282 



NUCLEIC ACIDS AND GROWTH 



Comparable findings have also 

 been made on frog oocytes (un- 

 published observations of A. Ficq) 

 and on ascites tumour cells (Ledoux 

 and Baltus, 1954; Ledoux and 

 Revell, 1955); in the latter, ribo- 

 nuclease induces an initial synthesis 

 of RNA, followed by a rapid break- 

 down; but, even during the first 

 synthetic phase, incorporation of 

 the amino acids into the proteins 

 is strongly inhibited. 



These results of Ledoux et al. 

 (1954, 1955) might very well have 

 considerable importance for the 

 chemotherapy of cancer: if growth 

 is linked to protein synthesis and 

 RNA metabolism, one might expect 

 ribonuclease — if it enters the ma- 

 lignant cells — to inhibit the growth 

 of tumours. In fact, recent experi- 

 ments by Ledoux, (1955a, 1955b) 

 show that the survival time of 

 tumour-bearing mice is markedly 

 increased when they are injected in- 

 traperitoneally with ribonuclease. 



Ledoux's (1954, 1955b) exper- 

 imental results obviously suggest 

 that the antimitotic activity of 

 ribonuclease, first discovered by 

 Kaufmann and Das (1954, 1955), 

 might be a fairly general phenom- 

 enon. Such an effect can very easily 

 be demonstrated in amphibian 

 eggs (Brachet and Ledoux, 1955). 

 Simple immersion of cleaving 

 urodeles eggs in ribonuclease (0.5 

 mg/ml) solutions is sufficient to 

 quickly bring cell division to a 

 standstill. Ribonuclease is most 

 effective during early cleavage 



8c 



Fig. 8. Autoradiographs after incorporation of phenylalanine into amoebae, a : control amoe- 

 ba; b: ribonuclease treated amoeba (loss of basophilia and of incorporation) ; c : recovery 

 of basophilia and incorporation in the ribonuclease-treated amoebae upon addition of RNA. 



