Diflunisal Derivatives as Modulators of ACMS Decarboxylase Targeting the Tryptophan–Kynurenine Pathway

In the kynurenine pathway for tryptophan
degradation, an unstable
metabolic intermediate, α-amino-β-carboxymuconate-ε-semialdehyde
(ACMS), can nonenzymatically cyclize to form quinolinic acid, the
precursor for de novo biosynthesis of nicotinamide adenine dinucleotide
(NAD+). In a competing reaction, ACMS is decarboxylated
by ACMS decarboxylase (ACMSD) for further metabolism and energy production.
Therefore, the inhibition of ACMSD increases NAD+ levels.
In this study, an Food and Drug Administration (FDA)-approved drug,
diflunisal, was found to competitively inhibit ACMSD. The complex
structure of ACMSD with diflunisal revealed a previously unknown ligand-binding
mode and was consistent with the results of inhibition assays, as
well as a structure–activity relationship (SAR) study. Moreover,
two synthesized diflunisal derivatives showed half-maximal inhibitory
concentration (IC50) values 1 order of magnitude better
than diflunisal at 1.32 ± 0.07 μM (22) and
3.10 ± 0.11 μM (20), respectively. The results
suggest that diflunisal derivatives have the potential to modulate
NAD+ levels. The ligand-binding mode revealed here provides
a new direction for developing inhibitors of ACMSD.

在色氨酸降解的犬尿氨酸途径中，不稳定代谢中间产物α-氨基-β-羧基粘康酸-ε-半醛（α-amino-β-carboxymuconate-ε-semialdehyde，ACMS）可经非酶环化反应生成喹啉酸——烟酰胺腺嘌呤二核苷酸（nicotinamide adenine dinucleotide，NAD+）从头生物合成的前体。而在另一竞争性反应中，ACMS可被ACMS脱羧酶（ACMS decarboxylase，ACMSD）催化脱羧，以进入后续代谢通路并产生能量。因此，抑制ACMSD可提升细胞内NAD+水平。本研究发现，经美国食品药品监督管理局（Food and Drug Administration，FDA）批准的药物二氟尼柳（diflunisal）可竞争性抑制ACMSD。ACMSD与二氟尼柳的复合物结构揭示了一种此前未被报道的配体结合模式，该结果与抑制实验及构效关系（structure–activity relationship，SAR）研究的结论相符。此外，两种合成的二氟尼柳衍生物的半最大抑制浓度（half-maximal inhibitory concentration，IC50）分别为1.32±0.07 μM（化合物22）与3.10±0.11 μM（化合物20），其活性较二氟尼柳提升了一个数量级。本研究结果表明，二氟尼柳衍生物具备调控NAD+水平的潜力；本次揭示的配体结合模式也为ACMSD抑制剂的开发提供了全新方向。