Investigating the binding mechanism of sphingosine kinase 1/2 inhibitors: Insights into subtype selectivity by homology modeling, molecular dynamics simulation and free energy calculation studies

Sphingosine kinase 2 in cancer: A review of its expression, function, and inhibitor development

Cancer is a major public health problem facing contemporary society. Notwithstanding considerable progress in medicine in recent decades, a cure for numerous cancer kinds continues to be unattainable. Thus, the pursuit of innovative therapeutic targets and methodologies remains paramount in medical research. The advancement of lipidomics has progressively revealed the essential roles of lipid metabolic pathways. Sphingosine kinase (SphK) and sphingosine-1-phosphate (S1P) are essential molecules in sphingolipid metabolism, significantly influencing physiological functions. Two isoforms of SphK exist including SphK1 and SphK2, both of which exhibit significant expression levels within a spectrum of cancers. The involvement of SphK1 in carcinogenesis has been thoroughly documented, whereas the significance of SphK2 in cancer remains inadequately elucidated. This review retrospectively and extensively elucidates the expression and distribution of SphK2 in cancer, its methods of action, and advancements in inhibitor research, emphasizing the varied functions of the SphK2 in oncogenesis. The objective is to furnish novel insights for study and therapeutic applications concerning SphK2 in oncology.

Discovery and biological evaluation of biaryl acetamide derivatives as selective and in vivo active sphingosine kinase-2 inhibitors

Sphingosine kinase 2 (SphK2) has emerged as a promising target for cancer therapy due to its critical role in tumor growth. However, the lack of potent and selective inhibitors has hindered its clinical application. Herein, we report the design and synthesis of a series of novel SphK2 inhibitors, culminating in the identification of compound 12q as a highly selective and potent inhibitor of SphK2. Molecular dynamics simulations suggest that the incorporation of larger substitution groups facilitates a more effective occupation of the binding site, thereby stabilizing the complex. Compared to the widely used inhibitor ABC294640, compound 12q exhibits superior anti-proliferative activity against various cancer cells, inducing G2 phase arrest and apoptosis in liver cancer cells HepG2. Notably, 12q inhibited migration and colony formation in HepG2 and altered intracellular sphingolipid content. Moreover, intraperitoneal administration of 12q in mice resulted in decreased levels of S1P. 12q provides a valuable tool compound for exploring the therapeutic potential of targeting SphK2 in cancer.

Second generation of pyrimidin-quinolone hybrids obtained from virtual screening acting as sphingosine kinase 1 inhibitors and potential anticancer agents

We report here the virtual screening design, synthesis and activity of eight new inhibitors of SphK1. For this study we used a pre-trained Graph Convolutional Network (GCN) combined with docking calculations. This exploratory analysis proposed nine compounds from which eight displayed significant inhibitory effect against sphingosine kinase 1 (SphK1) demonstrating a high level of efficacy for this approach. Four of these compounds also displayed anticancer activity against different tumor cell lines, and three of them (5), (6) and (7) have shown a wide inhibitory action against many of the cancer cell line tested, with GI50 below 5 µM, being (5) the most promising with TGI below 10 µM for the half of cell lines. Our results suggest that the three most promising compounds reported here are the pyrimidine-quinolone hybrids (1) and (6) linked by p-aminophenylsulfanyl and o-aminophenol fragments respectively, and (8) without such aryl linker. We also performed an exhaustive study about the molecular interactions that stabilize the different ligands at the binding site of SphK1. This molecular modeling analysis was carried out by using combined techniques: docking calculations, MD simulations and QTAIM analysis. In this study we also included PF543, as reference compound, in order to better understand the molecular behavior of these ligands at the binding site of SphK1.These results provide useful information for the design of new inhibitors of SphK1 possessing these structural scaffolds.

