Antiepileptic Drug Carbamazepine Binds to a Novel Pocket on the Wnt Receptor Frizzled‑8

Misregulation
of Wnt signaling is common in human cancer. The development
of small molecule inhibitors against the Wnt receptor, frizzled (FZD),
may have potential in cancer therapy. During small molecule screens,
we observed binding of carbamazepine to the cysteine-rich domain (CRD)
of the Wnt receptor FZD8 using surface plasmon resonance (SPR). Cellular
functional assays demonstrated that carbamazepine can suppress FZD8-mediated
Wnt/β-catenin signaling. We determined the crystal structure
of the complex at 1.7 Å resolution, which reveals that carbamazepine
binds at a novel pocket on the FZD8 CRD. The unique residue Tyr52
discriminates FZD8 from the closely related FZD5 and other FZDs for
carbamazepine binding. The first small molecule-bound FZD structure
provides a basis for anti-FZD drug development. Furthermore, the observed
carbamazepine-mediated Wnt signaling inhibition may help to explain
the phenomenon of bone loss and increased adipogenesis in some patients
during long-term carbamazepine treatment.

Wnt信号通路在人类癌症中的失调现象普遍存在。针对Wnt受体frizzled（FZD）的小分子抑制剂的开发，在癌症治疗领域具有潜在价值。在小分子筛选过程中，我们利用表面等离子体共振（SPR）技术观察到卡马西平与Wnt受体FZD8的半胱氨酸富集域（CRD）的结合。细胞功能实验表明，卡马西平能够抑制由FZD8介导的Wnt/β-连环蛋白信号通路。我们确定了该复合物在1.7埃分辨率下的晶体结构，揭示了卡马西平在FZD8 CRD上的一个新型口袋中结合。独特的残基Tyr52区分了FZD8与密切相关但不相同的FZD5以及其他FZD，使其能够与卡马西平结合。首个小分子结合的FZD结构为抗FZD药物的研发提供了基础。此外，观察到的卡马西平介导的Wnt信号通路抑制作用可能有助于解释某些患者在长期服用卡马西平过程中出现的骨量减少和脂肪生成增加的现象。