Activation of deoxycytidine kinase by deoxyadenosine: implications in deoxyadenosine-mediated cytotoxicity

Metabolic profiling of CD19+ cells in chronic lymphocytic leukemia by single-cell mass spectrometry imaging

BACKGROUND AND AIMS

Modern mass spectrometry imaging (MSI) enables single cells' metabolism exploration. Aims of this study were development of the single-cell MSI of human CD19+ lymphocytes and metabolic profiling of chronic lymphocytic leukemia (CLL).

MATERIALS AND METHODS

Blood donor (BD) samples were used for the optimization of CD19+ lymphocyte isolation and single-cell matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) MSI. Independent set of 200 CD19+ lymphocytes coming from 5 CLL patients and 5 BD was used for the CD19+ lymphocytes classification assessment and the untargeted metabolic profiling. CLL vs BD lymphocyte classification was performed using partial least squares-discriminant analysis (PLS-DA) using normalized single-cell mass spectra recorded in 300-600 and 600-950 Da ranges was applied.

RESULTS

Accuracy assessed by 10-fold cross-validation of CD19+ lymphocyte PLS-DA classification reached >90.0 %. Volcano plots showed 106 significantly altered m/z signals in CLL of which 9 were tentatively annotated. Among tentatively annotated m/z signals formaldehyde and glutathione metabolites and tetrahydrofolate stand out.

CONCLUSION

A method for single-cell MALDI TOF MSI of CD19+ lymphocytes was successfully developed. The method confirmed the significance of oxidative stress and single-carbon metabolism, pyruvate and fatty acid metabolism and apoptosis in CLL and it provided metabolic candidates for diagnostic applications.

Therapeutic potential of toosendanin: Novel applications of an old ascaris repellent as a drug candidate

Toosendanin (TSN), extracted from Melia. toosendan Sieb.et Zucc. and Melia. azedarach L., has been developed into an ascaris repellent in China. However, with the improvement of public health protection, the incidence of ascariasis has been reduced considerably, resulting in limited medical application of TSN. Therefore, it is questionable whether this old ascaris repellent can develop into a drug candidate. Modern studies have shown that TSN has strong pharmacological activities, including anti-tumor, anti-botulinum, anti-viral and anti-parasitic potentials. It also can regulate fat formation and improve inflammation. These researches indicate that TSN has great potential to be developed into a corresponding medical product. In order to better development and application of TSN, the availability, pharmacodynamics, pharmacokinetics and toxicology of TSN are summarized systematically. In addition, this review discusses shortcomings in the current researches and provides useful suggestions about how TSN developed into a drug candidate. Therefore, this paper illustrates the possibility of developing TSN as a medical product, aimed to provide directions for the clinical application and further research of TSN.

Potential Deoxycytidine Kinase Inhibitory Activity of Amaryllidaceae Alkaloids: An In Silico Approach

Background:

Plants of the Amaryllidaceae family have been under intense scrutiny for the presence of a couple of alkaloidal secondary metabolites with endued cytotoxic activity, such as pancratistatin (1), 7-deoxypancratistatin (2), narciclasine (3), 7-deoxynarciclasine (4), trans-dihydronarciclasine (5), and 7-deoxy-trans-dihydronarciclasine (6). Nevertheless, preclinical evaluation of these alkaloids has been put on hold because of the limited quantity of materials available from isolation.

Aim:

To explore the underlying cytotoxic molecular mechanisms of the Amaryllidaceae alkaloids (1–6) and to assess their absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles using chemoinformatic tools.

Materials And Methods:

AutoDock 4.0 software along with different in silico chemoinformatic tools, namely PharmMapper, Molinspiration, MetaPrint2D, and admetSAR servers, were used to assess the drugability of the Amaryllidaceae alkaloids (1–6).

Results:

Deoxycytidine kinase (dCK) (PDB: 1P60) was predicted as a potential target with fitting score of 5.574. In silico molecular docking of (1–6) into dCK revealed good interactions, where interesting hydrogen bonds were observed with the amino acid residues—Gly-28 and Ser-35—located in the highly conserved P-loop motif. This motif plays a special role in dCK function. Contrary to (1), in silico pharmacokinetic results have shown good absorption and permeation and thus good oral bioavailability for (2–6).

Conclusion:

The in silico docking data have proposed that the reported cytotoxic activity of the Amaryllidaceae alkaloids (1–6) could be mediated through dCK inhibition. In addition, the ADMET profile of these alkaloids is promising and thus (1–6) could be candidates for future drug development.

The apoptotic effects of toosendanin are partially mediated by activation of deoxycytidine kinase in HL-60 cells

Triterpenoid toosendanin (TSN) exhibits potent cytotoxic activity through inducing apoptosis in a variety of cancer cell lines. However, the target and mechanism of the apoptotic effects by TSN remain unknown. In this study, we captured a specific binding protein of TSN in HL-60 cells by serial affinity chromatography and further identified it as deoxycytidine kinase (dCK). Combination of direct activation of dCK and inhibition of TSN-induced apoptosis by a dCK inhibitor confirmed that dCK is a target for TSN partially responsible for the apoptosis in HL-60 cells. Moreover, the activation of dCK by TSN was a result of conformational change, rather than auto-phosphorylation. Our results further imply that, in addition to the dATP increase by dCK activation in tumor cells, dCK may also involve in the apoptotic regulation.

Mimicking phosphorylation of Ser-74 on human deoxycytidine kinase selectively increases catalytic activity for dC and dC analogues

Intracellular phosphorylation of dCK on Ser-74 results in increased nucleoside kinase activity. We mimicked this phosphorylation by a Ser-74-Glu mutation in bacterially produced dCK and investigated kinetic parameters using various nucleoside substrates. The S74E mutation increases the k(cat) values 11-fold for dC, and 3-fold for the anti-cancer analogues dFdC and AraC. In contrast, the rate is decreased for the purine substrates. In HEK293 cells, we found that by comparing transiently transfected dCK(S74E)-GFP and wild-type dCK-GFP, mimicking the phosphorylation of Ser-74 has no effect on cellular localisation. We note that phosphorylation may represent a mechanism to enhance the catalytic activity of the relatively slow dCK enzyme.

Pharmacological inhibition of the MAPK/ERK pathway increases sensitivity to 2-chloro-2'-deoxyadenosine (CdA) in the B-cell leukemia cell line EHEB

EHEB leukemic cells, which are derived from a patient suffering B-cell chronic lymphocytic leukemia (B-CLL), display intermediate sensitivity to the purine analogue 2-chloro-2'-deoxyadenosine (CdA). Because the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway can rescue cancer cells from apoptotic signals, we investigated MAPK/ERK signaling in EHEB cells in response to CdA. We observed that CdA, at concentrations around its IC50, dose- and time-dependently increased the phosphorylation state of ERK 1/2 (p-ERK), indicating an activation of the MAPK/ERK pathway. This activation required CdA metabolism and de novo protein synthesis, and was independent on caspase activation. Interruption of ERK signaling, using the specific MEK inhibitors U-0126 and PD-98059, significantly enhanced CdA cytotoxicity, evaluated by the MTT assay. Drug interaction analysis showed synergism in the majority of combinations between CdA and MEK inhibitors tested. MEK inhibitors also dramatically increased apoptosis induced by CdA alone, evaluated by caspase-3 activation and poly (ADP-ribose) polymerase (PARP) cleavage. Collectively, these observations show that ERK 1/2 activation elicited by CdA serves as a cytoprotective function and suggest that inhibitors of this pathway could be combined with CdA in the treatment of selected hematological malignancies.