Design, synthesis, antitumor activity, and molecular dynamics simulations of novel sphingosine kinase 2 inhibitors

Targeting sphingosine kinase 2 (SphK2) has become a novel strategy for the treatment of cancer. However, potent and selective SphK2 inhibitors are rare. In our work, a series of novel SphK2 inhibitors were innovatively designed, synthesized and screened. Compound 12e showed the best inhibitory activity. Molecular dynamics simulations were carried out to analyze the detailed interactions between the SphK2 and its inhibitors. Moreover, 12e exhibited anti-proliferative activity in various cancer cells, and inhibited the migration of human breast cancer cells MCF-7.

Structure-based virtual screening and molecular dynamics simulation for the identification of sphingosine kinase-2 inhibitors as potential analgesics

Neuropathic pain is due to an injury or disease of the somatosensory nervous system, which accounts for a significant economical and health burden to society. Due to poor understanding of their underlying mechanisms, the available treatments merely provide symptomatic relief and precipitates a variety of adverse effects. This suggests that there is an unmet medical need that must be addressed with effective strategies for the development of novel therapeutics. Sphingosine kinase 2 (SphK2) is an oncogenic lipid kinase that has emerged as a promising target for chronic pain and other diseases. In the present study, we have explored the structure-based virtual high-throughput screening of the Nuclei of Bioassays, Ecophysiology, and Biosynthesis of Natural Products Database (NuBBE) to identify potent natural products as inhibitors of SphK2. A molecular docking study was performed to calculate binding affinities and specificity to identify potential leads against SphK2. Initially, hits were selected by the implementation of absorption, distribution, metabolism, excretion and toxicity properties, Lipinski rule, and PAINS filters. The top-scoring hits also exhibiting an optimal ADMET profile were subjected to MM/GBSA free binding free energy calculation and molecular dynamics simulation. The results from molecular dynamics simulation revealed a stable ligand -SphK2 complex with protein and ligand RMSD within reasonable limits. Overall, we identified compounds, NuBBE_972 and NuBBE_1107 as potential inhibitors of SphK2 with optimal pharmacokinetic properties which have the potential to be developed as novel therapeutics for the management of chronic pain.Communicated by Ramaswamy H. Sarma.

Discovery of an SphK1 inhibitor: A hybrid approach involving a receptor–ligand-complex-based pharmacophore and docking-based virtual screening

Sphingosine kinase is a lipid kinase that catalyzes the phosphorylation of sphingosine to sphingosine-1-phosphate. Sphingosine-1-phosphate is a bioactive lipid that regulates biological processes. The overexpression of sphingosine kinases is related to a variety of pathophysiological conditions. For example, SphK1 has been shown to be highly expressed in various cancer cells including ovarian, cervical, colon, stomach, lung, and brain cancer. Inhibition of sphingosine kinases is a promising way to treat diseases such as cancer. Through computer-aided drug design, we have discovered a new SphK1 inhibitor named Amb30572637 (SAMS10). In this report, we describe the discovery process and biological characteristics. In biochemical experiments, SAMS10 shows a prominent inhibitory effect on SphK1, with an IC50 value of 9.8 μM. Subsequent MTT experiments show that SAMS10 has anticancer effects toward A549, SKVO3, A375, and LOVO cell lines and has essentially no cytotoxicity against the healthy cell L929. SAMS10 has significant inhibitory activity against the A549 and LOVO cell lines, with IC50 values of 14.64 and 14.48 μM, respectively. It belongs to a moderately active SphK1 inhibitor with lower anticancer activity than the control compound cisplatin, but the effect of SAMS10 toward SphK1 and its anticancer activity indicate that it is a promising lead compound for the development of effective SphK1 anticancer inhibitors.

