On the Nature of Cancer 129 



when compounds do bring about biological effects they may do so by 

 interference in such involved reactions as to preclude any facile idea 

 of single competitive inhibition. Although 8-azaguanine, its analogs, 

 and the compounds described in the following bear some resemblance 

 on paper to the naturally occurring purines it would be foolhardy 

 indeed at this time to ascribe their activity to structural similarity. 

 Furthermore, there is even no conclusive evidence that simple metabo- 

 lites like purines or pyrimidines play any role at all in the utilization 

 of foodstuffs for biosynthesis. 



Nevertheless our failures with the guanine analogs urged us on to 

 further synthetic efforts. Variations of the bicyclic rings such as 

 benzimidazoles, benzotriazoles, and quinoxalines were prepared as 

 shown in Fig. 3. 1T In addition simpler test systems were sought wherein 

 it was hoped that the finer nuances of biological reactivity could be 

 observed in line with the hypotheses bared above. Microorganisms 

 and Rcma pipiens embryos were employed to investigate the effects of 

 the compounds. 



Several of the compounds did in fact prove to be inhibitors of 

 Escherichia coli, but in a special way. They delayed growth, but only 

 by prolonging the lag phase, after which growth was resumed at its 

 normal rate. This behavior could be explained in either of two ways: 

 either the compounds were detoxicated metabolically, or the organisms 

 mutated to resistant types. Both phenomena were found to take place 

 in the various tests. Four of the 35 compounds tested on E. coli were 

 mutagenic. It is germane to Haddow's hypothesis alluded to earlier 

 that these four mutagens were all inhibitors and that only toxic com- 

 pounds were mutagenic. Mutation occurs, however, at concentration 

 levels far below those necessary to produce inhibition, i.e., lengthening 

 of the lag phase.* 



It would be an amiable gesture of nature if the bacterial mutagens 

 4-methoxy-6-nitrobenzotriazole and 6-hydroxy-4-nitrobenzimidazole, 

 for example, should turn out to be carcinogens also. But this is only 

 moderately to be hoped for, since carcinogens are thought to form 

 more or less stable compounds with cellular components. Bonding need 

 not be stable for mutagenic action on bacteria where the cells are 

 bathed in the toxic medium, but combination is probably necessary 

 in more highly differentiated systems where circulatory and detoxicat- 

 ing mechanisms might play a greater part. Neither does it follow 



* Unpublished work of Sheldon Greer and Professor Francis J. Ryan, Depart- 

 ment of Zoology. Columbia University. 



