Toxicity of quinoline alkaloids to cultured Cinchona ledgeriana cells

The toxicity of Cinchona alkaloids to cell cultures of C. ledgeriana has been studied in relation to alkaloid uptake and possibilities for selecting high-yielding cell lines. The most toxic, quinine, was completely toxic at 5.5 mM. Both quinine and quinidine were more toxic than their unmethoxylated precursors, cinchonidine and cinchonine. The permanently-charged metho-chlorides of quinine and cinchonidine were less toxic than the parent alkaloids, despite showing similar accumulation ratios in 5-day uptake experiments at sub-toxic concentrations (ca 1.7mM). The toxicity of the natural quinoline alkaloids appears to be a non-specific effect which may be caused by intracellular alkalinisation following uptake of the uncharged bases. The use of precursors of quinine and quinidine as toxic agents for the selection of cell lines with enhanced quinine and quinidine production is ruled out by the lower toxicity of these precursors and by the correlation of an apparently non-specific toxicity with uptake.