Warburg Effect Targeting Co(III) Cytotoxin Chaperone Complexes.

A glucose-based vector for targeting cancer cells conjugated to a tris(methylpyridyl)amine (tpa) ligand to generate targeted chaperone and caging complexes for active anticancer agents is described. The ligand, tpa(CONHPEGglucose)1, inhibits hexokinase, suggesting that it will be phosphorylated in the cell. A Co(III) complex incorporating this ligand and coumarin-343 hydroximate (C343ha), [Co(C343ha){tpa(CONHPEGglucose)1}]Cl, is shown to exhibit glucose-dependent cellular accumulation in DLD-1 colon cancer cells. Cellular accumulation of [Co(C343ha){tpa(CONHPEGglucose)1}]+ is slower than for the glucose null and glucosamine analogues, and the glucose complex also exhibits a lower ability to inhibit antiproliferative activity. Distributions of cobalt (X-ray fluorescence) and C343ha (visible light fluorescence) in DLD-1 cancer cell spheroids are consistent with uptake of [Co(C343ha){tpa(CONHPEGglucose)1}]+ by rapidly dividing cells, followed by release and efflux of C343ha and trapping of the Co{tpa(CONHPEGglucose)1} moiety. The Co{tpa(CONHPEGglucose)1} moiety is shown to have potential for the caged and targeted delivery of highly toxic anticancer agents.

A Warburg effect targeting vector designed to increase the uptake of compounds by cancer cells demonstrates glucose and hypoxia dependent uptake.

Glycoconjugation to target the Warburg effect provides the potential to enhance selective uptake of anticancer or imaging agents by cancer cells. A Warburg effect targeting group, rationally designed to facilitate uptake by glucose transporters and promote cellular accumulation due to phosphorylation by hexokinase (HK), has been synthesised. This targeting group, the C2 modified glucose analogue 2-(2-[2-(2-aminoethoxy)ethoxy]ethoxy)-D-glucose, has been conjugated to the fluorophore nitrobenzoxadiazole to evaluate its effect on uptake and accumulation in cancer cells. The targeting vector has demonstrated inhibition of glucose phosphorylation by HK, indicating its interaction with the enzyme and thereby confirming the potential to facilitate an intracellular trapping mechanism for compounds it is conjugated with. The cellular uptake of the fluorescent analogue is dependent on the glucose concentration and is so to a greater extent than is that of the widely used fluorescent glucose analogue, 2-NBDG. It also demonstrates selective uptake in the hypoxic regions of 3D spheroid tumour models whereas 2-NBDG is distributed primarily through the normoxic regions of the spheroid. The increased selectivity is consistent with the blocking of alternative uptake pathways.

The influence of the ancillary ligand on the potential of cobalt(iii) complexes to act as chaperones for hydroxamic acid-based drugs.

Cobalt(iii) chaperones are a promising class of bioreductive prodrugs under investigation for the delivery of cytotoxic ligands to hypoxic solid tumours. Here we investigate a series of cobalt complexes as chaperones for hydroxamic acid ligands, comparing the properties of the cyclic cyclen (1,4,7,10-tetraazacyclododecane) ancillary ligand with the tripodal tpa (tris-(2-pyridylmethyl)amine) and tren (tris-(2-aminoethyl)amine). A small library of complexes containing several different hydroxamic acids, including the MMP inhibitor Marimistat and the fluorescent ligand C343haH2, were prepared and their pKa values, reduction potentials, and in some cases X-ray crystal structures, were determined. The antiproliferative actitivity of the series was evaluated against DLD-1 colon cancer cells and the cellular accumulation of the fluorescent C343haH2 complexes was monitored by ICPMS and confocal fluorescence microscopy, revealing that the nature of the ancillary ligand significantly influences the complexes' properties, cytotoxicity and cellular distribution.