Chemosensitization of Plasmodium falciparum by Probenecid In Vitro

Abstract

Resistance to drugs can result from changes in drug transport, and this resistance can sometimes be overcome by a second drug that modifies the transport mechanisms of the cell. This strategy has been exploited to partly reverse resistance to chloroquine in Plasmodium falciparum. Studies with human tumor cells have shown that probenecid can reverse resistance to the antifolate methotrexate, but the potential for reversal of antifolate resistance has not been studied in P. falciparum. In the present study we tested the ability of probenecid to reverse antifolate resistance in P. falciparum in vitro. Probenecid, at concentrations that had no effect on parasite viability alone (50 M), was shown to increase the sensitivity of a highly resistant parasite isolate to the antifolates pyrimethamine, sulfadoxine, chlorcycloguanil, and dapsone by seven-, five-, three-, and threefold, respectively. The equivalent effects against an antifolate-sensitive isolate were activity enhancements of approximately 3-, 6-, 1.2-, and 19-fold, respectively. Probenecid decreased the level of uptake of radiolabeled folic acid, suggesting a transport-based mechanism linked to folate salvage. When probenecid was tested with chloroquine, it chemosensitized the resistant isolate to chloroquine (i.e., enhanced the activity of chloroquine). This enhancement of activity was associated with increased levels of chloroquine accumulation. In conclusion, we have shown that probenecid can chemosensitize malaria parasites to antifolate compounds via a mechanism linked to reduced folate uptake. Notably, this effect is observed in both folate-sensitive and -resistant parasites. In contrast to the activities of antifolate compounds, the effect of probenecid on chloroquine sensitivity was selective for chloroquine-resistant parasites (patent P407595GB [W. P. Thompson & Co., Liverpool, United Kingdom] has been filed to protect this intellectual property).

Involvement of Gap Junction Proteins in Infectious Diseases Caused by Parasites

“…These authors suggest that the increased ATP release from infected red cells could be mediated by by Panx1 channels [56]. Several studies have shown that probenecid has a marked antimalarial effect [57][58][59]. The incubation of P. falciparum with probenecid shows antimalarial activity at concentrations >150 μM at day 2 of treatment [57].…”

“…Several studies have shown that probenecid has a marked antimalarial effect [57][58][59]. The incubation of P. falciparum with probenecid shows antimalarial activity at concentrations >150 μM at day 2 of treatment [57]. However, probenecid at concentration <150 μM increases the P. falciparum sensitivity to antifolate drugs [57].…”

“…The incubation of P. falciparum with probenecid shows antimalarial activity at concentrations >150 μM at day 2 of treatment [57]. However, probenecid at concentration <150 μM increases the P. falciparum sensitivity to antifolate drugs [57]. For example, in the presence of 50 μM probenecid, the IC 50 (nM) was reduced from 1.42 ± 0.52 to 0.52 ± 0.36, from 215 ± 150 to 36.50 ± 26.80 and from 33.53 ± 12.30 to 1.77 ± 2.70 for pyrimethamine, sulfadoxine, and dapsone, respectively [57].…”

Selective killing of the human malaria parasite Plasmodium falciparum by a benzylthiazolium dye

“…Importantly, the methods employed in our study cannot distinguish between folic acid and PUR-1 competition for uptake through the PSAC channel on the outer membrane of the infected cell vs. competition for uptake across a carrier protein located on the parasite plasma membrane. However, taken together with the findings of Nzila et al (Nzila, et al, 2003) and Wang et al (Wang, et al, 1999) it seems reasonable to believe that a selective inhibitor of the NPP will block uptake of exogenous folic acid from the bloodstream and function synergistically with selective inhibitors of parasite dihydrofolate reductase, such as WR99210 (Canfield, et al, 1993,Kinyanjui, et al, 1999 and "biguanide" prodrugs of the Jacobus series (Jensen, et al, 2001). …”

“…We considered the findings of Ward and coworkers who have suggested that exogenous folates gain entry into PRBC via the broad specificity anion dependent channel (Nzila, et al, 2003). Considering that the heterocyclic purine ring in PUR-1 may be recognized as a pterin-like heterocycle in this biological system, we set up an experiment to test the ability of folic acid to interfere with PUR-1 staining of PRBC.…”