I. INTRODUCTION 



presence of rat liver S9, indicating that mamma- 

 lian liver enzymes are also capable of metabo- 

 lizing nitrofurantoin to a mutagenic interme- 

 diate. In numerous independent NTP-sponsored 

 tests on chemical mutagenicity in Salmonella 

 with a preincubation protocol, nitrofurantoin 

 was consistently mutagenic to strains TA98 and 

 TAIOO both with and without metabolic ac- 

 tivation by Aroclor 1254-induced male Sprague 

 Dawley rat or Syrian hamster liver 89. No sig- 

 nificant increase in mutant colonies was ob- 

 served in strains TA1535 or TA1537, which, un- 

 like TAIOO and TA98, do not exhibit enhanced 

 error prone repair of damaged DNA (Haworth et 

 al., 1983). A representative sample of these tests 

 as conducted by one laboratory is presented in 

 Table P:i 



Exposure to nitrofurantoin induced formation of 

 white (lacking chlorophyll) colonies of Kuglenu 

 gracilis strain z (McCalla, 1962, 1965, p:bringer 

 et a!., 1978); this bleached condition is heritable, 

 but whether it is the result of direct interaction 

 of the nitrofurantoin with chloroplast DNA is 

 unknown. Mitotic recombination in Saccharo- 

 myces cerevtsiae (Siebert et al., 1979; Callen, 

 1981) and mitotic nondisjunction in Aspergillus 

 nidulans (Bignami et al., 1974) were observed 

 after treatment with nitrofurantoin. 



Mutagenicity results from assay systems that 

 use cultured mammalian cells are variable. 

 Without S9, single-strand breaks in the DNA of 

 cultured mouse L cells were detected after incu- 

 bation with 430 pM nitrofurantoin for 1 hour 

 (Olive and McCalla, 1977), and resistance to 6- 

 thioguanine was induced in Chinese hamster 

 V79 spheroids after treatment with 100-300 

 pg/ml nitrofurantoin (Olive, 1981). Induction of 

 forward mutations at the TK locus of mouse 

 L5178Y lymphoma cells was observed after 

 treatment with 5-500 pg/ml nitrofurantoin in 

 the absence of S9; it was not tested with S9 (Ta- 

 ble E2). Incubation of Chinese hamster ovary 

 cells with 40 pM nitrofurantoin for 1 hour pro- 

 duced a 74% increase in sister chromatid ex- 

 changes over the baseline frequency (Shirai and 

 Wang, 1980). Chromosomal aberrations were 

 observed in 19% of cultured Chinese hamster fi- 

 broblast cells incubated with 062 mg/ml nitro- 

 furantoin (Ishidate et al., 1978) In NTF studies. 



nitrofurantoin induced increased numbers of sis- 

 ter chromatid exchanges and chromosomal aber- 

 rations in cultured Chinese hamster ovary cells 

 with and without metabolic activation (Ta- 

 bles E3 and P>4). Results of other investigations 

 with in vitro assays that use mammalian sys- 

 tems showed no effect of nitrofurantoin treat- 

 ment on sister chromatid exchange frequencies 

 (Sasaki et al., 1980), chromosomal aberrations 

 (Tonomura and Sasaki, 1973), and unscheduled 

 DNA synthesis (Tonomura and Sasaki, 1973). 

 No meiotic chromosomal abnormalities were ob- 

 served in mice (Fonatsch, 1977), induction of mi- 

 cronuclei was not observed in rats (Setnikar et 

 al , 1976, Goodman et al., 1977), sperm mor- 

 phologic abnormalities were absent in dosed 

 male mice (Topham, 1980), and dominant lethal 

 mutations were not detected in two strains of ex- 

 posed male mice (Epstein et al , 1972; Setnikar 

 etal., 1976). 



In tests by Kramers (1982), nitrofurantoin fed to 

 adult male Drosophila, strain Oregon R, at a 

 concentration of 5 mM produced a marginally 

 significant increase in the frequency of sex- 

 linked recessive lethal mutations, but considera- 

 ble inconsistency occurred between tests, leav- 

 ing the question of nitrofurantoin's mutagenic 

 activity in this assay unresolved In an NTI^ 

 Drosophila sex-linked recessive lethal assay, no 

 increase in mutations was observed in adult 

 male Canton-S flies after administration of ni- 

 trofurantoin orally (2,000 ppm in sucrose for 3 

 days) or by injection (10,000 ppm in saline) (Zim- 

 mering et al., 1985; Table E5). 



Study Rationale 



Nitrofurantoin was nominated and selected for 

 study by the National Cancer Institute as a re- 

 sult of a review of International Agency for Re- 

 search on Cancer chemicals, because it had the 

 largest production volume and was the most 

 widely used 5-nitrofuran drug, and because it is 

 structurally similar to other 5-nitrofuran deriv- 

 atives reported to be carcinogenic in rodent 

 studies. Administration of nitrofurantoin in 

 feed was chosen to obtain exposure by the oral 

 route, which is the primary route for administra- 

 tion of the drug in humans. 



Nitrofurantoin, NTP TR 341 



22 



