SAFit2

SAFit2 is a potent inhibitor of FK506-binding protein 51 (FKBP51), with the K_i value of 6nM^[1]. SAFit2 can reduce the phosphorylation levels of the inhibitory complex α (IκBα) and p65, as well as decrease the levels of chemokines and cytokines, thereby inhibiting the inflammatory response^[2]. SAFit2 has been widely used as a pharmacological probe for FKBP51 to alleviate pain and regulate neuroinflammation in animals^[3].

In vitro, SAFit2 treatment (60nM) for 4 days reduced PD-L1 expression and inhibited cell growth in mouse glioblastoma (GBM) cells^[4]. Treatment with 1μM SAFit2 for 48 hours can improve the function of isolated mouse β cells and upregulate the mRNA expression levels of Nkx6.1, Mafa, Ins1 and ins2^[5].

In vivo, SAFit2 treatment via intraperitoneal injection twice daily at a dose of 10mg/kg for 6 days restored lipid signaling and metabolism in the neural tissue of mice after nerve injury^[6]. Administering 10mg/kg SAFit2 by intraperitoneal injection twice a day for 6 consecutive days can alleviate mechanical hyperalgesia induced by paclitaxel in mice^[7]. A single intraperitoneal injection of 20mg/kg SAFit2, administered over a period of 4 hours, reduced the anxiety-like behaviors in female rats during the early stage of cocaine self-administration withdrawal^[8].

References:
[1] Gaali S, Feng X, Hähle A, et al. Rapid, structure-based exploration of pipecolic acid amides as novel selective antagonists of the FK506-binding protein 51[J]. Journal of medicinal chemistry, 2016, 59(6): 2410-2422.
[2] Buffa V, Knaup F H, Heymann T, et al. Analysis of the selective antagonist SAFit2 as a chemical probe for the FK506-binding protein 51[J]. ACS Pharmacology & Translational Science, 2023, 6(3): 361-371.
[3] Si Y, Zhao X, Wu L, et al. Inhibition of the NFATc2/FKBP5 axis alleviates microglial neuroinflammation by regulating arachidonic acid metabolism in Parkinson’s disease[J]. Brain, Behavior, and Immunity, 2026: 106296.
[4] D’Arrigo P, Digregorio M, Romano S, et al. The splicing FK506-binding protein-51 isoform plays a role in glioblastoma resistance through programmed cell death ligand-1 expression regulation[J]. Cell Death Discovery, 2019, 5(1): 137.
[5] Liu N, Li R, Cao J, et al. The inhibition of FKBP5 protects β-cell survival under inflammation stress via AKT/FOXO1 signaling[J]. Cell death discovery, 2023, 9(1): 247.
[6] Wedel S, Hahnefeld L, Alnouri M W, et al. The FKBP51 inhibitor SAFit2 restores the pain-relieving C16 dihydroceramide after nerve injury[J]. International journal of molecular sciences, 2022, 23(22): 14274.
[7] Wedel S, Hahnefeld L, Schreiber Y, et al. SAFit2 ameliorates paclitaxel-induced neuropathic pain by reducing spinal gliosis and elevating pro-resolving lipid mediators[J]. Journal of neuroinflammation, 2023, 20(1): 149.
[8] Connelly K L, Wolsh C C, Barr J L, et al. Sex differences in the effect of the FKBP5 inhibitor SAFit2 on anxiety and stress-induced reinstatement following cocaine self-administration[J]. Neurobiology of stress, 2020, 13: 100232.

SAFit2是一种强效的FK506-binding protein 51 (FKBP51)抑制剂，K_i值为6nM^[1]。SAFit2能够降低inhibitory complex α (IκBα)和p65的磷酸化水平，并减少趋化因子和细胞因子的水平，从而抑制炎症反应^[2]。SAFit2已被广泛用作FKBP51的药理学探针，以减轻动物疼痛和调节神经炎症^[3]。

在体外，使用60nM的SAFit2处理小鼠胶质母细胞瘤(GBM)细胞4天，降低了PD-L1的表达并抑制了细胞生长^[4]。使用1μM的SAFit2处理分离的小鼠β细胞48小时，可改善细胞功能，并上调Nkx6.1、Mafa、Ins1和Ins2的mRNA表达水平^[5]。

在体内，每日两次腹腔注射10mg/kg剂量的SAFit2，连续6天，恢复了神经损伤后小鼠神经组织中的脂质信号传导和代谢^[6]。连续6天每日两次腹腔注射10mg/kg的SAFit2，可减轻紫杉醇诱导的小鼠机械性痛觉过敏^[7]。单次腹腔注射20mg/kg的SAFit2，持续4小时，减少了雌性大鼠在可卡因自我给药戒断早期的焦虑样行为^[8]。