Antimalarial activity of sera from subjects taking HIV protease inhibitors

Signal peptide peptidase: A potential therapeutic target for parasitic and viral infections

INTRODUCTION

Signal peptide peptidase (SPP) is a GxGD-type intramembrane-cleaving aspartyl protease responsible for clearing accumulating signal peptides in the endoplasmic reticulum. SPP is conserved among all kingdoms and is essential for maintaining cell homeostasis. Inhibition of SPP with selective inhibitors and the structurally similar HIV protease inhibitors results in signal peptide accumulation and subsequent cell death. Identification of SPP homologues in major human parasitic infections has opened a new therapeutic opportunity. Moreover, the essentiality of mammalian SPP-mediated viral protein processing during infection is emerging.

AREAS COVERED

This review introduces the discovery and biological function of human SPP enzymes and identify parasitic homologues as pharmacological targets of both SPP and HIV protease inhibitors. Later, the role of mammalian SPP during viral infection and how disruption of host SPP can be employed as a novel antiviral therapy are examined and discussed.

EXPERT OPINION

Parasitic and viral infections cause severe health and economic burden, exacerbated by the lack of new therapeutics in the pipeline. SPP has been shown to be essential for malaria parasite growth and encouraging evidence in other parasites demonstrates broad essentiality of these proteases as therapeutic targets. As drug resistant parasite and viruses emerge, SPP inhibition will provide a new generation of compounds to counter the growing threat of antimicrobial resistance.

Brief Report: No Differences Between Lopinavir/Ritonavir and Nonnucleoside Reverse Transcriptase Inhibitor-Based Antiretroviral Therapy on Clearance of Plasmodium falciparum Subclinical Parasitemia in Adults Living With HIV Starting Treatment (A5297)

BACKGROUND

HIV protease inhibitors anti-Plasmodium falciparum activity in adults remains uncertain.

METHODS

Adults with HIV CD4+ counts >200 cells/mm3 starting antiretroviral therapy (ART) with P. falciparum subclinical parasitemia (Pf SCP) were randomized 1:1 to (step 1) protease inhibitor lopinavir/ritonavir (LPV/r)-based (arm A) or nonnucleoside reverse transcriptase inhibitor (nNRTI)-based ART (arm B) for 15 days. In step 2, participants received nNRTI-based ART and trimethoprim/sulfamethoxazole prophylaxis for 15 days. P. falciparum SCP clearance was measured by polymerase chain reaction. The Fisher exact test [95% exact confidence interval (CI)] was used to compare proportions of P. falciparum SCP clearance (<10 parasites/μL on 3 occasions within 24 hours) between LPV/r and nNRTI arms at day 15. The Kaplan-Meier method and log-rank test were used to compare time-to-clearance.

RESULTS

Fifty-two adults from Kenya, Malawi, and Uganda with a median age = 31 (Q1, Q3: 24-39) years, 33% women, with baseline median CD4+ counts of 324 (259-404) cells/mm3, median HIV-1 RNA viremia of 5.18 log10 copies/mL (4.60-5.71), and median estimated P. falciparum density of 454 parasites/μL (83-2219) enrolled in the study. Forty-nine (94%) participants completed the study. At day 15, there was no statistically significant difference in the proportions of P. falciparum SCP clearance between the LPV/r (23.1% clearance; 6 of the 26) and nNRTI (26.9% clearance; 7 of the 26) arms [between-arm difference 3.9% (95% CI, -21.1% to 28.4%; P = 1.00)]. No significant difference in time-to-clearance was observed between the arms (P = 0.80).

CONCLUSIONS

In a small randomized study of adults starting ART with P. falciparum SCP, no statistically significant differences were seen between LPV/r- and nNRTI-based ART in P. falciparum SCP clearance after 15 days of treatment.

Repurposing Drugs to Fight Hepatic Malaria Parasites

Malaria remains one of the most prevalent infectious diseases worldwide, primarily affecting some of the most vulnerable populations around the globe. Despite achievements in the treatment of this devastating disease, there is still an urgent need for the discovery of new drugs that tackle infection by Plasmodium parasites. However, de novo drug development is a costly and time-consuming process. An alternative strategy is to evaluate the anti-plasmodial activity of compounds that are already approved for other purposes, an approach known as drug repurposing. Here, we will review efforts to assess the anti-plasmodial activity of existing drugs, with an emphasis on the obligatory and clinically silent liver stage of infection. We will also review the current knowledge on the classes of compounds that might be therapeutically relevant against Plasmodium in the context of other communicable diseases that are prevalent in regions where malaria is endemic. Repositioning existing compounds may constitute a faster solution to the current gap of prophylactic and therapeutic drugs that act on Plasmodium parasites, overall contributing to the global effort of malaria eradication.

