Improved synthesis of a fluorogenic ceramidase substrate

The emergence of acid ceramidase as a therapeutic target for acute myeloid leukemia

INTRODUCTION

Acute myeloid leukemia (AML) is the most common adult leukemia. Only a fraction of AML patients will survive with existing chemotherapy regimens. Hence, there is an urgent and unmet need to identify novel targets and develop better therapeutics in AML. In the past decade, the field of sphingolipid metabolism has emerged into the forefront of cancer biology due to its importance in cancer cell proliferation and survival. In particular, acid ceramidase (AC) has emerged as a promising therapeutic target due to its role in neutralizing the pro-death effects of ceramide. Areas covered: This review highlights key information about AML biology as well as current knowledge on dysregulated sphingolipid metabolism in cancer and AML. We describe AC function and dysregulation in cancer, followed by a review of studies that report elevated AC in AML and compounds known to inhibit the enzyme. Expert opinion: AML has a great need for new drug targets and better therapeutic agents. The finding of elevated AC in AML supports the concept that this enzyme represents a novel and realistic therapeutic target for this common leukemia. More effort is needed towards developing better AC inhibitors for clinical use and combination treatment with existing AML therapies.

Fragment-Based Hologram QSAR Studies on a Series of 2,4-Dioxopyrimidine-1-Carboxamides As Highly Potent Inhibitors of Acid Ceramidase

A series of structurally related 2,4-dioxopyrimidine-1-carboxamide derivatives as highly potent inhibitors against acid ceramidase were subjected to hologram quantitative structure-activity relationship (HQSAR) analysis. A training set containing 24 compounds served to establish the HQSAR model. The best HQSAR model was generated using atoms, bond, connectivity, donor and acceptor as fragment distinction and 3-6 as fragment size with six components showing cross-validated q² value of 0.834 and conventional r² value of 0.965. The model was then employed to predict the potency of test set compounds that were excluded in the training set, and a good agreement between the experimental and predicted values was observed exhibiting the powerful predictable capability of this model [Formula: see text]. Atom contribution maps indicate that the electron-withdrawing effects at position 5 of the uracil ring, the preferential acyl substitution at N3 position and the substitution of eight-carbon alkyl chain length at N1 position predominantly contribute to the inhibitory activity. Based upon these key structural features derived from atom contribution maps, we have designed novel inhibitors of acid ceramidase possessing better inhibitory activity.

Novel fluorescent ceramide derivatives for probing ceramidase substrate specificity

Ceramidases are key regulators of cell fate. The biochemistry of different ceramidases and of their substrate ceramide appears to be complex, mainly due to specific biophysical characteristics at the water-membrane interface. In the present study, we describe the design and synthesis of a set of fluorescently labeled ceramides as substrates for acid and neutral ceramidases. For the first time we have replaced the commonly used polar NBD-dye with the lipophilic Nile Red (NR) dye. Analysis of kinetic data reveal that although both the dyes do not have any noticeable preference for the substitution at acyl or sphingosine (Sph) part in ceramide towards hydrolysis by acid ceramidase, the ceramides with acyl-substituted NBD and Sph-substituted NR dyes have been found to be a better substrate for neutral ceramidase.

Discovery and evaluation of inhibitors of human ceramidase

The ceramide/sphingosine-1-phosphate (S1P) rheostat has been hypothesized to play a critical role in regulating tumor cell fate, with elevated levels of ceramide inducing death and elevated levels of S1P leading to survival and proliferation. Ceramidases are key enzymes that control this rheostat by hydrolyzing ceramide to produce sphingosine and may also confer resistance to drugs and radiation. Therefore, ceramidase inhibitors have excellent potential for development as new anticancer drugs. In this study, we identify a novel ceramidase inhibitor (Ceranib-1) by screening a small molecule library and describe the synthesis of a more potent analogue (Ceranib-2). In a cell-based assay, both compounds were found to inhibit cellular ceramidase activity toward an exogenous ceramide analogue, induce the accumulation of multiple ceramide species, decrease levels of sphingosine and S1P, inhibit the proliferation of cells alone and in combination with paclitaxel, and induce cell-cycle arrest and cell death. In vivo, Ceranib-2 was found to delay tumor growth in a syngeneic tumor model without hematologic suppression or overt signs of toxicity. These data support the selection of ceramidases as suitable targets for anticancer drug development and provide the first nonlipid inhibitors of human ceramidase activity.