The Activity of Substituted Thiosemicarbazones against Trichomonas vaginalis and Trichomonas foetus In vitro and in Experimental Animals

Abstract

A series of derivatives of bis (thiosemicarbazone) and bis (4-methylthiosemicarbazone) have been examined for antitrichomonal activity in vitro and in vivo in the mouse, hamster, and rat. Derivatives of bis (4-methylthiosemicarbazone) were extremely active in vitro. The 90% growth inhibitory end point for pyruvaldehyde-bis(4-methylthiosemicarbazone) against T. vaginalis was 0.003 g/ml and 0.004 IL/ml against T. foetus. The CD50 of this compound in mice infected subcutaneously and treated orally was 0.2 mg/kg against T. vaginalis and 2.0 mg/kg against T. foetus when treatment was begun immediately after injection with the infecting organism. If treatment was delayed for as short a time as 1 hour, the CD50 was significantly increased. None of the derivatives of bis(4-methylthiosemicarbazone) would cure hamsters chronically infected intravaginally with T. foetus when administered systemically, or rats infected in the same manner with T. vaginalis and treated orally or locally. When the efficacy of pyruvaldehyde-bis (4-methylthiosemicarbazone) were compared simultaneously in mice and hamsters infected subcutaneously with T. foetus, it was found that infections in hamsters were more refractory to treatment than those in mice. This difference was not due to absorption per se since blood levels in hamsters were somewhat higher and more prolonged than those in mice. The differences in response of the same type of infection in two species of animals and the failure to cure vaginal infections have been attributed to a lack of local absorption of the drug by the host Trichomonas vaginalis Donne (1836) and Trichomonas foetus are flagellate parasites of the genitourinary tract of man and bovines, respectively. A recent review of the literature (Michaels and Strube, 1961) has shown that while several compounds are active in curing experimental infections in lower animals, only one, 2-methyl-5-nitro-1-imidazoleethanol, (Cosar and Julou, 1959) is efficacious in man when used systemically or locally (Durel, 1959). This report is concerned with pyruvaldehydebis (thiosemicarbazones) and a series of derivatives whose in vitro activity is on the order of one thousand times greater than any previously known compound. This order of activity is equal to that of the most active in vitro antibiotics, penicillin and erythromycin, against such species of bacteria as Str. hemolyticus. MATERIALS AND METHODS Trichomonads. One strain of Trichomonas vaginalis, designated (R) by us, was obtained from Dr. A. C. Cuckler, The Merck Institute for Therapeutic Research. The second strain (C.I.) was isolated by this laboratory during the course of the work. Strains of Trichomonas foetus, MSC and L, were obtained from Dr. W. P. Lindquist and Received for publication 13 November 1961. Dr. D. T. Clark of Michigan State University, respectively. The organisms were maintained in Fluid Thioglycollate Medium (FTM), which is commercially available from Baltimore Biological Laboratories (Baltim re, Maryland, #01-140). For the growth of T. vaginalis the medium was adjusted to a pH of 6. No adjustment in pH was required for the growth of T. foetus. After sterilization the medium was supplemented with horse serum to a concentration of 5%. Experimental animals. The Carworth strain of mice (Carworth Farms, New City, N. Y.), the Tumblebrook Farms strain of golden hamsters Cricetus auratus (Tumblebrook Farms, Madison, Wisconsin), and the Sprague-Dawley (The Upjohn Company, Kalamazoo, Michigan) and Long Evans (Rockland Farms, New City, New York) strains of rats were used. Mice were housed five to a cage, the other species singly. All animals received food and water ad libitum. Chemicals. Pyruvaldehyde-bis (4-methylthiosemicarbazone) and the corresponding hydroxy and ethoxy derivatives were synthesized by Dr. F. A. French (Mount Zion Hospital, San Francisco, California); butyraldehyde-3-ethoxy-2-oxo-bis (4-methylthiosemicarbazone) by Dr. G. E. Underwood (The Upjohn Company, Kalamazoo, Michigan); and pyruvaldehyde-bis ( 4-dimethylthiosemicarbazone) by Dr. W. Schroeder (The Upjohn Company, Kalamazoo, Michigan). The rest of the compounds were available at The Upjohn Company. Determination of in vitro end points. In vitro end points were determined on logarithmically