In vitro activity and interaction of clindamycin combined with dihydroartemisinin against Plasmodium falciparum

Effect of mild medical hypothermia on in vitro growth of Plasmodium falciparum and the activity of anti-malarial drugs

Background

Cerebral malaria remains a medical emergency with high mortality. Hypo-perfusion due to obstructed blood vessels in the brain is thought to play a key role in the pathophysiology of cerebral malaria leading to neurological impairment, long-term neuro-cognitive sequelae and, potentially, death. Due to the rapid reversibility of vascular obstruction caused by sequestered Plasmodium falciparum, it is hypothesized that mild medical hypothermia—a standard intervention for other medical emergencies—may improve clinical outcome. This preclinical in vitro study was performed to assess the impact of mild hypothermia on parasite growth and the intrinsic activity of anti-malarials drugs.

Methods

Three laboratory-adapted clones and two clinical isolates were used for growth assays and standardized drug sensitivity assessments using the standard HRP2 assay. All assays were performed in parallel under normothermic (37 °C), mild hypothermic (32 °C), and hyperthermic (41 °C) conditions.

Results

Parasite growth was higher under standard temperature condition than under hypo- or hyperthermia (growth ratio 0.85; IQR 0.25–1.06 and 0.09; IQR 0.05–0.32, respectively). Chloroquine and mefloquine had comparable in vitro activity under mild hypothermic conditions (ratios for IC50 at 37 °C/32 °C: 0.88; 95 % CI 0.25–1.50 and 0.86; 95 % CI 0.36–1.36, respectively) whereas dihydroartemisinin was more active under mild hypothermic conditions (ratio for IC50 at 37 °C/32 °C: 0.27; 95 % CI 0.19–0.27). Hyperthermia led by itself to almost complete growth inhibition and precluded further testing of the activity of anti-malarial drugs.

Conclusion

This preclinical evaluation demonstrates that mild medical hypothermia inhibits in vitro growth of P. falciparum and enhances the pharmacodynamic activity of artemisinin derivatives. Based on these preclinical pharmacodynamic data, the further clinical development of mild medical hypothermia as adjunctive treatment to parenteral artesunate for cerebral malaria is warranted.

In vitro activity of immunosuppressive drugs against Plasmodium falciparum

Background

Solid organ transplant recipients are particularly vulnerable for infectious diseases due to prolonged immunosuppressive treatment. Residents of endemic regions and travellers may be exposed to malaria and may, therefore, require prolonged antimalarial chemoprophylaxis. The hypothesis of this study was that certain immunosuppressive drugs may exert clinically relevant anti-malarial activity. It was therefore designed to assess the intrinsic anti-malarial activity of everolimus, mycophenolic acid, and rapamycin against Plasmodium falciparum in an in vitro model.

Methods

Three laboratory adapted clones of P. falciparum and two isolates were used to assess the potential of mycophenolic acid, rapamycin and everolimus to inhibit in vitro growth of P. falciparum. The standard histidine rich protein 2 assay was employed and inhibitory drug concentrations (IC) were computed by non-linear regression analysis.

Results

All drugs were associated with complete inhibition of P. falciparum growth in in vitro assays. Mycophenolic acid demonstrated IC₅₀ and IC₉₀ values of 5.4 μmol/L and 15.3 μmol/L. Rapamycin inhibited P. falciparum growth at 7.2 μmol/L (IC₅₀) and 12.5 μmol/L (IC₉₀), respectively. Finally, everolimus displayed IC₅₀ and IC₉₀ values of 6.2 μmol/L and 11.5 μmol/L. There was no difference in in vitro activity against chloroquine sensitive or chloroquine resistant parasites.

Conclusions

All immunosuppressive drugs evaluated in this in vitro study demonstrated activity against P. falciparum. Inhibitory concentrations of mycophenolic acid are within clinically achievable plasma concentrations when used in solid organ transplant recipients. Further in vivo evaluation of mycophenolic acid either alone or in combination regimens may prove promising for the concomitant prevention of P. falciparum in solid organ transplant recipients living or travelling in malaria endemic regions.

Mirincamycin, an old candidate for malaria combination treatment and prophylaxis in the 21st century: in vitro interaction profiles with potential partner drugs in continuous culture and field isolates

BACKGROUND

Spreading resistance of Plasmodium falciparum to existing drugs calls for the search for novel anti-malarial drugs and combinations for the treatment of falciparum malaria.

METHODS

In vitro and ex vivo investigations were conducted with fresh P. falciparum field isolates and culture-adapted P. falciparum clones to evaluate the anti-malarial potential of mirincamycin, a lincosamide, alone and in combination with tafenoquine (TQ), dihydroartemisinin (DHA), and chloroquine (CQ). All samples were tested in a histidine-rich protein 2 (HRP2) drug susceptibility assay.

