Probing the substitution pattern of indole-based scaffold reveals potent and selective sphingosine kinase 2 inhibitors

Eur J Med Chem. 2021 Feb 15:212:113121. doi: 10.1016/j.ejmech.2020.113121. Epub 2020 Dec 29.

Abstract

Elevated levels of sphingosine 1-phosphate (S1P) and increased expression of sphingosine kinase isoforms (SphK1 and SphK2) have been implicated in a variety of disease states including cancer, inflammation, and autoimmunity. Consequently, the S1P signaling axis has become an attractive target for drug discovery. Selective inhibition of either SphK1 or SphK2 has been demonstrated to be effective in modulating S1P levels in animal models. While SphK1 inhibitors have received much attention, the development of potent and selective SphK2 inhibitors are emerging. Previously, our group reported a SphK2 naphthalene-based selective inhibitor, SLC5081308, which displays approximately 7-fold selectivity for hSphK2 over hSphK1 and has a SphK2 Ki value of 1.0 μM. To improve SphK2 potency and selectivity, we designed, synthesized, and evaluated a series of indole-based compounds derived from SLC5081308. After investigating substitution patterns around the indole ring, we discovered that 1,5-disubstitution promoted optimal binding in the SphK2 substrate binding site and subsequent inhibition of enzymatic activity. Our studies led to the identification of SLC5101465 (6r, SphK2 Ki = 90 nM, >110 fold selective for SphK2 over SphK1). Molecular modeling studies revealed key nonpolar interactions with Val308, Phe548, His556, and Cys533 and hydrogen bonds with both Asp211 and Asp308 as responsible for the high SphK2 inhibition and selectivity.

Keywords: Molecular docking; SAR; SphK2; Sphingosine; Sphingosine 1-phosphate; Sphingosine kinase.

MeSH terms

  • Dose-Response Relationship, Drug
  • Enzyme Inhibitors / chemical synthesis
  • Enzyme Inhibitors / chemistry
  • Enzyme Inhibitors / pharmacology*
  • Humans
  • Indoles / chemical synthesis
  • Indoles / chemistry
  • Indoles / pharmacology*
  • Molecular Docking Simulation
  • Molecular Structure
  • Phosphotransferases (Alcohol Group Acceptor) / antagonists & inhibitors*
  • Phosphotransferases (Alcohol Group Acceptor) / metabolism
  • Structure-Activity Relationship

Substances

  • Enzyme Inhibitors
  • Indoles
  • indole
  • Phosphotransferases (Alcohol Group Acceptor)
  • sphingosine kinase 2, human