Studies on 4-aminopyrazolo(3, 4-d)pyrimidine: growth inhibition and relief in Neurospora crassa.

An analogue of adenine, 4-aminopyrazolo(3,4d)pyrimidine (4-APP), has recently been shown to be a potential antineoplastic agent. Skipper, Robins, and Thomson (1955) demonstrated that the growth of an adenocarcinoma and two leukemias of the mouse was inhibited or retarded by the administration of 4-APP. Hsu, Robins and Cheng (1956) showed that 4-aminopyrazolo(3,4d)pyrimidine exerts differential damage to malignant and nonmalignant tissues in vitro. In our laboratories adenocarcinoma E-0771 of the mouse was also found to be significantly inhibited by this agent, even after the tumor transplants had taken for seven days. Recent microbiological studies of the effect of 6-mercaptopurine on Lactobacillus casei (Elion, Singer, and Hitchings, 1954) and on Streptococcus faecalU (Hutchison, 1954) indicated that investigations of potential cancer chemotherapeutic agents with microorganisms are highly desirable, and constitute a useful system for primary screening. The ascomycete, Neurospora, seems to offer a good test system for screening because it grows fast and requires only inorganic salts, a carbon source, and a trace of biotin for growth, which can be easily measured by its dry mycelial weight. Since organic substances are not essential in the medium of Neurospora, their effects on the action of analogues in question can be eliminated whereas in Lactobacillus and Streptococcus, which require more complex media for growth, the problem is actually more complicated. Furthermore, Neurospora has been used extensively in genetic studies, and a large number of