RESULTS

Interaction analysis showed additive to synergistic interaction profiles with these potential partner drugs, with an overall geometric mean fractional inhibitory concentration at 50% inhibition (FIC₅₀) of 0.78, 0.80 and 0.80 for mirincamycin with TQ, DHA, and CQ, respectively. Antagonism was not found in any of the tested field isolates or clones. The strongest tendency toward synergy (i.e. the lowest FIC) was seen with a combination ratio of 1:0.27 to 1:7.2 (mean 1:2.7) for the combination with tafenoquine. The optimal combination ratios for DHA and CQ were 1:444.4 to 1:36,000 (mean 1:10,755.5) and 1:2.7 to 1:216 (mean 1:64.5), respectively. No evidence of an activity correlation (i.e. potential cross-resistance) with DHA, mefloquine, quinine or chloroquine was seen whereas a significant correlation with the activity of clindamycin and azithromycin was detected.

CONCLUSIONS

Mirincamycin combinations may be promising candidates for further clinical investigations in the therapy and prophylaxis of multidrug-resistant falciparum malaria or in combination with 4 or 8-aminoquinolines for the treatment and relapse prevention of vivax malaria.

In vitro antimalarial activity of tigecycline against Plasmodium falciparum culture-adapted reference strains and clinical isolates from the Brazilian Amazon

INTRODUCTION

We evaluated the in vitro antimalarial activity of tigecycline as an alternative drug for the treatment of severe malaria.

METHODS

A chloroquine-sensitive Plasmodium falciparum reference strain, a chloroquine-resistant reference strain, and three clinical isolates were tested for in vitro susceptibility to tigecycline. A histidine-rich protein in vitro assay was used to evaluate antimalarial activity.

RESULTS

The geometric-mean 50% effective concentration (EC50%) of tigecycline was 535.5 nM (confidence interval (CI): 344.3-726.8). No significant correlation was found between the EC50% of tigecycline and that of any other tested antimalarial drug.

CONCLUSIONS

Tigecycline may represent an alternative drug for the treatment of patients with severe malaria.

Prospective evaluation of artemether-lumefantrine for the treatment of non-falciparum and mixed-species malaria in Gabon

Background

The recommendation of artemisinin combination therapy (ACT) as first-line treatment for uncomplicated falciparum malaria is supported by a plethora of high quality clinical trials. However, their recommendation for the treatment of mixed-species malaria and the large-scale use for the treatment of non-falciparum malaria in endemic regions is based on anecdotal rather than systematic clinical evidence.

Methods

This study prospectively observed the efficacy of artemether-lumefantrine for the treatment of uncomplicated non-falciparum or mixed-species malaria in two routine district hospitals in the Central African country of Gabon.

Results

Forty patients suffering from uncomplicated Plasmodium malariae, Plasmodium ovale or mixed-species malaria (including Plasmodium falciparum) presenting at the hospital received artemether-lumefantrine treatment and were followed up. All evaluable patients (n = 38) showed an adequate clinical and parasitological response on Day 28 after oral treatment with artemether-lumefantrine (95% confidence interval: 0.91,1). All adverse events were of mild to moderate intensity and completely resolved by the end of study.

Conclusions

This first systematic assessment of artemether-lumefantrine treatment for P. malariae, P. ovale and mixed-species malaria demonstrated a high cure rate of 100% and a favourable tolerability profile, and thus lends support to the practice of treating non-falciparum or mixed-species malaria, or all cases of malaria without definite species differentiation, with artemether-lumefantrine in Gabon.

Trial Registration

ClinicalTrials.gov Identifier: NCT00725777

Automated red blood cell exchange as an adjunctive treatment for severe Plasmodium falciparum malaria at the Vienna General Hospital in Austria: a retrospective cohort study

Background

Severe falciparum malaria is associated with considerable rates of mortality, despite the administration of appropriate anti-malarial treatment. Since overall survival is associated with total parasite biomass, blood exchange transfusion has been proposed as a potential method to rapidly reduce peripheral parasitaemia. However, current evidence suggests that this treatment modality may not improve outcome. Automated red blood cell exchange (also referred to as “erythrocytapheresis”) has been advocated as an alternative method to rapidly remove parasites from circulating blood without affecting patients’ volume and electrolyte status. However, only limited evidence from case reports and case series is available for this adjunctive treatment. This retrospective cohort study describes the use of automated red blood cell exchange for the treatment of severe malaria at the Medical University of Vienna.

