Discovery of BNC375, a Potent, Selective, and Orally Available Type I Positive Allosteric Modulator of α7 nAChRs

Abstract

Positive allosteric modulators (PAMs) of α7 nAChRs can have different properties with respect to their effects on channel kinetics. Type I PAMs amplify peak channel response to acetylcholine but do not appear to influence channel desensitization kinetics, whereas Type II PAMs both increase channel response and delay receptor desensitization. Both Type I and Type II PAMs are reported in literature, but there are limited reports describing their structure−kinetic profile relationships. Here, we report a novel class of compounds with either Type I or Type II behavior that can be tuned by the relative stereochemistry around the central cyclopropyl ring: for example, (R,R)-13 (BNC375) and its analogues with RR stereochemistry around the central cyclopropyl ring are Type I PAMs, whereas compounds in the same series with SS stereochemistry (e.g., (S,S)-13) are Type II PAMs as measured using patch-clamp electrophysiology. Further fine control over the kinetics has been achieved by changing the substitutions on the aniline ring: generally the substitution of aniline with strong electron withdrawing groups reduces the Type II character of these compounds. Our structure−activity optimization efforts have led to the discovery of BNC375, a small molecule with good CNS-drug like properties and clinical candidate potential.

Pharmacological Characterization of the Novel and Selective α7 Nicotinic Acetylcholine Receptor–Positive Allosteric Modulator BNC375

“…Notably, BNC375 has little effect on channel activation or desensitization kinetics (Fig. 1B), indicating that this compound is a Type I PAM as reported by the manual patch-clamp recordings from GH4C1 cells (Harvey et al, 2019). Figure 1C shows that BNC375 potentiates EC 20 ACh peak current amplitude in a dose-dependent manner with EC 50 5 2.64 mM and E max 5 910%.…”

“…BNC375 (Fig. 1A) was initially discovered and optimized as a positive allosteric modulator of a7 nAChR using GH4C1 cells stably expressing human a7 nAChR (Harvey et al, 2019). Here we use IonFlux HT automated patch-clamp of HEK human a7/RIC3 cells to further characterize the effect of BNC375 on a7 nAChR.…”

“…Excessive Ca 21 influx through a7 receptor may induce cytotoxicity, which has been observed in a7 expressing cell lines upon treatment with Type II a7 PAMs that reduced or abolished receptor desensitization (Ng et al, 2007;Dinklo et al, 2011;Williams et al, 2012). To determine if Type I PAM BNC375 can induce cytotoxicity and differentiate BNC375 from Type II PAMs, we evaluated BNC375, PNU120596 (Type II PAM), and the enantiomer of BNC375 (Type II PAM) (Harvey et al, 2019) in a cytotoxicity assay with GH4C1 cells stably expressing rat a7 nAChR (Fig. 10).…”

“…The current study confirmed the previous finding that Type II PAM PNU120596 can induce cell death in GH4C1 cells expressing a7 receptor. In addition, we compared BNC375 (Type I PAM) and its enantiomer (Type II PAM) (Harvey et al, 2019) in the cytotoxicity assay. The only difference between the two molecules is the stereochemistry around the central cyclopropyl ring, which provides us an excellent tool to differentiate Type I versus Type II PAMs with regard to the impact on cell viability.…”

Differing Activity Profiles of the Stereoisomers of 2,3,5,6TMP-TQS, a Putative Silent Allosteric Modulator of α7 nAChR

“…This was shown to be the case for three functionally diverse analogs in the TQS family, TQS itself (Stokes et al, 2019), the ago-PAM 4BP-TQS (Papke et al, 2014;Thakur et al, 2013), and the allosteric antagonist presented in this work, 2,3,5,6TMP-TQS, as well as for the structurally unrelated ago-PAM B-973B (Garai et al, 2018;Quadri et al, MOL#119958 2019). Additionally, a recently published study of a family of sulfonamide-containing PAMs showed that the stereochemical orientation of side groups around a critical central cyclopropyl ring determine whether enantiomers function as Type I or Type II a7 PAMs (Harvey et al, 2019;Wang et al, 2020).…”