Radiprodil, formerly known as RGH-896, is an orally bioavailable and selective NMDA receptors antagonist which was evaluated as potential treatmen of neuropathic pain associated with diabetic peripheral neuropathy (DPNP). Treatment with radiprodil did not show statistically significant or clinically meaningful reductions in mean daily pain scores, the primary endpoint, compared to placebo for any of the dosages studied. Based on preclinical pharmacology Radiprodil was a potential therapeutic agent in treatment of neuropathic pain and possibly other chronic pain conditions.

Physicochemical Properties

Molecular Formula	C21H20FN3O4
Molecular Weight	397.4064
Exact Mass	397.144
Elemental Analysis	C, 63.47; H, 5.07; F, 4.78; N, 10.57; O, 16.10
CAS #	496054-87-6
Related CAS #	496054-87-6; 1204354-40-4 (dihydrate)
PubChem CID	10200813
Appearance	Typically exists as Light yellow to yellow solids at room temperature
LogP	3.103
Hydrogen Bond Donor Count	2
Hydrogen Bond Acceptor Count	5
Rotatable Bond Count	3
Heavy Atom Count	29
Complexity	629
Defined Atom Stereocenter Count	0
InChi Key	GKGRZLGAQZPEHO-UHFFFAOYSA-N
InChi Code	InChI=1S/C21H20FN3O4/c22-15-3-1-13(2-4-15)11-14-7-9-25(10-8-14)20(27)19(26)23-16-5-6-17-18(12-16)29-21(28)24-17/h1-6,12,14H,7-11H2,(H,23,26)(H,24,28)
Chemical Name	2-(4-((4-Fluorophenyl)methyl)piperidin-1-yl)-2-oxo-N-(2-oxo-2,3-dihydro-1,3-benzoxazol-6-yl)acetamide
Synonyms	RGH-896; RGH896; RGH 896; Radiprodil; Radiprodil [INN]; 5XGC17ZKUF; CHEMBL182066; 2-(4-(4-Fluorobenzyl)piperidin-1-yl)-2-oxo-N-(2-oxo-2,3-dihydrobenzo[d]oxazol-6-yl)acetamide; 2-(4-((4-Fluorophenyl)methyl)piperidin-1-yl)-2-oxo-N-(2-oxo-2,3-dihydro-1,3-benzoxazol-6-yl)acetamide;
HS Tariff Code	2934.99.9001
Storage	Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month
Shipping Condition	Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Biological Activity

