Leishmania Parasites Rewire Their Genes to Survive Antimony Drug Attacks

Leishmaniasis, a parasitic disease that afflicts millions of people across the tropical and subtropical world, has long frustrated clinicians with a stubborn pattern: patients are treated, they improve, and then the infection returns. A new study published in PLOS Pathogens offers a detailed molecular explanation for why this happens. Researchers led by Eyson Quiceno and Zemfira N. Karamysheva have shown that when Leishmania parasites are exposed to antimony-based drugs, a subpopulation of them does not simply hunker down and wait out the assault. Instead, these persister-like cells actively remodel their entire transcriptome, orchestrating a coordinated survival program that is far more sophisticated than a passive metabolic shutdown. The finding reframes drug tolerance in these parasites as an active, regulated strategy, and it suggests that the road to permanent drug resistance may begin with this transient, reversible state.

Persistence is a phenomenon familiar to microbiologists from bacterial studies, in which small subpopulations of cells enter a non-dividing or slow-growing state and thereby survive antibiotic exposures that kill their proliferating siblings. In Leishmania, persisters have been suspected as a major driver of treatment failure and clinical relapse, but the molecular mechanisms governing their formation remained poorly understood. The new work set out to change that by building an experimental model of persistence in Leishmania mexicana, a species widely used in laboratory studies of the parasite’s biology. The central question was deceptively simple: what, at the level of gene expression, distinguishes a parasite that survives a lethal drug challenge from one that does not?

To answer it, the team first had to isolate the survivors. They exposed promastigote parasites, the motile form of Leishmania grown in culture, to potassium antimonyl tartrate, or PAT, a laboratory stand-in for the antimony-containing drugs used clinically. The dose was deliberately harsh: it killed roughly 80 percent of the parasite population. The remaining viable parasites were then enriched using Ficoll density gradient centrifugation, a technique that separates cells by their physical properties and allowed the researchers to concentrate the persister-like subpopulation. When these survivors were placed back into drug-free medium, they displayed the hallmark behavior of persisters: their growth was delayed compared with untreated parasites, and when they were challenged with the drug again, they proved markedly more tolerant than parasites that had never been exposed.

With a reliable population of persister-like cells in hand, the researchers turned to transcriptomic profiling, sequencing the RNA of the parasites across three distinct phases: the acute stress of drug exposure, a drug-free recovery period, and a rechallenge with PAT. The results revealed a global remodeling of gene expression in the persister-like cells under all tested conditions. Rather than a narrow, targeted response, the parasites appeared to reorganize broad swaths of their biology. Induction of the persister state was characterized by the downregulation of numerous biological processes, paired with a robust upregulation of nucleolar pathways. The nucleolus is the cellular compartment where ribosomes, the molecular machines that build proteins, are assembled, and its prominence in the persister signature points toward epitranscriptomic changes, chemical modifications of RNA molecules themselves, during the formation of the persister-like state.

One of the most striking observations came when the drug was removed. The persister transcriptional profile did not linger; it reverted rapidly, initiating a program of ribosome biogenesis that allowed the parasites to exit their latent state and resume proliferation. During this resuscitation phase, the researchers detected active protein synthesis and the upregulation of biological processes associated with metabolic and mitochondrial functions. In other words, the persister state is not a one-way door. It is a dynamic, reversible condition with its own entry program and its own exit program, each executed with apparent precision. This reversibility is precisely what makes persisters so dangerous in a clinical setting: they can survive a course of treatment and then repopulate the infection once the drug pressure subsides.

The rechallenge experiments provided perhaps the most revealing window into the persister lifestyle. When the enriched persister-like parasites were exposed to PAT a second time, they did not respond the way their parental counterparts did. Instead, they rapidly implemented a highly conserved, coordinated survival reprogramming in which 316 genes were uniquely downregulated and 241 genes were upregulated. The downregulated genes were concentrated in mitochondrial function and protein synthesis, driving the parasites into a dormant state that minimizes the drug’s targets and conserves energy. The upregulated genes, by contrast, were enriched for drug-response and stress-tolerance functions, equipping the cells to withstand the immediate chemical toxicity. The parental parasites, facing the same drug for the first time, mounted a broad and disorganized response, a molecular scramble that contrasts sharply with the rehearsed efficiency of the persisters.