Inhibition of Plasmodium Hepatic Infection by Antiretroviral Compounds

Recent WHO guidelines on control of human immunodeficiency virus (HIV) call for the widespread use of antiretroviral (AR) therapy (ART) for people living with HIV. Given the considerable overlap between infections by HIV and Plasmodium, the causative agent of malaria, it is important to understand the impact of AR compounds and ART regimens on infections by malaria parasites. We undertook a systematic approach to identify AR drugs and ART drug combinations with inhibitory activity against the obligatory hepatic stage of Plasmodium infection. Our in vitro screen of a wide array of AR drugs identified the non-nucleoside reverse transcriptase inhibitors efavirenz and etravirine (ETV), and the protease inhibitor nelfinavir, as compounds that significantly impair the development of the rodent malaria parasite P. berghei in an hepatoma cell line. Furthermore, we show that WHO-recommended ART drug combinations currently employed in the field strongly inhibit Plasmodium liver infection in mice, an effect that may be significantly enhanced by the inclusion of ETV in the treatment. Our observations are the first report of ETV as an anti-Plasmodial drug, paving the way for further evaluation and potential use of ETV-containing ARTs in regions of geographical overlap between HIV and Plasmodium infections.

Antiretroviral Choice for HIV Impacts Antimalarial Exposure and Treatment Outcomes in Ugandan Children

Pharmacokinetic/pharmacodynamic studies of artemether-lumefantrine and 3 antiretroviral regimens were conducted in malaria-infected Ugandan children. Efavirenz-based treatment was associated with significant reductions in antimalarial exposure and higher risks of recurrent malaria. Caution in their concurrent use is warranted.

Background. The optimal treatment of malaria in human immunodeficiency virus (HIV)–infected children requires consideration of critical drug–drug interactions in coinfected children, as these may significantly impact drug exposure and clinical outcomes.

Methods. We conducted an intensive and sparse pharmacokinetic/pharmacodynamic study in Uganda of the most widely adopted artemisinin-based combination therapy, artemether-lumefantrine. HIV-infected children on 3 different first-line antiretroviral therapy (ART) regimens were compared to HIV-uninfected children not on ART, all of whom required treatment for Plasmodium falciparum malaria. Pharmacokinetic sampling for artemether, dihydroartemisinin, and lumefantrine exposure was conducted through day 21, and associations between drug exposure and outcomes through day 42 were investigated.

Results. One hundred forty-five and 225 children were included in the intensive and sparse pharmacokinetic analyses, respectively. Compared with no ART, efavirenz (EFV) reduced exposure to all antimalarial components by 2.1- to 3.4-fold; lopinavir/ritonavir (LPV/r) increased lumefantrine exposure by 2.1-fold; and nevirapine reduced artemether exposure only. Day 7 concentrations of lumefantrine were 10-fold lower in children on EFV vs LPV/r-based ART, changes that were associated with an approximate 4-fold higher odds of recurrent malaria by day 28 in those on EFV vs LPV/r-based ART.

Conclusions. The choice of ART in children living in a malaria-endemic region has highly significant impacts on the pharmacokinetics and pharmacodynamics of artemether-lumefantrine treatment. EFV-based ART reduces all antimalarial components and is associated with the highest risk of recurrent malaria following treatment. For those on EFV, close clinical follow-up for recurrent malaria following artemether-lumefantrine treatment, along with the study of modified dosing regimens that provide higher exposure, is warranted.

Presence of Plasmodium falciparum DNA in Plasma Does Not Predict Clinical Malaria in an HIV-1 Infected Population

BACKGROUND

HIV-1 and Plasmodium falciparum malaria cause substantial morbidity in Sub-Saharan Africa, especially as co-infecting pathogens. We examined the relationship between presence of P. falciparum DNA in plasma samples and clinical malaria as well as the impact of atazanavir, an HIV-1 protease inhibitor (PI), on P. falciparum PCR positivity.

METHODS

ACTG study A5175 compared two NNRTI-based regimens and one PI-based anti-retroviral (ARV) regimen in antiretroviral therapy naïve participants. We performed nested PCR on plasma samples for the P. falciparum 18s rRNA gene to detect the presence of malaria DNA in 215 of the 221 participants enrolled in Blantyre and Lilongwe, Malawi. We also studied the closest sample preceding the first malaria diagnosis from 102 persons with clinical malaria and randomly selected follow up samples from 88 persons without clinical malaria.

