Tumors cellular transport

The kidney, liver, and spleen had the highest specific activity after administration of labeled melphalan to rats and mice [68,98], while in dogs and monkeys the highest levels of drug were in the bile [3,75,99]. No significant concentrations in the tumor were noted, and the inhibition of the tumor growth could not be attributed to interactions with proteins, DNA, or RNA within the tumor cell [68]. Cellular transport of melphalan by amino acid carrier systems has been reported [100—105]. 

The placental fraction of alkaline phosphatase is a membrane-bound enzyme of 120 kD, normally synthesized by placental syncytiotrophoblasts and released into maternal circulation after the 12th week of pregnancy. However, it is also produced by many neoplasms and is a useful tumor marker. Physiologically, this enzyme is involved in cellular transport, proliferation and cellular differentiation, and regulation of metabolism and gene transcription. 

New examples of cellular rhythms have recently been uncovered (Table II). These include periodic changes in the intracellular concentration of the transcription factor NF-KB and of the tumor suppressors p53, stress-induced oscillations in the transport of the transcription factor Msn2 between cytoplasm and nucleus in yeast, the segmentation clock that is responsible for the... 

Within the cell, P-gp can be expressed in several organelles and as such can influence the cellular distribution of its substrates. Studies with tumor cells have shown P-gp expression on the cell surface, in cytoplasmic vesicles, in Golgi apparatus, and in the nuclear envelope (208,209). Within vesicles and in Golgi apparatus, P-gp acts to sequester compounds as the transport is directed within the vesicle. At the nuclear membrane, P-gp acts to restrict access of substrates to the nucleus by directing transport in a cytoplasmic direction. This subcellular localization of P-gp can be an important consideration for P-gp substrates with intracellular targets (208). 

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