Discovery and Structure–Activity Relationship (SAR) of a Series of Ethanolamine-Based Direct-Acting Agonists of Sphingosine-1-phosphate (S1P1)

Rational Design, Synthesis, and Biological Evaluation of Novel S1PR2 Antagonists for Reversing 5-FU-Resistance in Colorectal Cancer

Resistance to 5-FU reduces its clinical efficacy for the treatment of colorectal cancer. Sphingosine-1-phosphate receptor 2 (S1PR2) has emerged as a potential target to reverse 5-FU-resistance by inhibiting the expression of dihydropyrimidine dehydrogenase (DPD). In this study, 38 novel S1PR2 antagonists based on aryl urea structure were designed and synthesized, and the structure-activity relationship was investigated based on the S1PR2 binding assay. Representative compound 43 potently interacts with S1PR2 with a K_D value of 0.73 nM. It displays potent 5-FU resensitizing activity in multiple 5-FU-resistant tumor cell lines, particularly in SW620/5-FU (EC₅₀ = 1.99 ± 0.03 μM) but shows no cytotoxicity in the normal colon cell line NCM460 up to 1000 μM. Moreover, 43 significantly enhances the antitumor efficacy of 5-FU in the SW620/5-FU animal model. These data suggest that 43 could be a novel lead compound for developing a 5-FU resensitizing agent.

Syntheses and in vitro biological evaluation of S1PR1 ligands and PET studies of four F-18 labeled radiotracers in the brain of nonhuman primates

A series of seventeen hydroxyl-containing sphingosine 1-phosphate receptor 1 (S1PR1) ligands were designed and synthesized. Their in vitro binding potencies were determined using [32P]S1P competitive binding assays. Compounds 10a, 17a, 17b, and 24 exhibited high S1PR1 binding potencies with IC50 values ranging from 3.9 to 15.4 nM and also displayed high selectivity for S1PR1 over other S1P receptor subtypes (IC50 > 1000 nM for S1PR2-5). The most potent compounds 10a, 17a, 17b, and 24 were subsequently radiolabeled with F-18 in high yields and purities. MicroPET studies in cynomolgus macaque showed that [18F]10a, [18F]17a, and [18F]17b but not [18F]24 crossed the blood brain barrier and had high initial brain uptake. Further validation of [18F]10a, [18F]17a, and [18F]17b in preclinical models of neuroinflammation is warranted to identify a suitable PET radioligand to quantify S1PR1 expression in vivo as a metric of an inflammatory response.

Syntheses and in vitro evaluation of new S1PR1 compounds and initial evaluation of a lead F-18 radiotracer in rodents

Thirteen new sphingosine-1-phosphate receptor 1 (S1PR1) ligands were designed and synthesized by replacing azetidine-3-carboxylic acid moiety of compound 4 with new polar groups. The in vitro binding potency of these new analogs toward S1PR1 was determined. Out of 13 new compounds, four compounds 9a, 10c, 12b, and 16b displayed high S1PR1 binding potency with IC₅₀ values of 13.2 ± 3.2, 14.7 ± 1.7, 9.7 ± 1.6, and 6.3 ± 1.3 nM, respectively; further binding studies of these four ligands toward S1PR2-5 suggested they are highly selective for S1PR1 over other S1PRs. The radiosynthesis of the lead radiotracer [¹⁸F]12b was achieved with good radiochemical yield (∼14.1%), high radiochemical purity (>98%), and good specific activity (∼54.1 GBq/μmol, decay corrected to the end of synthesis, EOS). Ex vivo autoradiography and initial biodistribution studies in rodents were performed, suggesting that [¹⁸F]12b was able to penetrate the blood-brain barrier (BBB) with high brain uptake (0.71% ID/g at 60 min post-injection) and no defluorination was observed. In vitro autoradiography study in brain slices of lipopolysaccharides (LPS)-induced neuroinflammation mice indicated that SEW2871, a specific S1PR1 ligand was able to reduce the uptake of [¹⁸F]12b, suggesting [¹⁸F]12b has S1PR1 specific binding. These initial results suggested that [¹⁸F]12b has potential to be an F-18 labeled radiotracer for imaging S1PR1 in the brain of the animal in vivo.

Modulators of Sphingosine-1-phosphate Pathway Biology: Recent Advances of Sphingosine-1-phosphate Receptor 1 (S1P1) Agonists and Future Perspectives

The sphingoid base derived class of lipids (sphingolipids) is a family of interconverting molecules that play key roles in numerous structural and signaling processes. The biosynthetic pathway of the sphingolipids affords many opportunities for therapeutic intervention: targeting the ligands directly, targeting the various proteins involved in the interconversion of the ligands, or targeting the receptors that respond to the ligands. The focus of this article is on the most advanced of the sphingosine-related therapeutics, agonists of sphingosine-1-phosphate receptor 1 (S1P₁). The diverse structural classes of S1P₁ agonists will be discussed and the status of compounds of clinical relevance will be detailed. An examination of how potential safety concerns are being navigated with compounds currently under clinical evaluation is followed by a discussion of the novel methods being explored to identify next-generation S1P₁ agonists with improved safety profiles. Finally, therapeutic opportunities for sphingosine-related targets outside of S1P₁ are touched upon.