The results of the trial were published Thursday (Aug. 26) in the Journal of Experimental Medicine.
Discovery and the Ralph C. Corley Distinguished Professor of Chemistry, who co-directed the international research team. The patients receiving Imatinib also were relieved of their fevers in less than half of the time experienced by similar patients treated with the standard therapy.
“Delayed clearance rates are a precursor to and an indicator of potential drug resistance, which has been a problem with malaria for decades. So, this could be significant.”
“When we discovered the ability of Imatinib to block parasite propagation in human blood cultures in petri dishes, we initiated a human clinical trial where we combined Imatinib with the standard treatment (piperaquine plus dihydroartemisinin) used to treat malaria in much of the world,” Low said.
“The Phase 2 clinical trial that is described in the paper in Journal of Experimental Medicine compares the standard treatment with Imatinib plus the standard treatment. We did not test Imatinib alone, because it would have been unethical to treat patients suffering from a potentially lethal disease with an untested therapy.”
Low and his colleagues theorized that by blocking the critical red blood cell enzyme, they could stop the infection. The data from the drug trial confirms that.
Low said for the past 50 years, malaria treatments have used drugs that target the parasite itself, but the microorganism eventually developed resistance to the drugs.
“Because we’re targeting an enzyme that belongs to the red blood cell, the parasite can’t mutate to develop resistance – it simply can’t mutate proteins in our blood cells,” Low said. “This is a novel approach that will hopefully become a therapy that can’t be evaded by the parasite in the future. This would constitute an important contribution to human health.”
Malaria is caused by a single-cell parasite, Plasmodium, which is carried by mosquitoes. The World Health Organization estimates that the disease caused 409,000 deaths in 2019 (the most recent year for which data is available). The WHO also notes that 67% of those deaths were in children under five years old.
The deadliest form of the parasite is P. falciparum, and although most malaria deaths occur in sub-Saharan Africa, a variant of P. falciparum that is developing drug resistance has become established in a corner of Southeast Asia, particularly in Cambodia, Myanmar, Thailand, Laos and Vietnam. In some regions of the area, up to 80% of malaria parasites are at least partially drug resistant.
In 2019, professor Olivo Miotto from the Wellcome Sanger Institute of the University of Oxford, told the BBC the rise of the drug-resistant variant in Southeast Asia raises the “terrifying prospect” of the drug-resistant variety traveling to Africa. A similar event occurred in the 1980s with malaria resistant to the then-standard treatment of chloroquine, which resulted in millions of deaths.
Low and his colleagues tested Imatinib in a hot zone of drug-resistant malaria on the border of Vietnam and Laos, in the Quang Tri Province of Vietnam.
“It’s such a remote region of the country that most of the clinics are one- or two-room cinder block buildings with just six or seven cots where people can come in and get treated,” Low said. “Not only was the drug 100% effective after three days, but the patients saw their fever disappear on the first day, and they felt much better sooner.”
Although malaria is not a significant disease in North America, Low is planning to apply for approval by the U.S. Food and Drug Administration.
“The FDA is so widely respected around the world that if they approve it, almost all other nations, especially developing countries that suffer from malaria, will rapidly adopt it,” he said.
“The FDA requirements for Phase 3 approval are very rigorous. You have to demonstrate the drug combination’s efficacy and safety in a large patient population and then show that you can manufacture and store it safely and reproducibly. You also have to start from scratch and end up with a product that is more than 99% pure.”
An international priority patent application has been filed in Vietnam by Purdue Research Foundation, VinUniversity in Vietnam, University of Sassari in Italy and Italian company NUREX SRL.
Low said he has been in discussions with drug manufacturers in India and Vietnam to produce the drug and estimates that can be done for roughly $1 per pill.
“We’ll turn over the technology to any company committed to distributing it to developing malaria-infested areas,” he said. “I’m not interested in making a penny off of this. I just think it’s important for humanity to have it.”
With half of the world’s population at risk for malaria infection and with drug resistance on the rise, the search for mutation-resistant therapies has intensified. We report here a therapy for Plasmodium falciparum malaria that acts by inhibiting the phosphorylation of erythrocyte membrane band 3 by an erythrocyte tyrosine kinase.
Because tyrosine phosphorylation of band 3 causes a destabilization of the erythrocyte membrane required for parasite egress, inhibition of the erythrocyte tyrosine kinase leads to parasite entrapment and termination of the infection. Moreover, because one of the kinase inhibitors to demonstrate antimalarial activity is imatinib, i.e. an FDA-approved drug authorized for use in children, translation of the therapy into the clinic will be facilitated.
At a time when drug resistant strains of P. falciparum are emerging, a strategy that targets a host enzyme that cannot be mutated by the parasite should constitute a therapeutic mechanism that will retard evolution of resistance.
Discussion
Since the 2nd century BCE, all malaria therapies have targeted malaria-encoded processes that are critical to parasite survival. Artemisinin, originally obtained by chewing the plant, Artemisia annua, is thought to function by promoting oxidative stress and inhibiting hemozoin formation within the infected red cell [42]. Quinine, found in the bark of the cinchona tree, accumulates in the Plasmodium food vacuole and inhibits the formation of hemozoin among other mechanisms [43, 44].
Synthetic quinine substitutes such as chloroquine, piperaquine, and mefloquine have subsequently been introduced to offset the resistance that has emerged to each preceding quinine congener [45], and several promising new therapies have been designed to inhibit the P. falciparum cation ATPase (PfATP4), P. falciparum protein kinase G (PfPKG), and P. falciparum phosphatidylinositol-3 kinase (PfPI3K) in the parasite [7, 46–49].
