The Biocryst oral plasma kallikrein inhibitor, berotralstat (BCX7353), was recently approved as the first non-steroidal treatment for prevention of hereditary angioedema attacks. The molecule is given orally (150 mg QD) despite having two basic amines (dibasic). Interestingly for a chronically administered drug, the molecule is noted to have QT prolongation risk at ~3x the recommended dose (450 mg), which appears acceptable for this rare and underserved indication. The molecule was discovered after a structure-based drug design campaign starting with knowledge from a previously poorly bioavailable benzamidine-containing zwitterion, avoralstat (BCX4161). The benzamidine was successfully replaced with a similarly basic benzylamine, and the new benzylamine-containing fragment was elaborated into molecule with a highly dissimilar structure and binding mode from the original drug. There are several interesting features from the crystal structures including the fact that the highly hydrophilic primary amine is buried in a polar cleft of the protein. This approved drug is another great example of a “rule-breaker” succeeding in a rare disease setting.

The Biogen compound BIO-32546 is a potent (IC50 = 1 nM), selective, oral, non-zinc-binding reversible autotaxin (ATX) inhibitor, and is an interesting example of a relevantly large brain-penetrant zwitterion. The molecule has a distinct structure from ATX inhibitors previously highlighted (e.g. Small Molecules of the Month May, Jul., Nov. 2020) and was derived from an phosphonic acid-containing inhibitor hit (28 nM) from a lipid mimetic chemical library. If your first reaction was that this molecule looks like an S1P modulator, you’re not crazy – the chemical library was derived from Biogen’s S1P program. Optimization was guided by cocrystal structures and the window against a hERG liability (surprising for an acid-containing molecule) was mitigated with introduction of a benzylic methyl group. The compound demonstrated in vivo efficacy in a model of acute pain with good PK/PD correlation in a model of acute pain. No brain-penetrant ATX inhibitors appear to be in clinical trials, and Biogen doesn’t appear to have advanced an ATX inhibitor into the clinic.