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

Abstract

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.

FIG. 1.

Effect of the initial development stage of the P. vivax isolate, either predominantly ring stage (RT > 1) (filled circles) or predominantly trophozoite stage (RT < 1) (open circles) on RTV, SQV, CQ, artesunate (AS), and mefloquine (MQ) sensitivity. Lines indicate median IC₅₀s (nM) for an RT of >1 (solid) or an RT of <1 (dashed). NS, no significant difference. Subsequent analysis of P. vivax was restricted to isolates with an RT of >1.

FIG. 2.

Effect of Pvmdr1 (A) and Pfmdr1 (B) copy amplification on the sensitivity of P. vivax and P. falciparum to RTV, SQV, CQ, artesunate (AS), and mefloquine (MQ). Filled triangles represent isolates with mdr1 amplification (solid lines represent median IC₅₀s [nM]). Open triangles represent isolates with a single copy of mdr1 (dashed lines represent median IC₅₀s [nM]).