The obvious limitation of each of these approaches is that they target enzymes/processes encoded in the parasite genome, allowing the parasite to explore resistance mechanisms via constitutive mutagenesis. With many infected individuals containing >50,000,000 parasites/ml blood, the probability of selecting a resistant mutant would seem high, especially given the tendency of patients in remote regions to refrain from taking their full 3-day dosing regimen in order to save the remaining pills for a subsequent bout with the disease [50].
These observations all argue that complete eradication of malaria may require a pharmaceutical that can target a host enzyme that cannot be mutated by the parasite [36].
In this article, we describe a novel antimalarial agent that blocks parasitemia by inhibiting a process encoded in the host cell’s genome. As we have shown elsewhere, phosphorylation of band 3 on tyrosines 8 and 21 is catalyzed by syk tyrosine kinase [51], leading to a major reorganization of the RBC membrane that induces release of glyceraldehyde 3-phosphate dehydrogenase, lactate dehydrogenase, phosphofructokinase, pyruvate kinase, aldolase and deoxyhemoglobin from band 3 [52, 53].
More importantly, this phosphorylation also causes displacement of ankyrin from band 3, severing the major bridge connecting the RBC membrane to its structurally stabilizing cytoskeleton. The natural consequence of this membrane reorganization in uninfected red cells is membrane weakening, bilayer vesiculation, and erythrocyte hemolysis [11, 12, 26, 27].
The steady increase in tyrosine phosphorylation of band 3 in parasitized erythrocytes undoubtedly leads to a similar membrane weakening, contributing to the observed membrane crenations and vesiculation seen in later stage infected red cells, and ultimately to the successful egress of the parasite from the destabilized cell.
To inhibit this process, we treated the malaria infected cultures with imatinib, a tyrosine kinase inhibitor that has known activity against syk [28]. The result of this treatment was prevention of parasite egress. Although it cannot be ruled out that a P. falciparum encoded dual-specificity kinase might be capable of catalyzing the tyrosine phosphorylation of band 3, or that imatinib might inhibit this kinase or some other parasite protein and thereby block parasitemia, the likelihood that such an unknown target constitutes the site of action of imatinib seems remote, especially since the crystal structure of imatinib bound to syk shows a very high degree of structural complementarity and the remarkable specificity of imatinib for a very limited number of tyrosine kinases constitutes its source of notoriety [15, 16].
It is important to emphasize that the malaria parasite engages actively in erythrocyte membrane remodeling from the moment that it enters the red cell. Thus, novel malaria-encoded proteins are repeatedly inserted into the host cytoskeleton and plasma membrane [54, 55], while normal erythrocyte membrane proteins continually undergo parasite-induced phosphorylation and proteolysis [56, 57].
Although many of these modifications may have evolved to render the erythrocyte more hospitable to parasite maturation, some of the changes have undoubtedly emerged to weaken the red cell membrane and facilitate parasite egress at the end of its life cycle [58, 59]. It will be interesting to determine whether inhibition of any of these other parasite-encoded egress processes might synergize with inhibition of the band 3 tyrosine phosphorylation in preventing progression of the parasite through its life cycle.
It is important to note that previous work from prominent labs has provided additional motivation for seeking a malaria therapy that targets an erythrocyte-mediated process. Thus, Doerig and colleagues [60] have shown that inhibition of an erythrocyte MEK1 kinase using allosteric inhibitors has parasiticidal effects on P. falciparum, both in red cells and in hepatocytes in vitro. Millholland and coworkers [57] have similarly found that activation of host protein kinase C is responsible for initiating a signaling cascade leading to proteolysis of the host protein adducin, thus cleaving the second of the two major bridges (other than the ankyrin bridge) that anchors the red cell membrane to its underlying cytoskeleton; i.e. further weakening the erythrocyte membrane.
Along the same lines, this activation of protein kinase C or casein kinase is also found to lead to phosphorylation of protein 4.1, causing disruption of the spectrin-actin interaction and thereby contributing to the aforementioned membrane destabilization [61, 62]. In a similar manner, Murphy et al. [63] have demonstrated that P. falciparum co-opts an erythrocyte Gs protein to activate signaling pathways required for intra-erythrocytic parasite growth and invasion.
Finally, Brizuela et al. [64] have reported that the parasite utilizes a red cell antioxidant protein, peroxiredoxin 2, to compensate for its lack of catalase and inability to rapidly detoxify hydrogen peroxide. When considered together, these observations suggest that a wide variety of erythrocyte pathways can potentially be targeted to develop a more mutation resistant therapy for malaria.
In conclusion, we suggest that imatinib constitutes an excellent candidate for clinical evaluation as an anti-malaria therapy for several reasons:
i) it is FDA approved for use in both adults and children,
ii) it is generally non-toxic and can be taken daily in perpetuity,
iii) well tolerated concentrations demonstrating complete antimalarial activity can be achieved in patient’s plasma,
iv) imatinib has been well studied in nearly all human populations, and
v) imatinib’s mechanism of action renders development of resistance mutations unlikely. With the focus of the malaria field on the design of mutation-resistant drug cocktails that might collectively enable eradication of parasitemia with a single pill, the contribution of a drug like imatinib could prove valuable.
reference link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5074466/
More information: Huynh Dinh Chien et al, Imatinib augments standard malaria combination therapy without added toxicity, Journal of Experimental Medicine (2021). DOI: 10.1084/jem.20210724
