Gossypol is a natural product with good antimalarial activity against Plasmodium falciparum clinical isolates

Abstract

Gossypol has demonstrated significant antimalarial activity against chloroquine-resistant and susceptible Plasmodium falciparum parasites. However, data on its potency in clinical isolates of P. falciparum remains limited. This study aimed to assess the potency of gossypol against six laboratory strains and twenty-one clinical isolates of P. falciparum using optimized growth inhibition assays. Additionally, parasites with reduced susceptibility to gossypol were selected using the P. falciparum Dd2 background (Dd2_3.5 µM) and tested for cross-resistance to chloroquine, dihydroartemisinin (DHA), and three Malaria box compounds (MMV006087, MMV085203, and MMV008956). On average, gossypol was found to be twice as potent against the laboratory strains compared to the clinical isolates, with IC₅₀ values of 6.490 µM and 11.670 µM, respectively. Notably, Dd2_3.5 µM parasites displayed increased sensitivity after three months of exposure but developed decreased susceptibility after six months. Importantly, these gossypol-tolerant parasites showed no cross-resistance to chloroquine, DHA, or the three Malaria box compounds. These findings suggest that gossypol is effective against P. falciparum and holds potential as part of combination therapy with existing antimalarials. Furthermore, these results may support the identification of new antimalarial agents that are effective against drug-resistant malaria parasites.

Fig. 1

A plot of the mean IC₅₀ values of gossypol against the laboratory and clinical isolates of P. falciparum. The clinical isolates were generally less sensitive to gossypol compared to the laboratory strains of P. falciparum parasites (Unpaired t-test, *p < 0.05). Error bars denote SEM. The overall average (both clinical isolates and laboratory strains) average IC₅₀ was 10.46 µM.

Fig. 2

Selection of Dd2 P. falciparum parasites with reduced susceptibility (Dd2_3.5 µM) to gossypol. (A) Dose-response curves showing the susceptibility of Dd2_3.5 µM_1 parasites at baseline (IC₅₀ values of 5.049 µM (95% CI: 4.291–5.883)), three months (IC₅₀ values of 2.599 μM (95% CI: 1.826–3.737)) and finally at six months (14.94 µM (95% CI: 11.55–21.47) ; (B) Susceptibility pattern of the Dd2_3.5 µM parasites (two replicates) during the in vitro selection process.

Fig. 3

Dose-response curves for the Dd2_3.5 µM parasites, Dd2 parental strain and 3D7 parental strains of P. falciparum against standard antimalarial drugs. (A) Dose-response curves showing the response of chloroquine against Dd2_3.5 µM and Dd2 parental strain; (B) Dose-response curves showing the response of dihydroartemisinin (DHA) against Dd2_3.5 µM and Dd2 parental strain and (C) Dose-response curves showing the response of DHA and chloroquine against 3D7. Each data point represents the mean ± SEM (n = 2). The plot shows the percentage parasitemia against the log of the concentration of the compound.

Fig. 4

Dose-response curves for Dd2_3.5 µM against three Malaria box compounds. Panels A–C, are the dose-response curves showing the response of Dd2_3.5 µM parasites against (A)MMV006087, (B) MMV085203 and (C)MMV008956, at concentrations from 0.064 nM to 25 µM. Each data point represents the mean ± SEM (n = 2). The plot shows the percentage parasitemia against the log of the concentration of the compound.

Fig. 5

Graphs showing pfmdr1 and pfcrt copy number variation in Dd2 parental strain (Dd2), Dd2_3,5 μM parasites, 3D7 and clinical isolates. A All the clinical isolates had one pfmdr1 copy number, except for the clinical isolate 14400, which had a copy number of two. There was also no difference in pfmdr1 copy number between Dd2 parental strain and Dd2_3,5 μM parasites.

Fig. 6

Comparing the susceptibility of clinical isolates with two clones to those with more than two clones. The IC₅₀ values of the clinical isolates with two P. falciparum genotypes were not significantly different from those with more than two genotypes (Unpaired t-test, p = 0.56). Error bars denote SEM.