RESULTS

PCR positivity was observed in 18 (8%) baseline samples and was not significantly associated with age, sex, screening CD4+ T-cell count, baseline HIV-1 RNA level or co-trimoxazole use within the first 8 weeks. Neither baseline PCR positivity (p = 0.45) nor PCR positivity after initiation of antiretroviral therapy (p = 1.0) were significantly associated with subsequent clinical malaria. Randomization to the PI versus NNRTI ARV regimens was not significantly associated with either PCR positivity (p = 0.5) or clinical malaria (p = 0.609). Clinical malaria was associated with a history of tuberculosis (p = 0.006) and a lower BMI (p = 0.004).

CONCLUSION

P. falciparum DNA was detected in 8% of participants at baseline, but was not significantly associated with subsequent development of clinical malaria. HIV PI therapy did not decrease the prevalence of PCR positivity or incidence of clinical disease.

Neither the HIV protease inhibitor lopinavir-ritonavir nor the antimicrobial trimethoprim-sulfamethoxazole prevent malaria relapse in plasmodium cynomolgi-infected non-human primates

Plasmodium vivax malaria causes significant morbidity and mortality worldwide, and only one drug is in clinical use that can kill the hypnozoites that cause P. vivax relapses. HIV and P. vivax malaria geographically overlap in many areas of the world, including South America and Asia. Despite the increasing body of knowledge regarding HIV protease inhibitors (HIV PIs) on P. falciparum malaria, there are no data regarding the effects of these treatments on P. vivax's hypnozoite form and clinical relapses of malaria. We have previously shown that the HIV protease inhibitor lopinavir-ritonavir (LPV-RTV) and the antibiotic trimethoprim sulfamethoxazole (TMP-SMX) inhibit Plasmodium actively dividing liver stages in rodent malarias and in vitro in P. falciparum, but effect against Plasmodium dormant hypnozoite forms remains untested. Separately, although other antifolates have been tested against hypnozoites, the antibiotic trimethoprim sulfamethoxazole, commonly used in HIV infection and exposure management, has not been evaluated for hypnozoite-killing activity. Since Plasmodium cynomolgi is an established animal model for the study of liver stages of malaria as a surrogate for P. vivax infection, we investigated the antimalarial activity of these drugs on Plasmodium cynomolgi relapsing malaria in rhesus macaques. Herein, we demonstrate that neither TMP-SMX nor LPV-RTV kills hypnozoite parasite liver stage forms at the doses tested. Because HIV and malaria geographically overlap, and more patients are being managed for HIV infection and exposure, understanding HIV drug impact on malaria infection is important.

Plasmodium falciparum gametocytes: with a view to a kill

Drugs that kill or inhibit the sexual stages of Plasmodium in order to prevent transmission are important components of malaria control programmes. Reducing gametocyte carriage is central to the control of Plasmodium falciparum transmission as infection can result in extended periods of gametocytaemia. Unfortunately the number of drugs with activity against gametocytes is limited. Primaquine is currently the only licensed drug with activity against the sexual stages of malaria parasites and its use is hampered by safety concerns. This shortcoming is likely the result of the technical challenges associated with gametocyte studies together with the focus of previous drug discovery campaigns on asexual parasite stages. However recent emphasis on malaria eradication has resulted in an upsurge of interest in identifying compounds with activity against gametocytes. This review examines the gametocytocidal properties of currently available drugs as well as those in the development pipeline and examines the prospects for discovery of new anti-gametocyte compounds.

Prevalence of asymptomatic parasitemia and gametocytemia among HIV-infected Ugandan children randomized to receive different antiretroviral therapies

In a recent randomized controlled trial, the use of protease inhibitor (PI)-based antiretroviral therapy (ART) was associated with a significantly lower incidence of malaria compared with non-nucleoside reverse transcriptase inhibitor-based ART in a cohort of human immunodeficiency virus-infected Ugandan children living in an area of high malaria transmission intensity. In this report, we compared the prevalence of asymptomatic parasitemia and gametocytemia using data from the same cohort. The prevalence of asymptomatic parasitemia did not differ between the two ART treatment arms. The PI-based arm was associated with a lower risk of gametocytemia at the time of diagnosis of malaria (6.6% versus 14.5%, P = 0.03) and during the 28 days after malaria diagnosis (3.4% versus 6.5%, P = 0.04). Thus, in addition to decreasing the incidence of malaria, the use of PI-based ART may lower transmission, as a result of a decrease in gametocytemia, in areas of high malaria transmission intensity.

