Salt inducible kinases 2 and 3 are required for thymic T cell development

Discovery of Clinical Candidate GLPG3970: A Potent and Selective Dual SIK2/SIK3 Inhibitor for the Treatment of Autoimmune and Inflammatory Diseases

The salt-inducible kinases (SIKs) SIK1, SIK2, and SIK3 belong to the adenosine monophosphate-activated protein kinase (AMPK) family of serine/threonine kinases. SIK inhibition represents a new therapeutic approach modulating pro-inflammatory and immunoregulatory pathways that holds potential for the treatment of inflammatory diseases. Here, we describe the identification of GLPG3970 (32), a first-in-class dual SIK2/SIK3 inhibitor with selectivity against SIK1 (IC50 of 282.8 nM on SIK1, 7.8 nM on SIK2 and 3.8 nM on SIK3). We outline efforts made to increase selectivity against SIK1 and improve CYP time-dependent inhibition properties through the structure-activity relationship. The dual activity of 32 in modulating the pro-inflammatory cytokine TNFα and the immunoregulatory cytokine IL-10 is demonstrated in vitro in human primary myeloid cells and human whole blood, and in vivo in mice stimulated with lipopolysaccharide. Compound 32 shows dose-dependent activity in disease-relevant mouse pharmacological models.

Identification of highly selective SIK1/2 inhibitors that modulate innate immune activation and suppress intestinal inflammation

The salt-inducible kinases (SIK) 1-3 are key regulators of pro- versus anti-inflammatory cytokine responses during innate immune activation. The lack of highly SIK-family or SIK isoform-selective inhibitors suitable for repeat, oral dosing has limited the study of the optimal SIK isoform selectivity profile for suppressing inflammation in vivo. To overcome this challenge, we devised a structure-based design strategy for developing potent SIK inhibitors that are highly selective against other kinases by engaging two differentiating features of the SIK catalytic site. This effort resulted in SIK1/2-selective probes that inhibit key intracellular proximal signaling events including reducing phosphorylation of the SIK substrate cAMP response element binding protein (CREB) regulated transcription coactivator 3 (CRTC3) as detected with an internally generated phospho-Ser329-CRTC3-specific antibody. These inhibitors also suppress production of pro-inflammatory cytokines while inducing anti-inflammatory interleukin-10 in activated human and murine myeloid cells and in mice following a lipopolysaccharide challenge. Oral dosing of these compounds ameliorates disease in a murine colitis model. These findings define an approach to generate highly selective SIK1/2 inhibitors and establish that targeting these isoforms may be a useful strategy to suppress pathological inflammation.

SIKs Regulate HDAC7 Stabilization and Cytokine Recall in Late-Stage T Cell Effector Differentiation

Understanding the mechanisms underlying the acquisition and maintenance of effector function during T cell differentiation is important to unraveling how these processes can be dysregulated in the context of disease and manipulated for therapeutic intervention. In this study, we report the identification of a previously unappreciated regulator of murine T cell differentiation through the evaluation of a previously unreported activity of the kinase inhibitor, BioE-1197. Specifically, we demonstrate that liver kinase B1 (LKB1)-mediated activation of salt-inducible kinases epigenetically regulates cytokine recall potential in effector CD8+ and Th1 cells. Evaluation of this phenotype revealed that salt-inducible kinase-mediated phosphorylation-dependent stabilization of histone deacetylase 7 (HDAC7) occurred during late-stage effector differentiation. HDAC7 stabilization increased nuclear HDAC7 levels, which correlated with total and cytokine loci-specific reductions in the activating transcription mark histone 3 lysine 27 acetylation (H3K27Ac). Accordingly, HDAC7 stabilization diminished transcriptional induction of cytokine genes upon restimulation. Inhibition of this pathway during differentiation produced effector T cells epigenetically poised for enhanced cytokine recall. This work identifies a previously unrecognized target for enhancing effector T cell functionality.

Roles of salt‑inducible kinases in cancer (Review)

Salt inducible kinases (SIKs) with three subtypes SIK1, SIK2 and SIK3, belong to the AMP‑activated protein kinase family. They are expressed ubiquitously in humans. Under normal circumstances, SIK1 regulates adrenocortical function in response to high salt or adrenocorticotropic hormone stimulation, SIK2 is involved in cell metabolism, controlling insulin signaling and gluconeogenesis and SIK3 coordinates with the mTOR complex, promoting cancer. The dysregulation of SIKs has been widely detected in various types of cancers. Based on most of the existing studies, SIK1 is mostly considered a tumor inhibitor, SIK2 and SIK3 are usually associated with tumor promotion. However, the functions of SIKs have shown contradictory in certain tumors, suggesting that SIKs cannot be simply classified as oncogenes or tumor suppressor genes. The present review provided a comprehensive summary of the roles of SIKs in the initiation and progression of different cancers, aiming to elucidate their clinical value and discuss potential strategies for targeting SIKs in cancer therapy.