Intriguingly, the rechallenged persisters also exhibited transcriptomic features that transiently phenocopy stable genetic resistance. This pre-adapted state was characterized by the targeted upregulation of epigenetic and epitranscriptomic modulators, heavy metal transporters, and catabolic enzymes, all of which help maintain viability under drug pressure. Heavy metal transporters are particularly noteworthy in the context of antimony therapy, because antimony is a metalloid and pumping it out of the cell is a classic mechanism of resistance. The fact that persisters transiently ramp up these systems without any permanent genetic change suggests that the persister state may serve as a proving ground, a way for parasites to test and rehearse the molecular tools that, if later locked in by mutation or gene amplification, would constitute full-blown resistance.

This framing carries significant evolutionary weight. The authors argue that drug persistence in Leishmania is not merely a metabolic collapse but a sophisticated survival strategy involving active transcriptome remodeling, downregulation of translation, and epigenetic and epitranscriptomic changes. If the transient persister state constitutes an initial evolutionary step toward permanent drug resistance, then the population of persisters surviving each treatment cycle represents a reservoir of pre-adapted cells from which resistant lineages can emerge. That would help explain the familiar clinical trajectory of leishmaniasis: initial response to antimonial therapy, followed by relapse, and in some cases the eventual failure of the drug altogether. It also aligns with a broader theme in infectious disease research, in which phenotypic tolerance is increasingly recognized as a stepping stone to genotypic resistance across many microbial species.

The study also highlights new molecular vulnerabilities that could be exploited therapeutically. If persisters depend on specific nucleolar pathways, epigenetic modulators, and coordinated transcriptional programs to establish and maintain their tolerant state, then drugs that interfere with those programs could sensitize the cells to antimony and prevent the survival of the subpopulation that seeds relapse. Combination therapies that pair conventional antimonials with agents targeting the persister machinery are an obvious avenue for future investigation, although translating findings from cultured promastigotes to the intracellular amastigote stage that infects human patients will require further work. The experimental model developed by the research team, combining lethal drug exposure, density gradient enrichment, and time-resolved transcriptomics, provides a platform for such studies.

For a disease in which the therapeutic arsenal has remained narrow for decades, the demonstration that Leishmania persisters are active participants in their own survival, rather than passive casualties of slowed metabolism, is a conceptual advance with practical implications. It suggests that the battle against leishmaniasis is not only fought at the level of parasite killing but also at the level of parasite decision-making, in the regulatory networks that allow a subset of cells to rewrite their gene expression and wait out the storm. Intercepting that rewrite, before it hardens into permanent resistance, may prove to be one of the most promising strategies for preventing the relapses that have made this ancient disease so difficult to cure.

Subject of Research: Transcriptomic mechanisms of antimony-induced drug tolerance and persistence in Leishmania parasites

Article Title: Active transcriptome remodeling underlies antimony-induced drug tolerance in persister-like Leishmania parasites

Article References: Quiceno, E., Rodríguez-Almonacid, C. C., Omeir, K., Ancira, J., Phillips, C., & Karamysheva, Z. N. (2026). Active transcriptome remodeling underlies antimony-induced drug tolerance in persister-like Leishmania parasites. PLOS Pathogens, 22(10), e1014682. https://doi.org/10.1371/journal.ppat.1014682

Image Credits: AI Generated

DOI: 10.1371/journal.ppat.1014682

Keywords: Leishmania, leishmaniasis, drug tolerance, persister cells, antimony, transcriptomics, PLOS Pathogens, drug resistance, epitranscriptomics, ribosome biogenesis, parasitology, treatment relapse