Mutagenic effects of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and ethyl methanesulfonate (EMS) on chloroquine resistance in Plasmodium berghei ANKA strain

The influences of two chemical mutagens, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and ethyl methanesulfonate (EMS) on the chloroquine (CQ) resistance in Plasmodium berghei ANKA strain were studied, and totally four 30-fold CQ-resistant lines were established successfully using the mutagens. Both MNNG and EMS were shown to be effective in inducing CQ resistances and increasing the frequency of the appearance of CQ-resistant mutants when erythrocytes with P berghei were treated in vitro at 37 。C for 2 h. By using the relapse technique, one MNNG-mutagenized line developed a more than 30-fold CQ-resistance after 14 drug passages, while the parallel control one did not. EMS also showed mutagenic effectiveness on a sensitive clonal line, which changed into an over 30-fold CQ-resistant one following a single course of CQ therapy consisting of 6 d. The CQ resistance of 30 mg/kg ip for the mutagenized lines were stable after as many as 7 blood passages in the absence of drug pressure over a period of 82 d. All the CQ-resistant lines of the malaria parasites had 3 variations, ie. lack of pigment production, decreased virulence and slowed growth rate. It is concluded that the origin of the CQ resistance may lie in gene mutation and the application of mutagens may be in aid of rapid production of drug resistance in malaria parasites.