Methods

Epidemiologic data for imported malaria cases in Austria are reported and data of patients treated for malaria at the General Hospital/Medical University of Vienna were extracted from electronic hospital records.

Results

Between 2000 and 2010, 146 patients were hospitalized at the Medical University of Vienna due to malaria and 16 of those were classified as severe malaria cases. Eleven patients of this cohort were potentially eligible for an adjunctive treatment with automated red blood cell exchange. Five patients eventually underwent this procedure within a period of seven hours (range: 3–19 hours) after hospital admission. Six patients did not undergo this adjunctive treatment following the decision of the treating physician. The procedure was well tolerated in all cases and rapid reduction in parasite counts was achieved without occurrence of haemodynamic complications. One patient died within seven days, whereas four patients survived without any sequelae.

Discussion and conclusion

Automated red blood cell exchange was a safe and efficient procedure to rapidly clear peripheral parasitaemia. Whether the fast reduction in parasite biomass may ultimately improve patient survival remains however unclear. Randomized controlled trials are needed to conclusively appreciate the value of this adjunctive treatment.

Anti-bacterial activity of intermittent preventive treatment of malaria in pregnancy: comparative in vitro study of sulphadoxine-pyrimethamine, mefloquine, and azithromycin

BACKGROUND

Intermittent preventive treatment of malaria with sulphadoxine-pyrimethamine (SP) is recommended for the prevention of malaria in pregnancy in sub-Saharan Africa. Increasing drug resistance necessitates the urgent evaluation of alternative drugs. Currently, the most promising candidates in clinical development are mefloquine and azithromycin. Besides the anti-malarial activity, SP is also a potent antibiotic and incurs significant anti-microbial activity when given as IPTp - though systematic clinical evaluation of this action is still lacking.

METHODS

In this study, the intrinsic anti-bacterial activity of mefloquine and azithromycin was assessed in comparison to sulphadoxine-pyrimethamine against bacterial pathogens with clinical importance in pregnancy in a standard microdilution assay.

RESULTS

SP was highly active against Staphylococcus aureus and Streptococcus pneumoniae. All tested Gram-positive bacteria, except Enterococcus faecalis, were sensitive to azithromycin. Additionally, azithromycin was active against Neisseria gonorrhoeae. Mefloquine showed good activity against pneumococci but lower in vitro action against all other tested pathogens.

CONCLUSION

These data indicate important differences in the spectrum of anti-bacterial activity for the evaluated anti-malarial drugs. Given the large scale use of IPTp in Africa, the need for prospective clinical trials evaluating the impact of antibiotic activity of anti-malarials on maternal and foetal health and on the risk of promoting specific drug resistance of bacterial pathogens is discussed.

Antimalarial activity of tigecycline, a novel glycylcycline antibiotic

Tigecycline is a novel glycylcycline antibiotic with a broad antibacterial spectrum. Tigecycline was tested with 66 clinical isolates of Plasmodium falciparum from Bangladesh using the histidine-rich protein 2 in vitro drug susceptibility assay. The 50% and 90% inhibitory concentrations of tigecycline were 699 (95% confidence interval, 496 to 986) and 5,905 nM (4,344 to 8,028). Tigecycline shows no activity correlation with traditional antimalarials and has substantial antimalarial activity on its own.

Update on clindamycin in the management of bacterial, fungal and protozoal infections

Lincomycin and clindamycin are the only members of the relatively small lincosamide antimicrobial class marketed for use in humans. This paper only reviews data regarding clindamycin, with an emphasis on data published over the last decade. Clindamycin exhibits a broad spectrum of antimicrobial activity, including Gram-positive aerobes/anaerobes, Gram-negative anaerobes and select protozoa (Toxoplasma gondii, Plasmodium falciparum, Babesia spp.) and fungi (Pneumocystis jiroveci). It still enjoys use in the therapy and prophylaxis of a large number of bacterial, protozoal and fungal infections, despite > 40 years of clinical use. However, the spectre of resistance by an increasing number of microorganisms is beginning to cast a shadow over the future use of this valuable agent. With the emergence and spread of infections due to community-acquired methicillin-resistant Staphylococci (for which clindamycin is a first-line agent), it is hoped that the issues of resistance can be mitigated and the use of clindamycin extended for at least the foreseeable future.

