HONG KONG – An international study led by the University of South Florida (USF) has revealed important new information regarding the critical genes of the deadly malarial parasite, Plasmodium falciparum, which could help investigators prioritize targets for future development of newer, more effective antimalarial drugs.

Malaria infects more than 200 million people worldwide and kills around 650,000 each year, with P. falciparum being responsible for approximately half of those cases and 90 percent of all deaths.

"Currently available drugs remain effective in most regions of the world, but resistance to such treatments is rapidly increasing, especially in Southeast Asia," said study co-author Jenna Oberstaller, a USF postdoctoral fellow in the Department of Global Health in Tampa.

"There are no back-up treatments to deploy in the event of widespread failure of these drugs, and if the drug resistance that we are now seeing in Asia makes it to Africa as has been the case in the past emergence of treatment failure, gains made against malaria in the past decade could be rapidly reversed," she warned.

"We desperately need new treatments in order to keep ahead of this disease, but a lack of understanding of the basic biology of this parasite is a roadblock to developing these treatments. P. falciparum is very difficult to study in the laboratory for technical reasons, so researchers don't know the function of nearly half of all the parasite's genes, despite decades of advances," Oberstaller told BioWorld.

In the new study, published in the May 4, 2018, edition of Science, researchers led by John Adams, professor and head of the global health infectious disease research program at USF, reported having exploited features in the genetic make-up of P. falciparum to create 38,000 mutant strains.

The research team, which was supported by the National Institute of Allergy and Infectious Diseases (NIAID), then determined which of those genes were essential for the growth and survival of the parasite.

The complete genetic sequence of P. falciparum was determined more than a decade ago, but the functions of most of its genes remain unknown, and until now only a few hundred mutant strains had been created in the laboratory.

The difficulties in manipulating P. falciparum are due partly to the extremely high percentage of adenine or thymine in its genome. Standard methods for creating mutants rely on more variation in gene sequences and thus have high failure rates in P. falciparum.

In the new research, Adams and his collaborators, who included scientists from the Wellcome Trust Sanger Institute of the U.K., created mutated versions of nearly all of the parasite's approximately 6,000 genes using a technique known as "piggyBac transposon insertional mutagenesis," which preferentially targets sequences rich in adenine and thymine, thereby exploiting the very feature that had stymied previous attempts at genetic manipulation.

"Our work helps define one of the most critical pieces of functional information about each parasite gene in the context of developing new drugs, which is whether or not a gene is essential for the parasite to survive," explained Oberstaller.

"These mutant parasites are all genetically identical apart from a single, randomly disrupted gene. This means that any differences in a parasite living or dying can be attributed to the function of that disrupted gene and gives researchers a better idea of which genes to focus on for developing new drugs to kill the parasite."

A good start

The researchers used computational analysis to distinguish non-essential genes – i.e. those that could be mutated from essential, non-mutatable ones. About 2,600 genes were identified as being essential for growth and survival during the parasite's human blood stage, the stage of development responsible for the clinical symptoms of malaria.

Those newly identified essential genes included those associated with P. falciparum's ability to resist antimalarial drugs, highlighting them as high-priority targets for new or improved antimalarial compounds.

The research may also have significance beyond malaria, noted Oberstaller. "While P. falciparum is by far the most deadly malarial parasite, the information we have learned is likely to be useful for other malarial parasite types and possibly other more distantly related parasites of social and economic importance, as many of these essential genes could potentially be exploited as cross-species drug targets," she said.

"There are other considerations besides gene essentiality regarding what makes a good drug target, but this is certainly a good start," Oberstaller told BioWorld.

"Our goals were to screen for genes essential to parasite survival during that part of its life cycle causing clinical symptoms, while our next step will be to screen this library of mutant parasites for other information relevant to intervention," she added.

"There are practically limitless possibilities for how we and the field of parasitology at large can implement this research to demystify the biology of this parasite and ultimately to weaponize these findings in order to eradicate it."