Synthesis and mechanism of biological action of morpholinyl-bearing arylsquaramides as small-molecule lysosomal pH modulators.

Lysosomal pH is an important modulator for many cellular processes. An agent that is capable of regulating lysosomal pH may find a wide range of potential applications in the field of biomedicine. In this study, we describe the synthesis of a family of morpholinyl-bearing arylsquaramides as small-molecule lysosomal pH modulators. These compounds are able to efficiently facilitate the transmembrane transport of chloride anions as mobile carriers across vesicular and cellular phospholipid membranes. They are capable of specifically alkalizing liposomes, disrupting the homeostasis of lysosomal pH and inactivivating lysosomal Cathepsin B enzyme. Anion transport is considered as the probable mechanism of action for the high efficiency of these compounds to modulate lysosomal pH. The present findings present a novel means to efficiently regulate lysosomal pH, which is in contrast to the methods shown by conventional lysosomal pH modulators that generally function by either acting as a weak base/acid, or releasing a basic/acidic component in lysosomal environments to change lysosomal pH.

Synthesis and biological activity of squaramido-tethered bisbenzimidazoles as synthetic anion transporters.

A series of squaramido-tethered bisbenzimidazoles were synthesized from the reaction of diethyl squarate with substituted 2-aminomethylbenzimidazoles. These conjugates exhibit moderate binding affinity toward chloride anions. They are able to facilitate the transmembrane transport of chloride anions most probably via an anion exchange process, and tend to be more active at acidic pH than at physiological pH. The viability of these conjugates toward four selected solid tumor cell lines was evaluated using an MTT assay and the results suggest that some of these conjugates exhibit moderate cytotoxicity probably in an apoptotic fashion.

Synthesis and biological effect of lysosome-targeting fluorescent anion transporters with enhanced anionophoric activity.

Two lysosome-targeting fluorescent anion transporters derived from coumarins, trifluoromethylated arylsquaramides and morpholines were synthesized, and their specificity and efficiency to target and alkalize lysosomes were investigated. They are able to target lysosomes specifically. Compared with the previous analogue without trifluoromethyl substituents, these two conjugates, in particular the one having a 3,5-bis(trifluoromethyl) substituent, exhibit significantly higher ability to facilitate the transport of chloride anions, alkalize lysosomes and reduce the activity of lysosomal Cathepsin B enzyme. The present finding suggests that improving the anionophoric activity of lysosome-targeting fluorescent anion transporters is favorable to the efficiency to alkalize lysosomes and deactivate lysosomal Cathepsin B enzyme.

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.