Inhibitors of Nonhousekeeping Functions of the Apicoplast Defy Delayed Death in
            <i>Plasmodium falciparum</i>

Ramya, T.N.C.; Mishra, Satyendra; Karmodiya, Krishanpal; Surolia, Namita; Surolia, Avadhesha

doi:10.1128/aac.00808-06

Cited by 80 publications

(100 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Thus, unlike the results seen with prokaryotic translation inhibitors such as doxycycline and chloramphenicol, neither organellar genome expression nor organelle replication is affected by MMV-08138. The "immediate" death phenotype of MMV-08138 and maintenance of the apicoplast during drug treatment and IPP rescue are most consistent with an inhibition of apicoplast metabolic pathways rather than housekeeping, protein import, or organelle replication functions (18,26).…”

Section: Resultsmentioning

confidence: 83%

A Chemical Rescue Screen Identifies a Plasmodium falciparum Apicoplast Inhibitor Targeting MEP Isoprenoid Precursor Biosynthesis

Herrera

Ebert

et al. 2015

Antimicrob Agents Chemother

109

View full text Add to dashboard Cite

The apicoplast is an essential plastid organelle found in Plasmodium parasites which contains several clinically validated antimalarial-drug targets. A chemical rescue screen identified MMV-08138 from the "Malaria Box" library of growth-inhibitory antimalarial compounds as having specific activity against the apicoplast. MMV-08138 inhibition of blood-stage Plasmodium falciparum growth is stereospecific and potent, with the most active diastereomer demonstrating a 50% effective concentration (EC 50 ) of 110 nM. Whole-genome sequencing of 3 drug-resistant parasite populations from two independent selections revealed E688Q and L244I mutations in P. falciparum IspD, an enzyme in the MEP (methyl-D-erythritol-4-phosphate) isoprenoid precursor biosynthesis pathway in the apicoplast. The active diastereomer of MMV-08138 directly inhibited PfIspD activity in vitro with a 50% inhibitory concentration (IC 50 ) of 7.0 nM. MMV-08138 is the first PfIspD inhibitor to be identified and, together with heterologously expressed PfIspD, provides the foundation for further development of this promising antimalarial drug candidate lead. Furthermore, this report validates the use of the apicoplast chemical rescue screen coupled with target elucidation as a discovery tool to identify specific apicoplast-targeting compounds with new mechanisms of action. Despite encouraging progress over the past decade, malaria caused by Plasmodium parasites continues to pose an enormous disease burden (1). New antimalarials with novel mechanisms of action are needed to circumvent existing or emerging drug resistance (2). The apicoplast is a plastid organelle unique to Plasmodium spp. (and other pathogenic Apicomplexa parasites) and is a key target for development of new antimalarials. Due to its prokaryotic origin and evolution as a secondary plastid, it contains pathways that have no counterpart in the human host (3, 4). The apicoplast in Plasmodium is essential for both intraerythrocytic and intrahepatic development in the human host (5, 6).Despite efforts to develop inhibitors of apicoplast function, to date, there have been no primary agents for treatment of acute malaria whose mechanism of action targets this unusual plastid organelle. Antibiotics that inhibit prokaryotic transcription and translation, such as doxycycline and clindamycin, block expression of the apicoplast genome and are active against Plasmodium parasites (5). Unfortunately, these drugs show a "delayed death" phenotype, in which growth inhibition occurs only after 2 replication cycles (96 h). The slow kinetics limit the use of doxycycline and clindamycin to chemoprophylaxis or as partner drugs in combination therapies with faster-acting compounds. Fosmidomycin, which inhibits the enzyme DoxR/IspC for MEP (methyl-D-erythritol-4-phosphate) isoprenoid precursor biosynthesis in the apicoplast, has immediate onset but shows high recrudescence rates clinically when used as monotherapy (7,8). The efficacy of fosmidomycin-based combination therapy is currently being evaluated, with mixe...

show abstract

Section: Resultsmentioning

confidence: 83%

A Chemical Rescue Screen Identifies a Plasmodium falciparum Apicoplast Inhibitor Targeting MEP Isoprenoid Precursor Biosynthesis

Herrera

Ebert

et al. 2015

Antimicrob Agents Chemother

109

View full text Add to dashboard Cite

show abstract

“…In blood-stage P. falciparum parasites, the affect of the transcription-blocking drug rifampicin is not completely clear. Some groups found rifampicin to have a similar toxicity when applied at 48 or 96 h (Dahl and Rosenthal, 2007;Goodman et al, 2007), whereas others found the IC 50 to be 6-10 times higher at 48 h than at 96 h (Pradines et al, 2001;Ramya et al, 2007), with the drug causing a delayed-death phenotype, as is seen with azithromycin, clindamycin and doxycycline. In contrast with this, using rifampicin at a concentration more than 6 times higher than any of the IC 50 values determined for P. falciparum, we failed to see an effect of the antibiotic on the growth of the apicoplast and failed to see a block in the development of the mature form of the exo-erythrocytic stage parasite.…”

Section: Treatment Of Exo-erythrocytic Parasites With the Anti-microbmentioning

confidence: 99%

GFP‐targeting allows visualization of the apicoplast throughout the life cycle of live malaria parasites