Antiretroviral agents and prevention of malaria in HIV-infected Ugandan children

BACKGROUND

Human immunodeficiency virus (HIV) protease inhibitors show activity against Plasmodium falciparum in vitro. We hypothesized that the incidence of malaria in HIV-infected children would be lower among children receiving lopinavir-ritonavir-based antiretroviral therapy (ART) than among those receiving nonnucleoside reverse-transcriptase inhibitor (NNRTI)-based ART.

METHODS

We conducted an open-label trial in which HIV-infected children 2 months to 5 years of age who were eligible for ART or were currently receiving NNRTI-based ART were randomly assigned to either lopinavir-ritonavir-based ART or NNRTI-based ART and were followed for 6 months to 2 years. Cases of uncomplicated malaria were treated with artemether-lumefantrine. The primary end point was the incidence of malaria.

RESULTS

We enrolled 176 children, of whom 170 received the study regimen: 86 received NNRTI-based ART, and 84 lopinavir-ritonavir-based ART. The incidence of malaria was lower among children receiving the lopinavir-ritonavir-based regimen than among those receiving the NNRTI-based regimen (1.32 vs. 2.25 episodes per person-year; incidence-rate ratio, 0.59; 95% confidence interval [CI], 0.36 to 0.97; P=0.04), as was the risk of a recurrence of malaria after treatment with artemether-lumefantrine (28.1% vs. 54.2%; hazard ratio, 0.41; 95% CI, 0.22 to 0.76; P=0.004). The median lumefantrine level on day 7 after treatment for malaria was significantly higher in the lopinavir-ritonavir group than in the NNRTI group. In the lopinavir-ritonavir group, lumefantrine levels exceeding 300 ng per milliliter on day 7 were associated with a reduction of more than 85% in the 63-day risk of recurrent malaria. A greater number of serious adverse events occurred in the lopinavir-ritonavir group than in the NNRTI group (5.6% vs. 2.3%, P=0.16). Pruritus occurred significantly more frequently in the lopinavir-ritonavir group, and elevated alanine aminotransferase levels significantly more frequently in the NNRTI group.

CONCLUSIONS

Lopinavir-ritonavir-based ART as compared with NNRTI-based ART reduced the incidence of malaria by 41%, with the lower incidence attributable largely to a significant reduction in the recurrence of malaria after treatment with artemether-lumefantrine. Lopinavir-ritonavir-based ART was accompanied by an increase in serious adverse events. (Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development; ClinicalTrials.gov number, NCT00978068.).

Prevalence and clinical features of HIV and malaria co-infection in hospitalized adults in Beira, Mozambique

BACKGROUND

Mozambique presents a very high prevalence of both malaria and HIV infection, but the impact of co-cancel infection on morbidity in this population has been rarely investigated. The aim of this study was to describe the prevalence and clinical characteristics of malaria in hospitalized adult HIV-positive patients, treated and untreated with combination anti-retroviral therapy (ART) and cotrimoxazole (CTX)-based chemoprophylaxis, compared to HIV negatives.

METHODS

From November to December 2010, all adult patients consecutively admitted to the Department of Internal Medicine of Beira Central Hospital, Sofala Province, Mozambique, were submitted to HIV testing, malaria blood smear (MBS) and, in a subgroup of patients, also to the rapid malaria test (RDT). Socio-demographical and clinical data were collected for all patients. The association of both a positive MBS and/or RDT and diagnosis of clinical malaria with concomitant HIV infection (and use of CTX and/or ART) was assessed statistically. Frequency of symptoms and hematological alterations in HIV patients with clinical malaria compared to HIV negatives was also analysed. Sensitivity and specificity for RDT versus MBS were calculated for both HIV-positive and negative patients.

RESULTS

A total of 330 patients with available HIV test and MBS were included in the analysis, 220 of whom (66.7%) were HIV-positive. In 93 patients, malaria infection was documented by MBS and/or RDT. RDT sensitivity and specificity were 94% and 96%, respectively. According to laboratory results, the initial malaria suspicion was discarded in about 10% of cases, with no differences between HIV-positive and negative patients. A lower malaria risk was significantly associated with CTX prophylaxis (p=0.02), but not with ART based on non nucleoside reverse-transcriptase inhibitors (NNRTIs). Overall, severe malaria seemed to be more common in HIV-positive patients (61.7%) compared to HIV-negatives (47.2%), while a significantly lower haemoglobin level was observed in the group of HIV-positive patients (9.9 ± 2.8 mg/dl) compared to those HIV-negative (12.1 ± 2.8 mg/dl) (p=0.003).

