The genetics of resistance to quinoline-containing antimalarials in the rodent malaria parasite plasmodium chabaudi

• Main Author: Cravo, Pedro V. L
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2000
• Subjects: Genetics

Some studies on Plasmodium falciparum, the cause of human malaria, have shown a strong association between both mefloquine and quinine resistance and overexpression of the pfmdr1 gene (Plasmodium falciparum multi-drug resistance 1). However, other field studies and genetic crossing work have found no evident correlation between this gene and drug resistance. In order to clarify the role of mdr1 and other genes in mefloquine resistance, a stable mefloquine-resistant clone of the rodent malaria Plasmodium chabaudi, AS (15MF), has been selected from a chloroquine-resistant, but mefloquine-sensitive clone AS (15CQ) in this laboratory, prior to the start of this study. Pulsed-Field Gel Electrophoresis (PFGE) analysis of AS (15MF) revealed differences in karyotypes, and Southern blot analysis showed that these were due to duplication and subsequent translocation of the P. chabaudi mdr1 homologue. Northern hybridisation showed that the gene was being overexpressed in AS (15MF). In order to determine whether pcmdr1 duplication is an essential requirement for the mefloquine resistance phenotype, we performed two genetic crosses between AS (15MF) and a drug sensitive clone (AJ) that differ in a number of genetic markers. Sixteen independent progeny recombinants were produced which were tested for their mefloquine-response to determine whether co-segregation of mefloquine resistance with pcmdr1 amplification occurred. There appeared to be a strong correlation between mefloquine resistance and duplication of this gene, but there were four exceptions, pointing to the involvement of other genetic events other than pcmdr1 duplication. Progeny clones were also tested for their quinine-sensitivity, since the mefloquine resistant parent of the cross, AS (15MF), presented some degree of quinine resistance. Surprisingly, a negative correlation was found between resistance and psmdr1 duplication in the great majority of the cloned progeny, in contrast to earlier studies made in P. falciparum. The chloroquine response of the progeny clones was assessed, but there appeared to be no correlation between chloroquine resistance and psmdr1 amplification.