An important genetic mechanism of drug resistance in one of the deadliest human malaria parasites has been identified in a new study published in Nature Microbiology.
A second key gene, pfaat1, responsible for encoding a protein that transports amino acids in the membrane of Plasmodium falciparum, is involved in its resistance to the major anti-malaria drug, chloroquine.
The findings may have implications for the ongoing battle against malaria, which infects an estimated 247 million people worldwide and kills more than 619,000 each year, most of which are young children.
Chloroquine is a major antimalaria drug, however in recent years, resistance has emerged in malaria parasites, first spreading through Southeast Asia and then through Africa in the 1970s and 1980s. Although alternative antimalarial drugs have been developed, resistance to chloroquine remains a big challenge.
Since its discovery in 2000, only one gene has been believed to have been responsible for resistance to chloroquine - the resistance transporter pfcrt which helps the malaria parasite transport the drug out of a key region in their cells, subsequently rendering it ineffective.
In this study, researchers from the Medical Research Council (MRC) Unit The Gambia at the London School of Hygiene & Tropical Medicine (LSHTM) analysed more than 600 genomes of P. falciparum that were collected in The Gambia over a period of 30 years. The team found that mutant variants of a second gene, pfaat1, which encodes an amino acid transporter, increased in frequency from undetectable to very high levels between 1984 and 2014. Importantly, their genome-wide population analyses also indicated long term co-selection on this gene alongside the previously-known resistance gene pfcrt.
In the laboratory, a further team of researchers including from Texas Biomed, University of Notre Dame and Seattle Children's Research Institute found that replacing these mutations in parasite genomes using CRISPR gene-editing technology impacted drug resistance. A team from Nottingham University also found that these mutations could impact the function of pfaat1 in yeast, resulting in drug resistance.
Complementary analysis of malaria genome datasets additionally suggested that parasites from Africa and Asia may carry different mutations in pfaat1 which could help explain differences in the evolution of drug resistance across these continents.
Alfred Amambua-Ngwa, Professor of Genetic Epidemiology at MRC Unit The Gambia at LSHTM said: "This is a very clear example of natural selection in action - these mutations were preferred and passed on with extremely high frequency in a very short amount of time, suggesting they provide a significant survival advantage.
"The mutations in pfaat1 very closely mirror the increase of pfcrt mutations. This, and other genetic analyses in the paper demonstrate that the transporter AAT1 has a major role in chloroquine resistance."
Grappling with drug resistance, for malaria and other pathogens, requires taking a holistic approach to both drug development and pathogen surveillance. We must be aware that different genes and molecules will be working together to survive treatments. That is why looking at whole genomes and whole populations is so critical."
David Conway, Professor of Biology, LSHTM
Amambua-Ngwa, A., et al. (2023). Chloroquine resistance evolution in Plasmodium falciparum is mediated by the putative amino acid transporter AAT1. Nature Microbiology. doi.org/10.1038/s41564-023-01377-z.