CONCLUSIONS

Malaria infection was rare in HIV-positive individuals treated with CTX for opportunistic infections, while no independent anti-malarial effect for NNRTIs was noted. When HIV and malaria co-infection occurred, a high risk of complications, particularly anaemia, should be expected.

The frequency of malaria is similar among women receiving either lopinavir/ritonavir or nevirapine-based antiretroviral treatment

HIV protease inhibitors (PIs) show antimalarial activity in vitro and in animals. Whether this translates into a clinical benefit in HIV-infected patients residing in malaria-endemic regions is unknown. We studied the incidence of malaria, as defined by blood smear positivity or a positive Plasmodium falciparum histidine-rich protein 2 antigen test, among 444 HIV-infected women initiating antiretroviral treatment (ART) in the OCTANE trial (A5208; ClinicalTrials.gov: NCT00089505). Participants were randomized to treatment with PI-containing vs. PI-sparing ART, and were followed prospectively for ≥48 weeks; 73% also received cotrimoxazole prophylaxis. PI-containing treatment was not associated with protection against malaria in this study population.

Activity of antiretroviral drugs in human infections by opportunistic agents

Highly active antiretroviral therapy (HAART) is used in patients infected with HIV. This treatment has been shown to significantly decrease opportunist infections such as those caused by viruses, fungi and particularly, protozoa. The use of HAART in HIV-positive persons is associated with immune reconstitution as well as decreased prevalence of oral candidiasis and candidal carriage. Antiretroviral therapy benefits patients who are co-infected by the human immunodeficiency virus (HIV), human herpes virus 8 (HHV-8), Epstein-Barr virus, hepatitis B virus (HBV), parvovirus B19 and cytomegalovirus (CMV). HAART has also led to a significant reduction in the incidence, and the modification of characteristics, of bacteremia by etiological agents such as Staphylococcus aureus, coagulase negative staphylococcus, non-typhoid species of Salmonella, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Mycobacterium tuberculosis. HAART can modify the natural history of cryptosporidiosis and microsporidiosis, and restore mucosal immunity, leading to the eradication of Cryptosporidium parvum. A similar restoration of immune response occurs in infections by Toxoplasma gondii. The decline in the incidence of visceral leishmaniasis/HIV co-infection can be observed after the introduction of protease inhibitor therapy. Current findings are highly relevant for clinical medicine and may serve to reduce the number of prescribed drugs thereby improving the quality of life of patients with opportunistic diseases.

Saquinavir inhibits the malaria parasite's chloroquine resistance transporter

The antiretroviral protease inhibitors (APIs) ritonavir, saquinavir, and lopinavir, used to treat HIV infection, inhibit the growth of Plasmodium falciparum at clinically relevant concentrations. Moreover, it has been reported that these APIs potentiate the activity of chloroquine (CQ) against this parasite in vitro. The mechanism underlying this effect is not understood, but the degree of chemosensitization varies between the different APIs and, with the exception of ritonavir, appears to be dependent on the parasite exhibiting a CQ-resistant phenotype. Here we report a study of the role of the P. falciparum chloroquine resistance transporter (PfCRT) in the interaction between CQ and APIs, using transgenic parasites expressing different PfCRT alleles and using the Xenopus laevis oocyte system for the heterologous expression of PfCRT. Our data demonstrate that saquinavir behaves as a CQ resistance reverser and that this explains, at least in part, its ability to enhance the effects of CQ in CQ-resistant P. falciparum parasites.

HIV-1 protease inhibitors and clinical malaria: a secondary analysis of the AIDS Clinical Trials Group A5208 study

HIV-1 protease inhibitors (PIs) have antimalarial activity in vitro and in murine models. The potential beneficial effect of HIV-1 PIs on malaria has not been studied in clinical settings. We used data from Adult AIDS Clinical Trials Group A5208 sites where malaria is endemic to compare the incidence of clinically diagnosed malaria among HIV-infected adult women randomized to either lopinavir/ritonavir (LPV/r)-based antiretroviral therapy (ART) or to nevirapine (NVP)-based ART. We calculated hazard ratios and 95% confidence intervals. We conducted a recurrent events analysis that included both first and second clinical malarial episodes and also conducted analyses to assess the sensitivity of results to outcome misclassification. Among the 445 women in this analysis, 137 (31%) received a clinical diagnosis of malaria at least once during follow-up. Of these 137, 72 (53%) were randomized to LPV/r-based ART. Assignment to the LPV/r treatment group (n = 226) was not consistent with a large decrease in the hazard of first clinical malarial episode (hazard ratio = 1.11 [0.79 to 1.56]). The results were similar in the recurrent events analysis. Sensitivity analyses indicated the results were robust to reasonable levels of outcome misclassification. In this study, the treatment with LPV/r compared to NVP had no apparent beneficial effect on the incidence of clinical malaria among HIV-infected adult women. Additional research concerning the effects of PI-based therapy on the incidence of malaria diagnosed by more specific criteria and among groups at a higher risk for severe disease is warranted.

