| Plasmodium falciparum is a protozoan parasite that causes malaria, a disease that is widely spread in the tropical world. Chloroquine has been very effective against malaria since it was introduced into the field until the emergence of chloroquine resistant malaria. Chloroquine resistant malaria has become widely spread in the endemic area. In addition, cross resistance to other antimalarial drugs that are different in structure and function has been reported, even though some of these drugs had not been previously used in that particular region. The objective of this study was to determine the molecular mechanism of this resistance. Actinomycin D resistant Plasmodium falciparum was selected in vitro from the drug sensitive parental clone, 3D7. Interestingly, we found that the selected strain is resistant to chloroquine, mefloquine, antimalarial drugs, and Rhodamine 123. Comparison between 3D7 parental and 3D7R/act-D2 resistant P. falciparum did not show a difference in the level of expression of pfmdr1 previously implicated in the drug resistance. In addition we found that the level of accumulation of two drugs actinomycin D is reduced in the resistant parasite as compared with the sensitive one. Further studies indicated that the reduction in the drug accumulation was due to the increase in drug efflux. Furthermore, to identify if other P-glycoprotein homologues are involved in the resistance, oligonucleotide primers to conserved sequences in ABC domains have been used. An ABC protein homologous to subunit 4 of the 26S proteasome complex has been cloned. In vitro transcription, translation and immunoprecipitation analysis were done using reticulocytes lysate and polyclonal antibodies generated against peptide sequence in the P. falciparum S4 subunit. Surprisingly a decrease in the expression of this gene was found in the resistant clone, 3D7R/act-D2, compared to its parental cell line as determined by Northern blot analysis. Studies are in progress to determine the role of PFS4 subunit in the resistance phenotype of 3D7R /act-D2. |
