2BAct

2BAct is a highly selective, orally bioavailable, and central nervous system penetrant activator of eukaryotic initiation factor 2B (eIF2B), the heterodecameric guanine nucleotide exchange factor that controls the rate-limiting step of translational initiation in all eukaryotic cells. The compound was developed at Calico Life Sciences LLC as a next-generation analog of the prototype eIF2B activator ISRIB (integrated stress response inhibitor), retaining the low-nanomolar potency of ISRIB (EC50 of 33 nM in a cell-based integrated stress response reporter assay; EC50 of 7.3 nM in guanine nucleotide exchange factor activity assays using mutant eIF2B primary fibroblast lysates) while achieving substantially improved aqueous solubility, oral bioavailability, and suitability for chronic in vivo administration through the introduction of an asymmetric bicyclo[1.1.1]pentane (BCP) core scaffold in place of the symmetric cyclohexane linker of ISRIB.

The principal preclinical demonstration of 2BAct was reported by Wong et al. (2019) in the Eif2b5 R191H homozygous knock-in mouse model of vanishing white matter disease (VWM), a severe inherited leukoencephalopathy caused by hypomorphic mutations in eIF2B subunit genes that constitutively activate the integrated stress response (ISR) and produce progressive white-matter deterioration, motor dysfunction, and failure to thrive. In a 21-week blinded treatment study, 2BAct administered continuously in the diet at 300 parts per million achieved unbound brain exposures 15-fold above the in vitro EC50 and completely prevented all hallmark disease phenotypes: body weight gain normalized to wild-type rates within two weeks of treatment initiation; grip strength and beam-crossing motor performance were preserved at wild-type levels; corpus callosum and spinal cord myelin content was maintained at 91 and 85 percent of wild-type respectively; astrogliosis, microglial activation, and neuronal stress markers (GFAP, Iba-1, ATF3) were normalized; and whole-brain transcriptome and proteome analyses confirmed abolition of the ISR gene-expression signature. The compound was well tolerated in the rodent model with no effects on body weight in wild-type littermates, and a rat cardiovascular safety study did not identify relevant abnormalities.

However, significant cardiovascular anomalies were observed in a dog cardiovascular safety model at doses approximating the minimum efficacious exposure, rendering 2BAct unsuitable for direct human dosing and necessitating further medicinal chemistry optimization. The cardiovascular liability in the canine model has been the principal translational limitation of 2BAct and motivated the subsequent development of DNL343 (evetifator) by Denali Therapeutics as a structurally distinct eIF2B activator with an improved cardiovascular safety profile that advanced to Phase 1 and Phase 2/3 clinical trials in amyotrophic lateral sclerosis. 2BAct remains a premier research-grade tool compound for investigation of eIF2B pharmacology, the integrated stress response, vanishing white matter disease pathophysiology, and the therapeutic potential of eIF2B activation in neurological disease. The compound is not approved for human use in any jurisdiction and is supplied exclusively as a research-grade preparation.