Drugs for malaria: something old, something new, something borrowed

Malaria was estimated to cause 800,000 deaths and 225 million cases worldwide in 2010. Worryingly, the first-line treatment currently relies on a single drug class called artemisinins, and there are signs that the parasite is becoming resistant to these drugs. The good news is that new technology has given us new approaches to drug discovery. New drugs generated this way are probably 10-15 years away from the clinic. Other antimalarials that may offer hope include those rehabilitated after not being used for some time, those that act as inhibitors of resistance mechanisms, those that limit infection while allowing protective immunity to develop, and those which are drugs borrowed from other disease treatments. All of these offer new hope of turning the tables on malaria. In parallel with the effort to develop vaccines that interrupt malaria transmission, drugs that target the parasite during transmission to the mosquito or during its pre-erythrocytic development in the liver, may allow us to terminate the parasite's spread.

Consequences of HIV infection on malaria and therapeutic implications: a systematic review

Despite recent changes in the epidemiology of HIV infection and malaria and major improvements in their control, these diseases remain two of the most important infectious diseases and global health priorities. As they have overlapping distribution in tropical areas, particularly sub-Saharan Africa, any of their clinical, diagnostic, and therapeutic interactions might have important effects on patient care and public health policy. The biological basis of these interactions is well established. HIV infection induces cellular depletion and early abnormalities of CD4+ T cells, decreases CD8+ T-cell counts and function (cellular immunity), causes deterioration of specific antigen responses (humoral immunity), and leads to alteration of innate immunity through impairment of cytolytic activity and cytokine production by natural killer cells. Therefore, HIV infection affects the immune response to malaria, particularly premunition in adolescents and adults, and pregnancy-specific immunity, leading to different patterns of disease in HIV-infected patients compared with HIV-uninfected patients. In this systematic review, we collate data on the effects of HIV on malaria and discuss their therapeutic consequences. HIV infection is associated with increased prevalence and severity of clinical malaria and impaired response to antimalarial treatment, depending on age, immunodepression, and previous immunity to malaria. HIV also affects pregnancy-specific immunity to malaria and response to intermittent preventive treatment. Co-trimoxazole (trimethoprim-sulfamethoxazole) prophylaxis and antiretroviral treatment reduce occurrence of clinical malaria; however, these therapies interact with antimalarial drugs, and new therapeutic guidelines are needed for concomitant use.

In vitro activity of antiretroviral drugs against Plasmodium falciparum

Malaria and HIV infection are both very common in many developing countries. With the increasing availability of therapy for HIV infection, it was of interest to determine whether antiretroviral drugs exert antimalarial effects. We therefore tested the in vitro activity of 19 antiretroviral drugs against the W2 and 3D7 strains of Plasmodium falciparum at concentrations up to 50 μM. None of 5 tested nucleoside reverse transcriptase inhibitors demonstrated activity. Two nonnucleoside reverse transcriptase inhibitors, efavirenz (mean 50% inhibitory concentration [IC(50)] of 22 to 30 μM against the two strains) and etravirine (3.1 to 3.4 μM), were active; nevirapine was not active. Also active were the fusion inhibitor enfuvirtide (6.2 to 7.9 μM) and the entry inhibitor maraviroc (15 to 21 μM). Raltegravir was not active. However, for all active drugs mentioned above, the IC(50)s were considerably greater than the concentrations achieved with standard dosing. The effects most likely to be clinically relevant were with HIV protease inhibitors. Of the tested compounds, activity was seen with lopinavir (2.7 to 2.9 μM), atazanavir (3.3 to 13.0 μM), saquinavir (5.0 to 12.1 μM), nelfinavir (6.5 to 12.1 μM), ritonavir (9.5 to 10.9 μM), tipranavir (15.5 to 22.3 μM), and amprenavir (28.1 to 40.8) but not darunavir. Lopinavir was active at levels well below those achieved with standard dosing of coformulated lopinavir-ritonavir. Lopinavir also demonstrated modest synergy with the antimalarial lumefantrine (mean fractional inhibitory concentration index of 0.66 for W2 and 0.53 for 3D7). Prior data showed that lopinavir-ritonavir also extends the pharmacokinetic exposure of lumefantrine. Thus, when used to treat HIV infection, lopinavir-ritonavir may have clinically relevant antimalarial activity and also enhance the activity of antimalarials.

