Optimization of Prodiginines as Single-Dose Curative Antimalarials

Abstract

The emergence of drug-resistant malaria underscores the urgent need for novel, well-tolerated antimalarials with multistage activity and distinct mechanisms of action. Here, we report the design and synthesis of 54 new prodiginine (PG) analogs through systematic modification of the B and C rings of the core scaffold. This effort led to the identification of lead compound PG102 (6), which demonstrated curative oral efficacy in the erythrocytic Plasmodium yoelii murine model at both 25 mg/kg × 4 days and 80 mg/kg × 1 day dosing regimens. PG102 also provided protection against liver-stage Plasmodium berghei sporozoite-induced infection at 20 mg/kg × 3 days and retained high potency against artemisinin-resistant Plasmodium falciparum strains. Profiling of PG102 demonstrated a medium parasite-killing profile. Notably, PG102 exhibited low potential for genotoxicity and cardiotoxicity. This study provides the first demonstration of robust single-dose antimalarial efficacy within the prodiginine class, paving the way for the development of next-generation antimalarial agents.

Figure 1.

Antimalarial natural (1–3) and synthetic (4) PGs with structural diversity on the C-ring.

Figure 2.

Key 2,2′-bipyrrole-5-carboxaldehydes 59a–h for the synthesis of new target PG analogs. 59a is the common biosynthetic precursor of natural PGs and 59b–h are synthetic precursors.

Figure 3.

A) In vitro potency of PG102 (6) and PG112 (24) against P. berghei liver stage parasites, IC₅₀ (nM) values expressed as the mean ± S.E (n = 4); B) in vitro potency of PG102 against ART-resistant P. falciparum strains, IC₅₀ (nM) values expressed as the mean ± S.E (n = 3); C) and D). GRRA dose-response curves for DHA and PG102 in ART-resistant parasites SP044, SP060 and other ART-sensitive lines. Synchronized ring stage parasites were treated with 11 concentrations (in a 2-fold dilution series starting at 2800 nM DHA and 5120 nM PG102) for 6 h. C_t values were normalized to a standard curve of parasitemia’s for a measure of replicative viability (data are represented as mean ± S.D; n = 4). The dashed line in C indicates 700 nM which assays use to determine DHA susceptibility and the 0 RV threshold where very little growth occurred.

Figure 4.

Bioluminescence and real-time IVIS of parasite load in mice with and without treatment with test compounds (6 and 24). The brighter areas of the image (red or bright yellow) show a higher parasite load compared to the areas with a dimmer green or blue color. Lack of bioluminescence represents a parasite load below the limit of detection.

Figure 5.

A) Percentage of parasite survival after PG102 (6) treatment and standard antimalarials; and B) in vitro mutagenicity screening of PG102 (6) at 10 μM concentration and positive controls (2NF, 2-nitrofluorene; 2-AA, 2-aminoanthracene; NaN₃, sodium azide).

Figure 6.

Ex vivo susceptibility of natural (PG1, 1) and synthetic (PG47, 4) compounds against P. falciparum clinical Ugandan isolates (N = 53). The horizontal line shows the geometric mean. Mean IC₅₀ values for the control laboratory strains 3D7 (red) and Dd2 (green) are shown.

Scheme 1.

Synthesis of 2,4-Disubstituted Pyrroles (65a–d, 68a, 68b and 72a–c).

Scheme 2.

Synthesis of 2,3-Disubstituted Pyrroles (76a–d, 79a–c, 86 and 89).

Scheme 3.

Synthesis of New C-Ring Functionalized PGs (8–11), with 3,5-Diaryl Substitutions.

Scheme 4.

Synthesis of New C-Ring Functionalized PGs (12–17), with Ester, Acid, and Amide Functional Groups at the 5-Position.

Scheme 5.

Synthesis of Target B- and C-Ring Functionalized PGs (5–7 and 18–58).