The chemotherapeutic potential of glycol alkyl ethers: structure-activity studies of nine compounds in a Fischer-rat leukemia transplant model

Structure-activity studies with nine glycol alkyl ethers were conducted with a cellular leukemia transplant model in male Fischer rats. This in vivo assay measures the effects of chemical treatment on neoplastic progression in transplant recipients. Chemicals were given ad libitum in the drinking water simultaneously with the transplants and continued throughout the study. In all, 20 million leukemic cells were injected s.c. into syngeneic rats, which after 60 days resulted in a 10-fold increase in relative spleen weights, a 100-fold increase in white blood cell counts, and a 50% reduction in red blood cell (RBC) indices and platelet counts. At this interval, ethylene glycol monomethyl ether (2-ME) given at a dose of 2.5 mg/ml in the drinking water completely eliminated all clinical, morphological, and histopathological evidence of leukemia, whereas the same dose of ethylene glycol monoethyl ether (2-EE) reduced these responses by about 50%. Seven of the glycol ethers were ineffective as anti-leukemic agents, including ethylene glycol, the monopropyl, monobutyl, and monophenyl ethylene glycol ethers, diethylene glycol, and the monomethyl and monoethyl diethylene glycol ethers. 2-ME more than doubled the latency period of leukemia expression and extended survival for at least 210 days. A minimal effective dose for a 50% reduction in the leukemic responses was 0.25 mg/ml 2-ME in the drinking water (15 mg/kg body weight), whereas a 10-fold higher dose of 2-EE was required for equivalent antileukemic activity. In addition, the in vitro exposure of a leukemic spleen mononuclear cell culture to 2-ME caused a dose- and time-dependent reduction in the number of leukemia cells after a single exposure to 1–100 µM concentrations, whereas the 2-ME metabolite, 2-methyoxy-acetic acid, was only half as effective. The two glycol alkyl ethers with demonstrable anti-leukemic activity, 2-ME and 2-EE, also exhibited a favorable efficacy-to-toxicity ratio and should be considered for further development as chemotherapeutic agents.