A highly compartmentalized enzymatic network regulates the pro-apoptotic and proliferative effects of sphingolipids. Over-conversion of ceramide (Cer) correlates with insensitivity to apoptosis signaling (in response to chemotherapy) and to drug resistance of cancer cells. De novo sphingomyelin biosynthesis relies on non-vesicular ceramide trafficking by the CERT (CERamide Transfer) protein. Therefore, blocking CERT transfer, thus leading to increased intracellular ceramide availability, represents a potential anticancer strategy. Our study is based on the implementation of an in vitro binding assay, supported by in silico molecular docking. It constitutes the first attempt to explore at the molecular level for the identification of novel CERT ligands. This approach is the first step toward in silico design and optimization of CERT inhibitor candidates, potentially relevant as innovative ceramide-transfer-targeting therapeutic agents.
The conversion of ceramide into sphingomyelin (SM) was only recently considered in relation to cancer.Overexpression of the CERT protein, responsible for a highly specific inter-organelle ceramide transfer step along the de novo SM synthesis pathway, has been associated with multi-drug resistance of cancer cells.Identification of new CERT antagonists may therefore lead to potential resensitizing agents. This work describes the first attempt to design a ceramide-based fluorescent probe optimised to evaluate the binding of potential CERT ligands. A prototypical structure with an v-labelled sphingosine backbone was selected. Its possible recognition mode by CERT was first evaluated by means of a precursory molecular modelling study. Three derivatives with various amide chain lengths were prepared and tested. The binding efficiency was shown to be proportional to the lipophilicity of the acyl moiety. The best compound bearing a C16 amide fragment was used to implement a practical binding experiment. Facile assessment of the recognition by the CERT START domain of various structures was thus ensured. Metabolism and imaging experiments were also used to illustrate the capacity of the proposed fluorescent ceramide analogue to mimic the natural ceramide cellular behaviour. This work led to the synthesis and evaluation as an efficient CERT START domain ligand of a v-biotinylated ceramide, a potential probe to develop the screening of new CERT antagonists.
Sphingomyelin (SM) metabolism deregulation was recently associated with cell metastasis and chemoresistance, and several pharmacological strategies targeting SM metabolism have emerged. The ceramide (Cer) generated in the endoplasmic reticulum (ER) is transferred to the Golgi apparatus to be transformed into SM. CERamide Transfer (CERT) protein is responsible for the nonvesicular trafficking of Cer to Golgi. Blocking the CERT-mediated ER-to-Golgi Cer transfer is an interesting antioncogenic therapeutic approach. Here, we developed a protein-lipid interaction assay for the identification of new CERT-Cer interaction inhibitors. Frequently used for protein-protein interaction by enzymatic and analyte dosage assays, homogeneous time-resolved fluorescence technology was adapted for the first time to a lipid-protein binding assay. This test was developed for high-throughput screening, and a library of 672 molecules was screened. Seven hits were identified, and their inhibitory effect quantified by EC 50 measurements showed binding inhibition three orders of magnitude more potent than that of HPA12, the unique known CERT antagonist to date. Each compound was tested on an independent test, confirming its high affinity and pharmacological potential.
In 2001, two years before the disclosure of the CERT-associated Cer transfer machinery, N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)alkanamides (HPAs) were described as the first, and to date unique, family of intracellular Cer trafficking inhibitors. The dodecanamide derivative, HPA-12, turned out to be a benchmark as a cellular inhibitor of CERT-mediated de novo sphingomyelin biosynthesis. In only 15 years after its first disclosure, this compound has prompted a growing number of biological and chemical studies. Its initial chemical development closely paralleled the study of the CERT protein. It was only after its structural revision in 2011 that HPA-12 received broad attention from the synthetic chemistry community, leading to novel analogues with enhanced protein binding. This Minireview aims at presenting an exhaustive report of the syntheses of HPA-12 and analogues. Biological activities of this CERT inhibitor and structure-activity relationships are also presented to afford a comprehensive overview of the chemistry and biology of the HPA series.
A series of 12 analogues of the Cer transfer protein (CERT) antagonist HPA-12 with long aliphatic chains were prepared as their (1R,3S)-syn and (1R,3R)-anti stereoisomers from pivotal chiral oxoamino acids. The enantioselective access to these intermediates as well as their ensuing transformation relied on a practical crystallization-induced asymmetric transformation (CIAT) process. Sonogashira coupling followed by triple bond reduction and thiophene ring hydrodesulfurization (HDS) into the corresponding alkane moieties was then implemented to complete the synthetic routes delivering the targeted HPA-12 analogues in concise 4- to 6-step reaction sequences. Ten compounds were evaluated regarding their ability to bind to the CERT START domain by using the recently developed time-resolved FRET-based homogeneous (HTR-FRET) binding assay. The introduction of a lipophilic appendage on the phenyl moiety led to an overall 10- to 1000-fold enhancement of the protein binding, with the highest effect being observed for a n-hexyl residue in the meta position. The importance of the phenyl ring for the activity was indicated by the reduced potency of the 3-deoxyphytoceramide aliphatic analogues. The 1,3-syn stereoisomers were systematically more potent than their 1,3-anti analogues. In silico studies were used to rationalized these trends, leading to a model of protein recognition coherent with the stronger binding of (1R,3S)-syn HPAs.
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