Development of Novel Quinoxaline-Based κ-Opioid Receptor Agonists for the Treatment of Neuroinflammation

Abstract

Neuroinflammatory disorders, such as multiple sclerosis or experimental autoimmune encephalomyelitis (EAE), an established mouse model mimicking part of the human pathology, are characterized by inflammatory infiltrates containing T helper 1 (TH1) and TH17 cells, which cause demyelination and neurodegeneration. Disease onset and perpetuation are mediated by peripherally generated autoreactive T cells infiltrating into the central nervous system, where they are restimulated by antigen-presenting cells. Here, we show that newly designed peripherally active, potent, and selective κ-opioid receptor (KOR) agonists comprising the ethylenediamine KOR pharmacophore in a perhydroquinoxaline scaffold exhibit potent anti-inflammatory capacities in primary antigen presenting cells as well as T cells. In the EAE model, the secondary amine 12 and the triazole 14 were able to ameliorate disease severity and to delay disease onset by blocking effector T cell activation. Importantly, the beneficial effects were mediated via signaling through KOR because off-target effects were excluded by using KOR-deficient mouse mutants.

Synthesis and Pharmacological Evaluation of Fluorinated Quinoxaline‐Based κ‐Opioid Receptor (KOR) Agonists Designed for PET Studies

“…[12] Very recently, we showed that KOR agonists 1b (R=H) and 2 exhibit potent anti-inflammatory and immunomodulatory activity in primary mouse and human immune cells. Moreover, both KOR agonists led to almost complete protection of mice from developing MS-like symptoms in the MOG induced EAE [13] (Figure 1).…”

“…For the synthesis of hydroxy and fluoro substituted KOR agonists of type 3, the synthetic route previously reported by us to obtain cis,trans-configured perhydroquinoxalines was pursued. [13,33,34] At first, the cyclic sulfuric acid ester amide 10 was prepared in seven steps starting from tetrahydroquinoxaline 9. [13] Nucleophilic ring opening of 10 by (S)-3-hydroxypyrrolidine led to secondary amine 11, which was acylated with 2-(3,4-dichlorophenyl)acetyl chloride to afford the amide 12a.…”

“…[13,33,34] At first, the cyclic sulfuric acid ester amide 10 was prepared in seven steps starting from tetrahydroquinoxaline 9. [13] Nucleophilic ring opening of 10 by (S)-3-hydroxypyrrolidine led to secondary amine 11, which was acylated with 2-(3,4-dichlorophenyl)acetyl chloride to afford the amide 12a. Removal of the Boc-protective group with trifluoroacetic acid (TFA) provided the secondary amine 12b (Scheme 1).…”

“…In line with this, 2 significantly decreased diseases severity and delayed disease onset in a mouse model of experimental autoimmune encephalomyelitis, which was associated with downregulated numbers of effector T cells and upregulated levels of regulatory T cells in 2 treated mice compared to controls. [13] Having confirmed the anti-inflammatory and immunomodulatory properties of cis,trans-perhydroquinoxaline-based KOR agonists in general, we now intended to characterize more polar substances belonging to this class of compounds. For this purpose, we treated primary mouse or human T cells and dendritic cells (DCs) with 12b, 12c, 14b and 14c after the cells had been activated with phorbol 12-myristate 13-acetate (PMA) in combination with ionomycin (PMA/Iono) to assess the antiinflammatory properties of the compounds.…”

“…[5][6][7][8][9][10] Recent studies showed the central role of KOR in the pathogenesis of multiple sclerosis (MS), an inflammatory neurodegenerative disease. [11][12][13] A decreased level of KOR mRNA was found in Theiler's encephalomyelitis mouse model mimicking parts of the MS pathology. [11] In the myelin oligodendrocyte glycoprotein (MOG) induced experimental autoimmune encephalomyelitis (EAE) mouse model of MS activation of KOR was able to prevent neuronal damage and promote remyelination.…”