A Benchmark Dataset for Evaluating Practical Performance of Model Quality Assessment of Homology Models

Protein structure prediction is an important issue in structural bioinformatics. In this process, model quality assessment (MQA), which estimates the accuracy of the predicted structure, is also practically important. Currently, the most commonly used dataset to evaluate the performance of MQA is the critical assessment of the protein structure prediction (CASP) dataset. However, the CASP dataset does not contain enough targets with high-quality models, and thus cannot sufficiently evaluate the MQA performance in practical use. Additionally, most application studies employ homology modeling because of its reliability. However, the CASP dataset includes models generated by de novo methods, which may lead to the mis-estimation of MQA performance. In this study, we created new benchmark datasets, named a homology models dataset for model quality assessment (HMDM), that contain targets with high-quality models derived using homology modeling. We then benchmarked the performance of the MQA methods using the new datasets and compared their performance to that of the classical selection based on the sequence identity of the template proteins. The results showed that model selection by the latest MQA methods using deep learning is better than selection by template sequence identity and classical statistical potentials. Using HMDM, it is possible to verify the MQA performance for high-accuracy homology models.

E484K mutation in SARS-CoV-2 RBD enhances binding affinity with hACE2 but reduces interactions with neutralizing antibodies and nanobodies: Binding free energy calculation studies

The pandemic of the COVID-19 disease caused by SARS-CoV-2 has led to more than 200 million infections and over 4 million deaths worldwide. The progress in the developments of effective vaccines and neutralizing antibody therapeutics brings hopes to eliminate the threat of COVID-19. However, SARS-CoV-2 continues to mutate, and several new variants have been emerged. Among the various naturally-occurring mutations, the E484K mutation shared by many variants attracted serious concerns, which may potentially enhance the receptor binding affinity and reduce the immune response. In the present study, the molecular mechanism behind the impacts of E484K mutation on the binding affinity of the receptor-binding domain (RBD) with the receptor human angiotensin-converting enzyme 2 (hACE2) was investigated by using the molecular dynamics (MD) simulations combined with the molecular mechanics-generalized Born surface area (MMGBSA) method. Our results indicate that the E484K mutation results in more favorable electrostatic interactions compensating the burial of the charged and polar groups upon the binding of RBD with hACE2, which significantly improves the RBD-hACE2 binding affinity. Besides that, the E484K mutation also causes the conformational rearrangements of the loop region containing the mutant residue, which leads to tighter binding interface of RBD with hACE2 and formation of some new hydrogen bonds. The tighter binding interface and the new hydrogen bonds formation also contribute to the improved binding affinity of RBD to the receptor hACE2. In addition, six neutralizing antibodies and nanobodies complexed with RBD were selected to explore the effects of E484K mutation on the recognition of these antibodies to RBD. The simulation results show that the E484K mutation significantly reduces the binding affinities to RBD for most of the studied neutralizing antibodies/nanobodies, and the decrease in the binding affinities is mainly owing to the unfavorable electrostatic interactions caused by the mutation. Our studies revealed that the E484K mutation may improve the binding affinity between RBD and the receptor hACE2, implying more transmissibility of the E484K-containing variants, and weaken the binding affinities between RBD and the studied neutralizing antibodies/nanobodies, indicating reduced effectiveness of these antibodies/nanobodies. Our results provide valuable information for the effective vaccine development and antibody/nanobody drug design.

Rational design of SphK inhibitors using crystal structures aided by computer

Sphingosine kinases (SphKs) are lipid kinases that catalyze the phosphorylation of sphingosine (Sph) to sphingosine-1-phosphate (S1P). As a bioactive lipid, S1P plays a role outside and inside the cell to regulate biological processes. The overexpression of SphKs is related to a variety of pathophysiological conditions. Targeting the S1P signaling pathway is a potential treatment strategy for many diseases. SphKs are key kinases of the S1P signaling pathway. The SphK family includes two isoforms: SphK1 and SphK2. Determination of the co-crystal structure of SphK1 with various inhibitors has laid a solid foundation for the development of small molecule inhibitors targeting SphKs. This paper reviews the differences and connections between the two isoforms and the structure of SphK1 crystals, especially the structure of its Sph "J-shaped" channel binding site. This review also summarizes the recent development of SphK1 and SphK2 selective inhibitors and the exploration of the unresolved SphK2 structure.