Transport processes in tumours.

The characteristic features of transport systems controlling influx into tumour cells of nutrients and other chemicals are briefly described. Two notable features of transport of amino acids into tumour cells have been observed: extensive accumulation against a concentration gradient and equal accumulations, whether conditions are aerobic or anaerobic, provided glucose is present. This combination of features has not been observed in the majority of normal mammalian tissues so far examined. Important for considerations of chemotherapy is the ability of tumour transport carriers to transfer substances related in structure to amino acids and other nutrients. Amino acid analogues, for example, can either block transport of natural amino acids or can be transported into the cell where they may interfere with various aspects of amino acid metabolism. The study of transport carriers is essential for an understanding of tumour-host relationships and for considerations of chemotherapy.