Erythrocyte G Protein as a Novel Target for Malarial Chemotherapy

Department of Pharmacology, Vanderbilt University, Нашвилл, Michigan, United States
PLoS Medicine (Impact Factor: 14.43). 01/2007; 3(12):e528. DOI: 10.1371/journal.pmed.0030528
Source: PubMed


Malaria remains a serious health problem because resistance develops to all currently used drugs when their parasite targets mutate. Novel antimalarial drug targets are urgently needed to reduce global morbidity and mortality. Our prior results suggested that inhibiting erythrocyte Gs signaling blocked invasion by the human malaria parasite Plasmodium falciparum.
We investigated the erythrocyte guanine nucleotide regulatory protein Gs as a novel antimalarial target. Erythrocyte "ghosts" loaded with a Gs peptide designed to block Gs interaction with its receptors, were blocked in beta-adrenergic agonist-induced signaling. This finding directly demonstrates that erythrocyte Gs is functional and that propranolol, an antagonist of G protein-coupled beta-adrenergic receptors, dampens Gs activity in erythrocytes. We subsequently used the ghost system to directly link inhibition of host Gs to parasite entry. In addition, we discovered that ghosts loaded with the peptide were inhibited in intracellular parasite maturation. Propranolol also inhibited blood-stage parasite growth, as did other beta2-antagonists. beta-blocker growth inhibition appeared to be due to delay in the terminal schizont stage. When used in combination with existing antimalarials in cell culture, propranolol reduced the 50% and 90% inhibitory concentrations for existing drugs against P. falciparum by 5- to 10-fold and was also effective in reducing drug dose in animal models of infection.
Together these data establish that, in addition to invasion, erythrocyte G protein signaling is needed for intracellular parasite proliferation and thus may present a novel antimalarial target. The results provide proof of the concept that erythrocyte Gs antagonism offers a novel strategy to fight infection and that it has potential to be used to develop combination therapies with existing antimalarials.


Available from: Kasturi Haldar, Dec 24, 2014
    • "Ga subunits, components of heterotrimeric G proteins that interact with G protein coupled receptors to transduce signals from the membrane, are found in erythrocyte lipid rafts and within the PVM (Lauer et al, 2000). G protein coupled receptor signalling, through the b 2 -adrenergic receptor , is required for merozoite entry into erythrocytes, providing a possible explanation for the role of lipid rafts in malaria parasite invasion (Harrison et al, 2003; Murphy et al, 2006). A more indirect link between parasite invasion and signalling to the erythrocyte cytoskeleton is provided by studies on extracellular ligand binding to erythrocyte transmembrane proteins, especially those that are known receptors for merozoite invasion (Cowman & Crabb, 2006; Gaur et al, 2004). "

    Malaria Journal 09/2014; 13(Suppl 1):P96-P96. DOI:10.1186/1475-2875-13-S1-P96 · 3.11 Impact Factor
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    • "Recent research has identified an essential role for host erythrocyte enzymes in parasite development [51,52]. A number of the parasiticidal compounds may target a host cell enzyme rather than a molecule encoded by the parasite. "
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    ABSTRACT: The Coordination, Rationalization, and Integration of antiMALarial drug Discovery & Development Initiatives (CRIMALDDI) Consortium, funded by the EU Framework Seven Programme, has attempted, through a series of interactive and facilitated workshops, to develop priorities for research to expedite the discovery of new anti-malarials. This paper outlines the recommendations for the development of enabling technologies and the identification of novel targets. Screening systems must be robust, validated, reproducible, and represent human malaria. They also need to be cost-effective. While such systems exist to screen for activity against blood stage Plasmodium falciparum, they are lacking for other Plasmodium spp. and other stages of the parasite’s life cycle. Priority needs to be given to developing high-throughput screens that can identify activity against the liver and sexual stages. This in turn requires other enabling technologies to be developed to allow the study of these stages and to allow for the culture of liver cells and the parasite at all stages of its life cycle. As these enabling technologies become available, they will allow novel drug targets to be studied. Currently anti-malarials are mostly targeting the asexual blood stage of the parasite’s life cycle. There are many other attractive targets that need to be investigated. The liver stages and the sexual stages will become more important as malaria control moves towards malaria elimination. Sexual development is a process offering multiple targets, even though the mechanisms of differentiation are still not fully understood. However, designing a drug whose effect is not curative but would be used in asymptomatic patients is difficult given current safety thresholds. Compounds active against the liver schizont would have a prophylactic effect and Plasmodium vivax elimination requires effectors against the dormant liver hypnozoites. It may be that drugs to be used in elimination campaigns will also need to have utility in the control phase. Compounds with activity against blood stages need to be screened for activity against other stages. Natural products should also be a valuable source of new compounds. They often occupy non-Lipinski chemical space and so may reveal valuable new chemotypes.
    Malaria Journal 11/2013; 12(1):396. DOI:10.1186/1475-2875-12-396 · 3.11 Impact Factor
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    • "Four major families of α − subunits - Gαs, Gαi/o, Gαq11 and Gα12/13 have been described in eukaryotic cells and each specifies a distinct set of downstream signals. While there is little evidence that the Plasmodium falciparum genome encodes heterotrimeric G proteins [9,10], previous studies have indicated that the malaria parasite can interact with endogenous erythrocyte G proteins [11]. "
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    ABSTRACT: Background The production of gametocytes is essential for transmission of malaria parasites from the mammalian host to the mosquito vector. However the process by which the asexual blood-stage parasite undergoes commitment to sexual development is not well understood. This process is known to be sensitive to environmental stimuli and it has been suggested that a G protein dependent system may mediate the switch, but there is little evidence that the Plasmodium falciparum genome encodes heterotrimeric G proteins. Previous studies have indicated that the malaria parasite can interact with endogenous erythrocyte G proteins, and other components of the cyclic nucleotide pathway have been identified in P. falciparum. Also, the polypeptide cholera toxin, which induces commitment to gametocytogenesis is known to catalyze the ADP-ribosylation of the αs class of heterotrimeric G protein α subunits in mammalian systems has been reported to detect a number of Gα subunits in P. falciparum-infected red cells. Methods Cholera toxin and Mas 7 (a structural analogue of Mastoparan) were used to assess the role played by putative G protein signalling in the commitment process, both are reported to interact with different components of classical Gαs and Gαi/o signalling pathways. Their ability to induce gametocyte production in the transgenic P. falciparum line Pfs16-GFP was determined and downstream effects on the secondary messenger cAMP measured. Results Treatment of parasite cultures with either cholera toxin or MAS 7 resulted in increased gametocyte production, but only treatment with MAS 7 resulted in a significant increase in cAMP levels. This indicates that MAS 7 acts either directly or indirectly on the P. falciparum adenylyl cyclase. Conclusion The observation that cholera toxin treatment did not affect cAMP levels indicates that while addition of cholera toxin does increase gametocytogenesis the method by which it induces increased commitment is not immediately obvious, except that is unlikely to be via heterotrimeric G proteins.
    Malaria Journal 04/2013; 12(1):134. DOI:10.1186/1475-2875-12-134 · 3.11 Impact Factor
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