Biological effects and activity optimization of small-molecule, drug-like synthetic anion transporters.

The balance of normal anion concentrations in cells provides basis for maintaining cellular morphology and function. Disrupting the homeostasis of cellular anions and lysosomal pH, in particular with high selectivity for cancer cells over normal cells may serve as a promising approach for the treatment of cancers. Small-molecule organic compounds with transmembrane anion transport activity, namely synthetic anion transporters are able to destroy the homeostasis of cellular anions, in particular chloride anions to trigger cell death and thus may be developed as a new class of anti-tumor drugs. This paper reviews the latest advance in the investigation into the in vitro anion transport, promising anti-tumor activity and probable mechanism of biological action of synthetic anion transporters. The strategies for optimizing the biological activity of synthetic anion transporters and improving the selectivity for cancer cells over normal cells are also discussed.

Synthesis and biological evaluation of aza-crown ether-squaramide conjugates as anion/cation symporters.

Aim: Anion/cation symport across cellular membranes may lead to cell apoptosis and be developed as a strategy for new anticancer drug discovery. Methodology: Four aza-crown ether-squaramide conjugates were synthesized and characterized. Their anion recognition, anion/cation symport, cytotoxicity and probable mechanism of action were investigated in details. Conclusion: These conjugates are able to form ion-pairing complexes with chloride anions and facilitate the transmembrane transport of anions via an anion/cation symport process. They can disrupt the cellular homeostasis of chloride anions and sodium cations and induce the basification of acidic organelles in live cells. These conjugates exhibit moderate cytotoxicity toward the tested cancer cells and trigger cell apoptosis by mediating the influx of chloride anions and sodium cations into live cells.

Fluorinated bisbenzimidazoles: a new class of drug-like anion transporters with chloride-mediated, cell apoptosis-inducing activity.

Anion transporters have attracted substantial interest due to their ability to induce cell apoptosis by disrupting cellular anion homeostasis. In this paper we describe the synthesis, anion recognition, transmembrane anion transport and cell apoptosis-inducing activity of a series of fluorinated 1,3-bis(benzimidazol-2-yl)benzene derivatives. These compounds were synthesized from the condensation of 1,3-benzenedialdehyde or 5-fluoro-1,3-benzenedialdehyde with the corresponding 1,2-benzenediamines and fully characterized. They are able to form stable complexes with chloride anions, and exhibit potent liposomal and in vitro anionophoric activity. Their anion transport efficiency may be ameliorated by the total number of fluorine atoms, and the enhanced anionophoric activity was a likely consequence of the increased lipophilicity induced by fluorination. Most of these fluorinated bisbenzimidazoles exhibit potent cytotoxicity toward the selected cancer cells. Mechanistic investigations suggest that these compounds are able to trigger cell apoptosis probably by disrupting the homeostasis of chloride anions.

Synthesis and properties of a lysosome-targeting fluorescent ionophore based on coumarins and squaramides.

In this paper we present the first example of a lysosome-targeting fluorescent ionophore. Specifically, we synthesized a squaramide derivative bearing a coumarin fluorophore and a morpholinyl group, and found that it was able to target and efficiently deacidify lysosomes. In contrast, an analogue without a morpholinyl group exhibits much lower ability to localize in lysosomes and is much less active in regulating the lysosomal pH.

Synthesis, anionophoric activity and apoptosis-inducing bioactivity of benzimidazolyl-based transmembrane anion transporters.

In this paper we show that a series of 1,3-bis(benzimidazol-2-yl)benzene (m-Bimbe) derivatives exhibit excellent performance as transmembrane anion transporters with anticancer activity. The transport efficiency of m-Bimbe and its derivatives has been firstly optimized by adding a strong electron-withdrawing nitro group at the 5-position of the central phenyl subunits to enhance the CH···anion interactions. Evidences for the interactions were obtained from ESI MS, spectrophotometric and 1H NMR titrations. These compounds exhibit potent anionophoric activity in both liposomal models and live cells. In particular, the 5-nitrated derivatives having nitro or trifluoromethyl groups at the benzimidazoloyl subunits exhibit 2370- and 1721-fold enhanced anionophoric activity with the EC50 values as low as 36 and 50 nM, respectively. These compounds can disturb the cellular homeostasis of chloride anions, modify the intracellular pH and induce the basification of acidic organelles. Most of this series of m-Bimbe derivatives exhibit potent cytotoxicity toward the tested human solid tumor cell lines, and the 5-nitrated derivative bearing trifluoromethyl groups at the benzimidazoloyl subunits is the most active with the IC50 value in the low micromolar range. Mechanistic studies suggest that the transport of chloride anions across the cellular membranes plays a critical role in the cytotoxic effect and these compounds induce cell death probably via an apoptotic process.

Synthesis, Anion Recognition, and Transmembrane Anionophoric Activity of Tripodal Diaminocholoyl Conjugates.

In this paper, we present the synthesis, anion recognition, and anionophoric activity of 1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene-based tripodal 3α-hydroxy-7α,12α-diamino-5ß-cholan-24-oate conjugate 1 and the corresponding tris(2-aminoethyl)amine-based analogue 2 and choloyl analogue 3. Their affinity toward anions was evaluated by means of competitive displacement assay using 5-carboxyfluorescein (5-FAM) as a fluorescent indicator. The results indicate compounds 1 and 2 exhibit strong recognition toward a wide range of biologically important anions, in particular, toward sulfate and phosphate anions. In MeOH-HEPES (4/1, pH 7), the binding constants of compounds 1 and 2 are 416- and 168-fold higher for sulfate than for chloride and 35- and 25-fold higher for phosphate than for chloride, respectively. The anion transport activity was measured by use of pH discharge assay and chloride-ion-selective electrode technique. The results indicate that compounds 1 and 2 function as effective anion-selective transporters in the order of ClO4- > I- > NO3- > Br- > Cl- > SO42- > H2PO4- and exhibit anionophoric activity via a process of major anion exchange and minor anion/cation symport. In addition, some insights into the correlation of the anion binding affinity with the transport efficiency are also briefly discussed.