Abstract
Intracellular polyamine deprivation, produced by DL-alpha-difluoromethylornithine (DFMO), resulted in a striking enhancement of cellular transport of the natural polyamines and methylglyoxal bis(guanylhydrazone) (MGBG). In addition to the natural polyamines and MGBG, the uptake of other diamines and triamines was likewise enhanced in response to DFMO, although longer than three-carbon backbone was required for about 10-fold stimulation to occur. Intracellular deprivation of polyamines did not increase the affinity of the transport system for MGBG but greatly enhanced the maximum velocity of the drug transport. The uptake process of MGBG was temperature dependent and the activation energy (Ea = 67.5 kJ) for the uptake system was the same for both the polyamine-depleted tumour cells and for the untreated cells. The uptake of the drug appeared to be more dependent on the Na+-linked uptake, as indicated by the inhibitory effect of ouabain, than on energy production. Deprivation of putrescine and spermidine changed the intracellular distribution of MGBG since a major portion of the drug was concentrated in the microsomal fraction in polyamine-depleted cells.
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