landmark demonstrations of cognitive enhancement and neuroprotection in rodent models suffered from poor aqueous solubility, limited oral bioavailability, and pharmaceutical intractability [1, 2]. DNL343 retains the symmetric bis-glycolamide pharmacophore that stabilizes the eIF2B decameric complex at the subunit interface but replaces the central cyclohexane of ISRIB with a bicyclo[1.1.1]pentane (BCP) bioisostere, conferring improved solubility, metabolic stability, and CNS penetration [3]. The compound displays an IC50 of 3.2 nanomolar in a cellular ATF4 reporter assay, a brain-to-plasma unbound concentration ratio of approximately 0.8 in rat, and a plasma elimination half-life of 31 to 46 hours in healthy human subjects, supporting oral dosing [3, 4, 5].

Preclinically, DNL343 produced dose-dependent neuroprotection in an optic nerve crush model of acute retinal ganglion cell degeneration and, in the Eif2b5 R191H knock-in mouse model of vanishing white matter disease (a genetic ISR-driven leukoencephalopathy), restored body weight, normalized motor function, reversed ISR transcriptional signatures, normalized plasma neurofilament light chain (NfL), and extended survival from 25 percent to 84.6 percent of treated animals when administered therapeutically at advanced disease stages [1]. In inducible TDP-43 proteinopathy mouse models relevant to amyotrophic lateral sclerosis (ALS), DNL343 attenuated ISR activation and reduced markers of neurodegeneration [6].

Clinical development proceeded through a Phase 1 trial in 95 healthy volunteers (single ascending doses of 15 to 800 mg; multiple ascending doses of 45 to 260 mg for 14 days), which demonstrated dose-proportional pharmacokinetics, cerebrospinal fluid (CSF) to unbound plasma ratios of 0.66 to 0.92, robust suppression of ISR biomarkers (ATF4 protein, CHAC1 transcript) in peripheral blood mononuclear cells, and a favorable tolerability profile with no serious adverse events [4, 5]. A Phase 1b study in 28 participants with ALS (100 and 200 mg for 28 days, followed by an 18-month open-label extension) confirmed CNS penetration with CSF-to-unbound-plasma ratios of 1.02 to 1.23, pharmacodynamic target engagement, and acceptable safety, with headache and fatigue as the most common treatment-emergent adverse events [7, 8]. The compound was subsequently advanced to Regimen G of the Phase 2/3 HEALEY ALS Platform Trial, a 24-week randomized, placebo-controlled study enrolling 186 participants on DNL343 and 139 on placebo. In January 2025, Denali Therapeutics announced that the trial did not meet its primary endpoint of slowing disease progression as measured by the ALS Functional Rating Scale-Revised (ALSFRS-R) and survival, and key secondary endpoints including muscle strength and respiratory function showed no statistical separation from placebo [9, 10]. A subsequent SEC filing revealed that DNL343 did not alter NfL biomarker levels over the treatment period [10]. The compound is no longer in active clinical development for ALS.

This monograph reviews the chemistry and design rationale of DNL343; the molecular pharmacology of eIF2B activation and ISR suppression; the comprehensive preclinical neuroprotection evidence; human pharmacokinetics across Phase 1 and Phase 1b studies; the clinical evidence base in ALS; sourcing, reconstitution, and handling considerations for research applications; stack interactions; the adverse-event profile; and a structured comparative assessment of five ISR-modulating agents (ISRIB, 2BAct, fosigotifator/ABBV-CLS-7262, IFB-088/Sephin1, and trazodone) against DNL343 on five competency standards. The compound is not approved by any regulatory authority for any indication. It is available as a research-grade preparation from multiple chemical suppliers; investigators should confirm identity and purity on every lot.