Vanadyl complexes with dansyl-labelled di-picolinic acid ligands: synthesis, phosphatase inhibition activity and cellular uptake studies

Abstract

Vanadium complexes have been previously utilised as potent inhibitors of cysteine based phosphatases (CBPs). Herein, we present the synthesis and characterisation of two new fluorescently labelled vanadyl complexes (14 and 15) with bridged di-picolinic acid ligand.These compounds differ significantly from previous vanadyl complexes with phosphatase inhibition properties in that the metal-chelating part is a single tetradentate unit, which should afford greater stability and scope for synthetic elaboration then the earlier complexes. These new complexes inhibit a selection of cysteine based phosphatases (CBPs) in the nM range with some selectivity. Fluorescence spectroscopic studies (including fluorescence anisotropy)were carried out to demonstrate that the complexes are not simply acting as vanadyl delivery vehicles but they interact with the proteins. Finally, we present preliminary fluorescence microscopy studies to demonstrate that the complexes are cell permeable and localise throughout the cytoplasm of NIH3T3 cells.

A tri-functional vanadium(iv) complex to detect cysteine oxidation

“…These observations are in agreement with our earlier investigation on the dansyl-labelled [VO(pic)2] derivative ( Figure 1(b)), which possessed similar potencies against PTPs and PTEN. 26 However, the IC50 values for 16 against VHR and PTP1B are around two-fold higher than for PTEN, SHP2 and LMW-PTP, whereas the dansyl-labelled [VO(pic)2] derivative (see Figure 1(b)) favoured PTP1B, VHR and SHP2. This observation suggests that the new complex could have some selectivity towards specific CBPs compared to others, inhibiting better phosphatases with a large catalytic pocket (e.g.…”

“…36 Our in vitro data indicates that 16 retains the nM affinity of the 'arrowhead' towards CBPs (analogous to recent results with the simpler VO(pic)2 compound, shown in Figure 1(a)). 26 We have also demonstrated by preliminary flow cytometry and microscopy that the trifunctional probe can be taken up by live HCT116 cells (using a permeabilizing agent) and detect total changes in SOH levels upon treatment with H2O2. While our current data cannot confirm that CBPs are indeed being targeted inside the cell, it provides a first step towards the development of protein-selective intracellular probes to assess oxidative damage.…”

“…Two synthetic routes were originally investigated to prepare the protected precursor 14 starting with the bridged di-picolinic compound 1. 26 The full synthetic design is based on a tri-orthogonal strategy by using in parallel two lysine scaffolds (i.e.…”

“…Therefore, extensive work has gone into developing targeted tools to identify sulfenic residues. [12][13][14][15] [23][24][25] (b) Chemical structure of a previously reported optical probe based on coupling dansyl fluorophore with a VO(pic)2 core; 26 (c) Chemical structure of the trifunctional probe reported in this study containing a CPB-targeting moiety (i.e. VO(pic)2), a coumarine-based fluorophore for imaging and a dimedone derivative to target SOH.…”

“…More recently, we have successfully modified the dipicolinic vanadyl core through introduction of a bridge between the two picolinic residues. 26 This allowed us to further functionalize the vanadyl complex and introduce a dansyl fluorophore for optical visualization ( Figure 1(b)). Most importantly, the introduction of the fluorophore did not have a major impact on the activity of the [VO(pic)2] towards CBPs (the functionalized complex retained the nanomolar affinity for CBPs).…”