go8 METABOLISM OF THE CANCER CELL 12 



testine, spleen and liver in decreasing order. The specific activity of the DNA 

 cytosine was approximately the same as the DNA thymine. 



Purine metabolism in neoplastic tissues has been extensively investigated by 

 LePage (1953)- In Ehrlich carcinoma cells the antibiotic isomer of chlorampheni- 

 col inhibited the incorporation of glycine-2-''*C into proteins and nucleic acid 

 purines. The inactive isomer inhibited the glycine incorporation into purines but 

 not into protein. Both isomers were equally effective in inhibiting the incorpora- 

 tion into both the proteins and purines in lymphosarcoma cells (LePage, 1953a). 

 In a subsequent study, Edmonds and LePage (1955) investigated the in vivo 

 incorporation of glycine-2-''*C into the acid soluble purine nucleotides and into 

 the nucleic acids of rat liver and Flexner-Jobling carcinoma. More '''C was incor- 

 porated into the tumor than into the liver nucleotides. Soon after administration 

 of the labeled glycine, the acid soluble nucleotides were isolated from the liver and 

 tumor. IMP had a higher activity than AMP, ADP or ATP in both tissues. GMP, 

 GDP and GTP were more highly labeled than the corresponding adenine nucle- 

 otides in the tumor. Further studies in purine metabolism were also carried out 

 in Ehrlich carcinoma cells. (Edmonds and LePage, 1956). These cells were unable 

 to convert deoxy-AMP to the corresponding inosine compound, thus accovmting 

 for the ineffectiveness of deoxy-AMP in diluting the radioactivity of glycine-2-''*C 

 that is incorporated into the purines. The deoxyadenosine was converted to hypo- 

 xanthine or deoxyinosine. These investigators also found that AMP need not be 

 converted to inosinic acid prior to its incorporation into nucleic acid adenine. 

 These tumor cells utilized AMP more effectively than adenosine. 



De novo synthesis of nucleic acids from precursors such as glycine or adenine 

 occurs readily in intestines, liver or in mouse sarcoma 180. (Barclay and Garfinkel, 

 1955). Balis et al. (1955) reported that preformed purines were incorporated to a 

 smaller extent into a human tumor explant in hamsters than they were in several 

 of the normal tissues of the animal. Little guanine was utilized by the tumor, while 

 glycine was used to a considerable extent. Azaserine inhibits the incorporation of 

 glycine-2-'''C into acid soluble and nucleic acid purines in mouse ascites tumor 

 and in the spleen. 6-Mercaptopurine did not affect the incorporation of glycine 

 -2-^'*C or adenine-8-''*C into nucleic acid compounds (Fernandes et al., 1956). 

 Azaserine was shown by Greenlees and LePage (1956) to react with a tumor cell 

 constituent either in vivo or in vitro and to inhibit the de novo synthesis of purines. 

 An intermediate, glycineamide ribotide (GAR), accumulated in the ascites tumor 

 cells, indicating that these tumor cells are inhibited at the point where formylation 

 of GAR occurs. In pigeon liver systems the reaction involving the conversion of 

 a-N-formvl glycineamide ribotide to the corresponding amidine is the most sensi- 

 tive to azaserine. Whether or not this difference in the point of action of azaserine 

 is general for tumor cells and normal mammalian cells still must be ascertained. 



Studies on the incorporation of guanine-2-^'*C, 2,6-diaminopurine-2-^'*C, 

 adenine-8-''*C and formate ^"^C into polynucleotides of animal tumors and nor- 

 mal tissues were initiated by Bennett et al. (1955). Relative to the control tissues, 

 all tumors investigated incorporated gvianine poorly. The tumors utilized 2,6- 

 diaminopurine as a polynucleotide guanine source as well as did intestine or liver. 

 A comparable study was also carried out on the incorporation of these and other 