HIV proteinase inhibitors target the Ddi1-like protein of Leishmania parasites

HIV proteinase inhibitors reduce the levels of Leishmania parasites in vivo and in vitro, but their biochemical target is unknown. We have identified an ortholog of the yeast Ddi1 protein as the only member of the aspartic proteinase family in Leishmania parasites, and in this study we investigate this protein as a potential target for the drugs. To date, no enzyme assay has been developed for the Ddi1 proteins, but Saccharomyces cerevisiae lacking the DDI1 gene secrete high levels of protein into the medium. We developed an assay in which these knockout yeast were functionally complemented to low secretion by introduction of genes encoding Ddi1 orthologs from Leishmania major or humans. Plasmid alone controls gave no complementation. Treatment of the Ddi1 transformants with HIV proteinase inhibitors showed differential effects dependent on the origin of the Ddi1. Dose responses allowed calculation of IC₅₀ values; e.g., for nelfinavir, of 3.4 μM (human Ddi1) and 0.44 μM (Leishmania Ddi1). IC₅₀ values with Leishmania constructs mirror the potency of inhibitors against parasites. Our results show that Ddi1 proteins are targets of HIV proteinase inhibitors and indicates the Leishmania Ddi1 as the likely target for these drugs and a potential target for antiparasitic therapy.—White, R. E., Powell, D. J., Berry, C. HIV proteinase inhibitors target the Ddi1-Like protein of Leishmania parasites.

Evaluation of the effect of pyrimethamine, an anti-malarial drug, on HIV-1 replication

Co-infection of human immunodeficiency virus (HIV) with malaria is one of the pandemic problems in Africa and parts of Asia. Here we investigated the impact of pyrimethamine (PYR) and two other clinical anti-malarial drugs (chloroquine [CQ] or artemisinin [ART]) on HIV-1 replication. Peripheral blood mononuclear cells (PBMCs) or MT-2 cells were infected with HIV(NL4.3) strain and treated with different concentrations of the anti-malarial drugs. HIV-1 replication was measured using p24 ELISA. We show that 10 μM CQ and ART inhibited HIV-1 replication by 76% and 60% in PBMCs, respectively, but not in MT-2 cells. In contrast, 10 μM PYR enhanced HIV-1 replication in MT-2 cells by >10-fold. A series of molecular mechanism studies revealed that PYR increased intracellular HIV gag proteins without affecting the promoter or the reverse transcriptase activity. The effect of PYR was independent of HTLV-1 produced by MT-2 cells. Of interest, PYR treatment led to S-phase accumulation and increased AZT and d4T antiviral activity by ∼ 4-fold. Taken together, we show that PYR significantly enhances HIV-1 replication by affecting the cellular machinery. Our results could be relevant for the management of malaria and HIV particularly in regions where HIV-1 and malaria epidemics overlap.

Plasmodium falciparum: new molecular targets with potential for antimalarial drug development

Malaria remains one of the world's most devastating infectious diseases. Drug resistance to all classes of antimalarial agents has now been observed, highlighting the need for new agents that act against novel parasite targets. The complete sequencing of the Plasmodium falciparum genome has allowed the identification of new molecular targets within the parasite that may be amenable to chemotherapeutic intervention. In this review, we investigate four possible targets for the future development of new classes of antimalarial agents. These targets include histone deacetylase, the aspartic proteases or plasmepsins, aminopeptidases and the purine salvage enzyme hypoxanthine-xanthine-guanine phosphoribosyltransferase.

Antimalarial asexual stage-specific and gametocytocidal activities of HIV protease inhibitors

The stage-specific antimalarial activities of a panel of antiretroviral protease inhibitors (PIs), including two nonpeptidic PIs (tipranavir and darunavir), were tested in vitro against Plasmodium falciparum. While darunavir demonstrated limited antimalarial activity (effective concentration [EC(50)], >50 microM), tipranavir was active at clinically relevant concentrations (EC(50), 12 to 21 microM). Saquinavir, lopinavir, and tipranavir preferentially inhibited the growth of mature asexual-stage parasites (24 h postinvasion). While all of the PIs tested inhibited gametocytogenesis, tipranavir was the only one to exhibit gametocytocidal activity.

