Antimalarial Asexual Stage-Specific and Gametocytocidal Activities of HIV Protease Inhibitors

Abstract

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 M), tipranavir was active at clinically relevant concentrations (EC 50 , 12 to 21 M). 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.The global distributions of HIV and malaria overlap in many regions of the world (reviewed in reference 17). Although data on the number of individuals with both diseases are unavailable, rates of coinfection are likely to be high (7). Furthermore, coinfection often leads to severe disease (4,12,19,20). While the effects of antiretroviral therapy on the outcome of malaria infection are not understood, defining these interactions is important (11,13,16,18). Understanding the antimalarial activities of the antiretroviral protease inhibitors (PIs) (reviewed in reference 17), for example, may lead to treatment recommendations that improve clinical outcomes and may also result in the identification of a new antimalarial drug target.Current data suggest that PIs kill malaria parasites by inhibiting one or more of the six nondigestive vacuole plasmepsins (reviewed in reference 17). In the present study we investigated the stage-specific effects of the PIs on asexual-and sexual-stage Plasmodium falciparum parasites in order to help define the antimalarial target(s) of these drugs and to help guide partner drug choices in the field. To gain additional structure-activity data and information that may be relevant for coinfected individuals we also examined the activities of the nonpeptidic PIs tipranavir (Aptivus) and darunavir (Prezista), new-generation PIs that are active against HIV-1 strains resistant to first generation PIs (9).The antimalarial activities of saquinavir, lopinavir, ritonavir, tipranavir, darunavir, and chloroquine (diphosphate salt; Sigma) were determined as described previously (18). Concentrations required to achieve 10, 50, and 90% growth inhibition (Ϯ the standard error [SE]) were determined by nonlinear regression curve fitting. Each assay was performed in triplicate on at least two separate occasions. Stage-specific growth inhibition assays were performed on synchronized parasite cultures (8) at 0 (ring), 24 (trophozoite), and 36 h (schizont) postsynchronization. Cultures were washed post-drug exposure, resuspended in drug-free medium, and seeded into tissue culture plates containing 0.5 Ci/well [ 3 H]hypoxanthine for 40 h. Incorporation of [ 3 H]hypoxanthine was compared to that in vehicle controls.Drug-induced effects on gametocytogenesis were examined using Pfs16-GFP parasites (3) as previously described (14). Assays were performed in triplicate on three separat...

In Vitro Activity of Antiretroviral Drugs against Plasmodium falciparum

“…Also consistent with older reports, lopinavir was the most potent of these agents. When provided in standard dosing with ritonavir, lopinavir circulates in the plasma at 10 to 19 M, well above the IC 50 s of 2 to 3 M determined in this study and 1 to 5 M seen in other studies using a variety of methods (1,31,32,33). Serum from patients treated with lopinavir-ritonavir also exerted in vitro antimalarial activity (36).…”

New approaches in antimalarial drug discovery and development: a review

“…The mechanism of action of HIV protease inhibitors against malaria is attributed to the inhibition of the food vacuole protease, plasmepsin II (Parikh et al 2006). Tipranavir, although less active against malaria, demonstrates gametocytocidal activity and thus should have a significant effect on the transmission and control of malaria (Peatey et al 2010). …”

Prevalence of Asymptomatic Parasitemia and Gametocytemia among HIV-Infected Ugandan Children Randomized to Receive Different Antiretroviral Therapies

“…[4][5][6][7] In addition to activity against the asexual stage of the parasite, PIs have shown in vitro activity against gametoctyes, the sexual stage of the parasite responsible for transmission to mosquitoes. 8 However, there are limited clinical data on the effects of PIs on asymptomatic parasitemia and gametocytemia.We recently published the results of an open-label randomized trial comparing PI-based versus non-nucleoside reverse transcriptase inhibitor (NNRTI)-based ART for the prevention of malaria among HIV-infected children living in Tororo, a highly malaria-endemic area of Eastern Uganda. 9 In this study the use of PI-based ART was associated with a 41% reduction in the incidence of malaria, largely attributable to ART-antimalarial drug interactions resulting in a significant reduction in the risk of recurrent malaria after treatment with artemether-lumefantrine (AL).…”

“…[4][5][6][7] In addition to activity against the asexual stage of the parasite, PIs have shown in vitro activity against gametoctyes, the sexual stage of the parasite responsible for transmission to mosquitoes. 8 However, there are limited clinical data on the effects of PIs on asymptomatic parasitemia and gametocytemia.…”