New synthetic routes to seleno- and tellurorhodamine photosensitizers for photodynamic therapy
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Rhodamine dyes with an N-methyltetrahydroquinoline replacing one dialkylamino group are termed half-julolidyl rhodamines. Selenium (Se) and tellurium (Te) analogues of the half-julolidyl dyes were synthesized as an improvement over the half-julolidyl sulfur (S) analogue for P-gp inhibition and for use as a photosensitizer in photodynamic therapy (PDT). The Se analogues showed an increased absorption maxima, larger extinction coefficients, and a larger quantum yield of singlet oxygen. Phototoxicity assays for PDT showed the presence of the amide/thioamide `switch' in P-gp transport rates. The thioamide dyes had improved P-gp inhibition over the amides and showed greater cytotoxic effects. The Se analogues were also testing in activated and resting T-cells for selective uptake in activated T-cells followed by selective depletion of the active T-cells for extracorporeal photopheresis. Assays showed that the amide analogues had greater selective uptake in activated and malignant cells than the thioamide analogues.