Malaria Chemotherapeutics Part I: History of Antimalarial Drug Development, Currently Used Therapeutics, and Drugs in Clinical Development

Since ancient times, humankind has had to struggle against the persistent onslaught of pathogenic microorganisms. Nowadays, malaria is still the most important infectious disease worldwide. Considerable success in gaining control over malaria was achieved in the 1950s and 60s through landscaping measures, vector control with the insecticide DDT, and the widespread administration of chloroquine, the most important antimalarial agent ever. In the late 1960s, the final victory over malaria was believed to be within reach. However, the parasites could not be eradicated because they developed resistance against the most widely used and affordable drugs of that time. Today, cases of malaria infections are on the rise and have reached record numbers. This review gives a short description of the malaria disease, briefly addresses the history of antimalarial drug development, and focuses on drugs currently available for malaria therapy. The present knowledge regarding their mode of action and the mechanisms of resistance are explained, as are the attempts made by numerous research groups to overcome the resistance problem within classes of existing drugs and in some novel classes. Finally, this review covers all classes of antimalarials for which at least one drug candidate is in clinical development. Antimalarial agents that are solely in early development stages will be addressed in a separate review.

Antimalarial drug synergism and antagonism: mechanistic and clinical significance

Interactions between antimicrobial agents provide clues as to their mechanisms of action and influence the combinations chosen for therapy of infectious diseases. In the treatment of malaria, combinations of drugs, in many cases acting synergistically, are increasingly important in view of the frequency of resistance to single agents. The study of antimalarial drug interactions is therefore of great significance to both treatment and research. It is therefore worrying that the analysis of drug-interaction data is often inadequate, leading in some cases to dubious conclusions about synergism or antagonism. Furthermore, making mechanistic deductions from drug-interaction data is not straightforward and of the many reported instances of antimalarial synergism or antagonism, few have been fully explained biochemically. This review discusses recent findings on antimalarial drug interactions and some pitfalls in their analysis and interpretation. The conclusions are likely to have relevance to other antimicrobial agents.

Artesunate-clindamycin versus quinine-clindamycin in the treatment of Plasmodium falciparum malaria: a randomized controlled trial

BACKGROUND

Artemisinin-based drug combinations are the mainstay in the fight against drug-resistant malaria in Africa. Currently available antimalarial drug combinations that include artemisinins are pharmacokinetically unmatched and are therefore potentially increasing the risk of selection of resistant mutants in areas in which the rate of transmission of malaria is high. We tested the potential value of artemisinin-based combination therapy with a short elimination half-life for the treatment of uncomplicated Plasmodium falciparum malaria in sub-Saharan Africa.

METHODS

We conducted an open-label, randomized, controlled clinical trial to evaluate the efficacy and tolerability of oral artesunate-clindamycin therapy given twice daily for 3 days (artesunate, 2 mg/kg, and clindamycin, 7 mg/kg, per dose), compared with a standard quinine-clindamycin regimen given twice daily for 3 days (quinine, 15 mg/kg, and clindamycin, 7 mg/kg, per dose), for the treatment of uncomplicated falciparum malaria in 100 Gabonese children aged 3-12 years. The primary end point of the study was the polymerase chain reaction-corrected cure rate for the per-protocol population.

RESULTS

The activity of artesunate-clindamycin was comparable to that of quinine-clindamycin in the per-protocol analysis of cure rates at day 28 of follow-up (87% versus 94%). No serious adverse events were reported, and tolerability was good and was similar in both groups. Times to clearance of fever and clearance of parasites were significantly shorter in the artesunate-clindamycin group.

CONCLUSIONS

Artesunate-clindamycin and other matching artemisinin-based combinations with a short plasma half-life merit further attention for use in regions in which the rate of transmission of malaria is high.

The plastid-derived organelle ofprotozoan human parasites asa target of established and emerging drugs

Human diseases like malaria, toxoplasmosis or cryptosporidiosis are caused by intracellular protozoan parasites of the phylum Apicomplexa and are still a major health problem worldwide. In the case of Plasmodium falciparum, the causative agent of tropical malaria, resistance against previously highly effective drugs is widespread and requires the continued development of new and affordable drugs. Most apicomplexan parasites possess a single plastid-derived organelle called apicoplast, which offers the great opportunity to tailor highly specific inhibitors against vital metabolic pathways resident in this compartment. This is due to the fact that several of these pathways, being of bacterial or algal origin, are absent in the mammalian host. In fact, the targets of several antibiotics already in use for years against some of these diseases can now be traced to the apicoplast and by knowing the molecular entities which are affected by these substances, improved drugs or drug combinations can be envisaged to emerge from this knowledge. Likewise, apicoplast-resident pathways like fatty acid or isoprenoid biosynthesis have already been proven to be the likely targets of the next drug generation. In this review the current knowledge on the different targets and available inhibitors (both established and experimental) will be summarised and an overview of the clinical efficacy of drugs that inhibit functions in the apicoplast and which have been tested in humans so far will be given.