[Impact of malaria on HIV infection]

Malaria and HIV are two major public health issues, especially in sub-Saharan Africa. HIV infection increases the incidence of clinical malaria, inversely correlated with the degree of immunodepression. The effect of malaria on HIV infection is not as well established. Malaria, when fever and parasitemia are high, may be associated with transient increases in HIV viral load. The effect of subclinical malaria on HIV viral load is uncertain. During pregnancy, placental malaria is associated with higher plasma and placental HIV viral loads, independently of the severity of immunodeficiency. However, the clinical impact of these transient increases of HIV viral load remains unknown. Although some data suggests that malaria might enhance sexual and mother-to-child transmissions, no clinical study has confirmed this. Nevertheless pregnant women and children with malaria-induced anemia are also exposed to HIV through blood transfusions. Integrated HIV and malaria control programs in the regions where both infections overlap are necessary.

HIV protease inhibitors inhibit the development of preerythrocytic-stage plasmodium parasites

Recent studies have demonstrated that human immunodeficiency virus (HIV) protease inhibitors (PIs) exert inhibitory effects on erythrocytic stages of the human-malaria parasite Plasmodium falciparum in vitro and on erythrocytic stages of the rodent-malaria parasite Plasmodium chabaudi in vivo. Although it remains unclear how HIV PIs inhibit the parasite, the effect seen on parasite development in the erythrocytic stages is potent. The effect on preerythrocytic stages has not yet been investigated. Using the rodent parasite Plasmodium berghei, we screened a panel of HIV PIs in vitro for effects on the preerythrocytic stages. Our data indicated that the HIV PIs lopinavir and saquinavir affect preerythrocytic-stage parasite development in vitro. We then evaluated the effect of HIV PIs on preerythrocytic stages in vivo using the rodent parasite Plasmodium yoelii. We found that lopinavir/ritonavir had a dose-dependent effect on liver-stage parasite development. Given that sub-Saharan Africa is where the HIV/AIDS pandemic intersects with malaria, these results merit analysis in clinical settings.

Stronger activity of human immunodeficiency virus type 1 protease inhibitors against clinical isolates of Plasmodium vivax than against those of P. falciparum

Recent studies using laboratory clones have demonstrated that several antiretroviral protease inhibitors (PIs) inhibit the growth of Plasmodium falciparum at concentrations that may be of clinical significance, especially during human immunodeficiency virus type 1 (HIV-1) and malaria coinfection. Using clinical isolates, we now demonstrate the in vitro effectiveness of two HIV-1 aspartic PIs, saquinavir (SQV) and ritonavir (RTV), against P. vivax (n = 30) and P. falciparum (n = 20) from populations subjected to high levels of mefloquine and artesunate pressure on the Thailand-Myanmar border. The median 50% inhibitory concentration values of P. vivax to RTV and SQV were 2,233 nM (range, 732 to 7,738 nM) and 4,230 nM (range, 1,326 to 8,452 nM), respectively, both within the therapeutic concentration range commonly found for patients treated with these PIs. RTV was fourfold more effective at inhibiting P. vivax than it was at inhibiting P. falciparum, compared to a twofold difference in SQV sensitivity. An increased P. falciparum mdr1 copy number was present in 33% (3/9) of isolates and that of P. vivax mdr1 was present in 9% of isolates (2/22), but neither was associated with PI sensitivity. The inter-Plasmodium sp. variations in PI sensitivity indicate key differences between P. vivax and P. falciparum. PI-containing antiretroviral regimens may demonstrate prophylactic activity against both vivax and falciparum malaria in HIV-infected patients who reside in areas where multidrug-resistant P. vivax or P. falciparum is found.

HIV and malaria co-infection: interactions and consequences of chemotherapy

The global epidemiology of HIV/AIDS and malaria overlap because a significant number of HIV-infected individuals live in regions with different levels of malaria transmission. Although the consequences of co-infection with HIV and malaria parasites are not fully understood, available evidence suggests that the infections act synergistically and together result in worse outcomes. The importance of understanding chemotherapeutic interactions during malaria and HIV co-infection is now being recognized. We know that some antimalarial drugs have weak antiretroviral effects; however, recent studies have also demonstrated that certain antiretroviral agents can inhibit malaria-parasite growth. Here, we discuss recent findings on the impact of HIV/AIDS and malaria co-infection and the possible roles of chemotherapy in improving the treatment of these diseases.