Deficiency of salt-inducible kinase 2 (SIK2) promotes immune injury by inhibiting the maturation of lymphocytes

Salt-inducible kinase 2 (SIK2) belongs to the serine/threonine protein kinases of the AMPK/SNF1 family, which has important roles in cell cycle, tumor, melanogenesis, neuronal damage repair and apoptosis. Recent studies showed that SIK2 regulates the macrophage polarization to make a balance between inflammation and macrophage. Macrophage is critical to initiate immune regulation, however, whether SIK2 can be involved in immune regulation is not still well understood. Here, we revealed that the protein of SIK2 was highly expressed in thymus, spleen, lung, and brain. And SIK2 protein content increased in RAW264.7 and AHH1 cells with a time and dose-dependent after-ionizing radiation (IR). Inhibition of SIK2 could promote AHH1 cells apoptosis Moreover, we used the Cre-LoxP system to construct the SIK2+/- mice, and the research on function suggested that the deficiency of SIK2 could promote the sensitivity of IR. The deficiency of SIK2 promoted the immune injury via inhibiting the maturation of T cells and B cells. Furthermore, the TCRβ rearrangement was inhibited by the deficiency of SIK2. Collectively, this study demonstrated that SIK2 provides an essential function of regulating immune injury, which will provide new ideas for the treatment of immune injury-related diseases.

Discovery of novel and selective SIK2 inhibitors by the application of AlphaFold structures and generative models

Salt-inducible kinase 2 (SIK2) has been recognized as a potential target for anti-inflammation and anti-cancer therapy. In this paper, based on the binding pose of the reported compound (GLPG-3970, 3) with AlphaFold protein structure, a series of hinge cores were generated via AI-generative models (Chemistry42). After the molecular docking, synthesis, and biological evaluation, a hit molecule (7f) targeting SIK2 was obtained with a novel scaffold. Further SAR exploration led to the discovery of compound 8g with superior potency against SIK2 compared with the reported inhibitors. Furthermore, 8g also demonstrated excellent selectivity over other AMPK kinases, favorable in vitro ADMET profiles and decent cellular activities. This work provides an alternative approach to the discovery of novel and selective kinase inhibitors.

Discovery of pyrimidine-5-carboxamide derivatives as novel salt-inducible kinases (SIKs) inhibitors for inflammatory bowel disease (IBD) treatment

Salt-inducible kinases (SIKs) play a crucial role in inflammation process, acting as molecular switches that regulate the transformation of M1/M2 macrophages. HG-9-91-01 is a SIKs inhibitor with potent inhibitory activity against SIKs in the nanomolar range. However, its poor drug-like properties, including a rapid elimination rate, low in vivo exposure and high plasma protein binding rate, have hindered further research and clinical application. To improve the drug-like properties of HG-9-91-01, a series of pyrimidine-5-carboxamide derivatives were designed and synthesized through a molecular hybridization strategy. The most promising compound 8h was obtained with favorable activity and selectivity on SIK1/2, excellent metabolic stability in human liver microsome, enhanced in vivo exposure and suitable plasma protein binding rate. Mechanism research showed that compound 8h significantly up-regulated the expression of anti-inflammatory cytokine IL-10 and reduced the expression of pro-inflammatory cytokine IL-12 in bone marrow-derived macrophages. Furthermore, it significantly elevated expression of cAMP response element-binding protein (CREB) target genes IL-10, c-FOS and Nurr77. Compound 8h also induced the translocation of CREB-regulated transcriptional coactivator 3 (CRTC3) and elevated the expression of LIGHT, SPHK1 and Arginase 1. Additionally, compound 8h demonstrated excellent anti-inflammatory effects in a DSS-induced colitis model. Generally, this research indicated that compound 8h has the potential to be developed as an anti-inflammatory drug candidate.

Salt-inducible kinase 2 regulates fibrosis during bleomycin-induced lung injury

Idiopathic pulmonary fibrosis is a progressive and normally fatal disease with limited treatment options. The tyrosine kinase inhibitor nintedanib has recently been approved for the treatment of idiopathic pulmonary fibrosis, and its effectiveness has been linked to its ability to inhibit a number of receptor tyrosine kinases including the platelet-derived growth factor, vascular endothelial growth factor, and fibroblast growth factor receptors. We show here that nintedanib also inhibits salt-inducible kinase 2 (SIK2), with a similar IC50 to its reported tyrosine kinase targets. Nintedanib also inhibited the related kinases SIK1 and SIK3, although with 12-fold and 72-fold higher IC50s, respectively. To investigate if the inhibition of SIK2 may contribute to the effectiveness of nintedanib in treating lung fibrosis, mice with kinase-inactive knockin mutations were tested using a model of bleomycin-induced lung fibrosis. We found that loss of SIK2 activity protects against bleomycin-induced fibrosis, as judged by collagen deposition and histological scoring. Loss of both SIK1 and SIK2 activity had a similar effect to loss of SIK2 activity. Total SIK3 knockout mice have a developmental phenotype making them unsuitable for analysis in this model; however, we determined that conditional knockout of SIK3 in the immune system did not affect bleomycin-induced lung fibrosis. Together, these results suggest that SIK2 is a potential drug target for the treatment of lung fibrosis.