AP 18

AP 18 is a potent and selective TRPA1 inhibitor, blocking activation of TRPA1 by 50μM Cinnamaldehyde with an IC₅₀ value of 4.5μM for mouse TRPA1^[1]. AP 18 attenuates 30μM allyl isothiocyanate (AITC)-induced divalent cation Yo-Pro uptake in HEK-293F cells expressing rat TRPA1, with an IC₅₀ value of 10.3μM^[2]. AP 18 targets TRPA-1 to inhibit Ca²⁺ influx mediated by oxidative stress, prevent the Ca²⁺-dependent anti-apoptotic pathway, downregulate the expression of N-cadherin and vimentin, and upregulate the expression of E-cadherin^[3]. AP 18 has been used to inhibit cholinergic twitch responses evoked by electrical field stimulation of cholinergic nerves as well as contractions in response to acetylcholine and histamine in the guinea pig small intestine^[4].

In vitro, AP 18 treatment (100µM) for 48 hours reduced the viability of LU-NB-3 cells and altered the morphology, promoting the cells to transform into flat adherent structures with dendritic protrusions^[5]. Incubation of AP 18 (10µM) and Resveratrol (50µM) for 24h decreased the hypoxia-mediated upregulation of apoptotic (caspase -3, -8, and -9) and oxidative (ROS and lipid peroxidation) concentrations, and mitigated mitochondrial dysfunction in SH-SY5Y cells^[6]. The 12-day treatment with 1µM AP 18 weakened the inhibitory effect of 1µM trans-Pellitorine on lipid accumulation in 3T3-L1 cells and restored the expression levels of the PPARγ gene and protein^[7].

In vivo, AP 18 treatment via intraperitoneal administration at a dose of 3mg/kg 30min before intraplantar lipopolysaccharide (LPS) injection completely prevented development of the LPS-induced hyperalgesia in C57Bl/6 mice^[8]. In CD1 mice, intra-articular injection of AP 18 (25nmol/10µl) at 22 hours after Freund's complete adjuvant (CFA) injection alleviated CFA-induced mechanical hyperalgesia^[9].

References:
[1] Petrus M, Peier A M, Bandell M, et al. A role of TRPA1 in mechanical hyperalgesia is revealed by pharmacological inhibition[J]. Molecular pain, 2007, 3: 1744-8069-3-40.
[2] Chen J, Kim D, Bianchi B R, et al. Pore dilation occurs in TRPA1 but not in TRPM8 channels[J]. Molecular pain, 2009, 5: 1744-8069-5-3.
[3] Wang Y, Yin S, Mei L, et al. A dual receptors-targeting and size-switchable “cluster bomb” co-loading chemotherapeutic and transient receptor potential ankyrin 1 (TRPA-1) inhibitor for treatment of triple negative breast cancer[J]. Journal of Controlled Release, 2020, 321: 71-83.
[4] Bartho L, Sándor Z, Kelemen D, et al. Smooth muscle-depressant activity of AP-18, a putative TRPA1 antagonist in the guinea pig intestine[J]. Pharmacology, 2014, 94(3-4): 131-134.
[5] Seger A, Adamič D, Olmos E M, et al. Evaluation of TRPA1 as a Therapeutic Target in MYCN‐Amplified Neuroblastoma[J]. Pediatric Blood & Cancer, 2025, 72(9): e31875.
[6] Ertilav K. Resveratrol Reduces Hypoxia-Caused Increases of Apoptosis and Oxidative Neurotoxicity via TRPA1 Cation Channel Suppression in Glioblastoma Cells[J]. Online Turkish Journal of Health Sciences, 2025, 10(4): 382-389.
[7] Lieder B, Zaunschirm M, Holik A K, et al. The alkamide trans-pellitorine targets PPARγ via TRPV1 and TRPA1 to reduce lipid accumulation in developing 3T3-L1 adipocytes[J]. Frontiers in pharmacology, 2017, 8: 316.
[8] Andersson D A, Gentry C, Bevan S. TRPA1 has a key role in the somatic pro-nociceptive actions of hydrogen sulfide[J]. PLoS ONE, 2012, 7(10): e46917.
[9] Fernandes E S, Russell F A, Spina D, et al. A distinct role for transient receptor potential ankyrin 1, in addition to transient receptor potential vanilloid 1, in tumor necrosis factor α–induced inflammatory hyperalgesia and Freund's complete adjuvant–induced monarthritis[J]. Arthritis & Rheumatism, 2011, 63(3): 819-829.