IV POISONING OF THE SPINDLE 945 



A similar interpretation may be given to the mitotic figures regarded as somatic 

 reduction divisions observed in root meristems treated with sodium ribose nucleate 

 by Kodani (1948) and Huskins (1948). Adenosine did not show this activity (Woll, 



1953)- 



However, 2 mA/ concentration of adenosine was found to antagonize the sup- 

 pression of mitosis caused by its toxic analogue, 2-aminoadenosine, at the same 

 concentration in cultures of mouse sarcoma 180 and then to potentiate or to cause 

 an extensive metaphase arrest, followed either by chromosomal agglutination 

 and cell death or by nuclear reconstruction. In the latter case, a nucleus of doubled 

 size is formed in toroid shape because of the original disposition of the chromo- 

 somes in a hollow ring in the arrested metaphase. Guanosine alone at 4 mM causes 

 a few such figures in sarcoma 180 cultures, however they have not been observed 

 in mouse embryo skin cultures (Biesele, Berger, Clarke and Weiss, 1952). 



Amino acids. The prominence of protein in the composition of the mitotic appa- 

 ratus, which seems to be largely synthesized anew for each division, ofTers a ready 

 basis for metaphase arrest with amino acid analogues. It must not be forgotten, 

 of course, that protein enzymes instrumental in providing the energy for synthesis 

 and function of the apparatus may also be influenced. The amino acid analogues 

 to be discussed here are analogues of phenylalanine, which is a minor constituent 

 of the protein of the mitotic apparatus of isolated sea urchin egg, (Mazia, 1955). 



When mice bearing the Lewis sarcoma T241 are treated with massive doses of 

 P-(2-thienyl)-DL-alanine, some cells in the shrinking tumor become highly poly- 

 ploid and exhibit up to 20-polar mitotic figures (Jacquez, Stock and Barclay, 

 1953). Treatment of mice with [i-(j&-fluorophenyl)-DL-alanine raises the proportion 

 of metaphases among the mitotic figures in the tumor from abovit 20% to near 

 60% (Biesele and Jacquez, 1954). Many of the metaphases are blocked and revere 

 directly to the resting state. 



More information was gained on metaphasic delay through tissue culture 

 studies with the fluorophenylalanines (Biesele and Jacquez, 1954). The prolonga- 

 tion of metaphase caused by 0.25 and 0.5 mM [i-(/?-fluorophenyl)-DL-alanine in 

 cultures of newborn mouse heart cells and sarcoma T241 cells is prevented bv 

 equimolar L-phenylalanine. The fluorophenylalanines do not evoke a pronounced 

 response in cells of sarcoma 180 and of embryonic mouse skin, although some 

 effect can be produced in sarcoma 180 cells with ^-(m-fluorophenyl)-DL-alanine. 

 Some of the blocked metaphases revert to toroid resting nviclei, much as with 

 2-aminoadenosine plus adenosine. The metaphasic blocking with this meta isomer 

 can be increased by adding adenosine triphosphate to the cultures. This might 

 make for a greater incorporation of the phenylalanine analogue into protein of the 

 spindle or the kinetochore, which could thus become defective. 



Sarcoma 180 cells are also blocked in metaphase by ^-(/?-fluorophenyl)-DL- 

 alanine if liver explants are cultured in the same vessel. Tripolar mitoses also occur 

 in sarcoma 180 cultures as a result of treatment with any of the three fluorophenyl- 

 alanine isomers if liver explants are present, but not otherwise. This suggests that 

 perhaps the fluorophenylalanines are converted to more active derivatives. 



Literature p. g47 