Stanway

Witt

Zobiak

et al. 2009

Biology of the Cell

View full text Add to dashboard Cite

Background information. The Plasmodium parasite, during its life cycle, undergoes three phases of asexual reproduction, these being repeated rounds of erythrocytic schizogony, sporogony within oocysts on the mosquito midgut wall and exo-erythrocytic schizogony within the hepatocyte. During each phase of asexual reproduction, the parasite must ensure that every new daughter cell contains an apicoplast, as this organelle cannot be formed de novo and is essential for parasite survival. To date, studies visualizing the apicoplast in live Plasmodium parasites have been restricted to the blood stages of Plasmodium falciparum.Results. In the present study, we have generated Plasmodium berghei parasites in which GFP (green fluorescent protein) is targeted to the apicoplast using the specific targeting sequence of ACP (acyl carrier protein), which has allowed us to visualize this organelle in live Plasmodium parasites. During each phase of asexual reproduction, the apicoplast becomes highly branched, but remains as a single organelle until the completion of nuclear division, whereupon it divides and is rapidly segregated into newly forming daughter cells. We have shown that the antimicrobial agents azithromycin, clindamycin and doxycycline block development of the apicoplast during exo-erythrocytic schizogony in vitro, leading to impaired parasite maturation.Conclusions. Using a range of powerful live microscopy techniques, we show for the first time the development of a Plasmodium organelle through the entire life cycle of the parasite. Evidence is provided that interference with the development of the Plasmodium apicoplast results in the failure to produce red-blood-cell-infective merozoites.

show abstract

“…Quantitative Competitive PCR to Quantify Apicoplast: Nuclear DNA Ratio in DSG-treated Parasites-Using quantitative competitive PCR (36), we quantified the nuclear gene fabI (nuclear chromosomal gene coding for the protein enoylPfACP reductase) (37) and the plastid gene eftu (apicoplast gene coding for the elongation factor tu) (38).…”

Section: Inhibition Of Parasite Growth By Dsg-[mentioning

confidence: 99%

15-Deoxyspergualin Primarily Targets the Trafficking of Apicoplast Proteins in Plasmodium falciparum

Ramya

Karmodiya

Surolia

et al. 2007

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

15-Deoxyspergualin, an immunosuppressant with tumoricidal and antimalarial properties, has been implicated in the inhibition of a diverse array of cellular processes including polyamine synthesis and protein synthesis. Endeavoring to identify the mechanism of antimalarial action of this molecule, we examined its effect on Plasmodium falciparum protein synthesis, polyamine biosynthesis, and transport. 15-Deoxyspergualin stalled protein synthesis in P. falciparum through Hsp70 sequestration and subsequent phosphorylation of the eukaryotic initiation factor eIF2␣. However, protein synthesis inhibition as well as polyamine depletion were invoked only by high micromolar concentrations of 15-deoxyspergualin, in contrast to the submicromolar concentrations sufficient to inhibit parasite growth. Further investigations demonstrated that 15-deoxyspergualin in the malaria parasite primarily targets the hitherto underexplored process of trafficking of nucleus-encoded proteins to the apicoplast. Our finding that 15-deoxyspergualin kills the malaria parasite by interfering with targeting of nucleus-encoded proteins to the apicoplast not only exposes a chink in the armor of the malaria parasite, but also reveals new realms in our endeavors to study this intriguing biological process. 15-Deoxyspergualin (DSG)4 ( Fig. 1), an analog of spergualin isolated from the culture broth of Bacillus laterosporus, inhibits the growth of the malaria parasite, Plasmodium, in vitro and in vivo, presumably by depleting its polyamine reserves (1, 2). However, other known inhibitors of polyamine biosynthesis, methylglyoxal-bis-(guanylhydrazone) analog (MGBCP), irinotecan hydrochloride (CPT11), and ␣-difluoromethyl ornithine (DFMO) are known to be incapable of suppressing malaria in infected mice (2). This led us to question the speculated mechanism of antimalarial action of DSG.Despite the uncertainty in the actual mechanism of action of DSG, DSG is known to bind cellular chaperones, Hsp70 and Hsp90, potently, via their regulatory C-terminal motif EEVD (3, 4). DSG does not inhibit their chaperone activity (3-5). However, it selectively enhances the ATPase activity of heat shock proteins that have the C-terminal EEVD motif, and this could be the basis of a specific modulation of the function of proteins that bind the EEVD motif of heat shock proteins (5).One of the cellular milieus in which heat shock proteins are speculated to be involved is translational regulation. Translation of an mRNA requires the formation of a ternary complex of the methionyl-tRNA, the mRNA and the 40 S subunit of the ribosome, a feat achieved through the intervention of the GTPbound form of the initiation factor eIF2 (6). Phosphorylation of eIF2␣ at Ser 51 blocks protein synthesis by preventing eIF2 recycling and depleting the cell of its pool of eIF2-GTP required for translation initiation (7). Several conditions of cellular stress trigger the phosphorylation of eIF2␣ via the activation of four different eIF2␣ kinases: PERK (PKR-like endoplasmic reticulum-associated kina...

show abstract

Inhibitors of Nonhousekeeping Functions of the Apicoplast Defy Delayed Death in Plasmodium falciparum

Cited by 80 publications

References 35 publications

A Chemical Rescue Screen Identifies a Plasmodium falciparum Apicoplast Inhibitor Targeting MEP Isoprenoid Precursor Biosynthesis

A Chemical Rescue Screen Identifies a Plasmodium falciparum Apicoplast Inhibitor Targeting MEP Isoprenoid Precursor Biosynthesis

GFP‐targeting allows visualization of the apicoplast throughout the life cycle of live malaria parasites

15-Deoxyspergualin Primarily Targets the Trafficking of Apicoplast Proteins in Plasmodium falciparum

Contact Info

Product

Resources

About