PF-06305591 is a novel, potent and highly selective blocker of voltage gated sodium channel NaV1.8 with an IC50 of 15 nM and with excellent ADME and safety profiles. The voltage gated sodium channel NaV1.8 has been postulated to play a key role in the transmission of pain signals. Core hopping from our previously reported phenylimidazole leads has allowed the identification of a novel series of benzimidazole NaV1.8 blockers. Subsequent optimization allowed the identification of compound 9, PF-06305591, as a potent, highly selective blocker with an excellent preclinical in vitro ADME and safety profile.
Physicochemical Properties
| Molecular Formula | C15H22N4O |
| Molecular Weight | 274.361382961273 |
| Exact Mass | 274.179 |
| CAS # | 1449473-97-5 |
| Related CAS # | PF-06305591 dihydrate;2703582-76-5 |
| PubChem CID | 71666749 |
| Appearance | White to off-white solid powder |
| LogP | 1.5 |
| Hydrogen Bond Donor Count | 3 |
| Hydrogen Bond Acceptor Count | 3 |
| Rotatable Bond Count | 4 |
| Heavy Atom Count | 20 |
| Complexity | 365 |
| Defined Atom Stereocenter Count | 2 |
| SMILES | O=C([C@H](C)[C@@H](C1=NC2=CC=C(C=C2N1)C(C)(C)C)N)N |
| InChi Key | APWZIFIAVVFPNT-PELKAZGASA-N |
| InChi Code | InChI=1S/C15H22N4O/c1-8(13(17)20)12(16)14-18-10-6-5-9(15(2,3)4)7-11(10)19-14/h5-8,12H,16H2,1-4H3,(H2,17,20)(H,18,19)/t8-,12+/m1/s1 |
| Chemical Name | (2R,3S)-3-amino-3-(6-tert-butyl-1H-benzimidazol-2-yl)-2-methylpropanamide |
| Synonyms | PF-06305591; PF 06305591; PF06305591 |
| 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 |
Human Voltage-Gated Sodium Channel 1.8 (hNaV1.8) (IC50 = 15 ± 2 nM). [1] Other human NaV isoforms (hNaV1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7) (IC50 > 30 µM). [1] |
| ln Vitro |
PF-06305591 (compound 9) has favorable attributes such as passive permeability, hERG activity, NaV selectivity, and in vitro metabolic stability [1]. PF-06305591 potently inhibits hNaV1.8 with an IC50 of 15 ± 2 nM. [1] It shows exquisite selectivity (>2000-fold) over other human NaV isoforms (hNaV1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7), with IC50 values >30 µM for each. [1] PF-06305591 shows no significant activity (IC50 >30 µM) against a panel of other ion channels including: KVLQT1 (KCNQ1, KV7.1), KV1.5, KV1.1/1.2, SK2 (KCNN2), T-type and L-type calcium channels, and GABA-A (α1β2). [1] PF-06305591 exhibits no significant inhibition of the hERG potassium channel (IC50 >30 µM). [1] Wide ligand profiling (CEREP™ panel) at 10 µM showed no significant off-target activity (<20% activity). [1] PF-06305591 displays excellent passive permeability (Papp AB = 3.5 x 10^-6 cm/sec in RRCK cell line). [1] PF-06305591 exhibits low in vitro metabolic clearance in human liver microsomes (HLM < 11 µL/min/mg protein) and human hepatocytes (hHep < 2 µL/min/million cells). [1] PF-06305591 has good solubility (2 mg/mL at pH 7.4). [1] |
| ln Vivo | PF-06305591 (compound 9) exhibits high bioavailability in rats. PF-06305591 offers the option to explore higher fold IC50 of Nav1.8 blockage in the clinic, allowing for a more full assessment of the role of NaV1.8 in pain therapy [1]. |
| Animal Protocol |
Rat Pharmacokinetic Study: Rats were administered PF-06305591 intravenously (i.v.) at a dose of 1 mg/kg and orally (p.o.) at a dose of 3 mg/kg. [1] |
| ADME/Pharmacokinetics |
In rats, after a 1 mg/kg intravenous dose, PF-06305591 had a plasma clearance (Clp) of 39 mL/min/kg, a volume of distribution at steady state (Vss) of 2.7 L/kg, and a terminal half-life (T1/2) of 1.5 hours. [1] After a 3 mg/kg oral dose in rats, PF-06305591 showed an oral bioavailability (F) of 49%. [1] |
| Toxicity/Toxicokinetics |
PF-06305591 showed no significant inhibition of the hERG potassium channel (IC50 >30 µM) in vitro, suggesting a low potential for cardiac arrhythmia via this mechanism. [1] |
| References |
[1]. The discovery and optimization of benzimidazoles as selective NaV1.8 blockers for the treatment of pain. Bioorg Med Chem. 2019 Jan 1;27(1):230-239. |
| Additional Infomation |
Pf 06305591 is under investigation in clinical trial NCT01776619 (Safety and Tolerability Study of Multiple Doses of PF-06305591). PF-06305591 is a benzimidazole-based, potent, and highly selective small-molecule blocker of the NaV1.8 sodium channel. [1] It was identified as a backup clinical candidate to the previously reported PF-04531083. [1] Its development aimed to investigate higher multiples of NaV1.8 blockade IC50 in the clinic due to its enhanced solubility profile compared to PF-04531083. [1] The molecular weight is 274, calculated logP (clogP) is 1.5, measured LogD is 2.1, topological polar surface area (TPSA) is 98, and the pKa is 5.9. [1] The ligand efficiency (LipE) value is 6.3. [1] A multi-gram synthesis route was developed for further profiling. [1] |
Solubility Data
| Solubility (In Vitro) | DMSO : ~140 mg/mL (~510.28 mM) |
| Solubility (In Vivo) |
Solubility in Formulation 1: ≥ 2.5 mg/mL (9.11 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 25.0 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: ≥ 2.5 mg/mL (9.11 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 25.0 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: ≥ 2.5 mg/mL (9.11 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 25.0 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 | 3.6448 mL | 18.2242 mL | 36.4485 mL | |
| 5 mM | 0.7290 mL | 3.6448 mL | 7.2897 mL | |
| 10 mM | 0.3645 mL | 1.8224 mL | 3.6448 mL |