Targets	NMDA NR2B
ln Vitro	Long-term potentiation (LTP) was restored by preincubation with Radiprodil (10 nM) in the presence of Aβ1-42, 3NTyr10-Aβ, and Aβ1-40, but not in the presence of AβpE3 [2]. The synaptic toxicity of 3NTyr-AβAβ1-40 and Aβ1-42 is reversed for LTP by Radiodil (10 nM), but not for AβpE3-42[2].
ln Vivo	In Mg2+-insensitive versions, radiprodil inhibits NMDA currents with a strength akin to that which is achieved in the absence of Mg2+ [3]. Radiprodil's effectiveness at pH 7.0 was greater than that at pH 7.6, indicating that even in acidic environments like those seen in prolonged epileptic convulsions, Radiprodil may be able to block glutamate-induced NMDA currents [3]. When compared to the drugs tested alone, the drug combination led to a significant increase of motor activity and an improvement of motor disability in MPTP-treated marmosets. In addition, the motor restoration brought about by the combination was almost completely devoid of dyskinesia. Interestingly, treated primates were not overstimulated, but were able to move normally when motivated by the exploration of novel objects.[4] Conclusion: We have demonstrated in a primate model that, the "Radiprodil/Tozadenant" combination significantly improves motor activity, extending previous results obtained in unilaterally lesioned 6-OHDA-rats. The strength of the preclinical data accumulated so far suggests that the use of such an A2A and NR2B antagonist combination could bring significant motor improvement to PD patients, without inducing the motor complications induced by L-Dopa therapy. Although encouraging, these preclinical data need to be confirmed in the clinic.[4]
Enzyme Assay	Aβ1-42 is well accepted to be a primary early pathogenic agent in Alzheimer's disease (AD). However, other amyloid peptides are now gaining considerable attention as potential key participants in AD due to their proposed higher neuronal toxicity. Impairment of the glutamatergic system is also widely accepted to be associated with pathomechanisms underlying AD. There is ample evidence that Aβ1-42 affects GLUN2B subunit containing N-methyl-D-aspartate receptor function and abolishes the induction of long term potentiation (LTP). In this study we show that different β-amyloid species, 1-42 Aβ1-42 and 1-40 (Aβ1-40) as well as post-translationally modified forms such as pyroglutamate-modified amyloid-(AβpE3) and nitrated Aβ (3NTyr10-Aβ), when applied for 90 min to murine hippocampal slices, concentration-dependently prevented the development of CA1-LTP after tetanic stimulation of the Schaffer collaterals with IC50s of 2, 9, 2 and 35 nM, respectively whilst having no effect on baseline AMPA receptor mediated fEPSPs. Aβ1-43 had no effect. Interestingly, the combination of all Aβ species did not result in any synergistic or additive inhibitory effect on LTP - the calculated pooled Aβ species IC50 was 20 nM. A low concentration (10 nM) of the GLUN2B receptor antagonist Radiprodil restored LTP in the presence of Aβ1-42, 3NTyr10-Aβ, Aβ1-40, but not AβpE3. In contrast to AMPA receptor mediated fEPSPs, all different β-amyloid species tested at 50 nM supressed baseline NMDA-EPSC amplitudes. Similarly, all different Aβ species tested decreased spine density. As with LTP, Radiprodil (10 nM) reversed the synaptic toxicity of Aβ species but not that of AβpE3. These data do not support the enhanced toxic actions reported for some Aβ species such as AβpE3, nor synergistic toxicity of the combination of different Aβ species. However, whilst in our hands AβpE3-42 was actually less toxic than Aβ1-42, its effects were not reversed by Radiprodil indicating that the target receptors/subunits mediating such synaptotoxicity may differ between the different Aβ species tested[2].
Animal Protocol	GRIN1/GRIN2B human mRNA was injected with an automated micro-injector using a glass micropipette (5.5 μm diameter, MCS) into the cytoplasm of Xenopus oocytes (stage V–VI) previously dissected and de-folliculated. Oocytes were microinjected with ∼25 nl of mRNA dissolved in RNAse free water (Ambion, Thermo Fisher Scientific, Waltham, MA). Receptors were allowed to express for 3–6 days at 17 °C in a Barth's solution containing (in mM): NaCl (88), KCl (1), NaHCO3 (2.4), Ca(NO3)2 (0.33), CaCl2 (0.41), MgSO4 (0.82), Tris-HCl (5) pH 7.4 and supplemented with penicillin/streptomycin (100 IU/mL). Oocytes were washed every day with Barth's solution containing antibiotics.[3] For expression of GluN1/GluN2B receptors, the solution contained the transcripts coding for the different subunits at a concentration of 0.01 ng/nl. For the dose-response for glutamate experiments, all oocytes were injected with the same quantity of GRIN1/GRIN2B mRNAs (ratio 1:5, 0.25 ng total). However, GluN1/GluN2B (N615I) and GluN1/GluN2B (V618G) variants displayed currents that were smaller than those elicited in GluN1/GluN2B (WT) and in GluN1/GluN2B R540H. Therefore, for subsequent experiments, the mRNA quantity was adjusted (2.5 ng total; 0.1 ng/nl solution, total volume ± 25 nl) for GluN1/GluN2B (N615I) and GluN1/GluN2B (V618G) variants in order to obtain suitable currents.[3] Radiprodil was administered as a solution at a dose volume of 2 mL/kg by oral gavage.The vehicle was composed of 0.1% (w/v) Tween 80, 0.1% (w/v) silicone antifoam 1510 US, 20% (w/v) Kleptose HPB, 1.0% (w/v) methylcellulose in water. Before initiating the Radiprodil & Tozadenant combination experiment, 14 primates were challenged with a dose of 8 mg/kg (po) of L-Dopa and behaviour was recorded for 5 hours. This “Pre-L-Dopa-test” was used to select the 12 subjects required for the study. Their response to the L-Dopa challenge was subsequently used as a comparator to the ensuing response to the different drug treatments and combinations. The effects of the drugs alone or in combination were assessed after acute oral gavage.[4] This experiment investigated the effects on motor deficits of Radiprodil plus Tozadenant twice daily at an interval of 5 hrs according to a modified Latin square design in n = 12 MPTP-treated marmosets (S1 Table). At the time of the second drugs administration a novel object (cotton reel, table tennis ball) was placed into the cage. The four different treatments were (1) Tozadenant (150 mg/kg) plus Radiprodil (2.0 mg/kg), (2) Tozadenant (150 mg/kg) plus vehicle, (3) Radiprodil (2.0 mg/kg) plus vehicle, (4) vehicle.[4]
References	[1]. Mony L, et al. Allosteric modulators of NR2B-containing NMDA receptors: molecular mechanisms and therapeutic potential. Br J Pharmacol. 2009 Aug;157(8):1301-17. [2]. Rammes G, et al. The NMDA receptor antagonist Radiprodil reverses the synaptotoxic effects of different amyloid-beta (Aβ) species on long-term potentiation (LTP). Neuropharmacology. 2018 Sep 15;140:184-192. [3]. Mullier B, et al. GRIN2B gain of function mutations are sensitive to radiprodil, a negative allosteric modulator of GluN2B-containing NMDA receptors. Neuropharmacology. 2017 Sep 1;123:322-331. [4]. Antiparkinsonian effects of the "Radiprodil and Tozadenant" combination in MPTP-treated marmosets. PLoS One. 2017; 12(8): e0182887.
Additional Infomation	Radiprodil has been used in trials studying the treatment of Infantile Spasms (IS) and Diabetic Peripheral Neuropathic Pain.

Solubility Data

Solubility (In Vitro)

DMSO : ~250 mg/mL (~629.09 mM)

Solubility (In Vivo)

Solubility in Formulation 1: ≥ 2.08 mg/mL (5.23 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL. Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution. Solubility in Formulation 2: ≥ 2.08 mg/mL (5.23 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly. Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution. Solubility in Formulation 3: ≥ 2.08 mg/mL (5.23 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.  (Please use freshly prepared in vivo formulations for optimal results.)

Preparing Stock Solutions		1 mg	5 mg	10 mg
	1 mM	2.5163 mL	12.5815 mL	25.1629 mL
	5 mM	0.5033 mL	2.5163 mL	5.0326 mL
	10 mM	0.2516 mL	1.2581 mL	2.5163 mL

*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.