Antiamebic Studies on 5-chloro-7-(3-diethylaminopropylaminomethyl)-8-quinolinol In vitro and In Experimentally Infected Animals

Abstract

5-chloro-7-( 3-diethylaminopropylaminomethyl )-8-quinolinol (PAA-3854) was tested against Entamoeba histolytica in the form of the base, hydrochloride, pamoate, disalicylate, and bis-3-hydroxy2-naphthoate salts. In a liver-serum medium, PAA-3854 hydrochloride was amebicidal in concentrations of 20 to 40 gg/ml; the reference drug, emetine hydrochloride, was amebicidal at 2.5 ALg/ml. In rats, all forms of PAA-3854 were active by drug-diet administration in dose levels of 149 to 679 mg/kg/day for 7 days; the hydrochloride, pamoate, and disalicylate salts were effective by gavage in doses of 75 to 600 mg/kg/day for 4 days. The highest doses inhibited the growth of rats; otherwise, the drug was well tolerated on the basis of gross examination. In the oral treatment of dogs for 10 days, the hydrochloride and pamoate salts were curative, roughly proportional to the amount given, in respective doses of 3.13 to 50 mg/kg/day and 12.5 to 25 mg/kg/day. These doses were well tolerated, by gross examination. Hepatic amebiasis in hamsters was suppressed by 100 to 200 mg/kg/day oral doses of PAA-3854 hydrochloride; its effects were roughly comparable to those of the reference drug, chloroquine diphosphate. The substituted 8-quinolinols comprise one of the main classes of intestinal amebicides. A large number of them have been examined in these laboratories for antiamebic action (Thompson et al., 1955; Burckhalter et al., 1961). 5-chloro-7-(3-diethylaminopropylaminomethyl)-8-quinolinol, either as the base or certain salts, has shown a particularly interesting degree of activity. This paper deals with the effects of these substances against Entamoeba histolytica in vitro, in rats and dogs with experimental intestinal amebiasis, and in hamsters with experimental hepatic amebiasis. MATERIALS AND METHODS Detailed descriptions of the antiamebic test methods in vitro and in experimental animals have been presented elsewhere (Thompson et al., 1956). All tests were conducted with strain 200 Entamoeba histolytica in association with undefined mixtures of bacteria. The culture medium for in vitro tests was made to a final concentration of 0.5% liver extract (Wilson & Co., Liver Concentrate, N.F.), 14.3% calf serum, and rice starch (Stein Hall & Co., Imported, No. 42499) in approximately M/20 phosphate buffer-physiologic saline (pH 7.4). The latter was prepared by mixing 86 ml 1 M disodium hydrogen phosphate, 14 ml 1 M potassium dihydrogen phosphate, and 1,400 ml 0.86% NaCl in distilled water. The liver extract was added as a 5% aqueous solution. The test preparations consisted of 4 ml medium, 0.5 ml drug preparation, and 0.5 ml inoculum containing sufficient amebae for a final density of 7,500/mi. They were dispensed in screw-capped Received for publication 2 April 1965. tubes and incubated for 48 hr at 37 C in an atmosphere of CO2. Results were read by making semiquantitative estimates of the amebic population. Rats of the Yale (Y) strain (Maguran Farms), the CFE strain (Carworth Farms), or of the Sprague-Dawley (SD) strain (Sprague-Dawley, Inc.) of either sex were used. They were infected intracecally at 22 days of age with 10,000 to 100,000 amebae (depending upon their virulence) and were maintained on an enriched, low-residue die (Thompson, 1958). Drugs were given either in the diet for 7 days, starting approximately 3 hr after inoculation, or twice daily by gavage on the 3rd through the 6th days after inoculation. Doses given by gavage were administered in 10 ml vehicle/kg of body weight. The controls were sham-dosed with the vehicles. Results were read by autopsy on the 7th day after inoculation, in terms of the average degree of infection and the proportion of animals infected. Drug effects were computed by Abbott's formula (Abbott, 1925) on the basis of the parallel sham-treated controls. Five to 15 rats were used per test group and data from many experiments were compiled, with appropriate weighting for the variable numbers of rats used. Deaths are not recorded in the treated groups, as they occurred rarely. The effects of the drugs on growth of the rats is expressed as the "per cent tolerance" (the quotient of mean weight gains by treated and control groups during the medication periods). Dogs (4 to 9 kg weight range, either sex, mixed breeds) were infected intrarectally from donor animals or cultures and maintained on a strict diet of canned salmon, supplemented three times weekly with vitamins and minerals (Abdol? and Ferro Drops?, Parke, Davis & Co.). Drug was withheld until the animals developed dysentery and was given orally in gelatin capsules. Therapeutic effects were assayed by examining fresh colonic aspirates for amebae three times weekly. Animals